From 1079962e4c06f88a54e50d997c1b7e84303d30b4 Mon Sep 17 00:00:00 2001 From: Bernhard Schmidt Date: Sat, 15 Aug 2020 21:29:50 +0200 Subject: New upstream version 2.5~beta1 --- doc/Makefile.am | 59 +- doc/Makefile.in | 662 -- doc/README.man | 22 + doc/android.txt | 101 + doc/doxygen/Makefile.am | 21 + doc/doxygen/doc_compression.h | 91 + doc/doxygen/doc_control_processor.h | 184 + doc/doxygen/doc_control_tls.h | 104 + doc/doxygen/doc_data_control.h | 102 + doc/doxygen/doc_data_crypto.h | 70 + doc/doxygen/doc_eventloop.h | 66 + doc/doxygen/doc_external_multiplexer.h | 45 + doc/doxygen/doc_fragmentation.h | 95 + doc/doxygen/doc_internal_multiplexer.h | 43 + doc/doxygen/doc_key_generation.h | 148 + doc/doxygen/doc_mainpage.h | 161 + doc/doxygen/doc_memory_management.h | 98 + doc/doxygen/doc_protocol_overview.h | 195 + doc/doxygen/doc_reliable.h | 48 + doc/doxygen/doc_tunnel_state.h | 154 + doc/doxygen/openvpn.doxyfile.in | 279 + doc/keying-material-exporter.txt | 137 + doc/man-sections/advanced-options.rst | 107 + doc/man-sections/cipher-negotiation.rst | 96 + doc/man-sections/client-options.rst | 353 + doc/man-sections/connection-profiles.rst | 75 + doc/man-sections/encryption-options.rst | 135 + doc/man-sections/examples.rst | 240 + doc/man-sections/generic-options.rst | 438 ++ doc/man-sections/inline-files.rst | 25 + doc/man-sections/link-options.rst | 409 ++ doc/man-sections/log-options.rst | 73 + doc/man-sections/management-options.rst | 135 + doc/man-sections/network-config.rst | 10 + doc/man-sections/pkcs11-options.rst | 80 + doc/man-sections/plugin-options.rst | 57 + doc/man-sections/protocol-options.rst | 281 + doc/man-sections/proxy-options.rst | 65 + doc/man-sections/renegotiation.rst | 52 + doc/man-sections/script-options.rst | 842 +++ doc/man-sections/server-options.rst | 774 +++ doc/man-sections/signals.rst | 30 + doc/man-sections/tls-options.rst | 668 ++ doc/man-sections/unsupported-options.rst | 32 + .../virtual-routing-and-forwarding.rst | 78 + doc/man-sections/vpn-network-options.rst | 534 ++ doc/man-sections/windows-options.rst | 244 + doc/management-notes.txt | 171 +- doc/openvpn.8 | 7343 -------------------- doc/openvpn.8.rst | 170 + doc/tls-crypt-v2.txt | 189 + 51 files changed, 8570 insertions(+), 8021 deletions(-) delete mode 100644 doc/Makefile.in create mode 100644 doc/README.man create mode 100644 doc/android.txt create mode 100644 doc/doxygen/Makefile.am create mode 100644 doc/doxygen/doc_compression.h create mode 100644 doc/doxygen/doc_control_processor.h create mode 100644 doc/doxygen/doc_control_tls.h create mode 100644 doc/doxygen/doc_data_control.h create mode 100644 doc/doxygen/doc_data_crypto.h create mode 100644 doc/doxygen/doc_eventloop.h create mode 100644 doc/doxygen/doc_external_multiplexer.h create mode 100644 doc/doxygen/doc_fragmentation.h create mode 100644 doc/doxygen/doc_internal_multiplexer.h create mode 100644 doc/doxygen/doc_key_generation.h create mode 100644 doc/doxygen/doc_mainpage.h create mode 100644 doc/doxygen/doc_memory_management.h create mode 100644 doc/doxygen/doc_protocol_overview.h create mode 100644 doc/doxygen/doc_reliable.h create mode 100644 doc/doxygen/doc_tunnel_state.h create mode 100644 doc/doxygen/openvpn.doxyfile.in create mode 100644 doc/keying-material-exporter.txt create mode 100644 doc/man-sections/advanced-options.rst create mode 100644 doc/man-sections/cipher-negotiation.rst create mode 100644 doc/man-sections/client-options.rst create mode 100644 doc/man-sections/connection-profiles.rst create mode 100644 doc/man-sections/encryption-options.rst create mode 100644 doc/man-sections/examples.rst create mode 100644 doc/man-sections/generic-options.rst create mode 100644 doc/man-sections/inline-files.rst create mode 100644 doc/man-sections/link-options.rst create mode 100644 doc/man-sections/log-options.rst create mode 100644 doc/man-sections/management-options.rst create mode 100644 doc/man-sections/network-config.rst create mode 100644 doc/man-sections/pkcs11-options.rst create mode 100644 doc/man-sections/plugin-options.rst create mode 100644 doc/man-sections/protocol-options.rst create mode 100644 doc/man-sections/proxy-options.rst create mode 100644 doc/man-sections/renegotiation.rst create mode 100644 doc/man-sections/script-options.rst create mode 100644 doc/man-sections/server-options.rst create mode 100644 doc/man-sections/signals.rst create mode 100644 doc/man-sections/tls-options.rst create mode 100644 doc/man-sections/unsupported-options.rst create mode 100644 doc/man-sections/virtual-routing-and-forwarding.rst create mode 100644 doc/man-sections/vpn-network-options.rst create mode 100644 doc/man-sections/windows-options.rst delete mode 100644 doc/openvpn.8 create mode 100644 doc/openvpn.8.rst create mode 100644 doc/tls-crypt-v2.txt (limited to 'doc') diff --git a/doc/Makefile.am b/doc/Makefile.am index c091ce0..340dd55 100644 --- a/doc/Makefile.am +++ b/doc/Makefile.am @@ -5,27 +5,72 @@ # packet encryption, packet authentication, and # packet compression. # -# Copyright (C) 2002-2018 OpenVPN Inc +# Copyright (C) 2002-2020 OpenVPN Inc # Copyright (C) 2006-2012 Alon Bar-Lev # MAINTAINERCLEANFILES = \ $(srcdir)/Makefile.in -CLEANFILES = openvpn.8.html +SUBDIRS = doxygen dist_doc_DATA = \ management-notes.txt dist_noinst_DATA = \ - README.plugins interactive-service-notes.rst + README.plugins interactive-service-notes.rst \ + openvpn.8.rst \ + man-sections/advanced-options.rst \ + man-sections/client-options.rst \ + man-sections/connection-profiles.rst \ + man-sections/encryption-options.rst \ + man-sections/examples.rst \ + man-sections/generic-options.rst \ + man-sections/inline-files.rst \ + man-sections/link-options.rst \ + man-sections/log-options.rst \ + man-sections/management-options.rst \ + man-sections/network-config.rst \ + man-sections/pkcs11-options.rst \ + man-sections/plugin-options.rst \ + man-sections/protocol-options.rst \ + man-sections/proxy-options.rst \ + man-sections/renegotiation.rst \ + man-sections/signals.rst \ + man-sections/script-options.rst \ + man-sections/server-options.rst \ + man-sections/tls-options.rst \ + man-sections/unsupported-options.rst \ + man-sections/virtual-routing-and-forwarding.rst \ + man-sections/vpn-network-options.rst \ + man-sections/windows-options.rst -if WIN32 +openvpn.8 : +if HAVE_PYDOCUTILS + $(RST2MAN) $(srcdir)/$@.rst > $@ +else + @echo "Missing python-docutils - skipping man page generation" +endif + +openvpn.8.html: +if HAVE_PYDOCUTILS + $(RST2HTML) $(srcdir)/openvpn.8.rst > $@ +else + @echo "Missing python-docutils - skipping man/html page generation" +endif + +if HAVE_PYDOCUTILS dist_noinst_DATA += openvpn.8 -nodist_html_DATA = openvpn.8.html -openvpn.8.html: $(srcdir)/openvpn.8 - $(MAN2HTML) < $(srcdir)/openvpn.8 > openvpn.8.html +dist_html_DATA = openvpn.8.html + +# Failsafe - do not delete these files unless we can recreate them +CLEANFILES = \ + openvpn.8 openvpn.8.html + +if WIN32 else dist_man_MANS = openvpn.8 endif +endif +dist-hook : openvpn.8 openvpn.8.html diff --git a/doc/Makefile.in b/doc/Makefile.in deleted file mode 100644 index 6c86ac8..0000000 --- a/doc/Makefile.in +++ /dev/null @@ -1,662 +0,0 @@ -# Makefile.in generated by automake 1.16.1 from Makefile.am. -# @configure_input@ - -# Copyright (C) 1994-2018 Free Software Foundation, Inc. - -# This Makefile.in is free software; the Free Software Foundation -# gives unlimited permission to copy and/or distribute it, -# with or without modifications, as long as this notice is preserved. - -# This program is distributed in the hope that it will be useful, -# but WITHOUT ANY WARRANTY, to the extent permitted by law; without -# even the implied warranty of MERCHANTABILITY or FITNESS FOR A -# PARTICULAR PURPOSE. - -@SET_MAKE@ - -# -# OpenVPN -- An application to securely tunnel IP networks -# over a single UDP port, with support for 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-.NOEXPORT: diff --git a/doc/README.man b/doc/README.man new file mode 100644 index 0000000..29654c1 --- /dev/null +++ b/doc/README.man @@ -0,0 +1,22 @@ + +man page documentation +====================== + +The man page content maintained in the openvpn.8.rst file and proper man and +the html version of the man page are generated using python-docutils. Both +the man page and html file are generated during 'make dist' or 'make distcheck' +and should be distributed inside the tarball by default. + +Users compiling OpenVPN from the tarball should not need to regenerate the +man/html files unless the source file needs to be modified. + +Further information: + +* Python docutils project: + https://docutils.sourceforge.io/ + +* Quickstart on .rst + https://docutils.sourceforge.io/docs/user/rst/quickstart.html + +* reStructuredText Markup Specifictaion (.rst) + https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html diff --git a/doc/android.txt b/doc/android.txt new file mode 100644 index 0000000..e287be0 --- /dev/null +++ b/doc/android.txt @@ -0,0 +1,101 @@ +This file documents the support in OpenVPN for Android 4.0 and up. + +This support is primarily used in the "OpenVPN for Android" app +(https://github.com/schwabe/ics-openvpn). For building see the developer +README: https://github.com/schwabe/ics-openvpn/blob/master/doc/README.txt + +Android provides the VPNService API +(http://developer.android.com/reference/android/net/VpnService.html) +which allows establishing VPN connections without rooting the device. + +Since all the interfaces are are Android specific the calls to this +interface are made from the UI instead of OpenVPN directly. The API +needs the following parameters: + +- IP and netmask of tun interface +- Networks that should be routed to the tun interface +- DNS Servers and DNS Domain +- MTU + +All IPs/Routes are in CIDR style. Non CIDR routes are not supported. +Notable is the lack of support for setting routes to other interfaces +usually used to avoid the server connection going over the tun +interface. The Android VPNService API has the concept of protecting +a socket from being routed over a interface. Calling protect (fd) +will internally bind the socket to the interface used for the +external connection (usually WiFi or mobile data). + +To use OpenVPN with the VPNService API OpenVPN must be build with +the TARGET_ANDROID compile option. Also the UI must use a UNIX +domain socket to connect to OpenVPN. When compiled as TARGET_ANDROID +OpenVPN will use management callbacks instead of executing traditional +ifconfig/route commands use the need-ok callback mechanism which +will ask + +> NEED-OK command + +where command can be: + +IFCONFIG6 IPv6/netmask +IFCONFIG local remoteOrNetmask MTU topology + +To tell the UI which IPs addresses OpenVPN expects on the interface. +Topology is one of "net30","p2p","subnet" or "undef". + +ROUTE6 network/netmask +ROUTE network netmask + +To tell the UI which routes should be set on the tun interface. + +DNSSERVER IP server address +DNS6SERVER IPv6 server address +DNSDOMAIN searchdomain + +To set the DNS server and search domain. + +The GUI will then respond with a "needok 'command' ok' or "needok +'command' cancel', e.g. "needok 'IFCONFIG' ok". + +PERSIST_TUN_ACTION + +In Android 4.4-4.4.2 a bug exists that does not allow to open a new tun fd +while a tun fd is still open. When OpenVPN wants to open an fd it will do +this query. The UI should compare the last configuration of +the tun device with the current tun configuration and reply with either (or +always respond with OPEN_AFTER_BEFORE/OPEN_BEFORE_CLOSE) + +- NOACTION: Keep using the old fd +- OPEN_AFTER_CLOSE: First close the old fd and then open a new to workaround the bug +- OPEN_BEFORE_CLOSE: the normal behaviour when the VPN configuration changed + +For example the UI could respond with +needok 'PERSIST_TUN_ACTION' OPEN_AFTER_CLOSE + +To protect a socket the OpenVPN will send a PROTECTFD to the UI. +When sending the PROTECTFD command command to the UI it will send +the fd of the socket as ancillary message over the UNIX socket. +The UI will then call protect(fd) on the received socket protecting +it from being routed over the VPN. + +When opening a tun device the OpenVPN process will first send all +route, ifconfig and DNS related configuration to the UI and after +that calls the OPENTUN command to receive a tun fd with the requested +configuration. The UI will than use the collected information to +call the VPNService's establish() method to receive a fd which in +turn is send to the OpenVPN process as ancillary message to the +"needok 'OPENTUN' ok' response. + +The OpenVPN for Android UI extensively uses other features that +are not specific to Android but are rarely used on other platform. +For example using SIGUSR1 and management-hold to restart, pause, +continue the VPN on network changes or the external key management +--management-external-key option and inline files. + +To better support handover between networks, a the management command + +network-change [samenetwork] + +is used on the Android platform. It tells OpenVPN to do the necessary +action when the network changes. Currently this is just calling +the protect callback when using peer-id regardless of the samenetwork. +Without peer-id OpenVPN will generate USR1 when samenetwork is not set. diff --git a/doc/doxygen/Makefile.am b/doc/doxygen/Makefile.am new file mode 100644 index 0000000..299a76c --- /dev/null +++ b/doc/doxygen/Makefile.am @@ -0,0 +1,21 @@ +# +# OpenVPN -- An application to securely tunnel IP networks +# over a single UDP port, with support for SSL/TLS-based +# session authentication and key exchange, +# packet encryption, packet authentication, and +# packet compression. +# +# Copyright (C) 2017-2018 Fox-IT B.V. +# + +MAINTAINERCLEANFILES = \ + $(srcdir)/Makefile.in + +DISTCLEANFILES = openvpn.doxyfile + +.PHONY: doxygen +doxygen: openvpn.doxyfile + doxygen openvpn.doxyfile + +clean-local: + -rm -rf html latex diff --git a/doc/doxygen/doc_compression.h b/doc/doxygen/doc_compression.h new file mode 100644 index 0000000..3176bad --- /dev/null +++ b/doc/doxygen/doc_compression.h @@ -0,0 +1,91 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file Data Channel Compression module documentation file. + */ + +/** + * @defgroup compression Data Channel Compression module + * + * This module offers compression of data channel packets. + * + * @par State structures + * The Data Channel Compression module stores its internal state in a \c + * lzo_compress_workspace structure. This state includes flags which + * control the module's behavior and preallocated working memory. One + * such structure is present for each VPN tunnel, and is stored in the \c + * context.c2.lzo_compwork of the \c context associated with that VPN + * tunnel. + * + * @par Initialization and cleanup + * Every time a new \c lzo_compress_workspace is needed, it must be + * initialized using the \c lzo_compress_init() function. Similarly, + * every time a \c lzo_compress_workspace is no longer needed, it must be + * cleaned up using the \c lzo_compress_uninit() function. These + * functions take care of the allocation and freeing of internal working + * memory, but not of the \c lzo_compress_workspace structures themselves. + * + * @par + * Because of the one-to-one relationship between \c + * lzo_compress_workspace structures and VPN tunnels, the above-mentioned + * initialization and cleanup functions are called directly from the \c + * init_instance() and \c close_instance() functions, which control the + * initialization and cleanup of VPN tunnel instances and their associated + * \c context structures. + * + * @par Packet processing functions + * This module receives data channel packets from the \link data_control + * Data Channel Control module\endlink and processes them according to the + * settings of the packet's VPN tunnel. The \link data_control Data + * Channel Control module\endlink uses the following interface functions: + * - For packets which will be sent to a remote OpenVPN peer: \c + * lzo_compress() + * - For packets which have been received from a remote OpenVPN peer: \c + * lzo_decompress() + * + * @par Settings that control this module's activity + * Whether or not the Data Channel Compression module is active depends on + * the compile-time \c ENABLE_LZO preprocessor macro and the runtime flags + * stored in \c lzo_compress_workspace.flags of the associated VPN tunnel. + * The latter are initialized from \c options.lzo, which gets its value + * from the process's configuration sources, such as its configuration + * file or command line %options. + * + * @par Adaptive compression + * The compression module supports adaptive compression. If this feature + * is enabled, the compression routines monitor their own performance and + * turn compression on or off depending on whether it is leading to + * significantly reduced payload size. + * + * @par Compression algorithms + * This module uses the Lempel-Ziv-Oberhumer (LZO) compression algorithms. + * These offer lossless compression and are designed for high-performance + * decompression. This module uses the external \c lzo library's + * implementation of the algorithms. + * + * @par + * For more information on the LZO library, see:\n + * http://www.oberhumer.com/opensource/lzo/ + */ diff --git a/doc/doxygen/doc_control_processor.h b/doc/doxygen/doc_control_processor.h new file mode 100644 index 0000000..1bbf2d2 --- /dev/null +++ b/doc/doxygen/doc_control_processor.h @@ -0,0 +1,184 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * Control Channel Processor module documentation file. + */ + +/** + * @defgroup control_processor Control Channel Processor module + * + * This module controls the setup and maintenance of VPN tunnels and the + * associated security parameters. + * + * @par This module's role + * The Control Channel Processor module lies at the core of OpenVPN's + * activities. It handles the setup of new VPN tunnels, the negotiation + * of data channel security parameters, the managing of active VPN + * tunnels, and finally the cleanup of expired VPN tunnels. + * + * @par State structures + * A large amount of VPN tunnel state information must be stored within an + * OpenVPN process. A wide variety of container structures are used by + * this module for that purpose. Several of these structures are listed + * below, and the function of the first three VPN tunnel state containers + * is described in more detail later. + * - VPN tunnel state containers: + * - \c tls_multi, security parameter state for a single VPN tunnel. + * Contains three instances of the \c tls_session structure. + * - \c tls_session, security parameter state of a single session + * within a VPN tunnel. Contains two instances of the \c key_state + * structure. + * - \c key_state, security parameter state of one TLS and data + * channel %key set. + * - Data channel security parameter containers: + * - \c key_ctx_bi, container for two sets of OpenSSL cipher and/or + * HMAC context (both directions). Contains two instances of the \c + * key_ctx structure. + * - \c key_ctx, container for one set of OpenSSL cipher and/or HMAC + * context (one directions. + * - Key material containers: + * - \c key2, container for two sets of cipher and/or HMAC %key + * material (both directions). Contains two instances of the \c key + * structure. + * - \c key, container for one set of cipher and/or HMAC %key material + * (one direction). + * - \c key_direction_state, ordering of %key material within the \c + * key2.key array. + * - Key method 2 random material containers: + * - \c key_source2, container for both halves of random material used + * for %key method 2. Contains two instances of the \c key_source + * structure. + * - \c key_source, container for one half of random material used for + * %key method 2. + * + * @par The life of a \c tls_multi object + * A \c tls_multi structure contains all the security parameter state + * information related to the control and data channels of one VPN tunnel. + * Its life cycle can be summarized as follows: + * -# Initialization: \c tls_multi_init() and \c + * tls_multi_init_finalize(), which are called (indirectly) from \c + * init_instance() when initializing a new \c context structure. + * - Initializes a \c tls_multi structure. + * - Allocates the three \c tls_session objects contained by the \c + * tls_multi structure, and initializes as appropriate. + * -# Management: \c tls_multi_process() and \c tls_pre_decrypt() + * - If a new session is initiated by the remote peer, then \c + * tls_pre_decrypt() starts the new session negotiation in the + * un-trusted \c tls_session. + * - If the, as yet, un-trusted \c tls_session authenticates + * successfully, then \c tls_multi_process() moves it so as to be + * the active \c tls_session. + * - If an error occurs during processing of a \c key_state object, + * then \c tls_multi_process() cleans up and initializes the + * associated \c tls_session object. If the error occurred in the + * active \c key_state of the active \c tls_session and the + * lame-duck \c key_state of that \c tls_session has not yet + * expired, it is preserved as fallback. + * -# Cleanup: \c tls_multi_free(), which is called (indirectly) from \c + * close_instance() when cleaning up a \c context structure. + * - Cleans up a \c tls_multi structure. + * - Cleans up the three \c tls_session objects contained by the \c + * tls_multi structure. + * + * @par The life of a \c tls_session object + * A \c tls_session structure contains the state information related to an + * active and a lame-duck \c key_state. Its life cycle can be summarized + * as follows: + * -# Initialization: \c tls_session_init() + * - Initializes a \c tls_session structure. + * - Initializes the primary \c key_state by calling \c + * key_state_init(). + * -# Renegotiation: \c key_state_soft_reset() + * - Cleans up the old lame-duck \c key_state by calling \c + * key_state_free(). + * - Moves the old primary \c key_state to be the new lame-duck \c + * key_state. + * - Initializes a new primary \c key_state by calling \c + * key_state_init(). + * -# Cleanup: \c tls_session_free() + * - Cleans up a \c tls_session structure. + * - Cleans up all \c key_state objects associated with the session by + * calling \c key_state_free() for each. + * + * @par The life of a \c key_state object + * A \c key_state structure represents one control and data channel %key + * set. It contains an OpenSSL TLS object that encapsulates the control + * channel, and the data channel security parameters needed by the \link + * data_crypto Data Channel Crypto module\endlink to perform cryptographic + * operations on data channel packets. Its life cycle can be summarized + * as follows: + * -# Initialization: \c key_state_init() + * - Initializes a \c key_state structure. + * - Creates a new OpenSSL TLS object to encapsulate this new control + * channel session. + * - Sets \c key_state.state to \c S_INITIAL. + * - Allocates several internal buffers. + * - Initializes new reliability layer structures for this key set. + * -# Negotiation: \c tls_process() + * - The OpenSSL TLS object negotiates a TLS session between itself + * and the remote peer's TLS object. + * - Key material is generated and exchanged through the TLS session + * between OpenVPN peers. + * - Both peers initialize their data channel cipher and HMAC key + * contexts. + * - On successful negotiation, the \c key_state.state will progress + * from \c S_INITIAL to \c S_ACTIVE and \c S_NORMAL. + * -# Active tunneling: \link data_crypto Data Channel Crypto + * module\endlink + * - Data channel packet to be sent to a remote OpenVPN peer: + * - \c tls_pre_encrypt() loads the security parameters from the \c + * key_state into a \c crypto_options structure. + * - \c openvpn_encrypt() uses the \c crypto_options to an encrypt + * and HMAC sign the data channel packet. + * - Data channel packet received from a remote OpenVPN peer: + * - \c tls_pre_decrypt() loads the security parameters from the \c + * key_state into a \c crypto_options structure. + * - \c openvpn_encrypt() uses the \c crypto_options to + * authenticate and decrypt the data channel packet. + * -# Cleanup: \c key_state_free() + * - Cleans up a \c key_state structure together with its OpenSSL TLS + * object, key material, internal buffers, and reliability layer + * structures. + * + * @par Control functions + * The following two functions drive the Control Channel Processor's + * activities. + * - \c tls_multi_process(), iterates through the \c tls_session objects + * within a given \c tls_multi of a VPN tunnel, and calls \c + * tls_process() for each \c tls_session which is being set up, is + * already active, or is busy expiring. + * - \c tls_process(), performs the Control Channel Processor module's + * core handling of received control channel messages, and generates + * appropriate messages to be sent. + * + * @par Functions which control data channel key generation + * - Key method 1 key exchange functions were removed from OpenVPN 2.5 + * - Key method 2 key exchange functions: + * - \c key_method_2_write(), generates and processes key material to + * be sent to the remote OpenVPN peer. + * - \c key_method_2_read(), processes key material received from the + * remote OpenVPN peer. + */ diff --git a/doc/doxygen/doc_control_tls.h b/doc/doxygen/doc_control_tls.h new file mode 100644 index 0000000..5cb7c53 --- /dev/null +++ b/doc/doxygen/doc_control_tls.h @@ -0,0 +1,104 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * Control Channel TLS module documentation file. + */ + +/** + * @defgroup control_tls Control Channel TLS module + * + * This module provides secure encapsulation of control channel messages + * exchanged between OpenVPN peers. + * + * The Control Channel TLS module uses the Transport Layer Security (TLS) + * protocol to provide an encrypted communication channel between the + * local OpenVPN process and a remote peer. This protocol simultaneously + * offers certificate-based authentication of the communicating parties. + * + * @par This module's roles + * The Control Channel TLS module is essential for the security of any + * OpenVPN-based system. On the one hand, it performs the security + * operations necessary to protect control channel messages exchanged + * between OpenVPN peers. On the other hand, before the control and data + * channels are even setup, it controls the exchange of certificates and + * verification of the remote's identity during negotiation of VPN + * tunnels. + * + * @par + * The former role is described below. The latter is described in the + * documentation for the \c verify_callback() function. + * + * @par + * In other words, this module takes care of the confidentiality and + * integrity of data channel communications, and the authentication of + * both the communicating parties and the control channel messages + * exchanged. + * + * @par Initialization and cleanup + * Because of the one-to-one relationship between control channel TLS + * state and \c key_state structures, the initialization and cleanup of an + * instance of the Control Channel TLS module's state happens within the + * \c key_state_init() and \c key_state_free() functions. In other words, + * each \c key_state object contains exactly one OpenSSL SSL-BIO object, + * which is initialized and cleaned up together with the rest of the \c + * key_state object. + * + * @par Packet processing functions + * This object behaves somewhat like a black box with a ciphertext and a + * plaintext I/O port. Its interaction with OpenVPN's control channel + * during operation takes place within the \c tls_process() function of + * the \link control_processor Control Channel Processor\endlink. The + * following functions are available for processing packets: + * - If ciphertext received from the remote peer is available in the \link + * reliable Reliability Layer\endlink: + * - Insert it into the ciphertext-side of the SSL-BIO. + * - Use function: \c key_state_write_ciphertext() + * - If ciphertext can be extracted from the ciphertext-side of the + * SSL-BIO: + * - Pass it to the \link reliable Reliability Layer\endlink for sending + * to the remote peer. + * - Use function: \c key_state_read_ciphertext() + * - If plaintext can be extracted from the plaintext-side of the SSL-BIO: + * - Pass it on to the \link control_processor Control Channel + * Processor\endlink for local processing. + * - Use function: \c key_state_read_plaintext() + * - If plaintext from the \link control_processor Control Channel + * Processor\endlink is available to be sent to the remote peer: + * - Insert it into the plaintext-side of the SSL-BIO. + * - Use function: \c key_state_write_plaintext() or \c + * key_state_write_plaintext_const() + * + * @par Transport Layer Security protocol implementation + * This module uses the OpenSSL library's implementation of the TLS + * protocol in the form of an OpenSSL SSL-BIO object. + * + * @par + * For more information on the OpenSSL library's BIO objects, please see: + * - OpenSSL's generic BIO objects: + * http://www.openssl.org/docs/crypto/bio.html + * - OpenSSL's SSL-BIO object: + * http://www.openssl.org/docs/crypto/BIO_f_ssl.html + */ diff --git a/doc/doxygen/doc_data_control.h b/doc/doxygen/doc_data_control.h new file mode 100644 index 0000000..ad2a308 --- /dev/null +++ b/doc/doxygen/doc_data_control.h @@ -0,0 +1,102 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * Data Channel Control module documentation file. + */ + +/** + * @defgroup data_control Data Channel Control module + * + * This module controls the processing of packets as they pass through the + * data channel. + * + * The Data Channel Control module controls the processing of packets as + * they pass through the data channel. The processing includes packet + * compression, fragmentation, and the performing of security operations + * on the packets. This module does not do the processing itself, but + * passes the packet to other data channel modules to perform the + * appropriate actions. + * + * Packets can travel in two directions through the data channel. They + * can be going to a remote destination which is reachable through a VPN + * tunnel, in which case this module prepares them to be sent out through + * a VPN tunnel. On the other hand, they can have been received through a + * VPN tunnel from a remote OpenVPN peer, in which case this module + * retrieves the packet in its original form as it was before entering the + * VPN tunnel on the remote OpenVPN peer. How this module processes + * packets traveling in the two directions is discussed in more detail + * below. + * + * @par Packets to be sent to a remote OpenVPN peer + * This module's main function for processing packets traveling in this + * direction is \c encrypt_sign(), which performs the following processing + * steps: + * - Call the \link compression Data Channel Compression module\endlink to + * perform packet compression if necessary. + * - Call the \link fragmentation Data Channel Fragmentation + * module\endlink to perform packet fragmentation if necessary. + * - Call the \link data_crypto Data Channel Crypto module\endlink to + * perform the required security operations. + * + * @par + * See the \c encrypt_sign() documentation for details of these + * interactions. + * + * @par + * After the above processing is complete, the packet is ready to be sent + * to a remote OpenVPN peer as a VPN tunnel packet. The actual sending of + * the packet is handled by the \link external_multiplexer External + * Multiplexer\endlink. + * + * @par Packets received from a remote OpenVPN peer + * The function that controls how packets traveling in this direction are + * processed is \c process_incoming_link(). That function, however, also + * performs some of the tasks required for the \link external_multiplexer + * External Multiplexer\endlink and is therefore listed as part of that + * module, instead of here. + * + * @par + * After the \c process_incoming_link() function has determined that a + * received packet is a data channel packet, it performs the following + * processing steps: + * - Call the \link data_crypto Data Channel Crypto module\endlink to + * perform the required security operations. + * - Call the \link fragmentation Data Channel Fragmentation + * module\endlink to perform packet reassembly if necessary. + * - Call the \link compression Data Channel Compression module\endlink to + * perform packet decompression if necessary. + * + * @par + * See the \c process_incoming_link() documentation for details of these + * interactions. + * + * @par + * After the above processing is complete, the packet is in its original + * form again as it was received by the remote OpenVPN peer. It can now + * be routed further to its final destination. If that destination is a + * locally reachable host, then the \link internal_multiplexer Internal + * Multiplexer\endlink will send it there. + */ diff --git a/doc/doxygen/doc_data_crypto.h b/doc/doxygen/doc_data_crypto.h new file mode 100644 index 0000000..3828089 --- /dev/null +++ b/doc/doxygen/doc_data_crypto.h @@ -0,0 +1,70 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * Data Channel Crypto module documentation file. + */ + +/** + * @addtogroup data_crypto Data Channel Crypto module + * + * The Data Channel Crypto Module performs cryptographic operations on + * data channel packets. + * + * @par Security parameters + * This module is merely the user of a VPN tunnel's security parameters. + * It does not perform the negotiation and setup of the security + * parameters, nor the %key generation involved. These actions are done + * by the \link control_processor Control Channel Processor\endlink. This + * module receives the appropriate security parameters from that module in + * the form of a \c crypto_options structure when they are necessary for + * processing a packet. + * + * @par Packet processing functions + * This module receives data channel packets from the \link data_control + * Data Channel Control module\endlink and processes them according to the + * security parameters of the packet's VPN tunnel. The \link data_control + * Data Channel Control module\endlink uses the following interface + * functions: + * - For packets which will be sent to a remote OpenVPN peer: + * - \c tls_pre_encrypt() + * - \c openvpn_encrypt() + * - \c tls_post_encrypt() + * - For packets which have been received from a remote OpenVPN peer: + * - \c tls_pre_decrypt() (documented as part of the \link + * external_multiplexer External Multiplexer\endlink) + * - \c openvpn_decrypt() + * + * @par Settings that control this module's activity + * How the data channel processes packets received from the \link data_control + * Data Channel Control module\endlink at runtime depends on the associated + * \c crypto_options structure. To perform cryptographic operations, the + * \c crypto_options.key_ctx_bi must contain the correct cipher and HMAC + * security parameters for the direction the packet is traveling in. + * + * @par Crypto algorithms + * This module uses the crypto algorithm implementations of the external + * crypto library (currently either OpenSSL (default), or mbed TLS). + */ diff --git a/doc/doxygen/doc_eventloop.h b/doc/doxygen/doc_eventloop.h new file mode 100644 index 0000000..8bd2635 --- /dev/null +++ b/doc/doxygen/doc_eventloop.h @@ -0,0 +1,66 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * Main Event Loop module documentation file. + */ + +/** + * @defgroup eventloop Main Event Loop module + * + * This main event loop module drives the packet processing of OpenVPN. + * + * OpenVPN is an event driven system. Its activities are driven by a main + * event loop, which repeatedly waits for one of several predefined events + * to occur, and then calls the appropriate module to handle the event. + * The major types of network events that OpenVPN processes are: + * - A packet can be read from the external network interface. + * - The main event loop activates the \link external_multiplexer + * External Multiplexer\endlink to read and process the packet. + * - A packet can be read from the virtual tun/tap network interface. + * - The main event loop activates the \link internal_multiplexer + * Internal Multiplexer\endlink to read and process the packet. + * - If a packet is ready to be sent out as a VPN tunnel packet: the + * external network interface can be written to. + * - The main event loop activates the \link external_multiplexer + * External Multiplexer\endlink to send the packet. + * - If a packet is ready to be sent to a locally reachable destination: + * the virtual tun/tap network interface can be written to. + * - The main event loop activates the \link internal_multiplexer + * Internal Multiplexer\endlink to send the packet. + * + * Beside these external events, OpenVPN also processes other types of + * internal events. These include scheduled events, such as resending of + * non-acknowledged control channel messages. + * + * @par Main event loop implementations + * + * Depending on the mode in which OpenVPN is running, a different main + * event loop function is called to drive the event processing. The + * following implementations are available: + * - Client mode using UDP or TCP: \c tunnel_point_to_point() + * - Server mode using UDP: \c tunnel_server_udp_single_threaded() + * - Server mode using TCP: \c tunnel_server_tcp() + */ diff --git a/doc/doxygen/doc_external_multiplexer.h b/doc/doxygen/doc_external_multiplexer.h new file mode 100644 index 0000000..692c15c --- /dev/null +++ b/doc/doxygen/doc_external_multiplexer.h @@ -0,0 +1,45 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * External Multiplexer module documentation file. + */ + +/** + * @addtogroup external_multiplexer External Multiplexer module + * + * The External Multiplexer is the link between the external network + * interface and the other OpenVPN modules. It reads packets from the + * external network interface, determines which remote OpenVPN peer and + * VPN tunnel they are associated with, and whether they are data channel + * or control channel packets. It then passes the packets on to the + * appropriate processing module. + * + * This module also handles packets traveling in the reverse direction, + * which have been generated by the local control channel or which have + * already been processed by the \link data_control Data Channel Control + * module\endlink and are destined for a remote host reachable through a + * VPN tunnel. + */ diff --git a/doc/doxygen/doc_fragmentation.h b/doc/doxygen/doc_fragmentation.h new file mode 100644 index 0000000..90e8d9e --- /dev/null +++ b/doc/doxygen/doc_fragmentation.h @@ -0,0 +1,95 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * Data Channel Fragmentation module documentation file. + */ + +/** + * @defgroup fragmentation Data Channel Fragmentation module + * + * The Data Channel Fragmentation module offers fragmentation of data + * channel packets. + * + * @par State structures + * The Data Channel Fragmentation module stores its internal state in a \c + * fragment_master structure. One such structure is present for each VPN + * tunnel, and is stored in \c context.c2.fragment of the \c context + * associated with that VPN tunnel. + * + * @par + * The \c fragment_master structure contains one \c fragment_list + * structure \c fragment_master.incoming. This is a list of \c fragment + * structures, each of which can store the parts of one fragmented packet + * while it is being reassembled. The \c fragment_master structure also + * contains one \c buffer called \c fragment_master.outgoing, in which a + * data channel large packet to be sent to a remote OpenVPN peer can be + * broken up into parts to be sent one by one. + * + * @par Initialization and cleanup + * Every time a new \c fragment_master is needed, it must be allocated and + * initialized by the \c fragment_init() function. Similarly, every time + * a \c fragment_master is no longer needed, it must be cleaned up using + * the \c fragment_free() function. These functions take care of the + * allocation and freeing of the \c fragment_master structure itself and + * all internal memory required for the use of that structure. Note that + * this behavior is different from that displayed by the \link compression + * Data Channel Compression module\endlink. + * + * @par + * Because of the one-to-one relationship between \c fragment_master + * structures and VPN tunnels, the above-mentioned initialization and + * cleanup functions are called directly from the \c init_instance() and + * \c close_instance() functions, which control the initialization and + * cleanup of VPN tunnel instances and their associated \c context + * structures. + * + * @par Packet processing functions + * This module receives data channel packets from the \link data_control + * Data Channel Control module\endlink and processes them according to the + * settings of the packet's VPN tunnel. The \link data_control Data + * Channel Control module\endlink uses the following interface functions: + * - For packets which will be sent to a remote OpenVPN peer: \c + * fragment_outgoing() \n This function inspects data channel packets as + * they are being made ready to be sent as VPN tunnel packets to a + * remote OpenVPN peer. If a packet's size is larger than its + * destination VPN tunnel's maximum transmission unit (MTU), then this + * module breaks that packet up into smaller parts, each of which is + * smaller than or equal to the VPN tunnel's MTU. See \c + * fragment_outgoing() for details. + * - For packets which have been received from a remote OpenVPN peer: \c + * fragment_incoming() \n This function inspects data channel packets + * that have been received from a remote OpenVPN peer through a VPN + * tunnel. It reads the fragmentation header of the packet, and + * depending on its value performs the appropriate action. See \c + * fragment_incoming() for details. + * + * @par Settings that control this module's activity + * Whether the Data Channel Fragmentation module is active or not depends + * on the compile-time \c ENABLE_FRAGMENT preprocessor macro and the + * runtime flag \c options.fragment, which gets its value from the + * process's configuration sources, such as the configuration file and + * commandline %options. + */ diff --git a/doc/doxygen/doc_internal_multiplexer.h b/doc/doxygen/doc_internal_multiplexer.h new file mode 100644 index 0000000..c68a09c --- /dev/null +++ b/doc/doxygen/doc_internal_multiplexer.h @@ -0,0 +1,43 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * Internal Multiplexer module documentation file. + */ + +/** + * @addtogroup internal_multiplexer Internal Multiplexer module + * + * The Internal Multiplexer is the link between the virtual tun/tap + * network interface and the \link data_control Data Channel Control + * module\endlink. It reads packets from the virtual network interface, + * determines for which remote OpenVPN peer they are destined, and then + * passes the packets on to the Data Channel Control module together with + * information about their destination VPN tunnel instance. + * + * This module also handles packets traveling in the reverse direction, + * which have already been processed by the Data Channel Control module + * and are destined for a locally reachable host. + */ diff --git a/doc/doxygen/doc_key_generation.h b/doc/doxygen/doc_key_generation.h new file mode 100644 index 0000000..4bb9c70 --- /dev/null +++ b/doc/doxygen/doc_key_generation.h @@ -0,0 +1,148 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * Key generation documentation file. + */ + +/** + * @page key_generation Data channel %key generation + * + * This section describes how OpenVPN peers generate and exchange %key + * material necessary for the security operations performed on data + * channel packets. + * + * The %key generation and exchange process between OpenVPN client and + * server occurs every time data channel security parameters are + * negotiated, for example during the initial setup of a VPN tunnel or + * when the active security parameters expire. In source code terms, this + * is when a new key_state structure is initialized. + * + * @section key_generation_method Key methods + * + * OpenVPN supports two different ways of generating and exchanging %key + * material between client and server. These are known as %key method 1 + * and %key method 2. %Key method 2 is the recommended method. Both are + * explained below. + * + * @subsection key_generation_method_1 Key method 1 + * + * -# Each host generates its own random material. + * -# Each host uses its locally generated random material as %key data + * for encrypting and signing packets sent to the remote peer. + * -# Each host then sends its random material to the remote peer, so that + * the remote peer can use that %key data for authenticating and + * decrypting received packets. + * + * @subsection key_generation_method_2 Key method 2 + * + * -# The client generates random material in the following amounts: + * - Pre-master secret: 48 bytes + * - Client's PRF seed for master secret: 32 bytes + * - Client's PRF seed for %key expansion: 32 bytes + * -# The client sends its share of random material to the server. + * -# The server generates random material in the following amounts: + * - Server's PRF seed for master secret: 32 bytes + * - Server's PRF seed for %key expansion: 32 bytes + * -# The server computes the %key expansion using its own and the + * client's random material. + * -# The server sends its share of random material to the client. + * -# The client computes the %key expansion using its own and the + * server's random material. + * + * %Key method 2 %key expansion is performed by the \c + * generate_key_expansion() function. Please refer to its source code for + * details of the %key expansion process. + * + * @subsection key_generation_random Source of random material + * + * OpenVPN uses the either the OpenSSL library or the mbed TLS library as its + * source of random material. + * + * In OpenSSL, the \c RAND_bytes() function is called + * to supply cryptographically strong pseudo-random data. The following links + * contain more information on this subject: + * - For OpenSSL's \c RAND_bytes() function: + * http://www.openssl.org/docs/crypto/RAND_bytes.html + * - For OpenSSL's pseudo-random number generating system: + * http://www.openssl.org/docs/crypto/rand.html + * - For OpenSSL's support for external crypto modules: + * http://www.openssl.org/docs/crypto/engine.html + * + * In mbed TLS, the Havege random number generator is used. For details, see + * the mbed TLS documentation. + * + * @section key_generation_exchange Key exchange: + * + * The %key exchange process is initiated by the OpenVPN process running + * in client mode. After the initial three-way handshake has successfully + * completed, the client sends its share of random material to the server, + * after which the server responds with its part. This process is + * depicted below: + * +@verbatim + Client Client Server Server + State Action Action State +---------- -------------------- -------------------- ---------- + + ... waiting until three-way handshake complete ... +S_START S_START + key_method_?_write() + send to server --> --> --> --> receive from client +S_SENT_KEY key_method_?_read() + S_GOT_KEY + key_method_?_write() + receive from server <-- <-- <-- <-- send to client + key_method_?_read() S_SENT_KEY +S_GOT_KEY + ... waiting until control channel fully synchronized ... +S_ACTIVE S_ACTIVE +@endverbatim + * + * For more information about the client and server state values, see the + * \link control_processor Control Channel Processor module\endlink. + * + * Depending on which %key method is used, the \c ? in the function names + * of the diagram above is a \c 1 or a \c 2. For example, if %key method + * 2 is used, that %key exchange would be started by the client calling \c + * key_method_2_write(). These functions are called from the \link + * control_processor Control Channel Processor module's\endlink \c + * tls_process() function and control the %key generation and exchange + * process as follows: + * - %Key method 1 has been removed in OpenVPN 2.5 + * - %Key method 2: + * - \c key_method_2_write(): generate random material locally, and if + * in server mode generate %key expansion. + * - \c key_method_2_read(): read random material received from remote + * peer, and if in client mode generate %key expansion. + * + * @subsection key_generation_encapsulation Transmission of key material + * + * The OpenVPN client and server communicate with each other through their + * control channel. This means that all of the data transmitted over the + * network, such as random material for %key generation, is encapsulated + * in a TLS layer. For more details, see the \link control_tls Control + * Channel TLS module\endlink documentation. + */ diff --git a/doc/doxygen/doc_mainpage.h b/doc/doxygen/doc_mainpage.h new file mode 100644 index 0000000..6016d07 --- /dev/null +++ b/doc/doxygen/doc_mainpage.h @@ -0,0 +1,161 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * Main page documentation file. + */ + +/** + * @mainpage OpenVPN source code documentation + * + * This documentation describes the internal structure of OpenVPN. It was + * automatically generated from specially formatted comment blocks in + * OpenVPN's source code using Doxygen. (See + * http://www.stack.nl/~dimitri/doxygen/ for more information on Doxygen) + * + * The \ref mainpage_modules "Modules section" below gives an introduction + * into the high-level module concepts used throughout this documentation. + * The \ref mainpage_relatedpages "Related Pages section" below describes + * various special subjects related to OpenVPN's implementation which are + * discussed in the related pages section. + * + * @section mainpage_modules Modules + * + * For the purpose of describing the internal structure of OpenVPN, this + * documentation and the underlying source code has been broken up into a + * number of conceptually well-defined parts, known as modules. Each + * module plays a specific role within the OpenVPN process, and in most + * cases each module has a clear interfacing strategy for interacting with + * other modules. + * + * The following modules have been defined: + * - Driver module: + * - The \link eventloop Main Event Loop\endlink: this module drives the + * event handling of OpenVPN. It implements various types of + * select-loop which wait until an event happens, and then delegate + * the handling of that event to the appropriate module. + * - Network interface modules: + * - The \link external_multiplexer External Multiplexer\endlink: this + * module sends and receives packets to and from remote OpenVPN peers + * over the external network interface. It also takes care of + * demultiplexing received packets to their appropriate VPN tunnel and + * splitting control channel and data channel packets. + * - The \link internal_multiplexer Internal Multiplexer\endlink: this + * module sends and receives packets to and from locally reachable + * posts over the virtual tun/tap network interface. It also takes + * care of determining through which VPN tunnel a received packet must + * be sent to reach its destination. + * - Control channel modules: + * - The \link reliable Reliability Layer\endlink: this module offers a + * %reliable and sequential transport layer for control channel + * messages. + * - The \link control_tls Control Channel TLS module\endlink: this + * module offers a secure encapsulation of control channel messages + * using the TLS protocol. + * - The \link control_processor Control Channel Processor\endlink: his + * module manages the setup, maintenance, and shut down of VPN + * tunnels. + * - Data channel modules: + * - The \link data_control Data Channel Control module\endlink: this + * module controls the processing of data channel packets and, + * depending on the settings of the packet's VPN tunnel, passes the + * packet to the three modules below for handling. + * - The \link data_crypto Data Channel Crypto module\endlink: this + * module performs security operations on data channel packets. + * - The \link fragmentation Data Channel Fragmentation module\endlink: + * this module offers fragmentation of data channel packets larger + * than the VPN tunnel's MTU. + * - The \link compression Data Channel Compression module\endlink: this + * module offers compression of data channel packets. + * + * @subsection mainpage_modules_example Example event: receiving a packet + * + * OpenVPN handles many types of events during operation. These include + * external events, such as network traffic being received, and internal + * events, such as a %key session timing out causing renegotiation. An + * example event, receiving a packet over the network, is described here + * together with which modules play what roles: + * -# The \link eventloop Main Event Loop\endlink detects that a packet + * can be read from the external or the virtual tun/tap network + * interface. + * -# The \link eventloop Main Event Loop\endlink calls the \link + * external_multiplexer External Multiplexer\endlink or \link + * internal_multiplexer Internal Multiplexer\endlink to read and + * process the packet. + * -# The multiplexer module determines the type of packet and its + * destination, and passes the packet on to the appropriate handling + * module: + * - A control channel packet received by the \link + * external_multiplexer External Multiplexer\endlink is passed on + * through the \link reliable Reliability Layer\endlink and the \link + * control_tls Control Channel TLS module\endlink to the \link + * control_processor Control Channel Processor\endlink. + * - A data channel packet received by either multiplexer module is + * passed on to the \link data_control Data Channel Control + * module\endlink. + * -# The packet is processed by the appropriate control channel or data + * channel modules. + * -# If, after processing the packet, a resulting packet is generated + * that needs to be sent to a local or remote destination, it is given + * to the \link external_multiplexer External Multiplexer\endlink or + * \link internal_multiplexer Internal Multiplexer\endlink for sending. + * -# If a packet is waiting to be sent by either multiplexer module and + * the \link eventloop Main Event Loop\endlink detects that data can be + * written to the associated network interface, it calls the + * multiplexer module to send the packet. + * + * @section mainpage_relatedpages Related pages + * + * This documentation includes a number of descriptions of various aspects + * of OpenVPN and its implementation. These are not directly related to + * one module, function, or data structure, and are therefore listed + * separately under "Related Pages". + * + * @subsection mainpage_relatedpages_key_generation Data channel key generation + * + * The @ref key_generation "Data channel key generation" related page + * describes how, during VPN tunnel setup and renegotiation, OpenVPN peers + * generate and exchange the %key material required for the symmetric + * encryption/decryption and HMAC signing/verifying security operations + * performed on data channel packets. + * + * @subsection mainpage_relatedpages_tunnel_state VPN tunnel state + * + * The @ref tunnel_state "Structure of VPN tunnel state storage" related + * page describes how an OpenVPN process manages the state information + * associated with its active VPN tunnels. + * + * @subsection mainpage_relatedpages_network_protocol Network protocol + * + * The @ref network_protocol "Network protocol" related page describes the + * format and content of VPN tunnel packets exchanged between OpenVPN + * peers. + * + * @subsection mainpage_relatedpages_memory_management Memory management + * + * The @ref memory_management "Memory management strategies" related page + * gives a brief introduction into OpenVPN's memory %buffer library and + * garbage collection facilities. + */ diff --git a/doc/doxygen/doc_memory_management.h b/doc/doxygen/doc_memory_management.h new file mode 100644 index 0000000..1f16328 --- /dev/null +++ b/doc/doxygen/doc_memory_management.h @@ -0,0 +1,98 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * Memory management strategies documentation file. + */ + +/** + * @page memory_management OpenVPN's memory management strategies + * + * This section describes several implementation details relating to + * OpenVPN's memory management strategies. + * + * During operation, the OpenVPN process performs all kinds of operations + * on blocks of data. Receiving packets, encrypting content, prepending + * headers, etc. To make the programmer's job easier and to decrease the + * likelihood of memory-related bugs, OpenVPN uses its own memory %buffer + * library and garbage collection facilities. These are described in + * brief here. + * + * @section memory_management_buffer The buffer structure + * + * The \c buffer structure is a wrapper around a block of dynamically + * allocated memory which keeps track of the block's capacity \c + * buffer.capacity and location in memory \c buffer.data. This structure + * supports efficient prepending and appending within the allocated memory + * through the use of offset \c buffer.offset and length \c buffer.len + * fields. See the \c buffer documentation for more details on the + * structure itself. + * + * OpenVPN's %buffer library, implemented in the \c buffer.h and \c + * buffer.c files, contains many utility functions for working with \c + * buffer structures. These functions facilitate common operations, such + * as allocating, freeing, reading and writing to \c buffer structures, + * and even offer several more advanced operations, such as string + * matching and creating sub-buffers. + * + * Not only do these utility functions make working with \c buffer + * structures easy, they also perform extensive error checking. Each + * function, where necessary, checks whether enough space is available + * before performing its actions. This minimizes the chance of bugs + * leading to %buffer overflows and other vulnerabilities. + * + * @section memory_management_frame The frame structure + * + * The \c frame structure keeps track of the maximum allowed packet + * geometries of a network connection. + * + * It is used, for example, to determine the size of \c buffer structures + * in which to store data channel packets. This is done by having each + * data channel processing module register the maximum amount of extra + * space it will need for header prepending and content expansion in the + * \c frame structure. Once these parameters are known, \c buffer + * structures can be allocated, based on the \c frame parameters, so that + * they are large enough to allow efficient prepending of headers and + * processing of content. + * + * @section memory_management_garbage Garbage collection + * + * OpenVPN has many sizable functions which perform various actions + * depending on their %context. This makes it difficult to know in advance + * exactly how much memory must be allocated. The garbage collection + * facilities are used to keep track of dynamic allocations, thereby + * allowing easy collective freeing of the allocated memory. + * + * The garbage collection system is implemented by the \c gc_arena and \c + * gc_entry structures. The arena represents a garbage collecting unit, + * and contains a linked list of entries. Each entry represents one block + * of dynamically allocated memory. + * + * The garbage collection system also contains various utility functions + * for working with the garbage collection structures. These include + * functions for initializing new arenas, allocating memory of a given + * size and registering the allocation in an arena, and freeing all the + * allocated memory associated with an arena. + */ diff --git a/doc/doxygen/doc_protocol_overview.h b/doc/doxygen/doc_protocol_overview.h new file mode 100644 index 0000000..0821222 --- /dev/null +++ b/doc/doxygen/doc_protocol_overview.h @@ -0,0 +1,195 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file Network protocol overview documentation file. + */ + +/** + * @page network_protocol OpenVPN's network protocol + * + * Description of packet structure in OpenVPN's network protocol. + * + * This document describes the structure of packets exchanged between + * OpenVPN peers. It is based on the protocol description in the \c ssl.h + * file. + * + * @section network_protocol_external Outer structure of packets exchanged between OpenVPN peers + * + * VPN tunnel packets are transported between OpenVPN peers using the UDP + * or TCP protocols. Their structure is described below. + * + * @subsection network_protocol_external_structure External packet structure + * + * - packet length (16 bits, unsigned) [TCP-mode only]: always sent as + * plain text. Since TCP is a stream protocol, this packet length + * defines the packetization of the stream. + * - packet opcode and key_id (8 bits) [TLS-mode only]: + * - package message type (high 5 bits) + * - key_id (low 3 bits): the key_id refers to an already negotiated + * TLS session. OpenVPN seamlessly renegotiates the TLS session by + * using a new key_id for the new session. Overlap (controlled by + * user definable parameters) between old and new TLS sessions is + * allowed, providing a seamless transition during tunnel operation. + * - payload (n bytes) + * + * @subsection network_protocol_external_types Message types + * + * The type of a VPN tunnel packet is indicated by its opcode. The + * following describes the various opcodes available. + * + * - Control channel messages: + * - \ref P_CONTROL_HARD_RESET_CLIENT_V1 -- %Key method 1, initial %key + * from client, forget previous state. + * - \ref P_CONTROL_HARD_RESET_SERVER_V1 -- %Key method 1, initial %key + * from server, forget previous state. + * - \ref P_CONTROL_HARD_RESET_CLIENT_V2 -- %Key method 2, initial %key + * from client, forget previous state. + * - \ref P_CONTROL_HARD_RESET_SERVER_V2 -- %Key method 2, initial %key + * from server, forget previous state. + * - \ref P_CONTROL_SOFT_RESET_V1 -- New %key, with a graceful + * transition from old to new %key in the sense that a transition + * window exists where both the old or new key_id can be used. + * - \ref P_CONTROL_V1 -- Control channel packet (usually TLS + * ciphertext). + * - \ref P_ACK_V1 -- Acknowledgement for control channel packets + * received. + * - Data channel messages: + * - \ref P_DATA_V1 -- Data channel packet containing data channel + * ciphertext. + * - \ref P_DATA_V2 -- Data channel packet containing peer-id and data + * channel ciphertext. + * + * @subsection network_protocol_external_key_id Session IDs and Key IDs + * + * OpenVPN uses two different forms of packet identifiers: + * - The first form is 64 bits and is used for all control channel + * messages. This form is referred to as a \c session_id. + * - Data channel messages on the other hand use a shortened form of 3 + * bits for efficiency reasons since the vast majority of OpenVPN + * packets in an active tunnel will be data channel messages. This + * form is referred to as a \c key_id. + * + * The control and data channels use independent packet-id sequences, + * because the data channel is an unreliable channel while the control + * channel is a %reliable channel. Each use their own independent HMAC + * keys. + * + * @subsection network_protocol_external_reliable Control channel reliability layer + * + * Control channel messages (\c P_CONTROL_* and \c P_ACK_* message types) + * are TLS ciphertext packets which have been encapsulated inside of a + * reliability layer. The reliability layer is implemented as a + * straightforward acknowledge and retransmit model. + * + * Acknowledgments of received messages can be encoded in either the + * dedicated \c P_ACK_* record or they can be prepended to a \c + * P_CONTROL_* message. + * + * See the \link reliable Reliability Layer\endlink module for a detailed + * description. + * + * @section network_protocol_control Structure of control channel messages + * + * @subsection network_protocol_control_ciphertext Structure of ciphertext control channel messages + * + * Control channel packets in ciphertext form consist of the following + * parts: + * + * - local \c session_id (random 64 bit value to identify TLS session). + * - HMAC signature of entire encapsulation header for HMAC firewall + * [only if \c --tls-auth is specified] (usually 16 or 20 bytes). + * - packet-id for replay protection (4 or 8 bytes, includes sequence + * number and optional \c time_t timestamp). + * - acknowledgment packet-id array length (1 byte). + * - acknowledgment packet-id array (if length > 0). + * - acknowledgment remote session-id (if length > 0). + * - packet-id of this message (4 bytes). + * - TLS payload ciphertext (n bytes) (only for \c P_CONTROL_V1). + * + * Note that when \c --tls-auth is used, all message types are protected + * with an HMAC signature, even the initial packets of the TLS handshake. + * This makes it easy for OpenVPN to throw away bogus packets quickly, + * without wasting resources on attempting a TLS handshake which will + * ultimately fail. + * + * @subsection network_protocol_control_key_methods Control channel key methods + * + * Once the TLS session has been initialized and authenticated, the TLS + * channel is used to exchange random %key material for bidirectional + * cipher and HMAC keys which will be used to secure data channel packets. + * OpenVPN currently implements two %key methods. %Key method 1 directly + * derives keys using random bits obtained from the \c rand_bytes() function. + * %Key method 2 mixes random %key material from both sides of the connection + * using the TLS PRF mixing function. %Key method 2 is the preferred method and + * is the default for OpenVPN 2.0+. + * + * The @ref key_generation "Data channel key generation" related page + * describes the %key methods in more detail. + * + * @subsection network_protocol_control_plaintext Structure of plaintext control channel messages + * + * - %Key method 1 (support removed in OpenVPN 2.5): + * - Cipher %key length in bytes (1 byte). + * - Cipher %key (n bytes). + * - HMAC %key length in bytes (1 byte). + * - HMAC %key (n bytes). + * - %Options string (n bytes, null terminated, client/server %options + * string should match). + * - %Key method 2: + * - Literal 0 (4 bytes). + * - %Key method (1 byte). + * - \c key_source structure (\c key_source.pre_master only defined + * for client -> server). + * - %Options string length, including null (2 bytes). + * - %Options string (n bytes, null terminated, client/server %options + * string must match). + * - [The username/password data below is optional, record can end at + * this point.] + * - Username string length, including null (2 bytes). + * - Username string (n bytes, null terminated). + * - Password string length, including null (2 bytes). + * - Password string (n bytes, null terminated). + * + * @section network_protocol_data Structure of data channel messages + * + * The P_DATA_* payload represents encapsulated tunnel packets which tend to be + * either IP packets or Ethernet frames. This is essentially the "payload" of + * the VPN. Data channel packets consist of a data channel header, and a + * payload. There are two possible formats: + * + * @par P_DATA_V1 + * P_DATA_V1 packets have a 1-byte header, carrying the \ref P_DATA_V1 \c opcode + * and \c key_id, followed by the payload:\n + * [ 5-bit opcode | 3-bit key_id ] [ payload ] + * + * @par P_DATA_V2 + * P_DATA_V2 packets have the same 1-byte opcode/key_id, but carrying the \ref + * P_DATA_V2 opcode, followed by a 3-byte peer-id, which uniquely identifies + * the peer:\n + * [ 5-bit opcode | 3-bit key_id ] [ 24-bit peer-id ] [ payload ] + * + * See @ref data_crypto for details on the data channel payload format. + * + */ diff --git a/doc/doxygen/doc_reliable.h b/doc/doxygen/doc_reliable.h new file mode 100644 index 0000000..70556d7 --- /dev/null +++ b/doc/doxygen/doc_reliable.h @@ -0,0 +1,48 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * Reliability Layer module documentation file. + */ + +/** + * @defgroup reliable Reliability Layer module + * + * The Reliability Layer is part of OpenVPN's control channel. It + * provides a reliable and sequential transport mechanism for control + * channel messages between OpenVPN peers. This module forms the + * interface between the \link external_multiplexer External + * Multiplexer\endlink and the \link control_tls Control Channel TLS + * module\endlink. + * + * @par UDP or TCP as VPN tunnel transport + * + * This is especially important when OpenVPN is configured to communicate + * over UDP, because UDP does not offer a reliable and sequential + * transport. OpenVPN endpoints can also communicate over TCP which does + * provide a reliable and sequential transport. In both cases, using UDP + * or TCP as an external transport, the internal Reliability Layer is + * active. + */ diff --git a/doc/doxygen/doc_tunnel_state.h b/doc/doxygen/doc_tunnel_state.h new file mode 100644 index 0000000..46e750f --- /dev/null +++ b/doc/doxygen/doc_tunnel_state.h @@ -0,0 +1,154 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2010-2018 Fox Crypto B.V. + * + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/** + * @file + * VPN tunnel state documentation file. + */ + +/** + * @page tunnel_state Structure of the VPN tunnel state storage + * + * This section describes how OpenVPN stores its VPN tunnel state during + * operation. + * + * OpenVPN uses several data structures as storage containers for state + * information of active VPN tunnels. These are described in this + * section, together with a little bit of history to help understand the + * origin of the current architecture. + * + * Whether an OpenVPN process is running in client-mode or server-mode + * determines whether it can support only one or multiple simultaneously + * active VPN tunnels. This consequently also determines how the + * associated state information is wrapped up internally. This section + * gives an overview of the differences. + * + * @section tunnel_state_history Historic developments + * + * In the old v1.x series, an OpenVPN process managed only one single VPN + * tunnel. This allowed the VPN tunnel state to be stored together with + * process-global information in one single \c context structure. + * + * This changed, however, in the v2.x series, as new OpenVPN versions + * running in server-mode can support multiple simultaneously active VPN + * tunnels. This necessitated a redesign of the VPN tunnel state + * container structures, and modification of the \link + * external_multiplexer External Multiplexer\endlink and \link + * internal_multiplexer Internal Multiplexer\endlink systems. The + * majority of these changes are only relevant for OpenVPN processes + * running in server-mode, and the client-mode structure has remained very + * similar to the v1.x single-tunnel form. + * + * @section tunnel_state_client Client-mode state + * + * An OpenVPN process running in client-mode can manage at most one single + * VPN tunnel at any one time. The state information for a client's VPN + * tunnel is stored in a \c context structure. + * + * The \c context structure is created in the \c main() function. That is + * also where process-wide initialization takes place, such as parsing + * command line %options and reading configuration files. The \c context + * is then passed to \c tunnel_point_to_point() which drives OpenVPN's + * main event processing loop. These functions are both part of the \link + * eventloop Main Event Loop\endlink module. + * + * @subsection tunnel_state_client_init Initialization and cleanup + * + * Because there is only one \c context structure present, it can be + * initialized and cleaned up from the client's main event processing + * function. Before the \c tunnel_point_to_point() function enters its + * event loop, it calls \c init_instance_handle_signals() which calls \c + * init_instance() to initialize the single \c context structure. After + * the event loop stops, it calls \c close_instance() to clean up the \c + * context. + * + * @subsection tunnel_state_client_event Event processing + * + * When the main event processing loop activates the external or internal + * multiplexer to handle a network event, it is not necessary to determine + * which VPN tunnel the event is associated with, because there is only + * one VPN tunnel active. + * + * @section tunnel_state_server Server-mode state + * + * An OpenVPN process running in server-mode can manage multiple + * simultaneously active VPN tunnels. For every VPN tunnel active, in + * other words for every OpenVPN client which is connected to a server, + * the OpenVPN server has one \c context structure in which it stores that + * particular VPN tunnel's state information. + * + * @subsection tunnel_state_server_multi Multi_context and multi_instance structures + * + * To support multiple \c context structures, each is wrapped in a \c + * multi_instance structure, and all the \c multi_instance structures are + * registered in one single \c multi_context structure. The \link + * external_multiplexer External Multiplexer\endlink and \link + * internal_multiplexer Internal Multiplexer\endlink then use the \c + * multi_context to retrieve the correct \c multi_instance and \c context + * associated with a given network address. + * + * @subsection tunnel_state_server_init Startup and initialization + * + * An OpenVPN process running in server-mode starts in the same \c main() + * function as it would in client-mode. The same process-wide + * initialization is performed, and the resulting state and configuration + * is stored in a \c context structure. The server-mode and client-mode + * processes diverge when the \c main() function calls one of \c + * tunnel_point_to_point() or \c tunnel_server(). + * + * In server-mode, \c main() calls the \c tunnel_server() function, which + * transfers control to \c tunnel_server_udp_single_threaded() or \c + * tunnel_server_tcp() depending on the external transport protocol. + * + * These functions receive the \c context created in \c main(). This + * object has a special status in server-mode, as it does not represent an + * active VPN tunnel, but does contain process-wide configuration + * parameters. In the source code, it is often stored in "top" variables. + * To distinguish this object from other instances of the same type, its + * \c context.mode value is set to \c CM_TOP. Other \c context objects, + * which do represent active VPN tunnels, have a \c context.mode set to \c + * CM_CHILD_UDP or \c CM_CHILD_TCP, depending on the external transport + * protocol. + * + * Both \c tunnel_server_udp_single_threaded() and \c tunnel_server_tcp() + * perform similar initialization. In either case, a \c multi_context + * structure is created, and it is initialized according to the + * configuration stored in the top \c context by the \c multi_init() and + * \c multi_top_init() functions. + * + * @subsection tunnel_state_server_tunnels Creating and destroying VPN tunnels + * + * When an OpenVPN client makes a new connection to a server, the server + * creates a new \c context and \c multi_instance. The latter is + * registered in the \c multi_context, which makes it possible for the + * external and internal multiplexers to retrieve the correct \c + * multi_instance and \c context when a network event occurs. + * + * @subsection tunnel_state_server_cleanup Final cleanup + * + * After the main event loop exits, both \c + * tunnel_server_udp_single_threaded() and \c tunnel_server_tcp() perform + * similar cleanup. They call \c multi_uninit() followed by \c + * multi_top_free() to clean up the \c multi_context structure. + */ diff --git a/doc/doxygen/openvpn.doxyfile.in b/doc/doxygen/openvpn.doxyfile.in new file mode 100644 index 0000000..beb02d9 --- /dev/null +++ b/doc/doxygen/openvpn.doxyfile.in @@ -0,0 +1,279 @@ +# Doxyfile 1.5.5 + +#--------------------------------------------------------------------------- +# Project related configuration options +#--------------------------------------------------------------------------- +DOXYFILE_ENCODING = UTF-8 +PROJECT_NAME = "OpenVPN" +PROJECT_NUMBER = +OUTPUT_DIRECTORY = "@abs_top_builddir@/doc/doxygen" +CREATE_SUBDIRS = NO +OUTPUT_LANGUAGE = English +BRIEF_MEMBER_DESC = YES +REPEAT_BRIEF = YES +ABBREVIATE_BRIEF = "The $name class" \ + "The $name widget" \ + "The $name file" \ + is \ + provides \ + specifies \ + contains \ + represents \ + a \ + an \ + the +ALWAYS_DETAILED_SEC = NO +INLINE_INHERITED_MEMB = NO +FULL_PATH_NAMES = YES +STRIP_FROM_PATH = "@abs_top_srcdir@" +STRIP_FROM_INC_PATH = +SHORT_NAMES = NO +JAVADOC_AUTOBRIEF = YES # NO +QT_AUTOBRIEF = NO +MULTILINE_CPP_IS_BRIEF = NO +DETAILS_AT_TOP = NO +INHERIT_DOCS = YES +SEPARATE_MEMBER_PAGES = NO +TAB_SIZE = 8 +ALIASES = +OPTIMIZE_OUTPUT_FOR_C = YES +OPTIMIZE_OUTPUT_JAVA = NO +OPTIMIZE_FOR_FORTRAN = NO +OPTIMIZE_OUTPUT_VHDL = NO +BUILTIN_STL_SUPPORT = NO +CPP_CLI_SUPPORT = NO +SIP_SUPPORT = NO +DISTRIBUTE_GROUP_DOC = NO +SUBGROUPING = YES +TYPEDEF_HIDES_STRUCT = NO +#--------------------------------------------------------------------------- +# Build related configuration options +#--------------------------------------------------------------------------- +EXTRACT_ALL = YES +EXTRACT_PRIVATE = YES +EXTRACT_STATIC = YES +EXTRACT_LOCAL_CLASSES = YES +EXTRACT_LOCAL_METHODS = YES +EXTRACT_ANON_NSPACES = YES +HIDE_UNDOC_MEMBERS = NO +HIDE_UNDOC_CLASSES = NO +HIDE_FRIEND_COMPOUNDS = NO +HIDE_IN_BODY_DOCS = NO +INTERNAL_DOCS = NO +CASE_SENSE_NAMES = NO +HIDE_SCOPE_NAMES = NO +SHOW_INCLUDE_FILES = YES +INLINE_INFO = YES +SORT_MEMBER_DOCS = YES +SORT_BRIEF_DOCS = NO +SORT_GROUP_NAMES = NO +SORT_BY_SCOPE_NAME = NO +GENERATE_TODOLIST = YES +GENERATE_TESTLIST = YES +GENERATE_BUGLIST = YES +GENERATE_DEPRECATEDLIST= YES +ENABLED_SECTIONS = +MAX_INITIALIZER_LINES = 30 +SHOW_USED_FILES = YES +SHOW_DIRECTORIES = NO +FILE_VERSION_FILTER = +#--------------------------------------------------------------------------- +# configuration options related to warning and progress messages +#--------------------------------------------------------------------------- +QUIET = NO +WARNINGS = YES +WARN_IF_UNDOCUMENTED = YES +WARN_IF_DOC_ERROR = YES +WARN_NO_PARAMDOC = NO +WARN_FORMAT = "$file:$line: $text" +WARN_LOGFILE = +#--------------------------------------------------------------------------- +# configuration options related to the input files +#--------------------------------------------------------------------------- +INPUT = "@abs_top_srcdir@" +INPUT_ENCODING = UTF-8 +FILE_PATTERNS = *.c \ + *.cc \ + *.cxx \ + *.cpp \ + *.c++ \ + *.d \ + *.java \ + *.ii \ + *.ixx \ + *.ipp \ + *.i++ \ + *.inl \ + *.h \ + *.hh \ + *.hxx \ + *.hpp \ + *.h++ \ + *.idl \ + *.odl \ + *.cs \ + *.php \ + *.php3 \ + *.inc \ + *.m \ + *.mm \ + *.dox \ + *.py \ + *.f90 \ + *.f \ + *.vhd \ + *.vhdl +RECURSIVE = YES +EXCLUDE = +EXCLUDE_SYMLINKS = NO +EXCLUDE_PATTERNS = +EXCLUDE_SYMBOLS = +EXAMPLE_PATH = +EXAMPLE_PATTERNS = * +EXAMPLE_RECURSIVE = NO +IMAGE_PATH = +INPUT_FILTER = +FILTER_PATTERNS = +FILTER_SOURCE_FILES = NO +#--------------------------------------------------------------------------- +# configuration options related to source browsing +#--------------------------------------------------------------------------- +SOURCE_BROWSER = YES +INLINE_SOURCES = NO +STRIP_CODE_COMMENTS = YES +REFERENCED_BY_RELATION = YES +REFERENCES_RELATION = YES +REFERENCES_LINK_SOURCE = YES +USE_HTAGS = NO +VERBATIM_HEADERS = YES +#--------------------------------------------------------------------------- +# configuration options related to the alphabetical class index +#--------------------------------------------------------------------------- +ALPHABETICAL_INDEX = NO +COLS_IN_ALPHA_INDEX = 5 +IGNORE_PREFIX = +#--------------------------------------------------------------------------- +# configuration options related to the HTML output +#--------------------------------------------------------------------------- +GENERATE_HTML = YES +HTML_OUTPUT = html +HTML_FILE_EXTENSION = .html +HTML_HEADER = +HTML_FOOTER = +HTML_STYLESHEET = +HTML_ALIGN_MEMBERS = YES +GENERATE_HTMLHELP = NO +GENERATE_DOCSET = NO +DOCSET_FEEDNAME = "Doxygen generated docs" +DOCSET_BUNDLE_ID = org.doxygen.Project +HTML_DYNAMIC_SECTIONS = NO +CHM_FILE = +HHC_LOCATION = +GENERATE_CHI = NO +BINARY_TOC = NO +TOC_EXPAND = NO +DISABLE_INDEX = NO +ENUM_VALUES_PER_LINE = 4 +GENERATE_TREEVIEW = NO +TREEVIEW_WIDTH = 250 +#--------------------------------------------------------------------------- +# configuration options related to the LaTeX output +#--------------------------------------------------------------------------- +GENERATE_LATEX = YES +LATEX_OUTPUT = latex +LATEX_CMD_NAME = latex +MAKEINDEX_CMD_NAME = makeindex +COMPACT_LATEX = YES # NO +PAPER_TYPE = a4wide +EXTRA_PACKAGES = +LATEX_HEADER = +PDF_HYPERLINKS = YES +USE_PDFLATEX = YES +LATEX_BATCHMODE = NO +LATEX_HIDE_INDICES = NO +#--------------------------------------------------------------------------- +# configuration options related to the RTF output +#--------------------------------------------------------------------------- +GENERATE_RTF = NO +RTF_OUTPUT = rtf +COMPACT_RTF = NO +RTF_HYPERLINKS = NO +RTF_STYLESHEET_FILE = +RTF_EXTENSIONS_FILE = +#--------------------------------------------------------------------------- +# configuration options related to the man page output +#--------------------------------------------------------------------------- +GENERATE_MAN = NO +MAN_OUTPUT = man +MAN_EXTENSION = .3 +MAN_LINKS = NO +#--------------------------------------------------------------------------- +# configuration options related to the XML output +#--------------------------------------------------------------------------- +GENERATE_XML = NO +XML_OUTPUT = xml +XML_SCHEMA = +XML_DTD = +XML_PROGRAMLISTING = YES +#--------------------------------------------------------------------------- +# configuration options for the AutoGen Definitions output +#--------------------------------------------------------------------------- +GENERATE_AUTOGEN_DEF = NO +#--------------------------------------------------------------------------- +# configuration options related to the Perl module output +#--------------------------------------------------------------------------- +GENERATE_PERLMOD = NO +PERLMOD_LATEX = NO +PERLMOD_PRETTY = YES +PERLMOD_MAKEVAR_PREFIX = +#--------------------------------------------------------------------------- +# Configuration options related to the preprocessor +#--------------------------------------------------------------------------- +ENABLE_PREPROCESSING = YES +MACRO_EXPANSION = NO +EXPAND_ONLY_PREDEF = NO +SEARCH_INCLUDES = YES +INCLUDE_PATH = +INCLUDE_FILE_PATTERNS = +PREDEFINED = _WIN32 NTLM USE_LZO ENABLE_FRAGMENT P2MP ENABLE_CRYPTO_OPENSSL ENABLE_PLUGIN ENABLE_MANAGEMENT ENABLE_OCC HAVE_GETTIMEOFDAY +EXPAND_AS_DEFINED = +SKIP_FUNCTION_MACROS = YES +#--------------------------------------------------------------------------- +# Configuration::additions related to external references +#--------------------------------------------------------------------------- +TAGFILES = +GENERATE_TAGFILE = +ALLEXTERNALS = NO +EXTERNAL_GROUPS = YES +PERL_PATH = /usr/bin/perl +#--------------------------------------------------------------------------- +# Configuration options related to the dot tool +#--------------------------------------------------------------------------- +CLASS_DIAGRAMS = NO +MSCGEN_PATH = +HIDE_UNDOC_RELATIONS = YES +HAVE_DOT = YES +CLASS_GRAPH = YES +COLLABORATION_GRAPH = YES +GROUP_GRAPHS = YES +UML_LOOK = NO +TEMPLATE_RELATIONS = NO +INCLUDE_GRAPH = YES +INCLUDED_BY_GRAPH = YES +CALL_GRAPH = NO # YES +CALLER_GRAPH = NO # YES +GRAPHICAL_HIERARCHY = YES +DIRECTORY_GRAPH = YES +DOT_IMAGE_FORMAT = png +DOT_PATH = "/usr/bin/dot" +DOTFILE_DIRS = +DOT_GRAPH_MAX_NODES = 50 +MAX_DOT_GRAPH_DEPTH = 1000 +DOT_TRANSPARENT = YES +DOT_MULTI_TARGETS = NO +GENERATE_LEGEND = YES +DOT_CLEANUP = YES +#--------------------------------------------------------------------------- +# Configuration::additions related to the search engine +#--------------------------------------------------------------------------- +SEARCHENGINE = NO diff --git a/doc/keying-material-exporter.txt b/doc/keying-material-exporter.txt new file mode 100644 index 0000000..4c1addc --- /dev/null +++ b/doc/keying-material-exporter.txt @@ -0,0 +1,137 @@ +OpenVPN Daniel Kubec +RFC-5705 February 2015 + + + Added support for TLS Keying Material Exporters + +Keying Material Exporter [RFC-5705] allow additional keying material to be +derived from existing TLS channel. This exported keying material can then be +used for a variety of purposes. TLS allows client and server to establish +keying material for use in the upper layers between the TLS end-points and +channel bindings is straightforward and well-defined mechanism how to +authenticate other layers. + + +OpenVPN Configuration + +--keying-material-exporter label len + +Export Keying Material [RFC-5705] of len bytes (min. 16 bytes) using label in +environment (exported_keying_material) for use by plugins in +OPENVPN_PLUGIN_TLS_FINAL callback. + +Note that exporter labels have the potential to collide with existing PRF +labels. In order to prevent this, labels MUST begin with "EXPORTER". +(This option requires OpenSSL 1.0.1 or newer.) + + +Use Cases: + +Secure bindings of AAA information to application layer + + OpenVPN Client <------> OpenVPN Server + [KeyAgreement] [KeyAgreement] + + [TLSExportedKeyingMaterial] [TLSExportedKeyingMaterial] + [AAASessionKey] [AAASessionKey] + Client <------> Server + [Authenticated layer on top of (D)TLS] + + +TLS side channel authentication and straightforward bindings of AAA information +to application layer using well-defined mechanism. + + OpenVPN Client <------> OpenVPN Server + [KeyAgreement] [KeyAgreement] + + [TLSExportedKeyingMaterial] [TLSExportedKeyingMaterial] + [DerivedAAABindingKey] [DerivedAAABindingKey] + [AuthenticateBindingKeys] + Client -------> Server + [Confidential channel] + + +TLS Message flow for a full handshake + + ClientHello --------> + ServerHello + Certificate* + ServerKeyExchange* + CertificateRequest* + <-------- ServerHelloDone + Certificate* + ClientKeyExchange + CertificateVerify* + [ChangeCipherSpec] + Finished --------> + [ChangeCipherSpec] + <-------- Finished + + GenerateTLSBindingKey GenerateTLSBindingKey + + Application Data <-------> Application Data + + +Terminology + + AAA Authentication, Authorization, and Accounting: + functions that are generally required to control + access to a service and support auditing. + + Secure channel a packet, datagram, octet stream connection, or + sequence of connections between two end-points that + affords cryptographic integrity and confidentiality + to data exchanged over it. + + Channel binding the process of establishing that no man-in-the-middle + exists between two end-points that have been + authenticated using secure channel. + + TLS Binding Key Exported Keying Material [RFC5705] + + If no context is provided, it then computes: + PRF(SecurityParameters.master_secret, label, + SecurityParameters.client_random + + SecurityParameters.server_random + )[length] + + If context is provided, it computes: + PRF(SecurityParameters.master_secret, label, + SecurityParameters.client_random + + SecurityParameters.server_random + + context_value_length + context_value + )[length] + + AAA Binding Key TLS side channel authentication based on secure + channel bindings requires one more key derivation. + + SHA1(TLSExportedKeyingMaterial + ServerPublicKey) + +Reference + + [OPENAAA] "TLS side channel authentication and straightforward + bindings of AAA information to application + layer using well-defined mechanism." + Daniel Kubec March 2013 + https://github.com/n13l/openaaa + + [RFC5705] "Keying Material Exporters for TLS" + E. Rescorla, RFC 5705 March 2010 + http://tools.ietf.org/html/rfc5705 + + [RFC5929] "Channel Bindings for TLS" + J. Altman, N. Williams, L. Zhu, RFC 5929, July 2010 + http://tools.ietf.org/html/rfc5929 + + [RFC4680] "TLS Handshake Message for Supplemental Data" + S. Santesson, RFC 4680, September 2006 + http://tools.ietf.org/html/rfc4680 + + [RFC5878] "TLS Authorization Extension" + M. Brown, R. Housley, RFC 5878, May 2010 + http://tools.ietf.org/html/rfc5878 + + [RFC5746] "TLS Renegotiation Indication Extension" + E. Rescorla, M. Raym, S. Dispensa, N. Oskov + RFC 5746, February 2010 + http://tools.ietf.org/html/rfc5746 diff --git a/doc/man-sections/advanced-options.rst b/doc/man-sections/advanced-options.rst new file mode 100644 index 0000000..9b96e40 --- /dev/null +++ b/doc/man-sections/advanced-options.rst @@ -0,0 +1,107 @@ +Standalone Debug Options +------------------------ + +--show-gateway args + (Standalone) Show current IPv4 and IPv6 default gateway and interface + towards the gateway (if the protocol in question is enabled). + + Valid syntax: + :: + + --show-gateway + --show-gateway IPv6-target + + If an IPv6 target address is passed as argument, the IPv6 route for this + host is reported. + + +Advanced Expert Options +----------------------- +These are options only required when special tweaking is needed, often +used when debugging or testing out special usage scenarios. + +--hash-size args + Set the size of the real address hash table to ``r`` and the virtual + address table to ``v``. + + Valid syntax: + :: + + hash-size r v + + By default, both tables are sized at 256 buckets. + +--bcast-buffers n + Allocate ``n`` buffers for broadcast datagrams (default :code:`256`). + +--persist-local-ip + Preserve initially resolved local IP address and port number across + ``SIGUSR1`` or ``--ping-restart`` restarts. + +--persist-remote-ip + Preserve most recently authenticated remote IP address and port number + across :code:`SIGUSR1` or ``--ping-restart`` restarts. + +--prng args + *(Advanced)* Change the PRNG (Pseudo-random number generator) parameters + + Valid syntaxes: + :: + + prng alg + prng alg nsl + + Changes the PRNG to use digest algorithm **alg** (default :code:`sha1`), + and set ``nsl`` (default :code:`16`) to the size in bytes of the nonce + secret length (between 16 and 64). + + Set ``alg`` to :code:`none` to disable the PRNG and use the OpenSSL + RAND\_bytes function instead for all of OpenVPN's pseudo-random number + needs. + +--rcvbuf size + Set the TCP/UDP socket receive buffer size. Defaults to operating system + default. + +--shaper n + Limit bandwidth of outgoing tunnel data to ``n`` bytes per second on the + TCP/UDP port. Note that this will only work if mode is set to + :code:`p2p`. If you want to limit the bandwidth in both directions, use + this option on both peers. + + OpenVPN uses the following algorithm to implement traffic shaping: Given + a shaper rate of ``n`` bytes per second, after a datagram write of ``b`` + bytes is queued on the TCP/UDP port, wait a minimum of ``(b / n)`` + seconds before queuing the next write. + + It should be noted that OpenVPN supports multiple tunnels between the + same two peers, allowing you to construct full-speed and reduced + bandwidth tunnels at the same time, routing low-priority data such as + off-site backups over the reduced bandwidth tunnel, and other data over + the full-speed tunnel. + + Also note that for low bandwidth tunnels (under 1000 bytes per second), + you should probably use lower MTU values as well (see above), otherwise + the packet latency will grow so large as to trigger timeouts in the TLS + layer and TCP connections running over the tunnel. + + OpenVPN allows ``n`` to be between 100 bytes/sec and 100 Mbytes/sec. + +--sndbuf size + Set the TCP/UDP socket send buffer size. Defaults to operating system + default. + +--tcp-queue-limit n + Maximum number of output packets queued before TCP (default :code:`64`). + + When OpenVPN is tunneling data from a TUN/TAP device to a remote client + over a TCP connection, it is possible that the TUN/TAP device might + produce data at a faster rate than the TCP connection can support. When + the number of output packets queued before sending to the TCP socket + reaches this limit for a given client connection, OpenVPN will start to + drop outgoing packets directed at this client. + +--txqueuelen n + *(Linux only)* Set the TX queue length on the TUN/TAP interface. + Currently defaults to operating system default. + diff --git a/doc/man-sections/cipher-negotiation.rst b/doc/man-sections/cipher-negotiation.rst new file mode 100644 index 0000000..f143305 --- /dev/null +++ b/doc/man-sections/cipher-negotiation.rst @@ -0,0 +1,96 @@ +Data channel cipher negotiation +=============================== + +OpenVPN 2.4 and higher have the capability to negotiate the data cipher that +is used to encrypt data packets. This section describes the mechanism in more detail and the +different backwards compatibility mechanism with older server and clients. + +OpenVPN 2.5 and higher behaviour +-------------------------------- +When both client and server are at least running OpenVPN 2.5, that the order of +the ciphers of the server's ``--data-ciphers`` is used to pick the the data cipher. +That means that the first cipher in that list that is also in the client's +``--data-ciphers`` list is chosen. If no common cipher is found the client is rejected +with a AUTH_FAILED message (as seen in client log): + + AUTH: Received control message: AUTH_FAILED,Data channel cipher negotiation failed (no shared cipher) + +OpenVPN 2.5 will only allow the ciphers specified in ``--data-ciphers``. To ensure +backwards compatibility also if a cipher is specified using the ``--cipher`` option +it is automatically added to this list. If both options are unset the default is +:code:`AES-256-GCM:AES-128-GCM`. + +OpenVPN 2.4 clients +------------------- +The negotiation support in OpenVPN 2.4 was the first iteration of the implementation +and still had some quirks. Its main goal was "upgrade to AES-256-GCM when possible". +An OpenVPN 2.4 client that is built against a crypto library that supports AES in GCM +mode and does not have ``--ncp-disable`` will always announce support for +`AES-256-GCM` and `AES-128-GCM` to a server by sending :code:`IV_NCP=2`. + +This only causes a problem if ``--ncp-ciphers`` option has been changed from the +default of :code:`AES-256-GCM:AES-128-GCM` to a value that does not include +these two ciphers. When a OpenVPN servers try to use `AES-256-GCM` or +`AES-128-GCM` the connection will then fail. It is therefore recommended to +always have the `AES-256-GCM` and `AES-128-GCM` ciphers to the ``--ncp-ciphers`` +options to avoid this behaviour. + +OpenVPN 3 clients +----------------- +Clients based on the OpenVPN 3.x library (https://github.com/openvpn/openvpn3/) +do not have a configurable ``--ncp-ciphers`` or ``--data-cipher`` option. Instead +these clients will announce support for all their supported AEAD ciphers +(`AES-256-GCM`, `AES-128-GCM` and in newer versions also `Chacha20-Poly1305`). + +To support OpenVPN 3.x based clients at least one of these ciphers needs to be +included in the server's ``--data-ciphers`` option. + + +OpenVPN 2.3 and older clients (and clients with ``--ncp-disable``) +------------------------------------------------------------------ +When a client without cipher negotiation support connects to a server the +cipher specified with the ``--cipher`` option in the client configuration +must be included in the ``--data-ciphers`` option of the server to allow +the client to connect. Otherwise the client will be sent the ``AUTH_FAILED`` +message that indicates no shared cipher. + +If the client is 2.3 or older and has been configured with the +``--enable-small`` :code:`./configure` argument, using +``data-ciphers-fallback cipher`` in the server config file with the explicit +cipher used by the client is necessary. + +OpenVPN 2.4 server +------------------ +When a client indicates support for `AES-128-GCM` and `AES-256-GCM` +(with ``IV_NCP=2``) an OpenVPN 2.4 server will send the first +cipher of the ``--ncp-ciphers`` to the OpenVPN client regardless of what +the cipher is. To emulate the behaviour of an OpenVPN 2.4 client as close +as possible and have compatibility to a setup that depends on this quirk, +adding `AES-128-GCM` and `AES-256-GCM` to the client's ``--data-ciphers`` +option is required. OpenVPN 2.5+ will only announce the ``IV_NCP=2`` flag if +those ciphers are present. + +OpenVPN 2.3 and older servers (and servers with ``--ncp-disable``) +------------------------------------------------------------------ +The cipher used by the server must be included in ``--data-ciphers`` to +allow the client connecting to a server without cipher negotiation +support. +(For compatibility OpenVPN 2.5 will also accept the cipher set with +``--cipher``) + +If the server is 2.3 or older and has been configured with the +``--enable-small`` :code:`./configure` argument, adding +``data-ciphers-fallback cipher`` to the client config with the explicit +cipher used by the server is necessary. + +Blowfish in CBC mode (BF-CBC) deprecation +------------------------------------------ +The ``--cipher`` option defaulted to ``BF-CBC`` in OpenVPN 2.4 and older +version. The default was never changed to ensure backwards compatibility. +In OpenVPN 2.5 this behaviour has now been changed so that if the ``--cipher`` +is not explicitly set it does not allow the weak ``BF-CBC`` cipher any more +and needs to explicitly added as ``--cipher BFC-CBC`` or added to +``-data-ciphers``. + +We strongly recommend to switching away from BF-CBC to a +more secure cipher as soon as possible instead. diff --git a/doc/man-sections/client-options.rst b/doc/man-sections/client-options.rst new file mode 100644 index 0000000..ec1e3b1 --- /dev/null +++ b/doc/man-sections/client-options.rst @@ -0,0 +1,353 @@ +Client Options +-------------- +The client options are used when connecting to an OpenVPN server configured +to use ``--server``, ``--server-bridge``, or ``--mode server`` in its +configuration. + +--allow-pull-fqdn + Allow client to pull DNS names from server (rather than being limited to + IP address) for ``--ifconfig``, ``--route``, and ``--route-gateway``. + +--allow-recursive-routing + When this option is set, OpenVPN will not drop incoming tun packets with + same destination as host. + +--auth-token token + This is not an option to be used directly in any configuration files, + but rather push this option from a ``--client-connect`` script or a + ``--plugin`` which hooks into the :code:`OPENVPN_PLUGIN_CLIENT_CONNECT` + or :code:`OPENVPN_PLUGIN_CLIENT_CONNECT_V2` calls. This option provides a + possibility to replace the clients password with an authentication token + during the lifetime of the OpenVPN client. + + Whenever the connection is renegotiated and the + ``--auth-user-pass-verify`` script or ``--plugin`` making use of the + :code:`OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY` hook is triggered, it will + pass over this token as the password instead of the password the user + provided. The authentication token can only be reset by a full reconnect + where the server can push new options to the client. The password the + user entered is never preserved once an authentication token has been + set. If the OpenVPN server side rejects the authentication token then + the client will receive an :code:`AUTH_FAILED` and disconnect. + + The purpose of this is to enable two factor authentication methods, such + as HOTP or TOTP, to be used without needing to retrieve a new OTP code + each time the connection is renegotiated. Another use case is to cache + authentication data on the client without needing to have the users + password cached in memory during the life time of the session. + + To make use of this feature, the ``--client-connect`` script or + ``--plugin`` needs to put + :: + + push "auth-token UNIQUE_TOKEN_VALUE" + + into the file/buffer for dynamic configuration data. This will then make + the OpenVPN server to push this value to the client, which replaces the + local password with the ``UNIQUE_TOKEN_VALUE``. + + Newer clients (2.4.7+) will fall back to the original password method + after a failed auth. Older clients will keep using the token value and + react according to ``--auth-retry`` + +--auth-user-pass + Authenticate with server using username/password. + + Valid syntaxes: + :: + + auth-user-pass + auth-user-pass up + + If ``up`` is present, it must be a file containing username/password on 2 + lines. If the password line is missing, OpenVPN will prompt for one. + + If ``up`` is omitted, username/password will be prompted from the + console. + + The server configuration must specify an ``--auth-user-pass-verify`` + script to verify the username/password provided by the client. + +--auth-retry type + Controls how OpenVPN responds to username/password verification errors + such as the client-side response to an :code:`AUTH_FAILED` message from + the server or verification failure of the private key password. + + Normally used to prevent auth errors from being fatal on the client + side, and to permit username/password requeries in case of error. + + An :code:`AUTH_FAILED` message is generated by the server if the client + fails ``--auth-user-pass`` authentication, or if the server-side + ``--client-connect`` script returns an error status when the client + tries to connect. + + ``type`` can be one of: + + :code:`none` + Client will exit with a fatal error (this is the default). + + :code:`nointeract` + Client will retry the connection without requerying + for an ``--auth-user-pass`` username/password. Use this option for + unattended clients. + + :code:`interact` + Client will requery for an ``--auth-user-pass`` + username/password and/or private key password before attempting a + reconnection. + + Note that while this option cannot be pushed, it can be controlled from + the management interface. + +--client + A helper directive designed to simplify the configuration of OpenVPN's + client mode. This directive is equivalent to: + :: + + pull + tls-client + +--client-nat args + This pushable client option sets up a stateless one-to-one NAT rule on + packet addresses (not ports), and is useful in cases where routes or + ifconfig settings pushed to the client would create an IP numbering + conflict. + + Examples: + :: + + client-nat snat 192.168.0.0/255.255.0.0 + client-nat dnat 10.64.0.0/255.255.0.0 + + ``network/netmask`` (for example :code:`192.168.0.0/255.255.0.0`) defines + the local view of a resource from the client perspective, while + ``alias/netmask`` (for example :code:`10.64.0.0/255.255.0.0`) defines the + remote view from the server perspective. + + Use :code:`snat` (source NAT) for resources owned by the client and + :code:`dnat` (destination NAT) for remote resources. + + Set ``--verb 6`` for debugging info showing the transformation of + src/dest addresses in packets. + +--connect-retry n + Wait ``n`` seconds between connection attempts (default :code:`5`). + Repeated reconnection attempts are slowed down after 5 retries per + remote by doubling the wait time after each unsuccessful attempt. An + optional argument ``max`` specifies the maximum value of wait time in + seconds at which it gets capped (default :code:`300`). + +--connect-retry-max n + ``n`` specifies the number of times each ``--remote`` or + ```` entry is tried. Specifying ``n`` as :code:`1` would try + each entry exactly once. A successful connection resets the counter. + (default *unlimited*). + +--connect-timeout n + See ``--server-poll-timeout``. + +--explicit-exit-notify n + In UDP client mode or point-to-point mode, send server/peer an exit + notification if tunnel is restarted or OpenVPN process is exited. In + client mode, on exit/restart, this option will tell the server to + immediately close its client instance object rather than waiting for a + timeout. + + The **n** parameter (default :code:`1` if not present) controls the + maximum number of attempts that the client will try to resend the exit + notification message. + + In UDP server mode, send :code:`RESTART` control channel command to + connected clients. The ``n`` parameter (default :code:`1` if not present) + controls client behavior. With ``n`` = :code:`1` client will attempt to + reconnect to the same server, with ``n`` = :code:`2` client will advance + to the next server. + + OpenVPN will not send any exit notifications unless this option is + enabled. + +--inactive args + Causes OpenVPN to exit after ``n`` seconds of inactivity on the TUN/TAP + device. The time length of inactivity is measured since the last + incoming or outgoing tunnel packet. The default value is 0 seconds, + which disables this feature. + + Valid syntaxes: + :: + + inactive n + inactive n bytes + + If the optional ``bytes`` parameter is included, exit if less than + ``bytes`` of combined in/out traffic are produced on the tun/tap device + in ``n`` seconds. + + In any case, OpenVPN's internal ping packets (which are just keepalives) + and TLS control packets are not considered "activity", nor are they + counted as traffic, as they are used internally by OpenVPN and are not + an indication of actual user activity. + +--proto-force p + When iterating through connection profiles, only consider profiles using + protocol ``p`` (:code:`tcp` \| :code:`udp`). + +--pull + This option must be used on a client which is connecting to a + multi-client server. It indicates to OpenVPN that it should accept + options pushed by the server, provided they are part of the legal set of + pushable options (note that the ``--pull`` option is implied by + ``--client`` ). + + In particular, ``--pull`` allows the server to push routes to the + client, so you should not use ``--pull`` or ``--client`` in situations + where you don't trust the server to have control over the client's + routing table. + +--pull-filter args + Filter options on the client pushed by the server to the client. + + Valid syntaxes: + :: + + pull-filter accept text + pull-filter ignore text + pull-filter reject text + + Filter options received from the server if the option starts with + :code:`text`. The action flag :code:`accept` allows the option, + :code:`ignore` removes it and :code:`reject` flags an error and triggers + a :code:`SIGUSR1` restart. The filters may be specified multiple times, + and each filter is applied in the order it is specified. The filtering of + each option stops as soon as a match is found. Unmatched options are accepted + by default. + + Prefix comparison is used to match :code:`text` against the received option so + that + :: + + pull-filter ignore "route" + + would remove all pushed options starting with ``route`` which would + include, for example, ``route-gateway``. Enclose *text* in quotes to + embed spaces. + + :: + + pull-filter accept "route 192.168.1." + pull-filter ignore "route " + + would remove all routes that do not start with ``192.168.1``. + + *Note* that :code:`reject` may result in a repeated cycle of failure and + reconnect, unless multiple remotes are specified and connection to the + next remote succeeds. To silently ignore an option pushed by the server, + use :code:`ignore`. + +--remote args + Remote host name or IP address. It supports two additional optional + arguments: ``port`` and ``proto``. On the client, multiple ``--remote`` + options may be specified for redundancy, each referring to a different + OpenVPN server. Specifying multiple ``--remote`` options for this + purpose is a special case of the more general connection-profile + feature. See the ```` documentation below. + + The OpenVPN client will try to connect to a server at ``host:port`` in + the order specified by the list of ``--remote`` options. + + Examples: + :: + + remote server.example.net + remote server.example.net 1194 + remote server.example.net tcp + + ``proto`` indicates the protocol to use when connecting with the remote, + and may be :code:`tcp` or :code:`udp`. + + For forcing IPv4 or IPv6 connection suffix tcp or udp with 4/6 like + udp4/udp6/tcp4/tcp6. + + The client will move on to the next host in the list, in the event of + connection failure. Note that at any given time, the OpenVPN client will + at most be connected to one server. + + Note that since UDP is connectionless, connection failure is defined by + the ``--ping`` and ``--ping-restart`` options. + + Note the following corner case: If you use multiple ``--remote`` + options, AND you are dropping root privileges on the client with + ``--user`` and/or ``--group`` AND the client is running a non-Windows + OS, if the client needs to switch to a different server, and that server + pushes back different TUN/TAP or route settings, the client may lack the + necessary privileges to close and reopen the TUN/TAP interface. This + could cause the client to exit with a fatal error. + + If ``--remote`` is unspecified, OpenVPN will listen for packets from any + IP address, but will not act on those packets unless they pass all + authentication tests. This requirement for authentication is binding on + all potential peers, even those from known and supposedly trusted IP + addresses (it is very easy to forge a source IP address on a UDP + packet). + + When used in TCP mode, ``--remote`` will act as a filter, rejecting + connections from any host which does not match ``host``. + + If ``host`` is a DNS name which resolves to multiple IP addresses, + OpenVPN will try them in the order that the system getaddrinfo() + presents them, so priorization and DNS randomization is done by the + system library. Unless an IP version is forced by the protocol + specification (4/6 suffix), OpenVPN will try both IPv4 and IPv6 + addresses, in the order getaddrinfo() returns them. + +--remote-random + When multiple ``--remote`` address/ports are specified, or if connection + profiles are being used, initially randomize the order of the list as a + kind of basic load-balancing measure. + +--remote-random-hostname + Prepend a random string (6 bytes, 12 hex characters) to hostname to + prevent DNS caching. For example, "foo.bar.gov" would be modified to + ".foo.bar.gov". + +--resolv-retry n + If hostname resolve fails for ``--remote``, retry resolve for ``n`` + seconds before failing. + + Set ``n`` to "infinite" to retry indefinitely. + + By default, ``--resolv-retry infinite`` is enabled. You can disable by + setting n=0. + +--single-session + After initially connecting to a remote peer, disallow any new + connections. Using this option means that a remote peer cannot connect, + disconnect, and then reconnect. + + If the daemon is reset by a signal or ``--ping-restart``, it will allow + one new connection. + + ``--single-session`` can be used with ``--ping-exit`` or ``--inactive`` + to create a single dynamic session that will exit when finished. + +--server-poll-timeout n + When connecting to a remote server do not wait for more than ``n`` + seconds for a response before trying the next server. The default value + is 120s. This timeout includes proxy and TCP connect timeouts. + +--static-challenge args + Enable static challenge/response protocol + + Valid syntax: + :: + + static-challenge text echo + + The ``text`` challenge text is presented to the user which describes what + information is requested. The ``echo`` flag indicates if the user's + input should be echoed on the screen. Valid ``echo`` values are + :code:`0` or :code:`1`. + + See management-notes.txt in the OpenVPN distribution for a description of + the OpenVPN challenge/response protocol. + +.. include:: proxy-options.rst diff --git a/doc/man-sections/connection-profiles.rst b/doc/man-sections/connection-profiles.rst new file mode 100644 index 0000000..fd3382b --- /dev/null +++ b/doc/man-sections/connection-profiles.rst @@ -0,0 +1,75 @@ +CONNECTION PROFILES +=================== + +Client configuration files may contain multiple remote servers which +it will attempt to connect against. But there are some configuration +options which are related to specific ``--remote`` options. For these +use cases, connection profiles are the solution. + +By enacpulating the ``--remote`` option and related options within +```` and ````, these options are handled as a +group. + +An OpenVPN client will try each connection profile sequentially until it +achieves a successful connection. + +``--remote-random`` can be used to initially "scramble" the connection +list. + +Here is an example of connection profile usage: +:: + + client + dev tun + + + remote 198.19.34.56 1194 udp + + + + remote 198.19.34.56 443 tcp + + + + remote 198.19.34.56 443 tcp + http-proxy 192.168.0.8 8080 + + + + remote 198.19.36.99 443 tcp + http-proxy 192.168.0.8 8080 + + + persist-key + persist-tun + pkcs12 client.p12 + remote-cert-tls server + verb 3 + +First we try to connect to a server at 198.19.34.56:1194 using UDP. If +that fails, we then try to connect to 198.19.34.56:443 using TCP. If +that also fails, then try connecting through an HTTP proxy at +192.168.0.8:8080 to 198.19.34.56:443 using TCP. Finally, try to connect +through the same proxy to a server at 198.19.36.99:443 using TCP. + +The following OpenVPN options may be used inside of a ```` +block: + +``bind``, ``connect-retry``, ``connect-retry-max``, ``connect-timeout``, +``explicit-exit-notify``, ``float``, ``fragment``, ``http-proxy``, +``http-proxy-option``, ``key-direction``, ``link-mtu``, ``local``, +``lport``, ``mssfix``, ``mtu-disc``, ``nobind``, ``port``, ``proto``, +``remote``, ``rport``, ``socks-proxy``, ``tls-auth``, ``tls-crypt``, +``tun-mtu and``, ``tun-mtu-extra``. + +A defaulting mechanism exists for specifying options to apply to all +```` profiles. If any of the above options (with the +exception of ``remote`` ) appear outside of a ```` block, +but in a configuration file which has one or more ```` +blocks, the option setting will be used as a default for +```` blocks which follow it in the configuration file. + +For example, suppose the ``nobind`` option were placed in the sample +configuration file above, near the top of the file, before the first +```` block. The effect would be as if ``nobind`` were +declared in all ```` blocks below it. diff --git a/doc/man-sections/encryption-options.rst b/doc/man-sections/encryption-options.rst new file mode 100644 index 0000000..ee34f14 --- /dev/null +++ b/doc/man-sections/encryption-options.rst @@ -0,0 +1,135 @@ +Encryption Options +================== + +SSL Library information +----------------------- + +--show-ciphers + (Standalone) Show all cipher algorithms to use with the ``--cipher`` + option. + +--show-digests + (Standalone) Show all message digest algorithms to use with the + ``--auth`` option. + +--show-tls + (Standalone) Show all TLS ciphers supported by the crypto library. + OpenVPN uses TLS to secure the control channel, over which the keys that + are used to protect the actual VPN traffic are exchanged. The TLS + ciphers will be sorted from highest preference (most secure) to lowest. + + Be aware that whether a cipher suite in this list can actually work + depends on the specific setup of both peers (e.g. both peers must + support the cipher, and an ECDSA cipher suite will not work if you are + using an RSA certificate, etc.). + +--show-engines + (Standalone) Show currently available hardware-based crypto acceleration + engines supported by the OpenSSL library. + +--show-groups + (Standalone) Show all available elliptic curves/groups to use with the + ``--ecdh-curve`` and ``tls-groups`` options. + +Generating key material +----------------------- + +--genkey args + (Standalone) Generate a key to be used of the type keytype. if keyfile + is left out or empty the key will be output on stdout. See the following + sections for the different keytypes. + + Valid syntax: + :: + + --genkey keytype keyfile + + Valid keytype arguments are: + + :code:`secret` Standard OpenVPN shared secret keys + + :code:`tls-crypt` Alias for :code:`secret` + + :code:`tls-auth` Alias for :code:`secret` + + :code:`auth-token` Key used for ``--auth-gen-token-key`` + + :code:`tls-crypt-v2-server` TLS Crypt v2 server key + + :code:`tls-crypt-v2-client` TLS Crypt v2 client key + + + Examples: + :: + + $ openvpn --genkey secret shared.key + $ openvpn --genkey tls-crypt shared.key + $ openvpn --genkey tls-auth shared.key + $ openvpn --genkey tls-crypt-v2-server v2crypt-server.key + $ openvpn --tls-crypt-v2 v2crypt-server.key --genkey tls-crypt-v2-client v2crypt-client-1.key + + * Generating *Shared Secret Keys* + Generate a shared secret, for use with the ``--secret``, ``--tls-auth`` + or ``--tls-crypt`` options. + + Syntax: + :: + + $ openvpn --genkey secret|tls-crypt|tls-auth keyfile + + The key is saved in ``keyfile``. All three variants (``--secret``, + ``tls-crypt`` and ``tls-auth``) generate the same type of key. The + aliases are added for convenience. + + If using this for ``--secret``, this file must be shared with the peer + over a pre-existing secure channel such as ``scp``\(1). + + * Generating *TLS Crypt v2 Server key* + Generate a ``--tls-crypt-v2`` key to be used by an OpenVPN server. + The key is stored in ``keyfile``. + + Syntax: + :: + + --genkey tls-crypt-v2-server keyfile + + * Generating *TLS Crypt v2 Client key* + Generate a --tls-crypt-v2 key to be used by OpenVPN clients. The + key is stored in ``keyfile``. + + Syntax + :: + + --genkey tls-crypt-v2-client keyfile [metadata] + + If supplied, include the supplied ``metadata`` in the wrapped client + key. This metadata must be supplied in base64-encoded form. The + metadata must be at most 735 bytes long (980 bytes in base64). + + If no metadata is supplied, OpenVPN will use a 64-bit unix timestamp + representing the current time in UTC, encoded in network order, as + metadata for the generated key. + + A tls-crypt-v2 client key is wrapped using a server key. To generate a + client key, the user must therefore supply the server key using the + ``--tls-crypt-v2`` option. + + Servers can use ``--tls-crypt-v2-verify`` to specify a metadata + verification command. + + * Generate *Authentication Token key* + Generate a new secret that can be used with **--auth-gen-token-secret** + + Syntax: + :: + + --genkey auth-token [keyfile] + + *Note:* + This file should be kept secret to the server as anyone that has + access to this file will be able to generate auth tokens that the + OpenVPN server will accept as valid. + +.. include:: renegotiation.rst +.. include:: tls-options.rst +.. include:: pkcs11-options.rst diff --git a/doc/man-sections/examples.rst b/doc/man-sections/examples.rst new file mode 100644 index 0000000..3f494ea --- /dev/null +++ b/doc/man-sections/examples.rst @@ -0,0 +1,240 @@ +EXAMPLES +======== + +Prior to running these examples, you should have OpenVPN installed on +two machines with network connectivity between them. If you have not yet +installed OpenVPN, consult the INSTALL file included in the OpenVPN +distribution. + + +Firewall Setup: +--------------- + +If firewalls exist between the two machines, they should be set to +forward the port OpenVPN is configured to use, in both directions. +The default for OpenVPN is 1194/udp. If you do not have control +over the firewalls between the two machines, you may still be able to +use OpenVPN by adding ``--ping 15`` to each of the ``openvpn`` commands +used below in the examples (this will cause each peer to send out a UDP +ping to its remote peer once every 15 seconds which will cause many +stateful firewalls to forward packets in both directions without an +explicit firewall rule). + +Please see your operating system guides for how to configure the firewall +on your systems. + + +VPN Address Setup: +------------------ + +For purposes of our example, our two machines will be called +``bob.example.com`` and ``alice.example.com``. If you are constructing a +VPN over the internet, then replace ``bob.example.com`` and +``alice.example.com`` with the internet hostname or IP address that each +machine will use to contact the other over the internet. + +Now we will choose the tunnel endpoints. Tunnel endpoints are private IP +addresses that only have meaning in the context of the VPN. Each machine +will use the tunnel endpoint of the other machine to access it over the +VPN. In our example, the tunnel endpoint for bob.example.com will be +10.4.0.1 and for alice.example.com, 10.4.0.2. + +Once the VPN is established, you have essentially created a secure +alternate path between the two hosts which is addressed by using the +tunnel endpoints. You can control which network traffic passes between +the hosts (a) over the VPN or (b) independently of the VPN, by choosing +whether to use (a) the VPN endpoint address or (b) the public internet +address, to access the remote host. For example if you are on +bob.example.com and you wish to connect to ``alice.example.com`` via +``ssh`` without using the VPN (since **ssh** has its own built-in security) +you would use the command ``ssh alice.example.com``. However in the same +scenario, you could also use the command ``telnet 10.4.0.2`` to create a +telnet session with alice.example.com over the VPN, that would use the +VPN to secure the session rather than ``ssh``. + +You can use any address you wish for the tunnel endpoints but make sure +that they are private addresses (such as those that begin with 10 or +192.168) and that they are not part of any existing subnet on the +networks of either peer, unless you are bridging. If you use an address +that is part of your local subnet for either of the tunnel endpoints, +you will get a weird feedback loop. + + +Example 1: A simple tunnel without security +------------------------------------------- + +On bob: +:: + + openvpn --remote alice.example.com --dev tun1 \ + --ifconfig 10.4.0.1 10.4.0.2 --verb 9 + +On alice: +:: + + openvpn --remote bob.example.com --dev tun1 \ + --ifconfig 10.4.0.2 10.4.0.1 --verb 9 + +Now verify the tunnel is working by pinging across the tunnel. + +On bob: +:: + + ping 10.4.0.2 + +On alice: +:: + + ping 10.4.0.1 + +The ``--verb 9`` option will produce verbose output, similar to the +``tcpdump``\(8) program. Omit the ``--verb 9`` option to have OpenVPN run +quietly. + + +Example 2: A tunnel with static-key security (i.e. using a pre-shared secret) +----------------------------------------------------------------------------- + +First build a static key on bob. +:: + + openvpn --genkey --secret key + +This command will build a key file called ``key`` (in ascii format). Now +copy ``key`` to ``alice.example.com`` over a secure medium such as by using +the ``scp``\(1) program. + +On bob: +:: + + openvpn --remote alice.example.com --dev tun1 \ + --ifconfig 10.4.0.1 10.4.0.2 --verb 5 \ + --secret key + +On alice: +:: + + openvpn --remote bob.example.com --dev tun1 \ + --ifconfig 10.4.0.2 10.4.0.1 --verb 5 \ + --secret key + +Now verify the tunnel is working by pinging across the tunnel. + +On bob: +:: + + ping 10.4.0.2 + +On alice: +:: + + ping 10.4.0.1 + + +Example 3: A tunnel with full TLS-based security +------------------------------------------------ + +For this test, we will designate ``bob`` as the TLS client and ``alice`` +as the TLS server. + +*Note:* + The client or server designation only has + meaning for the TLS subsystem. It has no bearing on OpenVPN's + peer-to-peer, UDP-based communication model.* + +First, build a separate certificate/key pair for both bob and alice (see +above where ``--cert`` is discussed for more info). Then construct +Diffie Hellman parameters (see above where ``--dh`` is discussed for +more info). You can also use the included test files :code:`client.crt`, +:code:`client.key`, :code:`server.crt`, :code:`server.key` and +:code:`ca.crt`. The ``.crt`` files are certificates/public-keys, the +``.key`` files are private keys, and :code:`ca.crt` is a certification +authority who has signed both :code:`client.crt` and :code:`server.crt`. +For Diffie Hellman parameters you can use the included file +:code:`dh2048.pem`. + +*WARNING:* + All client, server, and certificate authority certificates + and keys included in the OpenVPN distribution are totally + insecure and should be used for testing only. + +On bob: +:: + + openvpn --remote alice.example.com --dev tun1 \ + --ifconfig 10.4.0.1 10.4.0.2 \ + --tls-client --ca ca.crt \ + --cert client.crt --key client.key \ + --reneg-sec 60 --verb 5 + +On alice: +:: + + openvpn --remote bob.example.com --dev tun1 \ + --ifconfig 10.4.0.2 10.4.0.1 \ + --tls-server --dh dh1024.pem --ca ca.crt \ + --cert server.crt --key server.key \ + --reneg-sec 60 --verb 5 + +Now verify the tunnel is working by pinging across the tunnel. + +On bob: +:: + + ping 10.4.0.2 + +On alice: +:: + + ping 10.4.0.1 + +Notice the ``--reneg-sec 60`` option we used above. That tells OpenVPN +to renegotiate the data channel keys every minute. Since we used +``--verb 5`` above, you will see status information on each new key +negotiation. + +For production operations, a key renegotiation interval of 60 seconds is +probably too frequent. Omit the ``--reneg-sec 60`` option to use +OpenVPN's default key renegotiation interval of one hour. + + +Routing: +-------- + +Assuming you can ping across the tunnel, the next step is to route a +real subnet over the secure tunnel. Suppose that bob and alice have two +network interfaces each, one connected to the internet, and the other to +a private network. Our goal is to securely connect both private +networks. We will assume that bob's private subnet is *10.0.0.0/24* and +alice's is *10.0.1.0/24*. + +First, ensure that IP forwarding is enabled on both peers. On Linux, +enable routing: +:: + + echo 1 > /proc/sys/net/ipv4/ip_forward + +This setting is not persistent. Please see your operating systems +documentation how to properly configure IP forwarding, which is also +persistent through system boots. + +If your system is configured with a firewall. Please see your operating +systems guide on how to configure the firewall. You typically want to +allow traffic coming from and going to the tun/tap adapter OpenVPN is +configured to use. + +On bob: +:: + + route add -net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2 + +On alice: +:: + + route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1 + +Now any machine on the *10.0.0.0/24* subnet can access any machine on the +*10.0.1.0/24* subnet over the secure tunnel (or vice versa). + +In a production environment, you could put the route command(s) in a +script and execute with the ``--up`` option. diff --git a/doc/man-sections/generic-options.rst b/doc/man-sections/generic-options.rst new file mode 100644 index 0000000..a07fe7e --- /dev/null +++ b/doc/man-sections/generic-options.rst @@ -0,0 +1,438 @@ +Generic Options +--------------- +This section covers generic options which are accessible regardless of +which mode OpenVPN is configured as. + +--help + + Show options. + +--auth-nocache + Don't cache ``--askpass`` or ``--auth-user-pass`` username/passwords in + virtual memory. + + If specified, this directive will cause OpenVPN to immediately forget + username/password inputs after they are used. As a result, when OpenVPN + needs a username/password, it will prompt for input from stdin, which + may be multiple times during the duration of an OpenVPN session. + + When using ``--auth-nocache`` in combination with a user/password file + and ``--chroot`` or ``--daemon``, make sure to use an absolute path. + + This directive does not affect the ``--http-proxy`` username/password. + It is always cached. + +--cd dir + Change directory to ``dir`` prior to reading any files such as + configuration files, key files, scripts, etc. ``dir`` should be an + absolute path, with a leading "/", and without any references to the + current directory such as :code:`.` or :code:`..`. + + This option is useful when you are running OpenVPN in ``--daemon`` mode, + and you want to consolidate all of your OpenVPN control files in one + location. + +--chroot dir + Chroot to ``dir`` after initialization. ``--chroot`` essentially + redefines ``dir`` as being the top level directory tree (/). OpenVPN + will therefore be unable to access any files outside this tree. This can + be desirable from a security standpoint. + + Since the chroot operation is delayed until after initialization, most + OpenVPN options that reference files will operate in a pre-chroot + context. + + In many cases, the ``dir`` parameter can point to an empty directory, + however complications can result when scripts or restarts are executed + after the chroot operation. + + Note: The SSL library will probably need /dev/urandom to be available + inside the chroot directory ``dir``. This is because SSL libraries + occasionally need to collect fresh random. Newer linux kernels and some + BSDs implement a getrandom() or getentropy() syscall that removes the + need for /dev/urandom to be available. + +--config file + Load additional config options from ``file`` where each line corresponds + to one command line option, but with the leading '--' removed. + + If ``--config file`` is the only option to the openvpn command, the + ``--config`` can be removed, and the command can be given as ``openvpn + file`` + + Note that configuration files can be nested to a reasonable depth. + + Double quotation or single quotation characters ("", '') can be used to + enclose single parameters containing whitespace, and "#" or ";" + characters in the first column can be used to denote comments. + + Note that OpenVPN 2.0 and higher performs backslash-based shell escaping + for characters not in single quotations, so the following mappings + should be observed: + :: + + \\ Maps to a single backslash character (\). + \" Pass a literal doublequote character ("), don't + interpret it as enclosing a parameter. + \[SPACE] Pass a literal space or tab character, don't + interpret it as a parameter delimiter. + + For example on Windows, use double backslashes to represent pathnames: + :: + + secret "c:\\OpenVPN\\secret.key" + + + For examples of configuration files, see + https://openvpn.net/community-resources/how-to/ + + Here is an example configuration file: + :: + + # + # Sample OpenVPN configuration file for + # using a pre-shared static key. + # + # '#' or ';' may be used to delimit comments. + + # Use a dynamic tun device. + dev tun + + # Our remote peer + remote mypeer.mydomain + + # 10.1.0.1 is our local VPN endpoint + # 10.1.0.2 is our remote VPN endpoint + ifconfig 10.1.0.1 10.1.0.2 + + # Our pre-shared static key + secret static.key + +--daemon progname + Become a daemon after all initialization functions are completed. This + option will cause all message and error output to be sent to the syslog + file (such as :code:`/var/log/messages`), except for the output of + scripts and ifconfig commands, which will go to :code:`/dev/null` unless + otherwise redirected. The syslog redirection occurs immediately at the + point that ``--daemon`` is parsed on the command line even though the + daemonization point occurs later. If one of the ``--log`` options is + present, it will supersede syslog redirection. + + The optional ``progname`` parameter will cause OpenVPN to report its + program name to the system logger as ``progname``. This can be useful in + linking OpenVPN messages in the syslog file with specific tunnels. When + unspecified, ``progname`` defaults to "openvpn". + + When OpenVPN is run with the ``--daemon`` option, it will try to delay + daemonization until the majority of initialization functions which are + capable of generating fatal errors are complete. This means that + initialization scripts can test the return status of the openvpn command + for a fairly reliable indication of whether the command has correctly + initialized and entered the packet forwarding event loop. + + In OpenVPN, the vast majority of errors which occur after initialization + are non-fatal. + + Note: as soon as OpenVPN has daemonized, it can not ask for usernames, + passwords, or key pass phrases anymore. This has certain consequences, + namely that using a password-protected private key will fail unless the + ``--askpass`` option is used to tell OpenVPN to ask for the pass phrase + (this requirement is new in v2.3.7, and is a consequence of calling + daemon() before initializing the crypto layer). + + Further, using ``--daemon`` together with ``--auth-user-pass`` (entered + on console) and ``--auth-nocache`` will fail as soon as key + renegotiation (and reauthentication) occurs. + +--disable-occ + Don't output a warning message if option inconsistencies are detected + between peers. An example of an option inconsistency would be where one + peer uses ``--dev tun`` while the other peer uses ``--dev tap``. + + Use of this option is discouraged, but is provided as a temporary fix in + situations where a recent version of OpenVPN must connect to an old + version. + +--engine engine-name + Enable OpenSSL hardware-based crypto engine functionality. + + If ``engine-name`` is specified, use a specific crypto engine. Use the + ``--show-engines`` standalone option to list the crypto engines which + are supported by OpenSSL. + +--fast-io + (Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a call to + poll/epoll/select prior to the write operation. The purpose of such a + call would normally be to block until the device or socket is ready to + accept the write. Such blocking is unnecessary on some platforms which + don't support write blocking on UDP sockets or TUN/TAP devices. In such + cases, one can optimize the event loop by avoiding the poll/epoll/select + call, improving CPU efficiency by 5% to 10%. + + This option can only be used on non-Windows systems, when ``--proto + udp`` is specified, and when ``--shaper`` is NOT specified. + +--group group + Similar to the ``--user`` option, this option changes the group ID of + the OpenVPN process to ``group`` after initialization. + +--ignore-unknown-option args + Valid syntax: + :: + + ignore-unknown-options opt1 opt2 opt3 ... optN + + When one of options ``opt1 ... optN`` is encountered in the configuration + file the configuration file parsing does not fail if this OpenVPN version + does not support the option. Multiple ``--ignore-unknown-option`` options + can be given to support a larger number of options to ignore. + + This option should be used with caution, as there are good security + reasons for having OpenVPN fail if it detects problems in a config file. + Having said that, there are valid reasons for wanting new software + features to gracefully degrade when encountered by older software + versions. + + ``--ignore-unknown-option`` is available since OpenVPN 2.3.3. + +--iproute cmd + Set alternate command to execute instead of default ``iproute2`` command. + May be used in order to execute OpenVPN in unprivileged environment. + +--keying-material-exporter args + Save Exported Keying Material [RFC5705] of len bytes (must be between 16 + and 4095 bytes) using ``label`` in environment + (:code:`exported_keying_material`) for use by plugins in + :code:`OPENVPN_PLUGIN_TLS_FINAL` callback. + + Valid syntax: + :: + + keying-material-exporter label len + + Note that exporter ``labels`` have the potential to collide with existing + PRF labels. In order to prevent this, labels *MUST* begin with + :code:`EXPORTER`. + +--mlock + Disable paging by calling the POSIX mlockall function. Requires that + OpenVPN be initially run as root (though OpenVPN can subsequently + downgrade its UID using the ``--user`` option). + + Using this option ensures that key material and tunnel data are never + written to disk due to virtual memory paging operations which occur + under most modern operating systems. It ensures that even if an attacker + was able to crack the box running OpenVPN, he would not be able to scan + the system swap file to recover previously used ephemeral keys, which + are used for a period of time governed by the ``--reneg`` options (see + below), then are discarded. + + The downside of using ``--mlock`` is that it will reduce the amount of + physical memory available to other applications. + +--nice n + Change process priority after initialization (``n`` greater than 0 is + lower priority, ``n`` less than zero is higher priority). + +--persist-key + Don't re-read key files across :code:`SIGUSR1` or ``--ping-restart``. + + This option can be combined with ``--user nobody`` to allow restarts + triggered by the :code:`SIGUSR1` signal. Normally if you drop root + privileges in OpenVPN, the daemon cannot be restarted since it will now + be unable to re-read protected key files. + + This option solves the problem by persisting keys across :code:`SIGUSR1` + resets, so they don't need to be re-read. + +--remap-usr1 signal + Control whether internally or externally generated :code:`SIGUSR1` signals + are remapped to :code:`SIGHUP` (restart without persisting state) or + SIGTERM (exit). + + ``signal`` can be set to :code:`SIGHUP` or :code:`SIGTERM`. By default, + no remapping occurs. + +--script-security level + This directive offers policy-level control over OpenVPN's usage of + external programs and scripts. Lower ``level`` values are more + restrictive, higher values are more permissive. Settings for ``level``: + + :code:`0` + Strictly no calling of external programs. + + :code:`1` + (Default) Only call built-in executables such as ifconfig, + ip, route, or netsh. + + :code:`2` + Allow calling of built-in executables and user-defined + scripts. + + :code:`3` + Allow passwords to be passed to scripts via environmental + variables (potentially unsafe). + + OpenVPN releases before v2.3 also supported a ``method`` flag which + indicated how OpenVPN should call external commands and scripts. This + could be either :code:`execve` or :code:`system`. As of OpenVPN 2.3, this + flag is no longer accepted. In most \*nix environments the execve() + approach has been used without any issues. + + Some directives such as ``--up`` allow options to be passed to the + external script. In these cases make sure the script name does not + contain any spaces or the configuration parser will choke because it + can't determine where the script name ends and script options start. + + To run scripts in Windows in earlier OpenVPN versions you needed to + either add a full path to the script interpreter which can parse the + script or use the ``system`` flag to run these scripts. As of OpenVPN + 2.3 it is now a strict requirement to have full path to the script + interpreter when running non-executables files. This is not needed for + executable files, such as .exe, .com, .bat or .cmd files. For example, + if you have a Visual Basic script, you must use this syntax now: + + :: + + --up 'C:\\Windows\\System32\\wscript.exe C:\\Program\ Files\\OpenVPN\\config\\my-up-script.vbs' + + Please note the single quote marks and the escaping of the backslashes + (\\) and the space character. + + The reason the support for the :code:`system` flag was removed is due to + the security implications with shell expansions when executing scripts + via the :code:`system()` call. + +--setcon context + Apply SELinux ``context`` after initialization. This essentially + provides the ability to restrict OpenVPN's rights to only network I/O + operations, thanks to SELinux. This goes further than ``--user`` and + ``--chroot`` in that those two, while being great security features, + unfortunately do not protect against privilege escalation by + exploitation of a vulnerable system call. You can of course combine all + three, but please note that since setcon requires access to /proc you + will have to provide it inside the chroot directory (e.g. with mount + --bind). + + Since the setcon operation is delayed until after initialization, + OpenVPN can be restricted to just network-related system calls, whereas + by applying the context before startup (such as the OpenVPN one provided + in the SELinux Reference Policies) you will have to allow many things + required only during initialization. + + Like with chroot, complications can result when scripts or restarts are + executed after the setcon operation, which is why you should really + consider using the ``--persist-key`` and ``--persist-tun`` options. + +--status args + Write operational status to ``file`` every ``n`` seconds. + + Valid syntaxes: + :: + + status file + status file n + + Status can also be written to the syslog by sending a :code:`SIGUSR2` + signal. + + With multi-client capability enabled on a server, the status file + includes a list of clients and a routing table. The output format can be + controlled by the ``--status-version`` option in that case. + + For clients or instances running in point-to-point mode, it will contain + the traffic statistics. + +--status-version n + Set the status file format version number to ``n``. + + This only affects the status file on servers with multi-client + capability enabled. Valid status version values: + + :code:`1` + Traditional format (default). The client list contains the + following fields comma-separated: Common Name, Real Address, Bytes + Received, Bytes Sent, Connected Since. + + :code:`2` + A more reliable format for external processing. Compared to + version :code:`1`, the client list contains some additional fields: + Virtual Address, Virtual IPv6 Address, Username, Client ID, Peer ID, + Data Channel Cipher. Future versions may extend the number of fields. + + :code:`3` + Identical to :code:`2`, but fields are tab-separated. + +--test-crypto + Do a self-test of OpenVPN's crypto options by encrypting and decrypting + test packets using the data channel encryption options specified above. + This option does not require a peer to function, and therefore can be + specified without ``--dev`` or ``--remote``. + + The typical usage of ``--test-crypto`` would be something like this: + :: + + openvpn --test-crypto --secret key + + or + + :: + + openvpn --test-crypto --secret key --verb 9 + + This option is very useful to test OpenVPN after it has been ported to a + new platform, or to isolate problems in the compiler, OpenSSL crypto + library, or OpenVPN's crypto code. Since it is a self-test mode, + problems with encryption and authentication can be debugged + independently of network and tunnel issues. + +--tmp-dir dir + Specify a directory ``dir`` for temporary files. This directory will be + used by openvpn processes and script to communicate temporary data with + openvpn main process. Note that the directory must be writable by the + OpenVPN process after it has dropped it's root privileges. + + This directory will be used by in the following cases: + + * ``--client-connect`` scripts and :code:`OPENVPN_PLUGIN_CLIENT_CONNECT` + plug-in hook to dynamically generate client-specific configuration + :code:`client_connect_config_file` and return success/failure via + :code:`client_connect_deferred_file` when using deferred client connect + method + + * :code:`OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY` plug-in hooks returns + success/failure via :code:`auth_control_file` when using deferred auth + method + + * :code:`OPENVPN_PLUGIN_ENABLE_PF` plugin hook to pass filtering rules + via ``pf_file`` + +--use-prediction-resistance + Enable prediction resistance on mbed TLS's RNG. + + Enabling prediction resistance causes the RNG to reseed in each call for + random. Reseeding this often can quickly deplete the kernel entropy + pool. + + If you need this option, please consider running a daemon that adds + entropy to the kernel pool. + +--user user + Change the user ID of the OpenVPN process to ``user`` after + initialization, dropping privileges in the process. This option is + useful to protect the system in the event that some hostile party was + able to gain control of an OpenVPN session. Though OpenVPN's security + features make this unlikely, it is provided as a second line of defense. + + By setting ``user`` to :code:`nobody` or somebody similarly unprivileged, + the hostile party would be limited in what damage they could cause. Of + course once you take away privileges, you cannot return them to an + OpenVPN session. This means, for example, that if you want to reset an + OpenVPN daemon with a :code:`SIGUSR1` signal (for example in response to + a DHCP reset), you should make use of one or more of the ``--persist`` + options to ensure that OpenVPN doesn't need to execute any privileged + operations in order to restart (such as re-reading key files or running + ``ifconfig`` on the TUN device). + +--writepid file + Write OpenVPN's main process ID to ``file``. diff --git a/doc/man-sections/inline-files.rst b/doc/man-sections/inline-files.rst new file mode 100644 index 0000000..819bd3c --- /dev/null +++ b/doc/man-sections/inline-files.rst @@ -0,0 +1,25 @@ +INLINE FILE SUPPORT +=================== + +OpenVPN allows including files in the main configuration for the ``--ca``, +``--cert``, ``--dh``, ``--extra-certs``, ``--key``, ``--pkcs12``, +``--secret``, ``--crl-verify``, ``--http-proxy-user-pass``, ``--tls-auth``, +``--auth-gen-token-secret``, ``--tls-crypt`` and ``--tls-crypt-v2`` +options. + +Each inline file started by the line ```` + +Here is an example of an inline file usage + +:: + + + -----BEGIN CERTIFICATE----- + [...] + -----END CERTIFICATE----- + + +When using the inline file feature with ``--pkcs12`` the inline file has +to be base64 encoded. Encoding of a .p12 file into base64 can be done +for example with OpenSSL by running :code:`openssl base64 -in input.p12` diff --git a/doc/man-sections/link-options.rst b/doc/man-sections/link-options.rst new file mode 100644 index 0000000..c132a62 --- /dev/null +++ b/doc/man-sections/link-options.rst @@ -0,0 +1,409 @@ +Link Options +------------ +This link options section covers options related to the connection between +the local and the remote host. + +--bind keywords + Bind to local address and port. This is the default unless any of + ``--proto tcp-client`` , ``--http-proxy`` or ``--socks-proxy`` are used. + + If the optional :code:`ipv6only` keyword is present OpenVPN will bind only + to IPv6 (as opposed to IPv6 and IPv4) when a IPv6 socket is opened. + +--float + Allow remote peer to change its IP address and/or port number, such as + due to DHCP (this is the default if ``--remote`` is not used). + ``--float`` when specified with ``--remote`` allows an OpenVPN session + to initially connect to a peer at a known address, however if packets + arrive from a new address and pass all authentication tests, the new + address will take control of the session. This is useful when you are + connecting to a peer which holds a dynamic address such as a dial-in + user or DHCP client. + + Essentially, ``--float`` tells OpenVPN to accept authenticated packets + from any address, not only the address which was specified in the + ``--remote`` option. + +--fragment max + Enable internal datagram fragmentation so that no UDP datagrams are sent + which are larger than ``max`` bytes. + + The ``max`` parameter is interpreted in the same way as the + ``--link-mtu`` parameter, i.e. the UDP packet size after encapsulation + overhead has been added in, but not including the UDP header itself. + + The ``--fragment`` option only makes sense when you are using the UDP + protocol (``--proto udp``). + + ``--fragment`` adds 4 bytes of overhead per datagram. + + See the ``--mssfix`` option below for an important related option to + ``--fragment``. + + It should also be noted that this option is not meant to replace UDP + fragmentation at the IP stack level. It is only meant as a last resort + when path MTU discovery is broken. Using this option is less efficient + than fixing path MTU discovery for your IP link and using native IP + fragmentation instead. + + Having said that, there are circumstances where using OpenVPN's internal + fragmentation capability may be your only option, such as tunneling a + UDP multicast stream which requires fragmentation. + +--keepalive args + A helper directive designed to simplify the expression of ``--ping`` and + ``--ping-restart``. + + Valid syntax: + :: + + keepalive interval timeout + + This option can be used on both client and server side, but it is enough + to add this on the server side as it will push appropriate ``--ping`` + and ``--ping-restart`` options to the client. If used on both server and + client, the values pushed from server will override the client local + values. + + The ``timeout`` argument will be twice as long on the server side. This + ensures that a timeout is detected on client side before the server side + drops the connection. + + For example, ``--keepalive 10 60`` expands as follows: + :: + + if mode server: + ping 10 # Argument: interval + ping-restart 120 # Argument: timeout*2 + push "ping 10" # Argument: interval + push "ping-restart 60" # Argument: timeout + else + ping 10 # Argument: interval + ping-restart 60 # Argument: timeout + +--link-mtu n + Sets an upper bound on the size of UDP packets which are sent between + OpenVPN peers. *It's best not to set this parameter unless you know what + you're doing.* + +--local host + Local host name or IP address for bind. If specified, OpenVPN will bind + to this address only. If unspecified, OpenVPN will bind to all + interfaces. + +--lport port + Set local TCP/UDP port number or name. Cannot be used together with + ``--nobind`` option. + +--mark value + Mark encrypted packets being sent with value. The mark value can be + matched in policy routing and packetfilter rules. This option is only + supported in Linux and does nothing on other operating systems. + +--mode m + Set OpenVPN major mode. By default, OpenVPN runs in point-to-point mode + (:code:`p2p`). OpenVPN 2.0 introduces a new mode (:code:`server`) which + implements a multi-client server capability. + +--mssfix max + Announce to TCP sessions running over the tunnel that they should limit + their send packet sizes such that after OpenVPN has encapsulated them, + the resulting UDP packet size that OpenVPN sends to its peer will not + exceed ``max`` bytes. The default value is :code:`1450`. + + The ``max`` parameter is interpreted in the same way as the + ``--link-mtu`` parameter, i.e. the UDP packet size after encapsulation + overhead has been added in, but not including the UDP header itself. + Resulting packet would be at most 28 bytes larger for IPv4 and 48 bytes + for IPv6 (20/40 bytes for IP header and 8 bytes for UDP header). Default + value of 1450 allows IPv4 packets to be transmitted over a link with MTU + 1473 or higher without IP level fragmentation. + + The ``--mssfix`` option only makes sense when you are using the UDP + protocol for OpenVPN peer-to-peer communication, i.e. ``--proto udp``. + + ``--mssfix`` and ``--fragment`` can be ideally used together, where + ``--mssfix`` will try to keep TCP from needing packet fragmentation in + the first place, and if big packets come through anyhow (from protocols + other than TCP), ``--fragment`` will internally fragment them. + + Both ``--fragment`` and ``--mssfix`` are designed to work around cases + where Path MTU discovery is broken on the network path between OpenVPN + peers. + + The usual symptom of such a breakdown is an OpenVPN connection which + successfully starts, but then stalls during active usage. + + If ``--fragment`` and ``--mssfix`` are used together, ``--mssfix`` will + take its default ``max`` parameter from the ``--fragment max`` option. + + Therefore, one could lower the maximum UDP packet size to 1300 (a good + first try for solving MTU-related connection problems) with the + following options: + :: + + --tun-mtu 1500 --fragment 1300 --mssfix + +--mtu-disc type + Should we do Path MTU discovery on TCP/UDP channel? Only supported on + OSes such as Linux that supports the necessary system call to set. + + Valid types: + + :code:`no` Never send DF (Don't Fragment) frames + + :code:`maybe` Use per-route hints + + :code:`yes` Always DF (Don't Fragment) + +--mtu-test + To empirically measure MTU on connection startup, add the ``--mtu-test`` + option to your configuration. OpenVPN will send ping packets of various + sizes to the remote peer and measure the largest packets which were + successfully received. The ``--mtu-test`` process normally takes about 3 + minutes to complete. + +--nobind + Do not bind to local address and port. The IP stack will allocate a + dynamic port for returning packets. Since the value of the dynamic port + could not be known in advance by a peer, this option is only suitable + for peers which will be initiating connections by using the --remote + option. + +--passtos + Set the TOS field of the tunnel packet to what the payload's TOS is. + +--ping n + Ping remote over the TCP/UDP control channel if no packets have been + sent for at least ``n`` seconds (specify ``--ping`` on both peers to + cause ping packets to be sent in both directions since OpenVPN ping + packets are not echoed like IP ping packets). When used in one of + OpenVPN's secure modes (where ``--secret``, ``--tls-server`` or + ``--tls-client`` is specified), the ping packet will be + cryptographically secure. + + This option has two intended uses: + + (1) Compatibility with stateful firewalls. The periodic ping will ensure + that a stateful firewall rule which allows OpenVPN UDP packets to + pass will not time out. + + (2) To provide a basis for the remote to test the existence of its peer + using the ``--ping-exit`` option. + +--ping-exit n + Causes OpenVPN to exit after ``n`` seconds pass without reception of a + ping or other packet from remote. This option can be combined with + ``--inactive``, ``--ping`` and ``--ping-exit`` to create a two-tiered + inactivity disconnect. + + For example, + :: + + openvpn [options...] --inactive 3600 --ping 10 --ping-exit 60 + + when used on both peers will cause OpenVPN to exit within 60 seconds if + its peer disconnects, but will exit after one hour if no actual tunnel + data is exchanged. + +--ping-restart n + Similar to ``--ping-exit``, but trigger a :code:`SIGUSR1` restart after + ``n`` seconds pass without reception of a ping or other packet from + remote. + + This option is useful in cases where the remote peer has a dynamic IP + address and a low-TTL DNS name is used to track the IP address using a + service such as http://dyndns.org/ + a dynamic DNS client such as + ``ddclient``. + + If the peer cannot be reached, a restart will be triggered, causing the + hostname used with ``--remote`` to be re-resolved (if ``--resolv-retry`` + is also specified). + + In server mode, ``--ping-restart``, ``--inactive`` or any other type of + internally generated signal will always be applied to individual client + instance objects, never to whole server itself. Note also in server mode + that any internally generated signal which would normally cause a + restart, will cause the deletion of the client instance object instead. + + In client mode, the ``--ping-restart`` parameter is set to 120 seconds + by default. This default will hold until the client pulls a replacement + value from the server, based on the ``--keepalive`` setting in the + server configuration. To disable the 120 second default, set + ``--ping-restart 0`` on the client. + + See the signals section below for more information on :code:`SIGUSR1`. + + Note that the behavior of ``SIGUSR1`` can be modified by the + ``--persist-tun``, ``--persist-key``, ``--persist-local-ip`` and + ``--persist-remote-ip`` options. + + Also note that ``--ping-exit`` and ``--ping-restart`` are mutually + exclusive and cannot be used together. + +--ping-timer-rem + Run the ``--ping-exit`` / ``--ping-restart`` timer only if we have a + remote address. Use this option if you are starting the daemon in listen + mode (i.e. without an explicit ``--remote`` peer), and you don't want to + start clocking timeouts until a remote peer connects. + +--proto p + Use protocol ``p`` for communicating with remote host. ``p`` can be + :code:`udp`, :code:`tcp-client`, or :code:`tcp-server`. + + The default protocol is :code:`udp` when ``--proto`` is not specified. + + For UDP operation, ``--proto udp`` should be specified on both peers. + + For TCP operation, one peer must use ``--proto tcp-server`` and the + other must use ``--proto tcp-client``. A peer started with + :code:`tcp-server` will wait indefinitely for an incoming connection. A peer + started with :code:`tcp-client` will attempt to connect, and if that fails, + will sleep for 5 seconds (adjustable via the ``--connect-retry`` option) + and try again infinite or up to N retries (adjustable via the + ``--connect-retry-max`` option). Both TCP client and server will + simulate a SIGUSR1 restart signal if either side resets the connection. + + OpenVPN is designed to operate optimally over UDP, but TCP capability is + provided for situations where UDP cannot be used. In comparison with + UDP, TCP will usually be somewhat less efficient and less robust when + used over unreliable or congested networks. + + This article outlines some of problems with tunneling IP over TCP: + http://sites.inka.de/sites/bigred/devel/tcp-tcp.html + + There are certain cases, however, where using TCP may be advantageous + from a security and robustness perspective, such as tunneling non-IP or + application-level UDP protocols, or tunneling protocols which don't + possess a built-in reliability layer. + +--port port + TCP/UDP port number or port name for both local and remote (sets both + ``--lport`` and ``--rport`` options to given port). The current default + of 1194 represents the official IANA port number assignment for OpenVPN + and has been used since version 2.0-beta17. Previous versions used port + 5000 as the default. + +--rport port + Set TCP/UDP port number or name used by the ``--remote`` option. The + port can also be set directly using the ``--remote`` option. + +--replay-window args + Modify the replay protection sliding-window size and time window. + + Valid syntax: + :: + + replay-window n [t] + + Use a replay protection sliding-window of size **n** and a time window + of **t** seconds. + + By default **n** is 64 (the IPSec default) and **t** is 15 seconds. + + This option is only relevant in UDP mode, i.e. when either **--proto + udp** is specified, or no **--proto** option is specified. + + When OpenVPN tunnels IP packets over UDP, there is the possibility that + packets might be dropped or delivered out of order. Because OpenVPN, + like IPSec, is emulating the physical network layer, it will accept an + out-of-order packet sequence, and will deliver such packets in the same + order they were received to the TCP/IP protocol stack, provided they + satisfy several constraints. + + (a) The packet cannot be a replay (unless ``--no-replay`` is + specified, which disables replay protection altogether). + + (b) If a packet arrives out of order, it will only be accepted if + the difference between its sequence number and the highest sequence + number received so far is less than ``n``. + + (c) If a packet arrives out of order, it will only be accepted if it + arrives no later than ``t`` seconds after any packet containing a higher + sequence number. + + If you are using a network link with a large pipeline (meaning that the + product of bandwidth and latency is high), you may want to use a larger + value for ``n``. Satellite links in particular often require this. + + If you run OpenVPN at ``--verb 4``, you will see the message + "Replay-window backtrack occurred [x]" every time the maximum sequence + number backtrack seen thus far increases. This can be used to calibrate + ``n``. + + There is some controversy on the appropriate method of handling packet + reordering at the security layer. + + Namely, to what extent should the security layer protect the + encapsulated protocol from attacks which masquerade as the kinds of + normal packet loss and reordering that occur over IP networks? + + The IPSec and OpenVPN approach is to allow packet reordering within a + certain fixed sequence number window. + + OpenVPN adds to the IPSec model by limiting the window size in time as + well as sequence space. + + OpenVPN also adds TCP transport as an option (not offered by IPSec) in + which case OpenVPN can adopt a very strict attitude towards message + deletion and reordering: Don't allow it. Since TCP guarantees + reliability, any packet loss or reordering event can be assumed to be an + attack. + + In this sense, it could be argued that TCP tunnel transport is preferred + when tunneling non-IP or UDP application protocols which might be + vulnerable to a message deletion or reordering attack which falls within + the normal operational parameters of IP networks. + + So I would make the statement that one should never tunnel a non-IP + protocol or UDP application protocol over UDP, if the protocol might be + vulnerable to a message deletion or reordering attack that falls within + the normal operating parameters of what is to be expected from the + physical IP layer. The problem is easily fixed by simply using TCP as + the VPN transport layer. + +--replay-persist file + Persist replay-protection state across sessions using ``file`` to save + and reload the state. + + This option will strengthen protection against replay attacks, + especially when you are using OpenVPN in a dynamic context (such as with + ``--inetd``) when OpenVPN sessions are frequently started and stopped. + + This option will keep a disk copy of the current replay protection state + (i.e. the most recent packet timestamp and sequence number received from + the remote peer), so that if an OpenVPN session is stopped and + restarted, it will reject any replays of packets which were already + received by the prior session. + + This option only makes sense when replay protection is enabled (the + default) and you are using either ``--secret`` (shared-secret key mode) + or TLS mode with ``--tls-auth``. + +--socket-flags flags + Apply the given flags to the OpenVPN transport socket. Currently, only + :code:`TCP_NODELAY` is supported. + + The :code:`TCP_NODELAY` socket flag is useful in TCP mode, and causes the + kernel to send tunnel packets immediately over the TCP connection without + trying to group several smaller packets into a larger packet. This can + result in a considerably improvement in latency. + + This option is pushable from server to client, and should be used on + both client and server for maximum effect. + +--tcp-nodelay + This macro sets the :code:`TCP_NODELAY` socket flag on the server as well + as pushes it to connecting clients. The :code:`TCP_NODELAY` flag disables + the Nagle algorithm on TCP sockets causing packets to be transmitted + immediately with low latency, rather than waiting a short period of time + in order to aggregate several packets into a larger containing packet. + In VPN applications over TCP, :code:`TCP_NODELAY` is generally a good + latency optimization. + + The macro expands as follows: + :: + + if mode server: + socket-flags TCP_NODELAY + push "socket-flags TCP_NODELAY" diff --git a/doc/man-sections/log-options.rst b/doc/man-sections/log-options.rst new file mode 100644 index 0000000..e385d18 --- /dev/null +++ b/doc/man-sections/log-options.rst @@ -0,0 +1,73 @@ +Log options +----------- + +--echo parms + Echo ``parms`` to log output. + + Designed to be used to send messages to a controlling application which + is receiving the OpenVPN log output. + +--errors-to-stderr + Output errors to stderr instead of stdout unless log output is + redirected by one of the ``--log`` options. + +--log file + Output logging messages to ``file``, including output to stdout/stderr + which is generated by called scripts. If ``file`` already exists it will + be truncated. This option takes effect immediately when it is parsed in + the command line and will supersede syslog output if ``--daemon`` or + ``--inetd`` is also specified. This option is persistent over the entire + course of an OpenVPN instantiation and will not be reset by + :code:`SIGHUP`, :code:`SIGUSR1`, or ``--ping-restart``. + + Note that on Windows, when OpenVPN is started as a service, logging + occurs by default without the need to specify this option. + +--log-append file + Append logging messages to ``file``. If ``file`` does not exist, it will + be created. This option behaves exactly like ``--log`` except that it + appends to rather than truncating the log file. + +--machine-readable-output + Always write timestamps and message flags to log messages, even when + they otherwise would not be prefixed. In particular, this applies to log + messages sent to stdout. + +--mute n + Log at most ``n`` consecutive messages in the same category. This is + useful to limit repetitive logging of similar message types. + +--mute-replay-warnings + Silence the output of replay warnings, which are a common false alarm on + WiFi networks. This option preserves the security of the replay + protection code without the verbosity associated with warnings about + duplicate packets. + +--suppress-timestamps + Avoid writing timestamps to log messages, even when they otherwise would + be prepended. In particular, this applies to log messages sent to + stdout. + +--syslog progname + Direct log output to system logger, but do not become a daemon. See + ``--daemon`` directive above for description of ``progname`` parameter. + +--verb n + Set output verbosity to ``n`` (default :code:`1`). Each level shows all + info from the previous levels. Level :code:`3` is recommended if you want + a good summary of what's happening without being swamped by output. + + :code:`0` + No output except fatal errors. + + :code:`1` to :code:`4` + Normal usage range. + + :code:`5` + Outputs :code:`R` and :code:`W` characters to the console for + each packet read and write, uppercase is used for TCP/UDP + packets and lowercase is used for TUN/TAP packets. + + :code:`6` to :code:`11` + Debug info range (see :code:`errlevel.h` in the source code for + additional information on debug levels). diff --git a/doc/man-sections/management-options.rst b/doc/man-sections/management-options.rst new file mode 100644 index 0000000..de0d47e --- /dev/null +++ b/doc/man-sections/management-options.rst @@ -0,0 +1,135 @@ +Management Interface Options +---------------------------- +OpenVPN provides a feature rich socket based management interface for both +server and client mode operations. + +--management args + Enable a management server on a ``socket-name`` Unix socket on those + platforms supporting it, or on a designated TCP port. + + Valid syntaxes: + :: + + management socket-name unix # + management socket-name unix pw-file # (recommended) + management IP port # (INSECURE) + management IP port pw-file # + + ``pw-file``, if specified, is a password file where the password must + be on first line. Instead of a filename it can use the keyword stdin + which will prompt the user for a password to use when OpenVPN is + starting. + + For unix sockets, the default behaviour is to create a unix domain + socket that may be connected to by any process. Use the + ``--management-client-user`` and ``--management-client-group`` + directives to restrict access. + + The management interface provides a special mode where the TCP + management link can operate over the tunnel itself. To enable this mode, + set IP to ``tunnel``. Tunnel mode will cause the management interface to + listen for a TCP connection on the local VPN address of the TUN/TAP + interface. + + ***BEWARE*** of enabling the management interface over TCP. In these cases + you should *ALWAYS* make use of ``pw-file`` to password protect the + management interface. Any user who can connect to this TCP ``IP:port`` + will be able to manage and control (and interfere with) the OpenVPN + process. It is also strongly recommended to set IP to 127.0.0.1 + (localhost) to restrict accessibility of the management server to local + clients. + + While the management port is designed for programmatic control of + OpenVPN by other applications, it is possible to telnet to the port, + using a telnet client in "raw" mode. Once connected, type :code:`help` + for a list of commands. + + For detailed documentation on the management interface, see the + *management-notes.txt* file in the management folder of the OpenVPN + source distribution. + +--management-client + Management interface will connect as a TCP/unix domain client to + ``IP:port`` specified by ``--management`` rather than listen as a TCP + server or on a unix domain socket. + + If the client connection fails to connect or is disconnected, a SIGTERM + signal will be generated causing OpenVPN to quit. + +--management-client-auth + Gives management interface client the responsibility to authenticate + clients after their client certificate has been verified. See + :code:`management-notes.txt` in OpenVPN distribution for detailed notes. + +--management-client-group g + When the management interface is listening on a unix domain socket, only + allow connections from group ``g``. + +--management-client-pf + Management interface clients must specify a packet filter file for each + connecting client. See :code:`management-notes.txt` in OpenVPN + distribution for detailed notes. + +--management-client-user u + When the management interface is listening on a unix domain socket, only + allow connections from user ``u``. + +--management-external-cert certificate-hint + Allows usage for external certificate instead of ``--cert`` option + (client-only). ``certificate-hint`` is an arbitrary string which is + passed to a management interface client as an argument of + *NEED-CERTIFICATE* notification. Requires ``--management-external-key``. + +--management-external-key args + Allows usage for external private key file instead of ``--key`` option + (client-only). + + Valid syntaxes: + :: + + management-external-key + management-external-key nopadding + management-external-key pkcs1 + management-external-key nopadding pkcs1 + + The optional parameters :code:`nopadding` and :code:`pkcs1` signal + support for different padding algorithms. See + :code:`doc/mangement-notes.txt` for a complete description of this + feature. + +--management-forget-disconnect + Make OpenVPN forget passwords when management session disconnects. + + This directive does not affect the ``--http-proxy`` username/password. + It is always cached. + +--management-hold + Start OpenVPN in a hibernating state, until a client of the management + interface explicitly starts it with the :code:`hold release` command. + +--management-log-cache n + Cache the most recent ``n`` lines of log file history for usage by the + management channel. + +--management-query-passwords + Query management channel for private key password and + ``--auth-user-pass`` username/password. Only query the management + channel for inputs which ordinarily would have been queried from the + console. + +--management-query-proxy + Query management channel for proxy server information for a specific + ``--remote`` (client-only). + +--management-query-remote + Allow management interface to override ``--remote`` directives + (client-only). + +--management-signal + Send SIGUSR1 signal to OpenVPN if management session disconnects. This + is useful when you wish to disconnect an OpenVPN session on user logoff. + For ``--management-client`` this option is not needed since a disconnect + will always generate a :code:`SIGTERM`. + +--management-up-down + Report tunnel up/down events to management interface. diff --git a/doc/man-sections/network-config.rst b/doc/man-sections/network-config.rst new file mode 100644 index 0000000..04b30aa --- /dev/null +++ b/doc/man-sections/network-config.rst @@ -0,0 +1,10 @@ +NETWORK CONFIGURATION +===================== + +OpenVPN consists of two sides of network configuration. One side is the +*link* between the local and remote side, the other side is the *virtual +network adapter* (tun/tap device). + +.. include:: link-options.rst +.. include:: vpn-network-options.rst +.. include:: virtual-routing-and-forwarding.rst diff --git a/doc/man-sections/pkcs11-options.rst b/doc/man-sections/pkcs11-options.rst new file mode 100644 index 0000000..c064aca --- /dev/null +++ b/doc/man-sections/pkcs11-options.rst @@ -0,0 +1,80 @@ +PKCS#11 / SmartCard options +--------------------------- + +--pkcs11-cert-private args + Set if access to certificate object should be performed after login. + Every provider has its own setting. + + Valid syntaxes: + :: + + pkcs11-cert-private 0 + pkcs11-cert-private 1 + +--pkcs11-id name + Specify the serialized certificate id to be used. The id can be gotten + by the standalone ``--show-pkcs11-ids`` option. + +--pkcs11-id-management + Acquire PKCS#11 id from management interface. In this case a + :code:`NEED-STR 'pkcs11-id-request'` real-time message will be triggered, + application may use pkcs11-id-count command to retrieve available number of + certificates, and pkcs11-id-get command to retrieve certificate id and + certificate body. + +--pkcs11-pin-cache seconds + Specify how many seconds the PIN can be cached, the default is until the + token is removed. + +--pkcs11-private-mode mode + Specify which method to use in order to perform private key operations. + A different mode can be specified for each provider. Mode is encoded as + hex number, and can be a mask one of the following: + + :code:`0` (default) Try to determine automatically. + + :code:`1` Use sign. + + :code:`2` Use sign recover. + + :code:`4` Use decrypt. + + :code:`8` Use unwrap. + +--pkcs11-protected-authentication args + Use PKCS#11 protected authentication path, useful for biometric and + external keypad devices. Every provider has its own setting. + + Valid syntaxes: + :: + + pkcs11-protected-authentication 0 + pkcs11-protected-authentication 1 + +--pkcs11-providers provider + Specify an RSA Security Inc. PKCS #11 Cryptographic Token Interface + (Cryptoki) providers to load. This option can be used instead of + ``--cert``, ``--key`` and ``--pkcs12``. + + If p11-kit is present on the system, its :code:`p11-kit-proxy.so` module + will be loaded by default if either the ``--pkcs11-id`` or + ``--pkcs11-id-management`` options are specified without + ``--pkcs11-provider`` being given. + +--show-pkcs11-ids args + (Standalone) Show PKCS#11 token object list. + + Valid syntax: + :: + + show-pkcs11 [provider] [cert_private] + + Specify ``cert_private`` as :code:`1` if certificates are stored as + private objects. + + If *p11-kit* is present on the system, the ``provider`` argument is + optional; if omitted the default :code:`p11-kit-proxy.so` module will be + queried. + + ``--verb`` option can be used BEFORE this option to produce debugging + information. diff --git a/doc/man-sections/plugin-options.rst b/doc/man-sections/plugin-options.rst new file mode 100644 index 0000000..51c574f --- /dev/null +++ b/doc/man-sections/plugin-options.rst @@ -0,0 +1,57 @@ +Plug-in Interface Options +------------------------- + +OpenVPN can be extended by loading external plug-in modules at runtime. These +plug-ins must be prebuilt and adhere to the OpenVPN Plug-In API. + +--plugin args + Loads an OpenVPN plug-in module. + + Valid syntax: + :: + + plugin module-name + plugin module-name "arguments" + + The ``module-name`` needs to be the first + argument, indicating the plug-in to load. The second argument is an + optional init string which will be passed directly to the plug-in. + If the init consists of multiple arguments it must be enclosed in + double-quotes (\"). Multiple plugin modules may be loaded into one + OpenVPN process. + + The ``module-name`` argument can be just a filename or a filename + with a relative or absolute path. The format of the filename and path + defines if the plug-in will be loaded from a default plug-in directory + or outside this directory. + :: + + --plugin path Effective directory used + ===================== ============================= + myplug.so DEFAULT_DIR/myplug.so + subdir/myplug.so DEFAULT_DIR/subdir/myplug.so + ./subdir/myplug.so CWD/subdir/myplug.so + /usr/lib/my/plug.so /usr/lib/my/plug.so + + + ``DEFAULT_DIR`` is replaced by the default plug-in directory, which is + configured at the build time of OpenVPN. ``CWD`` is the current directory + where OpenVPN was started or the directory OpenVPN have switched into + via the ``--cd`` option before the ``--plugin`` option. + + For more information and examples on how to build OpenVPN plug-in + modules, see the README file in the ``plugin`` folder of the OpenVPN + source distribution. + + If you are using an RPM install of OpenVPN, see + :code:`/usr/share/openvpn/plugin`. The documentation is in ``doc`` and + the actual plugin modules are in ``lib``. + + Multiple plugin modules can be cascaded, and modules can be used in + tandem with scripts. The modules will be called by OpenVPN in the order + that they are declared in the config file. If both a plugin and script + are configured for the same callback, the script will be called last. If + the return code of the module/script controls an authentication function + (such as tls-verify, auth-user-pass-verify, or client-connect), then + every module and script must return success (:code:`0`) in order for the + connection to be authenticated. diff --git a/doc/man-sections/protocol-options.rst b/doc/man-sections/protocol-options.rst new file mode 100644 index 0000000..e9d5d63 --- /dev/null +++ b/doc/man-sections/protocol-options.rst @@ -0,0 +1,281 @@ +Protocol options +---------------- +Options in this section affect features available in the OpenVPN wire +protocol. Many of these options also define the encryption options +of the data channel in the OpenVPN wire protocol. These options must be +configured in a compatible way between both the local and remote side. + +--allow-compression mode + As described in the ``--compress`` option, compression is a potentially + dangerous option. This option allows controlling the behaviour of + OpenVPN when compression is used and allowed. + + Valid syntaxes: + :: + + allow-compression + allow-compression mode + + The ``mode`` argument can be one of the following values: + + :code:`asym` (default) + OpenVPN will only *decompress downlink packets* but *not compress + uplink packets*. This also allows migrating to disable compression + when changing both server and client configurations to remove + compression at the same time is not a feasible option. + + :code:`no` + OpenVPN will refuse any non-stub compression. + + :code:`yes` + OpenVPN will send and receive compressed packets. + +--auth alg + Authenticate data channel packets and (if enabled) ``tls-auth`` control + channel packets with HMAC using message digest algorithm ``alg``. (The + default is ``SHA1`` ). HMAC is a commonly used message authentication + algorithm (MAC) that uses a data string, a secure hash algorithm and a + key to produce a digital signature. + + The OpenVPN data channel protocol uses encrypt-then-mac (i.e. first + encrypt a packet then HMAC the resulting ciphertext), which prevents + padding oracle attacks. + + If an AEAD cipher mode (e.g. GCM) is chosen then the specified ``--auth`` + algorithm is ignored for the data channel and the authentication method + of the AEAD cipher is used instead. Note that ``alg`` still specifies + the digest used for ``tls-auth``. + + In static-key encryption mode, the HMAC key is included in the key file + generated by ``--genkey``. In TLS mode, the HMAC key is dynamically + generated and shared between peers via the TLS control channel. If + OpenVPN receives a packet with a bad HMAC it will drop the packet. HMAC + usually adds 16 or 20 bytes per packet. Set ``alg=none`` to disable + authentication. + + For more information on HMAC see + http://www.cs.ucsd.edu/users/mihir/papers/hmac.html + +--cipher alg + This option is deprecated for server-client mode. ``--data-ciphers`` + or possibly `--data-ciphers-fallback`` should be used instead. + + Encrypt data channel packets with cipher algorithm ``alg``. + + The default is :code:`BF-CBC`, an abbreviation for Blowfish in Cipher + Block Chaining mode. When cipher negotiation (NCP) is allowed, + OpenVPN 2.4 and newer on both client and server side will automatically + upgrade to :code:`AES-256-GCM`. See ``--data-ciphers`` and + ``--ncp-disable`` for more details on NCP. + + Using :code:`BF-CBC` is no longer recommended, because of its 64-bit + block size. This small block size allows attacks based on collisions, as + demonstrated by SWEET32. See + https://community.openvpn.net/openvpn/wiki/SWEET32 + for details. Due to this, support for :code:`BF-CBC`, :code:`DES`, + :code:`CAST5`, :code:`IDEA` and :code:`RC2` ciphers will be removed in + OpenVPN 2.6. + + To see other ciphers that are available with OpenVPN, use the + ``--show-ciphers`` option. + + Set ``alg`` to :code:`none` to disable encryption. + +--compress algorithm + **DEPRECATED** Enable a compression algorithm. Compression is generally + not recommended. VPN tunnels which use compression are susceptible to + the VORALCE attack vector. + + The ``algorithm`` parameter may be :code:`lzo`, :code:`lz4`, + :code:`lz4-v2`, :code:`stub`, :code:`stub-v2` or empty. + LZO and LZ4 are different compression algorithms, with LZ4 generally + offering the best performance with least CPU usage. + + The :code:`lz4-v2` and :code:`stub-v2` variants implement a better + framing that does not add overhead when packets cannot be compressed. All + other variants always add one extra framing byte compared to no + compression framing. + + If the ``algorithm`` parameter is :code:`stub`, :code:`stub-v2` or empty, + compression will be turned off, but the packet framing for compression + will still be enabled, allowing a different setting to be pushed later. + Additionally, :code:`stub` and :code:`stub-v2` wil disable announcing + ``lzo`` and ``lz4`` compression support via *IV_* variables to the + server. + + Note: the :code:`stub` (or empty) option is NOT compatible with the older + option ``--comp-lzo no``. + + ***Security Considerations*** + + Compression and encryption is a tricky combination. If an attacker knows + or is able to control (parts of) the plain-text of packets that contain + secrets, the attacker might be able to extract the secret if compression + is enabled. See e.g. the *CRIME* and *BREACH* attacks on TLS and + *VORACLE* on VPNs which also leverage to break encryption. If you are not + entirely sure that the above does not apply to your traffic, you are + advised to *not* enable compression. + +--comp-lzo mode + **DEPRECATED** Enable LZO compression algorithm. Compression is + generally not recommended. VPN tunnels which uses compression are + suspectible to the VORALCE attack vector. + + Use LZO compression -- may add up to 1 byte per packet for incompressible + data. ``mode`` may be :code:`yes`, :code:`no`, or :code:`adaptive` + (default). + + In a server mode setup, it is possible to selectively turn compression + on or off for individual clients. + + First, make sure the client-side config file enables selective + compression by having at least one ``--comp-lzo`` directive, such as + ``--comp-lzo no``. This will turn off compression by default, but allow + a future directive push from the server to dynamically change the + :code:`on`/:code:`off`/:code:`adaptive` setting. + + Next in a ``--client-config-dir`` file, specify the compression setting + for the client, for example: + :: + + comp-lzo yes + push "comp-lzo yes" + + The first line sets the ``comp-lzo`` setting for the server side of the + link, the second sets the client side. + +--comp-noadapt + **DEPRECATED** When used in conjunction with ``--comp-lzo``, this option + will disable OpenVPN's adaptive compression algorithm. Normally, adaptive + compression is enabled with ``--comp-lzo``. + + Adaptive compression tries to optimize the case where you have + compression enabled, but you are sending predominantly incompressible + (or pre-compressed) packets over the tunnel, such as an FTP or rsync + transfer of a large, compressed file. With adaptive compression, OpenVPN + will periodically sample the compression process to measure its + efficiency. If the data being sent over the tunnel is already + compressed, the compression efficiency will be very low, triggering + openvpn to disable compression for a period of time until the next + re-sample test. + +--key-direction + Alternative way of specifying the optional direction parameter for the + ``--tls-auth`` and ``--secret`` options. Useful when using inline files + (See section on inline files). + +--keysize n + **DEPRECATED** This option will be removed in OpenVPN 2.6. + + Size of cipher key in bits (optional). If unspecified, defaults to + cipher-specific default. The ``--show-ciphers`` option (see below) shows + all available OpenSSL ciphers, their default key sizes, and whether the + key size can be changed. Use care in changing a cipher's default key + size. Many ciphers have not been extensively cryptanalyzed with + non-standard key lengths, and a larger key may offer no real guarantee + of greater security, or may even reduce security. + +--data-ciphers cipher-list + Restrict the allowed ciphers to be negotiated to the ciphers in + ``cipher-list``. ``cipher-list`` is a colon-separated list of ciphers, + and defaults to :code:`AES-256-GCM:AES-128-GCM`. + + For servers, the first cipher from ``cipher-list`` that is also + supported by the client will be pushed to clients that support cipher + negotiation. + + Cipher negotiation is enabled in client-server mode only. I.e. if + ``--mode`` is set to 'server' (server-side, implied by setting + ``--server`` ), or if ``--pull`` is specified (client-side, implied by + setting --client). + + If no common cipher is found during cipher negotiation, the connection + is terminated. To support old clients/old servers that do not provide any + cipher negotiation support see ``--data-ciphers-fallback``. + + Additionally, to allow for more smooth transition, if NCP is enabled, + OpenVPN will inherit the cipher of the peer if that cipher is different + from the local ``--cipher`` setting, but the peer cipher is one of the + ciphers specified in ``--data-ciphers``. E.g. a non-NCP client (<=v2.3, + or with --ncp-disabled set) connecting to a NCP server (v2.4+) with + ``--cipher BF-CBC`` and ``--data-ciphers AES-256-GCM:AES-256-CBC`` set can + either specify ``--cipher BF-CBC`` or ``--cipher AES-256-CBC`` and both + will work. + + Note for using NCP with an OpenVPN 2.4 peer: This list must include the + :code:`AES-256-GCM` and :code:`AES-128-GCM` ciphers. + + This list is restricted to be 127 chars long after conversion to OpenVPN + ciphers. + + This option was called ``--ncp-ciphers`` in OpenVPN 2.4 but has been renamed + to ``--data-ciphers`` in OpenVPN 2.5 to more accurately reflect its meaning. + +--data-ciphers-fallback alg + + Configure a cipher that is used to fall back to if we could not determine + which cipher the peer is willing to use. + + This option should only be needed to + connect to peers that are running OpenVPN 2.3 and older version, and + have been configured with `--enable-small` + (typically used on routers or other embedded devices). + +--ncp-disable + **DEPRECATED** Disable "Negotiable Crypto Parameters". This completely + disables cipher negotiation. + +--secret args + Enable Static Key encryption mode (non-TLS). Use pre-shared secret + ``file`` which was generated with ``--genkey``. + + Valid syntaxes: + :: + + secret file + secret file direction + + The optional ``direction`` parameter enables the use of 4 distinct keys + (HMAC-send, cipher-encrypt, HMAC-receive, cipher-decrypt), so that each + data flow direction has a different set of HMAC and cipher keys. This + has a number of desirable security properties including eliminating + certain kinds of DoS and message replay attacks. + + When the ``direction`` parameter is omitted, 2 keys are used + bidirectionally, one for HMAC and the other for encryption/decryption. + + The ``direction`` parameter should always be complementary on either + side of the connection, i.e. one side should use :code:`0` and the other + should use :code:`1`, or both sides should omit it altogether. + + The ``direction`` parameter requires that ``file`` contains a 2048 bit + key. While pre-1.5 versions of OpenVPN generate 1024 bit key files, any + version of OpenVPN which supports the ``direction`` parameter, will also + support 2048 bit key file generation using the ``--genkey`` option. + + Static key encryption mode has certain advantages, the primary being + ease of configuration. + + There are no certificates or certificate authorities or complicated + negotiation handshakes and protocols. The only requirement is that you + have a pre-existing secure channel with your peer (such as ``ssh``) to + initially copy the key. This requirement, along with the fact that your + key never changes unless you manually generate a new one, makes it + somewhat less secure than TLS mode (see below). If an attacker manages + to steal your key, everything that was ever encrypted with it is + compromised. Contrast that to the perfect forward secrecy features of + TLS mode (using Diffie Hellman key exchange), where even if an attacker + was able to steal your private key, he would gain no information to help + him decrypt past sessions. + + Another advantageous aspect of Static Key encryption mode is that it is + a handshake-free protocol without any distinguishing signature or + feature (such as a header or protocol handshake sequence) that would + mark the ciphertext packets as being generated by OpenVPN. Anyone + eavesdropping on the wire would see nothing but random-looking data. + +--tran-window n + Transition window -- our old key can live this many seconds after a new + a key renegotiation begins (default :code:`3600` seconds). This feature + allows for a graceful transition from old to new key, and removes the key + renegotiation sequence from the critical path of tunnel data forwarding. diff --git a/doc/man-sections/proxy-options.rst b/doc/man-sections/proxy-options.rst new file mode 100644 index 0000000..465bea0 --- /dev/null +++ b/doc/man-sections/proxy-options.rst @@ -0,0 +1,65 @@ +--show-proxy-settings + Show sensed HTTP or SOCKS proxy settings. Currently, only Windows + clients support this option. + +--http-proxy args + Connect to remote host through an HTTP proxy. This requires at least an + address ``server`` and ``port`` argument. If HTTP Proxy-Authenticate + is required, a file name to an ``authfile`` file containing a username + and password on 2 lines can be given, or :code:`stdin` to prompt from + console. Its content can also be specified in the config file with the + ``--http-proxy-user-pass`` option. (See section on inline files) + + The last optional argument is an ``auth-method`` which should be one + of :code:`none`, :code:`basic`, or :code:`ntlm`. + + HTTP Digest authentication is supported as well, but only via the + :code:`auto` or :code:`auto-nct` flags (below). This must replace + the ``authfile`` argument. + + The :code:`auto` flag causes OpenVPN to automatically determine the + ``auth-method`` and query stdin or the management interface for + username/password credentials, if required. This flag exists on OpenVPN + 2.1 or higher. + + The ``auto-nct`` flag (no clear-text auth) instructs OpenVPN to + automatically determine the authentication method, but to reject weak + authentication protocols such as HTTP Basic Authentication. + + Examples: + :: + + http-proxy proxy.example.net 3128 + http-proxy proxy.example.net 3128 authfile.txt + http-proxy proxy.example.net 3128 stdin + http-proxy proxy.example.net 3128 auto basic + http-proxy proxy.example.net 3128 auto-nct ntlm + +--http-proxy-option args + Set extended HTTP proxy options. Requires an option ``type`` as argument + and an optional ``parameter`` to the type. Repeat to set multiple + options. + + :code:`VERSION` ``version`` + Set HTTP version number to ``version`` (default :code:`1.0`). + + :code:`AGENT` ``user-agent`` + Set HTTP "User-Agent" string to ``user-agent``. + + :code:`CUSTOM-HEADER` ``name`` ``content`` + Adds the custom Header with ``name`` as name and ``content`` as + the content of the custom HTTP header. + + Examples: + :: + + http-proxy-option VERSION 1.1 + http-proxy-option AGENT OpenVPN/2.4 + http-proxy-option X-Proxy-Flag some-flags + +--socks-proxy args + Connect to remote host through a Socks5 proxy. A required ``server`` + argument is needed. Optionally a ``port`` (default :code:`1080`) and + ``authfile`` can be given. The ``authfile`` is a file containing a + username and password on 2 lines, or :code:`stdin` can be used to + prompt from console. diff --git a/doc/man-sections/renegotiation.rst b/doc/man-sections/renegotiation.rst new file mode 100644 index 0000000..b817cfa --- /dev/null +++ b/doc/man-sections/renegotiation.rst @@ -0,0 +1,52 @@ +Data Channel Renegotiation +-------------------------- + +When running OpenVPN in client/server mode, the data channel will use a +separate ephemeral encryption key which is rotated at regular intervals. + +--reneg-bytes n + Renegotiate data channel key after ``n`` bytes sent or received + (disabled by default with an exception, see below). OpenVPN allows the + lifetime of a key to be expressed as a number of bytes + encrypted/decrypted, a number of packets, or a number of seconds. A key + renegotiation will be forced if any of these three criteria are met by + either peer. + + If using ciphers with cipher block sizes less than 128-bits, + ``--reneg-bytes`` is set to 64MB by default, unless it is explicitly + disabled by setting the value to :code:`0`, but this is + **HIGHLY DISCOURAGED** as this is designed to add some protection against + the SWEET32 attack vector. For more information see the ``--cipher`` + option. + +--reneg-pkts n + Renegotiate data channel key after **n** packets sent and received + (disabled by default). + +--reneg-sec args + Renegotiate data channel key after at most ``max`` seconds + (default :code:`3600`) and at least ``min`` seconds (default is 90% of + ``max`` for servers, and equal to ``max`` for clients). + :: + + reneg-sec max [min] + + The effective ``--reneg-sec`` value used is per session + pseudo-uniform-randomized between ``min`` and ``max``. + + With the default value of :code:`3600` this results in an effective per + session value in the range of :code:`3240`..:code:`3600` seconds for + servers, or just 3600 for clients. + + When using dual-factor authentication, note that this default value may + cause the end user to be challenged to reauthorize once per hour. + + Also, keep in mind that this option can be used on both the client and + server, and whichever uses the lower value will be the one to trigger + the renegotiation. A common mistake is to set ``--reneg-sec`` to a + higher value on either the client or server, while the other side of the + connection is still using the default value of :code:`3600` seconds, + meaning that the renegotiation will still occur once per :code:`3600` + seconds. The solution is to increase --reneg-sec on both the client and + server, or set it to :code:`0` on one side of the connection (to + disable), and to your chosen value on the other side. diff --git a/doc/man-sections/script-options.rst b/doc/man-sections/script-options.rst new file mode 100644 index 0000000..b4bbf52 --- /dev/null +++ b/doc/man-sections/script-options.rst @@ -0,0 +1,842 @@ +SCRIPTING INTEGRATION +===================== + +OpenVPN can execute external scripts in various phases of the lifetime of +the OpenVPN process. + + +Script Order of Execution +------------------------- + +#. ``--up`` + + Executed after TCP/UDP socket bind and TUN/TAP open. + +#. ``--tls-verify`` + + Executed when we have a still untrusted remote peer. + +#. ``--ipchange`` + + Executed after connection authentication, or remote IP address change. + +#. ``--client-connect`` + + Executed in **--mode server** mode immediately after client + authentication. + +#. ``--route-up`` + + Executed after connection authentication, either immediately after, or + some number of seconds after as defined by the **--route-delay** option. + +#. ``--route-pre-down`` + + Executed right before the routes are removed. + +#. ``--client-disconnect`` + + Executed in ``--mode server`` mode on client instance shutdown. + +#. ``--down`` + + Executed after TCP/UDP and TUN/TAP close. + +#. ``--learn-address`` + + Executed in ``--mode server`` mode whenever an IPv4 address/route or MAC + address is added to OpenVPN's internal routing table. + +#. ``--auth-user-pass-verify`` + + Executed in ``--mode server`` mode on new client connections, when the + client is still untrusted. + +SCRIPT HOOKS +------------ + +--auth-user-pass-verify args + Require the client to provide a username/password (possibly in addition + to a client certificate) for authentication. + + Valid syntax: + :: + + auth-user-pass-verify cmd method + + OpenVPN will run command ``cmd`` to validate the username/password + provided by the client. + + ``cmd`` consists of a path to a script (or executable program), optionally + followed by arguments. The path and arguments may be single- or + double-quoted and/or escaped using a backslash, and should be separated + by one or more spaces. + + If ``method`` is set to :code:`via-env`, OpenVPN will call ``script`` + with the environmental variables :code:`username` and :code:`password` + set to the username/password strings provided by the client. *Beware* + that this method is insecure on some platforms which make the environment + of a process publicly visible to other unprivileged processes. + + If ``method`` is set to :code:`via-file`, OpenVPN will write the username + and password to the first two lines of a temporary file. The filename + will be passed as an argument to ``script``, and the file will be + automatically deleted by OpenVPN after the script returns. The location + of the temporary file is controlled by the ``--tmp-dir`` option, and + will default to the current directory if unspecified. For security, + consider setting ``--tmp-dir`` to a volatile storage medium such as + :code:`/dev/shm` (if available) to prevent the username/password file + from touching the hard drive. + + The script should examine the username and password, returning a success + exit code (:code:`0`) if the client's authentication request is to be + accepted, or a failure code (:code:`1`) to reject the client. + + This directive is designed to enable a plugin-style interface for + extending OpenVPN's authentication capabilities. + + To protect against a client passing a maliciously formed username or + password string, the username string must consist only of these + characters: alphanumeric, underbar (':code:`_`'), dash (':code:`-`'), + dot (':code:`.`'), or at (':code:`@`'). The password string can consist + of any printable characters except for CR or LF. Any illegal characters + in either the username or password string will be converted to + underbar (':code:`_`'). + + Care must be taken by any user-defined scripts to avoid creating a + security vulnerability in the way that these strings are handled. Never + use these strings in such a way that they might be escaped or evaluated + by a shell interpreter. + + For a sample script that performs PAM authentication, see + :code:`sample-scripts/auth-pam.pl` in the OpenVPN source distribution. + +--client-connect cmd + Run command ``cmd`` on client connection. + + ``cmd`` consists of a path to a script (or executable program), optionally + followed by arguments. The path and arguments may be single- or + double-quoted and/or escaped using a backslash, and should be separated + by one or more spaces. + + The command is passed the common name and IP address of the + just-authenticated client as environmental variables (see environmental + variable section below). The command is also passed the pathname of a + freshly created temporary file as the last argument (after any arguments + specified in ``cmd`` ), to be used by the command to pass dynamically + generated config file directives back to OpenVPN. + + If the script wants to generate a dynamic config file to be applied on + the server when the client connects, it should write it to the file + named by the last argument. + + See the ``--client-config-dir`` option below for options which can be + legally used in a dynamically generated config file. + + Note that the return value of ``script`` is significant. If ``script`` + returns a non-zero error status, it will cause the client to be + disconnected. + + If a ``--client-connect`` wants to defer the generating of the + configuration then the script needs to use the + :code:`client_connect_deferred_file` and + :code:`client_connect_config_file` environment variables, and write + status accordingly into these files. See the `Environmental Variables`_ + section for more details. + +--client-disconnect cmd + Like ``--client-connect`` but called on client instance shutdown. Will + not be called unless the ``--client-connect`` script and plugins (if + defined) were previously called on this instance with successful (0) + status returns. + + The exception to this rule is if the ``--client-disconnect`` command or + plugins are cascaded, and at least one client-connect function + succeeded, then ALL of the client-disconnect functions for scripts and + plugins will be called on client instance object deletion, even in cases + where some of the related client-connect functions returned an error + status. + + The ``--client-disconnect`` command is passed the same pathname as the + corresponding ``--client-connect`` command as its last argument (after + any arguments specified in ``cmd``). + +--down cmd + Run command ``cmd`` after TUN/TAP device close (post ``--user`` UID + change and/or ``--chroot`` ). ``cmd`` consists of a path to script (or + executable program), optionally followed by arguments. The path and + arguments may be single- or double-quoted and/or escaped using a + backslash, and should be separated by one or more spaces. + + Called with the same parameters and environmental variables as the + ``--up`` option above. + + Note that if you reduce privileges by using ``--user`` and/or + ``--group``, your ``--down`` script will also run at reduced privilege. + +--down-pre + Call ``--down`` cmd/script before, rather than after, TUN/TAP close. + +--ipchange cmd + Run command ``cmd`` when our remote ip-address is initially + authenticated or changes. + + ``cmd`` consists of a path to a script (or executable program), optionally + followed by arguments. The path and arguments may be single- or + double-quoted and/or escaped using a backslash, and should be separated + by one or more spaces. + + When ``cmd`` is executed two arguments are appended after any arguments + specified in ``cmd`` , as follows: + :: + + cmd ip address port number + + Don't use ``--ipchange`` in ``--mode server`` mode. Use a + ``--client-connect`` script instead. + + See the `Environmental Variables`_ section below for additional + parameters passed as environmental variables. + + If you are running in a dynamic IP address environment where the IP + addresses of either peer could change without notice, you can use this + script, for example, to edit the :code:`/etc/hosts` file with the current + address of the peer. The script will be run every time the remote peer + changes its IP address. + + Similarly if *our* IP address changes due to DHCP, we should configure + our IP address change script (see man page for ``dhcpcd``\(8)) to + deliver a ``SIGHUP`` or ``SIGUSR1`` signal to OpenVPN. OpenVPN will + then re-establish a connection with its most recently authenticated + peer on its new IP address. + +--learn-address cmd + Run command ``cmd`` to validate client virtual addresses or routes. + + ``cmd`` consists of a path to a script (or executable program), optionally + followed by arguments. The path and arguments may be single- or + double-quoted and/or escaped using a backslash, and should be separated + by one or more spaces. + + Three arguments will be appended to any arguments in ``cmd`` as follows: + + :code:`$1` - [operation] + :code:`"add"`, :code:`"update"`, or :code:`"delete"` based on whether + or not the address is being added to, modified, or deleted from + OpenVPN's internal routing table. + + :code:`$2` - [address] + The address being learned or unlearned. This can be an IPv4 address + such as :code:`"198.162.10.14"`, an IPv4 subnet such as + :code:`"198.162.10.0/24"`, or an ethernet MAC address (when + ``--dev tap`` is being used) such as :code:`"00:FF:01:02:03:04"`. + + :code:`$3` - [common name] + The common name on the certificate associated with the client linked + to this address. Only present for :code:`"add"` or :code:`"update"` + operations, not :code:`"delete"`. + + On :code:`"add"` or :code:`"update"` methods, if the script returns + a failure code (non-zero), OpenVPN will reject the address and will not + modify its internal routing table. + + Normally, the ``cmd`` script will use the information provided above to + set appropriate firewall entries on the VPN TUN/TAP interface. Since + OpenVPN provides the association between virtual IP or MAC address and + the client's authenticated common name, it allows a user-defined script + to configure firewall access policies with regard to the client's + high-level common name, rather than the low level client virtual + addresses. + +--route-up cmd + Run command ``cmd`` after routes are added, subject to ``--route-delay``. + + ``cmd`` consists of a path to a script (or executable program), optionally + followed by arguments. The path and arguments may be single- or + double-quoted and/or escaped using a backslash, and should be separated + by one or more spaces. + + See the `Environmental Variables`_ section below for additional + parameters passed as environmental variables. + +--route-pre-down cmd + Run command ``cmd`` before routes are removed upon disconnection. + + ``cmd`` consists of a path to a script (or executable program), optionally + followed by arguments. The path and arguments may be single- or + double-quoted and/or escaped using a backslash, and should be separated + by one or more spaces. + + See the `Environmental Variables`_ section below for additional + parameters passed as environmental variables. + +--setenv args + Set a custom environmental variable :code:`name=value` to pass to script. + + Valid syntaxes: + :: + + setenv name value + setenv FORWARD_COMPATIBLE 1 + setenv opt config_option + + By setting :code:`FORWARD_COMPATIBLE` to :code:`1`, the config file + syntax checking is relaxed so that unknown directives will trigger a + warning but not a fatal error, on the assumption that a given unknown + directive might be valid in future OpenVPN versions. + + This option should be used with caution, as there are good security + reasons for having OpenVPN fail if it detects problems in a config file. + Having said that, there are valid reasons for wanting new software + features to gracefully degrade when encountered by older software + versions. + + It is also possible to tag a single directive so as not to trigger a + fatal error if the directive isn't recognized. To do this, prepend the + following before the directive: ``setenv opt`` + + Versions prior to OpenVPN 2.3.3 will always ignore options set with the + ``setenv opt`` directive. + + See also ``--ignore-unknown-option`` + +--setenv-safe args + Set a custom environmental variable :code:`OPENVPN_name` to :code:`value` + to pass to scripts. + + Valid syntaxes: + :: + + setenv-safe name value + + This directive is designed to be pushed by the server to clients, and + the prepending of :code:`OPENVPN_` to the environmental variable is a + safety precaution to prevent a :code:`LD_PRELOAD` style attack from a + malicious or compromised server. + +--tls-verify cmd + Run command ``cmd`` to verify the X509 name of a pending TLS connection + that has otherwise passed all other tests of certification (except for + revocation via ``--crl-verify`` directive; the revocation test occurs + after the ``--tls-verify`` test). + + ``cmd`` should return :code:`0` to allow the TLS handshake to proceed, + or :code:`1` to fail. + + ``cmd`` consists of a path to a script (or executable program), optionally + followed by arguments. The path and arguments may be single- or + double-quoted and/or escaped using a backslash, and should be separated + by one or more spaces. + + When ``cmd`` is executed two arguments are appended after any arguments + specified in ``cmd``, as follows: + :: + + cmd certificate_depth subject + + These arguments are, respectively, the current certificate depth and the + X509 subject distinguished name (dn) of the peer. + + This feature is useful if the peer you want to trust has a certificate + which was signed by a certificate authority who also signed many other + certificates, where you don't necessarily want to trust all of them, but + rather be selective about which peer certificate you will accept. This + feature allows you to write a script which will test the X509 name on a + certificate and decide whether or not it should be accepted. For a + simple perl script which will test the common name field on the + certificate, see the file ``verify-cn`` in the OpenVPN distribution. + + See the `Environmental Variables`_ section below for additional + parameters passed as environmental variables. + +--up cmd + Run command ``cmd`` after successful TUN/TAP device open (pre ``--user`` + UID change). + + ``cmd`` consists of a path to a script (or executable program), optionally + followed by arguments. The path and arguments may be single- or + double-quoted and/or escaped using a backslash, and should be separated + by one or more spaces. + + The up command is useful for specifying route commands which route IP + traffic destined for private subnets which exist at the other end of the + VPN connection into the tunnel. + + For ``--dev tun`` execute as: + :: + + cmd tun_dev tun_mtu link_mtu ifconfig_local_ip ifconfig_remote_ip [init | restart] + + For ``--dev tap`` execute as: + :: + + cmd tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask [init | restart] + + See the `Environmental Variables`_ section below for additional + parameters passed as environmental variables. + + Note that if ``cmd`` includes arguments, all OpenVPN-generated arguments + will be appended to them to build an argument list with which the + executable will be called. + + Typically, ``cmd`` will run a script to add routes to the tunnel. + + Normally the up script is called after the TUN/TAP device is opened. In + this context, the last command line parameter passed to the script will + be *init.* If the ``--up-restart`` option is also used, the up script + will be called for restarts as well. A restart is considered to be a + partial reinitialization of OpenVPN where the TUN/TAP instance is + preserved (the ``--persist-tun`` option will enable such preservation). + A restart can be generated by a SIGUSR1 signal, a ``--ping-restart`` + timeout, or a connection reset when the TCP protocol is enabled with the + ``--proto`` option. If a restart occurs, and ``--up-restart`` has been + specified, the up script will be called with *restart* as the last + parameter. + + *NOTE:* + On restart, OpenVPN will not pass the full set of environment + variables to the script. Namely, everything related to routing and + gateways will not be passed, as nothing needs to be done anyway - all + the routing setup is already in place. Additionally, the up-restart + script will run with the downgraded UID/GID settings (if configured). + + The following standalone example shows how the ``--up`` script can be + called in both an initialization and restart context. (*NOTE:* for + security reasons, don't run the following example unless UDP port 9999 + is blocked by your firewall. Also, the example will run indefinitely, so + you should abort with control-c). + + :: + + openvpn --dev tun --port 9999 --verb 4 --ping-restart 10 \ + --up 'echo up' --down 'echo down' --persist-tun \ + --up-restart + + Note that OpenVPN also provides the ``--ifconfig`` option to + automatically ifconfig the TUN device, eliminating the need to define an + ``--up`` script, unless you also want to configure routes in the + ``--up`` script. + + If ``--ifconfig`` is also specified, OpenVPN will pass the ifconfig + local and remote endpoints on the command line to the ``--up`` script so + that they can be used to configure routes such as: + + :: + + route add -net 10.0.0.0 netmask 255.255.255.0 gw $5 + +--up-delay + Delay TUN/TAP open and possible ``--up`` script execution until after + TCP/UDP connection establishment with peer. + + In ``--proto udp`` mode, this option normally requires the use of + ``--ping`` to allow connection initiation to be sensed in the absence of + tunnel data, since UDP is a "connectionless" protocol. + + On Windows, this option will delay the TAP-Win32 media state + transitioning to "connected" until connection establishment, i.e. the + receipt of the first authenticated packet from the peer. + +--up-restart + Enable the ``--up`` and ``--down`` scripts to be called for restarts as + well as initial program start. This option is described more fully above + in the ``--up`` option documentation. + +String Types and Remapping +-------------------------- + +In certain cases, OpenVPN will perform remapping of characters in +strings. Essentially, any characters outside the set of permitted +characters for each string type will be converted to underbar ('\_'). + +*Q: Why is string remapping necessary?* + It's an important security feature to prevent the malicious + coding of strings from untrusted sources to be passed as parameters to + scripts, saved in the environment, used as a common name, translated to + a filename, etc. + +*Q: Can string remapping be disabled?* + Yes, by using the ``--no-name-remapping`` option, however this + should be considered an advanced option. + +Here is a brief rundown of OpenVPN's current string types and the +permitted character class for each string: + +*X509 Names* + Alphanumeric, underbar ('\_'), dash ('-'), dot ('.'), at + ('@'), colon (':'), slash ('/'), and equal ('='). Alphanumeric is + defined as a character which will cause the C library isalnum() function + to return true. + +*Common Names* + Alphanumeric, underbar ('\_'), dash ('-'), dot ('.'), and at ('@'). + +*--auth-user-pass username* + Same as Common Name, with one exception: + starting with OpenVPN 2.0.1, the username is passed to the + :code:`OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY` plugin in its raw form, + without string remapping. + +*--auth-user-pass password* + Any "printable" character except CR or LF. Printable is defined to be + a character which will cause the C library isprint() function to + return true. + +*--client-config-dir filename as derived from common name or`username* + Alphanumeric, underbar ('\_'), dash ('-'), and dot ('.') except for "." + or ".." as standalone strings. As of v2.0.1-rc6, the at ('@') character + has been added as well for compatibility with the common name character + class. + +*Environmental variable names* + Alphanumeric or underbar ('\_'). + +*Environmental variable values* + Any printable character. + +For all cases, characters in a string which are not members of the legal +character class for that string type will be remapped to underbar +('\_').   + + +Environmental Variables +----------------------- + +Once set, a variable is persisted indefinitely until it is reset by a +new value or a restart, + +As of OpenVPN 2.0-beta12, in server mode, environmental variables set by +OpenVPN are scoped according to the client objects they are associated +with, so there should not be any issues with scripts having access to +stale, previously set variables which refer to different client +instances. + +:code:`bytes_received` + Total number of bytes received from client during VPN session. Set prior + to execution of the ``--client-disconnect`` script. + +:code:`bytes_sent` + Total number of bytes sent to client during VPN session. Set prior to + execution of the ``--client-disconnect`` script. + +:code:`client_connect_config_file` + The path to the configuration file that should be written to by the + ``--client-connect`` script (optional, if per-session configuration + is desired). This is the same file name as passed via command line + argument on the call to the ``--client-connect`` script. + +:code:`client_connect_deferred_file` + This file can be optionally written to in order to to communicate a + status code of the ``--client-connect`` script or plgin. Only the + first character in the file is relevant. It must be either :code:`1` + to indicate normal script execution, :code:`0` indicates an error (in + the same way that a non zero exit status does) or :code:`2` to indicate + that the script deferred returning the config file. + + For deferred (background) handling, the script or plugin MUST write + :code:`2` to the file to indicate the deferral and then return with + exit code :code:`0` to signal ``deferred handler started OK``. + + A background process or similar must then take care of writing the + configuration to the file indicated by the + :code:`client_connect_config_file` environment variable and when + finished, write the a :code:`1` to this file (or :code:`0` in case of + an error). + + The absence of any character in the file when the script finishes + executing is interpreted the same as :code:`1`. This allows scripts + that are not written to support the defer mechanism to be used + unmodified. + +:code:`common_name` + The X509 common name of an authenticated client. Set prior to execution + of ``--client-connect``, ``--client-disconnect`` and + ``--auth-user-pass-verify`` scripts. + +:code:`config` + Name of first ``--config`` file. Set on program initiation and reset on + SIGHUP. + +:code:`daemon` + Set to "1" if the ``--daemon`` directive is specified, or "0" otherwise. + Set on program initiation and reset on SIGHUP. + +:code:`daemon_log_redirect` + Set to "1" if the ``--log`` or ``--log-append`` directives are + specified, or "0" otherwise. Set on program initiation and reset on + SIGHUP. + +:code:`dev` + The actual name of the TUN/TAP device, including a unit number if it + exists. Set prior to ``--up`` or ``--down`` script execution. + +:code:`dev_idx` + On Windows, the device index of the TUN/TAP adapter (to be used in + netsh.exe calls which sometimes just do not work right with interface + names). Set prior to ``--up`` or ``--down`` script execution. + +:code:`foreign_option_{n}` + An option pushed via ``--push`` to a client which does not natively + support it, such as ``--dhcp-option`` on a non-Windows system, will be + recorded to this environmental variable sequence prior to ``--up`` + script execution. + +:code:`ifconfig_broadcast` + The broadcast address for the virtual ethernet segment which is derived + from the ``--ifconfig`` option when ``--dev tap`` is used. Set prior to + OpenVPN calling the :code:`ifconfig` or :code:`netsh` (windows version + of ifconfig) commands which normally occurs prior to ``--up`` script + execution. + +:code:`ifconfig_ipv6_local` + The local VPN endpoint IPv6 address specified in the + ``--ifconfig-ipv6`` option (first parameter). Set prior to OpenVPN + calling the :code:`ifconfig` or code:`netsh` (windows version of + ifconfig) commands which normally occurs prior to ``--up`` script + execution. + +:code:`ifconfig_ipv6_netbits` + The prefix length of the IPv6 network on the VPN interface. Derived + from the /nnn parameter of the IPv6 address in the ``--ifconfig-ipv6`` + option (first parameter). Set prior to OpenVPN calling the + :code:`ifconfig` or :code:`netsh` (windows version of ifconfig) + commands which normally occurs prior to ``--up`` script execution. + +:code:`ifconfig_ipv6_remote` + The remote VPN endpoint IPv6 address specified in the + ``--ifconfig-ipv6`` option (second parameter). Set prior to OpenVPN + calling the :code:`ifconfig` or :code:`netsh` (windows version of + ifconfig) commands which normally occurs prior to ``--up`` script + execution. + +:code:`ifconfig_local` + The local VPN endpoint IP address specified in the ``--ifconfig`` + option (first parameter). Set prior to OpenVPN calling the + :code:`ifconfig` or :code:`netsh` (windows version of ifconfig) + commands which normally occurs prior to ``--up`` script execution. + +:code:`ifconfig_remote` + The remote VPN endpoint IP address specified in the ``--ifconfig`` + option (second parameter) when ``--dev tun`` is used. Set prior to + OpenVPN calling the :code:`ifconfig` or :code:`netsh` (windows version + of ifconfig) commands which normally occurs prior to ``--up`` script + execution. + +:code:`ifconfig_netmask` + The subnet mask of the virtual ethernet segment that is specified as + the second parameter to ``--ifconfig`` when ``--dev tap`` is being + used. Set prior to OpenVPN calling the :code:`ifconfig` or + :code:`netsh` (windows version of ifconfig) commands which normally + occurs prior to ``--up`` script execution. + +:code:`ifconfig_pool_local_ip` + The local virtual IP address for the TUN/TAP tunnel taken from an + ``--ifconfig-push`` directive if specified, or otherwise from the + ifconfig pool (controlled by the ``--ifconfig-pool`` config file + directive). Only set for ``--dev tun`` tunnels. This option is set on + the server prior to execution of the ``--client-connect`` and + ``--client-disconnect`` scripts. + +:code:`ifconfig_pool_netmask` + The virtual IP netmask for the TUN/TAP tunnel taken from an + ``--ifconfig-push`` directive if specified, or otherwise from the + ifconfig pool (controlled by the ``--ifconfig-pool`` config file + directive). Only set for ``--dev tap`` tunnels. This option is set on + the server prior to execution of the ``--client-connect`` and + ``--client-disconnect`` scripts. + +:code:`ifconfig_pool_remote_ip` + The remote virtual IP address for the TUN/TAP tunnel taken from an + ``--ifconfig-push`` directive if specified, or otherwise from the + ifconfig pool (controlled by the ``--ifconfig-pool`` config file + directive). This option is set on the server prior to execution of the + ``--client-connect`` and ``--client-disconnect`` scripts. + +:code:`link_mtu` + The maximum packet size (not including the IP header) of tunnel data in + UDP tunnel transport mode. Set prior to ``--up`` or ``--down`` script + execution. + +:code:`local` + The ``--local`` parameter. Set on program initiation and reset on + SIGHUP. + +:code:`local_port` + The local port number or name, specified by ``--port`` or ``--lport``. + Set on program initiation and reset on SIGHUP. + +:code:`password` + The password provided by a connecting client. Set prior to + ``--auth-user-pass-verify`` script execution only when the ``via-env`` + modifier is specified, and deleted from the environment after the script + returns. + +:code:`proto` + The ``--proto`` parameter. Set on program initiation and reset on + SIGHUP. + +:code:`remote_{n}` + The ``--remote`` parameter. Set on program initiation and reset on + SIGHUP. + +:code:`remote_port_{n}` + The remote port number, specified by ``--port`` or ``--rport``. Set on + program initiation and reset on SIGHUP. + +:code:`route_net_gateway` + The pre-existing default IP gateway in the system routing table. Set + prior to ``--up`` script execution. + +:code:`route_vpn_gateway` + The default gateway used by ``--route`` options, as specified in either + the ``--route-gateway`` option or the second parameter to + ``--ifconfig`` when ``--dev tun`` is specified. Set prior to ``--up`` + script execution. + +:code:`route_{parm}_{n}` + A set of variables which define each route to be added, and are set + prior to ``--up`` script execution. + + ``parm`` will be one of :code:`network`, :code:`netmask"`, + :code:`gateway`, or :code:`metric`. + + ``n`` is the OpenVPN route number, starting from 1. + + If the network or gateway are resolvable DNS names, their IP address + translations will be recorded rather than their names as denoted on the + command line or configuration file. + +:code:`route_ipv6_{parm}_{n}` + A set of variables which define each IPv6 route to be added, and are + set prior to **--up** script execution. + + ``parm`` will be one of :code:`network` or :code:`gateway` + (:code:`netmask` is contained as :code:`/nnn` in the + ``route_ipv6_network_{n}``, unlike IPv4 where it is passed in a + separate environment variable). + + ``n`` is the OpenVPN route number, starting from 1. + + If the network or gateway are resolvable DNS names, their IP address + translations will be recorded rather than their names as denoted on the + command line or configuration file. + +:code:`peer_cert` + Temporary file name containing the client certificate upon connection. + Useful in conjunction with ``--tls-verify``. + +:code:`script_context` + Set to "init" or "restart" prior to up/down script execution. For more + information, see documentation for ``--up``. + +:code:`script_type` + Prior to execution of any script, this variable is set to the type of + script being run. It can be one of the following: :code:`up`, + :code:`down`, :code:`ipchange`, :code:`route-up`, :code:`tls-verify`, + :code:`auth-user-pass-verify`, :code:`client-connect`, + :code:`client-disconnect` or :code:`learn-address`. Set prior to + execution of any script. + +:code:`signal` + The reason for exit or restart. Can be one of :code:`sigusr1`, + :code:`sighup`, :code:`sigterm`, :code:`sigint`, :code:`inactive` + (controlled by ``--inactive`` option), :code:`ping-exit` (controlled + by ``--ping-exit`` option), :code:`ping-restart` (controlled by + ``--ping-restart`` option), :code:`connection-reset` (triggered on TCP + connection reset), :code:`error` or :code:`unknown` (unknown signal). + This variable is set just prior to down script execution. + +:code:`time_ascii` + Client connection timestamp, formatted as a human-readable time string. + Set prior to execution of the ``--client-connect`` script. + +:code:`time_duration` + The duration (in seconds) of the client session which is now + disconnecting. Set prior to execution of the ``--client-disconnect`` + script. + +:code:`time_unix` + Client connection timestamp, formatted as a unix integer date/time + value. Set prior to execution of the ``--client-connect`` script. + +:code:`tls_digest_{n}` / :code:`tls_digest_sha256_{n}` + Contains the certificate SHA1 / SHA256 fingerprint, where ``n`` is the + verification level. Only set for TLS connections. Set prior to execution + of ``--tls-verify`` script. + +:code:`tls_id_{n}` + A series of certificate fields from the remote peer, where ``n`` is the + verification level. Only set for TLS connections. Set prior to execution + of ``--tls-verify`` script. + +:code:`tls_serial_{n}` + The serial number of the certificate from the remote peer, where ``n`` + is the verification level. Only set for TLS connections. Set prior to + execution of ``--tls-verify`` script. This is in the form of a decimal + string like "933971680", which is suitable for doing serial-based OCSP + queries (with OpenSSL, do not prepend "0x" to the string) If something + goes wrong while reading the value from the certificate it will be an + empty string, so your code should check that. See the + :code:`contrib/OCSP_check/OCSP_check.sh` script for an example. + +:code:`tls_serial_hex_{n}` + Like :code:`tls_serial_{n}`, but in hex form (e.g. + :code:`12:34:56:78:9A`). + +:code:`tun_mtu` + The MTU of the TUN/TAP device. Set prior to ``--up`` or ``--down`` + script execution. + +:code:`trusted_ip` / :code:`trusted_ip6`) + Actual IP address of connecting client or peer which has been + authenticated. Set prior to execution of ``--ipchange``, + ``--client-connect`` and ``--client-disconnect`` scripts. If using ipv6 + endpoints (udp6, tcp6), :code:`trusted_ip6` will be set instead. + +:code:`trusted_port` + Actual port number of connecting client or peer which has been + authenticated. Set prior to execution of ``--ipchange``, + ``--client-connect`` and ``--client-disconnect`` scripts. + +:code:`untrusted_ip` / :code:`untrusted_ip6` + Actual IP address of connecting client or peer which has not been + authenticated yet. Sometimes used to *nmap* the connecting host in a + ``--tls-verify`` script to ensure it is firewalled properly. Set prior + to execution of ``--tls-verify`` and ``--auth-user-pass-verify`` + scripts. If using ipv6 endpoints (udp6, tcp6), :code:`untrusted_ip6` + will be set instead. + +:code:`untrusted_port` + Actual port number of connecting client or peer which has not been + authenticated yet. Set prior to execution of ``--tls-verify`` and + ``--auth-user-pass-verify`` scripts. + +:code:`username` + The username provided by a connecting client. Set prior to + ``--auth-user-pass-verify`` script execution only when the + :code:`via-env` modifier is specified. + +:code:`X509_{n}_{subject_field}` + An X509 subject field from the remote peer certificate, where ``n`` is + the verification level. Only set for TLS connections. Set prior to + execution of ``--tls-verify`` script. This variable is similar to + :code:`tls_id_{n}` except the component X509 subject fields are broken + out, and no string remapping occurs on these field values (except for + remapping of control characters to ":code:`_`"). For example, the + following variables would be set on the OpenVPN server using the sample + client certificate in sample-keys (client.crt). Note that the + verification level is 0 for the client certificate and 1 for the CA + certificate. + + :: + + X509_0_emailAddress=me@myhost.mydomain + X509_0_CN=Test-Client + X509_0_O=OpenVPN-TEST + X509_0_ST=NA + X509_0_C=KG + X509_1_emailAddress=me@myhost.mydomain + X509_1_O=OpenVPN-TEST + X509_1_L=BISHKEK + X509_1_ST=NA + X509_1_C=KG diff --git a/doc/man-sections/server-options.rst b/doc/man-sections/server-options.rst new file mode 100644 index 0000000..f1f0667 --- /dev/null +++ b/doc/man-sections/server-options.rst @@ -0,0 +1,774 @@ +Server Options +-------------- +Starting with OpenVPN 2.0, a multi-client TCP/UDP server mode is +supported, and can be enabled with the ``--mode server`` option. In +server mode, OpenVPN will listen on a single port for incoming client +connections. All client connections will be routed through a single tun +or tap interface. This mode is designed for scalability and should be +able to support hundreds or even thousands of clients on sufficiently +fast hardware. SSL/TLS authentication must be used in this mode. + +--auth-gen-token args + Returns an authentication token to successfully authenticated clients. + + Valid syntax: + :: + + auth-gen-token [lifetime] [external-auth] + + After successful user/password authentication, the OpenVPN server will + with this option generate a temporary authentication token and push that + to the client. On the following renegotiations, the OpenVPN client will pass + this token instead of the users password. On the server side the server + will do the token authentication internally and it will NOT do any + additional authentications against configured external user/password + authentication mechanisms. + + The tokens implemented by this mechanism include an initial timestamp and + a renew timestamp and are secured by HMAC. + + The ``lifetime`` argument defines how long the generated token is valid. + The lifetime is defined in seconds. If lifetime is not set or it is set + to :code:`0`, the token will never expire. + + The token will expire either after the configured ``lifetime`` of the + token is reached or after not being renewed for more than 2 \* + ``reneg-sec`` seconds. Clients will be sent renewed tokens on every TLS + renogiation to keep the client's token updated. This is done to + invalidate a token if a client is disconnected for a sufficently long + time, while at the same time permitting much longer token lifetimes for + active clients. + + This feature is useful for environments which are configured to use One + Time Passwords (OTP) as part of the user/password authentications and + that authentication mechanism does not implement any auth-token support. + + When the :code:`external-auth` keyword is present the normal + authentication method will always be called even if auth-token succeeds. + Normally other authentications method are skipped if auth-token + verification suceeds or fails. + + This option postpones this decision to the external authentication + methods and checks the validity of the account and do other checks. + + In this mode the environment will have a ``session_id`` variable that + holds the session id from auth-gen-token. Also an environment variable + ``session_state`` is present. This variable indicates whether the + auth-token has succeeded or not. It can have the following values: + + :code:`Initial` + No token from client. + + :code:`Authenticated` + Token is valid and not expired. + + :code:`Expired` + Token is valid but has expired. + + :code:`Invalid` + Token is invalid (failed HMAC or wrong length) + + :code:`AuthenticatedEmptyUser` / :code:`ExpiredEmptyUser` + The token is not valid with the username sent from the client but + would be valid (or expired) if we assume an empty username was + used instead. These two cases are a workaround for behaviour in + OpenVPN 3. If this workaround is not needed these two cases should + be handled in the same way as :code:`Invalid`. + + **Warning:** Use this feature only if you want your authentication + method called on every verification. Since the external authentication + is called it needs to also indicate a success or failure of the + authentication. It is strongly recommended to return an authentication + failure in the case of the Invalid/Expired auth-token with the + external-auth option unless the client could authenticate in another + acceptable way (e.g. client certificate), otherwise returning success + will lead to authentication bypass (as does returning success on a wrong + password from a script). + +--auth-gen-token-secret file + Specifies a file that holds a secret for the HMAC used in + ``--auth-gen-token`` If ``file`` is not present OpenVPN will generate a + random secret on startup. This file should be used if auth-token should + validate after restarting a server or if client should be able to roam + between multiple OpenVPN servers with their auth-token. + +--auth-user-pass-optional + Allow connections by clients that do not specify a username/password. + Normally, when ``--auth-user-pass-verify`` or + ``--management-client-auth`` are specified (or an authentication plugin + module), the OpenVPN server daemon will require connecting clients to + specify a username and password. This option makes the submission of a + username/password by clients optional, passing the responsibility to the + user-defined authentication module/script to accept or deny the client + based on other factors (such as the setting of X509 certificate fields). + When this option is used, and a connecting client does not submit a + username/password, the user-defined authentication module/script will + see the username and password as being set to empty strings (""). The + authentication module/script MUST have logic to detect this condition + and respond accordingly. + +--ccd-exclusive + Require, as a condition of authentication, that a connecting client has + a ``--client-config-dir`` file. + +--client-config-dir dir + Specify a directory ``dir`` for custom client config files. After a + connecting client has been authenticated, OpenVPN will look in this + directory for a file having the same name as the client's X509 common + name. If a matching file exists, it will be opened and parsed for + client-specific configuration options. If no matching file is found, + OpenVPN will instead try to open and parse a default file called + "DEFAULT", which may be provided but is not required. Note that the + configuration files must be readable by the OpenVPN process after it has + dropped it's root privileges. + + This file can specify a fixed IP address for a given client using + ``--ifconfig-push``, as well as fixed subnets owned by the client using + ``--iroute``. + + One of the useful properties of this option is that it allows client + configuration files to be conveniently created, edited, or removed while + the server is live, without needing to restart the server. + + The following options are legal in a client-specific context: ``--push``, + ``--push-reset``, ``--push-remove``, ``--iroute``, ``--ifconfig-push``, + ``--vlan-pvid`` and ``--config``. + +--client-to-client + Because the OpenVPN server mode handles multiple clients through a + single tun or tap interface, it is effectively a router. The + ``--client-to-client`` flag tells OpenVPN to internally route + client-to-client traffic rather than pushing all client-originating + traffic to the TUN/TAP interface. + + When this option is used, each client will "see" the other clients which + are currently connected. Otherwise, each client will only see the + server. Don't use this option if you want to firewall tunnel traffic + using custom, per-client rules. + +--disable + Disable a particular client (based on the common name) from connecting. + Don't use this option to disable a client due to key or password + compromise. Use a CRL (certificate revocation list) instead (see the + ``--crl-verify`` option). + + This option must be associated with a specific client instance, which + means that it must be specified either in a client instance config file + using ``--client-config-dir`` or dynamically generated using a + ``--client-connect`` script. + +--connect-freq args + Allow a maximum of ``n`` new connections per ``sec`` seconds from + clients. + + Valid syntax: + :: + + connect-freq n sec + + This is designed to contain DoS attacks which flood the server + with connection requests using certificates which will ultimately fail + to authenticate. + + This is an imperfect solution however, because in a real DoS scenario, + legitimate connections might also be refused. + + For the best protection against DoS attacks in server mode, use + ``--proto udp`` and either ``--tls-auth`` or ``--tls-crypt``. + +--duplicate-cn + Allow multiple clients with the same common name to concurrently + connect. In the absence of this option, OpenVPN will disconnect a client + instance upon connection of a new client having the same common name. + +--ifconfig-pool args + Set aside a pool of subnets to be dynamically allocated to connecting + clients, similar to a DHCP server. + + Valid syntax: + :: + + ifconfig-pool start-IP end-IP [netmask] + + For tun-style tunnels, each client + will be given a /30 subnet (for interoperability with Windows clients). + For tap-style tunnels, individual addresses will be allocated, and the + optional ``netmask`` parameter will also be pushed to clients. + +--ifconfig-ipv6-pool args + Specify an IPv6 address pool for dynamic assignment to clients. + + Valid args: + :: + + ifconfig-ipv6-pool ipv6addr/bits + + The pool starts at ``ipv6addr`` and matches the offset determined from + the start of the IPv4 pool. + +--ifconfig-pool-persist args + Persist/unpersist ifconfig-pool data to ``file``, at ``seconds`` + intervals (default :code:`600`), as well as on program startup and shutdown. + + Valid syntax: + :: + + ifconfig-pool-persist file [seconds] + + The goal of this option is to provide a long-term association between + clients (denoted by their common name) and the virtual IP address + assigned to them from the ifconfig-pool. Maintaining a long-term + association is good for clients because it allows them to effectively + use the ``--persist-tun`` option. + + ``file`` is a comma-delimited ASCII file, formatted as + :code:`,`. + + If ``seconds`` = :code:`0`, ``file`` will be treated as read-only. This + is useful if you would like to treat ``file`` as a configuration file. + + Note that the entries in this file are treated by OpenVPN as + *suggestions* only, based on past associations between a common name and + IP address. They do not guarantee that the given common name will always + receive the given IP address. If you want guaranteed assignment, use + ``--ifconfig-push`` + +--ifconfig-push args + Push virtual IP endpoints for client tunnel, overriding the + ``--ifconfig-pool`` dynamic allocation. + + Valid syntax: + :: + + ifconfig-push local remote-netmask [alias] + + The parameters ``local`` and ``remote-netmask`` are set according to the + ``--ifconfig`` directive which you want to execute on the client machine + to configure the remote end of the tunnel. Note that the parameters + ``local`` and ``remote-netmask`` are from the perspective of the client, + not the server. They may be DNS names rather than IP addresses, in which + case they will be resolved on the server at the time of client + connection. + + The optional ``alias`` parameter may be used in cases where NAT causes + the client view of its local endpoint to differ from the server view. In + this case ``local/remote-netmask`` will refer to the server view while + ``alias/remote-netmask`` will refer to the client view. + + This option must be associated with a specific client instance, which + means that it must be specified either in a client instance config file + using ``--client-config-dir`` or dynamically generated using a + ``--client-connect`` script. + + Remember also to include a ``--route`` directive in the main OpenVPN + config file which encloses ``local``, so that the kernel will know to + route it to the server's TUN/TAP interface. + + OpenVPN's internal client IP address selection algorithm works as + follows: + + 1. Use ``--client-connect script`` generated file for static IP + (first choice). + + 2. Use ``--client-config-dir`` file for static IP (next choice). + + 3. Use ``--ifconfig-pool`` allocation for dynamic IP (last + choice). + +--ifconfig-ipv6-push args + for ``--client-config-dir`` per-client static IPv6 interface + configuration, see ``--client-config-dir`` and ``--ifconfig-push`` for + more details. + + Valid syntax: + :: + + ifconfig-ipv6-push ipv6addr/bits ipv6remote + +--inetd args + Valid syntaxes: + :: + + inetd + inetd wait + inetd nowait + inetd wait progname + + Use this option when OpenVPN is being run from the inetd or ``xinetd``\(8) + server. + + The :code:`wait` and :code:`nowait` option must match what is specified + in the inetd/xinetd config file. The :code:`nowait` mode can only be used + with ``--proto tcp-server`` The default is :code:`wait`. The + :code:`nowait` mode can be used to instantiate the OpenVPN daemon as a + classic TCP server, where client connection requests are serviced on a + single port number. For additional information on this kind of + configuration, see the OpenVPN FAQ: + https://community.openvpn.net/openvpn/wiki/325-openvpn-as-a--forking-tcp-server-which-can-service-multiple-clients-over-a-single-tcp-port + + This option precludes the use of ``--daemon``, ``--local`` or + ``--remote``. Note that this option causes message and error output to + be handled in the same way as the ``--daemon`` option. The optional + ``progname`` parameter is also handled exactly as in ``--daemon``. + + Also note that in ``wait`` mode, each OpenVPN tunnel requires a separate + TCP/UDP port and a separate inetd or xinetd entry. See the OpenVPN 1.x + HOWTO for an example on using OpenVPN with xinetd: + https://openvpn.net/community-resources/1xhowto/ + +--multihome + Configure a multi-homed UDP server. This option needs to be used when a + server has more than one IP address (e.g. multiple interfaces, or + secondary IP addresses), and is not using ``--local`` to force binding + to one specific address only. This option will add some extra lookups to + the packet path to ensure that the UDP reply packets are always sent + from the address that the client is talking to. This is not supported on + all platforms, and it adds more processing, so it's not enabled by + default. + + *Notes:* + - This option is only relevant for UDP servers. + - If you do an IPv6+IPv4 dual-stack bind on a Linux machine with + multiple IPv4 address, connections to IPv4 addresses will not + work right on kernels before 3.15, due to missing kernel + support for the IPv4-mapped case (some distributions have + ported this to earlier kernel versions, though). + +--iroute args + Generate an internal route to a specific client. The ``netmask`` + parameter, if omitted, defaults to :code:`255.255.255.255`. + + Valid syntax: + :: + + iroute network [netmask] + + This directive can be used to route a fixed subnet from the server to a + particular client, regardless of where the client is connecting from. + Remember that you must also add the route to the system routing table as + well (such as by using the ``--route`` directive). The reason why two + routes are needed is that the ``--route`` directive routes the packet + from the kernel to OpenVPN. Once in OpenVPN, the ``--iroute`` directive + routes to the specific client. + + This option must be specified either in a client instance config file + using ``--client-config-dir`` or dynamically generated using a + ``--client-connect`` script. + + The ``--iroute`` directive also has an important interaction with + ``--push "route ..."``. ``--iroute`` essentially defines a subnet which + is owned by a particular client (we will call this client *A*). If you + would like other clients to be able to reach *A*'s subnet, you can use + ``--push "route ..."`` together with ``--client-to-client`` to effect + this. In order for all clients to see *A*'s subnet, OpenVPN must push + this route to all clients EXCEPT for *A*, since the subnet is already + owned by *A*. OpenVPN accomplishes this by not not pushing a route to + a client if it matches one of the client's iroutes. + +--iroute-ipv6 args + for ``--client-config-dir`` per-client static IPv6 route configuration, + see ``--iroute`` for more details how to setup and use this, and how + ``--iroute`` and ``--route`` interact. + + Valid syntax: + :: + + iroute-ipv6 ipv6addr/bits + +--max-clients n + Limit server to a maximum of ``n`` concurrent clients. + +--max-routes-per-client n + Allow a maximum of ``n`` internal routes per client (default + :code:`256`). This is designed to help contain DoS attacks where an + authenticated client floods the server with packets appearing to come + from many unique MAC addresses, forcing the server to deplete virtual + memory as its internal routing table expands. This directive can be used + in a ``--client-config-dir`` file or auto-generated by a + ``--client-connect`` script to override the global value for a particular + client. + + Note that this directive affects OpenVPN's internal routing table, not + the kernel routing table. + +--opt-verify + Clients that connect with options that are incompatible with those of the + server will be disconnected. + + Options that will be compared for compatibility include ``dev-type``, + ``link-mtu``, ``tun-mtu``, ``proto``, ``ifconfig``, + ``comp-lzo``, ``fragment``, ``keydir``, ``cipher``, + ``auth``, ``keysize``, ``secret``, ``no-replay``, + ``tls-auth``, ``key-method``, ``tls-server`` + and ``tls-client``. + + This option requires that ``--disable-occ`` NOT be used. + +--port-share args + Share OpenVPN TCP with another service + + Valid syntax: + :: + + port-share host port [dir] + + When run in TCP server mode, share the OpenVPN port with another + application, such as an HTTPS server. If OpenVPN senses a connection to + its port which is using a non-OpenVPN protocol, it will proxy the + connection to the server at ``host``:``port``. Currently only designed to + work with HTTP/HTTPS, though it would be theoretically possible to + extend to other protocols such as ssh. + + ``dir`` specifies an optional directory where a temporary file with name + N containing content C will be dynamically generated for each proxy + connection, where N is the source IP:port of the client connection and C + is the source IP:port of the connection to the proxy receiver. This + directory can be used as a dictionary by the proxy receiver to determine + the origin of the connection. Each generated file will be automatically + deleted when the proxied connection is torn down. + + Not implemented on Windows. + +--push option + Push a config file option back to the client for remote execution. Note + that ``option`` must be enclosed in double quotes (:code:`""`). The + client must specify ``--pull`` in its config file. The set of options + which can be pushed is limited by both feasibility and security. Some + options such as those which would execute scripts are banned, since they + would effectively allow a compromised server to execute arbitrary code + on the client. Other options such as TLS or MTU parameters cannot be + pushed because the client needs to know them before the connection to the + server can be initiated. + + This is a partial list of options which can currently be pushed: + ``--route``, ``--route-gateway``, ``--route-delay``, + ``--redirect-gateway``, ``--ip-win32``, ``--dhcp-option``, + ``--inactive``, ``--ping``, ``--ping-exit``, ``--ping-restart``, + ``--setenv``, ``--auth-token``, ``--persist-key``, ``--persist-tun``, + ``--echo``, ``--comp-lzo``, ``--socket-flags``, ``--sndbuf``, + ``--rcvbuf`` + +--push-peer-info + Push additional information about the client to server. The following + data is always pushed to the server: + + :code:`IV_VER=` + The client OpenVPN version + + :code:`IV_PLAT=[linux|solaris|openbsd|mac|netbsd|freebsd|win]` + The client OS platform + + :code:`IV_LZO_STUB=1` + If client was built with LZO stub capability + + :code:`IV_LZ4=1` + If the client supports LZ4 compressions. + + :code:`IV_PROTO` + Details about protocol extensions that the peer supports. The + variable is a bitfield and the bits are defined as follows + (starting a bit 0 for the first (unused) bit: + + - bit 1: The peer supports peer-id floating mechanism + - bit 2: The client expects a push-reply and the server may + send this reply without waiting for a push-request first. + + :code:`IV_NCP=2` + Negotiable ciphers, client supports ``--cipher`` pushed by + the server, a value of 2 or greater indicates client supports + *AES-GCM-128* and *AES-GCM-256*. + + :code:`IV_CIPHERS=` + The client announces the list of supported ciphers configured with the + ``--data-ciphers`` option to the server. + + :code:`IV_GUI_VER= ` + The UI version of a UI if one is running, for example + :code:`de.blinkt.openvpn 0.5.47` for the Android app. + + When ``--push-peer-info`` is enabled the additional information consists + of the following data: + + :code:`IV_HWADDR=` + The MAC address of clients default gateway + + :code:`IV_SSL=` + The ssl version used by the client, e.g. + :code:`OpenSSL 1.0.2f 28 Jan 2016`. + + :code:`IV_PLAT_VER=x.y` + The version of the operating system, e.g. 6.1 for Windows 7. + + :code:`UV_=` + Client environment variables whose names start with + :code:`UV_` + +--push-remove opt + Selectively remove all ``--push`` options matching "opt" from the option + list for a client. ``opt`` is matched as a substring against the whole + option string to-be-pushed to the client, so ``--push-remove route`` + would remove all ``--push route ...`` and ``--push route-ipv6 ...`` + statements, while ``--push-remove "route-ipv6 2001:"`` would only remove + IPv6 routes for :code:`2001:...` networks. + + ``--push-remove`` can only be used in a client-specific context, like in + a ``--client-config-dir`` file, or ``--client-connect`` script or plugin + -- similar to ``--push-reset``, just more selective. + + *NOTE*: to *change* an option, ``--push-remove`` can be used to first + remove the old value, and then add a new ``--push`` option with the new + value. + + *NOTE 2*: due to implementation details, 'ifconfig' and 'ifconfig-ipv6' + can only be removed with an exact match on the option ( + :code:`push-remove ifconfig`), no substring matching and no matching on + the IPv4/IPv6 address argument is possible. + +--push-reset + Don't inherit the global push list for a specific client instance. + Specify this option in a client-specific context such as with a + ``--client-config-dir`` configuration file. This option will ignore + ``--push`` options at the global config file level. + +--server args + A helper directive designed to simplify the configuration of OpenVPN's + server mode. This directive will set up an OpenVPN server which will + allocate addresses to clients out of the given network/netmask. The + server itself will take the :code:`.1` address of the given network for + use as the server-side endpoint of the local TUN/TAP interface. If the + optional :code:`nopool` flag is given, no dynamic IP address pool will + prepared for VPN clients. + + Valid syntax: + :: + + server network netmask [nopool] + + For example, ``--server 10.8.0.0 255.255.255.0`` expands as follows: + :: + + mode server + tls-server + push "topology [topology]" + + if dev tun AND (topology == net30 OR topology == p2p): + ifconfig 10.8.0.1 10.8.0.2 + if !nopool: + ifconfig-pool 10.8.0.4 10.8.0.251 + route 10.8.0.0 255.255.255.0 + if client-to-client: + push "route 10.8.0.0 255.255.255.0" + else if topology == net30: + push "route 10.8.0.1" + + if dev tap OR (dev tun AND topology == subnet): + ifconfig 10.8.0.1 255.255.255.0 + if !nopool: + ifconfig-pool 10.8.0.2 10.8.0.253 255.255.255.0 + push "route-gateway 10.8.0.1" + if route-gateway unset: + route-gateway 10.8.0.2 + + Don't use ``--server`` if you are ethernet bridging. Use + ``--server-bridge`` instead. + +--server-bridge args + A helper directive similar to ``--server`` which is designed to simplify + the configuration of OpenVPN's server mode in ethernet bridging + configurations. + + Valid syntaxes: + :: + + server-bridge gateway netmask pool-start-IP pool-end-IP + server-bridge [nogw] + + If ``--server-bridge`` is used without any parameters, it will enable a + DHCP-proxy mode, where connecting OpenVPN clients will receive an IP + address for their TAP adapter from the DHCP server running on the + OpenVPN server-side LAN. Note that only clients that support the binding + of a DHCP client with the TAP adapter (such as Windows) can support this + mode. The optional :code:`nogw` flag (advanced) indicates that gateway + information should not be pushed to the client. + + To configure ethernet bridging, you must first use your OS's bridging + capability to bridge the TAP interface with the ethernet NIC interface. + For example, on Linux this is done with the :code:`brctl` tool, and with + Windows XP it is done in the Network Connections Panel by selecting the + ethernet and TAP adapters and right-clicking on "Bridge Connections". + + Next you you must manually set the IP/netmask on the bridge interface. + The ``gateway`` and ``netmask`` parameters to ``--server-bridge`` can be + set to either the IP/netmask of the bridge interface, or the IP/netmask + of the default gateway/router on the bridged subnet. + + Finally, set aside a IP range in the bridged subnet, denoted by + ``pool-start-IP`` and ``pool-end-IP``, for OpenVPN to allocate to + connecting clients. + + For example, ``server-bridge 10.8.0.4 255.255.255.0 10.8.0.128 + 10.8.0.254`` expands as follows: + :: + + mode server + tls-server + + ifconfig-pool 10.8.0.128 10.8.0.254 255.255.255.0 + push "route-gateway 10.8.0.4" + + In another example, ``--server-bridge`` (without parameters) expands as + follows: + :: + + mode server + tls-server + + push "route-gateway dhcp" + + Or ``--server-bridge nogw`` expands as follows: + :: + + mode server + tls-server + +--stale-routes-check args + Remove routes which haven't had activity for ``n`` seconds (i.e. the ageing + time). This check is run every ``t`` seconds (i.e. check interval). + + Valid syntax: + :: + + stale-routes-check n [t] + + If ``t`` is not present it defaults to ``n``. + + This option helps to keep the dynamic routing table small. See also + ``--max-routes-per-client`` + +--username-as-common-name + For ``--auth-user-pass-verify`` authentication, use the authenticated + username as the common name, rather than the common name from the client + cert. + +--verify-client-cert mode + Specify whether the client is required to supply a valid certificate. + + Possible ``mode`` options are: + + :code:`none` + A client certificate is not required. the client needs to + authenticate using username/password only. Be aware that using this + directive is less secure than requiring certificates from all + clients. + + If you use this directive, the entire responsibility of authentication + will rest on your ``--auth-user-pass-verify`` script, so keep in mind + that bugs in your script could potentially compromise the security of + your VPN. + + ``--verify-client-cert none`` is functionally equivalent to + ``--client-cert-not-required``. + + :code:`optional` + A client may present a certificate but it is not required to do so. + When using this directive, you should also use a + ``--auth-user-pass-verify`` script to ensure that clients are + authenticated using a certificate, a username and password, or + possibly even both. + + Again, the entire responsibility of authentication will rest on your + ``--auth-user-pass-verify`` script, so keep in mind that bugs in your + script could potentially compromise the security of your VPN. + + :code:`require` + This is the default option. A client is required to present a + certificate, otherwise VPN access is refused. + + If you don't use this directive (or use ``--verify-client-cert require``) + but you also specify an ``--auth-user-pass-verify`` script, then OpenVPN + will perform double authentication. The client certificate verification + AND the ``--auth-user-pass-verify`` script will need to succeed in order + for a client to be authenticated and accepted onto the VPN. + +--vlan-tagging + Server-only option. Turns the OpenVPN server instance into a switch that + understands VLAN-tagging, based on IEEE 802.1Q. + + The server TAP device and each of the connecting clients is seen as a + port of the switch. All client ports are in untagged mode and the server + TAP device is VLAN-tagged, untagged or accepts both, depending on the + ``--vlan-accept`` setting. + + Ethernet frames with a prepended 802.1Q tag are called "tagged". If the + VLAN Identifier (VID) field in such a tag is non-zero, the frame is + called "VLAN-tagged". If the VID is zero, but the Priority Control Point + (PCP) field is non-zero, the frame is called "prio-tagged". If there is + no 802.1Q tag, the frame is "untagged". + + Using the ``--vlan-pvid v`` option once per client (see + --client-config-dir), each port can be associated with a certain VID. + Packets can only be forwarded between ports having the same VID. + Therefore, clients with differing VIDs are completely separated from + one-another, even if ``--client-to-client`` is activated. + + The packet filtering takes place in the OpenVPN server. Clients should + not have any VLAN tagging configuration applied. + + The ``--vlan-tagging`` option is off by default. While turned off, + OpenVPN accepts any Ethernet frame and does not perform any special + processing for VLAN-tagged packets. + + This option can only be activated in ``--dev tap mode``. + +--vlan-accept args + Configure the VLAN tagging policy for the server TAP device. + + Valid syntax: + :: + + vlan-accept all|tagged|untagged + + The following modes are available: + + :code:`tagged` + Admit only VLAN-tagged frames. Only VLAN-tagged packets are accepted, + while untagged or priority-tagged packets are dropped when entering + the server TAP device. + + :code:`untagged` + Admit only untagged and prio-tagged frames. VLAN-tagged packets are + not accepted, while untagged or priority-tagged packets entering the + server TAP device are tagged with the value configured for the global + ``--vlan-pvid`` setting. + + :code:`all` (default) + Admit all frames. All packets are admitted and then treated like + untagged or tagged mode respectively. + + *Note*: + Some vendors refer to switch ports running in :code:`tagged` mode + as "trunk ports" and switch ports running in :code:`untagged` mode + as "access ports". + + Packets forwarded from clients to the server are VLAN-tagged with the + originating client's PVID, unless the VID matches the global + ``--vlan-pvid``, in which case the tag is removed. + + If no *PVID* is configured for a given client (see --vlan-pvid) packets + are tagged with 1 by default. + +--vlan-pvid v + Specifies which VLAN identifier a "port" is associated with. Only valid + when ``--vlan-tagging`` is speficied. + + In the client context, the setting specifies which VLAN ID a client is + associated with. In the global context, the VLAN ID of the server TAP + device is set. The latter only makes sense for ``--vlan-accept + untagged`` and ``--vlan-accept all`` modes. + + Valid values for ``v`` go from :code:`1` through to :code:`4094`. The + global value defaults to :code:`1`. If no ``--vlan-pvid`` is specified in + the client context, the global value is inherited. + + In some switch implementations, the *PVID* is also referred to as "Native + VLAN". diff --git a/doc/man-sections/signals.rst b/doc/man-sections/signals.rst new file mode 100644 index 0000000..63611b3 --- /dev/null +++ b/doc/man-sections/signals.rst @@ -0,0 +1,30 @@ +SIGNALS +======= + +:code:`SIGHUP` + Cause OpenVPN to close all TUN/TAP and network connections, restart, + re-read the configuration file (if any), and reopen TUN/TAP and network + connections. + +:code:`SIGUSR1` + Like :code:`SIGHUP``, except don't re-read configuration file, and + possibly don't close and reopen TUN/TAP device, re-read key files, + preserve local IP address/port, or preserve most recently authenticated + remote IP address/port based on ``--persist-tun``, ``--persist-key``, + ``--persist-local-ip`` and ``--persist-remote-ip`` options respectively + (see above). + + This signal may also be internally generated by a timeout condition, + governed by the ``--ping-restart`` option. + + This signal, when combined with ``--persist-remote-ip``, may be sent + when the underlying parameters of the host's network interface change + such as when the host is a DHCP client and is assigned a new IP address. + See ``--ipchange`` for more information. + +:code:`SIGUSR2` + Causes OpenVPN to display its current statistics (to the syslog file if + ``--daemon`` is used, or stdout otherwise). + +:code:`SIGINT`, :code:`SIGTERM` + Causes OpenVPN to exit gracefully. diff --git a/doc/man-sections/tls-options.rst b/doc/man-sections/tls-options.rst new file mode 100644 index 0000000..8c2db7c --- /dev/null +++ b/doc/man-sections/tls-options.rst @@ -0,0 +1,668 @@ +TLS Mode Options +---------------- + +TLS mode is the most powerful crypto mode of OpenVPN in both security +and flexibility. TLS mode works by establishing control and data +channels which are multiplexed over a single TCP/UDP port. OpenVPN +initiates a TLS session over the control channel and uses it to exchange +cipher and HMAC keys to protect the data channel. TLS mode uses a robust +reliability layer over the UDP connection for all control channel +communication, while the data channel, over which encrypted tunnel data +passes, is forwarded without any mediation. The result is the best of +both worlds: a fast data channel that forwards over UDP with only the +overhead of encrypt, decrypt, and HMAC functions, and a control channel +that provides all of the security features of TLS, including +certificate-based authentication and Diffie Hellman forward secrecy. + +To use TLS mode, each peer that runs OpenVPN should have its own local +certificate/key pair (``--cert`` and ``--key``), signed by the root +certificate which is specified in ``--ca``. + +When two OpenVPN peers connect, each presents its local certificate to +the other. Each peer will then check that its partner peer presented a +certificate which was signed by the master root certificate as specified +in ``--ca``. + +If that check on both peers succeeds, then the TLS negotiation will +succeed, both OpenVPN peers will exchange temporary session keys, and +the tunnel will begin passing data. + +The OpenVPN project provides a set of scripts for managing RSA +certificates and keys: https://github.com/OpenVPN/easy-rsa + +--askpass file + Get certificate password from console or ``file`` before we daemonize. + + Valid syntaxes: + :: + + askpass + askpass file + + For the extremely security conscious, it is possible to protect your + private key with a password. Of course this means that every time the + OpenVPN daemon is started you must be there to type the password. The + ``--askpass`` option allows you to start OpenVPN from the command line. + It will query you for a password before it daemonizes. To protect a + private key with a password you should omit the ``-nodes`` option when + you use the ``openssl`` command line tool to manage certificates and + private keys. + + If ``file`` is specified, read the password from the first line of + ``file``. Keep in mind that storing your password in a file to a certain + extent invalidates the extra security provided by using an encrypted + key. + +--ca file + Certificate authority (CA) file in .pem format, also referred to as the + *root* certificate. This file can have multiple certificates in .pem + format, concatenated together. You can construct your own certificate + authority certificate and private key by using a command such as: + :: + + openssl req -nodes -new -x509 -keyout ca.key -out ca.crt + + Then edit your openssl.cnf file and edit the ``certificate`` variable to + point to your new root certificate ``ca.crt``. + + For testing purposes only, the OpenVPN distribution includes a sample CA + certificate (ca.crt). Of course you should never use the test + certificates and test keys distributed with OpenVPN in a production + environment, since by virtue of the fact that they are distributed with + OpenVPN, they are totally insecure. + +--capath dir + Directory containing trusted certificates (CAs and CRLs). Not available + with mbed TLS. + + CAs in the capath directory are expected to be named .. CRLs + are expected to be named .r. See the ``-CApath`` option of + ``openssl verify``, and the ``-hash`` option of ``openssl x509``, + ``openssl crl`` and ``X509_LOOKUP_hash_dir()``\(3) + for more information. + + Similar to the ``--crl-verify`` option, CRLs are not mandatory - + OpenVPN will log the usual warning in the logs if the relevant CRL is + missing, but the connection will be allowed. + +--cert file + Local peer's signed certificate in .pem format -- must be signed by a + certificate authority whose certificate is in ``--ca file``. Each peer + in an OpenVPN link running in TLS mode should have its own certificate + and private key file. In addition, each certificate should have been + signed by the key of a certificate authority whose public key resides in + the ``--ca`` certificate authority file. You can easily make your own + certificate authority (see above) or pay money to use a commercial + service such as thawte.com (in which case you will be helping to finance + the world's second space tourist :). To generate a certificate, you can + use a command such as: + :: + + openssl req -nodes -new -keyout mycert.key -out mycert.csr + + If your certificate authority private key lives on another machine, copy + the certificate signing request (mycert.csr) to this other machine (this + can be done over an insecure channel such as email). Now sign the + certificate with a command such as: + :: + + openssl ca -out mycert.crt -in mycert.csr + + Now copy the certificate (mycert.crt) back to the peer which initially + generated the .csr file (this can be over a public medium). Note that + the ``openssl ca`` command reads the location of the certificate + authority key from its configuration file such as + :code:`/usr/share/ssl/openssl.cnf` -- note also that for certificate + authority functions, you must set up the files :code:`index.txt` (may be + empty) and :code:`serial` (initialize to :code:`01`). + +--crl-verify args + Check peer certificate against a Certificate Revocation List. + + Valid syntax: + :: + + crl-verify file/directory flag + + Examples: + :: + + crl-verify crl-file.pem + crl-verify /etc/openvpn/crls dir + + A CRL (certificate revocation list) is used when a particular key is + compromised but when the overall PKI is still intact. + + Suppose you had a PKI consisting of a CA, root certificate, and a number + of client certificates. Suppose a laptop computer containing a client + key and certificate was stolen. By adding the stolen certificate to the + CRL file, you could reject any connection which attempts to use it, + while preserving the overall integrity of the PKI. + + The only time when it would be necessary to rebuild the entire PKI from + scratch would be if the root certificate key itself was compromised. + + The option is not mandatory - if the relevant CRL is missing, OpenVPN + will log a warning in the logs - e.g. + :: + + VERIFY WARNING: depth=0, unable to get certificate CRL + + but the connection will be allowed. If the optional :code:`dir` flag + is specified, enable a different mode where the ``crl-verify`` is + pointed at a directory containing files named as revoked serial numbers + (the files may be empty, the contents are never read). If a client + requests a connection, where the client certificate serial number + (decimal string) is the name of a file present in the directory, it will + be rejected. + + *Note:* + As the crl file (or directory) is read every time a peer + connects, if you are dropping root privileges with + ``--user``, make sure that this user has sufficient + privileges to read the file. + + +--dh file + File containing Diffie Hellman parameters in .pem format (required for + ``--tls-server`` only). + + Set ``file`` to :code:`none` to disable Diffie Hellman key exchange (and + use ECDH only). Note that this requires peers to be using an SSL library + that supports ECDH TLS cipher suites (e.g. OpenSSL 1.0.1+, or + mbed TLS 2.0+). + + Use ``openssl dhparam -out dh2048.pem 2048`` to generate 2048-bit DH + parameters. Diffie Hellman parameters may be considered public. + +--ecdh-curve name + Specify the curve to use for elliptic curve Diffie Hellman. Available + curves can be listed with ``--show-curves``. The specified curve will + only be used for ECDH TLS-ciphers. + + This option is not supported in mbed TLS builds of OpenVPN. + +--extra-certs file + Specify a ``file`` containing one or more PEM certs (concatenated + together) that complete the local certificate chain. + + This option is useful for "split" CAs, where the CA for server certs is + different than the CA for client certs. Putting certs in this file + allows them to be used to complete the local certificate chain without + trusting them to verify the peer-submitted certificate, as would be the + case if the certs were placed in the ``ca`` file. + +--hand-window n + Handshake Window -- the TLS-based key exchange must finalize within + ``n`` seconds of handshake initiation by any peer (default :code:`60` + seconds). If the handshake fails we will attempt to reset our connection + with our peer and try again. Even in the event of handshake failure we + will still use our expiring key for up to ``--tran-window`` seconds to + maintain continuity of transmission of tunnel data. + +--key file + Local peer's private key in .pem format. Use the private key which was + generated when you built your peer's certificate (see ``--cert file`` + above). + +--pkcs12 file + Specify a PKCS #12 file containing local private key, local certificate, + and root CA certificate. This option can be used instead of ``--ca``, + ``--cert``, and ``--key``. Not available with mbed TLS. + +--remote-cert-eku oid + Require that peer certificate was signed with an explicit *extended key + usage*. + + This is a useful security option for clients, to ensure that the host + they connect to is a designated server. + + The extended key usage should be encoded in *oid notation*, or *OpenSSL + symbolic representation*. + +--remote-cert-ku key-usage + Require that peer certificate was signed with an explicit + ``key-usage``. + + If present in the certificate, the :code:`keyUsage` value is validated by + the TLS library during the TLS handshake. Specifying this option without + arguments requires this extension to be present (so the TLS library will + verify it). + + If ``key-usage`` is a list of usage bits, the :code:`keyUsage` field + must have *at least* the same bits set as the bits in *one of* the values + supplied in the ``key-usage`` list. + + The ``key-usage`` values in the list must be encoded in hex, e.g. + :: + + remote-cert-ku a0 + +--remote-cert-tls type + Require that peer certificate was signed with an explicit *key usage* + and *extended key usage* based on RFC3280 TLS rules. + + Valid syntaxes: + :: + + remote-cert-tls server + remote-cert-tls client + + This is a useful security option for clients, to ensure that the host + they connect to is a designated server. Or the other way around; for a + server to verify that only hosts with a client certificate can connect. + + The ``--remote-cert-tls client`` option is equivalent to + :: + + remote-cert-ku + remote-cert-eku "TLS Web Client Authentication" + + The ``--remote-cert-tls server`` option is equivalent to + :: + + remote-cert-ku + remote-cert-eku "TLS Web Server Authentication" + + This is an important security precaution to protect against a + man-in-the-middle attack where an authorized client attempts to connect + to another client by impersonating the server. The attack is easily + prevented by having clients verify the server certificate using any one + of ``--remote-cert-tls``, ``--verify-x509-name``, or ``--tls-verify``. + +--tls-auth args + Add an additional layer of HMAC authentication on top of the TLS control + channel to mitigate DoS attacks and attacks on the TLS stack. + + Valid syntaxes: + :: + + tls-auth file + tls-auth file 0 + tls-auth file 1 + + In a nutshell, ``--tls-auth`` enables a kind of "HMAC firewall" on + OpenVPN's TCP/UDP port, where TLS control channel packets bearing an + incorrect HMAC signature can be dropped immediately without response. + + ``file`` (required) is a file in OpenVPN static key format which can be + generated by ``--genkey``. + + Older versions (up to OpenVPN 2.3) supported a freeform passphrase file. + This is no longer supported in newer versions (v2.4+). + + See the ``--secret`` option for more information on the optional + ``direction`` parameter. + + ``--tls-auth`` is recommended when you are running OpenVPN in a mode + where it is listening for packets from any IP address, such as when + ``--remote`` is not specified, or ``--remote`` is specified with + ``--float``. + + The rationale for this feature is as follows. TLS requires a + multi-packet exchange before it is able to authenticate a peer. During + this time before authentication, OpenVPN is allocating resources (memory + and CPU) to this potential peer. The potential peer is also exposing + many parts of OpenVPN and the OpenSSL library to the packets it is + sending. Most successful network attacks today seek to either exploit + bugs in programs (such as buffer overflow attacks) or force a program to + consume so many resources that it becomes unusable. Of course the first + line of defense is always to produce clean, well-audited code. OpenVPN + has been written with buffer overflow attack prevention as a top + priority. But as history has shown, many of the most widely used network + applications have, from time to time, fallen to buffer overflow attacks. + + So as a second line of defense, OpenVPN offers this special layer of + authentication on top of the TLS control channel so that every packet on + the control channel is authenticated by an HMAC signature and a unique + ID for replay protection. This signature will also help protect against + DoS (Denial of Service) attacks. An important rule of thumb in reducing + vulnerability to DoS attacks is to minimize the amount of resources a + potential, but as yet unauthenticated, client is able to consume. + + ``--tls-auth`` does this by signing every TLS control channel packet + with an HMAC signature, including packets which are sent before the TLS + level has had a chance to authenticate the peer. The result is that + packets without the correct signature can be dropped immediately upon + reception, before they have a chance to consume additional system + resources such as by initiating a TLS handshake. ``--tls-auth`` can be + strengthened by adding the ``--replay-persist`` option which will keep + OpenVPN's replay protection state in a file so that it is not lost + across restarts. + + It should be emphasized that this feature is optional and that the key + file used with ``--tls-auth`` gives a peer nothing more than the power + to initiate a TLS handshake. It is not used to encrypt or authenticate + any tunnel data. + + Use ``--tls-crypt`` instead if you want to use the key file to not only + authenticate, but also encrypt the TLS control channel. + +--tls-groups list + A list of allowable groups/curves in order of preference. + + Set the allowed elliptic curves/groups for the TLS session. + These groups are allowed to be used in signatures and key exchange. + + mbedTLS currently allows all known curves per default. + + OpenSSL 1.1+ restricts the list per default to + :: + + "X25519:secp256r1:X448:secp521r1:secp384r1". + + If you use certificates that use non-standard curves, you + might need to add them here. If you do not force the ecdh curve + by using ``--ecdh-curve``, the groups for ecdh will also be picked + from this list. + + OpenVPN maps the curve name `secp256r1` to `prime256v1` to allow + specifying the same tls-groups option for mbedTLS and OpenSSL. + + Warning: this option not only affects elliptic curve certificates + but also the key exchange in TLS 1.3 and using this option improperly + will disable TLS 1.3. + +--tls-cert-profile profile + Set the allowed cryptographic algorithms for certificates according to + ``profile``. + + The following profiles are supported: + + :code:`legacy` (default) + SHA1 and newer, RSA 2048-bit+, any elliptic curve. + + :code:`preferred` + SHA2 and newer, RSA 2048-bit+, any elliptic curve. + + :code:`suiteb` + SHA256/SHA384, ECDSA with P-256 or P-384. + + This option is only fully supported for mbed TLS builds. OpenSSL builds + use the following approximation: + + :code:`legacy` (default) + sets "security level 1" + + :code:`preferred` + sets "security level 2" + + :code:`suiteb` + sets "security level 3" and ``--tls-cipher "SUITEB128"``. + + OpenVPN will migrate to 'preferred' as default in the future. Please + ensure that your keys already comply. + +*WARNING:* ``--tls-ciphers``, ``--tls-ciphersuites`` and ``tls-groups`` + These options are expert features, which - if used correctly - can + improve the security of your VPN connection. But it is also easy to + unwittingly use them to carefully align a gun with your foot, or just + break your connection. Use with care! + +--tls-cipher l + A list ``l`` of allowable TLS ciphers delimited by a colon (":code:`:`"). + + These setting can be used to ensure that certain cipher suites are used + (or not used) for the TLS connection. OpenVPN uses TLS to secure the + control channel, over which the keys that are used to protect the actual + VPN traffic are exchanged. + + The supplied list of ciphers is (after potential OpenSSL/IANA name + translation) simply supplied to the crypto library. Please see the + OpenSSL and/or mbed TLS documentation for details on the cipher list + interpretation. + + For OpenSSL, the ``--tls-cipher`` is used for TLS 1.2 and below. + + Use ``--show-tls`` to see a list of TLS ciphers supported by your crypto + library. + + The default for ``--tls-cipher`` is to use mbed TLS's default cipher list + when using mbed TLS or + :code:`DEFAULT:!EXP:!LOW:!MEDIUM:!kDH:!kECDH:!DSS:!PSK:!SRP:!kRSA` when + using OpenSSL. + + The default for `--tls-ciphersuites` is to use the crypto library's + default. + +--tls-ciphersuites l + Same as ``--tls-cipher`` but for TLS 1.3 and up. mbed TLS has no + TLS 1.3 support yet and only the ``--tls-cipher`` setting is used. + +--tls-client + Enable TLS and assume client role during TLS handshake. + +--tls-crypt keyfile + Encrypt and authenticate all control channel packets with the key from + ``keyfile``. (See ``--tls-auth`` for more background.) + + Encrypting (and authenticating) control channel packets: + + * provides more privacy by hiding the certificate used for the TLS + connection, + + * makes it harder to identify OpenVPN traffic as such, + + * provides "poor-man's" post-quantum security, against attackers who will + never know the pre-shared key (i.e. no forward secrecy). + + In contrast to ``--tls-auth``, ``--tls-crypt`` does *not* require the + user to set ``--key-direction``. + + **Security Considerations** + + All peers use the same ``--tls-crypt`` pre-shared group key to + authenticate and encrypt control channel messages. To ensure that IV + collisions remain unlikely, this key should not be used to encrypt more + than 2^48 client-to-server or 2^48 server-to-client control channel + messages. A typical initial negotiation is about 10 packets in each + direction. Assuming both initial negotiation and renegotiations are at + most 2^16 (65536) packets (to be conservative), and (re)negotiations + happen each minute for each user (24/7), this limits the tls-crypt key + lifetime to 8171 years divided by the number of users. So a setup with + 1000 users should rotate the key at least once each eight years. (And a + setup with 8000 users each year.) + + If IV collisions were to occur, this could result in the security of + ``--tls-crypt`` degrading to the same security as using ``--tls-auth``. + That is, the control channel still benefits from the extra protection + against active man-in-the-middle-attacks and DoS attacks, but may no + longer offer extra privacy and post-quantum security on top of what TLS + itself offers. + + For large setups or setups where clients are not trusted, consider using + ``--tls-crypt-v2`` instead. That uses per-client unique keys, and + thereby improves the bounds to 'rotate a client key at least once per + 8000 years'. + +--tls-crypt-v2 keyfile + Use client-specific tls-crypt keys. + + For clients, ``keyfile`` is a client-specific tls-crypt key. Such a key + can be generated using the :code:`--genkey tls-crypt-v2-client` option. + + For servers, ``keyfile`` is used to unwrap client-specific keys supplied + by the client during connection setup. This key must be the same as the + key used to generate the client-specific key (see :code:`--genkey + tls-crypt-v2-client`). + + On servers, this option can be used together with the ``--tls-auth`` or + ``--tls-crypt`` option. In that case, the server will detect whether the + client is using client-specific keys, and automatically select the right + mode. + +--tls-crypt-v2-verify cmd + Run command ``cmd`` to verify the metadata of the client-specific + tls-crypt-v2 key of a connecting client. This allows server + administrators to reject client connections, before exposing the TLS + stack (including the notoriously dangerous X.509 and ASN.1 stacks) to + the connecting client. + + OpenVPN supplies the following environment variables to the command: + + * :code:`script_type` is set to :code:`tls-crypt-v2-verify` + + * :code:`metadata_type` is set to :code:`0` if the metadata was user + supplied, or :code:`1` if it's a 64-bit unix timestamp representing + the key creation time. + + * :code:`metadata_file` contains the filename of a temporary file that + contains the client metadata. + + The command can reject the connection by exiting with a non-zero exit + code. + +--tls-exit + Exit on TLS negotiation failure. + +--tls-export-cert directory + Store the certificates the clients use upon connection to this + directory. This will be done before ``--tls-verify`` is called. The + certificates will use a temporary name and will be deleted when the + tls-verify script returns. The file name used for the certificate is + available via the ``peer_cert`` environment variable. + +--tls-server + Enable TLS and assume server role during TLS handshake. Note that + OpenVPN is designed as a peer-to-peer application. The designation of + client or server is only for the purpose of negotiating the TLS control + channel. + +--tls-timeout n + Packet retransmit timeout on TLS control channel if no acknowledgment + from remote within ``n`` seconds (default :code:`2`). When OpenVPN sends + a control packet to its peer, it will expect to receive an + acknowledgement within ``n`` seconds or it will retransmit the packet, + subject to a TCP-like exponential backoff algorithm. This parameter only + applies to control channel packets. Data channel packets (which carry + encrypted tunnel data) are never acknowledged, sequenced, or + retransmitted by OpenVPN because the higher level network protocols + running on top of the tunnel such as TCP expect this role to be left to + them. + +--tls-version-min args + Sets the minimum TLS version we will accept from the peer (default is + "1.0"). + + Valid syntax: + :: + + tls-version-min version ['or-highest'] + + Examples for version include :code:`1.0`, :code:`1.1`, or :code:`1.2`. If + :code:`or-highest` is specified and version is not recognized, we will + only accept the highest TLS version supported by the local SSL + implementation. + +--tls-version-max version + Set the maximum TLS version we will use (default is the highest version + supported). Examples for version include :code:`1.0`, :code:`1.1`, or + :code:`1.2`. + +--verify-hash args + Specify SHA1 or SHA256 fingerprint for level-1 cert. + + Valid syntax: + :: + + verify-hash hash [algo] + + The level-1 cert is the CA (or intermediate cert) that signs the leaf + certificate, and is one removed from the leaf certificate in the + direction of the root. When accepting a connection from a peer, the + level-1 cert fingerprint must match ``hash`` or certificate verification + will fail. Hash is specified as XX:XX:... For example: + :: + + AD:B0:95:D8:09:C8:36:45:12:A9:89:C8:90:09:CB:13:72:A6:AD:16 + + The ``algo`` flag can be either :code:`SHA1` or :code:`SHA256`. If not + provided, it defaults to :code:`SHA1`. + +--verify-x509-name args + Accept connections only if a host's X.509 name is equal to **name.** The + remote host must also pass all other tests of verification. + + Valid syntax: + :: + + verify-x509 name type + + Which X.509 name is compared to ``name`` depends on the setting of type. + ``type`` can be :code:`subject` to match the complete subject DN + (default), :code:`name` to match a subject RDN or :code:`name-prefix` to + match a subject RDN prefix. Which RDN is verified as name depends on the + ``--x509-username-field`` option. But it defaults to the common name + (CN), e.g. a certificate with a subject DN + :: + + C=KG, ST=NA, L=Bishkek, CN=Server-1 + + would be matched by: + :: + + verify-x509-name 'C=KG, ST=NA, L=Bishkek, CN=Server-1' + verify-x509-name Server-1 name + verify-x509-name Server- name-prefix + + The last example is useful if you want a client to only accept + connections to :code:`Server-1`, :code:`Server-2`, etc. + + ``--verify-x509-name`` is a useful replacement for the ``--tls-verify`` + option to verify the remote host, because ``--verify-x509-name`` works + in a ``--chroot`` environment without any dependencies. + + Using a name prefix is a useful alternative to managing a CRL + (Certificate Revocation List) on the client, since it allows the client + to refuse all certificates except for those associated with designated + servers. + + *NOTE:* + Test against a name prefix only when you are using OpenVPN + with a custom CA certificate that is under your control. Never use + this option with type :code:`name-prefix` when your client + certificates are signed by a third party, such as a commercial + web CA. + +--x509-track attribute + Save peer X509 **attribute** value in environment for use by plugins and + management interface. Prepend a :code:`+` to ``attribute`` to save values + from full cert chain. Values will be encoded as + :code:`X509__=`. Multiple ``--x509-track`` + options can be defined to track multiple attributes. + +--x509-username-field args + Field in the X.509 certificate subject to be used as the username + (default :code:`CN`). + + Valid syntax: + :: + + x509-username-field [ext:]fieldname + + Typically, this option is specified with **fieldname** as + either of the following: + :: + + x509-username-field emailAddress + x509-username-field ext:subjectAltName + + The first example uses the value of the :code:`emailAddress` attribute + in the certificate's Subject field as the username. The second example + uses the :code:`ext:` prefix to signify that the X.509 extension + ``fieldname`` :code:`subjectAltName` be searched for an rfc822Name + (email) field to be used as the username. In cases where there are + multiple email addresses in :code:`ext:fieldname`, the last occurrence + is chosen. + + When this option is used, the ``--verify-x509-name`` option will match + against the chosen ``fieldname`` instead of the Common Name. + + Only the :code:`subjectAltName` and :code:`issuerAltName` X.509 + extensions are supported. + + **Please note:** This option has a feature which will convert an + all-lowercase ``fieldname`` to uppercase characters, e.g., + :code:`ou` -> :code:`OU`. A mixed-case ``fieldname`` or one having the + :code:`ext:` prefix will be left as-is. This automatic upcasing feature is + deprecated and will be removed in a future release. diff --git a/doc/man-sections/unsupported-options.rst b/doc/man-sections/unsupported-options.rst new file mode 100644 index 0000000..05ba3ca --- /dev/null +++ b/doc/man-sections/unsupported-options.rst @@ -0,0 +1,32 @@ + +UNSUPPORTED OPTIONS +=================== + +Options listed in this section have been removed from OpenVPN and are no +longer supported + +--client-cert-not-required + Removed in OpenVPN 2.5. This should be replaxed with + ``--verify-client-cert none``. + +--ifconfig-pool-linear + Removed in OpenVPN 2.5. This should be replaced with ``--topology p2p``. + +--key-method + Removed in OpenVPN 2.5. This option should not be used, as using the old + ``key-method`` weakens the VPN tunnel security. The old ``key-method`` + was also only needed when the remote side was older than OpenVPN 2.0. + +--no-iv + Removed in OpenVPN 2.5. This option should not be used as it weakens the + VPN tunnel security. This has been a NOOP option since OpenVPN 2.4. + +--no-replay + Removed in OpenVPN 2.5. This option should not be used as it weakens the + VPN tunnel security. + +--ns-cert-type + Removed in OpenVPN 2.5. The ``nsCertType`` field is no longer supported + in recent SSL/TLS libraries. If your certificates does not include *key + usage* and *extended key usage* fields, they must be upgraded and the + ``--remote-cert-tls`` option should be used instead. diff --git a/doc/man-sections/virtual-routing-and-forwarding.rst b/doc/man-sections/virtual-routing-and-forwarding.rst new file mode 100644 index 0000000..28c13ee --- /dev/null +++ b/doc/man-sections/virtual-routing-and-forwarding.rst @@ -0,0 +1,78 @@ +Virtual Routing and Forwarding +------------------------------ + +Options in this section relates to configuration of virtual routing and +forwarding in combination with the underlying operating system. + +As of today this is only supported on Linux, a kernel >= 4.9 is +recommended. + +This could come in handy when for example the external network should be +only used as a means to connect to some VPN endpoints and all regular +traffic should only be routed through any tunnel(s). This could be +achieved by setting up a VRF and configuring the interface connected to +the external network to be part of the VRF. The examples below will cover +this setup. + +Another option would be to put the tun/tap interface into a VRF. This could +be done by an up-script which uses the :code:`ip link set` command shown +below. + + +VRF setup with iproute2 +``````````````````````` + +Create VRF :code:`vrf_external` and map it to routing table :code:`1023` +:: + + ip link add vrf_external type vrf table 1023 + +Move :code:`eth0` into :code:`vrf_external` +:: + + ip link set master vrf_external dev eth0 + +Any prefixes configured on :code:`eth0` will be moved from the :code`main` +routing table into routing table `1023` + + +VRF setup with ifupdown +``````````````````````` + +For Debian based Distributions :code:`ifupdown2` provides an almost drop-in +replacement for :code:`ifupdown` including VRFs and other features. +A configuration for an interface :code:`eth0` being part of VRF +code:`vrf_external` could look like this: +:: + + auto eth0 + iface eth0 + address 192.0.2.42/24 + address 2001:db8:08:15::42/64 + gateway 192.0.2.1 + gateway 2001:db8:08:15::1 + vrf vrf_external + + auto vrf_external + iface vrf_external + vrf-table 1023 + + +OpenVPN configuration +````````````````````` +The OpenVPN configuration needs to contain this line: +:: + + bind-dev vrf_external + + +Further reading +``````````````` + +Wikipedia has nice page one VRFs: https://en.wikipedia.org/wiki/Virtual_routing_and_forwarding + +This talk from the Network Track of FrOSCon 2018 provides an overview about +advanced layer 2 and layer 3 features of Linux + + - Slides: https://www.slideshare.net/BarbarossaTM/l2l3-fr-fortgeschrittene-helle-und-dunkle-magie-im-linuxnetzwerkstack + - Video (german): https://media.ccc.de/v/froscon2018-2247-l2\_l3\_fur\_fortgeschrittene\_-\_helle\_und\_dunkle\_magie\_im\_linux-netzwerkstack diff --git a/doc/man-sections/vpn-network-options.rst b/doc/man-sections/vpn-network-options.rst new file mode 100644 index 0000000..7100c1a --- /dev/null +++ b/doc/man-sections/vpn-network-options.rst @@ -0,0 +1,534 @@ +Virtual Network Adapter (VPN interface) +--------------------------------------- + +Options in this section relates to configuration of the virtual tun/tap +network interface, including setting the VPN IP address and network +routing. + +--bind-dev device + (Linux only) Set ``device`` to bind the server socket to a + `Virtual Routing and Forwarding`_ device + +--block-ipv6 + On the client, instead of sending IPv6 packets over the VPN tunnel, all + IPv6 packets are answered with an ICMPv6 no route host message. On the + server, all IPv6 packets from clients are answered with an ICMPv6 no + route to host message. This options is intended for cases when IPv6 + should be blocked and other options are not available. ``--block-ipv6`` + will use the remote IPv6 as source address of the ICMPv6 packets if set, + otherwise will use :code:`fe80::7` as source address. + + For this option to make sense you actually have to route traffic to the + tun interface. The following example config block would send all IPv6 + traffic to OpenVPN and answer all requests with no route to host, + effectively blocking IPv6. + + **Client config** + :: + + --ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1 + --redirect-gateway ipv6 + --block-ipv6 + + **Server config** + Push a "valid" ipv6 config to the client and block on the server + :: + + --push "ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1" + --push "redirect-gateway ipv6" + --block-ipv6 + +--dev device + TUN/TAP virtual network device which can be :code:`tunX`, :code:`tapX`, + :code:`null` or an arbitrary name string (:code:`X` can be omitted for + a dynamic device.) + + See examples section below for an example on setting up a TUN device. + + You must use either tun devices on both ends of the connection or tap + devices on both ends. You cannot mix them, as they represent different + underlying network layers: + + :code:`tun` + devices encapsulate IPv4 or IPv6 (OSI Layer 3) + + :code:`tap` + devices encapsulate Ethernet 802.3 (OSI Layer 2). + + Valid syntaxes: + :: + + dev tun2 + dev tap4 + dev ovpn + + When the device name starts with :code:`tun` or :code:`tap`, the device + type is extracted automatically. Otherwise the ``--dev-type`` option + needs to be added as well. + +--dev-node node + Explicitly set the device node rather than using :code:`/dev/net/tun`, + :code:`/dev/tun`, :code:`/dev/tap`, etc. If OpenVPN cannot figure out + whether ``node`` is a TUN or TAP device based on the name, you should + also specify ``--dev-type tun`` or ``--dev-type tap``. + + Under Mac OS X this option can be used to specify the default tun + implementation. Using ``--dev-node utun`` forces usage of the native + Darwin tun kernel support. Use ``--dev-node utunN`` to select a specific + utun instance. To force using the :code:`tun.kext` (:code:`/dev/tunX`) + use ``--dev-node tun``. When not specifying a ``--dev-node`` option + openvpn will first try to open utun, and fall back to tun.kext. + + On Windows systems, select the TAP-Win32 adapter which is named ``node`` + in the Network Connections Control Panel or the raw GUID of the adapter + enclosed by braces. The ``--show-adapters`` option under Windows can + also be used to enumerate all available TAP-Win32 adapters and will show + both the network connections control panel name and the GUID for each + TAP-Win32 adapter. + +--dev-type device-type + Which device type are we using? ``device-type`` should be :code:`tun` + (OSI Layer 3) or :code:`tap` (OSI Layer 2). Use this option only if + the TUN/TAP device used with ``--dev`` does not begin with :code:`tun` + or :code:`tap`. + +--dhcp-option args + Set additional network settings via DHCP. On Windows, this is parsed by + the ``tap-windows6`` or ``wintun`` driver. On other platforms these + options can be picked up by an ``--up`` script or plug-in if it has been + pushed by the OpenVPN server. The option will then be saved in the + client's environment before the ``--up`` script is called, under the name + :code:`foreign_option_{n}`. + + Valid syntax: + :: + + dhcp-options type [parm] + + :code:`DOMAIN` ``name`` + Set Connection-specific DNS Suffix to :code:`name`. + + :code:`DNS` ``address`` + Set primary domain name server IPv4 or IPv6 address. + Repeat this option to set secondary DNS server addresses. + + Note: DNS IPv6 servers are currently set using netsh (the existing + DHCP code can only do IPv4 DHCP, and that protocol only permits + IPv4 addresses anywhere). The option will be put into the + environment, so an ``--up`` script could act upon it if needed. + + :code:`WINS` ``address`` + Set primary WINS server address (NetBIOS over TCP/IP Name Server). + Repeat this option to set secondary WINS server addresses. + + :code:`NBDD` ``address`` + Set primary NBDD server address (NetBIOS over TCP/IP Datagram + Distribution Server). Repeat this option to set secondary NBDD + server addresses. + + :code:`NTP` ``address`` + Set primary NTP server address (Network Time Protocol). + Repeat this option to set secondary NTP server addresses. + + :code:`NBT` ``type`` + Set NetBIOS over TCP/IP Node type. Possible options: + + :code:`1` + b-node (broadcasts) + + :code:`2` + p-node (point-to-point name queries to a WINS server) + + :code:`4` + m-node (broadcast then query name server) + + :code:`8` + h-node (query name server, then broadcast). + + :code:`NBS` ``scope-id`` + Set NetBIOS over TCP/IP Scope. A NetBIOS Scope ID provides an + extended naming service for the NetBIOS over TCP/IP (Known as NBT) + module. The primary purpose of a NetBIOS scope ID is to isolate + NetBIOS traffic on a single network to only those nodes with the + same NetBIOS scope ID. The NetBIOS scope ID is a character string + that is appended to the NetBIOS name. The NetBIOS scope ID on two + hosts must match, or the two hosts will not be able to communicate. + The NetBIOS Scope ID also allows computers to use the same computer + name, as they have different scope IDs. The Scope ID becomes a part + of the NetBIOS name, making the name unique. (This description of + NetBIOS scopes courtesy of NeonSurge@abyss.com) + + :code:`DISABLE-NBT` + Disable Netbios-over-TCP/IP. + +--ifconfig args + Set TUN/TAP adapter parameters. It requires the *IP address* of the local + VPN endpoint. For TUN devices in point-to-point mode, the next argument + must be the VPN IP address of the remote VPN endpoint. For TAP devices, + or TUN devices used with ``--topology subnet``, the second argument + is the subnet mask of the virtual network segment which is being created + or connected to. + + For TUN devices, which facilitate virtual point-to-point IP connections + (when used in ``--topology net30`` or ``p2p`` mode), the proper usage of + ``--ifconfig`` is to use two private IP addresses which are not a member + of any existing subnet which is in use. The IP addresses may be + consecutive and should have their order reversed on the remote peer. + After the VPN is established, by pinging ``rn``, you will be pinging + across the VPN. + + For TAP devices, which provide the ability to create virtual ethernet + segments, or TUN devices in ``--topology subnet`` mode (which create + virtual "multipoint networks"), ``--ifconfig`` is used to set an IP + address and subnet mask just as a physical ethernet adapter would be + similarly configured. If you are attempting to connect to a remote + ethernet bridge, the IP address and subnet should be set to values which + would be valid on the the bridged ethernet segment (note also that DHCP + can be used for the same purpose). + + This option, while primarily a proxy for the ``ifconfig``\(8) command, + is designed to simplify TUN/TAP tunnel configuration by providing a + standard interface to the different ifconfig implementations on + different platforms. + + ``--ifconfig`` parameters which are IP addresses can also be specified + as a DNS or /etc/hosts file resolvable name. + + For TAP devices, ``--ifconfig`` should not be used if the TAP interface + will be getting an IP address lease from a DHCP server. + + Examples: + :: + + # tun device in net30/p2p mode + ifconfig 10.8.0.2 10.8.0.1 + + # tun/tap device in subnet mode + ifconfig 10.8.0.2 255.255.255.0 + +--ifconfig-ipv6 args + Configure an IPv6 address on the *tun* device. + + Valid syntax: + :: + + ifconfig-ipv6 ipv6addr/bits [ipv6remote] + + The ``ipv6addr/bits`` argument is the IPv6 address to use. The + second parameter is used as route target for ``--route-ipv6`` if no + gateway is specified. + + The ``--topology`` option has no influence with ``--ifconfig-ipv6`` + +--ifconfig-noexec + Don't actually execute ifconfig/netsh commands, instead pass + ``--ifconfig`` parameters to scripts using environmental variables. + +--ifconfig-nowarn + Don't output an options consistency check warning if the ``--ifconfig`` + option on this side of the connection doesn't match the remote side. + This is useful when you want to retain the overall benefits of the + options consistency check (also see ``--disable-occ`` option) while only + disabling the ifconfig component of the check. + + For example, if you have a configuration where the local host uses + ``--ifconfig`` but the remote host does not, use ``--ifconfig-nowarn`` + on the local host. + + This option will also silence warnings about potential address conflicts + which occasionally annoy more experienced users by triggering "false + positive" warnings. + +--lladdr address + Specify the link layer address, more commonly known as the MAC address. + Only applied to TAP devices. + +--persist-tun + Don't close and reopen TUN/TAP device or run up/down scripts across + :code:`SIGUSR1` or ``--ping-restart`` restarts. + + :code:`SIGUSR1` is a restart signal similar to :code:`SIGHUP`, but which + offers finer-grained control over reset options. + +--redirect-gateway flags + Automatically execute routing commands to cause all outgoing IP traffic + to be redirected over the VPN. This is a client-side option. + + This option performs three steps: + + (1) Create a static route for the ``--remote`` address which + forwards to the pre-existing default gateway. This is done so that + ``(3)`` will not create a routing loop. + + (2) Delete the default gateway route. + + (3) Set the new default gateway to be the VPN endpoint address + (derived either from ``--route-gateway`` or the second parameter to + ``--ifconfig`` when ``--dev tun`` is specified). + + When the tunnel is torn down, all of the above steps are reversed so + that the original default route is restored. + + Option flags: + + :code:`local` + Add the :code:`local` flag if both OpenVPN peers are directly + connected via a common subnet, such as with wireless. The + :code:`local` flag will cause step ``(1)`` above to be omitted. + + :code:`autolocal` + Try to automatically determine whether to enable :code:`local` + flag above. + + :code:`def1` + Use this flag to override the default gateway by using + :code:`0.0.0.0/1` and :code:`128.0.0.0/1` rather than + :code:`0.0.0.0/0`. This has the benefit of overriding but not + wiping out the original default gateway. + + :code:`bypass-dhcp` + Add a direct route to the DHCP server (if it is non-local) which + bypasses the tunnel (Available on Windows clients, may not be + available on non-Windows clients). + + :code:`bypass-dns` + Add a direct route to the DNS server(s) (if they are non-local) + which bypasses the tunnel (Available on Windows clients, may + not be available on non-Windows clients). + + :code:`block-local` + Block access to local LAN when the tunnel is active, except for + the LAN gateway itself. This is accomplished by routing the local + LAN (except for the LAN gateway address) into the tunnel. + + :code:`ipv6` + Redirect IPv6 routing into the tunnel. This works similar to + the :code:`def1` flag, that is, more specific IPv6 routes are added + (:code:`2000::/4`, :code:`3000::/4`), covering the whole IPv6 + unicast space. + + :code:`!ipv4` + Do not redirect IPv4 traffic - typically used in the flag pair + :code:`ipv6 !ipv4` to redirect IPv6-only. + +--redirect-private flags + Like ``--redirect-gateway``, but omit actually changing the default gateway. + Useful when pushing private subnets. + +--route args + Add route to routing table after connection is established. Multiple + routes can be specified. Routes will be automatically torn down in + reverse order prior to TUN/TAP device close. + + Valid syntaxes: + :: + + route network/IP + route network/IP netmask + route network/IP netmask gateway + route network/IP netmask gateway metric + + This option is intended as a convenience proxy for the ``route``\(8) + shell command, while at the same time providing portable semantics + across OpenVPN's platform space. + + ``netmask`` + defaults to :code:`255.255.255.255` when not given + + ``gateway`` + default taken from ``--route-gateway`` or the second + parameter to ``--ifconfig`` when ``--dev tun`` is specified. + + ``metric`` + default taken from ``--route-metric`` if set, otherwise :code:`0`. + + The default can be specified by leaving an option blank or setting it to + :code:`default`. + + The ``network`` and ``gateway`` parameters can also be specified as a + DNS or :code:`/etc/hosts` file resolvable name, or as one of three special + keywords: + + :code:`vpn_gateway` + The remote VPN endpoint address (derived either from + ``--route-gateway`` or the second parameter to ``--ifconfig`` + when ``--dev tun`` is specified). + + :code:`net_gateway` + The pre-existing IP default gateway, read from the + routing table (not supported on all OSes). + + :code:`remote_host` + The ``--remote`` address if OpenVPN is being run in + client mode, and is undefined in server mode. + +--route-delay args + Valid syntaxes: + :: + + route-delay + route-delay n + route-delay n m + + Delay ``n`` seconds (default :code:`0`) after connection establishment, + before adding routes. If ``n`` is :code:`0`, routes will be added + immediately upon connection establishment. If ``--route-delay`` is + omitted, routes will be added immediately after TUN/TAP device open and + ``--up`` script execution, before any ``--user`` or ``--group`` privilege + downgrade (or ``--chroot`` execution.) + + This option is designed to be useful in scenarios where DHCP is used to + set tap adapter addresses. The delay will give the DHCP handshake time + to complete before routes are added. + + On Windows, ``--route-delay`` tries to be more intelligent by waiting + ``w`` seconds (default :code:`30` by default) for the TAP-Win32 adapter + to come up before adding routes. + +--route-ipv6 args + Setup IPv6 routing in the system to send the specified IPv6 network into + OpenVPN's *tun*. + + Valid syntax: + :: + + route-ipv6 ipv6addr/bits [gateway] [metric] + + The gateway parameter is only used for IPv6 routes across *tap* devices, + and if missing, the ``ipv6remote`` field from ``--ifconfig-ipv6`` or + ``--route-ipv6-gateway`` is used. + +--route-gateway arg + Specify a default *gateway* for use with ``--route``. + + If :code:`dhcp` is specified as the parameter, the gateway address will + be extracted from a DHCP negotiation with the OpenVPN server-side LAN. + + Valid syntaxes: + :: + + route-gateway gateway + route-gateway dhcp + +--route-ipv6-gateway gw + Specify a default gateway ``gw`` for use with ``--route-ipv6``. + +--route-metric m + Specify a default metric ``m`` for use with ``--route``. + +--route-noexec + Don't add or remove routes automatically. Instead pass routes to + ``--route-up`` script using environmental variables. + +--route-nopull + When used with ``--client`` or ``--pull``, accept options pushed by + server EXCEPT for routes, block-outside-dns and dhcp options like DNS + servers. + + When used on the client, this option effectively bars the server from + adding routes to the client's routing table, however note that this + option still allows the server to set the TCP/IP properties of the + client's TUN/TAP interface. + +--topology mode + Configure virtual addressing topology when running in ``--dev tun`` + mode. This directive has no meaning in ``--dev tap`` mode, which always + uses a :code:`subnet` topology. + + If you set this directive on the server, the ``--server`` and + ``--server-bridge`` directives will automatically push your chosen + topology setting to clients as well. This directive can also be manually + pushed to clients. Like the ``--dev`` directive, this directive must + always be compatible between client and server. + + ``mode`` can be one of: + + :code:`net30` + Use a point-to-point topology, by allocating one /30 subnet + per client. This is designed to allow point-to-point semantics when some + or all of the connecting clients might be Windows systems. This is the + default on OpenVPN 2.0. + + :code:`p2p` + Use a point-to-point topology where the remote endpoint of + the client's tun interface always points to the local endpoint of the + server's tun interface. This mode allocates a single IP address per + connecting client. Only use when none of the connecting clients are + Windows systems. + + :code:`subnet` + Use a subnet rather than a point-to-point topology by + configuring the tun interface with a local IP address and subnet mask, + similar to the topology used in ``--dev tap`` and ethernet bridging + mode. This mode allocates a single IP address per connecting client and + works on Windows as well. Only available when server and clients are + OpenVPN 2.1 or higher, or OpenVPN 2.0.x which has been manually patched + with the ``--topology`` directive code. When used on Windows, requires + version 8.2 or higher of the TAP-Win32 driver. When used on \*nix, + requires that the tun driver supports an ``ifconfig``\(8) command which + sets a subnet instead of a remote endpoint IP address. + + *Note:* Using ``--topology subnet`` changes the interpretation of the + arguments of ``--ifconfig`` to mean "address netmask", no longer "local + remote". + +--tun-mtu n + Take the TUN device MTU to be **n** and derive the link MTU from it + (default :code:`1500`). In most cases, you will probably want to leave + this parameter set to its default value. + + The MTU (Maximum Transmission Units) is the maximum datagram size in + bytes that can be sent unfragmented over a particular network path. + OpenVPN requires that packets on the control and data channels be sent + unfragmented. + + MTU problems often manifest themselves as connections which hang during + periods of active usage. + + It's best to use the ``--fragment`` and/or ``--mssfix`` options to deal + with MTU sizing issues. + +--tun-mtu-extra n + Assume that the TUN/TAP device might return as many as ``n`` bytes more + than the ``--tun-mtu`` size on read. This parameter defaults to 0, which + is sufficient for most TUN devices. TAP devices may introduce additional + overhead in excess of the MTU size, and a setting of 32 is the default + when TAP devices are used. This parameter only controls internal OpenVPN + buffer sizing, so there is no transmission overhead associated with + using a larger value. + + +TUN/TAP standalone operations +----------------------------- +These two standalone operations will require ``--dev`` and optionally +``--user`` and/or ``--group``. + +--mktun + (Standalone) Create a persistent tunnel on platforms which support them + such as Linux. Normally TUN/TAP tunnels exist only for the period of + time that an application has them open. This option takes advantage of + the TUN/TAP driver's ability to build persistent tunnels that live + through multiple instantiations of OpenVPN and die only when they are + deleted or the machine is rebooted. + + One of the advantages of persistent tunnels is that they eliminate the + need for separate ``--up`` and ``--down`` scripts to run the appropriate + ``ifconfig``\(8) and ``route``\(8) commands. These commands can be + placed in the the same shell script which starts or terminates an + OpenVPN session. + + Another advantage is that open connections through the TUN/TAP-based + tunnel will not be reset if the OpenVPN peer restarts. This can be + useful to provide uninterrupted connectivity through the tunnel in the + event of a DHCP reset of the peer's public IP address (see the + ``--ipchange`` option above). + + One disadvantage of persistent tunnels is that it is harder to + automatically configure their MTU value (see ``--link-mtu`` and + ``--tun-mtu`` above). + + On some platforms such as Windows, TAP-Win32 tunnels are persistent by + default. + +--rmtun + (Standalone) Remove a persistent tunnel. diff --git a/doc/man-sections/windows-options.rst b/doc/man-sections/windows-options.rst new file mode 100644 index 0000000..eacb9af --- /dev/null +++ b/doc/man-sections/windows-options.rst @@ -0,0 +1,244 @@ +Windows-Specific Options +------------------------- + +--allow-nonadmin TAP-adapter + (Standalone) Set ``TAP-adapter`` to allow access from non-administrative + accounts. If ``TAP-adapter`` is omitted, all TAP adapters on the system + will be configured to allow non-admin access. The non-admin access + setting will only persist for the length of time that the TAP-Win32 + device object and driver remain loaded, and will need to be re-enabled + after a reboot, or if the driver is unloaded and reloaded. This + directive can only be used by an administrator. + +--block-outside-dns + Block DNS servers on other network adapters to prevent DNS leaks. This + option prevents any application from accessing TCP or UDP port 53 except + one inside the tunnel. It uses Windows Filtering Platform (WFP) and + works on Windows Vista or later. + + This option is considered unknown on non-Windows platforms and + unsupported on Windows XP, resulting in fatal error. You may want to use + ``--setenv opt`` or ``--ignore-unknown-option`` (not suitable for + Windows XP) to ignore said error. Note that pushing unknown options from + server does not trigger fatal errors. + +--cryptoapicert select-string + *(Windows/OpenSSL Only)* Load the certificate and private key from the + Windows Certificate System Store. + + Use this option instead of ``--cert`` and ``--key``. + + This makes it possible to use any smart card, supported by Windows, but + also any kind of certificate, residing in the Cert Store, where you have + access to the private key. This option has been tested with a couple of + different smart cards (GemSAFE, Cryptoflex, and Swedish Post Office eID) + on the client side, and also an imported PKCS12 software certificate on + the server side. + + To select a certificate, based on a substring search in the + certificate's subject: + :: + + cryptoapicert "SUBJ:Peter Runestig" + + To select a certificate, based on certificate's thumbprint: + :: + + cryptoapicert "THUMB:f6 49 24 41 01 b4 ..." + + The thumbprint hex string can easily be copy-and-pasted from the Windows + Certificate Store GUI. + +--dhcp-release + Ask Windows to release the TAP adapter lease on shutdown. This option + has no effect now, as it is enabled by default starting with + OpenVPN 2.4.1. + +--dhcp-renew + Ask Windows to renew the TAP adapter lease on startup. This option is + normally unnecessary, as Windows automatically triggers a DHCP + renegotiation on the TAP adapter when it comes up, however if you set + the TAP-Win32 adapter Media Status property to "Always Connected", you + may need this flag. + +--ip-win32 method + When using ``--ifconfig`` on Windows, set the TAP-Win32 adapter IP + address and netmask using ``method``. Don't use this option unless you + are also using ``--ifconfig``. + + :code:`manual` + Don't set the IP address or netmask automatically. Instead + output a message to the console telling the user to configure the + adapter manually and indicating the IP/netmask which OpenVPN + expects the adapter to be set to. + + :code:`dynamic [offset] [lease-time]` + Automatically set the IP address and netmask by replying to DHCP + query messages generated by the kernel. This mode is probably the + "cleanest" solution for setting the TCP/IP properties since it + uses the well-known DHCP protocol. There are, however, two + prerequisites for using this mode: + + (1) The TCP/IP properties for the TAP-Win32 adapter must be set + to "Obtain an IP address automatically", and + + (2) OpenVPN needs to claim an IP address in the subnet for use + as the virtual DHCP server address. + + By default in ``--dev tap`` mode, OpenVPN will take the normally + unused first address in the subnet. For example, if your subnet is + :code:`192.168.4.0 netmask 255.255.255.0`, then OpenVPN will take + the IP address :code:`192.168.4.0` to use as the virtual DHCP + server address. In ``--dev tun`` mode, OpenVPN will cause the DHCP + server to masquerade as if it were coming from the remote endpoint. + + The optional offset parameter is an integer which is > :code:`-256` + and < :code:`256` and which defaults to -1. If offset is positive, + the DHCP server will masquerade as the IP address at network + address + offset. If offset is negative, the DHCP server will + masquerade as the IP address at broadcast address + offset. + + The Windows :code:`ipconfig /all` command can be used to show what + Windows thinks the DHCP server address is. OpenVPN will "claim" + this address, so make sure to use a free address. Having said that, + different OpenVPN instantiations, including different ends of + the same connection, can share the same virtual DHCP server + address. + + The ``lease-time`` parameter controls the lease time of the DHCP + assignment given to the TAP-Win32 adapter, and is denoted in + seconds. Normally a very long lease time is preferred because it + prevents routes involving the TAP-Win32 adapter from being lost + when the system goes to sleep. The default lease time is one year. + + :code:`netsh` + Automatically set the IP address and netmask using the Windows + command-line "netsh" command. This method appears to work correctly + on Windows XP but not Windows 2000. + + :code:`ipapi` + Automatically set the IP address and netmask using the Windows IP + Helper API. This approach does not have ideal semantics, though + testing has indicated that it works okay in practice. If you use + this option, it is best to leave the TCP/IP properties for the + TAP-Win32 adapter in their default state, i.e. "Obtain an IP + address automatically." + + :code:`adaptive` (Default) + Try :code:`dynamic` method initially and fail over to :code:`netsh` + if the DHCP negotiation with the TAP-Win32 adapter does not succeed + in 20 seconds. Such failures have been known to occur when certain + third-party firewall packages installed on the client machine block + the DHCP negotiation used by the TAP-Win32 adapter. Note that if + the :code:`netsh` failover occurs, the TAP-Win32 adapter TCP/IP + properties will be reset from DHCP to static, and this will cause + future OpenVPN startups using the :code:`adaptive` mode to use + :code:`netsh` immediately, rather than trying :code:`dynamic` first. + + To "unstick" the :code:`adaptive` mode from using :code:`netsh`, + run OpenVPN at least once using the :code:`dynamic` mode to restore + the TAP-Win32 adapter TCP/IP properties to a DHCP configuration. + +--pause-exit + Put up a "press any key to continue" message on the console prior to + OpenVPN program exit. This option is automatically used by the Windows + explorer when OpenVPN is run on a configuration file using the + right-click explorer menu. + +--register-dns + Run :code:`ipconfig /flushdns` and :code:`ipconfig /registerdns` on + connection initiation. This is known to kick Windows into recognizing + pushed DNS servers. + +--route-method m + Which method ``m`` to use for adding routes on Windows? + + :code:`adaptive` (default) + Try IP helper API first. If that fails, fall back to the route.exe + shell command. + + :code:`ipapi` + Use IP helper API. + + :code:`exe` + Call the route.exe shell command. + +--service args + Should be used when OpenVPN is being automatically executed by another + program in such a context that no interaction with the user via display + or keyboard is possible. + + Valid syntax: + :: + + service exit-event [0|1] + + In general, end-users should never need to explicitly use this option, + as it is automatically added by the OpenVPN service wrapper when a given + OpenVPN configuration is being run as a service. + + ``exit-event`` is the name of a Windows global event object, and OpenVPN + will continuously monitor the state of this event object and exit when + it becomes signaled. + + The second parameter indicates the initial state of ``exit-event`` and + normally defaults to 0. + + Multiple OpenVPN processes can be simultaneously executed with the same + ``exit-event`` parameter. In any case, the controlling process can + signal ``exit-event``, causing all such OpenVPN processes to exit. + + When executing an OpenVPN process using the ``--service`` directive, + OpenVPN will probably not have a console window to output status/error + messages, therefore it is useful to use ``--log`` or ``--log-append`` to + write these messages to a file. + +--show-adapters + (Standalone) Show available TAP-Win32 adapters which can be selected + using the ``--dev-node`` option. On non-Windows systems, the + ``ifconfig``\(8) command provides similar functionality. + +--show-net + (Standalone) Show OpenVPN's view of the system routing table and network + adapter list. + +--show-net-up + Output OpenVPN's view of the system routing table and network adapter + list to the syslog or log file after the TUN/TAP adapter has been + brought up and any routes have been added. + +--show-valid-subnets + (Standalone) Show valid subnets for ``--dev tun`` emulation. Since the + TAP-Win32 driver exports an ethernet interface to Windows, and since TUN + devices are point-to-point in nature, it is necessary for the TAP-Win32 + driver to impose certain constraints on TUN endpoint address selection. + + Namely, the point-to-point endpoints used in TUN device emulation must + be the middle two addresses of a /30 subnet (netmask 255.255.255.252). + +--tap-sleep n + Cause OpenVPN to sleep for ``n`` seconds immediately after the TAP-Win32 + adapter state is set to "connected". + + This option is intended to be used to troubleshoot problems with the + ``--ifconfig`` and ``--ip-win32`` options, and is used to give the + TAP-Win32 adapter time to come up before Windows IP Helper API + operations are applied to it. + +--win-sys path + Set the Windows system directory pathname to use when looking for system + executables such as ``route.exe`` and ``netsh.exe``. By default, if this + directive is not specified, OpenVPN will use the SystemRoot environment + variable. + + This option has changed behaviour since OpenVPN 2.3. Earlier you had to + define ``--win-sys env`` to use the SystemRoot environment variable, + otherwise it defaulted to :code:`C:\\WINDOWS`. It is not needed to use + the ``env`` keyword any more, and it will just be ignored. A warning is + logged when this is found in the configuration file. + +--windows-driver drv + Specifies which tun driver to use. Values are :code:`tap-windows6` + (default) and :code:`wintun`. This is a Windows-only option. + :code:`wintun`" requires ``--dev tun`` and the OpenVPN process to run + elevated, or be invoked using the Interactive Service. diff --git a/doc/management-notes.txt b/doc/management-notes.txt index 96a0d7d..61daaf0 100644 --- a/doc/management-notes.txt +++ b/doc/management-notes.txt @@ -465,8 +465,12 @@ Command examples: COMMAND -- version ------------------ -Show the current OpenVPN and Management Interface versions. +Set the version (integer) of Management Interface supported by the +client or show the current OpenVPN and Management Interface versions. +Command examples: + version 2 -- Change management version of client to 2 (default = 1) + version -- Show the version of OpenVPN and its Management Interface COMMAND -- auth-retry --------------------- @@ -588,6 +592,92 @@ interface to approve client connections. CID,KID -- client ID and Key ID. See documentation for ">CLIENT:" notification for more info. +COMMAND -- client-pending-auth (OpenVPN 2.5 or higher) +---------------------------------------------------- + +Instruct OpenVPN server to send AUTH_PENDING and INFO_PRE message +to signal a pending authenticating to the client. A pending auth means +that the connecting requires extra authentication like a one time +password or doing a single sign one via web. + + client-pending-auth {CID} {EXTRA} + +The server will send AUTH_PENDING and INFO_PRE,{EXTRA} to the client. +The client is expected to inform the user that authentication is pending and +display the extra information. For the format of EXTRA see below +For the OpenVPN server this is stateless operation and needs to be +followed by a client-deny/client-auth[-nt] command (that is the result of the +out of band authentication). + +Before issuing a client-pending-auth to a client instead of a +client-auth/client-deny, the server should check the IV_SSO +environment variable if the method is support. The currently +defined method are crtext for challenge/response using text +(e.g. TOTP), openurl and proxy_url for opening an URL in the client to +continue authentication. A client supporting the first two methods would +set + + setenv IV_SSO openurl,crtext + +The variable name IV_SSO is historic as AUTH_PENDING was first used +to signal single sign on support. To keep compatiblity with existing +implementations the name IV_SSO is kept in lieu of a better name. + +openurl +======== +For a web based extra authentication (like for +SSO/SAML) EXTRA should be + + OPEN_URL:url + +and client should ask to the user to open the URL to continue. + +The space in a control message is limited, so this url should be kept +short to avoid issues. If a loger url is required a URL that redirects +to the longer URL should be sent instead. + +url_proxy +======== +To avoid issues with OpenVPN connection persist-tun and not able +to reach the web server, a variant of openurl via a HTTPS +Proxy exists. The client should announce url_proxy in its IV_SSO +and parse the PROXY_URL message. The format is + + PROXY_URL:::::url + +The proxy should be a literal IPv4 address or IPv6 address in [] to avoid +ambiguity in parsing. A literal IP address is preferred as DNS might not be +available when the client needs to open the url. The IP address will usually +be the address that client uses to connect to the VPN server. For dual-homed +VPN servers, the server should respond with the same address that the client +connects to. + +This address is also usually excluded from being redirected over the VPN +by a host route. If the platform (like Android) uses another way of protecting +the VPN connection routing loops the client needs to also exclude the +connection to the proxy in the same manner. + +Should another IP be used, then the VPN configuration should include a route +statement to exclude that route from being routed over the VPN. + +crtext +======= + +The format of EXTRA is similar to the already used two step authentication +described in Challenge/Response Protocol section of this document. Since +most of the fields are not necessary or can be infered only the +and fields are used: + + CR_TEXT:: + +: a series of optional, comma-separated flags: + E : echo the response when the user types it. + R : a response is required. + +: the challenge text to be shown to the user. + + + COMMAND -- client-deny (OpenVPN 2.1 or higher) ----------------------------------------------- @@ -802,34 +892,69 @@ To accept connecting to the host and port directly, use this command: proxy NONE -COMMAND -- rsa-sig (OpenVPN 2.3 or higher) ------------------------------------------- +COMMAND -- cr-response (OpenVPN 2.5 or higher) +------------------------------------------------- +Provides support for sending responses a challenge/response +query via INFOMSG,CR_TEXT. The response should be base64 encoded: + + cr-response SGFsbG8gV2VsdCE= + +The document is intended to be used after the client received a +CR_TEXT challenge (see send-pending-auth section). The answer is +the answer to the challenge and depends on the challenge itself +for a TOTP challenge this would the number encoded as base64 or +just a string for a challenge like "what day is it today?". + + +COMMAND -- pk-sig (OpenVPN 2.5 or higher, management version > 1) +COMMAND -- rsa-sig (OpenVPN 2.3 or higher, management version <= 1) +----------------------------------------------------------------- Provides support for external storage of the private key. Requires the --management-external-key option. This option can be used instead of "key" in client mode, and allows the client to run without the need to load the -actual private key. When the SSL protocol needs to perform an RSA sign +actual private key. When the SSL protocol needs to perform a sign operation, the data to be signed will be sent to the management interface via a notification as follows: ->RSA_SIGN:[BASE64_DATA] +>PK_SIGN:[BASE64_DATA],[ALG] (if client announces support for management version > 2) +>PK_SIGN:[BASE64_DATA] (if client announces support for management version > 1) +>RSA_SIGN:[BASE64_DATA] (only older clients will be prompted like this) -The management interface client should then create a PKCS#1 v1.5 signature of +The management interface client should then create an appropriate signature of the (decoded) BASE64_DATA using the private key and return the SSL signature as follows: -rsa-sig +pk-sig (or rsa-sig) [BASE64_SIG_LINE] . . . END -Base64 encoded output of RSA_private_encrypt() (OpenSSL) or mbedtls_pk_sign() -(mbed TLS) will provide a correct signature. +Base 64 encoded output of RSA_private_encrypt for RSA or ECDSA_sign() +for EC using OpenSSL or mbedtls_pk_sign() using mbed TLS will provide a +correct signature. +The rsa-sig interface expects PKCS1 padded signatures for RSA keys +(RSA_PKCS1_PADDING). EC signatures are always unpadded. This capability is intended to allow the use of arbitrary cryptographic service providers with OpenVPN via the management interface. +New and updated clients are expected to use the version command to announce +a version > 1 and handle '>PK_SIGN' prompt and respond with 'pk-sig'. + +The signature algorithm is indicated in the PK_SIGN request only if the +management client-version is > 2. In particular, to support TLS1.3 and +TLS1.2 using OpenSSL 1.1.1, unpadded signature support is required and this +can be indicated in the signing request only if the client version is > 2" + +The currently defined padding algorithms are: + + - RSA_PKCS1_PADDING - PKCS1 padding and RSA signature + - RSA_NO_PADDING - No padding may be added for the signature + - ECDSA - EC signature. + + COMMAND -- certificate (OpenVPN 2.4 or higher) ---------------------------------------------- Provides support for external storage of the certificate. Requires the @@ -969,6 +1094,34 @@ CLIENT notification types: >CLIENT:ADDRESS,{CID},{ADDR},{PRI} +(5) Text based challenge/Response + + >CLIENT:CR_RESPONSE,{CID},{KID},{response_base64} + >CLIENT:ENV,name1=val1 + >CLIENT:ENV,name2=val2 + >CLIENT:ENV,... + >CLIENT:ENV,END + + Using the cr-response command on the client side will trigger this + message on the server side. + + CR_RESPONSE notification. The >CR_RESPONSE fulfils the same purpose as the + CRV1 response in the traditional challenge/response. See that section + below for more details. Since this still uses the same cid as the original + response, we do not use the username and opaque session data in this + response but only contains the actual response. + + It is important to note that OpenVPN2 merely passes the authentication + information and does not do any further checks. (E.g. if a CR was issued + before or if multiple CR responses were sent from the client or if + data has a valid base64 encoding) + + This interface should be be sufficient for almost all challenge/response + system that can be implemented with a single round and base64 encoding the + response. Mechanisms that need multiple rounds or more complex answers + should implement a different response type than CR_RESPONSE. + + Variables: CID -- Client ID, numerical ID for each connecting client, sequence = 0,1,2,... diff --git a/doc/openvpn.8 b/doc/openvpn.8 deleted file mode 100644 index 8038e1f..0000000 --- a/doc/openvpn.8 +++ /dev/null @@ -1,7343 +0,0 @@ -.\" OpenVPN -- An application to securely tunnel IP networks -.\" over a single TCP/UDP port, with support for SSL/TLS-based -.\" session authentication and key exchange, -.\" packet encryption, packet authentication, and -.\" packet compression. -.\" -.\" Copyright (C) 2002-2018 OpenVPN Inc -.\" -.\" This program is free software; you can redistribute it and/or modify -.\" it under the terms of the GNU General Public License version 2 -.\" as published by the Free Software Foundation. -.\" -.\" This program is distributed in the hope that it will be useful, -.\" but WITHOUT ANY WARRANTY; without even the implied warranty of -.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the -.\" GNU General Public License for more details. -.\" -.\" You should have received a copy of the GNU General Public License along -.\" with this program; if not, write to the Free Software Foundation, Inc., -.\" 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. -.\" -.\" Manual page for openvpn -.\" -.\" SH section heading -.\" SS subsection heading -.\" LP paragraph -.\" IP indented paragraph -.\" TP hanging label -.\" -.\" .nf -- no formatting -.\" .fi -- resume formatting -.\" .ft 3 -- boldface -.\" .ft -- normal face -.\" .in +|-{n} -- indent -.\" -.\" Support macros - this is not present on all platforms -.\" Continuation line for .TP header. -.de TQ -. br -. ns -. TP \\$1\" no doublequotes around argument! -.. -.\" End of TQ macro -.TH openvpn 8 "28 February 2018" -.\"********************************************************* -.SH NAME -openvpn \- secure IP tunnel daemon. -.\"********************************************************* -.SH SYNOPSIS -.ft 3 -openvpn [ options ... ] -.ft -.\"********************************************************* -.SH INTRODUCTION -.LP -OpenVPN is an open source VPN daemon by James Yonan. -Because OpenVPN tries to -be a universal VPN tool offering a great deal of flexibility, -there are a lot of options on this manual page. -If you're new to OpenVPN, you might want to skip ahead to the -examples section where you will see how to construct simple -VPNs on the command line without even needing a configuration file. - -Also note that there's more documentation and examples on -the OpenVPN web site: -.I http://openvpn.net/ - -And if you would like to see a shorter version of this manual, -see the openvpn usage message which can be obtained by -running -.B openvpn -without any parameters. -.\"********************************************************* -.SH DESCRIPTION -.LP -OpenVPN is a robust and highly flexible VPN daemon. -OpenVPN supports SSL/TLS security, ethernet bridging, -TCP or UDP tunnel transport through proxies or NAT, -support for dynamic IP addresses and DHCP, -scalability to hundreds or thousands of users, -and portability to most major OS platforms. - -OpenVPN is tightly bound to the OpenSSL library, and derives much -of its crypto capabilities from it. - -OpenVPN supports -conventional encryption -using a pre\-shared secret key -.B (Static Key mode) -or -public key security -.B (SSL/TLS mode) -using client & server certificates. -OpenVPN also -supports non\-encrypted TCP/UDP tunnels. - -OpenVPN is designed to work with the -.B TUN/TAP -virtual networking interface that exists on most platforms. - -Overall, OpenVPN aims to offer many of the key features of IPSec but -with a relatively lightweight footprint. -.\"********************************************************* -.SH OPTIONS -OpenVPN allows any option to be placed either on the command line -or in a configuration file. Though all command line options are preceded -by a double\-leading\-dash ("\-\-"), this prefix can be removed when -an option is placed in a configuration file. -.\"********************************************************* -.TP -.B \-\-help -Show options. -.\"********************************************************* -.TP -.B \-\-config file -Load additional config options from -.B file -where each line corresponds to one command line option, -but with the leading '\-\-' removed. - -If -.B \-\-config file -is the only option to the openvpn command, -the -.B \-\-config -can be removed, and the command can be given as -.B openvpn file - -Note that -configuration files can be nested to a reasonable depth. - -Double quotation or single quotation characters ("", '') -can be used to enclose single parameters containing whitespace, -and "#" or ";" characters in the first column -can be used to denote comments. - -Note that OpenVPN 2.0 and higher performs backslash\-based shell -escaping for characters not in single quotations, -so the following mappings should be observed: - -.nf -.ft 3 -.in +4 -\\\\ Maps to a single backslash character (\\). -\\" Pass a literal doublequote character ("), don't - interpret it as enclosing a parameter. -\\[SPACE] Pass a literal space or tab character, don't - interpret it as a parameter delimiter. -.in -4 -.ft -.fi - -For example on Windows, use double backslashes to -represent pathnames: - -.nf -.ft 3 -.in +4 -secret "c:\\\\OpenVPN\\\\secret.key" -.in -4 -.ft -.fi - -For examples of configuration files, -see -.I http://openvpn.net/examples.html - -Here is an example configuration file: - -.nf -.ft 3 -.in +4 -# -# Sample OpenVPN configuration file for -# using a pre\-shared static key. -# -# '#' or ';' may be used to delimit comments. - -# Use a dynamic tun device. -dev tun - -# Our remote peer -remote mypeer.mydomain - -# 10.1.0.1 is our local VPN endpoint -# 10.1.0.2 is our remote VPN endpoint -ifconfig 10.1.0.1 10.1.0.2 - -# Our pre\-shared static key -secret static.key -.in -4 -.ft -.fi -.\"********************************************************* -.SS Tunnel Options: -.TP -.B \-\-mode m -Set OpenVPN major mode. By default, OpenVPN runs in -point\-to\-point mode ("p2p"). OpenVPN 2.0 introduces -a new mode ("server") which implements a multi\-client -server capability. -.\"********************************************************* -.TP -.B \-\-local host -Local host name or IP address for bind. -If specified, OpenVPN will bind to this address only. -If unspecified, OpenVPN will bind to all interfaces. -.\"********************************************************* -.TP -.B \-\-remote host [port] [proto] -Remote host name or IP address. On the client, multiple -.B \-\-remote -options may be specified for redundancy, each referring -to a different OpenVPN server. Specifying multiple -.B \-\-remote -options for this purpose is a special case of the more -general connection\-profile feature. See the -.B -documentation below. - -The OpenVPN client will try to connect to a server at -.B host:port -in the order specified by the list of -.B \-\-remote -options. - -.B proto -indicates the protocol to use when connecting with the -remote, and may be "tcp" or "udp". - -For forcing IPv4 or IPv6 connection suffix tcp or udp -with 4/6 like udp4/udp6/tcp4/tcp6. - -The client will move on to the next host in the list, -in the event of connection failure. -Note that at any given time, the OpenVPN client -will at most be connected to -one server. - -Note that since UDP is connectionless, connection failure -is defined by the -.B \-\-ping -and -.B \-\-ping\-restart -options. - -Note the following corner case: If you use multiple -.B \-\-remote -options, AND you are dropping root privileges on -the client with -.B \-\-user -and/or -.B \-\-group, -AND the client is running a non\-Windows OS, if the client needs -to switch to a different server, and that server pushes -back different TUN/TAP or route settings, the client may lack -the necessary privileges to close and reopen the TUN/TAP interface. -This could cause the client to exit with a fatal error. - -If -.B \-\-remote -is unspecified, OpenVPN will listen -for packets from any IP address, but will not act on those packets unless -they pass all authentication tests. This requirement for authentication -is binding on all potential peers, even those from known and supposedly -trusted IP addresses (it is very easy to forge a source IP address on -a UDP packet). - -When used in TCP mode, -.B \-\-remote -will act as a filter, rejecting connections from any host which does -not match -.B host. - -If -.B host -is a DNS name which resolves to multiple IP addresses, -OpenVPN will try them in the order that the system getaddrinfo() -presents them, so priorization and DNS randomization is done -by the system library. Unless an IP version is forced by the -protocol specification (4/6 suffix), OpenVPN will try both IPv4 -and IPv6 addresses, in the order getaddrinfo() returns them. -.\"********************************************************* -.TP -.B \-\-remote\-random\-hostname -Prepend a random string (6 bytes, 12 hex characters) to hostname to prevent -DNS caching. For example, "foo.bar.gov" would be modified to -".foo.bar.gov". -.\"********************************************************* -.TP -.B -Define a client connection -profile. Client connection profiles are groups of OpenVPN options that -describe how to connect to a given OpenVPN server. Client connection -profiles are specified within an OpenVPN configuration file, and -each profile is bracketed by -.B -and -.B . - -An OpenVPN client will try each connection profile sequentially -until it achieves a successful connection. - -.B \-\-remote\-random -can be used to initially "scramble" the connection -list. - -Here is an example of connection profile usage: - -.nf -.ft 3 -.in +4 -client -dev tun - - -remote 198.19.34.56 1194 udp - - - -remote 198.19.34.56 443 tcp - - - -remote 198.19.34.56 443 tcp -http\-proxy 192.168.0.8 8080 - - - -remote 198.19.36.99 443 tcp -http\-proxy 192.168.0.8 8080 - - -persist\-key -persist\-tun -pkcs12 client.p12 -remote\-cert\-tls server -verb 3 -.in -4 -.ft -.fi - -First we try to connect to a server at 198.19.34.56:1194 using UDP. -If that fails, we then try to connect to 198.19.34.56:443 using TCP. -If that also fails, then try connecting through an HTTP proxy at -192.168.0.8:8080 to 198.19.34.56:443 using TCP. Finally, try to -connect through the same proxy to a server at 198.19.36.99:443 -using TCP. - -The following OpenVPN options may be used inside of -a -.B -block: - -.B bind, -.B connect\-retry, -.B connect\-retry\-max, -.B connect\-timeout, -.B explicit\-exit\-notify, -.B float, -.B fragment, -.B http\-proxy, -.B http\-proxy\-option, -.B link\-mtu, -.B local, -.B lport, -.B mssfix, -.B mtu\-disc, -.B nobind, -.B port, -.B proto, -.B remote, -.B rport, -.B socks\-proxy, -.B tun\-mtu and -.B tun\-mtu\-extra. - -A defaulting mechanism exists for specifying options to apply to -all -.B -profiles. If any of the above options (with the exception of -.B remote -) appear outside of a -.B -block, but in a configuration file which has one or more -.B -blocks, the option setting will be used as a default for -.B -blocks which follow it in the configuration file. - -For example, suppose the -.B nobind -option were placed in the sample configuration file above, near -the top of the file, before the first -.B -block. The effect would be as if -.B nobind -were declared in all -.B -blocks below it. -.\"********************************************************* -.TP -.B \-\-proto\-force p -When iterating through connection profiles, -only consider profiles using protocol -.B p -('tcp'|'udp'). -.\"********************************************************* -.TP -.B \-\-remote\-random -When multiple -.B \-\-remote -address/ports are specified, or if connection profiles are being -used, initially randomize the order of the list -as a kind of basic load\-balancing measure. -.\"********************************************************* -.TP -.B \-\-proto p -Use protocol -.B p -for communicating with remote host. -.B p -can be -.B udp, -.B tcp\-client, -or -.B tcp\-server. - -The default protocol is -.B udp -when -.B \-\-proto -is not specified. - -For UDP operation, -.B \-\-proto udp -should be specified on both peers. - -For TCP operation, one peer must use -.B \-\-proto tcp\-server -and the other must use -.B \-\-proto tcp\-client. -A peer started with -.B tcp\-server -will wait indefinitely for an incoming connection. A peer -started with -.B tcp\-client -will attempt to connect, and if that fails, will sleep for 5 -seconds (adjustable via the -.B \-\-connect\-retry -option) and try again infinite or up to N retries (adjustable via the -.B \-\-connect\-retry\-max -option). Both TCP client and server will simulate -a SIGUSR1 restart signal if either side resets the connection. - -OpenVPN is designed to operate optimally over UDP, but TCP capability is provided -for situations where UDP cannot be used. -In comparison with UDP, TCP will usually be -somewhat less efficient and less robust when used over unreliable or congested -networks. - -This article outlines some of problems with tunneling IP over TCP: - -.I http://sites.inka.de/sites/bigred/devel/tcp\-tcp.html - -There are certain cases, however, where using TCP may be advantageous from -a security and robustness perspective, such as tunneling non\-IP or -application\-level UDP protocols, or tunneling protocols which don't -possess a built\-in reliability layer. -.\"********************************************************* -.TP -.B \-\-connect\-retry n [max] -Wait -.B n -seconds between connection attempts (default=5). Repeated reconnection -attempts are slowed down after 5 retries per remote by doubling the wait -time after each unsuccessful attempt. The optional argument -.B max -specifies the maximum value of wait time in seconds at which it gets -capped (default=300). -.\"********************************************************* -.TP -.B \-\-connect\-retry\-max n -.B n -specifies the number of times each -.B \-\-remote -or -.B -entry is tried. Specifying -.B n -as one would try each entry exactly once. A successful connection -resets the counter. (default=unlimited). -.\"********************************************************* -.TP -.B \-\-show\-proxy\-settings -Show sensed HTTP or SOCKS proxy settings. Currently, only Windows clients -support this option. -.\"********************************************************* -.TP -.B \-\-http\-proxy server port [authfile|'auto'|'auto\-nct'] [auth\-method] -Connect to remote host through an HTTP proxy at address -.B server -and port -.B port. -If HTTP Proxy\-Authenticate is required, -.B authfile -is a file containing a username and password on 2 lines, or -"stdin" to prompt from console. Its content can also be specified -in the config file with the -.B \-\-http\-proxy\-user\-pass -option. (See section on inline files) - -.B auth\-method -should be one of "none", "basic", or "ntlm". - -HTTP Digest authentication is supported as well, but only via -the -.B auto -or -.B auto\-nct -flags (below). - -The -.B auto -flag causes OpenVPN to automatically determine the -.B auth\-method -and query stdin or the management interface for -username/password credentials, if required. This flag -exists on OpenVPN 2.1 or higher. - -The -.B auto\-nct -flag (no clear\-text auth) instructs OpenVPN to automatically -determine the authentication method, but to reject weak -authentication protocols such as HTTP Basic Authentication. -.\"********************************************************* -.TP -.B \-\-http\-proxy\-option type [parm] -Set extended HTTP proxy options. -Repeat to set multiple options. - -.B VERSION version \-\- -Set HTTP version number to -.B version -(default=1.0). - -.B AGENT user\-agent \-\- -Set HTTP "User\-Agent" string to -.B user\-agent. - -.B CUSTOM\-HEADER name content \-\- -Adds the custom Header with -.B name -as name and -.B content -as the content of the custom HTTP header. -.\"********************************************************* -.TP -.B \-\-socks\-proxy server [port] [authfile] -Connect to remote host through a Socks5 proxy at address -.B server -and port -.B port -(default=1080). -.B authfile -(optional) is a file containing a username and password on 2 lines, or -"stdin" to prompt from console. -.\"********************************************************* -.TP -.B \-\-resolv\-retry n -If hostname resolve fails for -.B \-\-remote, -retry resolve for -.B n -seconds before failing. - -Set -.B n -to "infinite" to retry indefinitely. - -By default, -.B \-\-resolv\-retry infinite -is enabled. You can disable by setting n=0. -.\"********************************************************* -.TP -.B \-\-float -Allow remote peer to change its IP address and/or port number, such as due to -DHCP (this is the default if -.B \-\-remote -is not used). -.B \-\-float -when specified with -.B \-\-remote -allows an OpenVPN session to initially connect to a peer -at a known address, however if packets arrive from a new -address and pass all authentication tests, the new address -will take control of the session. This is useful when -you are connecting to a peer which holds a dynamic address -such as a dial\-in user or DHCP client. - -Essentially, -.B \-\-float -tells OpenVPN to accept authenticated packets -from any address, not only the address which was specified in the -.B \-\-remote -option. -.\"********************************************************* -.TP -.B \-\-ipchange cmd -Run command -.B cmd -when our remote ip\-address is initially authenticated or -changes. - -.B cmd -consists of a path to script (or executable program), optionally -followed by arguments. The path and arguments may be single\- or double\-quoted -and/or escaped using a backslash, and should be separated by one or more spaces. - -When -.B cmd -is executed two arguments are appended after any arguments specified in -.B cmd -, as follows: - -.B cmd ip_address port_number - -Don't use -.B \-\-ipchange -in -.B \-\-mode server -mode. Use a -.B \-\-client\-connect -script instead. - -See the "Environmental Variables" section below for -additional parameters passed as environmental variables. - -If you are running in a dynamic IP address environment where -the IP addresses of either peer could change without notice, -you can use this script, for example, to edit the -.I /etc/hosts -file with the current address of the peer. The script will -be run every time the remote peer changes its IP address. - -Similarly if -.I our -IP address changes due to DHCP, we should configure -our IP address change script (see man page for -.BR dhcpcd (8) -) to deliver a -.B SIGHUP -or -.B SIGUSR1 -signal to OpenVPN. OpenVPN will then -reestablish a connection with its most recently authenticated -peer on its new IP address. -.\"********************************************************* -.TP -.B \-\-port port -TCP/UDP port number or port name for both local and remote (sets both -.B \-\-lport -and -.B \-\-rport -options to given port). The current -default of 1194 represents the official IANA port number -assignment for OpenVPN and has been used since version 2.0\-beta17. -Previous versions used port 5000 as the default. -.\"********************************************************* -.TP -.B \-\-lport port -Set local TCP/UDP port number or name. Cannot be used together with -.B \-\-nobind -option. -.\"********************************************************* -.TP -.B \-\-rport port -Set TCP/UDP port number or name used by the -.B \-\-remote -option. The port can also be set directly using the -.B \-\-remote -option. -.\"********************************************************* -.TP -.B \-\-bind [ipv6only] -Bind to local address and port. This is the default unless any of -.B \-\-proto tcp\-client -, -.B \-\-http\-proxy -or -.B \-\-socks\-proxy -are used. - -If the -.B ipv6only -keyword is present OpenVPN will bind only to IPv6 (as oposed -to IPv6 and IPv4) when a IPv6 socket is opened. - -.\"********************************************************* -.TP -.B \-\-nobind -Do not bind to local address and port. The IP stack will allocate -a dynamic port for returning packets. Since the value of the dynamic port -could not be known in advance by a peer, this option is only suitable for -peers which will be initiating connections by using the -.B \-\-remote -option. -.\"********************************************************* -.TP -.B \-\-dev tunX | tapX | null -TUN/TAP virtual network device ( -.B X -can be omitted for a dynamic device.) - -See examples section below -for an example on setting up a TUN device. - -You must use either tun devices on both ends of the connection -or tap devices on both ends. You cannot mix them, as they -represent different underlying network layers. - -.B tun -devices encapsulate IPv4 or IPv6 (OSI Layer 3) while -.B tap -devices encapsulate Ethernet 802.3 (OSI Layer 2). -.\"********************************************************* -.TP -.B \-\-dev\-type device\-type -Which device type are we using? -.B device\-type -should be -.B tun -(OSI Layer 3) -or -.B tap -(OSI Layer 2). -Use this option only if the TUN/TAP device used with -.B \-\-dev -does not begin with -.B tun -or -.B tap. -.\"********************************************************* -.TP -.B \-\-topology mode -Configure virtual addressing topology when running in -.B \-\-dev tun -mode. This directive has no meaning in -.B \-\-dev tap -mode, which always uses a -.B subnet -topology. - -If you set this directive on the server, the -.B \-\-server -and -.B \-\-server\-bridge -directives will automatically push your chosen topology setting to clients -as well. This directive can also be manually pushed to clients. Like the -.B \-\-dev -directive, this directive must always be compatible between client and server. - -.B mode -can be one of: - -.B net30 \-\- -Use a point\-to\-point topology, by allocating one /30 subnet per client. -This is designed to allow point\-to\-point semantics when some -or all of the connecting clients might be Windows systems. This is the -default on OpenVPN 2.0. - -.B p2p \-\- -Use a point\-to\-point topology where the remote endpoint of the client's -tun interface always points to the local endpoint of the server's tun interface. -This mode allocates a single IP address per connecting client. -Only use -when none of the connecting clients are Windows systems. This mode -is functionally equivalent to the -.B \-\-ifconfig\-pool\-linear -directive which is available in OpenVPN 2.0, is deprecated and will be -removed in OpenVPN 2.5 - -.B subnet \-\- -Use a subnet rather than a point\-to\-point topology by -configuring the tun interface with a local IP address and subnet mask, -similar to the topology used in -.B \-\-dev tap -and ethernet bridging mode. -This mode allocates a single IP address per connecting client and works on -Windows as well. Only available when server and clients are OpenVPN 2.1 or -higher, or OpenVPN 2.0.x which has been manually patched with the -.B \-\-topology -directive code. When used on Windows, requires version 8.2 or higher -of the TAP\-Win32 driver. When used on *nix, requires that the tun -driver supports an -.BR ifconfig (8) -command which sets a subnet instead of a remote endpoint IP address. - -This option exists in OpenVPN 2.1 or higher. - -Note: Using -.B \-\-topology subnet -changes the interpretation of the arguments of -.B \-\-ifconfig -to mean "address netmask", no longer "local remote". -.\"********************************************************* -.TP -.B \-\-dev\-node node -Explicitly set the device node rather than using -/dev/net/tun, /dev/tun, /dev/tap, etc. If OpenVPN -cannot figure out whether -.B node -is a TUN or TAP device based on the name, you should -also specify -.B \-\-dev\-type tun -or -.B \-\-dev\-type tap. - -Under Mac OS X this option can be used to specify the default tun -implementation. Using -.B \-\-dev\-node utun -forces usage of the native Darwin tun kernel support. Use -.B \-\-dev\-node utunN -to select a specific utun instance. To force using the tun.kext (/dev/tunX) use -.B \-\-dev\-node tun\fR. -When not specifying a -.B \-\-dev\-node -option openvpn will first try to open utun, and fall back to tun.kext. - -On Windows systems, select the TAP\-Win32 adapter which -is named -.B node -in the Network Connections Control Panel or the -raw GUID of the adapter enclosed by braces. -The -.B \-\-show\-adapters -option under Windows can also be used -to enumerate all available TAP\-Win32 -adapters and will show both the network -connections control panel name and the GUID for -each TAP\-Win32 adapter. -.TP -.B \-\-lladdr address -Specify the link layer address, more commonly known as the MAC address. -Only applied to TAP devices. -.\"********************************************************* -.TP -.B \-\-iproute cmd -Set alternate command to execute instead of default iproute2 command. -May be used in order to execute OpenVPN in unprivileged environment. -.\"********************************************************* -.TP -.B \-\-ifconfig l rn -Set TUN/TAP adapter parameters. -.B l -is the IP address of the local VPN endpoint. -For TUN devices in point\-to\-point mode, -.B rn -is the IP address of the remote VPN endpoint. -For TAP devices, or TUN devices used with -.B \-\-topology subnet, -.B rn -is the subnet mask of the virtual network segment -which is being created or connected to. - -For TUN devices, which facilitate virtual -point\-to\-point IP connections (when used in -.B \-\-topology net30 -or -.B p2p -mode), -the proper usage of -.B \-\-ifconfig -is to use two private IP addresses -which are not a member of any -existing subnet which is in use. -The IP addresses may be consecutive -and should have their order reversed -on the remote peer. After the VPN -is established, by pinging -.B rn, -you will be pinging across the VPN. - -For TAP devices, which provide -the ability to create virtual -ethernet segments, or TUN devices in -.B \-\-topology subnet -mode (which create virtual "multipoint networks"), -.B \-\-ifconfig -is used to set an IP address and -subnet mask just as a physical -ethernet adapter would be -similarly configured. If you are -attempting to connect to a remote -ethernet bridge, the IP address -and subnet should be set to values -which would be valid on the -the bridged ethernet segment (note -also that DHCP can be used for the -same purpose). - -This option, while primarily a proxy for the -.BR ifconfig (8) -command, is designed to simplify TUN/TAP -tunnel configuration by providing a -standard interface to the different -ifconfig implementations on different -platforms. - -.B \-\-ifconfig -parameters which are IP addresses can -also be specified as a DNS or /etc/hosts -file resolvable name. - -For TAP devices, -.B \-\-ifconfig -should not be used if the TAP interface will be -getting an IP address lease from a DHCP -server. -.\"********************************************************* -.TP -.B \-\-ifconfig\-noexec -Don't actually execute ifconfig/netsh commands, instead -pass -.B \-\-ifconfig -parameters to scripts using environmental variables. -.\"********************************************************* -.TP -.B \-\-ifconfig\-nowarn -Don't output an options consistency check warning -if the -.B \-\-ifconfig -option on this side of the -connection doesn't match the remote side. This is useful -when you want to retain the overall benefits of the -options consistency check (also see -.B \-\-disable\-occ -option) while only disabling the ifconfig component of -the check. - -For example, -if you have a configuration where the local host uses -.B \-\-ifconfig -but the remote host does not, use -.B \-\-ifconfig\-nowarn -on the local host. - -This option will also silence warnings about potential -address conflicts which occasionally annoy more experienced -users by triggering "false positive" warnings. -.\"********************************************************* -.TP -.B \-\-route network/IP [netmask] [gateway] [metric] -Add route to routing table after connection is established. -Multiple routes can be specified. Routes will be -automatically torn down in reverse order prior to -TUN/TAP device close. - -This option is intended as -a convenience proxy for the -.BR route (8) -shell command, -while at the same time providing portable semantics -across OpenVPN's platform space. - -.B netmask -default \-\- 255.255.255.255 - -.B gateway -default \-\- taken from -.B \-\-route\-gateway -or the second parameter to -.B \-\-ifconfig -when -.B \-\-dev tun -is specified. - -.B metric -default \-\- taken from -.B \-\-route\-metric -otherwise 0. - -The default can be specified by leaving an option blank or setting -it to "default". - -The -.B network -and -.B gateway -parameters can -also be specified as a DNS or /etc/hosts -file resolvable name, or as one of three special keywords: - -.B vpn_gateway -\-\- The remote VPN endpoint address -(derived either from -.B \-\-route\-gateway -or the second parameter to -.B \-\-ifconfig -when -.B \-\-dev tun -is specified). - -.B net_gateway -\-\- The pre\-existing IP default gateway, read from the routing -table (not supported on all OSes). - -.B remote_host -\-\- The -.B \-\-remote -address if OpenVPN is being run in client mode, and is undefined in server mode. -.\"********************************************************* -.TP -.B \-\-route\-gateway gw|'dhcp' -Specify a default gateway -.B gw -for use with -.B \-\-route. - -If -.B dhcp -is specified as the parameter, -the gateway address will be extracted from a DHCP -negotiation with the OpenVPN server\-side LAN. -.\"********************************************************* -.TP -.B \-\-route\-metric m -Specify a default metric -.B m -for use with -.B \-\-route. -.\"********************************************************* -.TP -.B \-\-route\-delay [n] [w] -Delay -.B n -seconds (default=0) after connection -establishment, before adding routes. If -.B n -is 0, routes will be added immediately upon connection -establishment. If -.B \-\-route\-delay -is omitted, routes will be added immediately after TUN/TAP device -open and -.B \-\-up -script execution, before any -.B \-\-user -or -.B \-\-group -privilege downgrade (or -.B \-\-chroot -execution.) - -This option is designed to be useful in scenarios where DHCP is -used to set -tap adapter addresses. The delay will give the DHCP handshake -time to complete before routes are added. - -On Windows, -.B \-\-route\-delay -tries to be more intelligent by waiting -.B w -seconds (w=30 by default) -for the TAP\-Win32 adapter to come up before adding routes. -.\"********************************************************* -.TP -.B \-\-route\-up cmd -Run command -.B cmd -after routes are added, subject to -.B \-\-route\-delay. - -.B cmd -consists of a path to script (or executable program), optionally -followed by arguments. The path and arguments may be single\- or double\-quoted -and/or escaped using a backslash, and should be separated by one or more spaces. - -See the "Environmental Variables" section below for -additional parameters passed as environmental variables. -.\"********************************************************* -.TP -.B \-\-route\-pre\-down cmd -Run command -.B cmd -before routes are removed upon disconnection. - -.B cmd -consists of a path to script (or executable program), optionally -followed by arguments. The path and arguments may be single\- or double\-quoted -and/or escaped using a backslash, and should be separated by one or more spaces. - -See the "Environmental Variables" section below for -additional parameters passed as environmental variables. -.\"********************************************************* -.TP -.B \-\-route\-noexec -Don't add or remove routes automatically. Instead pass routes to -.B \-\-route\-up -script using environmental variables. -.\"********************************************************* -.TP -.B \-\-route\-nopull -When used with -.B \-\-client -or -.B \-\-pull, -accept options pushed by server EXCEPT for routes, block\-outside\-dns and dhcp -options like DNS servers. - -When used on the client, this option effectively bars the -server from adding routes to the client's routing table, -however note that this option still allows the server -to set the TCP/IP properties of the client's TUN/TAP interface. -.\"********************************************************* -.TP -.B \-\-allow\-pull\-fqdn -Allow client to pull DNS names from server (rather than being limited -to IP address) for -.B \-\-ifconfig, -.B \-\-route, -and -.B \-\-route\-gateway. -.\"********************************************************* -.TP -.B \-\-client\-nat snat|dnat network netmask alias -This pushable client option sets up a stateless one\-to\-one NAT -rule on packet addresses (not ports), and is useful in cases -where routes or ifconfig settings pushed to the client would -create an IP numbering conflict. - -.B network/netmask -(for example 192.168.0.0/255.255.0.0) -defines the local view of a resource from the client perspective, while -.B alias/netmask -(for example 10.64.0.0/255.255.0.0) -defines the remote view from the server perspective. - -Use -.B snat -(source NAT) for resources owned by the client and -.B dnat -(destination NAT) for remote resources. - -Set -.B \-\-verb 6 -for debugging info showing the transformation of src/dest -addresses in packets. -.\"********************************************************* -.TP -.B \-\-redirect\-gateway flags... -Automatically execute routing commands to cause all outgoing IP traffic -to be redirected over the VPN. This is a client\-side option. - -This option performs three steps: - -.B (1) -Create a static route for the -.B \-\-remote -address which forwards to the pre\-existing default gateway. -This is done so that -.B (3) -will not create a routing loop. - -.B (2) -Delete the default gateway route. - -.B (3) -Set the new default gateway to be the VPN endpoint address (derived either from -.B \-\-route\-gateway -or the second parameter to -.B \-\-ifconfig -when -.B \-\-dev tun -is specified). - -When the tunnel is torn down, all of the above steps are reversed so -that the original default route is restored. - -Option flags: - -.B local \-\- -Add the -.B local -flag if both OpenVPN peers are directly connected via a common subnet, -such as with wireless. The -.B local -flag will cause step -.B 1 -above to be omitted. - -.B autolocal \-\- -Try to automatically determine whether to enable -.B local -flag above. - -.B def1 \-\- -Use this flag to override -the default gateway by using 0.0.0.0/1 and 128.0.0.0/1 -rather than 0.0.0.0/0. This has the benefit of overriding -but not wiping out the original default gateway. - -.B bypass\-dhcp \-\- -Add a direct route to the DHCP server (if it is non\-local) which -bypasses the tunnel -(Available on Windows clients, may not be available -on non\-Windows clients). - -.B bypass\-dns \-\- -Add a direct route to the DNS server(s) (if they are non\-local) which -bypasses the tunnel -(Available on Windows clients, may not be available -on non\-Windows clients). - -.B block\-local \-\- -Block access to local LAN when the tunnel is active, except for -the LAN gateway itself. This is accomplished by routing the local -LAN (except for the LAN gateway address) into the tunnel. - -.B ipv6 \-\- -Redirect IPv6 routing into the tunnel. This works similar to the -.B def1 -flag, that is, more specific IPv6 routes are added (2000::/4, 3000::/4), -covering the whole IPv6 unicast space. - -.B !ipv4 \-\- -Do not redirect IPv4 traffic \- typically used in the flag pair -.B "ipv6 !ipv4" -to redirect IPv6\-only. -.\"********************************************************* -.TP -.B \-\-link\-mtu n -Sets an upper bound on the size of UDP packets which are sent -between OpenVPN peers. It's best not to set this parameter unless -you know what you're doing. -.\"********************************************************* -.\"********************************************************* -.TP -.B \-\-redirect\-private [flags] -Like \-\-redirect\-gateway, but omit actually changing the default -gateway. Useful when pushing private subnets. -.\"********************************************************* -.TP -.B \-\-tun\-mtu n -Take the TUN device MTU to be -.B n -and derive the link MTU -from it (default=1500). In most cases, you will probably want to -leave this parameter set to its default value. - -The MTU (Maximum Transmission Units) is -the maximum datagram size in bytes that can be sent unfragmented -over a particular network path. OpenVPN requires that packets -on the control or data channels be sent unfragmented. - -MTU problems often manifest themselves as connections which -hang during periods of active usage. - -It's best to use the -.B \-\-fragment -and/or -.B \-\-mssfix -options to deal with MTU sizing issues. -.\"********************************************************* -.TP -.B \-\-tun\-mtu\-extra n -Assume that the TUN/TAP device might return as many as -.B n -bytes more than the -.B \-\-tun\-mtu -size on read. This parameter defaults to 0, which is sufficient for -most TUN devices. TAP devices may introduce additional overhead in excess -of the MTU size, and a setting of 32 is the default when TAP devices are used. -This parameter only controls internal OpenVPN buffer sizing, -so there is no transmission overhead associated with using a larger value. -.\"********************************************************* -.TP -.B \-\-mtu\-disc type -Should we do Path MTU discovery on TCP/UDP channel? Only supported on OSes such -as Linux that supports the necessary system call to set. - -.B 'no' -\-\- Never send DF (Don't Fragment) frames -.br -.B 'maybe' -\-\- Use per\-route hints -.br -.B 'yes' -\-\- Always DF (Don't Fragment) -.br -.\"********************************************************* -.TP -.B \-\-mtu\-test -To empirically measure MTU on connection startup, -add the -.B \-\-mtu\-test -option to your configuration. -OpenVPN will send ping packets of various sizes -to the remote peer and measure the largest packets -which were successfully received. The -.B \-\-mtu\-test -process normally takes about 3 minutes to complete. -.\"********************************************************* -.TP -.B \-\-fragment max -Enable internal datagram fragmentation so -that no UDP datagrams are sent which -are larger than -.B max -bytes. - -The -.B max -parameter is interpreted in the same way as the -.B \-\-link\-mtu -parameter, i.e. the UDP packet size after encapsulation -overhead has been added in, but not including -the UDP header itself. - -The -.B \-\-fragment -option only makes sense when you are using the UDP protocol ( -.B \-\-proto udp -). - -.B \-\-fragment -adds 4 bytes of overhead per datagram. - -See the -.B \-\-mssfix -option below for an important related option to -.B \-\-fragment. - -It should also be noted that this option is not meant to replace -UDP fragmentation at the IP stack level. It is only meant as a -last resort when path MTU discovery is broken. Using this option -is less efficient than fixing path MTU discovery for your IP link and -using native IP fragmentation instead. - -Having said that, there are circumstances where using OpenVPN's -internal fragmentation capability may be your only option, such -as tunneling a UDP multicast stream which requires fragmentation. -.\"********************************************************* -.TP -.B \-\-mssfix max -Announce to TCP sessions running over the tunnel that they should limit -their send packet sizes such that after OpenVPN has encapsulated them, -the resulting UDP packet size that OpenVPN sends to its peer will not -exceed -.B max -bytes. The default value is -.B 1450. - -The -.B max -parameter is interpreted in the same way as the -.B \-\-link\-mtu -parameter, i.e. the UDP packet size after encapsulation -overhead has been added in, but not including -the UDP header itself. Resulting packet would be at most 28 -bytes larger for IPv4 and 48 bytes for IPv6 (20/40 bytes for IP -header and 8 bytes for UDP header). Default value of 1450 allows -IPv4 packets to be transmitted over a link with MTU 1473 or higher -without IP level fragmentation. - -The -.B \-\-mssfix -option only makes sense when you are using the UDP protocol -for OpenVPN peer\-to\-peer communication, i.e. -.B \-\-proto udp. - -.B \-\-mssfix -and -.B \-\-fragment -can be ideally used together, where -.B \-\-mssfix -will try to keep TCP from needing -packet fragmentation in the first place, -and if big packets come through anyhow -(from protocols other than TCP), -.B \-\-fragment -will internally fragment them. - -Both -.B \-\-fragment -and -.B \-\-mssfix -are designed to work around cases where Path MTU discovery -is broken on the network path between OpenVPN peers. - -The usual symptom of such a breakdown is an OpenVPN -connection which successfully starts, but then stalls -during active usage. - -If -.B \-\-fragment -and -.B \-\-mssfix -are used together, -.B \-\-mssfix -will take its default -.B max -parameter from the -.B \-\-fragment max -option. - -Therefore, one could lower the maximum UDP packet size -to 1300 (a good first try for solving MTU\-related -connection problems) with the following options: - -.B \-\-tun\-mtu 1500 \-\-fragment 1300 \-\-mssfix -.\"********************************************************* -.TP -.B \-\-sndbuf size -Set the TCP/UDP socket send buffer size. -Defaults to operation system default. -.\"********************************************************* -.TP -.B \-\-rcvbuf size -Set the TCP/UDP socket receive buffer size. -Defaults to operation system default. -.\"********************************************************* -.TP -.B \-\-mark value -Mark encrypted packets being sent with value. The mark value can be -matched in policy routing and packetfilter rules. This option is -only supported in Linux and does nothing on other operating systems. -.\"********************************************************* -.TP -.B \-\-socket\-flags flags... -Apply the given flags to the OpenVPN transport socket. -Currently, only -.B TCP_NODELAY -is supported. - -The -.B TCP_NODELAY -socket flag is useful in TCP mode, and causes the kernel -to send tunnel packets immediately over the TCP connection without -trying to group several smaller packets into a larger packet. -This can result in a considerably improvement in latency. - -This option is pushable from server to client, and should be used -on both client and server for maximum effect. -.\"********************************************************* -.TP -.B \-\-txqueuelen n -(Linux only) Set the TX queue length on the TUN/TAP interface. -Currently defaults to 100. -.\"********************************************************* -.TP -.B \-\-shaper n -Limit bandwidth of outgoing tunnel data to -.B n -bytes per second on the TCP/UDP port. -Note that this will only work if mode is set to p2p. -If you want to limit the bandwidth -in both directions, use this option on both peers. - -OpenVPN uses the following algorithm to implement -traffic shaping: Given a shaper rate of -.I n -bytes per second, after a datagram write of -.I b -bytes is queued on the TCP/UDP port, wait a minimum of -.I (b / n) -seconds before queuing the next write. - -It should be noted that OpenVPN supports multiple -tunnels between the same two peers, allowing you -to construct full\-speed and reduced bandwidth tunnels -at the same time, -routing low\-priority data such as off\-site backups -over the reduced bandwidth tunnel, and other data -over the full\-speed tunnel. - -Also note that for low bandwidth tunnels -(under 1000 bytes per second), you should probably -use lower MTU values as well (see above), otherwise -the packet latency will grow so large as to trigger -timeouts in the TLS layer and TCP connections running -over the tunnel. - -OpenVPN allows -.B n -to be between 100 bytes/sec and 100 Mbytes/sec. -.\"********************************************************* -.TP -.B \-\-inactive n [bytes] -Causes OpenVPN to exit after -.B n -seconds of inactivity on the TUN/TAP device. The time length of -inactivity is measured since the last incoming or outgoing tunnel -packet. The default value is 0 seconds, which disables this feature. - -If the optional -.B bytes -parameter is included, -exit if less than -.B bytes -of combined in/out traffic are produced on the tun/tap device -in -.B n -seconds. - -In any case, OpenVPN's internal ping packets (which are just -keepalives) and TLS control packets are not considered -"activity", nor are they counted as traffic, as they are used -internally by OpenVPN and are not an indication of actual user -activity. -.\"********************************************************* -.TP -.B \-\-ping n -Ping remote over the TCP/UDP control channel -if no packets have been sent for at least -.B n -seconds (specify -.B \-\-ping -on both peers to cause ping packets to be sent in both directions since -OpenVPN ping packets are not echoed like IP ping packets). -When used in one of OpenVPN's secure modes (where -.B \-\-secret, \-\-tls\-server, -or -.B \-\-tls\-client -is specified), the ping packet -will be cryptographically secure. - -This option has two intended uses: - -(1) Compatibility -with stateful firewalls. The periodic ping will ensure that -a stateful firewall rule which allows OpenVPN UDP packets to -pass will not time out. - -(2) To provide a basis for the remote to test the existence -of its peer using the -.B \-\-ping\-exit -option. -.\"********************************************************* -.TP -.B \-\-ping\-exit n -Causes OpenVPN to exit after -.B n -seconds pass without reception of a ping -or other packet from remote. -This option can be combined with -.B \-\-inactive, \-\-ping, -and -.B \-\-ping\-exit -to create a two\-tiered inactivity disconnect. - -For example, - -.B openvpn [options...] \-\-inactive 3600 \-\-ping 10 \-\-ping\-exit 60 - -when used on both peers will cause OpenVPN to exit within 60 -seconds if its peer disconnects, but will exit after one -hour if no actual tunnel data is exchanged. -.\"********************************************************* -.TP -.B \-\-ping\-restart n -Similar to -.B \-\-ping\-exit, -but trigger a -.B SIGUSR1 -restart after -.B n -seconds pass without reception of a ping -or other packet from remote. - -This option is useful in cases -where the remote peer has a dynamic IP address and -a low\-TTL DNS name is used to track the IP address using -a service such as -.I http://dyndns.org/ -+ a dynamic DNS client such -as -.B ddclient. - -If the peer cannot be reached, a restart will be triggered, causing -the hostname used with -.B \-\-remote -to be re\-resolved (if -.B \-\-resolv\-retry -is also specified). - -In server mode, -.B \-\-ping\-restart, \-\-inactive, -or any other type of internally generated signal will always be -applied to -individual client instance objects, never to whole server itself. -Note also in server mode that any internally generated signal -which would normally cause a restart, will cause the deletion -of the client instance object instead. - -In client mode, the -.B \-\-ping\-restart -parameter is set to 120 seconds by default. This default will -hold until the client pulls a replacement value from the server, based on -the -.B \-\-keepalive -setting in the server configuration. -To disable the 120 second default, set -.B \-\-ping\-restart 0 -on the client. - -See the signals section below for more information -on -.B SIGUSR1. - -Note that the behavior of -.B SIGUSR1 -can be modified by the -.B \-\-persist\-tun, \-\-persist\-key, \-\-persist\-local\-ip, -and -.B \-\-persist\-remote\-ip -options. - -Also note that -.B \-\-ping\-exit -and -.B \-\-ping\-restart -are mutually exclusive and cannot be used together. -.\"********************************************************* -.TP -.B \-\-keepalive interval timeout -A helper directive designed to simplify the expression of -.B \-\-ping -and -.B \-\-ping\-restart. - -This option can be used on both client and server side, but it is -enough to add this on the server side as it will push appropriate -.B \-\-ping -and -.B \-\-ping\-restart -options to the client. If used on both server and client, -the values pushed from server will override the client local values. - -The -.B timeout -argument will be twice as long on the server side. This ensures that -a timeout is detected on client side before the server side drops -the connection. - -For example, -.B \-\-keepalive 10 60 -expands as follows: - -.nf -.ft 3 -.in +4 - if mode server: - ping 10 # Argument: interval - ping\-restart 120 # Argument: timeout*2 - push "ping 10" # Argument: interval - push "ping\-restart 60" # Argument: timeout - else - ping 10 # Argument: interval - ping\-restart 60 # Argument: timeout -.in -4 -.ft -.fi -.\"********************************************************* -.TP -.B \-\-ping\-timer\-rem -Run the -.B \-\-ping\-exit -/ -.B \-\-ping\-restart -timer only if we have a remote address. Use this option if you are -starting the daemon in listen mode (i.e. without an explicit -.B \-\-remote -peer), and you don't want to start clocking timeouts until a remote -peer connects. -.\"********************************************************* -.TP -.B \-\-persist\-tun -Don't close and reopen TUN/TAP device or run up/down scripts -across -.B SIGUSR1 -or -.B \-\-ping\-restart -restarts. - -.B SIGUSR1 -is a restart signal similar to -.B SIGHUP, -but which offers finer\-grained control over -reset options. -.\"********************************************************* -.TP -.B \-\-persist\-key -Don't re\-read key files across -.B SIGUSR1 -or -.B \-\-ping\-restart. - -This option can be combined with -.B \-\-user nobody -to allow restarts triggered by the -.B SIGUSR1 -signal. -Normally if you drop root privileges in OpenVPN, -the daemon cannot be restarted since it will now be unable to re\-read protected -key files. - -This option solves the problem by persisting keys across -.B SIGUSR1 -resets, so they don't need to be re\-read. -.\"********************************************************* -.TP -.B \-\-persist\-local\-ip -Preserve initially resolved local IP address and port number -across -.B SIGUSR1 -or -.B \-\-ping\-restart -restarts. -.\"********************************************************* -.TP -.B \-\-persist\-remote\-ip -Preserve most recently authenticated remote IP address and port number -across -.B SIGUSR1 -or -.B \-\-ping\-restart -restarts. -.\"********************************************************* -.TP -.B \-\-mlock -Disable paging by calling the POSIX mlockall function. -Requires that OpenVPN be initially run as root (though -OpenVPN can subsequently downgrade its UID using the -.B \-\-user -option). - -Using this option ensures that key material and tunnel -data are never written to disk due to virtual -memory paging operations which occur under most -modern operating systems. It ensures that even if an -attacker was able to crack the box running OpenVPN, he -would not be able to scan the system swap file to -recover previously used -ephemeral keys, which are used for a period of time -governed by the -.B \-\-reneg -options (see below), then are discarded. - -The downside -of using -.B \-\-mlock -is that it will reduce the amount of physical -memory available to other applications. -.\"********************************************************* -.TP -.B \-\-up cmd -Run command -.B cmd -after successful TUN/TAP device open -(pre -.B \-\-user -UID change). - -.B cmd -consists of a path to script (or executable program), optionally -followed by arguments. The path and arguments may be single\- or double\-quoted -and/or escaped using a backslash, and should be separated by one or more spaces. - -The up command is useful for specifying route -commands which route IP traffic destined for -private subnets which exist at the other -end of the VPN connection into the tunnel. - -For -.B \-\-dev tun -execute as: - -.B cmd tun_dev tun_mtu link_mtu ifconfig_local_ip ifconfig_remote_ip [ init | restart ] - -For -.B \-\-dev tap -execute as: - -.B cmd tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask [ init | restart ] - -See the "Environmental Variables" section below for -additional parameters passed as environmental variables. - -Note that if -.B cmd -includes arguments, all OpenVPN\-generated arguments will be appended -to them to build an argument list with which the executable will be -called. - -Typically, -.B cmd -will run a script to add routes to the tunnel. - -Normally the up script is called after the TUN/TAP device is opened. -In this context, the last command line parameter passed to the script -will be -.I init. -If the -.B \-\-up\-restart -option is also used, the up script will be called for restarts as -well. A restart is considered to be a partial reinitialization -of OpenVPN where the TUN/TAP instance is preserved (the -.B \-\-persist\-tun -option will enable such preservation). A restart -can be generated by a SIGUSR1 signal, a -.B \-\-ping\-restart -timeout, or a connection reset when the TCP protocol is enabled -with the -.B \-\-proto -option. If a restart occurs, and -.B \-\-up\-restart -has been specified, the up script will be called with -.I restart -as the last parameter. - -NOTE: on restart, OpenVPN will not pass the full set of environment -variables to the script. Namely, everything related to routing and -gateways will not be passed, as nothing needs to be done anyway \- all -the routing setup is already in place. Additionally, the up\-restart -script will run with the downgraded UID/GID settings (if configured). - -The following standalone example shows how the -.B \-\-up -script can be called in both an initialization and restart context. -(NOTE: for security reasons, don't run the following example unless UDP port -9999 is blocked by your firewall. Also, the example will run indefinitely, -so you should abort with control\-c). - -.B openvpn \-\-dev tun \-\-port 9999 \-\-verb 4 \-\-ping\-restart 10 \-\-up 'echo up' \-\-down 'echo down' \-\-persist\-tun \-\-up\-restart - -Note that OpenVPN also provides the -.B \-\-ifconfig -option to automatically ifconfig the TUN device, -eliminating the need to define an -.B \-\-up -script, unless you also want to configure routes -in the -.B \-\-up -script. - -If -.B \-\-ifconfig -is also specified, OpenVPN will pass the ifconfig local -and remote endpoints on the command line to the -.B \-\-up -script so that they can be used to configure routes such as: - -.B route add \-net 10.0.0.0 netmask 255.255.255.0 gw $5 -.\"********************************************************* -.TP -.B \-\-up\-delay -Delay TUN/TAP open and possible -.B \-\-up -script execution -until after TCP/UDP connection establishment with peer. - -In -.B \-\-proto udp -mode, this option normally requires the use of -.B \-\-ping -to allow connection initiation to be sensed in the absence -of tunnel data, since UDP is a "connectionless" protocol. - -On Windows, this option will delay the TAP\-Win32 media state -transitioning to "connected" until connection establishment, -i.e. the receipt of the first authenticated packet from the peer. -.\"********************************************************* -.TP -.B \-\-down cmd -Run command -.B cmd -after TUN/TAP device close -(post -.B \-\-user -UID change and/or -.B \-\-chroot -). -.B cmd -consists of a path to script (or executable program), optionally -followed by arguments. The path and arguments may be single\- or double\-quoted -and/or escaped using a backslash, and should be separated by one or more spaces. - -Called with the same parameters and environmental -variables as the -.B \-\-up -option above. - -Note that if you reduce privileges by using -.B \-\-user -and/or -.B \-\-group, -your -.B \-\-down -script will also run at reduced privilege. -.\"********************************************************* -.TP -.B \-\-down\-pre -Call -.B \-\-down -cmd/script before, rather than after, TUN/TAP close. -.\"********************************************************* -.TP -.B \-\-up\-restart -Enable the -.B \-\-up -and -.B \-\-down -scripts to be called for restarts as well as initial program start. -This option is described more fully above in the -.B \-\-up -option documentation. -.\"********************************************************* -.TP -.B \-\-setenv name value -Set a custom environmental variable -.B name=value -to pass to script. -.\"********************************************************* -.TP -.B \-\-setenv FORWARD_COMPATIBLE 1 -Relax config file syntax checking so that unknown directives -will trigger a warning but not a fatal error, -on the assumption that a given unknown directive might be valid -in future OpenVPN versions. - -This option should be used with caution, as there are good security -reasons for having OpenVPN fail if it detects problems in a -config file. Having said that, there are valid reasons for wanting -new software features to gracefully degrade when encountered by -older software versions. - -It is also possible to tag a single directive so as not to trigger -a fatal error if the directive isn't recognized. To do this, -prepend the following before the directive: -.B setenv opt - -Versions prior to OpenVPN 2.3.3 will always ignore options set with the -.B setenv opt -directive. - -See also -.B \-\-ignore\-unknown\-option -.\"********************************************************* -.TP -.B \-\-setenv\-safe name value -Set a custom environmental variable -.B OPENVPN_name=value -to pass to script. - -This directive is designed to be pushed by the server to clients, -and the prepending of "OPENVPN_" to the environmental variable -is a safety precaution to prevent a LD_PRELOAD style attack -from a malicious or compromised server. -.\"********************************************************* -.TP -.B \-\-ignore\-unknown\-option opt1 opt2 opt3 ... optN -When one of options -.B opt1 ... optN -is encountered in the configuration file the configuration -file parsing does not fail if this OpenVPN version does not -support the option. Multiple -.B \-\-ignore\-unknown\-option -options can be given to support a larger number of options to ignore. - -This option should be used with caution, as there are good security -reasons for having OpenVPN fail if it detects problems in a -config file. Having said that, there are valid reasons for wanting -new software features to gracefully degrade when encountered by -older software versions. - -.B \-\-ignore\-unknown\-option -is available since OpenVPN 2.3.3. -.\"********************************************************* -.TP -.B \-\-script\-security level -This directive offers policy\-level control over OpenVPN's usage of external programs -and scripts. Lower -.B level -values are more restrictive, higher values are more permissive. Settings for -.B level: - -.B 0 \-\- -Strictly no calling of external programs. -.br -.B 1 \-\- -(Default) Only call built\-in executables such as ifconfig, ip, route, or netsh. -.br -.B 2 \-\- -Allow calling of built\-in executables and user\-defined scripts. -.br -.B 3 \-\- -Allow passwords to be passed to scripts via environmental variables (potentially unsafe). - -OpenVPN releases before v2.3 also supported a -.B method -flag which indicated how OpenVPN should call external commands and scripts. This -could be either -.B execve -or -.B system. -As of OpenVPN 2.3, this flag is no longer accepted. In most *nix environments the execve() -approach has been used without any issues. - -Some directives such as \-\-up allow options to be passed to the external -script. In these cases make sure the script name does not contain any spaces or -the configuration parser will choke because it can't determine where the script -name ends and script options start. - -To run scripts in Windows in earlier OpenVPN -versions you needed to either add a full path to the script interpreter which can parse the -script or use the -.B system -flag to run these scripts. As of OpenVPN 2.3 it is now a strict requirement to have -full path to the script interpreter when running non\-executables files. -This is not needed for executable files, such as .exe, .com, .bat or .cmd files. For -example, if you have a Visual Basic script, you must use this syntax now: - -.nf -.ft 3 -.in +4 -\-\-up 'C:\\\\Windows\\\\System32\\\\wscript.exe C:\\\\Program\\ Files\\\\OpenVPN\\\\config\\\\my\-up\-script.vbs' -.in -4 -.ft -.fi - -Please note the single quote marks and the escaping of the backslashes (\\) and -the space character. - -The reason the support for the -.B system -flag was removed is due to the security implications with shell expansions -when executing scripts via the system() call. -.\"********************************************************* -.TP -.B \-\-disable\-occ -Don't output a warning message if option inconsistencies are detected between -peers. An example of an option inconsistency would be where one peer uses -.B \-\-dev tun -while the other peer uses -.B \-\-dev tap. - -Use of this option is discouraged, but is provided as -a temporary fix in situations where a recent version of OpenVPN must -connect to an old version. -.\"********************************************************* -.TP -.B \-\-user user -Change the user ID of the OpenVPN process to -.B user -after initialization, dropping privileges in the process. -This option is useful to protect the system -in the event that some hostile party was able to gain control of -an OpenVPN session. Though OpenVPN's security features make -this unlikely, it is provided as a second line of defense. - -By setting -.B user -to -.I nobody -or somebody similarly unprivileged, the hostile party would be -limited in what damage they could cause. Of course once -you take away privileges, you cannot return them -to an OpenVPN session. This means, for example, that if -you want to reset an OpenVPN daemon with a -.B SIGUSR1 -signal -(for example in response -to a DHCP reset), you should make use of one or more of the -.B \-\-persist -options to ensure that OpenVPN doesn't need to execute any privileged -operations in order to restart (such as re\-reading key files -or running -.BR ifconfig -on the TUN device). -.\"********************************************************* -.TP -.B \-\-group group -Similar to the -.B \-\-user -option, -this option changes the group ID of the OpenVPN process to -.B group -after initialization. -.\"********************************************************* -.TP -.B \-\-cd dir -Change directory to -.B dir -prior to reading any files such as -configuration files, key files, scripts, etc. -.B dir -should be an absolute path, with a leading "/", -and without any references -to the current directory such as "." or "..". - -This option is useful when you are running -OpenVPN in -.B \-\-daemon -mode, and you want to consolidate all of -your OpenVPN control files in one location. -.\"********************************************************* -.TP -.B \-\-chroot dir -Chroot to -.B dir -after initialization. -.B \-\-chroot -essentially redefines -.B dir -as being the top -level directory tree (/). OpenVPN will therefore -be unable to access any files outside this tree. -This can be desirable from a security standpoint. - -Since the chroot operation is delayed until after -initialization, most OpenVPN options that reference -files will operate in a pre\-chroot context. - -In many cases, the -.B dir -parameter can point to an empty directory, however -complications can result when scripts or restarts -are executed after the chroot operation. - -Note: The SSL library will probably need /dev/urandom to be available inside -the chroot directory -.B dir. -This is because SSL libraries occasionally need to collect fresh random. Newer -linux kernels and some BSDs implement a getrandom() or getentropy() syscall -that removes the need for /dev/urandom to be available. -.\"********************************************************* -.TP -.B \-\-setcon context -Apply SELinux -.B context -after initialization. This -essentially provides the ability to restrict OpenVPN's -rights to only network I/O operations, thanks to -SELinux. This goes further than -.B \-\-user -and -.B \-\-chroot -in that those two, while being great security features, -unfortunately do not protect against privilege escalation -by exploitation of a vulnerable system call. You can of -course combine all three, but please note that since -setcon requires access to /proc you will have to provide -it inside the chroot directory (e.g. with mount \-\-bind). - -Since the setcon operation is delayed until after -initialization, OpenVPN can be restricted to just -network\-related system calls, whereas by applying the -context before startup (such as the OpenVPN one provided -in the SELinux Reference Policies) you will have to -allow many things required only during initialization. - -Like with chroot, complications can result when scripts -or restarts are executed after the setcon operation, -which is why you should really consider using the -.B \-\-persist\-key -and -.B \-\-persist\-tun -options. -.\"********************************************************* -.TP -.B \-\-daemon [progname] -Become a daemon after all initialization functions are completed. -This option will cause all message and error output to -be sent to the syslog file (such as /var/log/messages), -except for the output of scripts and -ifconfig commands, -which will go to /dev/null unless otherwise redirected. -The syslog redirection occurs immediately at the point -that -.B \-\-daemon -is parsed on the command line even though -the daemonization point occurs later. If one of the -.B \-\-log -options is present, it will supercede syslog -redirection. - -The optional -.B progname -parameter will cause OpenVPN to report its program name -to the system logger as -.B progname. -This can be useful in linking OpenVPN messages -in the syslog file with specific tunnels. -When unspecified, -.B progname -defaults to "openvpn". - -When OpenVPN is run with the -.B \-\-daemon -option, it will try to delay daemonization until the majority of initialization -functions which are capable of generating fatal errors are complete. This means -that initialization scripts can test the return status of the -openvpn command for a fairly reliable indication of whether the command -has correctly initialized and entered the packet forwarding event loop. - -In OpenVPN, the vast majority of errors which occur after initialization are non\-fatal. - -Note: as soon as OpenVPN has daemonized, it can not ask for usernames, -passwords, or key pass phrases anymore. This has certain consequences, -namely that using a password\-protected private key will fail unless the -.B \-\-askpass -option is used to tell OpenVPN to ask for the pass phrase (this -requirement is new in v2.3.7, and is a consequence of calling daemon() -before initializing the crypto layer). - -Further, using -.B \-\-daemon -together with -.B \-\-auth\-user\-pass -(entered on console) and -.B \-\-auth\-nocache -will fail as soon as key renegotiation (and reauthentication) occurs. -.\"********************************************************* -.TP -.B \-\-syslog [progname] -Direct log output to system logger, but do not become a daemon. -See -.B \-\-daemon -directive above for description of -.B progname -parameter. -.TP -.B \-\-errors\-to\-stderr -Output errors to stderr instead of stdout unless log output is redirected by one of the -.B \-\-log -options. -.\"********************************************************* -.TP -.B \-\-passtos -Set the TOS field of the tunnel packet to what the payload's TOS is. -.\"********************************************************* -.TP -.B \-\-inetd [wait|nowait] [progname] -Use this option when OpenVPN is being run from the inetd or -.BR xinetd(8) -server. - -The -.B wait/nowait -option must match what is specified in the inetd/xinetd -config file. The -.B nowait -mode can only be used with -.B \-\-proto tcp\-server. -The default is -.B wait. -The -.B nowait -mode can be used to instantiate the OpenVPN daemon as a classic TCP server, -where client connection requests are serviced on a single -port number. For additional information on this kind of configuration, -see the OpenVPN FAQ: -.I http://openvpn.net/faq.html#oneport - -This option precludes the use of -.B \-\-daemon, \-\-local, -or -.B \-\-remote. -Note that this option causes message and error output to be handled in the same -way as the -.B \-\-daemon -option. The optional -.B progname -parameter is also handled exactly as in -.B \-\-daemon. - -Also note that in -.B wait -mode, each OpenVPN tunnel requires a separate TCP/UDP port and -a separate inetd or xinetd entry. See the OpenVPN 1.x HOWTO for an example -on using OpenVPN with xinetd: -.I http://openvpn.net/1xhowto.html -.\"********************************************************* -.TP -.B \-\-log file -Output logging messages to -.B file, -including output to stdout/stderr which -is generated by called scripts. -If -.B file -already exists it will be truncated. -This option takes effect -immediately when it is parsed in the command line -and will supercede syslog output if -.B \-\-daemon -or -.B \-\-inetd -is also specified. -This option is persistent over the entire course of -an OpenVPN instantiation and will not be reset by SIGHUP, -SIGUSR1, or -.B \-\-ping\-restart. - -Note that on Windows, when OpenVPN is started as a service, -logging occurs by default without the need to specify -this option. -.\"********************************************************* -.TP -.B \-\-log\-append file -Append logging messages to -.B file. -If -.B file -does not exist, it will be created. -This option behaves exactly like -.B \-\-log -except that it appends to rather -than truncating the log file. -.\"********************************************************* -.TP -.B \-\-suppress\-timestamps -Avoid writing timestamps to log messages, even when they -otherwise would be prepended. In particular, this applies to -log messages sent to stdout. -.\"********************************************************* -.TP -.B \-\-machine\-readable\-output -Always write timestamps and message flags to log messages, even when they -otherwise would not be prefixed. In particular, this applies to -log messages sent to stdout. -.\"********************************************************* -.TP -.B \-\-writepid file -Write OpenVPN's main process ID to -.B file. -.\"********************************************************* -.TP -.B \-\-nice n -Change process priority after initialization -( -.B n -greater than 0 is lower priority, -.B n -less than zero is higher priority). -.\"********************************************************* -.\".TP -.\".B \-\-nice\-work n -.\"Change priority of background TLS work thread. The TLS thread -.\"feature is enabled when OpenVPN is built -.\"with pthread support, and you are running OpenVPN -.\"in TLS mode (i.e. with -.\".B \-\-tls\-client -.\"or -.\".B \-\-tls\-server -.\"specified). -.\" -.\"Using a TLS thread offloads the CPU\-intensive process of SSL/TLS\-based -.\"key exchange to a background thread so that it does not become -.\"a latency bottleneck in the tunnel packet forwarding process. -.\" -.\"The parameter -.\".B n -.\"is interpreted exactly as with the -.\".B \-\-nice -.\"option above, but in relation to the work thread rather -.\"than the main thread. -.\"********************************************************* -.TP -.B \-\-fast\-io -(Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding -a call to poll/epoll/select prior to the write operation. The purpose -of such a call would normally be to block until the device -or socket is ready to accept the write. Such blocking is unnecessary -on some platforms which don't support write blocking on UDP sockets -or TUN/TAP devices. In such cases, one can optimize the event loop -by avoiding the poll/epoll/select call, improving CPU efficiency -by 5% to 10%. - -This option can only be used on non\-Windows systems, when -.B \-\-proto udp -is specified, and when -.B \-\-shaper -is NOT specified. -.\"********************************************************* -.TP -.B \-\-multihome -Configure a multi\-homed UDP server. This option needs to be used when -a server has more than one IP address (e.g. multiple interfaces, or -secondary IP addresses), and is not using -.B \-\-local -to force binding to one specific address only. This option will -add some extra lookups to the packet path to ensure that the UDP reply -packets are always sent from the address that the client is -talking to. This is not supported on all platforms, and it adds more -processing, so it's not enabled by default. - -Note: this option is only relevant for UDP servers. - -Note 2: if you do an IPv6+IPv4 dual\-stack bind on a Linux machine with -multiple IPv4 address, connections to IPv4 addresses will not work -right on kernels before 3.15, due to missing kernel support for the -IPv4\-mapped case (some distributions have ported this to earlier kernel -versions, though). -.\"********************************************************* -.TP -.B \-\-echo [parms...] -Echo -.B parms -to log output. - -Designed to be used to send messages to a controlling application -which is receiving the OpenVPN log output. -.\"********************************************************* -.TP -.B \-\-remap\-usr1 signal -Control whether internally or externally -generated SIGUSR1 signals are remapped to -SIGHUP (restart without persisting state) or -SIGTERM (exit). - -.B signal -can be set to "SIGHUP" or "SIGTERM". By default, no remapping -occurs. -.\"********************************************************* -.TP -.B \-\-verb n -Set output verbosity to -.B n -(default=1). Each level shows all info from the previous levels. -Level 3 is recommended if you want a good summary -of what's happening without being swamped by output. - -.B 0 \-\- -No output except fatal errors. -.br -.B 1 to 4 \-\- -Normal usage range. -.br -.B 5 \-\- -Output -.B R -and -.B W -characters to the console for each packet read and write, uppercase is -used for TCP/UDP packets and lowercase is used for TUN/TAP packets. -.br -.B 6 to 11 \-\- -Debug info range (see errlevel.h for additional -information on debug levels). -.\"********************************************************* -.TP -.B \-\-status file [n] -Write operational status to -.B file -every -.B n -seconds. - -Status can also be written to the syslog by sending a -.B SIGUSR2 -signal. - -With multi\-client capability enabled on a server, the status file includes a -list of clients and a routing table. The output format can be controlled by the -.B \-\-status\-version -option in that case. - -For clients or instances running in point\-to\-point mode, it will contain the -traffic statistics. -.\"********************************************************* -.TP -.B \-\-status\-version [n] -Set the status file format version number to -.B n\fR. - -This only affects the status file on servers with multi\-client capability -enabled. - -.B 1 -\-\- traditional format (default). The client list contains the following -fields comma\-separated: Common Name, Real Address, Bytes Received, Bytes Sent, -Connected Since. -.br -.B 2 -\-\- a more reliable format for external processing. Compared to version 1, the -client list contains some additional fields: Virtual Address, Virtual IPv6 -Address, Username, Client ID, Peer ID. -Future versions may extend the number of fields. -.br -.B 3 -\-\- identical to 2, but fields are tab\-separated. - -.\"********************************************************* -.TP -.B \-\-mute n -Log at most -.B n -consecutive messages in the same category. This is useful to -limit repetitive logging of similar message types. -.\"********************************************************* -.TP -.B \-\-compress [algorithm] -Enable a compression algorithm. - -The -.B algorithm -parameter may be "lzo", "lz4", or empty. LZO and LZ4 -are different compression algorithms, with LZ4 generally -offering the best performance with least CPU usage. -For backwards compatibility with OpenVPN versions before v2.4, use "lzo" -(which is identical to the older option "\-\-comp\-lzo yes"). - -If the -.B algorithm -parameter is empty, compression will be turned off, but the packet -framing for compression will still be enabled, allowing a different -setting to be pushed later. - -.B Security Considerations - -Compression and encryption is a tricky combination. If an attacker knows or is -able to control (parts of) the plaintext of packets that contain secrets, the -attacker might be able to extract the secret if compression is enabled. See -e.g. the CRIME and BREACH attacks on TLS which also leverage compression to -break encryption. If you are not entirely sure that the above does not apply -to your traffic, you are advised to *not* enable compression. - -.\"********************************************************* -.TP -.B \-\-comp\-lzo [mode] -.B DEPRECATED -This option will be removed in a future OpenVPN release. Use the -newer -.B \-\-compress -instead. - -Use LZO compression \-\- may add up to 1 byte per -packet for incompressible data. -.B mode -may be "yes", "no", or "adaptive" (default). - -In a server mode setup, it is possible to selectively turn -compression on or off for individual clients. - -First, make sure the client\-side config file enables selective -compression by having at least one -.B \-\-comp\-lzo -directive, such as -.B \-\-comp\-lzo no. -This will turn off compression by default, -but allow a future directive push from the server to -dynamically change the -on/off/adaptive setting. - -Next in a -.B \-\-client\-config\-dir -file, specify the compression setting for the client, -for example: - -.nf -.ft 3 -.in +4 -comp\-lzo yes -push "comp\-lzo yes" -.in -4 -.ft -.fi - -The first line sets the -.B comp\-lzo -setting for the server -side of the link, the second sets the client side. -.\"********************************************************* -.TP -.B \-\-comp\-noadapt -When used in conjunction with -.B \-\-comp\-lzo, -this option will disable OpenVPN's adaptive compression algorithm. -Normally, adaptive compression is enabled with -.B \-\-comp\-lzo. - -Adaptive compression tries to optimize the case where you have -compression enabled, but you are sending predominantly incompressible -(or pre\-compressed) packets over the tunnel, such as an FTP or rsync transfer -of a large, compressed file. With adaptive compression, -OpenVPN will periodically sample the compression process to measure its -efficiency. If the data being sent over the tunnel is already compressed, -the compression efficiency will be very low, triggering openvpn to disable -compression for a period of time until the next re\-sample test. -.\"********************************************************* -.TP -.B \-\-management socket\-name unix [pw\-file] \ \ \ \ \ (recommended) -.TQ -.B \-\-management IP port [pw\-file] -Enable a management server on a -.B socket\-name -Unix socket on those platforms supporting it, or on -a designated TCP port. - -.B pw\-file -, if specified, is a password file where the password must be on first line. -Instead of a filename it can use the keyword stdin which will prompt the user -for a password to use when OpenVPN is starting. - -For unix sockets, the default behaviour is to create a unix domain socket -that may be connected to by any process. Use the -.B \-\-management\-client\-user -and -.B \-\-management\-client\-group -directives to restrict access. - -The management interface provides a special mode where the TCP management link -can operate over the tunnel itself. To enable this mode, set IP to -.B tunnel. -Tunnel mode will cause the management interface to listen for a -TCP connection on the local VPN address of the TUN/TAP interface. - -.B BEWARE -of enabling the management interface over TCP. In these cases you should -.I ALWAYS -make use of -.B pw\-file -to password protect the management interface. Any user who can connect to this -TCP -.B IP:port -will be able to manage and control (and interfere with) the OpenVPN process. -It is also strongly recommended to set IP to 127.0.0.1 (localhost) to restrict -accessibility of the management server to local clients. - -While the management port is designed for programmatic control of OpenVPN by -other applications, it is possible to telnet to the port, using a telnet client -in "raw" mode. Once connected, type "help" for a list of commands. - -For detailed documentation on the management interface, see the -.I management\-notes.txt -file in the management folder of the OpenVPN source distribution. - -.TP -.B \-\-management\-client -Management interface will connect as a TCP/unix domain client to -.B IP:port -specified by -.B \-\-management -rather than listen as a TCP server or on a unix domain socket. - -If the client connection fails to connect or is disconnected, -a SIGTERM signal will be generated causing OpenVPN to quit. -.\"********************************************************* -.TP -.B \-\-management\-query\-passwords -Query management channel for private key password and -.B \-\-auth\-user\-pass -username/password. Only query the management channel -for inputs which ordinarily would have been queried from the -console. -.\"********************************************************* -.TP -.B \-\-management\-query\-proxy -Query management channel for proxy server information for a specific -.B \-\-remote -(client\-only). -.\"********************************************************* -.TP -.B \-\-management\-query\-remote -Allow management interface to override -.B \-\-remote -directives (client\-only). -.\"********************************************************* -.TP -.B \-\-management\-external\-key -Allows usage for external private key file instead of -.B \-\-key -option (client\-only). -.\"********************************************************* -.TP -.B \-\-management\-external\-cert certificate\-hint -Allows usage for external certificate instead of -.B \-\-cert -option (client\-only). -.B certificate\-hint -is an arbitrary string which is passed to a management -interface client as an argument of NEED\-CERTIFICATE notification. -Requires \-\-management\-external\-key. -.\"********************************************************* -.TP -.B \-\-management\-forget\-disconnect -Make OpenVPN forget passwords when management session -disconnects. - -This directive does not affect the -.B \-\-http\-proxy -username/password. It is always cached. -.\"********************************************************* -.TP -.B \-\-management\-hold -Start OpenVPN in a hibernating state, until a client -of the management interface explicitly starts it -with the -.B hold release -command. -.\"********************************************************* -.TP -.B \-\-management\-signal -Send SIGUSR1 signal to OpenVPN if management session disconnects. -This is useful when you wish to disconnect an OpenVPN session on -user logoff. For \-\-management\-client this option is not needed since -a disconnect will always generate a SIGTERM. -.\"********************************************************* -.TP -.B \-\-management\-log\-cache n -Cache the most recent -.B n -lines of log file history for usage -by the management channel. -.\"********************************************************* -.TP -.B \-\-management\-up\-down -Report tunnel up/down events to management interface. -.B -.\"********************************************************* -.TP -.B \-\-management\-client\-auth -Gives management interface client the responsibility -to authenticate clients after their client certificate -has been verified. See management\-notes.txt in OpenVPN -distribution for detailed notes. -.\"********************************************************* -.TP -.B \-\-management\-client\-pf -Management interface clients must specify a packet -filter file for each connecting client. See management\-notes.txt -in OpenVPN distribution for detailed notes. -.\"********************************************************* -.TP -.B \-\-management\-client\-user u -When the management interface is listening on a unix domain socket, -only allow connections from user -.B u. -.\"********************************************************* -.TP -.B \-\-management\-client\-group g -When the management interface is listening on a unix domain socket, -only allow connections from group -.B g. -.\"********************************************************* -.TP -.B \-\-plugin module\-pathname [init\-string] -Load plug\-in module from the file -.B module\-pathname, -passing -.B init\-string -as an argument -to the module initialization function. Multiple -plugin modules may be loaded into one OpenVPN -process. - -The -.B module\-pathname -argument can be just a filename or a filename with a relative -or absolute path. The format of the filename and path defines -if the plug\-in will be loaded from a default plug\-in directory -or outside this directory. - -.nf -.ft 3 -.in +4 -.B \-\-plugin path\ \ \ \ \ \ \ \ Effective directory used -==================================================== - myplug.so DEFAULT_DIR/myplug.so - subdir/myplug.so DEFAULT_DIR/subdir/myplug.so - ./subdir/myplug.so CWD/subdir/myplug.so - /usr/lib/my/plug.so /usr/lib/my/plug.so -.in -4 -.fi - -DEFAULT_DIR is replaced by the default plug\-in directory, -which is configured at the build time of OpenVPN. CWD is the -current directory where OpenVPN was started or the directory -OpenVPN have swithed into via the -.B \-\-cd -option before the -.B \-\-plugin -option. - -For more information and examples on how to build OpenVPN -plug\-in modules, see the README file in the -.B plugin -folder of the OpenVPN source distribution. - -If you are using an RPM install of OpenVPN, see -/usr/share/openvpn/plugin. The documentation is -in -.B doc -and the actual plugin modules are in -.B lib. - -Multiple plugin modules can be cascaded, and modules can be -used in tandem with scripts. The modules will be called by -OpenVPN in the order that they are declared in the config -file. If both a plugin and script are configured for the same -callback, the script will be called last. If the -return code of the module/script controls an authentication -function (such as tls\-verify, auth\-user\-pass\-verify, or -client\-connect), then -every module and script must return success (0) in order for -the connection to be authenticated. -.\"********************************************************* -.TP -.B \-\-keying\-material\-exporter label len -Save Exported Keying Material [RFC5705] of len bytes (must be -between 16 and 4095 bytes) using label in environment -(exported_keying_material) for use by plugins in -OPENVPN_PLUGIN_TLS_FINAL callback. - -Note that exporter labels have the potential to collide with existing PRF -labels. In order to prevent this, labels MUST begin with "EXPORTER". - -This option requires OpenSSL 1.0.1 or newer. -.\"********************************************************* -.SS Server Mode -Starting with OpenVPN 2.0, a multi\-client TCP/UDP server mode -is supported, and can be enabled with the -.B \-\-mode server -option. In server mode, OpenVPN will listen on a single -port for incoming client connections. All client -connections will be routed through a single tun or tap -interface. This mode is designed for scalability and should -be able to support hundreds or even thousands of clients -on sufficiently fast hardware. SSL/TLS authentication must -be used in this mode. -.\"********************************************************* -.TP -.B \-\-server network netmask ['nopool'] -A helper directive designed to simplify the configuration -of OpenVPN's server mode. This directive will set up an -OpenVPN server which will allocate addresses to clients -out of the given network/netmask. The server itself -will take the ".1" address of the given network -for use as the server\-side endpoint of the local -TUN/TAP interface. - -For example, -.B \-\-server 10.8.0.0 255.255.255.0 -expands as follows: - -.nf -.ft 3 -.in +4 - mode server - tls\-server - push "topology [topology]" - - if dev tun AND (topology == net30 OR topology == p2p): - ifconfig 10.8.0.1 10.8.0.2 - if !nopool: - ifconfig\-pool 10.8.0.4 10.8.0.251 - route 10.8.0.0 255.255.255.0 - if client\-to\-client: - push "route 10.8.0.0 255.255.255.0" - else if topology == net30: - push "route 10.8.0.1" - - if dev tap OR (dev tun AND topology == subnet): - ifconfig 10.8.0.1 255.255.255.0 - if !nopool: - ifconfig\-pool 10.8.0.2 10.8.0.253 255.255.255.0 - push "route\-gateway 10.8.0.1" - if route\-gateway unset: - route\-gateway 10.8.0.2 - -.in -4 -.ft -.fi - -Don't use -.B \-\-server -if you are ethernet bridging. Use -.B \-\-server\-bridge -instead. -.\"********************************************************* -.TP -.B \-\-server\-bridge gateway netmask pool\-start\-IP pool\-end\-IP -.TP -.B \-\-server\-bridge ['nogw'] - -A helper directive similar to -.B \-\-server -which is designed to simplify the configuration -of OpenVPN's server mode in ethernet bridging configurations. - -If -.B \-\-server\-bridge -is used without any parameters, it will enable a DHCP\-proxy -mode, where connecting OpenVPN clients will receive an IP -address for their TAP adapter from the DHCP server running -on the OpenVPN server\-side LAN. -Note that only clients that support -the binding of a DHCP client with the TAP adapter (such as -Windows) can support this mode. The optional -.B nogw -flag (advanced) indicates that gateway information should not be -pushed to the client. - -To configure ethernet bridging, you -must first use your OS's bridging capability -to bridge the TAP interface with the ethernet -NIC interface. For example, on Linux this is done -with the -.B brctl -tool, and with Windows XP it is done in the Network -Connections Panel by selecting the ethernet and -TAP adapters and right\-clicking on "Bridge Connections". - -Next you you must manually set the -IP/netmask on the bridge interface. The -.B gateway -and -.B netmask -parameters to -.B \-\-server\-bridge -can be set to either the IP/netmask of the -bridge interface, or the IP/netmask of the -default gateway/router on the bridged -subnet. - -Finally, set aside a IP range in the bridged -subnet, -denoted by -.B pool\-start\-IP -and -.B pool\-end\-IP, -for OpenVPN to allocate to connecting -clients. - -For example, -.B server\-bridge 10.8.0.4 255.255.255.0 10.8.0.128 10.8.0.254 -expands as follows: - -.nf -.ft 3 -.in +4 -mode server -tls\-server - -ifconfig\-pool 10.8.0.128 10.8.0.254 255.255.255.0 -push "route\-gateway 10.8.0.4" -.in -4 -.ft -.fi - -In another example, -.B \-\-server\-bridge -(without parameters) expands as follows: - -.nf -.ft 3 -.in +4 -mode server -tls\-server - -push "route\-gateway dhcp" -.in -4 -.ft -.fi - -Or -.B \-\-server\-bridge nogw -expands as follows: - -.nf -.ft 3 -.in +4 -mode server -tls\-server -.in -4 -.ft -.fi -.\"********************************************************* -.TP -.B \-\-push "option" -Push a config file option back to the client for remote -execution. Note that -.B -option -must be enclosed in double quotes (""). The client must specify -.B \-\-pull -in its config file. The set of options which can be -pushed is limited by both feasibility and security. -Some options such as those which would execute scripts -are banned, since they would effectively allow a compromised -server to execute arbitrary code on the client. -Other options such as TLS or MTU parameters -cannot be pushed because the client needs to know -them before the connection to the server can be initiated. - -This is a partial list of options which can currently be pushed: -.B \-\-route, \-\-route\-gateway, \-\-route\-delay, \-\-redirect\-gateway, -.B \-\-ip\-win32, \-\-dhcp\-option, -.B \-\-inactive, \-\-ping, \-\-ping\-exit, \-\-ping\-restart, -.B \-\-setenv, -.B \-\-auth\-token, -.B \-\-persist\-key, \-\-persist\-tun, \-\-echo, -.B \-\-comp\-lzo, -.B \-\-socket\-flags, -.B \-\-sndbuf, \-\-rcvbuf -.\"********************************************************* -.TP -.B \-\-push\-reset -Don't inherit the global push list for a specific client instance. -Specify this option in a client\-specific context such -as with a -.B \-\-client\-config\-dir -configuration file. This option will ignore -.B \-\-push -options at the global config file level. -.\"********************************************************* -.TP -.B \-\-push\-remove opt -selectively remove all -.B \-\-push -options matching "opt" from the option list for a client. "opt" is matched -as a substring against the whole option string to\-be\-pushed to the client, so -.B \-\-push\-remove route -would remove all -.B \-\-push route ... -and -.B \-\-push route\-ipv6 ... -statements, while -.B \-\-push\-remove 'route\-ipv6 2001:' -would only remove IPv6 routes for 2001:... networks. - -.B \-\-push\-remove -can only be used in a client\-specific context, like in a -.B \-\-client\-config\-dir -file, or -.B \-\-client\-connect -script or plugin \-\- similar to -.B \-\-push\-reset, -just more selective. - -NOTE: to -.I change -an option, -.B \-\-push\-remove -can be used to first remove the old value, and then add a new -.B \-\-push -option with the new value. -.\"********************************************************* -.TP -.B \-\-push\-peer\-info -Push additional information about the client to server. -The following data is always pushed to the server: - -IV_VER= \-\- the client OpenVPN version - -IV_PLAT=[linux|solaris|openbsd|mac|netbsd|freebsd|win] \-\- the client OS platform - -IV_LZO_STUB=1 \-\- if client was built with LZO stub capability - -IV_LZ4=1 \-\- if the client supports LZ4 compressions. - -IV_PROTO=2 \-\- if the client supports peer\-id floating mechansim - -IV_NCP=2 \-\- negotiable ciphers, client supports -.B \-\-cipher -pushed by the server, a value of 2 or greater indicates client -supports AES\-GCM\-128 and AES\-GCM\-256. - -IV_GUI_VER= \-\- the UI version of a UI if one is -running, for example "de.blinkt.openvpn 0.5.47" for the -Android app. - -When -.B \-\-push\-peer\-info -is enabled the additional information consists of the following data: - -IV_HWADDR= \-\- the MAC address of clients default gateway - -IV_SSL= \-\- the ssl version used by the client, e.g. "OpenSSL 1.0.2f 28 Jan 2016". - -IV_PLAT_VER=x.y \- the version of the operating system, e.g. 6.1 for Windows 7. - -UV_= \-\- client environment variables whose names start with "UV_" -.\"********************************************************* -.TP -.B \-\-disable -Disable a particular client (based on the common name) -from connecting. Don't use this option to disable a client -due to key or password compromise. Use a CRL (certificate -revocation list) instead (see the -.B \-\-crl\-verify -option). - -This option must be associated with a specific client instance, -which means that it must be specified either in a client -instance config file using -.B \-\-client\-config\-dir -or dynamically generated using a -.B \-\-client\-connect -script. -.\"********************************************************* -.TP -.B \-\-ifconfig\-pool start\-IP end\-IP [netmask] -Set aside a pool of subnets to be -dynamically allocated to connecting clients, similar -to a DHCP server. For tun\-style -tunnels, each client will be given a /30 subnet (for -interoperability with Windows clients). For tap\-style -tunnels, individual addresses will be allocated, and the -optional -.B netmask -parameter will also be pushed to clients. - -.\"********************************************************* -.TP -.B \-\-ifconfig\-pool\-persist file [seconds] -Persist/unpersist ifconfig\-pool -data to -.B file, -at -.B seconds -intervals (default=600), as well as on program startup and -shutdown. - -The goal of this option is to provide a long\-term association -between clients (denoted by their common name) and the virtual -IP address assigned to them from the ifconfig\-pool. -Maintaining a long\-term -association is good for clients because it allows them -to effectively use the -.B \-\-persist\-tun -option. - -.B file -is a comma\-delimited ASCII file, formatted as -,. - -If -.B seconds -= 0, -.B file -will be treated as read\-only. This is useful if -you would like to treat -.B file -as a configuration file. - -Note that the entries in this file are treated by OpenVPN as -suggestions only, based on past associations between -a common name and IP address. They do not guarantee that the given common -name will always receive the given IP address. If you want guaranteed -assignment, use -.B \-\-ifconfig\-push - -.\"********************************************************* -.TP -.B \-\-ifconfig\-pool\-linear -.B DEPRECATED -This option will be removed in OpenVPN 2.5 - -Modifies the -.B \-\-ifconfig\-pool -directive to -allocate individual TUN interface addresses for -clients rather than /30 subnets. NOTE: This option -is incompatible with Windows clients. - -This option is deprecated, and should be replaced with -.B \-\-topology p2p -which is functionally equivalent. -.\"********************************************************* -.TP -.B \-\-ifconfig\-push local remote\-netmask [alias] -Push virtual IP endpoints for client tunnel, -overriding the \-\-ifconfig\-pool dynamic allocation. - -The parameters -.B local -and -.B remote\-netmask -are set according to the -.B \-\-ifconfig -directive which you want to execute on the client machine to -configure the remote end of the tunnel. Note that the parameters -.B local -and -.B remote\-netmask -are from the perspective of the client, not the server. They may be -DNS names rather than IP addresses, in which case they will be resolved -on the server at the time of client connection. - -The optional -.B alias -parameter may be used in cases where NAT causes the client view -of its local endpoint to differ from the server view. In this case -.B local/remote\-netmask -will refer to the server view while -.B alias/remote\-netmask -will refer to the client view. - -This option must be associated with a specific client instance, -which means that it must be specified either in a client -instance config file using -.B \-\-client\-config\-dir -or dynamically generated using a -.B \-\-client\-connect -script. - -Remember also to include a -.B \-\-route -directive in the main OpenVPN config file which encloses -.B local, -so that the kernel will know to route it -to the server's TUN/TAP interface. - -OpenVPN's internal client IP address selection algorithm works as -follows: - -.B 1 -\-\- Use -.B \-\-client\-connect script -generated file for static IP (first choice). -.br -.B 2 -\-\- Use -.B \-\-client\-config\-dir -file for static IP (next choice). -.br -.B 3 -\-\- Use -.B \-\-ifconfig\-pool -allocation for dynamic IP (last choice). -.br -.\"********************************************************* -.TP -.B \-\-iroute network [netmask] -Generate an internal route to a specific -client. The -.B netmask -parameter, if omitted, defaults to 255.255.255.255. - -This directive can be used to route a fixed subnet from -the server to a particular client, regardless -of where the client is connecting from. Remember -that you must also add the route to the system -routing table as well (such as by using the -.B \-\-route -directive). The reason why two routes are needed -is that the -.B \-\-route -directive routes the packet from the kernel -to OpenVPN. Once in OpenVPN, the -.B \-\-iroute -directive routes to the specific client. - -This option must be specified either in a client -instance config file using -.B \-\-client\-config\-dir -or dynamically generated using a -.B \-\-client\-connect -script. - -The -.B \-\-iroute -directive also has an important interaction with -.B \-\-push -"route ...". -.B \-\-iroute -essentially defines a subnet which is owned by a -particular client (we will call this client A). -If you would like other clients to be able to reach A's -subnet, you can use -.B \-\-push -"route ..." -together with -.B \-\-client\-to\-client -to effect this. In order for all clients to see -A's subnet, OpenVPN must push this route to all clients -EXCEPT for A, since the subnet is already owned by A. -OpenVPN accomplishes this by not -not pushing a route to a client -if it matches one of the client's iroutes. -.\"********************************************************* -.TP -.B \-\-client\-to\-client -Because the OpenVPN server mode handles multiple clients -through a single tun or tap interface, it is effectively -a router. The -.B \-\-client\-to\-client -flag tells OpenVPN to internally route client\-to\-client -traffic rather than pushing all client\-originating traffic -to the TUN/TAP interface. - -When this option is used, each client will "see" the other -clients which are currently connected. Otherwise, each -client will only see the server. Don't use this option -if you want to firewall tunnel traffic using -custom, per\-client rules. -.\"********************************************************* -.TP -.B \-\-duplicate\-cn -Allow multiple clients with the same common name to concurrently connect. -In the absence of this option, OpenVPN will disconnect a client instance -upon connection of a new client having the same common name. -.\"********************************************************* -.TP -.B \-\-client\-connect cmd -Run -.B command cmd -on client connection. - -.B cmd -consists of a path to script (or executable program), optionally -followed by arguments. The path and arguments may be single\- or double\-quoted -and/or escaped using a backslash, and should be separated by one or more spaces. - -The command is passed the common name -and IP address of the just\-authenticated client -as environmental variables (see environmental variable section -below). The command is also passed -the pathname of a freshly created temporary file as the last argument -(after any arguments specified in -.B cmd -), to be used by the command -to pass dynamically generated config file directives back to OpenVPN. - -If the script wants to generate a dynamic config file -to be applied on the server when the client connects, -it should write it to the file named by the last argument. - -See the -.B \-\-client\-config\-dir -option below for options which -can be legally used in a dynamically generated config file. - -Note that the return value of -.B script -is significant. If -.B script -returns a non\-zero error status, it will cause the client -to be disconnected. -.\"********************************************************* -.TP -.B \-\-client\-disconnect cmd -Like -.B \-\-client\-connect -but called on client instance shutdown. Will not be called -unless the -.B \-\-client\-connect -script and plugins (if defined) -were previously called on this instance with -successful (0) status returns. - -The exception to this rule is if the -.B \-\-client\-disconnect -command or plugins are cascaded, and at least one client\-connect -function succeeded, then ALL of the client\-disconnect functions for -scripts and plugins will be called on client instance object deletion, -even in cases where some of the related client\-connect functions returned -an error status. - -The -.B \-\-client\-disconnect -command is passed the same pathname as the corresponding -.B \-\-client\-connect -command as its last argument. (after any arguments specified in -.B cmd -). -.B -.\"********************************************************* -.TP -.B \-\-client\-config\-dir dir -Specify a directory -.B dir -for custom client config files. After -a connecting client has been authenticated, OpenVPN will -look in this directory for a file having the same name -as the client's X509 common name. If a matching file -exists, it will be opened and parsed for client\-specific -configuration options. If no matching file is found, OpenVPN -will instead try to open and parse a default file called -"DEFAULT", which may be provided but is not required. Note that -the configuration files must be readable by the OpenVPN process -after it has dropped it's root privileges. - -This file can specify a fixed IP address for a given -client using -.B \-\-ifconfig\-push, -as well as fixed subnets owned by the client using -.B \-\-iroute. - -One of the useful properties of this option is that it -allows client configuration files to be conveniently -created, edited, or removed while the server is live, -without needing to restart the server. - -The following -options are legal in a client\-specific context: -.B \-\-push, \-\-push\-reset, \-\-push\-remove, \-\-iroute, \-\-ifconfig\-push, -and -.B \-\-config. -.\"********************************************************* -.TP -.B \-\-ccd\-exclusive -Require, as a -condition of authentication, that a connecting client has a -.B \-\-client\-config\-dir -file. -.\"********************************************************* -.TP -.B \-\-tmp\-dir dir -Specify a directory -.B dir -for temporary files. This directory will be used by -openvpn processes and script to communicate temporary -data with openvpn main process. Note that -the directory must be writable by the OpenVPN process -after it has dropped it's root privileges. - -This directory will be used by in the following cases: - -* -.B \-\-client\-connect -scripts to dynamically generate client\-specific -configuration files. - -* -.B OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY -plugin hook to return success/failure via auth_control_file -when using deferred auth method - -* -.B OPENVPN_PLUGIN_ENABLE_PF -plugin hook to pass filtering rules via pf_file -.\"********************************************************* -.TP -.B \-\-hash\-size r v -Set the size of the real address hash table to -.B r -and the virtual address table to -.B v. -By default, both tables are sized at 256 buckets. -.\"********************************************************* -.TP -.B \-\-bcast\-buffers n -Allocate -.B n -buffers for broadcast datagrams (default=256). -.\"********************************************************* -.TP -.B \-\-tcp\-queue\-limit n -Maximum number of output packets queued before TCP (default=64). - -When OpenVPN is tunneling data from a TUN/TAP device to a -remote client over a TCP connection, it is possible that the TUN/TAP device -might produce data at a faster rate than the TCP connection -can support. When the number of output packets queued before sending to -the TCP socket reaches this limit for a given client connection, -OpenVPN will start to drop outgoing packets directed -at this client. -.\"********************************************************* -.TP -.B \-\-tcp\-nodelay -This macro sets the TCP_NODELAY socket flag on the server -as well as pushes it to connecting clients. The TCP_NODELAY -flag disables the Nagle algorithm on TCP sockets causing -packets to be transmitted immediately with low latency, -rather than waiting a short period of time in order -to aggregate several packets into a larger containing -packet. In VPN applications over TCP, TCP_NODELAY -is generally a good latency optimization. - -The macro expands as follows: - -.nf -.ft 3 -.in +4 - if mode server: - socket\-flags TCP_NODELAY - push "socket\-flags TCP_NODELAY" -.in -4 -.ft -.fi -.\"********************************************************* -.TP -.B \-\-max\-clients n -Limit server to a maximum of -.B n -concurrent clients. -.\"********************************************************* -.TP -.B \-\-max\-routes\-per\-client n -Allow a maximum of -.B n -internal routes per client (default=256). -This is designed to -help contain DoS attacks where an authenticated client floods the -server with packets appearing to come from many unique MAC addresses, -forcing the server to deplete -virtual memory as its internal routing table expands. -This directive can be used in a -.B \-\-client\-config\-dir -file or auto\-generated by a -.B \-\-client\-connect -script to override the global value for a particular client. - -Note that this -directive affects OpenVPN's internal routing table, not the -kernel routing table. -.\"********************************************************* -.TP -.B \-\-stale\-routes\-check n [t] -Remove routes haven't had activity for -.B n -seconds (i.e. the ageing time). - -This check is ran every -.B t -seconds (i.e. check interval). - -If -.B t -is not present it defaults to -.B n - -This option helps to keep the dynamic routing table small. -See also -.B \-\-max\-routes\-per\-client -.\"********************************************************* -.TP -.B \-\-connect\-freq n sec -Allow a maximum of -.B n -new connections per -.B sec -seconds from clients. This is designed to contain DoS attacks which flood -the server with connection requests using certificates which -will ultimately fail to authenticate. - -This is an imperfect solution however, because in a real -DoS scenario, legitimate connections might also be refused. - -For the best protection against DoS attacks in server mode, -use -.B \-\-proto udp -and either -.B \-\-tls\-auth -or -.B \-\-tls\-crypt\fR. -.\"********************************************************* -.TP -.B \-\-learn\-address cmd -Run command -.B cmd -to validate client virtual addresses or routes. - -.B cmd -consists of a path to script (or executable program), optionally -followed by arguments. The path and arguments may be single\- or double\-quoted -and/or escaped using a backslash, and should be separated by one or more spaces. - -Three arguments will be appended to any arguments in -.B cmd -as follows: - -.B [1] operation \-\- -"add", "update", or "delete" based on whether or not -the address is being added to, modified, or deleted from -OpenVPN's internal routing table. -.br -.B [2] address \-\- -The address being learned or unlearned. This can be -an IPv4 address such as "198.162.10.14", an IPv4 subnet -such as "198.162.10.0/24", or an ethernet MAC address (when -.B \-\-dev tap -is being used) such as "00:FF:01:02:03:04". -.br -.B [3] common name \-\- -The common name on the certificate associated with the -client linked to this address. Only present for "add" -or "update" operations, not "delete". - -On "add" or "update" methods, if the script returns -a failure code (non\-zero), OpenVPN will reject the address -and will not modify its internal routing table. - -Normally, the -.B cmd -script will use the information provided above to set -appropriate firewall entries on the VPN TUN/TAP interface. -Since OpenVPN provides the association between virtual IP -or MAC address and the client's authenticated common name, -it allows a user\-defined script to configure firewall access -policies with regard to the client's high\-level common name, -rather than the low level client virtual addresses. -.\"********************************************************* -.TP -.B \-\-auth\-user\-pass\-verify cmd method -Require the client to provide a username/password (possibly -in addition to a client certificate) for authentication. - -OpenVPN will run -.B command cmd -to validate the username/password -provided by the client. - -.B cmd -consists of a path to script (or executable program), optionally -followed by arguments. The path and arguments may be single\- or double\-quoted -and/or escaped using a backslash, and should be separated by one or more spaces. - -If -.B method -is set to "via\-env", OpenVPN will call -.B script -with the environmental variables -.B username -and -.B password -set to the username/password strings provided by the client. -Be aware that this method is insecure on some platforms which -make the environment of a process publicly visible to other -unprivileged processes. - -If -.B method -is set to "via\-file", OpenVPN will write the username and -password to the first two lines of a temporary file. The filename -will be passed as an argument to -.B script, -and the file will be automatically deleted by OpenVPN after -the script returns. The location of the temporary file is -controlled by the -.B \-\-tmp\-dir -option, and will default to the current directory if unspecified. -For security, consider setting -.B \-\-tmp\-dir -to a volatile storage medium such as -.B /dev/shm -(if available) to prevent the username/password file from touching the hard drive. - -The script should examine the username -and password, -returning a success exit code (0) if the -client's authentication request is to be accepted, or a failure -code (1) to reject the client. - -This directive is designed to enable a plugin\-style interface -for extending OpenVPN's authentication capabilities. - -To protect against a client passing a maliciously formed -username or password string, the username string must -consist only of these characters: alphanumeric, underbar -('_'), dash ('\-'), dot ('.'), or at ('@'). The password -string can consist of any printable characters except for -CR or LF. Any illegal characters in either the username -or password string will be converted to underbar ('_'). - -Care must be taken by any user\-defined scripts to avoid -creating a security vulnerability in the way that these -strings are handled. Never use these strings in such a way -that they might be escaped or evaluated by a shell interpreter. - -For a sample script that performs PAM authentication, see -.B sample\-scripts/auth\-pam.pl -in the OpenVPN source distribution. -.\"********************************************************* -.TP -.B \-\-auth\-gen\-token [lifetime] -After successful user/password authentication, the OpenVPN -server will with this option generate a temporary -authentication token and push that to client. On the following -renegotiations, the OpenVPN client will pass this token instead -of the users password. On the server side the server will do -the token authentication internally and it will NOT do any -additional authentications against configured external -user/password authentication mechanisms. - -The -.B lifetime -argument defines how long the generated token is valid. The -lifetime is defined in seconds. If lifetime is not set -or it is set to 0, the token will never expire. - -This feature is useful for environments which is configured -to use One Time Passwords (OTP) as part of the user/password -authentications and that authentication mechanism does not -implement any auth\-token support. -.\"********************************************************* -.TP -.B \-\-opt\-verify -Clients that connect with options that are incompatible -with those of the server will be disconnected. - -Options that will be compared for compatibility include -dev\-type, link\-mtu, tun\-mtu, proto, ifconfig, -comp\-lzo, fragment, keydir, cipher, auth, keysize, secret, -no\-replay, no\-iv, tls\-auth, key\-method, tls\-server, and tls\-client. - -This option requires that -.B \-\-disable\-occ -NOT be used. -.\"********************************************************* -.TP -.B \-\-auth\-user\-pass\-optional -Allow connections by clients that do not specify a username/password. -Normally, when -.B \-\-auth\-user\-pass\-verify -or -.B \-\-management\-client\-auth -is specified (or an authentication plugin module), the -OpenVPN server daemon will require connecting clients to specify a -username and password. This option makes the submission of a username/password -by clients optional, passing the responsibility to the user\-defined authentication -module/script to accept or deny the client based on other factors -(such as the setting of X509 certificate fields). When this option is used, -and a connecting client does not submit a username/password, the user\-defined -authentication module/script will see the username and password as being set -to empty strings (""). The authentication module/script MUST have logic -to detect this condition and respond accordingly. -.\"********************************************************* -.TP -.B \-\-client\-cert\-not\-required -.B DEPRECATED -This option will be removed in OpenVPN 2.5 - -Don't require client certificate, client will authenticate -using username/password only. Be aware that using this directive -is less secure than requiring certificates from all clients. - -.B Please note: -This is replaced by -.B \-\-verify\-client\-cert -which allows for more flexibility. The option -.B \-\-verify\-client\-cert none -is functionally equivalent to -.B \-\-client\-cert\-not\-required -. - -.\"********************************************************* -.TP -.B \-\-verify\-client\-cert none|optional|require -Specify whether the client is required to supply a valid certificate. - -Possible options are - -.B none -: a client certificate is not required. the client need to authenticate -using username/password only. Be aware that using this directive -is less secure than requiring certificates from all clients. - -If you use this directive, the -entire responsibility of authentication will rest on your -.B \-\-auth\-user\-pass\-verify -script, so keep in mind that bugs in your script -could potentially compromise the security of your VPN. - -.B \-\-verify\-client\-cert none -is functionally equivalent to -.B \-\-client\-cert\-not\-required. - -.B optional -: a client may present a certificate but it is not required to do so. -When using this directive, you should also use a -.B \-\-auth\-user\-pass\-verify -script to ensure that clients are authenticated using a -certificate, a username and password, or possibly even both. - -Again, the entire responsibility of authentication will rest on your -.B \-\-auth\-user\-pass\-verify -script, so keep in mind that bugs in your script -could potentially compromise the security of your VPN. - -.B require -: this is the default option. A client is required to present a -certificate, otherwise VPN access is refused. - -If you don't use this directive (or use -.B \-\-verify\-client\-cert require -) but you also specify an -.B \-\-auth\-user\-pass\-verify -script, then OpenVPN will perform double authentication. The -client certificate verification AND the -.B \-\-auth\-user\-pass\-verify -script will need to succeed in order for a client to be -authenticated and accepted onto the VPN. -.\"********************************************************* -.TP -.B \-\-username\-as\-common\-name -For -.B \-\-auth\-user\-pass\-verify -authentication, use -the authenticated username as the common name, -rather than the common name from the client cert. -.\"********************************************************* -.TP -.B \-\-compat\-names [no\-remapping] -.B DEPRECATED -This option will be removed in OpenVPN 2.5 - -Until OpenVPN v2.3 the format of the X.509 Subject fields was formatted -like this: -.IP -.B -/C=US/L=Somewhere/CN=John Doe/emailAddress=john@example.com -.IP -In addition the old behaviour was to remap any character other than -alphanumeric, underscore ('_'), dash ('\-'), dot ('.'), and slash ('/') to -underscore ('_'). The X.509 Subject string as returned by the -.B tls_id -environmental variable, could additionally contain colon (':') or equal ('='). -.IP -When using the -.B \-\-compat\-names -option, this old formatting and remapping will be re\-enabled again. This is -purely implemented for compatibility reasons when using older plug\-ins or -scripts which does not handle the new formatting or UTF\-8 characters. -.IP -In OpenVPN 2.3 the formatting of these fields changed into a more -standardised format. It now looks like: -.IP -.B -C=US, L=Somewhere, CN=John Doe, emailAddress=john@example.com -.IP -The new default format in OpenVPN 2.3 also does not do the character remapping -which happened earlier. This new format enables proper support for UTF\-8 -characters in the usernames, X.509 Subject fields and Common Name variables and -it complies to the RFC 2253, UTF\-8 String Representation of Distinguished -Names. - -The -.B no\-remapping -mode flag can be used with the -.B -\-\-compat\-names -option to be compatible with the now deprecated \-\-no\-name\-remapping option. -It is only available at the server. When this mode flag is used, the Common Name, -Subject, and username strings are allowed to include any printable character -including space, but excluding control characters such as tab, newline, and -carriage\-return. no\-remapping is only available on the server side. - -.B Please note: -This option is immediately deprecated. It is only implemented -to make the transition to the new formatting less intrusive. It will be -removed in OpenVPN 2.5. So please update your scripts/plug\-ins where necessary. -.\"********************************************************* -.TP -.B \-\-no\-name\-remapping -.B DEPRECATED -This option will be removed in OpenVPN 2.5 - -The -.B \-\-no\-name\-remapping -option is an alias for -.B \-\-compat\-names\ no\-remapping. -It ensures compatibility with server configurations using the -.B \-\-no\-name\-remapping -option. - -.B Please note: -This option is now deprecated. It will be removed in OpenVPN 2.5. -So please make sure you support the new X.509 name formatting -described with the -.B \-\-compat\-names -option as soon as possible. -.\"********************************************************* -.TP -.B \-\-port\-share host port [dir] -When run in TCP server mode, share the OpenVPN port with -another application, such as an HTTPS server. If OpenVPN -senses a connection to its port which is using a non\-OpenVPN -protocol, it will proxy the connection to the server at -.B host:port. -Currently only designed to work with HTTP/HTTPS, -though it would be theoretically possible to extend to -other protocols such as ssh. - -.B dir -specifies an optional directory where a temporary file with name N -containing content C will be dynamically generated for each proxy -connection, where N is the source IP:port of the client connection -and C is the source IP:port of the connection to the proxy -receiver. This directory can be used as a dictionary by -the proxy receiver to determine the origin of the connection. -Each generated file will be automatically deleted when the proxied -connection is torn down. - -Not implemented on Windows. -.\"********************************************************* -.SS Client Mode -Use client mode when connecting to an OpenVPN server -which has -.B \-\-server, \-\-server\-bridge, -or -.B \-\-mode server -in it's configuration. -.\"********************************************************* -.TP -.B \-\-client -A helper directive designed to simplify the configuration -of OpenVPN's client mode. This directive is equivalent to: - -.nf -.ft 3 -.in +4 - pull - tls\-client -.in -4 -.ft -.fi -.\"********************************************************* -.TP -.B \-\-pull -This option must be used on a client which is connecting -to a multi\-client server. It indicates to OpenVPN that it -should accept options pushed by the server, provided they -are part of the legal set of pushable options (note that the -.B \-\-pull -option is implied by -.B \-\-client -). - -In particular, -.B \-\-pull -allows the server to push routes to the client, so you should -not use -.B \-\-pull -or -.B \-\-client -in situations where you don't trust the server to have control -over the client's routing table. -.\"********************************************************* -.TP -.B \-\-pull\-filter accept|ignore|reject \fItext\fR -Filter options received from the server if the option starts with -\fItext\fR. Runs on client. The action flag -.B accept -allows the option, -.B ignore -removes it and -.B reject -flags an error and triggers a SIGUSR1 restart. -The filters may be specified multiple times, and each filter is -applied in the order it is specified. The filtering of each -option stops as soon as a match is found. Unmatched options are accepted -by default. - -Prefix comparison is used to match \fItext\fR against the -received option so that - -.nf -.ft 3 -.in +4 -\-\-pull\-filter ignore "route" -.in -4 -.ft -.fi - -would remove all pushed options starting with -.B route -which would include, for example, -.B route\-gateway. -Enclose \fItext\fR in quotes to embed spaces. - -.nf -.ft 3 -.in +4 -\-\-pull\-filter accept "route 192.168.1." -\-\-pull\-filter ignore "route " -.in -4 -.ft -.fi - -would remove all routes that do not start with 192.168.1. - -This option may be used only on clients. -Note that -.B reject -may result in a repeated cycle of failure and reconnect, -unless multiple remotes are specified and connection to the next remote -succeeds. To silently ignore an option pushed by the server, use -.B ignore. -.\"********************************************************* -.TP -.B \-\-auth\-user\-pass [up] -Authenticate with server using username/password. -.B up -is a file containing username/password on 2 lines. If the -password line is missing, OpenVPN will prompt for one. - -If -.B up -is omitted, username/password will be prompted from the -console. - -The server configuration must specify an -.B \-\-auth\-user\-pass\-verify -script to verify the username/password provided by -the client. -.\"********************************************************* -.TP -.B \-\-auth\-retry type -Controls how OpenVPN responds to username/password verification -errors such as the client\-side response to an AUTH_FAILED message from the server -or verification failure of the private key password. - -Normally used to prevent auth errors from being fatal -on the client side, and to permit username/password requeries in case -of error. - -An AUTH_FAILED message is generated by the server if the client -fails -.B \-\-auth\-user\-pass -authentication, or if the server\-side -.B \-\-client\-connect -script returns an error status when the client -tries to connect. - -.B type -can be one of: - -.B none \-\- -Client will exit with a fatal error (this is the default). -.br -.B nointeract \-\- -Client will retry the connection without requerying for an -.B \-\-auth\-user\-pass -username/password. Use this option for unattended clients. -.br -.B interact \-\- -Client will requery for an -.B \-\-auth\-user\-pass -username/password and/or private key password before attempting a reconnection. - -Note that while this option cannot be pushed, it can be controlled -from the management interface. -.\"********************************************************* -.TP -.B \-\-static\-challenge t e -Enable static challenge/response protocol using challenge text -.B t, -with -echo flag given by -.B e -(0|1). - -The echo flag indicates whether or not the user's response -to the challenge should be echoed. - -See management\-notes.txt in the OpenVPN distribution for a -description of the OpenVPN challenge/response protocol. -.\"********************************************************* -.TP -\fB\-\-server\-poll\-timeout n\fR, \fB\-\-connect\-timeout n\fR -When connecting to a remote server do not wait for more than -.B n -seconds waiting for a response before trying the next server. -The default value is 120s. This timeout includes proxy and TCP -connect timeouts. -.\"********************************************************* -.TP -.B \-\-explicit\-exit\-notify [n] -In UDP client mode or point\-to\-point mode, send server/peer an exit notification -if tunnel is restarted or OpenVPN process is exited. In client mode, on -exit/restart, this -option will tell the server to immediately close its client instance object -rather than waiting for a timeout. The -.B n -parameter (default=1) controls the maximum number of attempts that the client -will try to resend the exit notification message. - -In UDP server mode, send RESTART control channel command to connected clients. The -.B n -parameter (default=1) controls client behavior. With -.B n -= 1 client will attempt to reconnect -to the same server, with -.B n -= 2 client will advance to the next server. - -OpenVPN will not send any exit -notifications unless this option is enabled. -.TP -.B \-\-allow\-recursive\-routing -When this option is set, OpenVPN will not drop incoming tun packets -with same destination as host. -.\"********************************************************* -.SS Data Channel Encryption Options: -These options are meaningful for both Static & TLS\-negotiated key modes -(must be compatible between peers). -.\"********************************************************* -.TP -.B \-\-secret file [direction] -Enable Static Key encryption mode (non\-TLS). -Use pre\-shared secret -.B file -which was generated with -.B \-\-genkey. - -The optional -.B direction -parameter enables the use of 4 distinct keys -(HMAC\-send, cipher\-encrypt, HMAC\-receive, cipher\-decrypt), so that -each data flow direction has a different set of HMAC and cipher keys. -This has a number of desirable security properties including -eliminating certain kinds of DoS and message replay attacks. - -When the -.B direction -parameter is omitted, 2 keys are used bidirectionally, one for HMAC -and the other for encryption/decryption. - -The -.B direction -parameter should always be complementary on either side of the connection, -i.e. one side should use "0" and the other should use "1", or both sides -should omit it altogether. - -The -.B direction -parameter requires that -.B file -contains a 2048 bit key. While pre\-1.5 versions of OpenVPN -generate 1024 bit key files, any version of OpenVPN which -supports the -.B direction -parameter, will also support 2048 bit key file generation -using the -.B \-\-genkey -option. - -Static key encryption mode has certain advantages, -the primary being ease of configuration. - -There are no certificates -or certificate authorities or complicated negotiation handshakes and protocols. -The only requirement is that you have a pre\-existing secure channel with -your peer (such as -.B ssh -) to initially copy the key. This requirement, along with the -fact that your key never changes unless you manually generate a new one, -makes it somewhat less secure than TLS mode (see below). If an attacker -manages to steal your key, everything that was ever encrypted with -it is compromised. Contrast that to the perfect forward secrecy features of -TLS mode (using Diffie Hellman key exchange), where even if an attacker -was able to steal your private key, he would gain no information to help -him decrypt past sessions. - -Another advantageous aspect of Static Key encryption mode is that -it is a handshake\-free protocol -without any distinguishing signature or feature -(such as a header or protocol handshake sequence) -that would mark the ciphertext packets as being -generated by OpenVPN. Anyone eavesdropping on the wire -would see nothing -but random\-looking data. -.\"********************************************************* -.TP -.B \-\-key\-direction -Alternative way of specifying the optional direction parameter for the -.B \-\-tls\-auth -and -.B \-\-secret -options. Useful when using inline files (See section on inline files). -.\"********************************************************* -.TP -.B \-\-auth alg -Authenticate data channel packets and (if enabled) -.B tls\-auth -control channel packets with HMAC using message digest algorithm -.B alg. -(The default is -.B SHA1 -). -HMAC is a commonly used message authentication algorithm (MAC) that uses -a data string, a secure hash algorithm, and a key, to produce -a digital signature. - -The OpenVPN data channel protocol uses encrypt\-then\-mac (i.e. first encrypt a -packet, then HMAC the resulting ciphertext), which prevents padding oracle -attacks. - -If an AEAD cipher mode (e.g. GCM) is chosen, the specified -.B \-\-auth -algorithm is ignored for the data channel, and the authentication method of the -AEAD cipher is used instead. Note that -.B alg -still specifies the digest used for -.B tls\-auth\fR. - -In static\-key encryption mode, the HMAC key -is included in the key file generated by -.B \-\-genkey. -In TLS mode, the HMAC key is dynamically generated and shared -between peers via the TLS control channel. If OpenVPN receives a packet with -a bad HMAC it will drop the packet. -HMAC usually adds 16 or 20 bytes per packet. -Set -.B alg=none -to disable authentication. - -For more information on HMAC see -.I http://www.cs.ucsd.edu/users/mihir/papers/hmac.html -.\"********************************************************* -.TP -.B \-\-cipher alg -Encrypt data channel packets with cipher algorithm -.B alg. - -The default is -.B BF\-CBC, -an abbreviation for Blowfish in Cipher Block Chaining mode. When cipher -negotiation (NCP) is allowed, OpenVPN 2.4 and newer on both client and server -side will automatically upgrade to -.B AES\-256\-GCM. -See -.B \-\-ncp\-ciphers -and -.B \-\-ncp\-disable -for more details on NCP. - -Using -.B BF\-CBC -is no longer recommended, because of its 64\-bit block size. This -small block size allows attacks based on collisions, as demonstrated by SWEET32. -See https://community.openvpn.net/openvpn/wiki/SWEET32 for details. Due to -this, support for -.B BF\-CBC, DES, CAST5, IDEA -and -.B RC2 -ciphers will be removed in OpenVPN 2.6. - -To see other ciphers that are available with OpenVPN, use the -.B \-\-show\-ciphers -option. - -Set -.B alg=none -to disable encryption. - -.\"********************************************************* -.TP -.B \-\-ncp\-ciphers cipher_list -Restrict the allowed ciphers to be negotiated to the ciphers in -.B cipher_list\fR. -.B cipher_list -is a colon\-separated list of ciphers, and defaults to -"AES\-256\-GCM:AES\-128\-GCM". - -For servers, the first cipher from -.B cipher_list -will be pushed to clients that support cipher negotiation. - -Cipher negotiation is enabled in client\-server mode only. I.e. if -.B \-\-mode -is set to 'server' (server\-side, implied by setting -.B \-\-server -), or if -.B \-\-pull -is specified (client\-side, implied by setting \-\-client). - -If both peers support and do not disable NCP, the negotiated cipher will -override the cipher specified by -.B \-\-cipher\fR. - -Additionally, to allow for more smooth transition, if NCP is enabled, OpenVPN -will inherit the cipher of the peer if that cipher is different from the local -.B \-\-cipher -setting, but the peer cipher is one of the ciphers specified in -.B \-\-ncp\-ciphers\fR. -E.g. a non\-NCP client (<=v2.3, or with \-\-ncp\-disabled set) connecting to a -NCP server (v2.4+) with "\-\-cipher BF\-CBC" and "\-\-ncp\-ciphers -AES\-256\-GCM:AES\-256\-CBC" set can either specify "\-\-cipher BF\-CBC" or -"\-\-cipher AES\-256\-CBC" and both will work. - -.\"********************************************************* -.TP -.B \-\-ncp\-disable -Disable "negotiable crypto parameters". This completely disables cipher -negotiation. -.\"********************************************************* -.TP -.B \-\-keysize n -.B DEPRECATED -This option will be removed in OpenVPN 2.6. - -Size of cipher key in bits (optional). -If unspecified, defaults to cipher\-specific default. The -.B \-\-show\-ciphers -option (see below) shows all available OpenSSL ciphers, -their default key sizes, and whether the key size can -be changed. Use care in changing a cipher's default -key size. Many ciphers have not been extensively -cryptanalyzed with non\-standard key lengths, and a -larger key may offer no real guarantee of greater -security, or may even reduce security. -.\"********************************************************* -.TP -.B \-\-prng alg [nsl] -(Advanced) For PRNG (Pseudo\-random number generator), -use digest algorithm -.B alg -(default=sha1), and set -.B nsl -(default=16) -to the size in bytes of the nonce secret length (between 16 and 64). - -Set -.B alg=none -to disable the PRNG and use the OpenSSL RAND_bytes function -instead for all of OpenVPN's pseudo\-random number needs. -.\"********************************************************* -.TP -.B \-\-engine [engine\-name] -Enable OpenSSL hardware\-based crypto engine functionality. - -If -.B engine\-name -is specified, -use a specific crypto engine. Use the -.B \-\-show\-engines -standalone option to list the crypto engines which are -supported by OpenSSL. -.\"********************************************************* -.TP -.B \-\-no\-replay -.B DEPRECATED -This option will be removed in OpenVPN 2.5. - -(Advanced) Disable OpenVPN's protection against replay attacks. -Don't use this option unless you are prepared to make -a tradeoff of greater efficiency in exchange for less -security. - -OpenVPN provides datagram replay protection by default. - -Replay protection is accomplished -by tagging each outgoing datagram with an identifier -that is guaranteed to be unique for the key being used. -The peer that receives the datagram will check for -the uniqueness of the identifier. If the identifier -was already received in a previous datagram, OpenVPN -will drop the packet. Replay protection is important -to defeat attacks such as a SYN flood attack, where -the attacker listens in the wire, intercepts a TCP -SYN packet (identifying it by the context in which -it occurs in relation to other packets), then floods -the receiving peer with copies of this packet. - -OpenVPN's replay protection is implemented in slightly -different ways, depending on the key management mode -you have selected. - -In Static Key mode -or when using an CFB or OFB mode cipher, OpenVPN uses a -64 bit unique identifier that combines a time stamp with -an incrementing sequence number. - -When using TLS mode for key exchange and a CBC cipher -mode, OpenVPN uses only a 32 bit sequence number without -a time stamp, since OpenVPN can guarantee the uniqueness -of this value for each key. As in IPSec, if the sequence number is -close to wrapping back to zero, OpenVPN will trigger -a new key exchange. - -To check for replays, OpenVPN uses -the -.I sliding window -algorithm used -by IPSec. -.\"********************************************************* -.TP -.B \-\-replay\-window n [t] -Use a replay protection sliding\-window of size -.B n -and a time window of -.B t -seconds. - -By default -.B n -is 64 (the IPSec default) and -.B t -is 15 seconds. - -This option is only relevant in UDP mode, i.e. -when either -.B \-\-proto udp -is specified, or no -.B \-\-proto -option is specified. - -When OpenVPN tunnels IP packets over UDP, there is the possibility that -packets might be dropped or delivered out of order. Because OpenVPN, like IPSec, -is emulating the physical network layer, -it will accept an out\-of\-order packet sequence, and -will deliver such packets in the same order they were received to -the TCP/IP protocol stack, provided they satisfy several constraints. - -.B (a) -The packet cannot be a replay (unless -.B \-\-no\-replay -is specified, which disables replay protection altogether). - -.B (b) -If a packet arrives out of order, it will only be accepted if the difference -between its sequence number and the highest sequence number received -so far is less than -.B n. - -.B (c) -If a packet arrives out of order, it will only be accepted if it arrives no later -than -.B t -seconds after any packet containing a higher sequence number. - -If you are using a network link with a large pipeline (meaning that -the product of bandwidth and latency is high), you may want to use -a larger value for -.B n. -Satellite links in particular often require this. - -If you run OpenVPN at -.B \-\-verb 4, -you will see the message "Replay\-window backtrack occurred [x]" -every time the maximum sequence number backtrack seen thus far -increases. This can be used to calibrate -.B n. - -There is some controversy on the appropriate method of handling packet -reordering at the security layer. - -Namely, to what extent should the -security layer protect the encapsulated protocol from attacks which masquerade -as the kinds of normal packet loss and reordering that occur over IP networks? - -The IPSec and OpenVPN approach is to allow packet reordering within a certain -fixed sequence number window. - -OpenVPN adds to the IPSec model by limiting the window size in time as well as -sequence space. - -OpenVPN also adds TCP transport as an option (not offered by IPSec) in which -case OpenVPN can adopt a very strict attitude towards message deletion and -reordering: Don't allow it. Since TCP guarantees reliability, any packet -loss or reordering event can be assumed to be an attack. - -In this sense, it could be argued that TCP tunnel transport is preferred when -tunneling non\-IP or UDP application protocols which might be vulnerable to a -message deletion or reordering attack which falls within the normal -operational parameters of IP networks. - -So I would make the statement that one should never tunnel a non\-IP protocol -or UDP application protocol over UDP, if the protocol might be vulnerable to a -message deletion or reordering attack that falls within the normal operating -parameters of what is to be expected from the physical IP layer. The problem -is easily fixed by simply using TCP as the VPN transport layer. -.\"********************************************************* -.TP -.B \-\-mute\-replay\-warnings -Silence the output of replay warnings, which are a common -false alarm on WiFi networks. This option preserves -the security of the replay protection code without -the verbosity associated with warnings about duplicate -packets. -.\"********************************************************* -.TP -.B \-\-replay\-persist file -Persist replay\-protection state across sessions using -.B file -to save and reload the state. - -This option will strengthen protection against replay attacks, -especially when you are using OpenVPN in a dynamic context (such -as with -.B \-\-inetd) -when OpenVPN sessions are frequently started and stopped. - -This option will keep a disk copy of the current replay protection -state (i.e. the most recent packet timestamp and sequence number -received from the remote peer), so that if an OpenVPN session -is stopped and restarted, it will reject any replays of packets -which were already received by the prior session. - -This option only makes sense when replay protection is enabled -(the default) and you are using either -.B \-\-secret -(shared\-secret key mode) or TLS mode with -.B \-\-tls\-auth. -.\"********************************************************* -.TP -.B \-\-no\-iv -.B DEPRECATED -This option will be removed in OpenVPN 2.5. - -(Advanced) Disable OpenVPN's use of IV (cipher initialization vector). -Don't use this option unless you are prepared to make -a tradeoff of greater efficiency in exchange for less -security. - -OpenVPN uses an IV by default, and requires it for CFB and -OFB cipher modes (which are totally insecure without it). -Using an IV is important for security when multiple -messages are being encrypted/decrypted with the same key. - -IV is implemented differently depending on the cipher mode used. - -In CBC mode, OpenVPN uses a pseudo\-random IV for each packet. - -In CFB/OFB mode, OpenVPN uses a unique sequence number and time stamp -as the IV. In fact, in CFB/OFB mode, OpenVPN uses a datagram -space\-saving optimization that uses the unique identifier for -datagram replay protection as the IV. -.\"********************************************************* -.TP -.B \-\-use\-prediction\-resistance -Enable prediction resistance on mbed TLS's RNG. - -Enabling prediction resistance causes the RNG to reseed in each -call for random. Reseeding this often can quickly deplete the kernel -entropy pool. - -If you need this option, please consider running a daemon that adds -entropy to the kernel pool. - -.\"********************************************************* -.TP -.B \-\-test\-crypto -Do a self\-test of OpenVPN's crypto options by encrypting and -decrypting test packets using the data channel encryption options -specified above. This option does not require a peer to function, -and therefore can be specified without -.B \-\-dev -or -.B \-\-remote. - -The typical usage of -.B \-\-test\-crypto -would be something like this: - -.B openvpn \-\-test\-crypto \-\-secret key - -or - -.B openvpn \-\-test\-crypto \-\-secret key \-\-verb 9 - -This option is very useful to test OpenVPN after it has been ported to -a new platform, or to isolate problems in the compiler, OpenSSL -crypto library, or OpenVPN's crypto code. Since it is a self\-test mode, -problems with encryption and authentication can be debugged independently -of network and tunnel issues. -.\"********************************************************* -.SS TLS Mode Options: -TLS mode is the most powerful crypto mode of OpenVPN in both security and flexibility. -TLS mode works by establishing control and -data channels which are multiplexed over a single TCP/UDP port. OpenVPN initiates -a TLS session over the control channel and uses it to exchange cipher -and HMAC keys to protect the data channel. TLS mode uses a robust reliability -layer over the UDP connection for all control channel communication, while -the data channel, over which encrypted tunnel data passes, is forwarded without -any mediation. The result is the best of both worlds: a fast data channel -that forwards over UDP with only the overhead of encrypt, -decrypt, and HMAC functions, -and a control channel that provides all of the security features of TLS, -including certificate\-based authentication and Diffie Hellman forward secrecy. - -To use TLS mode, each peer that runs OpenVPN should have its own local -certificate/key pair ( -.B \-\-cert -and -.B \-\-key -), signed by the root certificate which is specified -in -.B \-\-ca. - -When two OpenVPN peers connect, each presents its local certificate to the -other. Each peer will then check that its partner peer presented a -certificate which was signed by the master root certificate as specified in -.B \-\-ca. - -If that check on both peers succeeds, then the TLS negotiation -will succeed, both OpenVPN -peers will exchange temporary session keys, and the tunnel will begin -passing data. - -The OpenVPN project provides a set of scripts for -managing RSA certificates & keys: -.I https://github.com/OpenVPN/easy\-rsa -.\"********************************************************* -.TP -.B \-\-tls\-server -Enable TLS and assume server role during TLS handshake. Note that -OpenVPN is designed as a peer\-to\-peer application. The designation -of client or server is only for the purpose of negotiating the TLS -control channel. -.\"********************************************************* -.TP -.B \-\-tls\-client -Enable TLS and assume client role during TLS handshake. -.\"********************************************************* -.TP -.B \-\-ca file -Certificate authority (CA) file in .pem format, also referred to as the -.I root -certificate. This file can have multiple -certificates in .pem format, concatenated together. You can construct your own -certificate authority certificate and private key by using a command such as: - -.B openssl req \-nodes \-new \-x509 \-keyout ca.key \-out ca.crt - -Then edit your openssl.cnf file and edit the -.B certificate -variable to point to your new root certificate -.B ca.crt. - -For testing purposes only, the OpenVPN distribution includes a sample -CA certificate (ca.crt). -Of course you should never use -the test certificates and test keys distributed with OpenVPN in a -production environment, since by virtue of the fact that -they are distributed with OpenVPN, they are totally insecure. -.\"********************************************************* -.TP -.B \-\-capath dir -Directory containing trusted certificates (CAs and CRLs). -Not available with mbed TLS. - -CAs in the capath directory are expected to be named .. CRLs are -expected to be named .r. See the -.B \-CApath -option of -.B openssl verify -, and the -.B \-hash -option of -.B openssl x509 -, -.B openssl crl -and -.BR X509_LOOKUP_hash_dir (3) -for more information. - -Similarly to the -.B \-\-crl\-verify -option CRLs are not mandatory \- OpenVPN will log the usual warning in the logs -if the relevant CRL is missing, but the connection will be allowed. -.\"********************************************************* -.TP -.B \-\-dh file -File containing Diffie Hellman parameters -in .pem format (required for -.B \-\-tls\-server -only). - -Set -.B file=none -to disable Diffie Hellman key exchange (and use ECDH only). Note that this -requires peers to be using an SSL library that supports ECDH TLS cipher suites -(e.g. OpenSSL 1.0.1+, or mbed TLS 2.0+). - -Use -.B openssl dhparam \-out dh2048.pem 2048 -to generate 2048\-bit DH parameters. Diffie Hellman parameters may be considered -public. -.\"********************************************************* -.TP -.B \-\-ecdh\-curve name -Specify the curve to use for elliptic curve Diffie Hellman. Available -curves can be listed with -.BR \-\-show\-curves . -The specified curve will only be used for ECDH TLS\-ciphers. - -This option is not supported in mbed TLS builds of OpenVPN. -.\"********************************************************* -.TP -.B \-\-cert file -Local peer's signed certificate in .pem format \-\- must be signed -by a certificate authority whose certificate is in -.B \-\-ca file. -Each peer in an OpenVPN link running in TLS mode should have its own -certificate and private key file. In addition, each certificate should -have been signed by the key of a certificate -authority whose public key resides in the -.B \-\-ca -certificate authority file. -You can easily make your own certificate authority (see above) or pay money -to use a commercial service such as thawte.com (in which case you will be -helping to finance the world's second space tourist :). -To generate a certificate, -you can use a command such as: - -.B openssl req \-nodes \-new \-keyout mycert.key \-out mycert.csr - -If your certificate authority private key lives on another machine, copy -the certificate signing request (mycert.csr) to this other machine (this can -be done over an insecure channel such as email). Now sign the certificate -with a command such as: - -.B openssl ca \-out mycert.crt \-in mycert.csr - -Now copy the certificate (mycert.crt) -back to the peer which initially generated the .csr file (this -can be over a public medium). -Note that the -.B openssl ca -command reads the location of the certificate authority key from its -configuration file such as -.B /usr/share/ssl/openssl.cnf -\-\- note also -that for certificate authority functions, you must set up the files -.B index.txt -(may be empty) and -.B serial -(initialize to -.B -01 -). -.\"********************************************************* -.TP -.B \-\-extra\-certs file -Specify a -.B file -containing one or more PEM certs (concatenated together) -that complete the -local certificate chain. - -This option is useful for "split" CAs, where the CA for server -certs is different than the CA for client certs. Putting certs -in this file allows them to be used to complete the local -certificate chain without trusting them to verify the peer\-submitted -certificate, as would be the case if the certs were placed in the -.B ca -file. -.\"********************************************************* -.TP -.B \-\-key file -Local peer's private key in .pem format. Use the private key which was generated -when you built your peer's certificate (see -.B \-\-cert file -above). -.\"********************************************************* -.TP -.B \-\-tls\-version\-min version ['or\-highest'] -Sets the minimum -TLS version we will accept from the peer (default is "1.0"). -Examples for version -include "1.0", "1.1", or "1.2". If 'or\-highest' is specified -and version is not recognized, we will only accept the highest TLS -version supported by the local SSL implementation. -.\"********************************************************* -.TP -.B \-\-tls\-version\-max version -Set the maximum TLS version we will use (default is the highest version -supported). Examples for version include "1.0", "1.1", or "1.2". -.\"********************************************************* -.TP -.B \-\-pkcs12 file -Specify a PKCS #12 file containing local private key, -local certificate, and root CA certificate. -This option can be used instead of -.B \-\-ca, \-\-cert, -and -.B \-\-key. -Not available with mbed TLS. -.\"********************************************************* -.TP -.B \-\-verify\-hash hash [algo] -Specify SHA1 or SHA256 fingerprint for level\-1 cert. The level\-1 cert is the -CA (or intermediate cert) that signs the leaf certificate, and is -one removed from the leaf certificate in the direction of the root. -When accepting a connection from a peer, the level\-1 cert -fingerprint must match -.B hash -or certificate verification will fail. Hash is specified -as XX:XX:... For example: - -.nf -.ft 3 -.in +4 -AD:B0:95:D8:09:C8:36:45:12:A9:89:C8:90:09:CB:13:72:A6:AD:16 -.in -4 -.ft -.fi - -The -.B algo -flag can be either SHA1 or SHA256. If not provided, it defaults to SHA1. -.\"********************************************************* -.TP -.B \-\-pkcs11\-cert\-private [0|1]... -Set if access to certificate object should be performed after login. -Every provider has its own setting. -.\"********************************************************* -.TP -.B \-\-pkcs11\-id name -Specify the serialized certificate id to be used. The id can be gotten -by the standalone -.B \-\-show\-pkcs11\-ids -option. -.\"********************************************************* -.TP -.B \-\-pkcs11\-id\-management -Acquire PKCS#11 id from management interface. In this case a NEED\-STR 'pkcs11\-id\-request' -real\-time message will be triggered, application may use pkcs11\-id\-count command to -retrieve available number of certificates, and pkcs11\-id\-get command to retrieve certificate -id and certificate body. -.\"********************************************************* -.TP -.B \-\-pkcs11\-pin\-cache seconds -Specify how many seconds the PIN can be cached, the default is until the token is removed. -.\"********************************************************* -.TP -.B \-\-pkcs11\-protected\-authentication [0|1]... -Use PKCS#11 protected authentication path, useful for biometric and external -keypad devices. -Every provider has its own setting. -.\"********************************************************* -.TP -.B \-\-pkcs11\-providers provider... -Specify a RSA Security Inc. PKCS #11 Cryptographic Token Interface (Cryptoki) providers -to load. -This option can be used instead of -.B \-\-cert, \-\-key, -and -.B \-\-pkcs12. - -If p11\-kit is present on the system, its -.B p11\-kit\-proxy.so -module will be loaded by default if either the -.B \-\-pkcs11\-id -or -.B \-\-pkcs11\-id\-management -options are specified without -.B \-\-pkcs11\-provider -being given. -.\"********************************************************* -.TP -.B \-\-pkcs11\-private\-mode mode... -Specify which method to use in order to perform private key operations. -A different mode can be specified for each provider. -Mode is encoded as hex number, and can be a mask one of the following: - -.B 0 -(default) \-\- Try to determine automatically. -.br -.B 1 -\-\- Use sign. -.br -.B 2 -\-\- Use sign recover. -.br -.B 4 -\-\- Use decrypt. -.br -.B 8 -\-\- Use unwrap. -.br -.\"********************************************************* -.TP -.B \-\-cryptoapicert select\-string -Load the certificate and private key from the -Windows Certificate System Store (Windows/OpenSSL Only). - -Use this option instead of -.B \-\-cert -and -.B \-\-key. - -This makes -it possible to use any smart card, supported by Windows, but also any -kind of certificate, residing in the Cert Store, where you have access to -the private key. This option has been tested with a couple of different -smart cards (GemSAFE, Cryptoflex, and Swedish Post Office eID) on the -client side, and also an imported PKCS12 software certificate on the -server side. - -To select a certificate, based on a substring search in the -certificate's subject: - -.B cryptoapicert -"SUBJ:Peter Runestig" - -To select a certificate, based on certificate's thumbprint: - -.B cryptoapicert -"THUMB:f6 49 24 41 01 b4 ..." - -The thumbprint hex string can easily be copy\-and\-pasted from the Windows -Certificate Store GUI. - -.\"********************************************************* -.TP -.B \-\-key\-method m -.B DEPRECATED -This option will be removed in OpenVPN 2.5 - -Use data channel key negotiation method -.B m. -The key method must match on both sides of the connection. - -After OpenVPN negotiates a TLS session, a new set of keys -for protecting the tunnel data channel is generated and -exchanged over the TLS session. - -In method 1 (the default for OpenVPN 1.x), both sides generate -random encrypt and HMAC\-send keys which are forwarded to -the other host over the TLS channel. Method 1 is -.B deprecated in OpenVPN 2.4 -, and -.B will be removed in OpenVPN 2.5\fR. - -In method 2, (the default for OpenVPN 2.0) -the client generates a random key. Both client -and server also generate some random seed material. All key source -material is exchanged over the TLS channel. The actual -keys are generated using the TLS PRF function, taking source -entropy from both client and server. Method 2 is designed to -closely parallel the key generation process used by TLS 1.0. - -Note that in TLS mode, two separate levels -of keying occur: - -(1) The TLS connection is initially negotiated, with both sides -of the connection producing certificates and verifying the certificate -(or other authentication info provided) of -the other side. The -.B \-\-key\-method -parameter has no effect on this process. - -(2) After the TLS connection is established, the tunnel session keys are -separately negotiated over the existing secure TLS channel. Here, -.B \-\-key\-method -determines the derivation of the tunnel session keys. -.\"********************************************************* -.TP -.B \-\-tls\-cipher l -.TQ -.B \-\-tls\-ciphersuites l -A list -.B l -of allowable TLS ciphers delimited by a colon (":"). - -These setting can be used to ensure that certain cipher suites are used (or -not used) for the TLS connection. OpenVPN uses TLS to secure the control -channel, over which the keys that are used to protect the actual VPN traffic -are exchanged. - -The supplied list of ciphers is (after potential OpenSSL/IANA name translation) -simply supplied to the crypto library. Please see the OpenSSL and/or mbed TLS -documentation for details on the cipher list interpretation. - -For OpenSSL, the -.B \-\-tls-cipher -is used for TLS 1.2 and below. For TLS 1.3 and up, the -.B \-\-tls\-ciphersuites -setting is used. mbed TLS has no TLS 1.3 support yet and only the -.B \-\-tls-cipher -setting is used. - -Use -.B \-\-show\-tls -to see a list of TLS ciphers supported by your crypto library. - -Warning! -.B \-\-tls\-cipher -and -.B \-\-tls\-ciphersuites -are expert features, which \- if used correcly \- can improve the security of -your VPN connection. But it is also easy to unwittingly use them to carefully -align a gun with your foot, or just break your connection. Use with care! - -The default for \-\-tls\-cipher is to use mbed TLS's default cipher list -when using mbed TLS or -"DEFAULT:!EXP:!LOW:!MEDIUM:!kDH:!kECDH:!DSS:!PSK:!SRP:!kRSA" when using -OpenSSL. - -The default for \-\-tls\-ciphersuites is to use the crypto library's default. -.\"********************************************************* -.TP -.B \-\-tls\-cert\-profile profile -Set the allowed cryptographic algorithms for certificates according to -.B profile\fN. - -The following profiles are supported: - -.B legacy -(default): SHA1 and newer, RSA 2048-bit+, any elliptic curve. - -.B preferred -: SHA2 and newer, RSA 2048-bit+, any elliptic curve. - -.B suiteb -: SHA256/SHA384, ECDSA with P-256 or P-384. - -This option is only fully supported for mbed TLS builds. OpenSSL builds use -the following approximation: - -.B legacy -(default): sets "security level 1" - -.B preferred -: sets "security level 2" - -.B suiteb -: sets "security level 3" and \-\-tls\-cipher "SUITEB128". - -OpenVPN will migrate to 'preferred' as default in the future. Please ensure -that your keys already comply. -.\"********************************************************* -.TP -.B \-\-tls\-timeout n -Packet retransmit timeout on TLS control channel -if no acknowledgment from remote within -.B n -seconds (default=2). When OpenVPN sends a control -packet to its peer, it will expect to receive an -acknowledgement within -.B n -seconds or it will retransmit the packet, subject -to a TCP\-like exponential backoff algorithm. This parameter -only applies to control channel packets. Data channel -packets (which carry encrypted tunnel data) are never -acknowledged, sequenced, or retransmitted by OpenVPN because -the higher level network protocols running on top of the tunnel -such as TCP expect this role to be left to them. -.\"********************************************************* -.TP -.B \-\-reneg\-bytes n -Renegotiate data channel key after -.B n -bytes sent or received (disabled by default with an exception, see below). -OpenVPN allows the lifetime of a key -to be expressed as a number of bytes encrypted/decrypted, a number of packets, -or a number of seconds. A key renegotiation will be forced -if any of these three criteria are met by either peer. - -If using ciphers with cipher block sizes less than 128\-bits, \-\-reneg\-bytes is -set to 64MB by default, unless it is explicitly disabled by setting the value to -0, but this is -.B HIGHLY DISCOURAGED -as this is designed to add some protection against the SWEET32 attack vector. -For more information see the \-\-cipher option. -.\"********************************************************* -.TP -.B \-\-reneg\-pkts n -Renegotiate data channel key after -.B n -packets sent and received (disabled by default). -.\"********************************************************* -.TP -.B \-\-reneg\-sec n -Renegotiate data channel key after -.B n -seconds (default=3600). - -When using dual\-factor authentication, note that this default value may -cause the end user to be challenged to reauthorize once per hour. - -Also, keep in mind that this option can be used on both the client and server, -and whichever uses the lower value will be the one to trigger the renegotiation. -A common mistake is to set -.B \-\-reneg\-sec -to a higher value on either the client or server, while the other side of the connection -is still using the default value of 3600 seconds, meaning that the renegotiation will -still occur once per 3600 seconds. The solution is to increase \-\-reneg\-sec on both the -client and server, or set it to 0 on one side of the connection (to disable), and to -your chosen value on the other side. -.\"********************************************************* -.TP -.B \-\-hand\-window n -Handshake Window \-\- the TLS\-based key exchange must finalize within -.B n -seconds -of handshake initiation by any peer (default = 60 seconds). -If the handshake fails -we will attempt to reset our connection with our peer and try again. -Even in the event of handshake failure we will still use -our expiring key for up to -.B \-\-tran\-window -seconds to maintain continuity of transmission of tunnel -data. -.\"********************************************************* -.TP -.B \-\-tran\-window n -Transition window \-\- our old key can live this many seconds -after a new a key renegotiation begins (default = 3600 seconds). -This feature allows for a graceful transition from old to new -key, and removes the key renegotiation sequence from the critical -path of tunnel data forwarding. -.\"********************************************************* -.TP -.B \-\-single\-session -After initially connecting to a remote peer, disallow any new connections. -Using this -option means that a remote peer cannot connect, disconnect, and then -reconnect. - -If the daemon is reset by a signal or -.B \-\-ping\-restart, -it will allow one new connection. - -.B \-\-single\-session -can be used with -.B \-\-ping\-exit -or -.B \-\-inactive -to create a single dynamic session that will exit when finished. -.\"********************************************************* -.TP -.B \-\-tls\-exit -Exit on TLS negotiation failure. -.\"********************************************************* -.TP -.B \-\-tls\-auth file [direction] -Add an additional layer of HMAC authentication on top of the TLS control channel -to mitigate DoS attacks and attacks on the TLS stack. - -In a nutshell, -.B \-\-tls\-auth -enables a kind of "HMAC firewall" on OpenVPN's TCP/UDP port, -where TLS control channel packets -bearing an incorrect HMAC signature can be dropped immediately without -response. - -.B file -(required) is a file in OpenVPN static key format which can be generated by -.B \-\-genkey - -Older versions (up to OpenVPN 2.3) supported a freeform passphrase file. -This is no longer supported in newer versions (v2.4+). - -See the -.B \-\-secret -option for more information on the optional -.B direction -parameter. - -.B \-\-tls\-auth -is recommended when you are running OpenVPN in a mode where -it is listening for packets from any IP address, such as when -.B \-\-remote -is not specified, or -.B \-\-remote -is specified with -.B \-\-float. - -The rationale for -this feature is as follows. TLS requires a multi\-packet exchange -before it is able to authenticate a peer. During this time -before authentication, OpenVPN is allocating resources (memory -and CPU) to this potential peer. The potential peer is also -exposing many parts of OpenVPN and the OpenSSL library to the packets -it is sending. Most successful network attacks today seek -to either exploit bugs in programs (such as buffer overflow attacks) or -force a program to consume so many resources that it becomes unusable. -Of course the first line of defense is always to produce clean, -well\-audited code. OpenVPN has been written with buffer overflow -attack prevention as a top priority. -But as history has shown, many of the most widely used -network applications have, from time to time, -fallen to buffer overflow attacks. - -So as a second line of defense, OpenVPN offers -this special layer of authentication on top of the TLS control channel so that -every packet on the control channel is authenticated by an -HMAC signature and a unique ID for replay protection. -This signature will also help protect against DoS (Denial of Service) attacks. -An important rule of thumb in reducing vulnerability to DoS attacks is to -minimize the amount of resources a potential, but as yet unauthenticated, -client is able to consume. - -.B \-\-tls\-auth -does this by signing every TLS control channel packet with an HMAC signature, -including packets which are sent before the TLS level has had a chance -to authenticate the peer. -The result is that packets without -the correct signature can be dropped immediately upon reception, -before they have a chance to consume additional system resources -such as by initiating a TLS handshake. -.B \-\-tls\-auth -can be strengthened by adding the -.B \-\-replay\-persist -option which will keep OpenVPN's replay protection state -in a file so that it is not lost across restarts. - -It should be emphasized that this feature is optional and that the -key file used with -.B \-\-tls\-auth -gives a peer nothing more than the power to initiate a TLS -handshake. It is not used to encrypt or authenticate any tunnel data. - -Use -.B \-\-tls\-crypt -instead if you want to use the key file to not only authenticate, but also -encrypt the TLS control channel. -.\"********************************************************* -.TP -.B \-\-tls\-crypt keyfile - -Encrypt and authenticate all control channel packets with the key from -.B keyfile. -(See -.B \-\-tls\-auth -for more background.) - -Encrypting (and authenticating) control channel packets: -.RS -.IP \[bu] 2 -provides more privacy by hiding the certificate used for the TLS connection, -.IP \[bu] -makes it harder to identify OpenVPN traffic as such, -.IP \[bu] -provides "poor\-man's" post\-quantum security, against attackers who will never -know the pre\-shared key (i.e. no forward secrecy). -.RE - -.IP -In contrast to -.B \-\-tls\-auth\fR, -.B \-\-tls\-crypt -does *not* require the user to set -.B \-\-key\-direction\fR. - -.B Security Considerations - -All peers use the same -.B \-\-tls\-crypt -pre\-shared group key to authenticate and encrypt control channel messages. To -ensure that IV collisions remain unlikely, this key should not be used to -encrypt more than 2^48 client\-to\-server or 2^48 server\-to\-client control -channel messages. A typical initial negotiation is about 10 packets in each -direction. Assuming both initial negotiation and renegotiations are at most -2^16 (65536) packets (to be conservative), and (re)negotiations happen each -minute for each user (24/7), this limits the tls\-crypt key lifetime to 8171 -years divided by the number of users. So a setup with 1000 users should rotate -the key at least once each eight years. (And a setup with 8000 users each -year.) - -If IV collisions were to occur, this could result in the security of -.B \-\-tls\-crypt -degrading to the same security as using -.B \-\-tls\-auth\fR. -That is, the control channel still benefits from the extra protection against -active man\-in\-the\-middle\-attacks and DoS attacks, but may no longer offer -extra privacy and post\-quantum security on top of what TLS itself offers. -.\"********************************************************* -.TP -.B \-\-askpass [file] -Get certificate password from console or -.B file -before we daemonize. - -For the extremely -security conscious, it is possible to protect your private key with -a password. Of course this means that every time the OpenVPN -daemon is started you must be there to type the password. The -.B \-\-askpass -option allows you to start OpenVPN from the command line. It will -query you for a password before it daemonizes. To protect a private -key with a password you should omit the -.B \-nodes -option when you use the -.B openssl -command line tool to manage certificates and private keys. - -If -.B file -is specified, read the password from the first line of -.B file. -Keep in mind that storing your password in a file -to a certain extent invalidates the extra security provided by -using an encrypted key. -.\"********************************************************* -.TP -.B \-\-auth\-nocache -Don't cache -.B \-\-askpass -or -.B \-\-auth\-user\-pass -username/passwords in virtual memory. - -If specified, this directive will cause OpenVPN to immediately -forget username/password inputs after they are used. As a result, -when OpenVPN needs a username/password, it will prompt for input -from stdin, which may be multiple times during the duration of an -OpenVPN session. - -When using \-\-auth\-nocache in combination with a user/password file -and \-\-chroot or \-\-daemon, make sure to use an absolute path. - -This directive does not affect the -.B \-\-http\-proxy -username/password. It is always cached. -.\"********************************************************* -.TP -.B \-\-auth\-token token -This is not an option to be used directly in any configuration files, -but rather push this option from a -.B \-\-client\-connect -script or a -.B \-\-plugin -which hooks into the OPENVPN_PLUGIN_CLIENT_CONNECT or -OPENVPN_PLUGIN_CLIENT_CONNECT_V2 calls. This option provides -a possibility to replace the clients password with an authentication -token during the lifetime of the OpenVPN client. - -Whenever the connection is renegotiated and the -.B \-\-auth\-user\-pass\-verify -script or -.B \-\-plugin -making use of the OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY hook is -triggered, it will pass over this token as the password -instead of the password the user provided. The authentication -token can only be reset by a full reconnect where the server -can push new options to the client. The password the user entered -is never preserved once an authentication token have been set. If -the OpenVPN server side rejects the authentication token, the -client will receive an AUTH_FAIL and disconnect. - -The purpose of this is to enable two factor authentication -methods, such as HOTP or TOTP, to be used without needing to -retrieve a new OTP code each time the connection is renegotiated. -Another use case is to cache authentication data on the client -without needing to have the users password cached in memory -during the life time of the session. - -To make use of this feature, the -.B \-\-client\-connect -script or -.B \-\-plugin -needs to put - -.nf -.ft 3 -.in +4 -push "auth\-token UNIQUE_TOKEN_VALUE" -.in -4 -.ft -.fi - -into the file/buffer for dynamic configuration data. This -will then make the OpenVPN server to push this value to the -client, which replaces the local password with the -UNIQUE_TOKEN_VALUE. - -Newer clients (2.4.7+) will fall back to the original password method -after a failed auth. Older clients will keep using the token value -and react acording to -.B \-\-auth-retry -. -.\"********************************************************* -.TP -.B \-\-tls\-verify cmd -Run command -.B cmd -to verify the X509 name of a -pending TLS connection that has otherwise passed all other -tests of certification (except for revocation via -.B \-\-crl\-verify -directive; the revocation test occurs after the -.B \-\-tls\-verify -test). - -.B cmd -should return 0 to allow the TLS handshake to proceed, or 1 to fail. - -.B cmd -consists of a path to script (or executable program), optionally -followed by arguments. The path and arguments may be single\- or double\-quoted -and/or escaped using a backslash, and should be separated by one or more spaces. - -When -.B cmd -is executed two arguments are appended after any arguments specified in -.B cmd -, as follows: - -.B cmd certificate_depth subject - -These arguments are, respectively, the current certificate depth and -the X509 subject distinguished name (dn) of the peer. - -This feature is useful if the peer you want to trust has a certificate -which was signed by a certificate authority who also signed many -other certificates, where you don't necessarily want to trust all of them, -but rather be selective about which -peer certificate you will accept. This feature allows you to write a script -which will test the X509 name on a certificate and decide whether or -not it should be accepted. For a simple perl script which will test -the common name field on the certificate, see the file -.B verify\-cn -in the OpenVPN distribution. - -See the "Environmental Variables" section below for -additional parameters passed as environmental variables. -.\"********************************************************* -.TP -.B \-\-tls\-export\-cert directory -Store the certificates the clients uses upon connection to this -directory. This will be done before \-\-tls\-verify is called. The -certificates will use a temporary name and will be deleted when -the tls\-verify script returns. The file name used for the certificate -is available via the peer_cert environment variable. -.\"********************************************************* -.TP -.B \-\-x509\-username\-field [ext:\]fieldname -Field in the X.509 certificate subject to be used as the username (default=CN). -Typically, this option is specified with -.B fieldname -as either of the following: - -.B \-\-x509\-username\-field -emailAddress -.br -.B \-\-x509\-username\-field ext:\fRsubjectAltName - -The first example uses the value of the "emailAddress" attribute in the -certificate's Subject field as the username. The second example uses -the -.B ext: -prefix to signify that the X.509 extension -.B fieldname -"subjectAltName" be searched for an rfc822Name (email) field to be used -as the username. In cases where there are multiple email addresses -in -.B ext:fieldname\fR, -the last occurrence is chosen. - -When this option is used, the -.B \-\-verify\-x509\-name -option will match against the chosen -.B fieldname -instead of the Common Name. - -Only the subjectAltName and issuerAltName X.509 extensions are supported. - -.B Please note: -This option has a feature which will convert an all\-lowercase -.B fieldname -to uppercase characters, e.g., ou \-> OU. A mixed\-case -.B fieldname -or one having the -.B ext: -prefix will be left as\-is. This automatic upcasing feature -is deprecated and will be removed in a future release. -.\"********************************************************* -.TP -.B \-\-verify\-x509\-name name type -Accept connections only if a host's X.509 name is equal to -.B name. -The remote host must also pass all other tests of verification. - -Which X.509 name is compared to -.B name -depends on the setting of type. -.B type -can be "subject" to match the complete subject DN (default), -"name" to match a subject RDN or "name\-prefix" to match a subject RDN prefix. -Which RDN is verified as name depends on the -.B \-\-x509\-username\-field -option. But it defaults to the common name (CN), e.g. a certificate with a -subject DN "C=KG, ST=NA, L=Bishkek, CN=Server\-1" would be matched by: - -.B \-\-verify\-x509\-name 'C=KG, ST=NA, L=Bishkek, CN=Server\-1' -and -.B \-\-verify\-x509\-name Server\-1 name -or you could use -.B \-\-verify\-x509\-name Server\- name\-prefix -if you want a client to only accept connections to "Server\-1", "Server\-2", etc. - -.B \-\-verify\-x509\-name -is a useful replacement for the -.B \-\-tls\-verify -option to verify the remote host, because -.B \-\-verify\-x509\-name -works in a -.B \-\-chroot -environment without any dependencies. - -Using a name prefix is a useful alternative to managing -a CRL (Certificate Revocation List) on the client, since it allows the client -to refuse all certificates except for those associated -with designated servers. - -.B NOTE: -Test against a name prefix only when you are using OpenVPN with -a custom CA certificate that is under your control. -Never use this option with type "name\-prefix" when your client certificates -are signed by a third party, such as a commercial web CA. -.\"********************************************************* -.TP -.B \-\-x509\-track attribute -Save peer X509 -.B attribute -value in environment for use by plugins and management interface. -Prepend a '+' to -.B attribute -to save values from full cert chain. Values will be encoded -as X509__=. Multiple -.B \-\-x509\-track -options can be defined to track multiple attributes. -.\"********************************************************* -.TP -.B \-\-ns\-cert\-type client|server -.B DEPRECATED -This option will be removed in OpenVPN 2.5. Use the more modern equivalent -.B \-\-remote\-cert\-tls -instead. This option will be removed in OpenVPN 2.5. - -Require that peer certificate was signed with an explicit -.B nsCertType -designation of "client" or "server". - -This is a useful security option for clients, to ensure that -the host they connect with is a designated server. - -See the easy\-rsa/build\-key\-server script for an example -of how to generate a certificate with the -.B nsCertType -field set to "server". - -If the server certificate's nsCertType field is set -to "server", then the clients can verify this with -.B \-\-ns\-cert\-type server. - -This is an important security precaution to protect against -a man\-in\-the\-middle attack where an authorized client -attempts to connect to another client by impersonating the server. -The attack is easily prevented by having clients verify -the server certificate using any one of -.B \-\-ns\-cert\-type, \-\-verify\-x509\-name, -or -.B \-\-tls\-verify. -.\"********************************************************* -.TP -.B \-\-remote\-cert\-ku [v...] -Require that peer certificate was signed with an explicit -.B key usage. - -If present in the certificate, the keyUsage value is validated by the TLS -library during the TLS handshake. Specifying this option without arguments -requires this extension to be present (so the TLS library will verify it). - -If the list -.B v... -is also supplied, the keyUsage field must have -.B at least -the same bits set as the bits in -.B one of -the values supplied in the list -.B v... - -The key usage values in the list must be encoded in hex, e.g. -"\-\-remote\-cert\-ku a0" -.\"********************************************************* -.TP -.B \-\-remote\-cert\-eku oid -Require that peer certificate was signed with an explicit -.B extended key usage. - -This is a useful security option for clients, to ensure that -the host they connect to is a designated server. - -The extended key usage should be encoded in oid notation, or -OpenSSL symbolic representation. -.\"********************************************************* -.TP -.B \-\-remote\-cert\-tls client|server -Require that peer certificate was signed with an explicit -.B key usage -and -.B extended key usage -based on RFC3280 TLS rules. - -This is a useful security option for clients, to ensure that the host they -connect to is a designated server. Or the other way around; for a server to -verify that only hosts with a client certificate can connect. - -The -.B \-\-remote\-cert\-tls client -option is equivalent to -.B -\-\-remote\-cert\-ku \-\-remote\-cert\-eku "TLS Web Client Authentication" - -The -.B \-\-remote\-cert\-tls server -option is equivalent to -.B -\-\-remote\-cert\-ku \-\-remote\-cert\-eku "TLS Web Server Authentication" - -This is an important security precaution to protect against -a man\-in\-the\-middle attack where an authorized client -attempts to connect to another client by impersonating the server. -The attack is easily prevented by having clients verify -the server certificate using any one of -.B \-\-remote\-cert\-tls, \-\-verify\-x509\-name, -or -.B \-\-tls\-verify. -.\"********************************************************* -.TP -.B \-\-crl\-verify crl ['dir'] -Check peer certificate against the file -.B crl -in PEM format. - -A CRL (certificate revocation list) is used when a particular key is -compromised but when the overall PKI is still intact. - -Suppose you had a PKI consisting of a CA, root certificate, and a number of -client certificates. Suppose a laptop computer containing a client key and -certificate was stolen. By adding the stolen certificate to the CRL file, -you could reject any connection which attempts to use it, while preserving the -overall integrity of the PKI. - -The only time when it would be necessary to rebuild the entire PKI from scratch would be -if the root certificate key itself was compromised. - -The option is not mandatory \- if the relevant CRL is missing, OpenVPN will log -a warning in the logs \- e.g. "\fIVERIFY WARNING: depth=0, unable to get -certificate CRL\fR" \- but the connection will be allowed. - -If the optional -.B dir -flag is specified, enable a different mode where -.B crl -is a directory containing files named as revoked serial numbers -(the files may be empty, the contents are never read). If a client -requests a connection, where the client certificate serial number -(decimal string) is the name of a file present in the directory, -it will be rejected. - -Note: As the crl file (or directory) is read every time a peer connects, -if you are dropping root privileges with -.B \-\-user, -make sure that this user has sufficient privileges to read the file. -.\"********************************************************* -.SS SSL Library information: -.\"********************************************************* -.TP -.B \-\-show\-ciphers -(Standalone) -Show all cipher algorithms to use with the -.B \-\-cipher -option. -.\"********************************************************* -.TP -.B \-\-show\-digests -(Standalone) -Show all message digest algorithms to use with the -.B \-\-auth -option. -.\"********************************************************* -.TP -.B \-\-show\-tls -(Standalone) -Show all TLS ciphers supported by the crypto library. OpenVPN uses TLS to -secure the control channel, over which the keys that are used to protect the -actual VPN traffic are exchanged. The TLS ciphers will be sorted from highest -preference (most secure) to lowest. - -Be aware that whether a cipher suite in this list can actually work depends on -the specific setup of both peers (e.g. both peers must support the cipher, and -an ECDSA cipher suite will not work if you are using an RSA certificate, etc.). -.\"********************************************************* -.TP -.B \-\-show\-engines -(Standalone) -Show currently available hardware\-based crypto acceleration -engines supported by the OpenSSL library. -.\"********************************************************* -.TP -.B \-\-show\-curves -(Standalone) -Show all available elliptic curves to use with the -.B \-\-ecdh\-curve -option. -.\"********************************************************* -.SS Generate a random key: -Used only for non\-TLS static key encryption mode. -.\"********************************************************* -.TP -.B \-\-genkey -(Standalone) -Generate a random key to be used as a shared secret, -for use with the -.B \-\-secret -option. This file must be shared with the -peer over a pre\-existing secure channel such as -.BR scp (1) -. -.\"********************************************************* -.TP -.B \-\-secret file -Write key to -.B file. -.\"********************************************************* -.SS TUN/TAP persistent tunnel config mode: -Available with Linux 2.4.7+. These options comprise a standalone mode -of OpenVPN which can be used to create and delete persistent tunnels. -.\"********************************************************* -.TP -.B \-\-mktun -(Standalone) -Create a persistent tunnel on platforms which support them such -as Linux. Normally TUN/TAP tunnels exist only for -the period of time that an application has them open. This option -takes advantage of the TUN/TAP driver's ability to build persistent -tunnels that live through multiple instantiations of OpenVPN and die -only when they are deleted or the machine is rebooted. - -One of the advantages of persistent tunnels is that they eliminate the -need for separate -.B \-\-up -and -.B \-\-down -scripts to run the appropriate -.BR ifconfig (8) -and -.BR route (8) -commands. These commands can be placed in the the same shell script -which starts or terminates an OpenVPN session. - -Another advantage is that open connections through the TUN/TAP\-based tunnel -will not be reset if the OpenVPN peer restarts. This can be useful to -provide uninterrupted connectivity through the tunnel in the event of a DHCP -reset of the peer's public IP address (see the -.B \-\-ipchange -option above). - -One disadvantage of persistent tunnels is that it is harder to automatically -configure their MTU value (see -.B \-\-link\-mtu -and -.B \-\-tun\-mtu -above). - -On some platforms such as Windows, TAP\-Win32 tunnels are persistent by -default. -.\"********************************************************* -.TP -.B \-\-rmtun -(Standalone) -Remove a persistent tunnel. -.\"********************************************************* -.TP -.B \-\-dev tunX | tapX -TUN/TAP device -.\"********************************************************* -.TP -.B \-\-user user -Optional user to be owner of this tunnel. -.\"********************************************************* -.TP -.B \-\-group group -Optional group to be owner of this tunnel. -.\"********************************************************* -.SS Windows\-Specific Options: -.\"********************************************************* -.TP -.B \-\-win\-sys path -Set the Windows system directory pathname to use when looking for system -executables such as -.B route.exe -and -.B netsh.exe. -By default, if this directive is -not specified, OpenVPN will use the SystemRoot environment variable. - -This option have changed behaviour in OpenVPN 2.3. Earlier you had to -define -.B \-\-win\-sys env -to use the SystemRoot environment variable, otherwise it defaulted to C:\\WINDOWS. -It is not needed to use the -.B env -keyword any more, and it will just be ignored. A warning is logged when this -is found in the configuration file. -.\"********************************************************* -.TP -.B \-\-ip\-win32 method -When using -.B \-\-ifconfig -on Windows, set the TAP\-Win32 adapter -IP address and netmask using -.B method. -Don't use this option unless you are also using -.B \-\-ifconfig. - -.B manual \-\- -Don't set the IP address or netmask automatically. -Instead output a message -to the console telling the user to configure the -adapter manually and indicating the IP/netmask which -OpenVPN expects the adapter to be set to. - -.B dynamic [offset] [lease\-time] \-\- -Automatically set the IP address and netmask by replying to -DHCP query messages generated by the kernel. This mode is -probably the "cleanest" solution -for setting the TCP/IP properties since it uses the well\-known -DHCP protocol. There are, however, two prerequisites for using -this mode: (1) The TCP/IP properties for the TAP\-Win32 -adapter must be set to "Obtain an IP address automatically," and -(2) OpenVPN needs to claim an IP address in the subnet for use -as the virtual DHCP server address. By default in -.B \-\-dev tap -mode, OpenVPN will -take the normally unused first address in the subnet. For example, -if your subnet is 192.168.4.0 netmask 255.255.255.0, then -OpenVPN will take the IP address 192.168.4.0 to use as the -virtual DHCP server address. In -.B \-\-dev tun -mode, OpenVPN will cause the DHCP server to masquerade as if it were -coming from the remote endpoint. The optional offset parameter is -an integer which is > \-256 and < 256 and which defaults to \-1. -If offset is positive, the DHCP server will masquerade as the IP -address at network address + offset. -If offset is negative, the DHCP server will masquerade as the IP -address at broadcast address + offset. The Windows -.B ipconfig /all -command can be used to show what Windows thinks the DHCP server -address is. OpenVPN will "claim" this address, so make sure to -use a free address. Having said that, different OpenVPN instantiations, -including different ends of the same connection, can share the same -virtual DHCP server address. The -.B lease\-time -parameter controls the lease time of the DHCP assignment given to -the TAP\-Win32 adapter, and is denoted in seconds. -Normally a very long lease time is preferred -because it prevents routes involving the TAP\-Win32 adapter from -being lost when the system goes to sleep. The default -lease time is one year. - -.B netsh \-\- -Automatically set the IP address and netmask using -the Windows command\-line "netsh" -command. This method appears to work correctly on -Windows XP but not Windows 2000. - -.B ipapi \-\- -Automatically set the IP address and netmask using the -Windows IP Helper API. This approach -does not have ideal semantics, though testing has indicated -that it works okay in practice. If you use this option, -it is best to leave the TCP/IP properties for the TAP\-Win32 -adapter in their default state, i.e. "Obtain an IP address -automatically." - -.B adaptive \-\- -(Default) Try -.B dynamic -method initially and fail over to -.B netsh -if the DHCP negotiation with the TAP\-Win32 adapter does -not succeed in 20 seconds. Such failures have been known -to occur when certain third\-party firewall packages installed -on the client machine block the DHCP negotiation used by -the TAP\-Win32 adapter. -Note that if the -.B netsh -failover occurs, the TAP\-Win32 adapter -TCP/IP properties will be reset from DHCP to static, and this -will cause future OpenVPN startups using the -.B adaptive -mode to use -.B netsh -immediately, rather than trying -.B dynamic -first. To "unstick" the -.B adaptive -mode from using -.B netsh, -run OpenVPN at least once using the -.B dynamic -mode to restore the TAP\-Win32 adapter TCP/IP properties -to a DHCP configuration. -.\"********************************************************* -.TP -.B \-\-route\-method m -Which method -.B m -to use for adding routes on Windows? - -.B adaptive -(default) \-\- Try IP helper API first. If that fails, fall -back to the route.exe shell command. -.br -.B ipapi -\-\- Use IP helper API. -.br -.B exe -\-\- Call the route.exe shell command. -.\"********************************************************* -.TP -.B \-\-dhcp\-option type [parm] -Set extended TAP\-Win32 TCP/IP properties, must -be used with -.B \-\-ip\-win32 dynamic -or -.B \-\-ip\-win32 adaptive. -This option can be used to set additional TCP/IP properties -on the TAP\-Win32 adapter, and is particularly useful for -configuring an OpenVPN client to access a Samba server -across the VPN. - -.B DOMAIN name \-\- -Set Connection\-specific DNS Suffix. - -.B DNS addr \-\- -Set primary domain name server IPv4 or IPv6 address. Repeat -this option to set secondary DNS server addresses. - -Note: DNS IPv6 servers are currently set using netsh (the existing -DHCP code can only do IPv4 DHCP, and that protocol only permits IPv4 -addresses anywhere). The option will be put into the environment, so -an -.B \-\-up -script could act upon it if needed. - -.B WINS addr \-\- -Set primary WINS server address (NetBIOS over TCP/IP Name Server). -Repeat this option to set secondary WINS server addresses. - -.B NBDD addr \-\- -Set primary NBDD server address (NetBIOS over TCP/IP Datagram Distribution Server) -Repeat this option -to set secondary NBDD server addresses. - -.B NTP addr \-\- -Set primary NTP server address (Network Time Protocol). -Repeat this option -to set secondary NTP server addresses. - -.B NBT type \-\- -Set NetBIOS over TCP/IP Node type. Possible options: -.B 1 -= b\-node (broadcasts), -.B 2 -= p\-node (point\-to\-point -name queries to a WINS server), -.B 4 -= m\-node (broadcast -then query name server), and -.B 8 -= h\-node (query name server, then broadcast). - -.B NBS scope\-id \-\- -Set NetBIOS over TCP/IP Scope. A NetBIOS Scope ID provides an extended -naming service for the NetBIOS over TCP/IP (Known as NBT) module. The -primary purpose of a NetBIOS scope ID is to isolate NetBIOS traffic on -a single network to only those nodes with the same NetBIOS scope ID. -The NetBIOS scope ID is a character string that is appended to the NetBIOS -name. The NetBIOS scope ID on two hosts must match, or the two hosts -will not be able to communicate. The NetBIOS Scope ID also allows -computers to use the same computer name, as they have different -scope IDs. The Scope ID becomes a part of the NetBIOS name, making the name unique. -(This description of NetBIOS scopes courtesy of NeonSurge@abyss.com) - -.B DISABLE\-NBT \-\- -Disable Netbios\-over\-TCP/IP. - -Note that if -.B \-\-dhcp\-option -is pushed via -.B \-\-push -to a non\-windows client, the option will be saved in the client's -environment before the up script is called, under -the name "foreign_option_{n}". -.\"********************************************************* -.TP -.B \-\-tap\-sleep n -Cause OpenVPN to sleep for -.B n -seconds immediately after the TAP\-Win32 adapter state -is set to "connected". - -This option is intended to be used to troubleshoot problems -with the -.B \-\-ifconfig -and -.B \-\-ip\-win32 -options, and is used to give -the TAP\-Win32 adapter time to come up before -Windows IP Helper API operations are applied to it. -.\"********************************************************* -.TP -.B \-\-show\-net\-up -Output OpenVPN's view of the system routing table and network -adapter list to the syslog or log file after the TUN/TAP adapter -has been brought up and any routes have been added. -.\"********************************************************* -.TP -.B \-\-block\-outside\-dns -Block DNS servers on other network adapters to prevent -DNS leaks. This option prevents any application from accessing -TCP or UDP port 53 except one inside the tunnel. It uses -Windows Filtering Platform (WFP) and works on Windows Vista or -later. - -This option is considered unknown on non\-Windows platforms -and unsupported on Windows XP, resulting in fatal error. -You may want to use -.B \-\-setenv opt -or -.B \-\-ignore\-unknown\-option -(not suitable for Windows XP) to ignore said error. -Note that pushing unknown options from server does not trigger -fatal errors. -.\"********************************************************* -.TP -.B \-\-dhcp\-renew -Ask Windows to renew the TAP adapter lease on startup. -This option is normally unnecessary, as Windows automatically -triggers a DHCP renegotiation on the TAP adapter when it -comes up, however if you set the TAP\-Win32 adapter -Media Status property to "Always Connected", you may need this -flag. -.\"********************************************************* -.TP -.B \-\-dhcp\-release -Ask Windows to release the TAP adapter lease on shutdown. -This option has no effect now, as it is enabled by default starting with OpenVPN 2.4.1. -.\"********************************************************* -.TP -.B \-\-register\-dns -Run ipconfig /flushdns and ipconfig /registerdns on connection initiation. -This is known to kick Windows into -recognizing pushed DNS servers. -.\"********************************************************* -.TP -.B \-\-pause\-exit -Put up a "press any key to continue" message on the console prior -to OpenVPN program exit. This option is automatically used by the -Windows explorer when OpenVPN is run on a configuration -file using the right\-click explorer menu. -.\"********************************************************* -.TP -.B \-\-service exit\-event [0|1] -Should be used when OpenVPN is being automatically executed by another -program in such -a context that no interaction with the user via display or keyboard -is possible. In general, end\-users should never need to explicitly -use this option, as it is automatically added by the OpenVPN service wrapper -when a given OpenVPN configuration is being run as a service. - -.B exit\-event -is the name of a Windows global event object, and OpenVPN will continuously -monitor the state of this event object and exit when it becomes signaled. - -The second parameter indicates the initial state of -.B exit\-event -and normally defaults to 0. - -Multiple OpenVPN processes can be simultaneously executed with the same -.B exit\-event -parameter. In any case, the controlling process can signal -.B exit\-event, -causing all such OpenVPN processes to exit. - -When executing an OpenVPN process using the -.B \-\-service -directive, OpenVPN will probably not have a console -window to output status/error -messages, therefore it is useful to use -.B \-\-log -or -.B \-\-log\-append -to write these messages to a file. -.\"********************************************************* -.TP -.B \-\-show\-adapters -(Standalone) -Show available TAP\-Win32 adapters which can be selected using the -.B \-\-dev\-node -option. On non\-Windows systems, the -.BR ifconfig (8) -command provides similar functionality. -.\"********************************************************* -.TP -.B \-\-allow\-nonadmin [TAP\-adapter] -(Standalone) -Set -.B TAP\-adapter -to allow access from non\-administrative accounts. If -.B TAP\-adapter -is omitted, all TAP adapters on the system will be configured to allow -non\-admin access. -The non\-admin access setting will only persist for the length of time that -the TAP\-Win32 device object and driver remain loaded, and will need -to be re\-enabled after a reboot, or if the driver is unloaded -and reloaded. -This directive can only be used by an administrator. -.\"********************************************************* -.TP -.B \-\-show\-valid\-subnets -(Standalone) -Show valid subnets for -.B \-\-dev tun -emulation. Since the TAP\-Win32 driver -exports an ethernet interface to Windows, and since TUN devices are -point\-to\-point in nature, it is necessary for the TAP\-Win32 driver -to impose certain constraints on TUN endpoint address selection. - -Namely, the point\-to\-point endpoints used in TUN device emulation -must be the middle two addresses of a /30 subnet (netmask 255.255.255.252). -.\"********************************************************* -.TP -.B \-\-show\-net -(Standalone) -Show OpenVPN's view of the system routing table and network -adapter list. -.\"********************************************************* -.SS PKCS#11 Standalone Options: -.\"********************************************************* -.TP -.B \-\-show\-pkcs11\-ids [provider] [cert_private] -(Standalone) -Show PKCS#11 token object list. Specify cert_private as 1 -if certificates are stored as private objects. - -If p11\-kit is present on the system, the -.B provider -argument is optional; if omitted the default -.B p11\-kit\-proxy.so -module will be queried. - -.B \-\-verb -option can be used BEFORE this option to produce debugging information. -.\"********************************************************* -.SS Standalone Debug Options: -.\"********************************************************* -.TP -.B \-\-show\-gateway [v6target] -(Standalone) -Show current IPv4 and IPv6 default gateway and interface towards the -gateway (if the protocol in question is enabled). If an IPv6 address -is passed as argument, the IPv6 route for this host is reported. -.\"********************************************************* -.SS IPv6 Related Options -.\"********************************************************* -The following options exist to support IPv6 tunneling in peer\-to\-peer -and client\-server mode. All options are modeled after their IPv4 -counterparts, so more detailed explanations given there apply here -as well (except for -.B \-\-topology -, which has no effect on IPv6). -.TP -.B \-\-ifconfig\-ipv6 ipv6addr/bits ipv6remote -configure IPv6 address -.B ipv6addr/bits -on the ``tun'' device. The second parameter is used as route target for -.B \-\-route\-ipv6 -if no gateway is specified. -.TP -.B \-\-route\-ipv6 ipv6addr/bits [gateway] [metric] -setup IPv6 routing in the system to send the specified IPv6 network -into OpenVPN's ``tun''. The gateway parameter is only used for -IPv6 routes across ``tap'' devices, and if missing, the ``ipv6remote'' -field from -.B \-\-ifconfig\-ipv6 -is used. -.TP -.B \-\-server\-ipv6 ipv6addr/bits -convenience\-function to enable a number of IPv6 related options at -once, namely -.B \-\-ifconfig\-ipv6, \-\-ifconfig\-ipv6\-pool -and -.B \-\-push tun\-ipv6 -Is only accepted if ``\-\-mode server'' or ``\-\-server'' is set. Pushing of the -.B \-\-tun\-ipv6 -directive is done for older clients which require an explicit -``\-\-tun\-ipv6'' in their configuration. -.TP -.B \-\-ifconfig\-ipv6\-pool ipv6addr/bits -Specify an IPv6 address pool for dynamic assignment to clients. The -pool starts at -.B ipv6addr -and matches the offset determined from the start of the IPv4 pool. -.TP -.B \-\-ifconfig\-ipv6\-push ipv6addr/bits ipv6remote -for ccd/ per\-client static IPv6 interface configuration, see -.B \-\-client\-config\-dir -and -.B \-\-ifconfig\-push -for more details. -.TP -.B \-\-iroute\-ipv6 ipv6addr/bits -for ccd/ per\-client static IPv6 route configuration, see -.B \-\-iroute -for more details how to setup and use this, and how -.B \-\-iroute -and -.B \-\-route -interact. - -.\"********************************************************* -.SH SCRIPTING AND ENVIRONMENTAL VARIABLES -OpenVPN exports a series -of environmental variables for use by user\-defined scripts. -.\"********************************************************* -.SS Script Order of Execution -.\"********************************************************* -.TP -.B \-\-up -Executed after TCP/UDP socket bind and TUN/TAP open. -.\"********************************************************* -.TP -.B \-\-tls\-verify -Executed when we have a still untrusted remote peer. -.\"********************************************************* -.TP -.B \-\-ipchange -Executed after connection authentication, or remote IP address change. -.\"********************************************************* -.TP -.B \-\-client\-connect -Executed in -.B \-\-mode server -mode immediately after client authentication. -.\"********************************************************* -.TP -.B \-\-route\-up -Executed after connection authentication, either -immediately after, or some number of seconds after -as defined by the -.B \-\-route\-delay -option. -.\"********************************************************* -.TP -.B \-\-route\-pre\-down -Executed right before the routes are removed. -.\"********************************************************* -.TP -.B \-\-client\-disconnect -Executed in -.B \-\-mode server -mode on client instance shutdown. -.\"********************************************************* -.TP -.B \-\-down -Executed after TCP/UDP and TUN/TAP close. -.\"********************************************************* -.TP -.B \-\-learn\-address -Executed in -.B \-\-mode server -mode whenever an IPv4 address/route or MAC address is added to OpenVPN's -internal routing table. -.\"********************************************************* -.TP -.B \-\-auth\-user\-pass\-verify -Executed in -.B \-\-mode server -mode on new client connections, when the client is -still untrusted. -.\"********************************************************* -.SS String Types and Remapping -In certain cases, OpenVPN will perform remapping of characters -in strings. Essentially, any characters outside the set of -permitted characters for each string type will be converted -to underbar ('_'). - -.B Q: -Why is string remapping necessary? - -.B A: -It's an important security feature to prevent the malicious coding of -strings from untrusted sources to be passed as parameters to scripts, -saved in the environment, used as a common name, translated to a filename, -etc. - -.B Q: -Can string remapping be disabled? - -.B A: -Yes, by using the -.B \-\-no\-name\-remapping -option, however this should be considered an advanced option. - -Here is a brief rundown of OpenVPN's current string types and the -permitted character class for each string: - -.B X509 Names: -Alphanumeric, underbar ('_'), dash ('\-'), dot ('.'), at -('@'), colon (':'), slash ('/'), and equal ('='). Alphanumeric is defined -as a character which will cause the C library isalnum() function to return -true. - -.B Common Names: -Alphanumeric, underbar ('_'), dash ('\-'), dot ('.'), and at -('@'). - -.B \-\-auth\-user\-pass username: -Same as Common Name, with one exception: starting with OpenVPN 2.0.1, -the username is passed to the OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY plugin in its raw form, -without string remapping. - -.B \-\-auth\-user\-pass password: -Any "printable" character except CR or LF. -Printable is defined to be a character which will cause the C library -isprint() function to return true. - -.B \-\-client\-config\-dir filename as derived from common name or username: -Alphanumeric, underbar ('_'), dash ('\-'), and dot ('.') except for "." or -".." as standalone strings. As of v2.0.1\-rc6, the at ('@') character has -been added as well for compatibility with the common name character class. - -.B Environmental variable names: -Alphanumeric or underbar ('_'). - -.B Environmental variable values: -Any printable character. - -For all cases, characters in a string which are not members of the legal -character class for that string type will be remapped to underbar ('_'). -.\"********************************************************* -.SS Environmental Variables -Once set, a variable is persisted -indefinitely until it is reset by a new value or a restart, - -As of OpenVPN 2.0\-beta12, in server mode, environmental -variables set by OpenVPN -are scoped according to the client objects -they are -associated with, so there should not be any issues with -scripts having access to stale, previously set variables -which refer to different client instances. -.\"********************************************************* -.TP -.B bytes_received -Total number of bytes received from client during VPN session. -Set prior to execution of the -.B \-\-client\-disconnect -script. -.\"********************************************************* -.TP -.B bytes_sent -Total number of bytes sent to client during VPN session. -Set prior to execution of the -.B \-\-client\-disconnect -script. -.\"********************************************************* -.TP -.B common_name -The X509 common name of an authenticated client. -Set prior to execution of -.B \-\-client\-connect, \-\-client\-disconnect, -and -.B \-\-auth\-user\-pass\-verify -scripts. -.\"********************************************************* -.TP -.B config -Name of first -.B \-\-config -file. -Set on program initiation and reset on SIGHUP. -.\"********************************************************* -.TP -.B daemon -Set to "1" if the -.B \-\-daemon -directive is specified, or "0" otherwise. -Set on program initiation and reset on SIGHUP. -.\"********************************************************* -.TP -.B daemon_log_redirect -Set to "1" if the -.B \-\-log -or -.B \-\-log\-append -directives are specified, or "0" otherwise. -Set on program initiation and reset on SIGHUP. -.\"********************************************************* -.TP -.B dev -The actual name of the TUN/TAP device, including -a unit number if it exists. -Set prior to -.B \-\-up -or -.B \-\-down -script execution. -.\"********************************************************* -.TP -.B dev_idx -On Windows, the device index of the TUN/TAP adapter (to -be used in netsh.exe calls which sometimes just do not work -right with interface names). -Set prior to -.B \-\-up -or -.B \-\-down -script execution. -.\"********************************************************* -.TP -.B foreign_option_{n} -An option pushed via -.B \-\-push -to a client which does not natively support it, -such as -.B \-\-dhcp\-option -on a non\-Windows system, will be recorded to this -environmental variable sequence prior to -.B \-\-up -script execution. -.\"********************************************************* -.TP -.B ifconfig_broadcast -The broadcast address for the virtual -ethernet segment which is derived from the -.B \-\-ifconfig -option when -.B \-\-dev tap -is used. -Set prior to OpenVPN calling the -.I ifconfig -or -.I netsh -(windows version of ifconfig) commands which -normally occurs prior to -.B \-\-up -script execution. -.\"********************************************************* -.TP -.B ifconfig_ipv6_local -The local VPN endpoint IPv6 address specified in the -.B \-\-ifconfig\-ipv6 -option (first parameter). -Set prior to OpenVPN calling the -.I ifconfig -or -.I netsh -(windows version of ifconfig) commands which -normally occurs prior to -.B \-\-up -script execution. -.\"********************************************************* -.TP -.B ifconfig_ipv6_netbits -The prefix length of the IPv6 network on the VPN interface. Derived from -the /nnn parameter of the IPv6 address in the -.B \-\-ifconfig\-ipv6 -option (first parameter). -Set prior to OpenVPN calling the -.I ifconfig -or -.I netsh -(windows version of ifconfig) commands which -normally occurs prior to -.B \-\-up -script execution. -.\"********************************************************* -.TP -.B ifconfig_ipv6_remote -The remote VPN endpoint IPv6 address specified in the -.B \-\-ifconfig\-ipv6 -option (second parameter). -Set prior to OpenVPN calling the -.I ifconfig -or -.I netsh -(windows version of ifconfig) commands which -normally occurs prior to -.B \-\-up -script execution. -.\"********************************************************* -.TP -.B ifconfig_local -The local VPN endpoint IP address specified in the -.B \-\-ifconfig -option (first parameter). -Set prior to OpenVPN calling the -.I ifconfig -or -.I netsh -(windows version of ifconfig) commands which -normally occurs prior to -.B \-\-up -script execution. -.\"********************************************************* -.TP -.B ifconfig_remote -The remote VPN endpoint IP address specified in the -.B \-\-ifconfig -option (second parameter) when -.B \-\-dev tun -is used. -Set prior to OpenVPN calling the -.I ifconfig -or -.I netsh -(windows version of ifconfig) commands which -normally occurs prior to -.B \-\-up -script execution. -.\"********************************************************* -.TP -.B ifconfig_netmask -The subnet mask of the virtual ethernet segment -that is specified as the second parameter to -.B \-\-ifconfig -when -.B \-\-dev tap -is being used. -Set prior to OpenVPN calling the -.I ifconfig -or -.I netsh -(windows version of ifconfig) commands which -normally occurs prior to -.B \-\-up -script execution. -.\"********************************************************* -.TP -.B ifconfig_pool_local_ip -The local -virtual IP address for the TUN/TAP tunnel taken from an -.B \-\-ifconfig\-push -directive if specified, or otherwise from -the ifconfig pool (controlled by the -.B \-\-ifconfig\-pool -config file directive). -Only set for -.B \-\-dev tun -tunnels. -This option is set on the server prior to execution -of the -.B \-\-client\-connect -and -.B \-\-client\-disconnect -scripts. -.\"********************************************************* -.TP -.B ifconfig_pool_netmask -The -virtual IP netmask for the TUN/TAP tunnel taken from an -.B \-\-ifconfig\-push -directive if specified, or otherwise from -the ifconfig pool (controlled by the -.B \-\-ifconfig\-pool -config file directive). -Only set for -.B \-\-dev tap -tunnels. -This option is set on the server prior to execution -of the -.B \-\-client\-connect -and -.B \-\-client\-disconnect -scripts. -.\"********************************************************* -.TP -.B ifconfig_pool_remote_ip -The remote -virtual IP address for the TUN/TAP tunnel taken from an -.B \-\-ifconfig\-push -directive if specified, or otherwise from -the ifconfig pool (controlled by the -.B \-\-ifconfig\-pool -config file directive). -This option is set on the server prior to execution -of the -.B \-\-client\-connect -and -.B \-\-client\-disconnect -scripts. -.\"********************************************************* -.TP -.B link_mtu -The maximum packet size (not including the IP header) -of tunnel data in UDP tunnel transport mode. -Set prior to -.B \-\-up -or -.B \-\-down -script execution. -.\"********************************************************* -.TP -.B local -The -.B \-\-local -parameter. -Set on program initiation and reset on SIGHUP. -.\"********************************************************* -.TP -.B local_port -The local port number or name, specified by -.B \-\-port -or -.B \-\-lport. -Set on program initiation and reset on SIGHUP. -.\"********************************************************* -.TP -.B password -The password provided by a connecting client. -Set prior to -.B \-\-auth\-user\-pass\-verify -script execution only when the -.B via\-env -modifier is specified, and deleted from the environment -after the script returns. -.\"********************************************************* -.TP -.B proto -The -.B \-\-proto -parameter. -Set on program initiation and reset on SIGHUP. -.\"********************************************************* -.TP -.B remote_{n} -The -.B \-\-remote -parameter. -Set on program initiation and reset on SIGHUP. -.\"********************************************************* -.TP -.B remote_port_{n} -The remote port number, specified by -.B \-\-port -or -.B \-\-rport. -Set on program initiation and reset on SIGHUP. -.\"********************************************************* -.TP -.B route_net_gateway -The pre\-existing default IP gateway in the system routing -table. -Set prior to -.B \-\-up -script execution. -.\"********************************************************* -.TP -.B route_vpn_gateway -The default gateway used by -.B \-\-route -options, as specified in either the -.B \-\-route\-gateway -option or the second parameter to -.B \-\-ifconfig -when -.B \-\-dev tun -is specified. -Set prior to -.B \-\-up -script execution. -.\"********************************************************* -.TP -.B route_{parm}_{n} -A set of variables which define each route to be added, and -are set prior to -.B \-\-up -script execution. - -.B parm -will be one of "network", "netmask", "gateway", or "metric". - -.B n -is the OpenVPN route number, starting from 1. - -If the network or gateway are resolvable DNS names, -their IP address translations will be recorded rather -than their names as denoted on the command line -or configuration file. -.\"********************************************************* -.TP -.B route_ipv6_{parm}_{n} -A set of variables which define each IPv6 route to be added, and -are set prior to -.B \-\-up -script execution. - -.B parm -will be one of "network" or "gateway" ("netmask" is contained as "/nnn" -in the route_ipv6_network_{n}, unlike IPv4 where it is passed in a separate -environment variable). - -.B n -is the OpenVPN route number, starting from 1. - -If the network or gateway are resolvable DNS names, -their IP address translations will be recorded rather -than their names as denoted on the command line -or configuration file. -.\"********************************************************* -.TP -.B peer_cert -Temporary file name containing the client certificate upon -connection. Useful in conjunction with \-\-tls\-verify -.\"********************************************************* -.TP -.B script_context -Set to "init" or "restart" prior to up/down script execution. -For more information, see -documentation for -.B \-\-up. -.\"********************************************************* -.TP -.B script_type -Prior to execution of any script, this variable is set to the type of -script being run. It can be one of the following: -.B up, down, ipchange, route\-up, tls\-verify, auth\-user\-pass\-verify, -.B client\-connect, client\-disconnect, -or -.B learn\-address. -Set prior to execution of any script. -.\"********************************************************* -.TP -.B signal -The reason for exit or restart. Can be one of -.B sigusr1, sighup, sigterm, sigint, inactive -(controlled by -.B \-\-inactive -option), -.B ping\-exit -(controlled by -.B \-\-ping\-exit -option), -.B ping\-restart -(controlled by -.B \-\-ping\-restart -option), -.B connection\-reset -(triggered on TCP connection reset), -.B error, -or -.B unknown -(unknown signal). This variable is set just prior to down script execution. -.\"********************************************************* -.TP -.B time_ascii -Client connection timestamp, formatted as a human\-readable -time string. -Set prior to execution of the -.B \-\-client\-connect -script. -.\"********************************************************* -.TP -.B time_duration -The duration (in seconds) of the client session which is now -disconnecting. -Set prior to execution of the -.B \-\-client\-disconnect -script. -.\"********************************************************* -.TP -.B time_unix -Client connection timestamp, formatted as a unix integer -date/time value. -Set prior to execution of the -.B \-\-client\-connect -script. -.\"********************************************************* -.TP -.B tls_digest_{n} / tls_digest_sha256_{n} -Contains the certificate SHA1 / SHA256 fingerprint, where -.B n -is the verification level. Only set for TLS connections. Set prior -to execution of -.B \-\-tls\-verify -script. -.\"********************************************************* -.TP -.B tls_id_{n} -A series of certificate fields from the remote peer, -where -.B n -is the verification level. Only set for TLS connections. Set prior -to execution of -.B \-\-tls\-verify -script. -.\"********************************************************* -.TP -.B tls_serial_{n} -The serial number of the certificate from the remote peer, -where -.B n -is the verification level. Only set for TLS connections. Set prior -to execution of -.B \-\-tls\-verify -script. This is in the form of a decimal string like "933971680", which is -suitable for doing serial\-based OCSP queries (with OpenSSL, do not -prepend "0x" to the string) If something goes wrong while reading -the value from the certificate it will be an empty string, so your -code should check that. -See the contrib/OCSP_check/OCSP_check.sh script for an example. -.\"********************************************************* -.TP -.B tls_serial_hex_{n} -Like -.B tls_serial_{n}\fR, -but in hex form (e.g. "12:34:56:78:9A"). -.\"********************************************************* -.TP -.B tun_mtu -The MTU of the TUN/TAP device. -Set prior to -.B \-\-up -or -.B \-\-down -script execution. -.\"********************************************************* -.TP -.B trusted_ip (or trusted_ip6) -Actual IP address of connecting client or peer which has been authenticated. -Set prior to execution of -.B \-\-ipchange, \-\-client\-connect, -and -.B \-\-client\-disconnect -scripts. -If using ipv6 endpoints (udp6, tcp6), -.B trusted_ip6 -will be set instead. -.\"********************************************************* -.TP -.B trusted_port -Actual port number of connecting client or peer which has been authenticated. -Set prior to execution of -.B \-\-ipchange, \-\-client\-connect, -and -.B \-\-client\-disconnect -scripts. -.\"********************************************************* -.TP -.B untrusted_ip (or untrusted_ip6) -Actual IP address of connecting client or peer which has not been authenticated -yet. Sometimes used to -.B nmap -the connecting host in a -.B \-\-tls\-verify -script to ensure it is firewalled properly. -Set prior to execution of -.B \-\-tls\-verify -and -.B \-\-auth\-user\-pass\-verify -scripts. -If using ipv6 endpoints (udp6, tcp6), -.B untrusted_ip6 -will be set instead. -.\"********************************************************* -.TP -.B untrusted_port -Actual port number of connecting client or peer which has not been authenticated -yet. -Set prior to execution of -.B \-\-tls\-verify -and -.B \-\-auth\-user\-pass\-verify -scripts. -.\"********************************************************* -.TP -.B username -The username provided by a connecting client. -Set prior to -.B \-\-auth\-user\-pass\-verify -script execution only when the -.B via\-env -modifier is specified. -.\"********************************************************* -.TP -.B X509_{n}_{subject_field} -An X509 subject field from the remote peer certificate, -where -.B n -is the verification level. Only set for TLS connections. Set prior -to execution of -.B \-\-tls\-verify -script. This variable is similar to -.B tls_id_{n} -except the component X509 subject fields are broken out, and -no string remapping occurs on these field values (except for remapping -of control characters to "_"). -For example, the following variables would be set on the -OpenVPN server using the sample client certificate -in sample\-keys (client.crt). -Note that the verification level is 0 for the client certificate -and 1 for the CA certificate. - -.nf -.ft 3 -.in +4 -X509_0_emailAddress=me@myhost.mydomain -X509_0_CN=Test\-Client -X509_0_O=OpenVPN\-TEST -X509_0_ST=NA -X509_0_C=KG -X509_1_emailAddress=me@myhost.mydomain -X509_1_O=OpenVPN\-TEST -X509_1_L=BISHKEK -X509_1_ST=NA -X509_1_C=KG -.in -4 -.ft -.fi -.\"********************************************************* -.SH INLINE FILE SUPPORT -OpenVPN allows including files in the main configuration for the -.B \-\-ca, \-\-cert, \-\-dh, \-\-extra\-certs, \-\-key, \-\-pkcs12, \-\-secret, -.B \-\-crl\-verify, \-\-http\-proxy\-user\-pass, \-\-tls\-auth -and -.B \-\-tls\-crypt -options. - -Each inline file started by the line -.B - -Here is an example of an inline file usage - -.nf -.ft 3 -.in +4 - -\-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\- -[...] -\-\-\-\-\-END CERTIFICATE\-\-\-\-\- - -.in -4 -.ft -.fi - -When using the inline file feature with -.B \-\-pkcs12 -the inline file has to be base64 encoded. Encoding of a .p12 file into base64 can be done for example with OpenSSL by running -.B openssl base64 \-in input.p12 - -.SH SIGNALS -.TP -.B SIGHUP -Cause OpenVPN to close all TUN/TAP and -network connections, -restart, re\-read the configuration file (if any), -and reopen TUN/TAP and network connections. -.\"********************************************************* -.TP -.B SIGUSR1 -Like -.B SIGHUP, -except don't re\-read configuration file, and possibly don't close and reopen TUN/TAP -device, re\-read key files, preserve local IP address/port, or preserve most recently authenticated -remote IP address/port based on -.B \-\-persist\-tun, \-\-persist\-key, \-\-persist\-local\-ip, -and -.B \-\-persist\-remote\-ip -options respectively (see above). - -This signal may also be internally generated by a timeout condition, governed -by the -.B \-\-ping\-restart -option. - -This signal, when combined with -.B \-\-persist\-remote\-ip, -may be -sent when the underlying parameters of the host's network interface change -such as when the host is a DHCP client and is assigned a new IP address. -See -.B \-\-ipchange -above for more information. -.\"********************************************************* -.TP -.B SIGUSR2 -Causes OpenVPN to display its current statistics (to the syslog -file if -.B \-\-daemon -is used, or stdout otherwise). -.\"********************************************************* -.TP -.B SIGINT, SIGTERM -Causes OpenVPN to exit gracefully. -.\"********************************************************* -.SH TUN/TAP DRIVER SETUP -If you are running Linux 2.4.7 or higher, you probably have the TUN/TAP driver -already installed. If so, there are still a few things you need to do: - -Make device: -.B mknod /dev/net/tun c 10 200 - -Load driver: -.B modprobe tun -.\"********************************************************* -.SH EXAMPLES -Prior to running these examples, you should have OpenVPN installed on two -machines with network connectivity between them. If you have not -yet installed OpenVPN, consult the INSTALL file included in the OpenVPN -distribution. -.\"********************************************************* -.SS TUN/TAP Setup: -If you are using Linux 2.4 or higher, -make the tun device node and load the tun module: -.IP -.B mknod /dev/net/tun c 10 200 -.LP -.IP -.B modprobe tun -.LP -If you installed from RPM, the -.B mknod -step may be omitted, because the RPM install does that for you. - -Only Linux 2.4 and newer are supported. - -For other platforms, consult the INSTALL file at -.I http://openvpn.net/install.html -for more information. -.\"********************************************************* -.SS Firewall Setup: -If firewalls exist between -the two machines, they should be set to forward UDP port 1194 -in both directions. If you do not have control over the firewalls -between the two machines, you may still be able to use OpenVPN by adding -.B \-\-ping 15 -to each of the -.B openvpn -commands used below in the examples (this will cause each peer to send out -a UDP ping to its remote peer once every 15 seconds which will cause many -stateful firewalls to forward packets in both directions -without an explicit firewall rule). - -If you are using a Linux iptables\-based firewall, you may need to enter -the following command to allow incoming packets on the TUN device: -.IP -.B iptables \-A INPUT \-i tun+ \-j ACCEPT -.LP -See the firewalls section below for more information on configuring firewalls -for use with OpenVPN. -.\"********************************************************* -.SS VPN Address Setup: -For purposes -of our example, our two machines will be called -.B bob.example.com -and -.B alice.example.com. -If you are constructing a VPN over the internet, then replace -.B bob.example.com -and -.B alice.example.com -with the internet hostname or IP address that each machine will use -to contact the other over the internet. - -Now we will choose the tunnel endpoints. Tunnel endpoints are -private IP addresses that only have meaning in the context of -the VPN. Each machine will use the tunnel endpoint of the other -machine to access it over the VPN. In our example, -the tunnel endpoint for bob.example.com -will be 10.4.0.1 and for alice.example.com, 10.4.0.2. - -Once the VPN is established, you have essentially -created a secure alternate path between the two hosts -which is addressed by using the tunnel endpoints. You can -control which network -traffic passes between the hosts -(a) over the VPN or (b) independently of the VPN, by choosing whether to use -(a) the VPN endpoint address or (b) the public internet address, -to access the remote host. For example if you are on bob.example.com and you wish to connect to alice.example.com -via -.B ssh -without using the VPN (since -.B ssh -has its own built\-in security) you would use the command -.B ssh alice.example.com. -However in the same scenario, you could also use the command -.B telnet 10.4.0.2 -to create a telnet session with alice.example.com over the VPN, that would -use the VPN to secure the session rather than -.B ssh. - -You can use any address you wish for the -tunnel endpoints -but make sure that they are private addresses -(such as those that begin with 10 or 192.168) and that they are -not part of any existing subnet on the networks of -either peer, unless you are bridging. If you use an address that is part of -your local subnet for either of the tunnel endpoints, -you will get a weird feedback loop. -.\"********************************************************* -.SS Example 1: A simple tunnel without security -.LP -On bob: -.IP -.B openvpn \-\-remote alice.example.com \-\-dev tun1 \-\-ifconfig 10.4.0.1 10.4.0.2 \-\-verb 9 -.LP -On alice: -.IP -.B openvpn \-\-remote bob.example.com \-\-dev tun1 \-\-ifconfig 10.4.0.2 10.4.0.1 \-\-verb 9 -.LP -Now verify the tunnel is working by pinging across the tunnel. -.LP -On bob: -.IP -.B ping 10.4.0.2 -.LP -On alice: -.IP -.B ping 10.4.0.1 -.LP -The -.B \-\-verb 9 -option will produce verbose output, similar to the -.BR tcpdump (8) -program. Omit the -.B \-\-verb 9 -option to have OpenVPN run quietly. -.\"********************************************************* -.SS Example 2: A tunnel with static\-key security (i.e. using a pre\-shared secret) -First build a static key on bob. -.IP -.B openvpn \-\-genkey \-\-secret key -.LP -This command will build a random key file called -.B key -(in ascii format). -Now copy -.B key -to alice over a secure medium such as by -using the -.BR scp (1) -program. -.LP -On bob: -.IP -.B openvpn \-\-remote alice.example.com \-\-dev tun1 \-\-ifconfig 10.4.0.1 10.4.0.2 \-\-verb 5 \-\-secret key -.LP -On alice: -.IP -.B openvpn \-\-remote bob.example.com \-\-dev tun1 \-\-ifconfig 10.4.0.2 10.4.0.1 \-\-verb 5 \-\-secret key -.LP -Now verify the tunnel is working by pinging across the tunnel. -.LP -On bob: -.IP -.B ping 10.4.0.2 -.LP -On alice: -.IP -.B ping 10.4.0.1 -.\"********************************************************* -.SS Example 3: A tunnel with full TLS\-based security -For this test, we will designate -.B bob -as the TLS client and -.B alice -as the TLS server. -.I Note that client or server designation only has meaning for the TLS subsystem. It has no bearing on OpenVPN's peer\-to\-peer, UDP\-based communication model. - -First, build a separate certificate/key pair -for both bob and alice (see above where -.B \-\-cert -is discussed for more info). Then construct -Diffie Hellman parameters (see above where -.B \-\-dh -is discussed for more info). You can also use the -included test files client.crt, client.key, -server.crt, server.key and ca.crt. -The .crt files are certificates/public\-keys, the .key -files are private keys, and ca.crt is a certification -authority who has signed both -client.crt and server.crt. For Diffie Hellman -parameters you can use the included file dh1024.pem. -.I Note that all client, server, and certificate authority certificates and keys included in the OpenVPN distribution are totally insecure and should be used for testing only. -.LP -On bob: -.IP -.B openvpn \-\-remote alice.example.com \-\-dev tun1 \-\-ifconfig 10.4.0.1 10.4.0.2 \-\-tls\-client \-\-ca ca.crt \-\-cert client.crt \-\-key client.key \-\-reneg\-sec 60 \-\-verb 5 -.LP -On alice: -.IP -.B openvpn \-\-remote bob.example.com \-\-dev tun1 \-\-ifconfig 10.4.0.2 10.4.0.1 \-\-tls\-server \-\-dh dh1024.pem \-\-ca ca.crt \-\-cert server.crt \-\-key server.key \-\-reneg\-sec 60 \-\-verb 5 -.LP -Now verify the tunnel is working by pinging across the tunnel. -.LP -On bob: -.IP -.B ping 10.4.0.2 -.LP -On alice: -.IP -.B ping 10.4.0.1 -.LP -Notice the -.B \-\-reneg\-sec 60 -option we used above. That tells OpenVPN to renegotiate -the data channel keys every minute. -Since we used -.B \-\-verb 5 -above, you will see status information on each new key negotiation. - -For production operations, a key renegotiation interval of 60 seconds -is probably too frequent. Omit the -.B \-\-reneg\-sec 60 -option to use OpenVPN's default key renegotiation interval of one hour. -.\"********************************************************* -.SS Routing: -Assuming you can ping across the tunnel, -the next step is to route a real subnet over -the secure tunnel. Suppose that bob and alice have two network -interfaces each, one connected -to the internet, and the other to a private -network. Our goal is to securely connect -both private networks. We will assume that bob's private subnet -is 10.0.0.0/24 and alice's is 10.0.1.0/24. -.LP -First, ensure that IP forwarding is enabled on both peers. -On Linux, enable routing: -.IP -.B echo 1 > /proc/sys/net/ipv4/ip_forward -.LP -and enable TUN packet forwarding through the firewall: -.IP -.B iptables \-A FORWARD \-i tun+ \-j ACCEPT -.LP -On bob: -.IP -.B route add \-net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2 -.LP -On alice: -.IP -.B route add \-net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1 -.LP -Now any machine on the 10.0.0.0/24 subnet can -access any machine on the 10.0.1.0/24 subnet -over the secure tunnel (or vice versa). - -In a production environment, you could put the route command(s) -in a script and execute with the -.B \-\-up -option. -.\"********************************************************* -.SH FIREWALLS -OpenVPN's usage of a single UDP port makes it fairly firewall\-friendly. -You should add an entry to your firewall rules to allow incoming OpenVPN -packets. On Linux 2.4+: -.IP -.B iptables \-A INPUT \-p udp \-s 1.2.3.4 \-\-dport 1194 \-j ACCEPT -.LP -This will allow incoming packets on UDP port 1194 (OpenVPN's default UDP port) -from an OpenVPN peer at 1.2.3.4. - -If you are using HMAC\-based packet authentication (the default in any of -OpenVPN's secure modes), having the firewall filter on source -address can be considered optional, since HMAC packet authentication -is a much more secure method of verifying the authenticity of -a packet source. In that case: -.IP -.B iptables \-A INPUT \-p udp \-\-dport 1194 \-j ACCEPT -.LP -would be adequate and would not render the host inflexible with -respect to its peer having a dynamic IP address. - -OpenVPN also works well on stateful firewalls. In some cases, you may -not need to add any static rules to the firewall list if you are -using a stateful firewall that knows how to track UDP connections. -If you specify -.B \-\-ping n, -OpenVPN will be guaranteed -to send a packet to its peer at least once every -.B n -seconds. If -.B n -is less than the stateful firewall connection timeout, you can -maintain an OpenVPN connection indefinitely without explicit -firewall rules. - -You should also add firewall rules to allow incoming IP traffic on -TUN or TAP devices such as: -.IP -.B iptables \-A INPUT \-i tun+ \-j ACCEPT -.LP -to allow input packets from tun devices, -.IP -.B iptables \-A FORWARD \-i tun+ \-j ACCEPT -.LP -to allow input packets from tun devices to be forwarded to -other hosts on the local network, -.IP -.B iptables \-A INPUT \-i tap+ \-j ACCEPT -.LP -to allow input packets from tap devices, and -.IP -.B iptables \-A FORWARD \-i tap+ \-j ACCEPT -.LP -to allow input packets from tap devices to be forwarded to -other hosts on the local network. - -These rules are secure if you use packet authentication, -since no incoming packets will arrive on a TUN or TAP -virtual device -unless they first pass an HMAC authentication test. -.\"********************************************************* -.SH FAQ -.I http://openvpn.net/faq.html -.\"********************************************************* -.SH HOWTO -For a more comprehensive guide to setting up OpenVPN -in a production setting, see the OpenVPN HOWTO at -.I http://openvpn.net/howto.html -.\"********************************************************* -.SH PROTOCOL -For a description of OpenVPN's underlying protocol, -see -.I http://openvpn.net/security.html -.\"********************************************************* -.SH WEB -OpenVPN's web site is at -.I http://openvpn.net/ - -Go here to download the latest version of OpenVPN, subscribe -to the mailing lists, read the mailing list -archives, or browse the SVN repository. -.\"********************************************************* -.SH BUGS -Report all bugs to the OpenVPN team . -.\"********************************************************* -.SH "SEE ALSO" -.BR dhcpcd (8), -.BR ifconfig (8), -.BR openssl (1), -.BR route (8), -.BR scp (1) -.BR ssh (1) -.\"********************************************************* -.SH NOTES -.LP -This product includes software developed by the -OpenSSL Project ( -.I http://www.openssl.org/ -) - -For more information on the TLS protocol, see -.I http://www.ietf.org/rfc/rfc2246.txt - -For more information on the LZO real\-time compression library see -.I http://www.oberhumer.com/opensource/lzo/ -.\"********************************************************* -.SH COPYRIGHT -Copyright (C) 2002\-2018 OpenVPN Inc This program is free software; -you can redistribute it and/or modify -it under the terms of the GNU General Public License version 2 -as published by the Free Software Foundation. -.\"********************************************************* -.SH AUTHORS -James Yonan diff --git a/doc/openvpn.8.rst b/doc/openvpn.8.rst new file mode 100644 index 0000000..db81274 --- /dev/null +++ b/doc/openvpn.8.rst @@ -0,0 +1,170 @@ +========= + openvpn +========= +------------------------- + Secure IP tunnel daemon +------------------------- + +:Manual section: 8 +:Manual group: System Manager's Manual + + + +SYNOPSIS +======== +| ``openvpn`` [ options ... ] +| ``openvpn`` ``--help`` + + + +INTRODUCTION +============ + +OpenVPN is an open source VPN daemon by James Yonan. Because OpenVPN +tries to be a universal VPN tool offering a great deal of flexibility, +there are a lot of options on this manual page. If you're new to +OpenVPN, you might want to skip ahead to the examples section where you +will see how to construct simple VPNs on the command line without even +needing a configuration file. + +Also note that there's more documentation and examples on the OpenVPN +web site: https://openvpn.net/ + +And if you would like to see a shorter version of this manual, see the +openvpn usage message which can be obtained by running **openvpn** +without any parameters. + + + +DESCRIPTION +=========== + +OpenVPN is a robust and highly flexible VPN daemon. OpenVPN supports +SSL/TLS security, ethernet bridging, TCP or UDP tunnel transport through +proxies or NAT, support for dynamic IP addresses and DHCP, scalability +to hundreds or thousands of users, and portability to most major OS +platforms. + +OpenVPN is tightly bound to the OpenSSL library, and derives much of its +crypto capabilities from it. + +OpenVPN supports conventional encryption using a pre-shared secret key +**(Static Key mode)** or public key security **(SSL/TLS mode)** using +client & server certificates. OpenVPN also supports non-encrypted +TCP/UDP tunnels. + +OpenVPN is designed to work with the **TUN/TAP** virtual networking +interface that exists on most platforms. + +Overall, OpenVPN aims to offer many of the key features of IPSec but +with a relatively lightweight footprint. + + + +OPTIONS +======= + +OpenVPN allows any option to be placed either on the command line or in +a configuration file. Though all command line options are preceded by a +double-leading-dash ("--"), this prefix can be removed when an option is +placed in a configuration file. + +.. include:: man-sections/generic-options.rst +.. include:: man-sections/log-options.rst +.. include:: man-sections/protocol-options.rst +.. include:: man-sections/client-options.rst +.. include:: man-sections/server-options.rst +.. include:: man-sections/encryption-options.rst +.. include:: man-sections/cipher-negotiation.rst +.. include:: man-sections/network-config.rst +.. include:: man-sections/script-options.rst +.. include:: man-sections/management-options.rst +.. include:: man-sections/plugin-options.rst +.. include:: man-sections/windows-options.rst +.. include:: man-sections/advanced-options.rst +.. include:: man-sections/unsupported-options.rst +.. include:: man-sections/connection-profiles.rst +.. include:: man-sections/inline-files.rst +.. include:: man-sections/signals.rst +.. include:: man-sections/examples.rst + + +FAQ +=== + +https://community.openvpn.net/openvpn/wiki/FAQ + + + +HOWTO +===== + +For a more comprehensive guide to setting up OpenVPN in a production +setting, see the OpenVPN HOWTO at +https://openvpn.net/community-resources/how-to/ + + + +PROTOCOL +======== + +For a description of OpenVPN's underlying protocol, see +https://openvpn.net/community-resources/openvpn-protocol/ + + + +WEB +=== + +OpenVPN's web site is at https://openvpn.net/ + +Go here to download the latest version of OpenVPN, subscribe to the +mailing lists, read the mailing list archives, or browse the SVN +repository. + + + +BUGS +==== + +Report all bugs to the OpenVPN team info@openvpn.net + + + +SEE ALSO +======== + +``dhcpcd``\(8), +``ifconfig``\(8), +``openssl``\(1), +``route``\(8), +``scp``\(1) +``ssh``\(1) + + + +NOTES +===== + +This product includes software developed by the OpenSSL Project +(https://www.openssl.org/) + +For more information on the TLS protocol, see +http://www.ietf.org/rfc/rfc2246.txt + +For more information on the LZO real-time compression library see +https://www.oberhumer.com/opensource/lzo/ + + + +COPYRIGHT +========= + +Copyright (C) 2002-2020 OpenVPN Inc This program is free software; you +can redistribute it and/or modify it under the terms of the GNU General +Public License version 2 as published by the Free Software Foundation. + +AUTHORS +======= + +James Yonan james@openvpn.net diff --git a/doc/tls-crypt-v2.txt b/doc/tls-crypt-v2.txt new file mode 100644 index 0000000..3798791 --- /dev/null +++ b/doc/tls-crypt-v2.txt @@ -0,0 +1,189 @@ +Client-specific tls-crypt keys (--tls-crypt-v2) +=============================================== + +This document describes the ``--tls-crypt-v2`` option, which enables OpenVPN +to use client-specific ``--tls-crypt`` keys. + +Rationale +--------- + +``--tls-auth`` and ``tls-crypt`` use a pre-shared group key, which is shared +among all clients and servers in an OpenVPN deployment. If any client or +server is compromised, the attacker will have access to this shared key, and it +will no longer provide any security. To reduce the risk of losing pre-shared +keys, ``tls-crypt-v2`` adds the ability to supply each client with a unique +tls-crypt key. This allows large organisations and VPN providers to profit +from the same DoS and TLS stack protection that small deployments can already +achieve using ``tls-auth`` or ``tls-crypt``. + +Also, for ``tls-crypt``, even if all these peers succeed in keeping the key +secret, the key lifetime is limited to roughly 8000 years, divided by the +number of clients (see the ``--tls-crypt`` section of the man page). Using +client-specific keys, we lift this lifetime requirement to roughly 8000 years +for each client key (which "Should Be Enough For Everybody (tm)"). + + +Introduction +------------ + +``tls-crypt-v2`` uses an encrypted cookie mechanism to introduce +client-specific tls-crypt keys without introducing a lot of server-side state. +The client-specific key is encrypted using a server key. The server key is the +same for all servers in a group. When a client connects, it first sends the +encrypted key to the server, such that the server can decrypt the key and all +messages can thereafter be encrypted using the client-specific key. + +A wrapped (encrypted and authenticated) client-specific key can also contain +metadata. The metadata is wrapped together with the key, and can be used to +allow servers to identify clients and/or key validity. This allows the server +to abort the connection immediately after receiving the first packet, rather +than performing an entire TLS handshake. Aborting the connection this early +greatly improves the DoS resilience and reduces attack surface against +malicious clients that have the ``tls-crypt`` or ``tls-auth`` key. This is +particularly relevant for large deployments (think lost key or disgruntled +employee) and VPN providers (clients are not trusted). + +To allow for a smooth transition, ``tls-crypt-v2`` is designed such that a +server can enable both ``tls-crypt-v2`` and either ``tls-crypt`` or +``tls-auth``. This is achieved by introducing a P_CONTROL_HARD_RESET_CLIENT_V3 +opcode, that indicates that the client wants to use ``tls-crypt-v2`` for the +current connection. + +For an exact specification and more details, read the Implementation section. + + +Implementation +-------------- + +When setting up a tls-crypt-v2 group (similar to generating a tls-crypt or +tls-auth key previously): + +1. Generate a tls-crypt-v2 server key using OpenVPN's ``--tls-crypt-v2-genkey server``. + This key contains 2 512-bit keys, of which we use: + + * the first 256 bits of key 1 as AES-256-CTR encryption key ``Ke`` + * the first 256 bits of key 2 as HMAC-SHA-256 authentication key ``Ka`` + + This format is similar to the format for regular ``tls-crypt``/``tls-auth`` + and data channel keys, which allows us to reuse code. + +2. Add the tls-crypt-v2 server key to all server configs + (``tls-crypt-v2 /path/to/server.key``) + + +When provisioning a client, create a client-specific tls-crypt key: + +1. Generate 2048 bits client-specific key ``Kc`` using OpenVPN's ``--tls-crypt-v2-genkey client`` + +2. Optionally generate metadata + + The first byte of the metadata determines the type. The initial + implementation supports the following types: + + 0x00 (USER): User-defined free-form data. + 0x01 (TIMESTAMP): 64-bit network order unix timestamp of key generation. + + The timestamp can be used to reject too-old tls-crypt-v2 client keys. + + User metadata could for example contain the users certificate serial, such + that the incoming connection can be verified against a CRL. + + If no metadata is supplied during key generation, openvpn defaults to the + TIMESTAMP metadata type. + +3. Create a wrapped client key ``WKc``, using the same nonce-misuse-resistant + SIV construction we use for tls-crypt: + + ``len = len(WKc)`` (16 bit, network byte order) + + ``T = HMAC-SHA256(Ka, len || Kc || metadata)`` + + ``IV = 128 most significant bits of T`` + + ``WKc = T || AES-256-CTR(Ke, IV, Kc || metadata) || len`` + + Note that the length of ``WKc`` can be computed before composing ``WKc``, + because the length of each component is known (and AES-256-CTR does not add + any padding). + +4. Create a tls-crypt-v2 client key: PEM-encode ``Kc || WKc`` and store in a + file, using the header ``-----BEGIN OpenVPN tls-crypt-v2 client key-----`` + and the footer ``-----END OpenVPN tls-crypt-v2 client key-----``. (The PEM + format is simple, and following PEM allows us to use the crypto lib function + for en/decoding.) + +5. Add the tls-crypt-v2 client key to the client config + (``tls-crypt-v2 /path/to/client-specific.key``) + + +When setting up the openvpn connection: + +1. The client reads the tls-crypt-v2 key from its config, and: + + 1. loads ``Kc`` as its tls-crypt key, + 2. stores ``WKc`` in memory for sending to the server. + +2. To start the connection, the client creates a P_CONTROL_HARD_RESET_CLIENT_V3 + message, wraps it with tls-crypt using ``Kc`` as the key, and appends + ``WKc``. (``WKc`` must not be encrypted, to prevent a chicken-and-egg + problem.) + +3. The server receives the P_CONTROL_HARD_RESET_CLIENT_V3 message, and + + 1. reads the WKc length field from the end of the message, and extracts WKc + from the message + 2. unwraps ``WKc`` + 3. uses unwrapped ``Kc`` to verify the remaining + P_CONTROL_HARD_RESET_CLIENT_V3 message's (encryption and) authentication. + + The message is dropped and no error response is sent when either 3.1, 3.2 or + 3.3 fails (DoS protection). + +4. Server optionally checks metadata using a --tls-crypt-v2-verify script + + This allows early abort of connection, *before* we expose any of the + notoriously dangerous TLS, X.509 and ASN.1 parsers and thereby reduces the + attack surface of the server. + + The metadata is checked *after* the OpenVPN three-way handshake has + completed, to prevent DoS attacks. (That is, once the client has proved to + the server that it possesses Kc, by authenticating a packet that contains the + session ID picked by the server.) + + A server should not send back any error messages if metadata verification + fails, to reduce attack surface and maximize DoS resilience. + +6. Client and server use ``Kc`` for (un)wrapping any following control channel + messages. + + +Considerations +-------------- + +To allow for a smooth transition, the server implementation allows +``tls-crypt`` or ``tls-auth`` to be used simultaneously with ``tls-crypt-v2``. +This specification does not allow simultaneously using ``tls-crypt-v2`` and +connections without any control channel wrapping, because that would break DoS +resilience. + +WKc includes a length field, so we leave the option for future extension of the +P_CONTROL_HEAD_RESET_CLIENT_V3 message open. (E.g. add payload to the reset to +indicate low-level protocol features.) + +``tls-crypt-v2`` uses fixed crypto algorithms, because: + + * The crypto is used before we can do any negotiation, so the algorithms have + to be predefined. + * The crypto primitives are chosen conservatively, making problems with these + primitives unlikely. + * Making anything configurable adds complexity, both in implementation and + usage. We should not add any more complexity than is absolutely necessary. + +Potential ``tls-crypt-v2`` risks: + + * Slightly more work on first connection (``WKc`` unwrap + hard reset unwrap) + than with ``tls-crypt`` (hard reset unwrap) or ``tls-auth`` (hard reset auth). + * Flexible metadata allow mistakes + (So we should make it easy to do it right. Provide tooling to create client + keys based on cert serial + CA fingerprint, provide script that uses CRL (if + available) to drop revoked keys.) -- cgit v1.2.3 From 57f0b7b331088e489e93ae89ee0aed98381d8806 Mon Sep 17 00:00:00 2001 From: Bernhard Schmidt Date: Tue, 1 Sep 2020 16:53:26 +0200 Subject: New upstream version 2.5~beta3 --- doc/Makefile.in | 899 ++++ doc/README.man | 22 - doc/android.txt | 101 - doc/doxygen/Makefile.in | 532 +++ doc/doxygen/doc_compression.h | 91 - doc/doxygen/doc_control_processor.h | 184 - doc/doxygen/doc_control_tls.h | 104 - doc/doxygen/doc_data_control.h | 102 - doc/doxygen/doc_data_crypto.h | 70 - doc/doxygen/doc_eventloop.h | 66 - doc/doxygen/doc_external_multiplexer.h | 45 - doc/doxygen/doc_fragmentation.h | 95 - doc/doxygen/doc_internal_multiplexer.h | 43 - doc/doxygen/doc_key_generation.h | 148 - doc/doxygen/doc_mainpage.h | 161 - doc/doxygen/doc_memory_management.h | 98 - doc/doxygen/doc_protocol_overview.h | 195 - doc/doxygen/doc_reliable.h | 48 - doc/doxygen/doc_tunnel_state.h | 154 - doc/keying-material-exporter.txt | 137 - doc/man-sections/cipher-negotiation.rst | 96 - doc/man-sections/vpn-network-options.rst | 23 +- doc/openvpn.8 | 6954 ++++++++++++++++++++++++++++++ doc/openvpn.8.html | 6023 ++++++++++++++++++++++++++ doc/tls-crypt-v2.txt | 189 - 25 files changed, 14425 insertions(+), 2155 deletions(-) create mode 100644 doc/Makefile.in delete mode 100644 doc/README.man delete mode 100644 doc/android.txt create mode 100644 doc/doxygen/Makefile.in delete mode 100644 doc/doxygen/doc_compression.h delete mode 100644 doc/doxygen/doc_control_processor.h delete mode 100644 doc/doxygen/doc_control_tls.h delete mode 100644 doc/doxygen/doc_data_control.h delete mode 100644 doc/doxygen/doc_data_crypto.h delete mode 100644 doc/doxygen/doc_eventloop.h delete mode 100644 doc/doxygen/doc_external_multiplexer.h delete mode 100644 doc/doxygen/doc_fragmentation.h delete mode 100644 doc/doxygen/doc_internal_multiplexer.h delete mode 100644 doc/doxygen/doc_key_generation.h delete mode 100644 doc/doxygen/doc_mainpage.h delete mode 100644 doc/doxygen/doc_memory_management.h delete mode 100644 doc/doxygen/doc_protocol_overview.h delete mode 100644 doc/doxygen/doc_reliable.h delete mode 100644 doc/doxygen/doc_tunnel_state.h delete mode 100644 doc/keying-material-exporter.txt delete mode 100644 doc/man-sections/cipher-negotiation.rst create mode 100644 doc/openvpn.8 create mode 100644 doc/openvpn.8.html delete mode 100644 doc/tls-crypt-v2.txt (limited to 'doc') diff --git a/doc/Makefile.in b/doc/Makefile.in new file mode 100644 index 0000000..beabdc0 --- /dev/null +++ b/doc/Makefile.in @@ -0,0 +1,899 @@ +# Makefile.in generated by automake 1.16.1 from Makefile.am. +# @configure_input@ + +# Copyright (C) 1994-2018 Free Software Foundation, Inc. + +# This Makefile.in is free software; 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+@HAVE_PYDOCUTILS_FALSE@ @echo "Missing python-docutils - skipping man page generation" + +openvpn.8.html: +@HAVE_PYDOCUTILS_TRUE@ $(RST2HTML) $(srcdir)/openvpn.8.rst > $@ +@HAVE_PYDOCUTILS_FALSE@ @echo "Missing python-docutils - skipping man/html page generation" + +dist-hook : openvpn.8 openvpn.8.html + +# Tell versions [3.59,3.63) of GNU make to not export all variables. +# Otherwise a system limit (for SysV at least) may be exceeded. +.NOEXPORT: diff --git a/doc/README.man b/doc/README.man deleted file mode 100644 index 29654c1..0000000 --- a/doc/README.man +++ /dev/null @@ -1,22 +0,0 @@ - -man page documentation -====================== - -The man page content maintained in the openvpn.8.rst file and proper man and -the html version of the man page are generated using python-docutils. Both -the man page and html file are generated during 'make dist' or 'make distcheck' -and should be distributed inside the tarball by default. - -Users compiling OpenVPN from the tarball should not need to regenerate the -man/html files unless the source file needs to be modified. - -Further information: - -* Python docutils project: - https://docutils.sourceforge.io/ - -* Quickstart on .rst - https://docutils.sourceforge.io/docs/user/rst/quickstart.html - -* reStructuredText Markup Specifictaion (.rst) - https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html diff --git a/doc/android.txt b/doc/android.txt deleted file mode 100644 index e287be0..0000000 --- a/doc/android.txt +++ /dev/null @@ -1,101 +0,0 @@ -This file documents the support in OpenVPN for Android 4.0 and up. - -This support is primarily used in the "OpenVPN for Android" app -(https://github.com/schwabe/ics-openvpn). For building see the developer -README: https://github.com/schwabe/ics-openvpn/blob/master/doc/README.txt - -Android provides the VPNService API -(http://developer.android.com/reference/android/net/VpnService.html) -which allows establishing VPN connections without rooting the device. - -Since all the interfaces are are Android specific the calls to this -interface are made from the UI instead of OpenVPN directly. The API -needs the following parameters: - -- IP and netmask of tun interface -- Networks that should be routed to the tun interface -- DNS Servers and DNS Domain -- MTU - -All IPs/Routes are in CIDR style. Non CIDR routes are not supported. -Notable is the lack of support for setting routes to other interfaces -usually used to avoid the server connection going over the tun -interface. The Android VPNService API has the concept of protecting -a socket from being routed over a interface. Calling protect (fd) -will internally bind the socket to the interface used for the -external connection (usually WiFi or mobile data). - -To use OpenVPN with the VPNService API OpenVPN must be build with -the TARGET_ANDROID compile option. Also the UI must use a UNIX -domain socket to connect to OpenVPN. When compiled as TARGET_ANDROID -OpenVPN will use management callbacks instead of executing traditional -ifconfig/route commands use the need-ok callback mechanism which -will ask - -> NEED-OK command - -where command can be: - -IFCONFIG6 IPv6/netmask -IFCONFIG local remoteOrNetmask MTU topology - -To tell the UI which IPs addresses OpenVPN expects on the interface. -Topology is one of "net30","p2p","subnet" or "undef". - -ROUTE6 network/netmask -ROUTE network netmask - -To tell the UI which routes should be set on the tun interface. - -DNSSERVER IP server address -DNS6SERVER IPv6 server address -DNSDOMAIN searchdomain - -To set the DNS server and search domain. - -The GUI will then respond with a "needok 'command' ok' or "needok -'command' cancel', e.g. "needok 'IFCONFIG' ok". - -PERSIST_TUN_ACTION - -In Android 4.4-4.4.2 a bug exists that does not allow to open a new tun fd -while a tun fd is still open. When OpenVPN wants to open an fd it will do -this query. The UI should compare the last configuration of -the tun device with the current tun configuration and reply with either (or -always respond with OPEN_AFTER_BEFORE/OPEN_BEFORE_CLOSE) - -- NOACTION: Keep using the old fd -- OPEN_AFTER_CLOSE: First close the old fd and then open a new to workaround the bug -- OPEN_BEFORE_CLOSE: the normal behaviour when the VPN configuration changed - -For example the UI could respond with -needok 'PERSIST_TUN_ACTION' OPEN_AFTER_CLOSE - -To protect a socket the OpenVPN will send a PROTECTFD to the UI. -When sending the PROTECTFD command command to the UI it will send -the fd of the socket as ancillary message over the UNIX socket. -The UI will then call protect(fd) on the received socket protecting -it from being routed over the VPN. - -When opening a tun device the OpenVPN process will first send all -route, ifconfig and DNS related configuration to the UI and after -that calls the OPENTUN command to receive a tun fd with the requested -configuration. The UI will than use the collected information to -call the VPNService's establish() method to receive a fd which in -turn is send to the OpenVPN process as ancillary message to the -"needok 'OPENTUN' ok' response. - -The OpenVPN for Android UI extensively uses other features that -are not specific to Android but are rarely used on other platform. -For example using SIGUSR1 and management-hold to restart, pause, -continue the VPN on network changes or the external key management ---management-external-key option and inline files. - -To better support handover between networks, a the management command - -network-change [samenetwork] - -is used on the Android platform. It tells OpenVPN to do the necessary -action when the network changes. 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a/doc/doxygen/doc_compression.h +++ /dev/null @@ -1,91 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file Data Channel Compression module documentation file. - */ - -/** - * @defgroup compression Data Channel Compression module - * - * This module offers compression of data channel packets. - * - * @par State structures - * The Data Channel Compression module stores its internal state in a \c - * lzo_compress_workspace structure. This state includes flags which - * control the module's behavior and preallocated working memory. One - * such structure is present for each VPN tunnel, and is stored in the \c - * context.c2.lzo_compwork of the \c context associated with that VPN - * tunnel. - * - * @par Initialization and cleanup - * Every time a new \c lzo_compress_workspace is needed, it must be - * initialized using the \c lzo_compress_init() function. Similarly, - * every time a \c lzo_compress_workspace is no longer needed, it must be - * cleaned up using the \c lzo_compress_uninit() function. These - * functions take care of the allocation and freeing of internal working - * memory, but not of the \c lzo_compress_workspace structures themselves. - * - * @par - * Because of the one-to-one relationship between \c - * lzo_compress_workspace structures and VPN tunnels, the above-mentioned - * initialization and cleanup functions are called directly from the \c - * init_instance() and \c close_instance() functions, which control the - * initialization and cleanup of VPN tunnel instances and their associated - * \c context structures. - * - * @par Packet processing functions - * This module receives data channel packets from the \link data_control - * Data Channel Control module\endlink and processes them according to the - * settings of the packet's VPN tunnel. The \link data_control Data - * Channel Control module\endlink uses the following interface functions: - * - For packets which will be sent to a remote OpenVPN peer: \c - * lzo_compress() - * - For packets which have been received from a remote OpenVPN peer: \c - * lzo_decompress() - * - * @par Settings that control this module's activity - * Whether or not the Data Channel Compression module is active depends on - * the compile-time \c ENABLE_LZO preprocessor macro and the runtime flags - * stored in \c lzo_compress_workspace.flags of the associated VPN tunnel. - * The latter are initialized from \c options.lzo, which gets its value - * from the process's configuration sources, such as its configuration - * file or command line %options. - * - * @par Adaptive compression - * The compression module supports adaptive compression. If this feature - * is enabled, the compression routines monitor their own performance and - * turn compression on or off depending on whether it is leading to - * significantly reduced payload size. - * - * @par Compression algorithms - * This module uses the Lempel-Ziv-Oberhumer (LZO) compression algorithms. - * These offer lossless compression and are designed for high-performance - * decompression. This module uses the external \c lzo library's - * implementation of the algorithms. - * - * @par - * For more information on the LZO library, see:\n - * http://www.oberhumer.com/opensource/lzo/ - */ diff --git a/doc/doxygen/doc_control_processor.h b/doc/doxygen/doc_control_processor.h deleted file mode 100644 index 1bbf2d2..0000000 --- a/doc/doxygen/doc_control_processor.h +++ /dev/null @@ -1,184 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * Control Channel Processor module documentation file. - */ - -/** - * @defgroup control_processor Control Channel Processor module - * - * This module controls the setup and maintenance of VPN tunnels and the - * associated security parameters. - * - * @par This module's role - * The Control Channel Processor module lies at the core of OpenVPN's - * activities. It handles the setup of new VPN tunnels, the negotiation - * of data channel security parameters, the managing of active VPN - * tunnels, and finally the cleanup of expired VPN tunnels. - * - * @par State structures - * A large amount of VPN tunnel state information must be stored within an - * OpenVPN process. A wide variety of container structures are used by - * this module for that purpose. Several of these structures are listed - * below, and the function of the first three VPN tunnel state containers - * is described in more detail later. - * - VPN tunnel state containers: - * - \c tls_multi, security parameter state for a single VPN tunnel. - * Contains three instances of the \c tls_session structure. - * - \c tls_session, security parameter state of a single session - * within a VPN tunnel. Contains two instances of the \c key_state - * structure. - * - \c key_state, security parameter state of one TLS and data - * channel %key set. - * - Data channel security parameter containers: - * - \c key_ctx_bi, container for two sets of OpenSSL cipher and/or - * HMAC context (both directions). Contains two instances of the \c - * key_ctx structure. - * - \c key_ctx, container for one set of OpenSSL cipher and/or HMAC - * context (one directions. - * - Key material containers: - * - \c key2, container for two sets of cipher and/or HMAC %key - * material (both directions). Contains two instances of the \c key - * structure. - * - \c key, container for one set of cipher and/or HMAC %key material - * (one direction). - * - \c key_direction_state, ordering of %key material within the \c - * key2.key array. - * - Key method 2 random material containers: - * - \c key_source2, container for both halves of random material used - * for %key method 2. Contains two instances of the \c key_source - * structure. - * - \c key_source, container for one half of random material used for - * %key method 2. - * - * @par The life of a \c tls_multi object - * A \c tls_multi structure contains all the security parameter state - * information related to the control and data channels of one VPN tunnel. - * Its life cycle can be summarized as follows: - * -# Initialization: \c tls_multi_init() and \c - * tls_multi_init_finalize(), which are called (indirectly) from \c - * init_instance() when initializing a new \c context structure. - * - Initializes a \c tls_multi structure. - * - Allocates the three \c tls_session objects contained by the \c - * tls_multi structure, and initializes as appropriate. - * -# Management: \c tls_multi_process() and \c tls_pre_decrypt() - * - If a new session is initiated by the remote peer, then \c - * tls_pre_decrypt() starts the new session negotiation in the - * un-trusted \c tls_session. - * - If the, as yet, un-trusted \c tls_session authenticates - * successfully, then \c tls_multi_process() moves it so as to be - * the active \c tls_session. - * - If an error occurs during processing of a \c key_state object, - * then \c tls_multi_process() cleans up and initializes the - * associated \c tls_session object. If the error occurred in the - * active \c key_state of the active \c tls_session and the - * lame-duck \c key_state of that \c tls_session has not yet - * expired, it is preserved as fallback. - * -# Cleanup: \c tls_multi_free(), which is called (indirectly) from \c - * close_instance() when cleaning up a \c context structure. - * - Cleans up a \c tls_multi structure. - * - Cleans up the three \c tls_session objects contained by the \c - * tls_multi structure. - * - * @par The life of a \c tls_session object - * A \c tls_session structure contains the state information related to an - * active and a lame-duck \c key_state. Its life cycle can be summarized - * as follows: - * -# Initialization: \c tls_session_init() - * - Initializes a \c tls_session structure. - * - Initializes the primary \c key_state by calling \c - * key_state_init(). - * -# Renegotiation: \c key_state_soft_reset() - * - Cleans up the old lame-duck \c key_state by calling \c - * key_state_free(). - * - Moves the old primary \c key_state to be the new lame-duck \c - * key_state. - * - Initializes a new primary \c key_state by calling \c - * key_state_init(). - * -# Cleanup: \c tls_session_free() - * - Cleans up a \c tls_session structure. - * - Cleans up all \c key_state objects associated with the session by - * calling \c key_state_free() for each. - * - * @par The life of a \c key_state object - * A \c key_state structure represents one control and data channel %key - * set. It contains an OpenSSL TLS object that encapsulates the control - * channel, and the data channel security parameters needed by the \link - * data_crypto Data Channel Crypto module\endlink to perform cryptographic - * operations on data channel packets. Its life cycle can be summarized - * as follows: - * -# Initialization: \c key_state_init() - * - Initializes a \c key_state structure. - * - Creates a new OpenSSL TLS object to encapsulate this new control - * channel session. - * - Sets \c key_state.state to \c S_INITIAL. - * - Allocates several internal buffers. - * - Initializes new reliability layer structures for this key set. - * -# Negotiation: \c tls_process() - * - The OpenSSL TLS object negotiates a TLS session between itself - * and the remote peer's TLS object. - * - Key material is generated and exchanged through the TLS session - * between OpenVPN peers. - * - Both peers initialize their data channel cipher and HMAC key - * contexts. - * - On successful negotiation, the \c key_state.state will progress - * from \c S_INITIAL to \c S_ACTIVE and \c S_NORMAL. - * -# Active tunneling: \link data_crypto Data Channel Crypto - * module\endlink - * - Data channel packet to be sent to a remote OpenVPN peer: - * - \c tls_pre_encrypt() loads the security parameters from the \c - * key_state into a \c crypto_options structure. - * - \c openvpn_encrypt() uses the \c crypto_options to an encrypt - * and HMAC sign the data channel packet. - * - Data channel packet received from a remote OpenVPN peer: - * - \c tls_pre_decrypt() loads the security parameters from the \c - * key_state into a \c crypto_options structure. - * - \c openvpn_encrypt() uses the \c crypto_options to - * authenticate and decrypt the data channel packet. - * -# Cleanup: \c key_state_free() - * - Cleans up a \c key_state structure together with its OpenSSL TLS - * object, key material, internal buffers, and reliability layer - * structures. - * - * @par Control functions - * The following two functions drive the Control Channel Processor's - * activities. - * - \c tls_multi_process(), iterates through the \c tls_session objects - * within a given \c tls_multi of a VPN tunnel, and calls \c - * tls_process() for each \c tls_session which is being set up, is - * already active, or is busy expiring. - * - \c tls_process(), performs the Control Channel Processor module's - * core handling of received control channel messages, and generates - * appropriate messages to be sent. - * - * @par Functions which control data channel key generation - * - Key method 1 key exchange functions were removed from OpenVPN 2.5 - * - Key method 2 key exchange functions: - * - \c key_method_2_write(), generates and processes key material to - * be sent to the remote OpenVPN peer. - * - \c key_method_2_read(), processes key material received from the - * remote OpenVPN peer. - */ diff --git a/doc/doxygen/doc_control_tls.h b/doc/doxygen/doc_control_tls.h deleted file mode 100644 index 5cb7c53..0000000 --- a/doc/doxygen/doc_control_tls.h +++ /dev/null @@ -1,104 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * Control Channel TLS module documentation file. - */ - -/** - * @defgroup control_tls Control Channel TLS module - * - * This module provides secure encapsulation of control channel messages - * exchanged between OpenVPN peers. - * - * The Control Channel TLS module uses the Transport Layer Security (TLS) - * protocol to provide an encrypted communication channel between the - * local OpenVPN process and a remote peer. This protocol simultaneously - * offers certificate-based authentication of the communicating parties. - * - * @par This module's roles - * The Control Channel TLS module is essential for the security of any - * OpenVPN-based system. On the one hand, it performs the security - * operations necessary to protect control channel messages exchanged - * between OpenVPN peers. On the other hand, before the control and data - * channels are even setup, it controls the exchange of certificates and - * verification of the remote's identity during negotiation of VPN - * tunnels. - * - * @par - * The former role is described below. The latter is described in the - * documentation for the \c verify_callback() function. - * - * @par - * In other words, this module takes care of the confidentiality and - * integrity of data channel communications, and the authentication of - * both the communicating parties and the control channel messages - * exchanged. - * - * @par Initialization and cleanup - * Because of the one-to-one relationship between control channel TLS - * state and \c key_state structures, the initialization and cleanup of an - * instance of the Control Channel TLS module's state happens within the - * \c key_state_init() and \c key_state_free() functions. In other words, - * each \c key_state object contains exactly one OpenSSL SSL-BIO object, - * which is initialized and cleaned up together with the rest of the \c - * key_state object. - * - * @par Packet processing functions - * This object behaves somewhat like a black box with a ciphertext and a - * plaintext I/O port. Its interaction with OpenVPN's control channel - * during operation takes place within the \c tls_process() function of - * the \link control_processor Control Channel Processor\endlink. The - * following functions are available for processing packets: - * - If ciphertext received from the remote peer is available in the \link - * reliable Reliability Layer\endlink: - * - Insert it into the ciphertext-side of the SSL-BIO. - * - Use function: \c key_state_write_ciphertext() - * - If ciphertext can be extracted from the ciphertext-side of the - * SSL-BIO: - * - Pass it to the \link reliable Reliability Layer\endlink for sending - * to the remote peer. - * - Use function: \c key_state_read_ciphertext() - * - If plaintext can be extracted from the plaintext-side of the SSL-BIO: - * - Pass it on to the \link control_processor Control Channel - * Processor\endlink for local processing. - * - Use function: \c key_state_read_plaintext() - * - If plaintext from the \link control_processor Control Channel - * Processor\endlink is available to be sent to the remote peer: - * - Insert it into the plaintext-side of the SSL-BIO. - * - Use function: \c key_state_write_plaintext() or \c - * key_state_write_plaintext_const() - * - * @par Transport Layer Security protocol implementation - * This module uses the OpenSSL library's implementation of the TLS - * protocol in the form of an OpenSSL SSL-BIO object. - * - * @par - * For more information on the OpenSSL library's BIO objects, please see: - * - OpenSSL's generic BIO objects: - * http://www.openssl.org/docs/crypto/bio.html - * - OpenSSL's SSL-BIO object: - * http://www.openssl.org/docs/crypto/BIO_f_ssl.html - */ diff --git a/doc/doxygen/doc_data_control.h b/doc/doxygen/doc_data_control.h deleted file mode 100644 index ad2a308..0000000 --- a/doc/doxygen/doc_data_control.h +++ /dev/null @@ -1,102 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * Data Channel Control module documentation file. - */ - -/** - * @defgroup data_control Data Channel Control module - * - * This module controls the processing of packets as they pass through the - * data channel. - * - * The Data Channel Control module controls the processing of packets as - * they pass through the data channel. The processing includes packet - * compression, fragmentation, and the performing of security operations - * on the packets. This module does not do the processing itself, but - * passes the packet to other data channel modules to perform the - * appropriate actions. - * - * Packets can travel in two directions through the data channel. They - * can be going to a remote destination which is reachable through a VPN - * tunnel, in which case this module prepares them to be sent out through - * a VPN tunnel. On the other hand, they can have been received through a - * VPN tunnel from a remote OpenVPN peer, in which case this module - * retrieves the packet in its original form as it was before entering the - * VPN tunnel on the remote OpenVPN peer. How this module processes - * packets traveling in the two directions is discussed in more detail - * below. - * - * @par Packets to be sent to a remote OpenVPN peer - * This module's main function for processing packets traveling in this - * direction is \c encrypt_sign(), which performs the following processing - * steps: - * - Call the \link compression Data Channel Compression module\endlink to - * perform packet compression if necessary. - * - Call the \link fragmentation Data Channel Fragmentation - * module\endlink to perform packet fragmentation if necessary. - * - Call the \link data_crypto Data Channel Crypto module\endlink to - * perform the required security operations. - * - * @par - * See the \c encrypt_sign() documentation for details of these - * interactions. - * - * @par - * After the above processing is complete, the packet is ready to be sent - * to a remote OpenVPN peer as a VPN tunnel packet. The actual sending of - * the packet is handled by the \link external_multiplexer External - * Multiplexer\endlink. - * - * @par Packets received from a remote OpenVPN peer - * The function that controls how packets traveling in this direction are - * processed is \c process_incoming_link(). That function, however, also - * performs some of the tasks required for the \link external_multiplexer - * External Multiplexer\endlink and is therefore listed as part of that - * module, instead of here. - * - * @par - * After the \c process_incoming_link() function has determined that a - * received packet is a data channel packet, it performs the following - * processing steps: - * - Call the \link data_crypto Data Channel Crypto module\endlink to - * perform the required security operations. - * - Call the \link fragmentation Data Channel Fragmentation - * module\endlink to perform packet reassembly if necessary. - * - Call the \link compression Data Channel Compression module\endlink to - * perform packet decompression if necessary. - * - * @par - * See the \c process_incoming_link() documentation for details of these - * interactions. - * - * @par - * After the above processing is complete, the packet is in its original - * form again as it was received by the remote OpenVPN peer. It can now - * be routed further to its final destination. If that destination is a - * locally reachable host, then the \link internal_multiplexer Internal - * Multiplexer\endlink will send it there. - */ diff --git a/doc/doxygen/doc_data_crypto.h b/doc/doxygen/doc_data_crypto.h deleted file mode 100644 index 3828089..0000000 --- a/doc/doxygen/doc_data_crypto.h +++ /dev/null @@ -1,70 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * Data Channel Crypto module documentation file. - */ - -/** - * @addtogroup data_crypto Data Channel Crypto module - * - * The Data Channel Crypto Module performs cryptographic operations on - * data channel packets. - * - * @par Security parameters - * This module is merely the user of a VPN tunnel's security parameters. - * It does not perform the negotiation and setup of the security - * parameters, nor the %key generation involved. These actions are done - * by the \link control_processor Control Channel Processor\endlink. This - * module receives the appropriate security parameters from that module in - * the form of a \c crypto_options structure when they are necessary for - * processing a packet. - * - * @par Packet processing functions - * This module receives data channel packets from the \link data_control - * Data Channel Control module\endlink and processes them according to the - * security parameters of the packet's VPN tunnel. The \link data_control - * Data Channel Control module\endlink uses the following interface - * functions: - * - For packets which will be sent to a remote OpenVPN peer: - * - \c tls_pre_encrypt() - * - \c openvpn_encrypt() - * - \c tls_post_encrypt() - * - For packets which have been received from a remote OpenVPN peer: - * - \c tls_pre_decrypt() (documented as part of the \link - * external_multiplexer External Multiplexer\endlink) - * - \c openvpn_decrypt() - * - * @par Settings that control this module's activity - * How the data channel processes packets received from the \link data_control - * Data Channel Control module\endlink at runtime depends on the associated - * \c crypto_options structure. To perform cryptographic operations, the - * \c crypto_options.key_ctx_bi must contain the correct cipher and HMAC - * security parameters for the direction the packet is traveling in. - * - * @par Crypto algorithms - * This module uses the crypto algorithm implementations of the external - * crypto library (currently either OpenSSL (default), or mbed TLS). - */ diff --git a/doc/doxygen/doc_eventloop.h b/doc/doxygen/doc_eventloop.h deleted file mode 100644 index 8bd2635..0000000 --- a/doc/doxygen/doc_eventloop.h +++ /dev/null @@ -1,66 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * Main Event Loop module documentation file. - */ - -/** - * @defgroup eventloop Main Event Loop module - * - * This main event loop module drives the packet processing of OpenVPN. - * - * OpenVPN is an event driven system. Its activities are driven by a main - * event loop, which repeatedly waits for one of several predefined events - * to occur, and then calls the appropriate module to handle the event. - * The major types of network events that OpenVPN processes are: - * - A packet can be read from the external network interface. - * - The main event loop activates the \link external_multiplexer - * External Multiplexer\endlink to read and process the packet. - * - A packet can be read from the virtual tun/tap network interface. - * - The main event loop activates the \link internal_multiplexer - * Internal Multiplexer\endlink to read and process the packet. - * - If a packet is ready to be sent out as a VPN tunnel packet: the - * external network interface can be written to. - * - The main event loop activates the \link external_multiplexer - * External Multiplexer\endlink to send the packet. - * - If a packet is ready to be sent to a locally reachable destination: - * the virtual tun/tap network interface can be written to. - * - The main event loop activates the \link internal_multiplexer - * Internal Multiplexer\endlink to send the packet. - * - * Beside these external events, OpenVPN also processes other types of - * internal events. These include scheduled events, such as resending of - * non-acknowledged control channel messages. - * - * @par Main event loop implementations - * - * Depending on the mode in which OpenVPN is running, a different main - * event loop function is called to drive the event processing. The - * following implementations are available: - * - Client mode using UDP or TCP: \c tunnel_point_to_point() - * - Server mode using UDP: \c tunnel_server_udp_single_threaded() - * - Server mode using TCP: \c tunnel_server_tcp() - */ diff --git a/doc/doxygen/doc_external_multiplexer.h b/doc/doxygen/doc_external_multiplexer.h deleted file mode 100644 index 692c15c..0000000 --- a/doc/doxygen/doc_external_multiplexer.h +++ /dev/null @@ -1,45 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * External Multiplexer module documentation file. - */ - -/** - * @addtogroup external_multiplexer External Multiplexer module - * - * The External Multiplexer is the link between the external network - * interface and the other OpenVPN modules. It reads packets from the - * external network interface, determines which remote OpenVPN peer and - * VPN tunnel they are associated with, and whether they are data channel - * or control channel packets. It then passes the packets on to the - * appropriate processing module. - * - * This module also handles packets traveling in the reverse direction, - * which have been generated by the local control channel or which have - * already been processed by the \link data_control Data Channel Control - * module\endlink and are destined for a remote host reachable through a - * VPN tunnel. - */ diff --git a/doc/doxygen/doc_fragmentation.h b/doc/doxygen/doc_fragmentation.h deleted file mode 100644 index 90e8d9e..0000000 --- a/doc/doxygen/doc_fragmentation.h +++ /dev/null @@ -1,95 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * Data Channel Fragmentation module documentation file. - */ - -/** - * @defgroup fragmentation Data Channel Fragmentation module - * - * The Data Channel Fragmentation module offers fragmentation of data - * channel packets. - * - * @par State structures - * The Data Channel Fragmentation module stores its internal state in a \c - * fragment_master structure. One such structure is present for each VPN - * tunnel, and is stored in \c context.c2.fragment of the \c context - * associated with that VPN tunnel. - * - * @par - * The \c fragment_master structure contains one \c fragment_list - * structure \c fragment_master.incoming. This is a list of \c fragment - * structures, each of which can store the parts of one fragmented packet - * while it is being reassembled. The \c fragment_master structure also - * contains one \c buffer called \c fragment_master.outgoing, in which a - * data channel large packet to be sent to a remote OpenVPN peer can be - * broken up into parts to be sent one by one. - * - * @par Initialization and cleanup - * Every time a new \c fragment_master is needed, it must be allocated and - * initialized by the \c fragment_init() function. Similarly, every time - * a \c fragment_master is no longer needed, it must be cleaned up using - * the \c fragment_free() function. These functions take care of the - * allocation and freeing of the \c fragment_master structure itself and - * all internal memory required for the use of that structure. Note that - * this behavior is different from that displayed by the \link compression - * Data Channel Compression module\endlink. - * - * @par - * Because of the one-to-one relationship between \c fragment_master - * structures and VPN tunnels, the above-mentioned initialization and - * cleanup functions are called directly from the \c init_instance() and - * \c close_instance() functions, which control the initialization and - * cleanup of VPN tunnel instances and their associated \c context - * structures. - * - * @par Packet processing functions - * This module receives data channel packets from the \link data_control - * Data Channel Control module\endlink and processes them according to the - * settings of the packet's VPN tunnel. The \link data_control Data - * Channel Control module\endlink uses the following interface functions: - * - For packets which will be sent to a remote OpenVPN peer: \c - * fragment_outgoing() \n This function inspects data channel packets as - * they are being made ready to be sent as VPN tunnel packets to a - * remote OpenVPN peer. If a packet's size is larger than its - * destination VPN tunnel's maximum transmission unit (MTU), then this - * module breaks that packet up into smaller parts, each of which is - * smaller than or equal to the VPN tunnel's MTU. See \c - * fragment_outgoing() for details. - * - For packets which have been received from a remote OpenVPN peer: \c - * fragment_incoming() \n This function inspects data channel packets - * that have been received from a remote OpenVPN peer through a VPN - * tunnel. It reads the fragmentation header of the packet, and - * depending on its value performs the appropriate action. See \c - * fragment_incoming() for details. - * - * @par Settings that control this module's activity - * Whether the Data Channel Fragmentation module is active or not depends - * on the compile-time \c ENABLE_FRAGMENT preprocessor macro and the - * runtime flag \c options.fragment, which gets its value from the - * process's configuration sources, such as the configuration file and - * commandline %options. - */ diff --git a/doc/doxygen/doc_internal_multiplexer.h b/doc/doxygen/doc_internal_multiplexer.h deleted file mode 100644 index c68a09c..0000000 --- a/doc/doxygen/doc_internal_multiplexer.h +++ /dev/null @@ -1,43 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * Internal Multiplexer module documentation file. - */ - -/** - * @addtogroup internal_multiplexer Internal Multiplexer module - * - * The Internal Multiplexer is the link between the virtual tun/tap - * network interface and the \link data_control Data Channel Control - * module\endlink. It reads packets from the virtual network interface, - * determines for which remote OpenVPN peer they are destined, and then - * passes the packets on to the Data Channel Control module together with - * information about their destination VPN tunnel instance. - * - * This module also handles packets traveling in the reverse direction, - * which have already been processed by the Data Channel Control module - * and are destined for a locally reachable host. - */ diff --git a/doc/doxygen/doc_key_generation.h b/doc/doxygen/doc_key_generation.h deleted file mode 100644 index 4bb9c70..0000000 --- a/doc/doxygen/doc_key_generation.h +++ /dev/null @@ -1,148 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * Key generation documentation file. - */ - -/** - * @page key_generation Data channel %key generation - * - * This section describes how OpenVPN peers generate and exchange %key - * material necessary for the security operations performed on data - * channel packets. - * - * The %key generation and exchange process between OpenVPN client and - * server occurs every time data channel security parameters are - * negotiated, for example during the initial setup of a VPN tunnel or - * when the active security parameters expire. In source code terms, this - * is when a new key_state structure is initialized. - * - * @section key_generation_method Key methods - * - * OpenVPN supports two different ways of generating and exchanging %key - * material between client and server. These are known as %key method 1 - * and %key method 2. %Key method 2 is the recommended method. Both are - * explained below. - * - * @subsection key_generation_method_1 Key method 1 - * - * -# Each host generates its own random material. - * -# Each host uses its locally generated random material as %key data - * for encrypting and signing packets sent to the remote peer. - * -# Each host then sends its random material to the remote peer, so that - * the remote peer can use that %key data for authenticating and - * decrypting received packets. - * - * @subsection key_generation_method_2 Key method 2 - * - * -# The client generates random material in the following amounts: - * - Pre-master secret: 48 bytes - * - Client's PRF seed for master secret: 32 bytes - * - Client's PRF seed for %key expansion: 32 bytes - * -# The client sends its share of random material to the server. - * -# The server generates random material in the following amounts: - * - Server's PRF seed for master secret: 32 bytes - * - Server's PRF seed for %key expansion: 32 bytes - * -# The server computes the %key expansion using its own and the - * client's random material. - * -# The server sends its share of random material to the client. - * -# The client computes the %key expansion using its own and the - * server's random material. - * - * %Key method 2 %key expansion is performed by the \c - * generate_key_expansion() function. Please refer to its source code for - * details of the %key expansion process. - * - * @subsection key_generation_random Source of random material - * - * OpenVPN uses the either the OpenSSL library or the mbed TLS library as its - * source of random material. - * - * In OpenSSL, the \c RAND_bytes() function is called - * to supply cryptographically strong pseudo-random data. The following links - * contain more information on this subject: - * - For OpenSSL's \c RAND_bytes() function: - * http://www.openssl.org/docs/crypto/RAND_bytes.html - * - For OpenSSL's pseudo-random number generating system: - * http://www.openssl.org/docs/crypto/rand.html - * - For OpenSSL's support for external crypto modules: - * http://www.openssl.org/docs/crypto/engine.html - * - * In mbed TLS, the Havege random number generator is used. For details, see - * the mbed TLS documentation. - * - * @section key_generation_exchange Key exchange: - * - * The %key exchange process is initiated by the OpenVPN process running - * in client mode. After the initial three-way handshake has successfully - * completed, the client sends its share of random material to the server, - * after which the server responds with its part. This process is - * depicted below: - * -@verbatim - Client Client Server Server - State Action Action State ----------- -------------------- -------------------- ---------- - - ... waiting until three-way handshake complete ... -S_START S_START - key_method_?_write() - send to server --> --> --> --> receive from client -S_SENT_KEY key_method_?_read() - S_GOT_KEY - key_method_?_write() - receive from server <-- <-- <-- <-- send to client - key_method_?_read() S_SENT_KEY -S_GOT_KEY - ... waiting until control channel fully synchronized ... -S_ACTIVE S_ACTIVE -@endverbatim - * - * For more information about the client and server state values, see the - * \link control_processor Control Channel Processor module\endlink. - * - * Depending on which %key method is used, the \c ? in the function names - * of the diagram above is a \c 1 or a \c 2. For example, if %key method - * 2 is used, that %key exchange would be started by the client calling \c - * key_method_2_write(). These functions are called from the \link - * control_processor Control Channel Processor module's\endlink \c - * tls_process() function and control the %key generation and exchange - * process as follows: - * - %Key method 1 has been removed in OpenVPN 2.5 - * - %Key method 2: - * - \c key_method_2_write(): generate random material locally, and if - * in server mode generate %key expansion. - * - \c key_method_2_read(): read random material received from remote - * peer, and if in client mode generate %key expansion. - * - * @subsection key_generation_encapsulation Transmission of key material - * - * The OpenVPN client and server communicate with each other through their - * control channel. This means that all of the data transmitted over the - * network, such as random material for %key generation, is encapsulated - * in a TLS layer. For more details, see the \link control_tls Control - * Channel TLS module\endlink documentation. - */ diff --git a/doc/doxygen/doc_mainpage.h b/doc/doxygen/doc_mainpage.h deleted file mode 100644 index 6016d07..0000000 --- a/doc/doxygen/doc_mainpage.h +++ /dev/null @@ -1,161 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * Main page documentation file. - */ - -/** - * @mainpage OpenVPN source code documentation - * - * This documentation describes the internal structure of OpenVPN. It was - * automatically generated from specially formatted comment blocks in - * OpenVPN's source code using Doxygen. (See - * http://www.stack.nl/~dimitri/doxygen/ for more information on Doxygen) - * - * The \ref mainpage_modules "Modules section" below gives an introduction - * into the high-level module concepts used throughout this documentation. - * The \ref mainpage_relatedpages "Related Pages section" below describes - * various special subjects related to OpenVPN's implementation which are - * discussed in the related pages section. - * - * @section mainpage_modules Modules - * - * For the purpose of describing the internal structure of OpenVPN, this - * documentation and the underlying source code has been broken up into a - * number of conceptually well-defined parts, known as modules. Each - * module plays a specific role within the OpenVPN process, and in most - * cases each module has a clear interfacing strategy for interacting with - * other modules. - * - * The following modules have been defined: - * - Driver module: - * - The \link eventloop Main Event Loop\endlink: this module drives the - * event handling of OpenVPN. It implements various types of - * select-loop which wait until an event happens, and then delegate - * the handling of that event to the appropriate module. - * - Network interface modules: - * - The \link external_multiplexer External Multiplexer\endlink: this - * module sends and receives packets to and from remote OpenVPN peers - * over the external network interface. It also takes care of - * demultiplexing received packets to their appropriate VPN tunnel and - * splitting control channel and data channel packets. - * - The \link internal_multiplexer Internal Multiplexer\endlink: this - * module sends and receives packets to and from locally reachable - * posts over the virtual tun/tap network interface. It also takes - * care of determining through which VPN tunnel a received packet must - * be sent to reach its destination. - * - Control channel modules: - * - The \link reliable Reliability Layer\endlink: this module offers a - * %reliable and sequential transport layer for control channel - * messages. - * - The \link control_tls Control Channel TLS module\endlink: this - * module offers a secure encapsulation of control channel messages - * using the TLS protocol. - * - The \link control_processor Control Channel Processor\endlink: his - * module manages the setup, maintenance, and shut down of VPN - * tunnels. - * - Data channel modules: - * - The \link data_control Data Channel Control module\endlink: this - * module controls the processing of data channel packets and, - * depending on the settings of the packet's VPN tunnel, passes the - * packet to the three modules below for handling. - * - The \link data_crypto Data Channel Crypto module\endlink: this - * module performs security operations on data channel packets. - * - The \link fragmentation Data Channel Fragmentation module\endlink: - * this module offers fragmentation of data channel packets larger - * than the VPN tunnel's MTU. - * - The \link compression Data Channel Compression module\endlink: this - * module offers compression of data channel packets. - * - * @subsection mainpage_modules_example Example event: receiving a packet - * - * OpenVPN handles many types of events during operation. These include - * external events, such as network traffic being received, and internal - * events, such as a %key session timing out causing renegotiation. An - * example event, receiving a packet over the network, is described here - * together with which modules play what roles: - * -# The \link eventloop Main Event Loop\endlink detects that a packet - * can be read from the external or the virtual tun/tap network - * interface. - * -# The \link eventloop Main Event Loop\endlink calls the \link - * external_multiplexer External Multiplexer\endlink or \link - * internal_multiplexer Internal Multiplexer\endlink to read and - * process the packet. - * -# The multiplexer module determines the type of packet and its - * destination, and passes the packet on to the appropriate handling - * module: - * - A control channel packet received by the \link - * external_multiplexer External Multiplexer\endlink is passed on - * through the \link reliable Reliability Layer\endlink and the \link - * control_tls Control Channel TLS module\endlink to the \link - * control_processor Control Channel Processor\endlink. - * - A data channel packet received by either multiplexer module is - * passed on to the \link data_control Data Channel Control - * module\endlink. - * -# The packet is processed by the appropriate control channel or data - * channel modules. - * -# If, after processing the packet, a resulting packet is generated - * that needs to be sent to a local or remote destination, it is given - * to the \link external_multiplexer External Multiplexer\endlink or - * \link internal_multiplexer Internal Multiplexer\endlink for sending. - * -# If a packet is waiting to be sent by either multiplexer module and - * the \link eventloop Main Event Loop\endlink detects that data can be - * written to the associated network interface, it calls the - * multiplexer module to send the packet. - * - * @section mainpage_relatedpages Related pages - * - * This documentation includes a number of descriptions of various aspects - * of OpenVPN and its implementation. These are not directly related to - * one module, function, or data structure, and are therefore listed - * separately under "Related Pages". - * - * @subsection mainpage_relatedpages_key_generation Data channel key generation - * - * The @ref key_generation "Data channel key generation" related page - * describes how, during VPN tunnel setup and renegotiation, OpenVPN peers - * generate and exchange the %key material required for the symmetric - * encryption/decryption and HMAC signing/verifying security operations - * performed on data channel packets. - * - * @subsection mainpage_relatedpages_tunnel_state VPN tunnel state - * - * The @ref tunnel_state "Structure of VPN tunnel state storage" related - * page describes how an OpenVPN process manages the state information - * associated with its active VPN tunnels. - * - * @subsection mainpage_relatedpages_network_protocol Network protocol - * - * The @ref network_protocol "Network protocol" related page describes the - * format and content of VPN tunnel packets exchanged between OpenVPN - * peers. - * - * @subsection mainpage_relatedpages_memory_management Memory management - * - * The @ref memory_management "Memory management strategies" related page - * gives a brief introduction into OpenVPN's memory %buffer library and - * garbage collection facilities. - */ diff --git a/doc/doxygen/doc_memory_management.h b/doc/doxygen/doc_memory_management.h deleted file mode 100644 index 1f16328..0000000 --- a/doc/doxygen/doc_memory_management.h +++ /dev/null @@ -1,98 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * Memory management strategies documentation file. - */ - -/** - * @page memory_management OpenVPN's memory management strategies - * - * This section describes several implementation details relating to - * OpenVPN's memory management strategies. - * - * During operation, the OpenVPN process performs all kinds of operations - * on blocks of data. Receiving packets, encrypting content, prepending - * headers, etc. To make the programmer's job easier and to decrease the - * likelihood of memory-related bugs, OpenVPN uses its own memory %buffer - * library and garbage collection facilities. These are described in - * brief here. - * - * @section memory_management_buffer The buffer structure - * - * The \c buffer structure is a wrapper around a block of dynamically - * allocated memory which keeps track of the block's capacity \c - * buffer.capacity and location in memory \c buffer.data. This structure - * supports efficient prepending and appending within the allocated memory - * through the use of offset \c buffer.offset and length \c buffer.len - * fields. See the \c buffer documentation for more details on the - * structure itself. - * - * OpenVPN's %buffer library, implemented in the \c buffer.h and \c - * buffer.c files, contains many utility functions for working with \c - * buffer structures. These functions facilitate common operations, such - * as allocating, freeing, reading and writing to \c buffer structures, - * and even offer several more advanced operations, such as string - * matching and creating sub-buffers. - * - * Not only do these utility functions make working with \c buffer - * structures easy, they also perform extensive error checking. Each - * function, where necessary, checks whether enough space is available - * before performing its actions. This minimizes the chance of bugs - * leading to %buffer overflows and other vulnerabilities. - * - * @section memory_management_frame The frame structure - * - * The \c frame structure keeps track of the maximum allowed packet - * geometries of a network connection. - * - * It is used, for example, to determine the size of \c buffer structures - * in which to store data channel packets. This is done by having each - * data channel processing module register the maximum amount of extra - * space it will need for header prepending and content expansion in the - * \c frame structure. Once these parameters are known, \c buffer - * structures can be allocated, based on the \c frame parameters, so that - * they are large enough to allow efficient prepending of headers and - * processing of content. - * - * @section memory_management_garbage Garbage collection - * - * OpenVPN has many sizable functions which perform various actions - * depending on their %context. This makes it difficult to know in advance - * exactly how much memory must be allocated. The garbage collection - * facilities are used to keep track of dynamic allocations, thereby - * allowing easy collective freeing of the allocated memory. - * - * The garbage collection system is implemented by the \c gc_arena and \c - * gc_entry structures. The arena represents a garbage collecting unit, - * and contains a linked list of entries. Each entry represents one block - * of dynamically allocated memory. - * - * The garbage collection system also contains various utility functions - * for working with the garbage collection structures. These include - * functions for initializing new arenas, allocating memory of a given - * size and registering the allocation in an arena, and freeing all the - * allocated memory associated with an arena. - */ diff --git a/doc/doxygen/doc_protocol_overview.h b/doc/doxygen/doc_protocol_overview.h deleted file mode 100644 index 0821222..0000000 --- a/doc/doxygen/doc_protocol_overview.h +++ /dev/null @@ -1,195 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file Network protocol overview documentation file. - */ - -/** - * @page network_protocol OpenVPN's network protocol - * - * Description of packet structure in OpenVPN's network protocol. - * - * This document describes the structure of packets exchanged between - * OpenVPN peers. It is based on the protocol description in the \c ssl.h - * file. - * - * @section network_protocol_external Outer structure of packets exchanged between OpenVPN peers - * - * VPN tunnel packets are transported between OpenVPN peers using the UDP - * or TCP protocols. Their structure is described below. - * - * @subsection network_protocol_external_structure External packet structure - * - * - packet length (16 bits, unsigned) [TCP-mode only]: always sent as - * plain text. Since TCP is a stream protocol, this packet length - * defines the packetization of the stream. - * - packet opcode and key_id (8 bits) [TLS-mode only]: - * - package message type (high 5 bits) - * - key_id (low 3 bits): the key_id refers to an already negotiated - * TLS session. OpenVPN seamlessly renegotiates the TLS session by - * using a new key_id for the new session. Overlap (controlled by - * user definable parameters) between old and new TLS sessions is - * allowed, providing a seamless transition during tunnel operation. - * - payload (n bytes) - * - * @subsection network_protocol_external_types Message types - * - * The type of a VPN tunnel packet is indicated by its opcode. The - * following describes the various opcodes available. - * - * - Control channel messages: - * - \ref P_CONTROL_HARD_RESET_CLIENT_V1 -- %Key method 1, initial %key - * from client, forget previous state. - * - \ref P_CONTROL_HARD_RESET_SERVER_V1 -- %Key method 1, initial %key - * from server, forget previous state. - * - \ref P_CONTROL_HARD_RESET_CLIENT_V2 -- %Key method 2, initial %key - * from client, forget previous state. - * - \ref P_CONTROL_HARD_RESET_SERVER_V2 -- %Key method 2, initial %key - * from server, forget previous state. - * - \ref P_CONTROL_SOFT_RESET_V1 -- New %key, with a graceful - * transition from old to new %key in the sense that a transition - * window exists where both the old or new key_id can be used. - * - \ref P_CONTROL_V1 -- Control channel packet (usually TLS - * ciphertext). - * - \ref P_ACK_V1 -- Acknowledgement for control channel packets - * received. - * - Data channel messages: - * - \ref P_DATA_V1 -- Data channel packet containing data channel - * ciphertext. - * - \ref P_DATA_V2 -- Data channel packet containing peer-id and data - * channel ciphertext. - * - * @subsection network_protocol_external_key_id Session IDs and Key IDs - * - * OpenVPN uses two different forms of packet identifiers: - * - The first form is 64 bits and is used for all control channel - * messages. This form is referred to as a \c session_id. - * - Data channel messages on the other hand use a shortened form of 3 - * bits for efficiency reasons since the vast majority of OpenVPN - * packets in an active tunnel will be data channel messages. This - * form is referred to as a \c key_id. - * - * The control and data channels use independent packet-id sequences, - * because the data channel is an unreliable channel while the control - * channel is a %reliable channel. Each use their own independent HMAC - * keys. - * - * @subsection network_protocol_external_reliable Control channel reliability layer - * - * Control channel messages (\c P_CONTROL_* and \c P_ACK_* message types) - * are TLS ciphertext packets which have been encapsulated inside of a - * reliability layer. The reliability layer is implemented as a - * straightforward acknowledge and retransmit model. - * - * Acknowledgments of received messages can be encoded in either the - * dedicated \c P_ACK_* record or they can be prepended to a \c - * P_CONTROL_* message. - * - * See the \link reliable Reliability Layer\endlink module for a detailed - * description. - * - * @section network_protocol_control Structure of control channel messages - * - * @subsection network_protocol_control_ciphertext Structure of ciphertext control channel messages - * - * Control channel packets in ciphertext form consist of the following - * parts: - * - * - local \c session_id (random 64 bit value to identify TLS session). - * - HMAC signature of entire encapsulation header for HMAC firewall - * [only if \c --tls-auth is specified] (usually 16 or 20 bytes). - * - packet-id for replay protection (4 or 8 bytes, includes sequence - * number and optional \c time_t timestamp). - * - acknowledgment packet-id array length (1 byte). - * - acknowledgment packet-id array (if length > 0). - * - acknowledgment remote session-id (if length > 0). - * - packet-id of this message (4 bytes). - * - TLS payload ciphertext (n bytes) (only for \c P_CONTROL_V1). - * - * Note that when \c --tls-auth is used, all message types are protected - * with an HMAC signature, even the initial packets of the TLS handshake. - * This makes it easy for OpenVPN to throw away bogus packets quickly, - * without wasting resources on attempting a TLS handshake which will - * ultimately fail. - * - * @subsection network_protocol_control_key_methods Control channel key methods - * - * Once the TLS session has been initialized and authenticated, the TLS - * channel is used to exchange random %key material for bidirectional - * cipher and HMAC keys which will be used to secure data channel packets. - * OpenVPN currently implements two %key methods. %Key method 1 directly - * derives keys using random bits obtained from the \c rand_bytes() function. - * %Key method 2 mixes random %key material from both sides of the connection - * using the TLS PRF mixing function. %Key method 2 is the preferred method and - * is the default for OpenVPN 2.0+. - * - * The @ref key_generation "Data channel key generation" related page - * describes the %key methods in more detail. - * - * @subsection network_protocol_control_plaintext Structure of plaintext control channel messages - * - * - %Key method 1 (support removed in OpenVPN 2.5): - * - Cipher %key length in bytes (1 byte). - * - Cipher %key (n bytes). - * - HMAC %key length in bytes (1 byte). - * - HMAC %key (n bytes). - * - %Options string (n bytes, null terminated, client/server %options - * string should match). - * - %Key method 2: - * - Literal 0 (4 bytes). - * - %Key method (1 byte). - * - \c key_source structure (\c key_source.pre_master only defined - * for client -> server). - * - %Options string length, including null (2 bytes). - * - %Options string (n bytes, null terminated, client/server %options - * string must match). - * - [The username/password data below is optional, record can end at - * this point.] - * - Username string length, including null (2 bytes). - * - Username string (n bytes, null terminated). - * - Password string length, including null (2 bytes). - * - Password string (n bytes, null terminated). - * - * @section network_protocol_data Structure of data channel messages - * - * The P_DATA_* payload represents encapsulated tunnel packets which tend to be - * either IP packets or Ethernet frames. This is essentially the "payload" of - * the VPN. Data channel packets consist of a data channel header, and a - * payload. There are two possible formats: - * - * @par P_DATA_V1 - * P_DATA_V1 packets have a 1-byte header, carrying the \ref P_DATA_V1 \c opcode - * and \c key_id, followed by the payload:\n - * [ 5-bit opcode | 3-bit key_id ] [ payload ] - * - * @par P_DATA_V2 - * P_DATA_V2 packets have the same 1-byte opcode/key_id, but carrying the \ref - * P_DATA_V2 opcode, followed by a 3-byte peer-id, which uniquely identifies - * the peer:\n - * [ 5-bit opcode | 3-bit key_id ] [ 24-bit peer-id ] [ payload ] - * - * See @ref data_crypto for details on the data channel payload format. - * - */ diff --git a/doc/doxygen/doc_reliable.h b/doc/doxygen/doc_reliable.h deleted file mode 100644 index 70556d7..0000000 --- a/doc/doxygen/doc_reliable.h +++ /dev/null @@ -1,48 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * Reliability Layer module documentation file. - */ - -/** - * @defgroup reliable Reliability Layer module - * - * The Reliability Layer is part of OpenVPN's control channel. It - * provides a reliable and sequential transport mechanism for control - * channel messages between OpenVPN peers. This module forms the - * interface between the \link external_multiplexer External - * Multiplexer\endlink and the \link control_tls Control Channel TLS - * module\endlink. - * - * @par UDP or TCP as VPN tunnel transport - * - * This is especially important when OpenVPN is configured to communicate - * over UDP, because UDP does not offer a reliable and sequential - * transport. OpenVPN endpoints can also communicate over TCP which does - * provide a reliable and sequential transport. In both cases, using UDP - * or TCP as an external transport, the internal Reliability Layer is - * active. - */ diff --git a/doc/doxygen/doc_tunnel_state.h b/doc/doxygen/doc_tunnel_state.h deleted file mode 100644 index 46e750f..0000000 --- a/doc/doxygen/doc_tunnel_state.h +++ /dev/null @@ -1,154 +0,0 @@ -/* - * OpenVPN -- An application to securely tunnel IP networks - * over a single TCP/UDP port, with support for SSL/TLS-based - * session authentication and key exchange, - * packet encryption, packet authentication, and - * packet compression. - * - * Copyright (C) 2010-2018 Fox Crypto B.V. - * - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 - * as published by the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - */ - -/** - * @file - * VPN tunnel state documentation file. - */ - -/** - * @page tunnel_state Structure of the VPN tunnel state storage - * - * This section describes how OpenVPN stores its VPN tunnel state during - * operation. - * - * OpenVPN uses several data structures as storage containers for state - * information of active VPN tunnels. These are described in this - * section, together with a little bit of history to help understand the - * origin of the current architecture. - * - * Whether an OpenVPN process is running in client-mode or server-mode - * determines whether it can support only one or multiple simultaneously - * active VPN tunnels. This consequently also determines how the - * associated state information is wrapped up internally. This section - * gives an overview of the differences. - * - * @section tunnel_state_history Historic developments - * - * In the old v1.x series, an OpenVPN process managed only one single VPN - * tunnel. This allowed the VPN tunnel state to be stored together with - * process-global information in one single \c context structure. - * - * This changed, however, in the v2.x series, as new OpenVPN versions - * running in server-mode can support multiple simultaneously active VPN - * tunnels. This necessitated a redesign of the VPN tunnel state - * container structures, and modification of the \link - * external_multiplexer External Multiplexer\endlink and \link - * internal_multiplexer Internal Multiplexer\endlink systems. The - * majority of these changes are only relevant for OpenVPN processes - * running in server-mode, and the client-mode structure has remained very - * similar to the v1.x single-tunnel form. - * - * @section tunnel_state_client Client-mode state - * - * An OpenVPN process running in client-mode can manage at most one single - * VPN tunnel at any one time. The state information for a client's VPN - * tunnel is stored in a \c context structure. - * - * The \c context structure is created in the \c main() function. That is - * also where process-wide initialization takes place, such as parsing - * command line %options and reading configuration files. The \c context - * is then passed to \c tunnel_point_to_point() which drives OpenVPN's - * main event processing loop. These functions are both part of the \link - * eventloop Main Event Loop\endlink module. - * - * @subsection tunnel_state_client_init Initialization and cleanup - * - * Because there is only one \c context structure present, it can be - * initialized and cleaned up from the client's main event processing - * function. Before the \c tunnel_point_to_point() function enters its - * event loop, it calls \c init_instance_handle_signals() which calls \c - * init_instance() to initialize the single \c context structure. After - * the event loop stops, it calls \c close_instance() to clean up the \c - * context. - * - * @subsection tunnel_state_client_event Event processing - * - * When the main event processing loop activates the external or internal - * multiplexer to handle a network event, it is not necessary to determine - * which VPN tunnel the event is associated with, because there is only - * one VPN tunnel active. - * - * @section tunnel_state_server Server-mode state - * - * An OpenVPN process running in server-mode can manage multiple - * simultaneously active VPN tunnels. For every VPN tunnel active, in - * other words for every OpenVPN client which is connected to a server, - * the OpenVPN server has one \c context structure in which it stores that - * particular VPN tunnel's state information. - * - * @subsection tunnel_state_server_multi Multi_context and multi_instance structures - * - * To support multiple \c context structures, each is wrapped in a \c - * multi_instance structure, and all the \c multi_instance structures are - * registered in one single \c multi_context structure. The \link - * external_multiplexer External Multiplexer\endlink and \link - * internal_multiplexer Internal Multiplexer\endlink then use the \c - * multi_context to retrieve the correct \c multi_instance and \c context - * associated with a given network address. - * - * @subsection tunnel_state_server_init Startup and initialization - * - * An OpenVPN process running in server-mode starts in the same \c main() - * function as it would in client-mode. The same process-wide - * initialization is performed, and the resulting state and configuration - * is stored in a \c context structure. The server-mode and client-mode - * processes diverge when the \c main() function calls one of \c - * tunnel_point_to_point() or \c tunnel_server(). - * - * In server-mode, \c main() calls the \c tunnel_server() function, which - * transfers control to \c tunnel_server_udp_single_threaded() or \c - * tunnel_server_tcp() depending on the external transport protocol. - * - * These functions receive the \c context created in \c main(). This - * object has a special status in server-mode, as it does not represent an - * active VPN tunnel, but does contain process-wide configuration - * parameters. In the source code, it is often stored in "top" variables. - * To distinguish this object from other instances of the same type, its - * \c context.mode value is set to \c CM_TOP. Other \c context objects, - * which do represent active VPN tunnels, have a \c context.mode set to \c - * CM_CHILD_UDP or \c CM_CHILD_TCP, depending on the external transport - * protocol. - * - * Both \c tunnel_server_udp_single_threaded() and \c tunnel_server_tcp() - * perform similar initialization. In either case, a \c multi_context - * structure is created, and it is initialized according to the - * configuration stored in the top \c context by the \c multi_init() and - * \c multi_top_init() functions. - * - * @subsection tunnel_state_server_tunnels Creating and destroying VPN tunnels - * - * When an OpenVPN client makes a new connection to a server, the server - * creates a new \c context and \c multi_instance. The latter is - * registered in the \c multi_context, which makes it possible for the - * external and internal multiplexers to retrieve the correct \c - * multi_instance and \c context when a network event occurs. - * - * @subsection tunnel_state_server_cleanup Final cleanup - * - * After the main event loop exits, both \c - * tunnel_server_udp_single_threaded() and \c tunnel_server_tcp() perform - * similar cleanup. They call \c multi_uninit() followed by \c - * multi_top_free() to clean up the \c multi_context structure. - */ diff --git a/doc/keying-material-exporter.txt b/doc/keying-material-exporter.txt deleted file mode 100644 index 4c1addc..0000000 --- a/doc/keying-material-exporter.txt +++ /dev/null @@ -1,137 +0,0 @@ -OpenVPN Daniel Kubec -RFC-5705 February 2015 - - - Added support for TLS Keying Material Exporters - -Keying Material Exporter [RFC-5705] allow additional keying material to be -derived from existing TLS channel. This exported keying material can then be -used for a variety of purposes. TLS allows client and server to establish -keying material for use in the upper layers between the TLS end-points and -channel bindings is straightforward and well-defined mechanism how to -authenticate other layers. - - -OpenVPN Configuration - ---keying-material-exporter label len - -Export Keying Material [RFC-5705] of len bytes (min. 16 bytes) using label in -environment (exported_keying_material) for use by plugins in -OPENVPN_PLUGIN_TLS_FINAL callback. - -Note that exporter labels have the potential to collide with existing PRF -labels. In order to prevent this, labels MUST begin with "EXPORTER". -(This option requires OpenSSL 1.0.1 or newer.) - - -Use Cases: - -Secure bindings of AAA information to application layer - - OpenVPN Client <------> OpenVPN Server - [KeyAgreement] [KeyAgreement] - - [TLSExportedKeyingMaterial] [TLSExportedKeyingMaterial] - [AAASessionKey] [AAASessionKey] - Client <------> Server - [Authenticated layer on top of (D)TLS] - - -TLS side channel authentication and straightforward bindings of AAA information -to application layer using well-defined mechanism. - - OpenVPN Client <------> OpenVPN Server - [KeyAgreement] [KeyAgreement] - - [TLSExportedKeyingMaterial] [TLSExportedKeyingMaterial] - [DerivedAAABindingKey] [DerivedAAABindingKey] - [AuthenticateBindingKeys] - Client -------> Server - [Confidential channel] - - -TLS Message flow for a full handshake - - ClientHello --------> - ServerHello - Certificate* - ServerKeyExchange* - CertificateRequest* - <-------- ServerHelloDone - Certificate* - ClientKeyExchange - CertificateVerify* - [ChangeCipherSpec] - Finished --------> - [ChangeCipherSpec] - <-------- Finished - - GenerateTLSBindingKey GenerateTLSBindingKey - - Application Data <-------> Application Data - - -Terminology - - AAA Authentication, Authorization, and Accounting: - functions that are generally required to control - access to a service and support auditing. - - Secure channel a packet, datagram, octet stream connection, or - sequence of connections between two end-points that - affords cryptographic integrity and confidentiality - to data exchanged over it. - - Channel binding the process of establishing that no man-in-the-middle - exists between two end-points that have been - authenticated using secure channel. - - TLS Binding Key Exported Keying Material [RFC5705] - - If no context is provided, it then computes: - PRF(SecurityParameters.master_secret, label, - SecurityParameters.client_random + - SecurityParameters.server_random - )[length] - - If context is provided, it computes: - PRF(SecurityParameters.master_secret, label, - SecurityParameters.client_random + - SecurityParameters.server_random + - context_value_length + context_value - )[length] - - AAA Binding Key TLS side channel authentication based on secure - channel bindings requires one more key derivation. - - SHA1(TLSExportedKeyingMaterial + ServerPublicKey) - -Reference - - [OPENAAA] "TLS side channel authentication and straightforward - bindings of AAA information to application - layer using well-defined mechanism." - Daniel Kubec March 2013 - https://github.com/n13l/openaaa - - [RFC5705] "Keying Material Exporters for TLS" - E. Rescorla, RFC 5705 March 2010 - http://tools.ietf.org/html/rfc5705 - - [RFC5929] "Channel Bindings for TLS" - J. Altman, N. Williams, L. Zhu, RFC 5929, July 2010 - http://tools.ietf.org/html/rfc5929 - - [RFC4680] "TLS Handshake Message for Supplemental Data" - S. Santesson, RFC 4680, September 2006 - http://tools.ietf.org/html/rfc4680 - - [RFC5878] "TLS Authorization Extension" - M. Brown, R. Housley, RFC 5878, May 2010 - http://tools.ietf.org/html/rfc5878 - - [RFC5746] "TLS Renegotiation Indication Extension" - E. Rescorla, M. Raym, S. Dispensa, N. Oskov - RFC 5746, February 2010 - http://tools.ietf.org/html/rfc5746 diff --git a/doc/man-sections/cipher-negotiation.rst b/doc/man-sections/cipher-negotiation.rst deleted file mode 100644 index f143305..0000000 --- a/doc/man-sections/cipher-negotiation.rst +++ /dev/null @@ -1,96 +0,0 @@ -Data channel cipher negotiation -=============================== - -OpenVPN 2.4 and higher have the capability to negotiate the data cipher that -is used to encrypt data packets. This section describes the mechanism in more detail and the -different backwards compatibility mechanism with older server and clients. - -OpenVPN 2.5 and higher behaviour --------------------------------- -When both client and server are at least running OpenVPN 2.5, that the order of -the ciphers of the server's ``--data-ciphers`` is used to pick the the data cipher. -That means that the first cipher in that list that is also in the client's -``--data-ciphers`` list is chosen. If no common cipher is found the client is rejected -with a AUTH_FAILED message (as seen in client log): - - AUTH: Received control message: AUTH_FAILED,Data channel cipher negotiation failed (no shared cipher) - -OpenVPN 2.5 will only allow the ciphers specified in ``--data-ciphers``. To ensure -backwards compatibility also if a cipher is specified using the ``--cipher`` option -it is automatically added to this list. If both options are unset the default is -:code:`AES-256-GCM:AES-128-GCM`. - -OpenVPN 2.4 clients -------------------- -The negotiation support in OpenVPN 2.4 was the first iteration of the implementation -and still had some quirks. Its main goal was "upgrade to AES-256-GCM when possible". -An OpenVPN 2.4 client that is built against a crypto library that supports AES in GCM -mode and does not have ``--ncp-disable`` will always announce support for -`AES-256-GCM` and `AES-128-GCM` to a server by sending :code:`IV_NCP=2`. - -This only causes a problem if ``--ncp-ciphers`` option has been changed from the -default of :code:`AES-256-GCM:AES-128-GCM` to a value that does not include -these two ciphers. When a OpenVPN servers try to use `AES-256-GCM` or -`AES-128-GCM` the connection will then fail. It is therefore recommended to -always have the `AES-256-GCM` and `AES-128-GCM` ciphers to the ``--ncp-ciphers`` -options to avoid this behaviour. - -OpenVPN 3 clients ------------------ -Clients based on the OpenVPN 3.x library (https://github.com/openvpn/openvpn3/) -do not have a configurable ``--ncp-ciphers`` or ``--data-cipher`` option. Instead -these clients will announce support for all their supported AEAD ciphers -(`AES-256-GCM`, `AES-128-GCM` and in newer versions also `Chacha20-Poly1305`). - -To support OpenVPN 3.x based clients at least one of these ciphers needs to be -included in the server's ``--data-ciphers`` option. - - -OpenVPN 2.3 and older clients (and clients with ``--ncp-disable``) ------------------------------------------------------------------- -When a client without cipher negotiation support connects to a server the -cipher specified with the ``--cipher`` option in the client configuration -must be included in the ``--data-ciphers`` option of the server to allow -the client to connect. Otherwise the client will be sent the ``AUTH_FAILED`` -message that indicates no shared cipher. - -If the client is 2.3 or older and has been configured with the -``--enable-small`` :code:`./configure` argument, using -``data-ciphers-fallback cipher`` in the server config file with the explicit -cipher used by the client is necessary. - -OpenVPN 2.4 server ------------------- -When a client indicates support for `AES-128-GCM` and `AES-256-GCM` -(with ``IV_NCP=2``) an OpenVPN 2.4 server will send the first -cipher of the ``--ncp-ciphers`` to the OpenVPN client regardless of what -the cipher is. To emulate the behaviour of an OpenVPN 2.4 client as close -as possible and have compatibility to a setup that depends on this quirk, -adding `AES-128-GCM` and `AES-256-GCM` to the client's ``--data-ciphers`` -option is required. OpenVPN 2.5+ will only announce the ``IV_NCP=2`` flag if -those ciphers are present. - -OpenVPN 2.3 and older servers (and servers with ``--ncp-disable``) ------------------------------------------------------------------- -The cipher used by the server must be included in ``--data-ciphers`` to -allow the client connecting to a server without cipher negotiation -support. -(For compatibility OpenVPN 2.5 will also accept the cipher set with -``--cipher``) - -If the server is 2.3 or older and has been configured with the -``--enable-small`` :code:`./configure` argument, adding -``data-ciphers-fallback cipher`` to the client config with the explicit -cipher used by the server is necessary. - -Blowfish in CBC mode (BF-CBC) deprecation ------------------------------------------- -The ``--cipher`` option defaulted to ``BF-CBC`` in OpenVPN 2.4 and older -version. The default was never changed to ensure backwards compatibility. -In OpenVPN 2.5 this behaviour has now been changed so that if the ``--cipher`` -is not explicitly set it does not allow the weak ``BF-CBC`` cipher any more -and needs to explicitly added as ``--cipher BFC-CBC`` or added to -``-data-ciphers``. - -We strongly recommend to switching away from BF-CBC to a -more secure cipher as soon as possible instead. diff --git a/doc/man-sections/vpn-network-options.rst b/doc/man-sections/vpn-network-options.rst index 7100c1a..825dd1c 100644 --- a/doc/man-sections/vpn-network-options.rst +++ b/doc/man-sections/vpn-network-options.rst @@ -93,12 +93,18 @@ routing. or :code:`tap`. --dhcp-option args - Set additional network settings via DHCP. On Windows, this is parsed by - the ``tap-windows6`` or ``wintun`` driver. On other platforms these - options can be picked up by an ``--up`` script or plug-in if it has been - pushed by the OpenVPN server. The option will then be saved in the - client's environment before the ``--up`` script is called, under the name - :code:`foreign_option_{n}`. + Set additional network parameters on supported platforms. May be specified + on the client or pushed from the server. On Windows these options are + handled by the ``tap-windows6`` driver by default or directly by OpenVPN + if dhcp is disabled or the ``wintun`` driver is in use. The + ``OpenVPN for Android`` client also handles them internally. + + On all other platforms these options are only saved in the client's + environment under the name :code:`foreign_options_{n}` before the + ``--up`` script is called. A plugin or an ``--up`` script must be used to + pick up and interpret these as required. Many Linux distributions include + such scripts and some third-party user interfaces such as tunnelblick also + come with scripts that process these options. Valid syntax: :: @@ -108,6 +114,11 @@ routing. :code:`DOMAIN` ``name`` Set Connection-specific DNS Suffix to :code:`name`. + :code:`DOMAIN-SEARCH` ``name`` + Add :code:`name` to the domain search list. + Repeat this option to add more entries. Up to + 10 domains are supported. + :code:`DNS` ``address`` Set primary domain name server IPv4 or IPv6 address. Repeat this option to set secondary DNS server addresses. diff --git a/doc/openvpn.8 b/doc/openvpn.8 new file mode 100644 index 0000000..b914f32 --- /dev/null +++ b/doc/openvpn.8 @@ -0,0 +1,6954 @@ +.\" Man page generated from reStructuredText. +. +.TH OPENVPN 8 "" "" "System Manager's Manual" +.SH NAME +openvpn \- Secure IP tunnel daemon +. +.nr rst2man-indent-level 0 +. +.de1 rstReportMargin +\\$1 \\n[an-margin] +level \\n[rst2man-indent-level] +level margin: \\n[rst2man-indent\\n[rst2man-indent-level]] +- +\\n[rst2man-indent0] +\\n[rst2man-indent1] +\\n[rst2man-indent2] +.. +.de1 INDENT +.\" .rstReportMargin pre: +. RS \\$1 +. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin] +. nr rst2man-indent-level +1 +.\" .rstReportMargin post: +.. +.de UNINDENT +. RE +.\" indent \\n[an-margin] +.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]] +.nr rst2man-indent-level -1 +.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]] +.in \\n[rst2man-indent\\n[rst2man-indent-level]]u +.. +.SH SYNOPSIS +.nf +\fBopenvpn\fP [ options ... ] +\fBopenvpn\fP \fB\-\-help\fP +.fi +.sp +.SH INTRODUCTION +.sp +OpenVPN is an open source VPN daemon by James Yonan. Because OpenVPN +tries to be a universal VPN tool offering a great deal of flexibility, +there are a lot of options on this manual page. If you\(aqre new to +OpenVPN, you might want to skip ahead to the examples section where you +will see how to construct simple VPNs on the command line without even +needing a configuration file. +.sp +Also note that there\(aqs more documentation and examples on the OpenVPN +web site: \fI\%https://openvpn.net/\fP +.sp +And if you would like to see a shorter version of this manual, see the +openvpn usage message which can be obtained by running \fBopenvpn\fP +without any parameters. +.SH DESCRIPTION +.sp +OpenVPN is a robust and highly flexible VPN daemon. OpenVPN supports +SSL/TLS security, ethernet bridging, TCP or UDP tunnel transport through +proxies or NAT, support for dynamic IP addresses and DHCP, scalability +to hundreds or thousands of users, and portability to most major OS +platforms. +.sp +OpenVPN is tightly bound to the OpenSSL library, and derives much of its +crypto capabilities from it. +.sp +OpenVPN supports conventional encryption using a pre\-shared secret key +\fB(Static Key mode)\fP or public key security \fB(SSL/TLS mode)\fP using +client & server certificates. OpenVPN also supports non\-encrypted +TCP/UDP tunnels. +.sp +OpenVPN is designed to work with the \fBTUN/TAP\fP virtual networking +interface that exists on most platforms. +.sp +Overall, OpenVPN aims to offer many of the key features of IPSec but +with a relatively lightweight footprint. +.SH OPTIONS +.sp +OpenVPN allows any option to be placed either on the command line or in +a configuration file. Though all command line options are preceded by a +double\-leading\-dash ("\-\-"), this prefix can be removed when an option is +placed in a configuration file. +.SS Generic Options +.sp +This section covers generic options which are accessible regardless of +which mode OpenVPN is configured as. +.INDENT 0.0 +.TP +.B \-\-help +Show options. +.TP +.B \-\-auth\-nocache +Don\(aqt cache \fB\-\-askpass\fP or \fB\-\-auth\-user\-pass\fP username/passwords in +virtual memory. +.sp +If specified, this directive will cause OpenVPN to immediately forget +username/password inputs after they are used. As a result, when OpenVPN +needs a username/password, it will prompt for input from stdin, which +may be multiple times during the duration of an OpenVPN session. +.sp +When using \fB\-\-auth\-nocache\fP in combination with a user/password file +and \fB\-\-chroot\fP or \fB\-\-daemon\fP, make sure to use an absolute path. +.sp +This directive does not affect the \fB\-\-http\-proxy\fP username/password. +It is always cached. +.TP +.BI \-\-cd \ dir +Change directory to \fBdir\fP prior to reading any files such as +configuration files, key files, scripts, etc. \fBdir\fP should be an +absolute path, with a leading "/", and without any references to the +current directory such as \fB\&.\fP or \fB\&..\fP\&. +.sp +This option is useful when you are running OpenVPN in \fB\-\-daemon\fP mode, +and you want to consolidate all of your OpenVPN control files in one +location. +.TP +.BI \-\-chroot \ dir +Chroot to \fBdir\fP after initialization. \fB\-\-chroot\fP essentially +redefines \fBdir\fP as being the top level directory tree (/). OpenVPN +will therefore be unable to access any files outside this tree. This can +be desirable from a security standpoint. +.sp +Since the chroot operation is delayed until after initialization, most +OpenVPN options that reference files will operate in a pre\-chroot +context. +.sp +In many cases, the \fBdir\fP parameter can point to an empty directory, +however complications can result when scripts or restarts are executed +after the chroot operation. +.sp +Note: The SSL library will probably need /dev/urandom to be available +inside the chroot directory \fBdir\fP\&. This is because SSL libraries +occasionally need to collect fresh random. Newer linux kernels and some +BSDs implement a getrandom() or getentropy() syscall that removes the +need for /dev/urandom to be available. +.TP +.BI \-\-config \ file +Load additional config options from \fBfile\fP where each line corresponds +to one command line option, but with the leading \(aq\-\-\(aq removed. +.sp +If \fB\-\-config file\fP is the only option to the openvpn command, the +\fB\-\-config\fP can be removed, and the command can be given as \fBopenvpn +file\fP +.sp +Note that configuration files can be nested to a reasonable depth. +.sp +Double quotation or single quotation characters ("", \(aq\(aq) can be used to +enclose single parameters containing whitespace, and "#" or ";" +characters in the first column can be used to denote comments. +.sp +Note that OpenVPN 2.0 and higher performs backslash\-based shell escaping +for characters not in single quotations, so the following mappings +should be observed: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +\e\e Maps to a single backslash character (\e). +\e" Pass a literal doublequote character ("), don\(aqt + interpret it as enclosing a parameter. +\e[SPACE] Pass a literal space or tab character, don\(aqt + interpret it as a parameter delimiter. +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +For example on Windows, use double backslashes to represent pathnames: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +secret "c:\e\eOpenVPN\e\esecret.key" +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +For examples of configuration files, see +\fI\%https://openvpn.net/community\-resources/how\-to/\fP +.sp +Here is an example configuration file: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +# +# Sample OpenVPN configuration file for +# using a pre\-shared static key. +# +# \(aq#\(aq or \(aq;\(aq may be used to delimit comments. + +# Use a dynamic tun device. +dev tun + +# Our remote peer +remote mypeer.mydomain + +# 10.1.0.1 is our local VPN endpoint +# 10.1.0.2 is our remote VPN endpoint +ifconfig 10.1.0.1 10.1.0.2 + +# Our pre\-shared static key +secret static.key +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-daemon \ progname +Become a daemon after all initialization functions are completed. This +option will cause all message and error output to be sent to the syslog +file (such as \fB/var/log/messages\fP), except for the output of +scripts and ifconfig commands, which will go to \fB/dev/null\fP unless +otherwise redirected. The syslog redirection occurs immediately at the +point that \fB\-\-daemon\fP is parsed on the command line even though the +daemonization point occurs later. If one of the \fB\-\-log\fP options is +present, it will supersede syslog redirection. +.sp +The optional \fBprogname\fP parameter will cause OpenVPN to report its +program name to the system logger as \fBprogname\fP\&. This can be useful in +linking OpenVPN messages in the syslog file with specific tunnels. When +unspecified, \fBprogname\fP defaults to "openvpn". +.sp +When OpenVPN is run with the \fB\-\-daemon\fP option, it will try to delay +daemonization until the majority of initialization functions which are +capable of generating fatal errors are complete. This means that +initialization scripts can test the return status of the openvpn command +for a fairly reliable indication of whether the command has correctly +initialized and entered the packet forwarding event loop. +.sp +In OpenVPN, the vast majority of errors which occur after initialization +are non\-fatal. +.sp +Note: as soon as OpenVPN has daemonized, it can not ask for usernames, +passwords, or key pass phrases anymore. This has certain consequences, +namely that using a password\-protected private key will fail unless the +\fB\-\-askpass\fP option is used to tell OpenVPN to ask for the pass phrase +(this requirement is new in v2.3.7, and is a consequence of calling +daemon() before initializing the crypto layer). +.sp +Further, using \fB\-\-daemon\fP together with \fB\-\-auth\-user\-pass\fP (entered +on console) and \fB\-\-auth\-nocache\fP will fail as soon as key +renegotiation (and reauthentication) occurs. +.TP +.B \-\-disable\-occ +Don\(aqt output a warning message if option inconsistencies are detected +between peers. An example of an option inconsistency would be where one +peer uses \fB\-\-dev tun\fP while the other peer uses \fB\-\-dev tap\fP\&. +.sp +Use of this option is discouraged, but is provided as a temporary fix in +situations where a recent version of OpenVPN must connect to an old +version. +.TP +.BI \-\-engine \ engine\-name +Enable OpenSSL hardware\-based crypto engine functionality. +.sp +If \fBengine\-name\fP is specified, use a specific crypto engine. Use the +\fB\-\-show\-engines\fP standalone option to list the crypto engines which +are supported by OpenSSL. +.TP +.B \-\-fast\-io +(Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a call to +poll/epoll/select prior to the write operation. The purpose of such a +call would normally be to block until the device or socket is ready to +accept the write. Such blocking is unnecessary on some platforms which +don\(aqt support write blocking on UDP sockets or TUN/TAP devices. In such +cases, one can optimize the event loop by avoiding the poll/epoll/select +call, improving CPU efficiency by 5% to 10%. +.sp +This option can only be used on non\-Windows systems, when \fB\-\-proto +udp\fP is specified, and when \fB\-\-shaper\fP is NOT specified. +.TP +.BI \-\-group \ group +Similar to the \fB\-\-user\fP option, this option changes the group ID of +the OpenVPN process to \fBgroup\fP after initialization. +.TP +.BI \-\-ignore\-unknown\-option \ args +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +ignore\-unknown\-options opt1 opt2 opt3 ... optN +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +When one of options \fBopt1 ... optN\fP is encountered in the configuration +file the configuration file parsing does not fail if this OpenVPN version +does not support the option. Multiple \fB\-\-ignore\-unknown\-option\fP options +can be given to support a larger number of options to ignore. +.sp +This option should be used with caution, as there are good security +reasons for having OpenVPN fail if it detects problems in a config file. +Having said that, there are valid reasons for wanting new software +features to gracefully degrade when encountered by older software +versions. +.sp +\fB\-\-ignore\-unknown\-option\fP is available since OpenVPN 2.3.3. +.TP +.BI \-\-iproute \ cmd +Set alternate command to execute instead of default \fBiproute2\fP command. +May be used in order to execute OpenVPN in unprivileged environment. +.TP +.BI \-\-keying\-material\-exporter \ args +Save Exported Keying Material [RFC5705] of len bytes (must be between 16 +and 4095 bytes) using \fBlabel\fP in environment +(\fBexported_keying_material\fP) for use by plugins in +\fBOPENVPN_PLUGIN_TLS_FINAL\fP callback. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +keying\-material\-exporter label len +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Note that exporter \fBlabels\fP have the potential to collide with existing +PRF labels. In order to prevent this, labels \fIMUST\fP begin with +\fBEXPORTER\fP\&. +.TP +.B \-\-mlock +Disable paging by calling the POSIX mlockall function. Requires that +OpenVPN be initially run as root (though OpenVPN can subsequently +downgrade its UID using the \fB\-\-user\fP option). +.sp +Using this option ensures that key material and tunnel data are never +written to disk due to virtual memory paging operations which occur +under most modern operating systems. It ensures that even if an attacker +was able to crack the box running OpenVPN, he would not be able to scan +the system swap file to recover previously used ephemeral keys, which +are used for a period of time governed by the \fB\-\-reneg\fP options (see +below), then are discarded. +.sp +The downside of using \fB\-\-mlock\fP is that it will reduce the amount of +physical memory available to other applications. +.TP +.BI \-\-nice \ n +Change process priority after initialization (\fBn\fP greater than 0 is +lower priority, \fBn\fP less than zero is higher priority). +.TP +.B \-\-persist\-key +Don\(aqt re\-read key files across \fBSIGUSR1\fP or \fB\-\-ping\-restart\fP\&. +.sp +This option can be combined with \fB\-\-user nobody\fP to allow restarts +triggered by the \fBSIGUSR1\fP signal. Normally if you drop root +privileges in OpenVPN, the daemon cannot be restarted since it will now +be unable to re\-read protected key files. +.sp +This option solves the problem by persisting keys across \fBSIGUSR1\fP +resets, so they don\(aqt need to be re\-read. +.TP +.BI \-\-remap\-usr1 \ signal +Control whether internally or externally generated \fBSIGUSR1\fP signals +are remapped to \fBSIGHUP\fP (restart without persisting state) or +SIGTERM (exit). +.sp +\fBsignal\fP can be set to \fBSIGHUP\fP or \fBSIGTERM\fP\&. By default, +no remapping occurs. +.TP +.BI \-\-script\-security \ level +This directive offers policy\-level control over OpenVPN\(aqs usage of +external programs and scripts. Lower \fBlevel\fP values are more +restrictive, higher values are more permissive. Settings for \fBlevel\fP: +.INDENT 7.0 +.TP +.B \fB0\fP +Strictly no calling of external programs. +.TP +.B \fB1\fP +(Default) Only call built\-in executables such as ifconfig, +ip, route, or netsh. +.TP +.B \fB2\fP +Allow calling of built\-in executables and user\-defined +scripts. +.TP +.B \fB3\fP +Allow passwords to be passed to scripts via environmental +variables (potentially unsafe). +.UNINDENT +.sp +OpenVPN releases before v2.3 also supported a \fBmethod\fP flag which +indicated how OpenVPN should call external commands and scripts. This +could be either \fBexecve\fP or \fBsystem\fP\&. As of OpenVPN 2.3, this +flag is no longer accepted. In most *nix environments the execve() +approach has been used without any issues. +.sp +Some directives such as \fB\-\-up\fP allow options to be passed to the +external script. In these cases make sure the script name does not +contain any spaces or the configuration parser will choke because it +can\(aqt determine where the script name ends and script options start. +.sp +To run scripts in Windows in earlier OpenVPN versions you needed to +either add a full path to the script interpreter which can parse the +script or use the \fBsystem\fP flag to run these scripts. As of OpenVPN +2.3 it is now a strict requirement to have full path to the script +interpreter when running non\-executables files. This is not needed for +executable files, such as .exe, .com, .bat or .cmd files. For example, +if you have a Visual Basic script, you must use this syntax now: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +\-\-up \(aqC:\e\eWindows\e\eSystem32\e\ewscript.exe C:\e\eProgram\e Files\e\eOpenVPN\e\econfig\e\emy\-up\-script.vbs\(aq +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Please note the single quote marks and the escaping of the backslashes +(\e) and the space character. +.sp +The reason the support for the \fBsystem\fP flag was removed is due to +the security implications with shell expansions when executing scripts +via the \fBsystem()\fP call. +.TP +.BI \-\-setcon \ context +Apply SELinux \fBcontext\fP after initialization. This essentially +provides the ability to restrict OpenVPN\(aqs rights to only network I/O +operations, thanks to SELinux. This goes further than \fB\-\-user\fP and +\fB\-\-chroot\fP in that those two, while being great security features, +unfortunately do not protect against privilege escalation by +exploitation of a vulnerable system call. You can of course combine all +three, but please note that since setcon requires access to /proc you +will have to provide it inside the chroot directory (e.g. with mount +\-\-bind). +.sp +Since the setcon operation is delayed until after initialization, +OpenVPN can be restricted to just network\-related system calls, whereas +by applying the context before startup (such as the OpenVPN one provided +in the SELinux Reference Policies) you will have to allow many things +required only during initialization. +.sp +Like with chroot, complications can result when scripts or restarts are +executed after the setcon operation, which is why you should really +consider using the \fB\-\-persist\-key\fP and \fB\-\-persist\-tun\fP options. +.TP +.BI \-\-status \ args +Write operational status to \fBfile\fP every \fBn\fP seconds. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +status file +status file n +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Status can also be written to the syslog by sending a \fBSIGUSR2\fP +signal. +.sp +With multi\-client capability enabled on a server, the status file +includes a list of clients and a routing table. The output format can be +controlled by the \fB\-\-status\-version\fP option in that case. +.sp +For clients or instances running in point\-to\-point mode, it will contain +the traffic statistics. +.TP +.BI \-\-status\-version \ n +Set the status file format version number to \fBn\fP\&. +.sp +This only affects the status file on servers with multi\-client +capability enabled. Valid status version values: +.INDENT 7.0 +.TP +.B \fB1\fP +Traditional format (default). The client list contains the +following fields comma\-separated: Common Name, Real Address, Bytes +Received, Bytes Sent, Connected Since. +.TP +.B \fB2\fP +A more reliable format for external processing. Compared to +version \fB1\fP, the client list contains some additional fields: +Virtual Address, Virtual IPv6 Address, Username, Client ID, Peer ID, +Data Channel Cipher. Future versions may extend the number of fields. +.TP +.B \fB3\fP +Identical to \fB2\fP, but fields are tab\-separated. +.UNINDENT +.TP +.B \-\-test\-crypto +Do a self\-test of OpenVPN\(aqs crypto options by encrypting and decrypting +test packets using the data channel encryption options specified above. +This option does not require a peer to function, and therefore can be +specified without \fB\-\-dev\fP or \fB\-\-remote\fP\&. +.sp +The typical usage of \fB\-\-test\-crypto\fP would be something like this: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +openvpn \-\-test\-crypto \-\-secret key +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +or +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +openvpn \-\-test\-crypto \-\-secret key \-\-verb 9 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +This option is very useful to test OpenVPN after it has been ported to a +new platform, or to isolate problems in the compiler, OpenSSL crypto +library, or OpenVPN\(aqs crypto code. Since it is a self\-test mode, +problems with encryption and authentication can be debugged +independently of network and tunnel issues. +.TP +.BI \-\-tmp\-dir \ dir +Specify a directory \fBdir\fP for temporary files. This directory will be +used by openvpn processes and script to communicate temporary data with +openvpn main process. Note that the directory must be writable by the +OpenVPN process after it has dropped it\(aqs root privileges. +.sp +This directory will be used by in the following cases: +.INDENT 7.0 +.IP \(bu 2 +\fB\-\-client\-connect\fP scripts and \fBOPENVPN_PLUGIN_CLIENT_CONNECT\fP +plug\-in hook to dynamically generate client\-specific configuration +\fBclient_connect_config_file\fP and return success/failure via +\fBclient_connect_deferred_file\fP when using deferred client connect +method +.IP \(bu 2 +\fBOPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY\fP plug\-in hooks returns +success/failure via \fBauth_control_file\fP when using deferred auth +method +.IP \(bu 2 +\fBOPENVPN_PLUGIN_ENABLE_PF\fP plugin hook to pass filtering rules +via \fBpf_file\fP +.UNINDENT +.TP +.B \-\-use\-prediction\-resistance +Enable prediction resistance on mbed TLS\(aqs RNG. +.sp +Enabling prediction resistance causes the RNG to reseed in each call for +random. Reseeding this often can quickly deplete the kernel entropy +pool. +.sp +If you need this option, please consider running a daemon that adds +entropy to the kernel pool. +.TP +.BI \-\-user \ user +Change the user ID of the OpenVPN process to \fBuser\fP after +initialization, dropping privileges in the process. This option is +useful to protect the system in the event that some hostile party was +able to gain control of an OpenVPN session. Though OpenVPN\(aqs security +features make this unlikely, it is provided as a second line of defense. +.sp +By setting \fBuser\fP to \fBnobody\fP or somebody similarly unprivileged, +the hostile party would be limited in what damage they could cause. Of +course once you take away privileges, you cannot return them to an +OpenVPN session. This means, for example, that if you want to reset an +OpenVPN daemon with a \fBSIGUSR1\fP signal (for example in response to +a DHCP reset), you should make use of one or more of the \fB\-\-persist\fP +options to ensure that OpenVPN doesn\(aqt need to execute any privileged +operations in order to restart (such as re\-reading key files or running +\fBifconfig\fP on the TUN device). +.TP +.BI \-\-writepid \ file +Write OpenVPN\(aqs main process ID to \fBfile\fP\&. +.UNINDENT +.SS Log options +.INDENT 0.0 +.TP +.BI \-\-echo \ parms +Echo \fBparms\fP to log output. +.sp +Designed to be used to send messages to a controlling application which +is receiving the OpenVPN log output. +.TP +.B \-\-errors\-to\-stderr +Output errors to stderr instead of stdout unless log output is +redirected by one of the \fB\-\-log\fP options. +.TP +.BI \-\-log \ file +Output logging messages to \fBfile\fP, including output to stdout/stderr +which is generated by called scripts. If \fBfile\fP already exists it will +be truncated. This option takes effect immediately when it is parsed in +the command line and will supersede syslog output if \fB\-\-daemon\fP or +\fB\-\-inetd\fP is also specified. This option is persistent over the entire +course of an OpenVPN instantiation and will not be reset by +\fBSIGHUP\fP, \fBSIGUSR1\fP, or \fB\-\-ping\-restart\fP\&. +.sp +Note that on Windows, when OpenVPN is started as a service, logging +occurs by default without the need to specify this option. +.TP +.BI \-\-log\-append \ file +Append logging messages to \fBfile\fP\&. If \fBfile\fP does not exist, it will +be created. This option behaves exactly like \fB\-\-log\fP except that it +appends to rather than truncating the log file. +.TP +.B \-\-machine\-readable\-output +Always write timestamps and message flags to log messages, even when +they otherwise would not be prefixed. In particular, this applies to log +messages sent to stdout. +.TP +.BI \-\-mute \ n +Log at most \fBn\fP consecutive messages in the same category. This is +useful to limit repetitive logging of similar message types. +.TP +.B \-\-mute\-replay\-warnings +Silence the output of replay warnings, which are a common false alarm on +WiFi networks. This option preserves the security of the replay +protection code without the verbosity associated with warnings about +duplicate packets. +.TP +.B \-\-suppress\-timestamps +Avoid writing timestamps to log messages, even when they otherwise would +be prepended. In particular, this applies to log messages sent to +stdout. +.TP +.BI \-\-syslog \ progname +Direct log output to system logger, but do not become a daemon. See +\fB\-\-daemon\fP directive above for description of \fBprogname\fP parameter. +.TP +.BI \-\-verb \ n +Set output verbosity to \fBn\fP (default \fB1\fP). Each level shows all +info from the previous levels. Level \fB3\fP is recommended if you want +a good summary of what\(aqs happening without being swamped by output. +.INDENT 7.0 +.TP +.B \fB0\fP +No output except fatal errors. +.TP +.B \fB1\fP to \fB4\fP +Normal usage range. +.TP +.B \fB5\fP +Outputs \fBR\fP and \fBW\fP characters to the console for +each packet read and write, uppercase is used for TCP/UDP +packets and lowercase is used for TUN/TAP packets. +.TP +.B \fB6\fP to \fB11\fP +Debug info range (see \fBerrlevel.h\fP in the source code for +additional information on debug levels). +.UNINDENT +.UNINDENT +.SS Protocol options +.sp +Options in this section affect features available in the OpenVPN wire +protocol. Many of these options also define the encryption options +of the data channel in the OpenVPN wire protocol. These options must be +configured in a compatible way between both the local and remote side. +.INDENT 0.0 +.TP +.BI \-\-allow\-compression \ mode +As described in the \fB\-\-compress\fP option, compression is a potentially +dangerous option. This option allows controlling the behaviour of +OpenVPN when compression is used and allowed. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +allow\-compression +allow\-compression mode +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The \fBmode\fP argument can be one of the following values: +.INDENT 7.0 +.TP +.B \fBasym\fP (default) +OpenVPN will only \fIdecompress downlink packets\fP but \fInot compress +uplink packets\fP\&. This also allows migrating to disable compression +when changing both server and client configurations to remove +compression at the same time is not a feasible option. +.TP +.B \fBno\fP +OpenVPN will refuse any non\-stub compression. +.TP +.B \fByes\fP +OpenVPN will send and receive compressed packets. +.UNINDENT +.TP +.BI \-\-auth \ alg +Authenticate data channel packets and (if enabled) \fBtls\-auth\fP control +channel packets with HMAC using message digest algorithm \fBalg\fP\&. (The +default is \fBSHA1\fP ). HMAC is a commonly used message authentication +algorithm (MAC) that uses a data string, a secure hash algorithm and a +key to produce a digital signature. +.sp +The OpenVPN data channel protocol uses encrypt\-then\-mac (i.e. first +encrypt a packet then HMAC the resulting ciphertext), which prevents +padding oracle attacks. +.sp +If an AEAD cipher mode (e.g. GCM) is chosen then the specified \fB\-\-auth\fP +algorithm is ignored for the data channel and the authentication method +of the AEAD cipher is used instead. Note that \fBalg\fP still specifies +the digest used for \fBtls\-auth\fP\&. +.sp +In static\-key encryption mode, the HMAC key is included in the key file +generated by \fB\-\-genkey\fP\&. In TLS mode, the HMAC key is dynamically +generated and shared between peers via the TLS control channel. If +OpenVPN receives a packet with a bad HMAC it will drop the packet. HMAC +usually adds 16 or 20 bytes per packet. Set \fBalg=none\fP to disable +authentication. +.sp +For more information on HMAC see +\fI\%http://www.cs.ucsd.edu/users/mihir/papers/hmac.html\fP +.TP +.BI \-\-cipher \ alg +This option is deprecated for server\-client mode. \fB\-\-data\-ciphers\fP +or possibly \fI\-\-data\-ciphers\-fallback\(ga\fP should be used instead. +.sp +Encrypt data channel packets with cipher algorithm \fBalg\fP\&. +.sp +The default is \fBBF\-CBC\fP, an abbreviation for Blowfish in Cipher +Block Chaining mode. When cipher negotiation (NCP) is allowed, +OpenVPN 2.4 and newer on both client and server side will automatically +upgrade to \fBAES\-256\-GCM\fP\&. See \fB\-\-data\-ciphers\fP and +\fB\-\-ncp\-disable\fP for more details on NCP. +.sp +Using \fBBF\-CBC\fP is no longer recommended, because of its 64\-bit +block size. This small block size allows attacks based on collisions, as +demonstrated by SWEET32. See +\fI\%https://community.openvpn.net/openvpn/wiki/SWEET32\fP +for details. Due to this, support for \fBBF\-CBC\fP, \fBDES\fP, +\fBCAST5\fP, \fBIDEA\fP and \fBRC2\fP ciphers will be removed in +OpenVPN 2.6. +.sp +To see other ciphers that are available with OpenVPN, use the +\fB\-\-show\-ciphers\fP option. +.sp +Set \fBalg\fP to \fBnone\fP to disable encryption. +.TP +.BI \-\-compress \ algorithm +\fBDEPRECATED\fP Enable a compression algorithm. Compression is generally +not recommended. VPN tunnels which use compression are susceptible to +the VORALCE attack vector. +.sp +The \fBalgorithm\fP parameter may be \fBlzo\fP, \fBlz4\fP, +\fBlz4\-v2\fP, \fBstub\fP, \fBstub\-v2\fP or empty. +LZO and LZ4 are different compression algorithms, with LZ4 generally +offering the best performance with least CPU usage. +.sp +The \fBlz4\-v2\fP and \fBstub\-v2\fP variants implement a better +framing that does not add overhead when packets cannot be compressed. All +other variants always add one extra framing byte compared to no +compression framing. +.sp +If the \fBalgorithm\fP parameter is \fBstub\fP, \fBstub\-v2\fP or empty, +compression will be turned off, but the packet framing for compression +will still be enabled, allowing a different setting to be pushed later. +Additionally, \fBstub\fP and \fBstub\-v2\fP wil disable announcing +\fBlzo\fP and \fBlz4\fP compression support via \fIIV_\fP variables to the +server. +.sp +Note: the \fBstub\fP (or empty) option is NOT compatible with the older +option \fB\-\-comp\-lzo no\fP\&. +.sp +\fB*Security Considerations*\fP +.sp +Compression and encryption is a tricky combination. If an attacker knows +or is able to control (parts of) the plain\-text of packets that contain +secrets, the attacker might be able to extract the secret if compression +is enabled. See e.g. the \fICRIME\fP and \fIBREACH\fP attacks on TLS and +\fIVORACLE\fP on VPNs which also leverage to break encryption. If you are not +entirely sure that the above does not apply to your traffic, you are +advised to \fInot\fP enable compression. +.TP +.BI \-\-comp\-lzo \ mode +\fBDEPRECATED\fP Enable LZO compression algorithm. Compression is +generally not recommended. VPN tunnels which uses compression are +suspectible to the VORALCE attack vector. +.sp +Use LZO compression \-\- may add up to 1 byte per packet for incompressible +data. \fBmode\fP may be \fByes\fP, \fBno\fP, or \fBadaptive\fP +(default). +.sp +In a server mode setup, it is possible to selectively turn compression +on or off for individual clients. +.sp +First, make sure the client\-side config file enables selective +compression by having at least one \fB\-\-comp\-lzo\fP directive, such as +\fB\-\-comp\-lzo no\fP\&. This will turn off compression by default, but allow +a future directive push from the server to dynamically change the +\fBon\fP/\fBoff\fP/\fBadaptive\fP setting. +.sp +Next in a \fB\-\-client\-config\-dir\fP file, specify the compression setting +for the client, for example: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +comp\-lzo yes +push "comp\-lzo yes" +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The first line sets the \fBcomp\-lzo\fP setting for the server side of the +link, the second sets the client side. +.TP +.B \-\-comp\-noadapt +\fBDEPRECATED\fP When used in conjunction with \fB\-\-comp\-lzo\fP, this option +will disable OpenVPN\(aqs adaptive compression algorithm. Normally, adaptive +compression is enabled with \fB\-\-comp\-lzo\fP\&. +.sp +Adaptive compression tries to optimize the case where you have +compression enabled, but you are sending predominantly incompressible +(or pre\-compressed) packets over the tunnel, such as an FTP or rsync +transfer of a large, compressed file. With adaptive compression, OpenVPN +will periodically sample the compression process to measure its +efficiency. If the data being sent over the tunnel is already +compressed, the compression efficiency will be very low, triggering +openvpn to disable compression for a period of time until the next +re\-sample test. +.TP +.B \-\-key\-direction +Alternative way of specifying the optional direction parameter for the +\fB\-\-tls\-auth\fP and \fB\-\-secret\fP options. Useful when using inline files +(See section on inline files). +.TP +.BI \-\-keysize \ n +\fBDEPRECATED\fP This option will be removed in OpenVPN 2.6. +.sp +Size of cipher key in bits (optional). If unspecified, defaults to +cipher\-specific default. The \fB\-\-show\-ciphers\fP option (see below) shows +all available OpenSSL ciphers, their default key sizes, and whether the +key size can be changed. Use care in changing a cipher\(aqs default key +size. Many ciphers have not been extensively cryptanalyzed with +non\-standard key lengths, and a larger key may offer no real guarantee +of greater security, or may even reduce security. +.TP +.BI \-\-data\-ciphers \ cipher\-list +Restrict the allowed ciphers to be negotiated to the ciphers in +\fBcipher\-list\fP\&. \fBcipher\-list\fP is a colon\-separated list of ciphers, +and defaults to \fBAES\-256\-GCM:AES\-128\-GCM\fP\&. +.sp +For servers, the first cipher from \fBcipher\-list\fP that is also +supported by the client will be pushed to clients that support cipher +negotiation. +.sp +Cipher negotiation is enabled in client\-server mode only. I.e. if +\fB\-\-mode\fP is set to \(aqserver\(aq (server\-side, implied by setting +\fB\-\-server\fP ), or if \fB\-\-pull\fP is specified (client\-side, implied by +setting \-\-client). +.sp +If no common cipher is found during cipher negotiation, the connection +is terminated. To support old clients/old servers that do not provide any +cipher negotiation support see \fB\-\-data\-ciphers\-fallback\fP\&. +.sp +Additionally, to allow for more smooth transition, if NCP is enabled, +OpenVPN will inherit the cipher of the peer if that cipher is different +from the local \fB\-\-cipher\fP setting, but the peer cipher is one of the +ciphers specified in \fB\-\-data\-ciphers\fP\&. E.g. a non\-NCP client (<=v2.3, +or with \-\-ncp\-disabled set) connecting to a NCP server (v2.4+) with +\fB\-\-cipher BF\-CBC\fP and \fB\-\-data\-ciphers AES\-256\-GCM:AES\-256\-CBC\fP set can +either specify \fB\-\-cipher BF\-CBC\fP or \fB\-\-cipher AES\-256\-CBC\fP and both +will work. +.sp +Note for using NCP with an OpenVPN 2.4 peer: This list must include the +\fBAES\-256\-GCM\fP and \fBAES\-128\-GCM\fP ciphers. +.sp +This list is restricted to be 127 chars long after conversion to OpenVPN +ciphers. +.sp +This option was called \fB\-\-ncp\-ciphers\fP in OpenVPN 2.4 but has been renamed +to \fB\-\-data\-ciphers\fP in OpenVPN 2.5 to more accurately reflect its meaning. +.TP +.BI \-\-data\-ciphers\-fallback \ alg +Configure a cipher that is used to fall back to if we could not determine +which cipher the peer is willing to use. +.sp +This option should only be needed to +connect to peers that are running OpenVPN 2.3 and older version, and +have been configured with \fI\-\-enable\-small\fP +(typically used on routers or other embedded devices). +.TP +.B \-\-ncp\-disable +\fBDEPRECATED\fP Disable "Negotiable Crypto Parameters". This completely +disables cipher negotiation. +.TP +.BI \-\-secret \ args +Enable Static Key encryption mode (non\-TLS). Use pre\-shared secret +\fBfile\fP which was generated with \fB\-\-genkey\fP\&. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +secret file +secret file direction +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The optional \fBdirection\fP parameter enables the use of 4 distinct keys +(HMAC\-send, cipher\-encrypt, HMAC\-receive, cipher\-decrypt), so that each +data flow direction has a different set of HMAC and cipher keys. This +has a number of desirable security properties including eliminating +certain kinds of DoS and message replay attacks. +.sp +When the \fBdirection\fP parameter is omitted, 2 keys are used +bidirectionally, one for HMAC and the other for encryption/decryption. +.sp +The \fBdirection\fP parameter should always be complementary on either +side of the connection, i.e. one side should use \fB0\fP and the other +should use \fB1\fP, or both sides should omit it altogether. +.sp +The \fBdirection\fP parameter requires that \fBfile\fP contains a 2048 bit +key. While pre\-1.5 versions of OpenVPN generate 1024 bit key files, any +version of OpenVPN which supports the \fBdirection\fP parameter, will also +support 2048 bit key file generation using the \fB\-\-genkey\fP option. +.sp +Static key encryption mode has certain advantages, the primary being +ease of configuration. +.sp +There are no certificates or certificate authorities or complicated +negotiation handshakes and protocols. The only requirement is that you +have a pre\-existing secure channel with your peer (such as \fBssh\fP) to +initially copy the key. This requirement, along with the fact that your +key never changes unless you manually generate a new one, makes it +somewhat less secure than TLS mode (see below). If an attacker manages +to steal your key, everything that was ever encrypted with it is +compromised. Contrast that to the perfect forward secrecy features of +TLS mode (using Diffie Hellman key exchange), where even if an attacker +was able to steal your private key, he would gain no information to help +him decrypt past sessions. +.sp +Another advantageous aspect of Static Key encryption mode is that it is +a handshake\-free protocol without any distinguishing signature or +feature (such as a header or protocol handshake sequence) that would +mark the ciphertext packets as being generated by OpenVPN. Anyone +eavesdropping on the wire would see nothing but random\-looking data. +.TP +.BI \-\-tran\-window \ n +Transition window \-\- our old key can live this many seconds after a new +a key renegotiation begins (default \fB3600\fP seconds). This feature +allows for a graceful transition from old to new key, and removes the key +renegotiation sequence from the critical path of tunnel data forwarding. +.UNINDENT +.SS Client Options +.sp +The client options are used when connecting to an OpenVPN server configured +to use \fB\-\-server\fP, \fB\-\-server\-bridge\fP, or \fB\-\-mode server\fP in its +configuration. +.INDENT 0.0 +.TP +.B \-\-allow\-pull\-fqdn +Allow client to pull DNS names from server (rather than being limited to +IP address) for \fB\-\-ifconfig\fP, \fB\-\-route\fP, and \fB\-\-route\-gateway\fP\&. +.TP +.B \-\-allow\-recursive\-routing +When this option is set, OpenVPN will not drop incoming tun packets with +same destination as host. +.TP +.BI \-\-auth\-token \ token +This is not an option to be used directly in any configuration files, +but rather push this option from a \fB\-\-client\-connect\fP script or a +\fB\-\-plugin\fP which hooks into the \fBOPENVPN_PLUGIN_CLIENT_CONNECT\fP +or \fBOPENVPN_PLUGIN_CLIENT_CONNECT_V2\fP calls. This option provides a +possibility to replace the clients password with an authentication token +during the lifetime of the OpenVPN client. +.sp +Whenever the connection is renegotiated and the +\fB\-\-auth\-user\-pass\-verify\fP script or \fB\-\-plugin\fP making use of the +\fBOPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY\fP hook is triggered, it will +pass over this token as the password instead of the password the user +provided. The authentication token can only be reset by a full reconnect +where the server can push new options to the client. The password the +user entered is never preserved once an authentication token has been +set. If the OpenVPN server side rejects the authentication token then +the client will receive an \fBAUTH_FAILED\fP and disconnect. +.sp +The purpose of this is to enable two factor authentication methods, such +as HOTP or TOTP, to be used without needing to retrieve a new OTP code +each time the connection is renegotiated. Another use case is to cache +authentication data on the client without needing to have the users +password cached in memory during the life time of the session. +.sp +To make use of this feature, the \fB\-\-client\-connect\fP script or +\fB\-\-plugin\fP needs to put +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +push "auth\-token UNIQUE_TOKEN_VALUE" +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +into the file/buffer for dynamic configuration data. This will then make +the OpenVPN server to push this value to the client, which replaces the +local password with the \fBUNIQUE_TOKEN_VALUE\fP\&. +.sp +Newer clients (2.4.7+) will fall back to the original password method +after a failed auth. Older clients will keep using the token value and +react according to \fB\-\-auth\-retry\fP +.TP +.B \-\-auth\-user\-pass +Authenticate with server using username/password. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +auth\-user\-pass +auth\-user\-pass up +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +If \fBup\fP is present, it must be a file containing username/password on 2 +lines. If the password line is missing, OpenVPN will prompt for one. +.sp +If \fBup\fP is omitted, username/password will be prompted from the +console. +.sp +The server configuration must specify an \fB\-\-auth\-user\-pass\-verify\fP +script to verify the username/password provided by the client. +.TP +.BI \-\-auth\-retry \ type +Controls how OpenVPN responds to username/password verification errors +such as the client\-side response to an \fBAUTH_FAILED\fP message from +the server or verification failure of the private key password. +.sp +Normally used to prevent auth errors from being fatal on the client +side, and to permit username/password requeries in case of error. +.sp +An \fBAUTH_FAILED\fP message is generated by the server if the client +fails \fB\-\-auth\-user\-pass\fP authentication, or if the server\-side +\fB\-\-client\-connect\fP script returns an error status when the client +tries to connect. +.sp +\fBtype\fP can be one of: +.INDENT 7.0 +.TP +.B \fBnone\fP +Client will exit with a fatal error (this is the default). +.TP +.B \fBnointeract\fP +Client will retry the connection without requerying +for an \fB\-\-auth\-user\-pass\fP username/password. Use this option for +unattended clients. +.TP +.B \fBinteract\fP +Client will requery for an \fB\-\-auth\-user\-pass\fP +username/password and/or private key password before attempting a +reconnection. +.UNINDENT +.sp +Note that while this option cannot be pushed, it can be controlled from +the management interface. +.TP +.B \-\-client +A helper directive designed to simplify the configuration of OpenVPN\(aqs +client mode. This directive is equivalent to: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +pull +tls\-client +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-client\-nat \ args +This pushable client option sets up a stateless one\-to\-one NAT rule on +packet addresses (not ports), and is useful in cases where routes or +ifconfig settings pushed to the client would create an IP numbering +conflict. +.sp +Examples: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +client\-nat snat 192.168.0.0/255.255.0.0 +client\-nat dnat 10.64.0.0/255.255.0.0 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +\fBnetwork/netmask\fP (for example \fB192.168.0.0/255.255.0.0\fP) defines +the local view of a resource from the client perspective, while +\fBalias/netmask\fP (for example \fB10.64.0.0/255.255.0.0\fP) defines the +remote view from the server perspective. +.sp +Use \fBsnat\fP (source NAT) for resources owned by the client and +\fBdnat\fP (destination NAT) for remote resources. +.sp +Set \fB\-\-verb 6\fP for debugging info showing the transformation of +src/dest addresses in packets. +.TP +.BI \-\-connect\-retry \ n +Wait \fBn\fP seconds between connection attempts (default \fB5\fP). +Repeated reconnection attempts are slowed down after 5 retries per +remote by doubling the wait time after each unsuccessful attempt. An +optional argument \fBmax\fP specifies the maximum value of wait time in +seconds at which it gets capped (default \fB300\fP). +.TP +.BI \-\-connect\-retry\-max \ n +\fBn\fP specifies the number of times each \fB\-\-remote\fP or +\fB\fP entry is tried. Specifying \fBn\fP as \fB1\fP would try +each entry exactly once. A successful connection resets the counter. +(default \fIunlimited\fP). +.TP +.BI \-\-connect\-timeout \ n +See \fB\-\-server\-poll\-timeout\fP\&. +.TP +.BI \-\-explicit\-exit\-notify \ n +In UDP client mode or point\-to\-point mode, send server/peer an exit +notification if tunnel is restarted or OpenVPN process is exited. In +client mode, on exit/restart, this option will tell the server to +immediately close its client instance object rather than waiting for a +timeout. +.sp +The \fBn\fP parameter (default \fB1\fP if not present) controls the +maximum number of attempts that the client will try to resend the exit +notification message. +.sp +In UDP server mode, send \fBRESTART\fP control channel command to +connected clients. The \fBn\fP parameter (default \fB1\fP if not present) +controls client behavior. With \fBn\fP = \fB1\fP client will attempt to +reconnect to the same server, with \fBn\fP = \fB2\fP client will advance +to the next server. +.sp +OpenVPN will not send any exit notifications unless this option is +enabled. +.TP +.BI \-\-inactive \ args +Causes OpenVPN to exit after \fBn\fP seconds of inactivity on the TUN/TAP +device. The time length of inactivity is measured since the last +incoming or outgoing tunnel packet. The default value is 0 seconds, +which disables this feature. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +inactive n +inactive n bytes +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +If the optional \fBbytes\fP parameter is included, exit if less than +\fBbytes\fP of combined in/out traffic are produced on the tun/tap device +in \fBn\fP seconds. +.sp +In any case, OpenVPN\(aqs internal ping packets (which are just keepalives) +and TLS control packets are not considered "activity", nor are they +counted as traffic, as they are used internally by OpenVPN and are not +an indication of actual user activity. +.TP +.BI \-\-proto\-force \ p +When iterating through connection profiles, only consider profiles using +protocol \fBp\fP (\fBtcp\fP | \fBudp\fP). +.TP +.B \-\-pull +This option must be used on a client which is connecting to a +multi\-client server. It indicates to OpenVPN that it should accept +options pushed by the server, provided they are part of the legal set of +pushable options (note that the \fB\-\-pull\fP option is implied by +\fB\-\-client\fP ). +.sp +In particular, \fB\-\-pull\fP allows the server to push routes to the +client, so you should not use \fB\-\-pull\fP or \fB\-\-client\fP in situations +where you don\(aqt trust the server to have control over the client\(aqs +routing table. +.TP +.BI \-\-pull\-filter \ args +Filter options on the client pushed by the server to the client. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +pull\-filter accept text +pull\-filter ignore text +pull\-filter reject text +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Filter options received from the server if the option starts with +\fBtext\fP\&. The action flag \fBaccept\fP allows the option, +\fBignore\fP removes it and \fBreject\fP flags an error and triggers +a \fBSIGUSR1\fP restart. The filters may be specified multiple times, +and each filter is applied in the order it is specified. The filtering of +each option stops as soon as a match is found. Unmatched options are accepted +by default. +.sp +Prefix comparison is used to match \fBtext\fP against the received option so +that +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +pull\-filter ignore "route" +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +would remove all pushed options starting with \fBroute\fP which would +include, for example, \fBroute\-gateway\fP\&. Enclose \fItext\fP in quotes to +embed spaces. +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +pull\-filter accept "route 192.168.1." +pull\-filter ignore "route " +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +would remove all routes that do not start with \fB192.168.1\fP\&. +.sp +\fINote\fP that \fBreject\fP may result in a repeated cycle of failure and +reconnect, unless multiple remotes are specified and connection to the +next remote succeeds. To silently ignore an option pushed by the server, +use \fBignore\fP\&. +.TP +.BI \-\-remote \ args +Remote host name or IP address. It supports two additional optional +arguments: \fBport\fP and \fBproto\fP\&. On the client, multiple \fB\-\-remote\fP +options may be specified for redundancy, each referring to a different +OpenVPN server. Specifying multiple \fB\-\-remote\fP options for this +purpose is a special case of the more general connection\-profile +feature. See the \fB\fP documentation below. +.sp +The OpenVPN client will try to connect to a server at \fBhost:port\fP in +the order specified by the list of \fB\-\-remote\fP options. +.sp +Examples: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +remote server.example.net +remote server.example.net 1194 +remote server.example.net tcp +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +\fBproto\fP indicates the protocol to use when connecting with the remote, +and may be \fBtcp\fP or \fBudp\fP\&. +.sp +For forcing IPv4 or IPv6 connection suffix tcp or udp with 4/6 like +udp4/udp6/tcp4/tcp6. +.sp +The client will move on to the next host in the list, in the event of +connection failure. Note that at any given time, the OpenVPN client will +at most be connected to one server. +.sp +Note that since UDP is connectionless, connection failure is defined by +the \fB\-\-ping\fP and \fB\-\-ping\-restart\fP options. +.sp +Note the following corner case: If you use multiple \fB\-\-remote\fP +options, AND you are dropping root privileges on the client with +\fB\-\-user\fP and/or \fB\-\-group\fP AND the client is running a non\-Windows +OS, if the client needs to switch to a different server, and that server +pushes back different TUN/TAP or route settings, the client may lack the +necessary privileges to close and reopen the TUN/TAP interface. This +could cause the client to exit with a fatal error. +.sp +If \fB\-\-remote\fP is unspecified, OpenVPN will listen for packets from any +IP address, but will not act on those packets unless they pass all +authentication tests. This requirement for authentication is binding on +all potential peers, even those from known and supposedly trusted IP +addresses (it is very easy to forge a source IP address on a UDP +packet). +.sp +When used in TCP mode, \fB\-\-remote\fP will act as a filter, rejecting +connections from any host which does not match \fBhost\fP\&. +.sp +If \fBhost\fP is a DNS name which resolves to multiple IP addresses, +OpenVPN will try them in the order that the system getaddrinfo() +presents them, so priorization and DNS randomization is done by the +system library. Unless an IP version is forced by the protocol +specification (4/6 suffix), OpenVPN will try both IPv4 and IPv6 +addresses, in the order getaddrinfo() returns them. +.TP +.B \-\-remote\-random +When multiple \fB\-\-remote\fP address/ports are specified, or if connection +profiles are being used, initially randomize the order of the list as a +kind of basic load\-balancing measure. +.TP +.B \-\-remote\-random\-hostname +Prepend a random string (6 bytes, 12 hex characters) to hostname to +prevent DNS caching. For example, "foo.bar.gov" would be modified to +".foo.bar.gov". +.TP +.BI \-\-resolv\-retry \ n +If hostname resolve fails for \fB\-\-remote\fP, retry resolve for \fBn\fP +seconds before failing. +.sp +Set \fBn\fP to "infinite" to retry indefinitely. +.sp +By default, \fB\-\-resolv\-retry infinite\fP is enabled. You can disable by +setting n=0. +.TP +.B \-\-single\-session +After initially connecting to a remote peer, disallow any new +connections. Using this option means that a remote peer cannot connect, +disconnect, and then reconnect. +.sp +If the daemon is reset by a signal or \fB\-\-ping\-restart\fP, it will allow +one new connection. +.sp +\fB\-\-single\-session\fP can be used with \fB\-\-ping\-exit\fP or \fB\-\-inactive\fP +to create a single dynamic session that will exit when finished. +.TP +.BI \-\-server\-poll\-timeout \ n +When connecting to a remote server do not wait for more than \fBn\fP +seconds for a response before trying the next server. The default value +is 120s. This timeout includes proxy and TCP connect timeouts. +.TP +.BI \-\-static\-challenge \ args +Enable static challenge/response protocol +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +static\-challenge text echo +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The \fBtext\fP challenge text is presented to the user which describes what +information is requested. The \fBecho\fP flag indicates if the user\(aqs +input should be echoed on the screen. Valid \fBecho\fP values are +\fB0\fP or \fB1\fP\&. +.sp +See management\-notes.txt in the OpenVPN distribution for a description of +the OpenVPN challenge/response protocol. +.UNINDENT +.INDENT 0.0 +.TP +.B \-\-show\-proxy\-settings +Show sensed HTTP or SOCKS proxy settings. Currently, only Windows +clients support this option. +.TP +.BI \-\-http\-proxy \ args +Connect to remote host through an HTTP proxy. This requires at least an +address \fBserver\fP and \fBport\fP argument. If HTTP Proxy\-Authenticate +is required, a file name to an \fBauthfile\fP file containing a username +and password on 2 lines can be given, or \fBstdin\fP to prompt from +console. Its content can also be specified in the config file with the +\fB\-\-http\-proxy\-user\-pass\fP option. (See section on inline files) +.sp +The last optional argument is an \fBauth\-method\fP which should be one +of \fBnone\fP, \fBbasic\fP, or \fBntlm\fP\&. +.sp +HTTP Digest authentication is supported as well, but only via the +\fBauto\fP or \fBauto\-nct\fP flags (below). This must replace +the \fBauthfile\fP argument. +.sp +The \fBauto\fP flag causes OpenVPN to automatically determine the +\fBauth\-method\fP and query stdin or the management interface for +username/password credentials, if required. This flag exists on OpenVPN +2.1 or higher. +.sp +The \fBauto\-nct\fP flag (no clear\-text auth) instructs OpenVPN to +automatically determine the authentication method, but to reject weak +authentication protocols such as HTTP Basic Authentication. +.sp +Examples: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +http\-proxy proxy.example.net 3128 +http\-proxy proxy.example.net 3128 authfile.txt +http\-proxy proxy.example.net 3128 stdin +http\-proxy proxy.example.net 3128 auto basic +http\-proxy proxy.example.net 3128 auto\-nct ntlm +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-http\-proxy\-option \ args +Set extended HTTP proxy options. Requires an option \fBtype\fP as argument +and an optional \fBparameter\fP to the type. Repeat to set multiple +options. +.INDENT 7.0 +.TP +.B \fBVERSION\fP \fBversion\fP +Set HTTP version number to \fBversion\fP (default \fB1.0\fP). +.TP +.B \fBAGENT\fP \fBuser\-agent\fP +Set HTTP "User\-Agent" string to \fBuser\-agent\fP\&. +.TP +.B \fBCUSTOM\-HEADER\fP \fBname\fP \fBcontent\fP +Adds the custom Header with \fBname\fP as name and \fBcontent\fP as +the content of the custom HTTP header. +.UNINDENT +.sp +Examples: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +http\-proxy\-option VERSION 1.1 +http\-proxy\-option AGENT OpenVPN/2.4 +http\-proxy\-option X\-Proxy\-Flag some\-flags +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-socks\-proxy \ args +Connect to remote host through a Socks5 proxy. A required \fBserver\fP +argument is needed. Optionally a \fBport\fP (default \fB1080\fP) and +\fBauthfile\fP can be given. The \fBauthfile\fP is a file containing a +username and password on 2 lines, or \fBstdin\fP can be used to +prompt from console. +.UNINDENT +.SS Server Options +.sp +Starting with OpenVPN 2.0, a multi\-client TCP/UDP server mode is +supported, and can be enabled with the \fB\-\-mode server\fP option. In +server mode, OpenVPN will listen on a single port for incoming client +connections. All client connections will be routed through a single tun +or tap interface. This mode is designed for scalability and should be +able to support hundreds or even thousands of clients on sufficiently +fast hardware. SSL/TLS authentication must be used in this mode. +.INDENT 0.0 +.TP +.BI \-\-auth\-gen\-token \ args +Returns an authentication token to successfully authenticated clients. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +auth\-gen\-token [lifetime] [external\-auth] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +After successful user/password authentication, the OpenVPN server will +with this option generate a temporary authentication token and push that +to the client. On the following renegotiations, the OpenVPN client will pass +this token instead of the users password. On the server side the server +will do the token authentication internally and it will NOT do any +additional authentications against configured external user/password +authentication mechanisms. +.sp +The tokens implemented by this mechanism include an initial timestamp and +a renew timestamp and are secured by HMAC. +.sp +The \fBlifetime\fP argument defines how long the generated token is valid. +The lifetime is defined in seconds. If lifetime is not set or it is set +to \fB0\fP, the token will never expire. +.sp +The token will expire either after the configured \fBlifetime\fP of the +token is reached or after not being renewed for more than 2 * +\fBreneg\-sec\fP seconds. Clients will be sent renewed tokens on every TLS +renogiation to keep the client\(aqs token updated. This is done to +invalidate a token if a client is disconnected for a sufficently long +time, while at the same time permitting much longer token lifetimes for +active clients. +.sp +This feature is useful for environments which are configured to use One +Time Passwords (OTP) as part of the user/password authentications and +that authentication mechanism does not implement any auth\-token support. +.sp +When the \fBexternal\-auth\fP keyword is present the normal +authentication method will always be called even if auth\-token succeeds. +Normally other authentications method are skipped if auth\-token +verification suceeds or fails. +.sp +This option postpones this decision to the external authentication +methods and checks the validity of the account and do other checks. +.sp +In this mode the environment will have a \fBsession_id\fP variable that +holds the session id from auth\-gen\-token. Also an environment variable +\fBsession_state\fP is present. This variable indicates whether the +auth\-token has succeeded or not. It can have the following values: +.INDENT 7.0 +.TP +.B \fBInitial\fP +No token from client. +.TP +.B \fBAuthenticated\fP +Token is valid and not expired. +.TP +.B \fBExpired\fP +Token is valid but has expired. +.TP +.B \fBInvalid\fP +Token is invalid (failed HMAC or wrong length) +.TP +.B \fBAuthenticatedEmptyUser\fP / \fBExpiredEmptyUser\fP +The token is not valid with the username sent from the client but +would be valid (or expired) if we assume an empty username was +used instead. These two cases are a workaround for behaviour in +OpenVPN 3. If this workaround is not needed these two cases should +be handled in the same way as \fBInvalid\fP\&. +.UNINDENT +.sp +\fBWarning:\fP Use this feature only if you want your authentication +method called on every verification. Since the external authentication +is called it needs to also indicate a success or failure of the +authentication. It is strongly recommended to return an authentication +failure in the case of the Invalid/Expired auth\-token with the +external\-auth option unless the client could authenticate in another +acceptable way (e.g. client certificate), otherwise returning success +will lead to authentication bypass (as does returning success on a wrong +password from a script). +.TP +.BI \-\-auth\-gen\-token\-secret \ file +Specifies a file that holds a secret for the HMAC used in +\fB\-\-auth\-gen\-token\fP If \fBfile\fP is not present OpenVPN will generate a +random secret on startup. This file should be used if auth\-token should +validate after restarting a server or if client should be able to roam +between multiple OpenVPN servers with their auth\-token. +.TP +.B \-\-auth\-user\-pass\-optional +Allow connections by clients that do not specify a username/password. +Normally, when \fB\-\-auth\-user\-pass\-verify\fP or +\fB\-\-management\-client\-auth\fP are specified (or an authentication plugin +module), the OpenVPN server daemon will require connecting clients to +specify a username and password. This option makes the submission of a +username/password by clients optional, passing the responsibility to the +user\-defined authentication module/script to accept or deny the client +based on other factors (such as the setting of X509 certificate fields). +When this option is used, and a connecting client does not submit a +username/password, the user\-defined authentication module/script will +see the username and password as being set to empty strings (""). The +authentication module/script MUST have logic to detect this condition +and respond accordingly. +.TP +.B \-\-ccd\-exclusive +Require, as a condition of authentication, that a connecting client has +a \fB\-\-client\-config\-dir\fP file. +.TP +.BI \-\-client\-config\-dir \ dir +Specify a directory \fBdir\fP for custom client config files. After a +connecting client has been authenticated, OpenVPN will look in this +directory for a file having the same name as the client\(aqs X509 common +name. If a matching file exists, it will be opened and parsed for +client\-specific configuration options. If no matching file is found, +OpenVPN will instead try to open and parse a default file called +"DEFAULT", which may be provided but is not required. Note that the +configuration files must be readable by the OpenVPN process after it has +dropped it\(aqs root privileges. +.sp +This file can specify a fixed IP address for a given client using +\fB\-\-ifconfig\-push\fP, as well as fixed subnets owned by the client using +\fB\-\-iroute\fP\&. +.sp +One of the useful properties of this option is that it allows client +configuration files to be conveniently created, edited, or removed while +the server is live, without needing to restart the server. +.sp +The following options are legal in a client\-specific context: \fB\-\-push\fP, +\fB\-\-push\-reset\fP, \fB\-\-push\-remove\fP, \fB\-\-iroute\fP, \fB\-\-ifconfig\-push\fP, +\fB\-\-vlan\-pvid\fP and \fB\-\-config\fP\&. +.TP +.B \-\-client\-to\-client +Because the OpenVPN server mode handles multiple clients through a +single tun or tap interface, it is effectively a router. The +\fB\-\-client\-to\-client\fP flag tells OpenVPN to internally route +client\-to\-client traffic rather than pushing all client\-originating +traffic to the TUN/TAP interface. +.sp +When this option is used, each client will "see" the other clients which +are currently connected. Otherwise, each client will only see the +server. Don\(aqt use this option if you want to firewall tunnel traffic +using custom, per\-client rules. +.TP +.B \-\-disable +Disable a particular client (based on the common name) from connecting. +Don\(aqt use this option to disable a client due to key or password +compromise. Use a CRL (certificate revocation list) instead (see the +\fB\-\-crl\-verify\fP option). +.sp +This option must be associated with a specific client instance, which +means that it must be specified either in a client instance config file +using \fB\-\-client\-config\-dir\fP or dynamically generated using a +\fB\-\-client\-connect\fP script. +.TP +.BI \-\-connect\-freq \ args +Allow a maximum of \fBn\fP new connections per \fBsec\fP seconds from +clients. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +connect\-freq n sec +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +This is designed to contain DoS attacks which flood the server +with connection requests using certificates which will ultimately fail +to authenticate. +.sp +This is an imperfect solution however, because in a real DoS scenario, +legitimate connections might also be refused. +.sp +For the best protection against DoS attacks in server mode, use +\fB\-\-proto udp\fP and either \fB\-\-tls\-auth\fP or \fB\-\-tls\-crypt\fP\&. +.TP +.B \-\-duplicate\-cn +Allow multiple clients with the same common name to concurrently +connect. In the absence of this option, OpenVPN will disconnect a client +instance upon connection of a new client having the same common name. +.TP +.BI \-\-ifconfig\-pool \ args +Set aside a pool of subnets to be dynamically allocated to connecting +clients, similar to a DHCP server. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +ifconfig\-pool start\-IP end\-IP [netmask] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +For tun\-style tunnels, each client +will be given a /30 subnet (for interoperability with Windows clients). +For tap\-style tunnels, individual addresses will be allocated, and the +optional \fBnetmask\fP parameter will also be pushed to clients. +.TP +.BI \-\-ifconfig\-ipv6\-pool \ args +Specify an IPv6 address pool for dynamic assignment to clients. +.sp +Valid args: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +ifconfig\-ipv6\-pool ipv6addr/bits +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The pool starts at \fBipv6addr\fP and matches the offset determined from +the start of the IPv4 pool. +.TP +.BI \-\-ifconfig\-pool\-persist \ args +Persist/unpersist ifconfig\-pool data to \fBfile\fP, at \fBseconds\fP +intervals (default \fB600\fP), as well as on program startup and shutdown. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +ifconfig\-pool\-persist file [seconds] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The goal of this option is to provide a long\-term association between +clients (denoted by their common name) and the virtual IP address +assigned to them from the ifconfig\-pool. Maintaining a long\-term +association is good for clients because it allows them to effectively +use the \fB\-\-persist\-tun\fP option. +.sp +\fBfile\fP is a comma\-delimited ASCII file, formatted as +\fB,\fP\&. +.sp +If \fBseconds\fP = \fB0\fP, \fBfile\fP will be treated as read\-only. This +is useful if you would like to treat \fBfile\fP as a configuration file. +.sp +Note that the entries in this file are treated by OpenVPN as +\fIsuggestions\fP only, based on past associations between a common name and +IP address. They do not guarantee that the given common name will always +receive the given IP address. If you want guaranteed assignment, use +\fB\-\-ifconfig\-push\fP +.TP +.BI \-\-ifconfig\-push \ args +Push virtual IP endpoints for client tunnel, overriding the +\fB\-\-ifconfig\-pool\fP dynamic allocation. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +ifconfig\-push local remote\-netmask [alias] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The parameters \fBlocal\fP and \fBremote\-netmask\fP are set according to the +\fB\-\-ifconfig\fP directive which you want to execute on the client machine +to configure the remote end of the tunnel. Note that the parameters +\fBlocal\fP and \fBremote\-netmask\fP are from the perspective of the client, +not the server. They may be DNS names rather than IP addresses, in which +case they will be resolved on the server at the time of client +connection. +.sp +The optional \fBalias\fP parameter may be used in cases where NAT causes +the client view of its local endpoint to differ from the server view. In +this case \fBlocal/remote\-netmask\fP will refer to the server view while +\fBalias/remote\-netmask\fP will refer to the client view. +.sp +This option must be associated with a specific client instance, which +means that it must be specified either in a client instance config file +using \fB\-\-client\-config\-dir\fP or dynamically generated using a +\fB\-\-client\-connect\fP script. +.sp +Remember also to include a \fB\-\-route\fP directive in the main OpenVPN +config file which encloses \fBlocal\fP, so that the kernel will know to +route it to the server\(aqs TUN/TAP interface. +.sp +OpenVPN\(aqs internal client IP address selection algorithm works as +follows: +.INDENT 7.0 +.IP 1. 3 +Use \fB\-\-client\-connect script\fP generated file for static IP +(first choice). +.IP 2. 3 +Use \fB\-\-client\-config\-dir\fP file for static IP (next choice). +.IP 3. 3 +Use \fB\-\-ifconfig\-pool\fP allocation for dynamic IP (last +choice). +.UNINDENT +.TP +.BI \-\-ifconfig\-ipv6\-push \ args +for \fB\-\-client\-config\-dir\fP per\-client static IPv6 interface +configuration, see \fB\-\-client\-config\-dir\fP and \fB\-\-ifconfig\-push\fP for +more details. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +ifconfig\-ipv6\-push ipv6addr/bits ipv6remote +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-inetd \ args +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +inetd +inetd wait +inetd nowait +inetd wait progname +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Use this option when OpenVPN is being run from the inetd or \fBxinetd\fP(8) +server. +.sp +The \fBwait\fP and \fBnowait\fP option must match what is specified +in the inetd/xinetd config file. The \fBnowait\fP mode can only be used +with \fB\-\-proto tcp\-server\fP The default is \fBwait\fP\&. The +\fBnowait\fP mode can be used to instantiate the OpenVPN daemon as a +classic TCP server, where client connection requests are serviced on a +single port number. For additional information on this kind of +configuration, see the OpenVPN FAQ: +\fI\%https://community.openvpn.net/openvpn/wiki/325\-openvpn\-as\-a\-\-forking\-tcp\-server\-which\-can\-service\-multiple\-clients\-over\-a\-single\-tcp\-port\fP +.sp +This option precludes the use of \fB\-\-daemon\fP, \fB\-\-local\fP or +\fB\-\-remote\fP\&. Note that this option causes message and error output to +be handled in the same way as the \fB\-\-daemon\fP option. The optional +\fBprogname\fP parameter is also handled exactly as in \fB\-\-daemon\fP\&. +.sp +Also note that in \fBwait\fP mode, each OpenVPN tunnel requires a separate +TCP/UDP port and a separate inetd or xinetd entry. See the OpenVPN 1.x +HOWTO for an example on using OpenVPN with xinetd: +\fI\%https://openvpn.net/community\-resources/1xhowto/\fP +.TP +.B \-\-multihome +Configure a multi\-homed UDP server. This option needs to be used when a +server has more than one IP address (e.g. multiple interfaces, or +secondary IP addresses), and is not using \fB\-\-local\fP to force binding +to one specific address only. This option will add some extra lookups to +the packet path to ensure that the UDP reply packets are always sent +from the address that the client is talking to. This is not supported on +all platforms, and it adds more processing, so it\(aqs not enabled by +default. +.INDENT 7.0 +.TP +.B \fINotes:\fP +.INDENT 7.0 +.IP \(bu 2 +This option is only relevant for UDP servers. +.IP \(bu 2 +If you do an IPv6+IPv4 dual\-stack bind on a Linux machine with +multiple IPv4 address, connections to IPv4 addresses will not +work right on kernels before 3.15, due to missing kernel +support for the IPv4\-mapped case (some distributions have +ported this to earlier kernel versions, though). +.UNINDENT +.UNINDENT +.TP +.BI \-\-iroute \ args +Generate an internal route to a specific client. The \fBnetmask\fP +parameter, if omitted, defaults to \fB255.255.255.255\fP\&. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +iroute network [netmask] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +This directive can be used to route a fixed subnet from the server to a +particular client, regardless of where the client is connecting from. +Remember that you must also add the route to the system routing table as +well (such as by using the \fB\-\-route\fP directive). The reason why two +routes are needed is that the \fB\-\-route\fP directive routes the packet +from the kernel to OpenVPN. Once in OpenVPN, the \fB\-\-iroute\fP directive +routes to the specific client. +.sp +This option must be specified either in a client instance config file +using \fB\-\-client\-config\-dir\fP or dynamically generated using a +\fB\-\-client\-connect\fP script. +.sp +The \fB\-\-iroute\fP directive also has an important interaction with +\fB\-\-push "route ..."\fP\&. \fB\-\-iroute\fP essentially defines a subnet which +is owned by a particular client (we will call this client \fIA\fP). If you +would like other clients to be able to reach \fIA\fP\(aqs subnet, you can use +\fB\-\-push "route ..."\fP together with \fB\-\-client\-to\-client\fP to effect +this. In order for all clients to see \fIA\fP\(aqs subnet, OpenVPN must push +this route to all clients EXCEPT for \fIA\fP, since the subnet is already +owned by \fIA\fP\&. OpenVPN accomplishes this by not not pushing a route to +a client if it matches one of the client\(aqs iroutes. +.TP +.BI \-\-iroute\-ipv6 \ args +for \fB\-\-client\-config\-dir\fP per\-client static IPv6 route configuration, +see \fB\-\-iroute\fP for more details how to setup and use this, and how +\fB\-\-iroute\fP and \fB\-\-route\fP interact. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +iroute\-ipv6 ipv6addr/bits +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-max\-clients \ n +Limit server to a maximum of \fBn\fP concurrent clients. +.TP +.BI \-\-max\-routes\-per\-client \ n +Allow a maximum of \fBn\fP internal routes per client (default +\fB256\fP). This is designed to help contain DoS attacks where an +authenticated client floods the server with packets appearing to come +from many unique MAC addresses, forcing the server to deplete virtual +memory as its internal routing table expands. This directive can be used +in a \fB\-\-client\-config\-dir\fP file or auto\-generated by a +\fB\-\-client\-connect\fP script to override the global value for a particular +client. +.sp +Note that this directive affects OpenVPN\(aqs internal routing table, not +the kernel routing table. +.TP +.B \-\-opt\-verify +Clients that connect with options that are incompatible with those of the +server will be disconnected. +.sp +Options that will be compared for compatibility include \fBdev\-type\fP, +\fBlink\-mtu\fP, \fBtun\-mtu\fP, \fBproto\fP, \fBifconfig\fP, +\fBcomp\-lzo\fP, \fBfragment\fP, \fBkeydir\fP, \fBcipher\fP, +\fBauth\fP, \fBkeysize\fP, \fBsecret\fP, \fBno\-replay\fP, +\fBtls\-auth\fP, \fBkey\-method\fP, \fBtls\-server\fP +and \fBtls\-client\fP\&. +.sp +This option requires that \fB\-\-disable\-occ\fP NOT be used. +.TP +.BI \-\-port\-share \ args +Share OpenVPN TCP with another service +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +port\-share host port [dir] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +When run in TCP server mode, share the OpenVPN port with another +application, such as an HTTPS server. If OpenVPN senses a connection to +its port which is using a non\-OpenVPN protocol, it will proxy the +connection to the server at \fBhost\fP:\fBport\fP\&. Currently only designed to +work with HTTP/HTTPS, though it would be theoretically possible to +extend to other protocols such as ssh. +.sp +\fBdir\fP specifies an optional directory where a temporary file with name +N containing content C will be dynamically generated for each proxy +connection, where N is the source IP:port of the client connection and C +is the source IP:port of the connection to the proxy receiver. This +directory can be used as a dictionary by the proxy receiver to determine +the origin of the connection. Each generated file will be automatically +deleted when the proxied connection is torn down. +.sp +Not implemented on Windows. +.TP +.BI \-\-push \ option +Push a config file option back to the client for remote execution. Note +that \fBoption\fP must be enclosed in double quotes (\fB""\fP). The +client must specify \fB\-\-pull\fP in its config file. The set of options +which can be pushed is limited by both feasibility and security. Some +options such as those which would execute scripts are banned, since they +would effectively allow a compromised server to execute arbitrary code +on the client. Other options such as TLS or MTU parameters cannot be +pushed because the client needs to know them before the connection to the +server can be initiated. +.sp +This is a partial list of options which can currently be pushed: +\fB\-\-route\fP, \fB\-\-route\-gateway\fP, \fB\-\-route\-delay\fP, +\fB\-\-redirect\-gateway\fP, \fB\-\-ip\-win32\fP, \fB\-\-dhcp\-option\fP, +\fB\-\-inactive\fP, \fB\-\-ping\fP, \fB\-\-ping\-exit\fP, \fB\-\-ping\-restart\fP, +\fB\-\-setenv\fP, \fB\-\-auth\-token\fP, \fB\-\-persist\-key\fP, \fB\-\-persist\-tun\fP, +\fB\-\-echo\fP, \fB\-\-comp\-lzo\fP, \fB\-\-socket\-flags\fP, \fB\-\-sndbuf\fP, +\fB\-\-rcvbuf\fP +.TP +.B \-\-push\-peer\-info +Push additional information about the client to server. The following +data is always pushed to the server: +.INDENT 7.0 +.TP +.B \fBIV_VER=\fP +The client OpenVPN version +.TP +.B \fBIV_PLAT=[linux|solaris|openbsd|mac|netbsd|freebsd|win]\fP +The client OS platform +.TP +.B \fBIV_LZO_STUB=1\fP +If client was built with LZO stub capability +.TP +.B \fBIV_LZ4=1\fP +If the client supports LZ4 compressions. +.TP +.B \fBIV_PROTO\fP +Details about protocol extensions that the peer supports. The +variable is a bitfield and the bits are defined as follows +(starting a bit 0 for the first (unused) bit: +.INDENT 7.0 +.IP \(bu 2 +bit 1: The peer supports peer\-id floating mechanism +.IP \(bu 2 +bit 2: The client expects a push\-reply and the server may +send this reply without waiting for a push\-request first. +.UNINDENT +.TP +.B \fBIV_NCP=2\fP +Negotiable ciphers, client supports \fB\-\-cipher\fP pushed by +the server, a value of 2 or greater indicates client supports +\fIAES\-GCM\-128\fP and \fIAES\-GCM\-256\fP\&. +.TP +.B \fBIV_CIPHERS=\fP +The client announces the list of supported ciphers configured with the +\fB\-\-data\-ciphers\fP option to the server. +.TP +.B \fBIV_GUI_VER= \fP +The UI version of a UI if one is running, for example +\fBde.blinkt.openvpn 0.5.47\fP for the Android app. +.UNINDENT +.sp +When \fB\-\-push\-peer\-info\fP is enabled the additional information consists +of the following data: +.INDENT 7.0 +.TP +.B \fBIV_HWADDR=\fP +The MAC address of clients default gateway +.TP +.B \fBIV_SSL=\fP +The ssl version used by the client, e.g. +\fBOpenSSL 1.0.2f 28 Jan 2016\fP\&. +.TP +.B \fBIV_PLAT_VER=x.y\fP +The version of the operating system, e.g. 6.1 for Windows 7. +.TP +.B \fBUV_=\fP +Client environment variables whose names start with +\fBUV_\fP +.UNINDENT +.TP +.BI \-\-push\-remove \ opt +Selectively remove all \fB\-\-push\fP options matching "opt" from the option +list for a client. \fBopt\fP is matched as a substring against the whole +option string to\-be\-pushed to the client, so \fB\-\-push\-remove route\fP +would remove all \fB\-\-push route ...\fP and \fB\-\-push route\-ipv6 ...\fP +statements, while \fB\-\-push\-remove "route\-ipv6 2001:"\fP would only remove +IPv6 routes for \fB2001:...\fP networks. +.sp +\fB\-\-push\-remove\fP can only be used in a client\-specific context, like in +a \fB\-\-client\-config\-dir\fP file, or \fB\-\-client\-connect\fP script or plugin +\-\- similar to \fB\-\-push\-reset\fP, just more selective. +.sp +\fINOTE\fP: to \fIchange\fP an option, \fB\-\-push\-remove\fP can be used to first +remove the old value, and then add a new \fB\-\-push\fP option with the new +value. +.sp +\fINOTE 2\fP: due to implementation details, \(aqifconfig\(aq and \(aqifconfig\-ipv6\(aq +can only be removed with an exact match on the option ( +\fBpush\-remove ifconfig\fP), no substring matching and no matching on +the IPv4/IPv6 address argument is possible. +.TP +.B \-\-push\-reset +Don\(aqt inherit the global push list for a specific client instance. +Specify this option in a client\-specific context such as with a +\fB\-\-client\-config\-dir\fP configuration file. This option will ignore +\fB\-\-push\fP options at the global config file level. +.TP +.BI \-\-server \ args +A helper directive designed to simplify the configuration of OpenVPN\(aqs +server mode. This directive will set up an OpenVPN server which will +allocate addresses to clients out of the given network/netmask. The +server itself will take the \fB\&.1\fP address of the given network for +use as the server\-side endpoint of the local TUN/TAP interface. If the +optional \fBnopool\fP flag is given, no dynamic IP address pool will +prepared for VPN clients. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +server network netmask [nopool] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +For example, \fB\-\-server 10.8.0.0 255.255.255.0\fP expands as follows: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +mode server +tls\-server +push "topology [topology]" + +if dev tun AND (topology == net30 OR topology == p2p): + ifconfig 10.8.0.1 10.8.0.2 + if !nopool: + ifconfig\-pool 10.8.0.4 10.8.0.251 + route 10.8.0.0 255.255.255.0 + if client\-to\-client: + push "route 10.8.0.0 255.255.255.0" + else if topology == net30: + push "route 10.8.0.1" + +if dev tap OR (dev tun AND topology == subnet): + ifconfig 10.8.0.1 255.255.255.0 + if !nopool: + ifconfig\-pool 10.8.0.2 10.8.0.253 255.255.255.0 + push "route\-gateway 10.8.0.1" + if route\-gateway unset: + route\-gateway 10.8.0.2 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Don\(aqt use \fB\-\-server\fP if you are ethernet bridging. Use +\fB\-\-server\-bridge\fP instead. +.TP +.BI \-\-server\-bridge \ args +A helper directive similar to \fB\-\-server\fP which is designed to simplify +the configuration of OpenVPN\(aqs server mode in ethernet bridging +configurations. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +server\-bridge gateway netmask pool\-start\-IP pool\-end\-IP +server\-bridge [nogw] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +If \fB\-\-server\-bridge\fP is used without any parameters, it will enable a +DHCP\-proxy mode, where connecting OpenVPN clients will receive an IP +address for their TAP adapter from the DHCP server running on the +OpenVPN server\-side LAN. Note that only clients that support the binding +of a DHCP client with the TAP adapter (such as Windows) can support this +mode. The optional \fBnogw\fP flag (advanced) indicates that gateway +information should not be pushed to the client. +.sp +To configure ethernet bridging, you must first use your OS\(aqs bridging +capability to bridge the TAP interface with the ethernet NIC interface. +For example, on Linux this is done with the \fBbrctl\fP tool, and with +Windows XP it is done in the Network Connections Panel by selecting the +ethernet and TAP adapters and right\-clicking on "Bridge Connections". +.sp +Next you you must manually set the IP/netmask on the bridge interface. +The \fBgateway\fP and \fBnetmask\fP parameters to \fB\-\-server\-bridge\fP can be +set to either the IP/netmask of the bridge interface, or the IP/netmask +of the default gateway/router on the bridged subnet. +.sp +Finally, set aside a IP range in the bridged subnet, denoted by +\fBpool\-start\-IP\fP and \fBpool\-end\-IP\fP, for OpenVPN to allocate to +connecting clients. +.sp +For example, \fBserver\-bridge 10.8.0.4 255.255.255.0 10.8.0.128 +10.8.0.254\fP expands as follows: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +mode server +tls\-server + +ifconfig\-pool 10.8.0.128 10.8.0.254 255.255.255.0 +push "route\-gateway 10.8.0.4" +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +In another example, \fB\-\-server\-bridge\fP (without parameters) expands as +follows: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +mode server +tls\-server + +push "route\-gateway dhcp" +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Or \fB\-\-server\-bridge nogw\fP expands as follows: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +mode server +tls\-server +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-stale\-routes\-check \ args +Remove routes which haven\(aqt had activity for \fBn\fP seconds (i.e. the ageing +time). This check is run every \fBt\fP seconds (i.e. check interval). +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +stale\-routes\-check n [t] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +If \fBt\fP is not present it defaults to \fBn\fP\&. +.sp +This option helps to keep the dynamic routing table small. See also +\fB\-\-max\-routes\-per\-client\fP +.TP +.B \-\-username\-as\-common\-name +For \fB\-\-auth\-user\-pass\-verify\fP authentication, use the authenticated +username as the common name, rather than the common name from the client +cert. +.TP +.BI \-\-verify\-client\-cert \ mode +Specify whether the client is required to supply a valid certificate. +.sp +Possible \fBmode\fP options are: +.INDENT 7.0 +.TP +.B \fBnone\fP +A client certificate is not required. the client needs to +authenticate using username/password only. Be aware that using this +directive is less secure than requiring certificates from all +clients. +.sp +If you use this directive, the entire responsibility of authentication +will rest on your \fB\-\-auth\-user\-pass\-verify\fP script, so keep in mind +that bugs in your script could potentially compromise the security of +your VPN. +.sp +\fB\-\-verify\-client\-cert none\fP is functionally equivalent to +\fB\-\-client\-cert\-not\-required\fP\&. +.TP +.B \fBoptional\fP +A client may present a certificate but it is not required to do so. +When using this directive, you should also use a +\fB\-\-auth\-user\-pass\-verify\fP script to ensure that clients are +authenticated using a certificate, a username and password, or +possibly even both. +.sp +Again, the entire responsibility of authentication will rest on your +\fB\-\-auth\-user\-pass\-verify\fP script, so keep in mind that bugs in your +script could potentially compromise the security of your VPN. +.TP +.B \fBrequire\fP +This is the default option. A client is required to present a +certificate, otherwise VPN access is refused. +.UNINDENT +.sp +If you don\(aqt use this directive (or use \fB\-\-verify\-client\-cert require\fP) +but you also specify an \fB\-\-auth\-user\-pass\-verify\fP script, then OpenVPN +will perform double authentication. The client certificate verification +AND the \fB\-\-auth\-user\-pass\-verify\fP script will need to succeed in order +for a client to be authenticated and accepted onto the VPN. +.TP +.B \-\-vlan\-tagging +Server\-only option. Turns the OpenVPN server instance into a switch that +understands VLAN\-tagging, based on IEEE 802.1Q. +.sp +The server TAP device and each of the connecting clients is seen as a +port of the switch. All client ports are in untagged mode and the server +TAP device is VLAN\-tagged, untagged or accepts both, depending on the +\fB\-\-vlan\-accept\fP setting. +.sp +Ethernet frames with a prepended 802.1Q tag are called "tagged". If the +VLAN Identifier (VID) field in such a tag is non\-zero, the frame is +called "VLAN\-tagged". If the VID is zero, but the Priority Control Point +(PCP) field is non\-zero, the frame is called "prio\-tagged". If there is +no 802.1Q tag, the frame is "untagged". +.sp +Using the \fB\-\-vlan\-pvid v\fP option once per client (see +\-\-client\-config\-dir), each port can be associated with a certain VID. +Packets can only be forwarded between ports having the same VID. +Therefore, clients with differing VIDs are completely separated from +one\-another, even if \fB\-\-client\-to\-client\fP is activated. +.sp +The packet filtering takes place in the OpenVPN server. Clients should +not have any VLAN tagging configuration applied. +.sp +The \fB\-\-vlan\-tagging\fP option is off by default. While turned off, +OpenVPN accepts any Ethernet frame and does not perform any special +processing for VLAN\-tagged packets. +.sp +This option can only be activated in \fB\-\-dev tap mode\fP\&. +.TP +.BI \-\-vlan\-accept \ args +Configure the VLAN tagging policy for the server TAP device. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +vlan\-accept all|tagged|untagged +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The following modes are available: +.INDENT 7.0 +.TP +.B \fBtagged\fP +Admit only VLAN\-tagged frames. Only VLAN\-tagged packets are accepted, +while untagged or priority\-tagged packets are dropped when entering +the server TAP device. +.TP +.B \fBuntagged\fP +Admit only untagged and prio\-tagged frames. VLAN\-tagged packets are +not accepted, while untagged or priority\-tagged packets entering the +server TAP device are tagged with the value configured for the global +\fB\-\-vlan\-pvid\fP setting. +.TP +.B \fBall\fP (default) +Admit all frames. All packets are admitted and then treated like +untagged or tagged mode respectively. +.TP +.B \fINote\fP: +Some vendors refer to switch ports running in \fBtagged\fP mode +as "trunk ports" and switch ports running in \fBuntagged\fP mode +as "access ports". +.UNINDENT +.sp +Packets forwarded from clients to the server are VLAN\-tagged with the +originating client\(aqs PVID, unless the VID matches the global +\fB\-\-vlan\-pvid\fP, in which case the tag is removed. +.sp +If no \fIPVID\fP is configured for a given client (see \-\-vlan\-pvid) packets +are tagged with 1 by default. +.TP +.BI \-\-vlan\-pvid \ v +Specifies which VLAN identifier a "port" is associated with. Only valid +when \fB\-\-vlan\-tagging\fP is speficied. +.sp +In the client context, the setting specifies which VLAN ID a client is +associated with. In the global context, the VLAN ID of the server TAP +device is set. The latter only makes sense for \fB\-\-vlan\-accept +untagged\fP and \fB\-\-vlan\-accept all\fP modes. +.sp +Valid values for \fBv\fP go from \fB1\fP through to \fB4094\fP\&. The +global value defaults to \fB1\fP\&. If no \fB\-\-vlan\-pvid\fP is specified in +the client context, the global value is inherited. +.sp +In some switch implementations, the \fIPVID\fP is also referred to as "Native +VLAN". +.UNINDENT +.SH ENCRYPTION OPTIONS +.SS SSL Library information +.INDENT 0.0 +.TP +.B \-\-show\-ciphers +(Standalone) Show all cipher algorithms to use with the \fB\-\-cipher\fP +option. +.TP +.B \-\-show\-digests +(Standalone) Show all message digest algorithms to use with the +\fB\-\-auth\fP option. +.TP +.B \-\-show\-tls +(Standalone) Show all TLS ciphers supported by the crypto library. +OpenVPN uses TLS to secure the control channel, over which the keys that +are used to protect the actual VPN traffic are exchanged. The TLS +ciphers will be sorted from highest preference (most secure) to lowest. +.sp +Be aware that whether a cipher suite in this list can actually work +depends on the specific setup of both peers (e.g. both peers must +support the cipher, and an ECDSA cipher suite will not work if you are +using an RSA certificate, etc.). +.TP +.B \-\-show\-engines +(Standalone) Show currently available hardware\-based crypto acceleration +engines supported by the OpenSSL library. +.TP +.B \-\-show\-groups +(Standalone) Show all available elliptic curves/groups to use with the +\fB\-\-ecdh\-curve\fP and \fBtls\-groups\fP options. +.UNINDENT +.SS Generating key material +.INDENT 0.0 +.TP +.BI \-\-genkey \ args +(Standalone) Generate a key to be used of the type keytype. if keyfile +is left out or empty the key will be output on stdout. See the following +sections for the different keytypes. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +\-\-genkey keytype keyfile +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Valid keytype arguments are: +.sp +\fBsecret\fP Standard OpenVPN shared secret keys +.sp +\fBtls\-crypt\fP Alias for \fBsecret\fP +.sp +\fBtls\-auth\fP Alias for \fBsecret\fP +.sp +\fBauth\-token\fP Key used for \fB\-\-auth\-gen\-token\-key\fP +.sp +\fBtls\-crypt\-v2\-server\fP TLS Crypt v2 server key +.sp +\fBtls\-crypt\-v2\-client\fP TLS Crypt v2 client key +.sp +Examples: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +$ openvpn \-\-genkey secret shared.key +$ openvpn \-\-genkey tls\-crypt shared.key +$ openvpn \-\-genkey tls\-auth shared.key +$ openvpn \-\-genkey tls\-crypt\-v2\-server v2crypt\-server.key +$ openvpn \-\-tls\-crypt\-v2 v2crypt\-server.key \-\-genkey tls\-crypt\-v2\-client v2crypt\-client\-1.key +.ft P +.fi +.UNINDENT +.UNINDENT +.INDENT 7.0 +.IP \(bu 2 +Generating \fIShared Secret Keys\fP +Generate a shared secret, for use with the \fB\-\-secret\fP, \fB\-\-tls\-auth\fP +or \fB\-\-tls\-crypt\fP options. +.sp +Syntax: +.INDENT 2.0 +.INDENT 3.5 +.sp +.nf +.ft C +$ openvpn \-\-genkey secret|tls\-crypt|tls\-auth keyfile +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The key is saved in \fBkeyfile\fP\&. All three variants (\fB\-\-secret\fP, +\fBtls\-crypt\fP and \fBtls\-auth\fP) generate the same type of key. The +aliases are added for convenience. +.sp +If using this for \fB\-\-secret\fP, this file must be shared with the peer +over a pre\-existing secure channel such as \fBscp\fP(1). +.IP \(bu 2 +Generating \fITLS Crypt v2 Server key\fP +Generate a \fB\-\-tls\-crypt\-v2\fP key to be used by an OpenVPN server. +The key is stored in \fBkeyfile\fP\&. +.sp +Syntax: +.INDENT 2.0 +.INDENT 3.5 +.sp +.nf +.ft C +\-\-genkey tls\-crypt\-v2\-server keyfile +.ft P +.fi +.UNINDENT +.UNINDENT +.IP \(bu 2 +Generating \fITLS Crypt v2 Client key\fP +Generate a \-\-tls\-crypt\-v2 key to be used by OpenVPN clients. The +key is stored in \fBkeyfile\fP\&. +.sp +Syntax +.INDENT 2.0 +.INDENT 3.5 +.sp +.nf +.ft C +\-\-genkey tls\-crypt\-v2\-client keyfile [metadata] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +If supplied, include the supplied \fBmetadata\fP in the wrapped client +key. This metadata must be supplied in base64\-encoded form. The +metadata must be at most 735 bytes long (980 bytes in base64). +.sp +If no metadata is supplied, OpenVPN will use a 64\-bit unix timestamp +representing the current time in UTC, encoded in network order, as +metadata for the generated key. +.sp +A tls\-crypt\-v2 client key is wrapped using a server key. To generate a +client key, the user must therefore supply the server key using the +\fB\-\-tls\-crypt\-v2\fP option. +.sp +Servers can use \fB\-\-tls\-crypt\-v2\-verify\fP to specify a metadata +verification command. +.IP \(bu 2 +Generate \fIAuthentication Token key\fP +Generate a new secret that can be used with \fB\-\-auth\-gen\-token\-secret\fP +.sp +Syntax: +.INDENT 2.0 +.INDENT 3.5 +.sp +.nf +.ft C +\-\-genkey auth\-token [keyfile] +.ft P +.fi +.UNINDENT +.UNINDENT +.INDENT 2.0 +.TP +.B \fINote:\fP +This file should be kept secret to the server as anyone that has +access to this file will be able to generate auth tokens that the +OpenVPN server will accept as valid. +.UNINDENT +.UNINDENT +.UNINDENT +.SS Data Channel Renegotiation +.sp +When running OpenVPN in client/server mode, the data channel will use a +separate ephemeral encryption key which is rotated at regular intervals. +.INDENT 0.0 +.TP +.BI \-\-reneg\-bytes \ n +Renegotiate data channel key after \fBn\fP bytes sent or received +(disabled by default with an exception, see below). OpenVPN allows the +lifetime of a key to be expressed as a number of bytes +encrypted/decrypted, a number of packets, or a number of seconds. A key +renegotiation will be forced if any of these three criteria are met by +either peer. +.sp +If using ciphers with cipher block sizes less than 128\-bits, +\fB\-\-reneg\-bytes\fP is set to 64MB by default, unless it is explicitly +disabled by setting the value to \fB0\fP, but this is +\fBHIGHLY DISCOURAGED\fP as this is designed to add some protection against +the SWEET32 attack vector. For more information see the \fB\-\-cipher\fP +option. +.TP +.BI \-\-reneg\-pkts \ n +Renegotiate data channel key after \fBn\fP packets sent and received +(disabled by default). +.TP +.BI \-\-reneg\-sec \ args +Renegotiate data channel key after at most \fBmax\fP seconds +(default \fB3600\fP) and at least \fBmin\fP seconds (default is 90% of +\fBmax\fP for servers, and equal to \fBmax\fP for clients). +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +reneg\-sec max [min] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The effective \fB\-\-reneg\-sec\fP value used is per session +pseudo\-uniform\-randomized between \fBmin\fP and \fBmax\fP\&. +.sp +With the default value of \fB3600\fP this results in an effective per +session value in the range of \fB3240\fP\&..:code:\fI3600\fP seconds for +servers, or just 3600 for clients. +.sp +When using dual\-factor authentication, note that this default value may +cause the end user to be challenged to reauthorize once per hour. +.sp +Also, keep in mind that this option can be used on both the client and +server, and whichever uses the lower value will be the one to trigger +the renegotiation. A common mistake is to set \fB\-\-reneg\-sec\fP to a +higher value on either the client or server, while the other side of the +connection is still using the default value of \fB3600\fP seconds, +meaning that the renegotiation will still occur once per \fB3600\fP +seconds. The solution is to increase \-\-reneg\-sec on both the client and +server, or set it to \fB0\fP on one side of the connection (to +disable), and to your chosen value on the other side. +.UNINDENT +.SS TLS Mode Options +.sp +TLS mode is the most powerful crypto mode of OpenVPN in both security +and flexibility. TLS mode works by establishing control and data +channels which are multiplexed over a single TCP/UDP port. OpenVPN +initiates a TLS session over the control channel and uses it to exchange +cipher and HMAC keys to protect the data channel. TLS mode uses a robust +reliability layer over the UDP connection for all control channel +communication, while the data channel, over which encrypted tunnel data +passes, is forwarded without any mediation. The result is the best of +both worlds: a fast data channel that forwards over UDP with only the +overhead of encrypt, decrypt, and HMAC functions, and a control channel +that provides all of the security features of TLS, including +certificate\-based authentication and Diffie Hellman forward secrecy. +.sp +To use TLS mode, each peer that runs OpenVPN should have its own local +certificate/key pair (\fB\-\-cert\fP and \fB\-\-key\fP), signed by the root +certificate which is specified in \fB\-\-ca\fP\&. +.sp +When two OpenVPN peers connect, each presents its local certificate to +the other. Each peer will then check that its partner peer presented a +certificate which was signed by the master root certificate as specified +in \fB\-\-ca\fP\&. +.sp +If that check on both peers succeeds, then the TLS negotiation will +succeed, both OpenVPN peers will exchange temporary session keys, and +the tunnel will begin passing data. +.sp +The OpenVPN project provides a set of scripts for managing RSA +certificates and keys: \fI\%https://github.com/OpenVPN/easy\-rsa\fP +.INDENT 0.0 +.TP +.BI \-\-askpass \ file +Get certificate password from console or \fBfile\fP before we daemonize. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +askpass +askpass file +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +For the extremely security conscious, it is possible to protect your +private key with a password. Of course this means that every time the +OpenVPN daemon is started you must be there to type the password. The +\fB\-\-askpass\fP option allows you to start OpenVPN from the command line. +It will query you for a password before it daemonizes. To protect a +private key with a password you should omit the \fB\-nodes\fP option when +you use the \fBopenssl\fP command line tool to manage certificates and +private keys. +.sp +If \fBfile\fP is specified, read the password from the first line of +\fBfile\fP\&. Keep in mind that storing your password in a file to a certain +extent invalidates the extra security provided by using an encrypted +key. +.TP +.BI \-\-ca \ file +Certificate authority (CA) file in .pem format, also referred to as the +\fIroot\fP certificate. This file can have multiple certificates in .pem +format, concatenated together. You can construct your own certificate +authority certificate and private key by using a command such as: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +openssl req \-nodes \-new \-x509 \-keyout ca.key \-out ca.crt +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Then edit your openssl.cnf file and edit the \fBcertificate\fP variable to +point to your new root certificate \fBca.crt\fP\&. +.sp +For testing purposes only, the OpenVPN distribution includes a sample CA +certificate (ca.crt). Of course you should never use the test +certificates and test keys distributed with OpenVPN in a production +environment, since by virtue of the fact that they are distributed with +OpenVPN, they are totally insecure. +.TP +.BI \-\-capath \ dir +Directory containing trusted certificates (CAs and CRLs). Not available +with mbed TLS. +.sp +CAs in the capath directory are expected to be named .. CRLs +are expected to be named .r. See the \fB\-CApath\fP option of +\fBopenssl verify\fP, and the \fB\-hash\fP option of \fBopenssl x509\fP, +\fBopenssl crl\fP and \fBX509_LOOKUP_hash_dir()\fP(3) +for more information. +.sp +Similar to the \fB\-\-crl\-verify\fP option, CRLs are not mandatory \- +OpenVPN will log the usual warning in the logs if the relevant CRL is +missing, but the connection will be allowed. +.TP +.BI \-\-cert \ file +Local peer\(aqs signed certificate in .pem format \-\- must be signed by a +certificate authority whose certificate is in \fB\-\-ca file\fP\&. Each peer +in an OpenVPN link running in TLS mode should have its own certificate +and private key file. In addition, each certificate should have been +signed by the key of a certificate authority whose public key resides in +the \fB\-\-ca\fP certificate authority file. You can easily make your own +certificate authority (see above) or pay money to use a commercial +service such as thawte.com (in which case you will be helping to finance +the world\(aqs second space tourist :). To generate a certificate, you can +use a command such as: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +openssl req \-nodes \-new \-keyout mycert.key \-out mycert.csr +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +If your certificate authority private key lives on another machine, copy +the certificate signing request (mycert.csr) to this other machine (this +can be done over an insecure channel such as email). Now sign the +certificate with a command such as: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +openssl ca \-out mycert.crt \-in mycert.csr +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Now copy the certificate (mycert.crt) back to the peer which initially +generated the .csr file (this can be over a public medium). Note that +the \fBopenssl ca\fP command reads the location of the certificate +authority key from its configuration file such as +\fB/usr/share/ssl/openssl.cnf\fP \-\- note also that for certificate +authority functions, you must set up the files \fBindex.txt\fP (may be +empty) and \fBserial\fP (initialize to \fB01\fP). +.TP +.BI \-\-crl\-verify \ args +Check peer certificate against a Certificate Revocation List. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +crl\-verify file/directory flag +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Examples: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +crl\-verify crl\-file.pem +crl\-verify /etc/openvpn/crls dir +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +A CRL (certificate revocation list) is used when a particular key is +compromised but when the overall PKI is still intact. +.sp +Suppose you had a PKI consisting of a CA, root certificate, and a number +of client certificates. Suppose a laptop computer containing a client +key and certificate was stolen. By adding the stolen certificate to the +CRL file, you could reject any connection which attempts to use it, +while preserving the overall integrity of the PKI. +.sp +The only time when it would be necessary to rebuild the entire PKI from +scratch would be if the root certificate key itself was compromised. +.sp +The option is not mandatory \- if the relevant CRL is missing, OpenVPN +will log a warning in the logs \- e.g. +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +VERIFY WARNING: depth=0, unable to get certificate CRL +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +but the connection will be allowed. If the optional \fBdir\fP flag +is specified, enable a different mode where the \fBcrl\-verify\fP is +pointed at a directory containing files named as revoked serial numbers +(the files may be empty, the contents are never read). If a client +requests a connection, where the client certificate serial number +(decimal string) is the name of a file present in the directory, it will +be rejected. +.INDENT 7.0 +.TP +.B \fINote:\fP +As the crl file (or directory) is read every time a peer +connects, if you are dropping root privileges with +\fB\-\-user\fP, make sure that this user has sufficient +privileges to read the file. +.UNINDENT +.TP +.BI \-\-dh \ file +File containing Diffie Hellman parameters in .pem format (required for +\fB\-\-tls\-server\fP only). +.sp +Set \fBfile\fP to \fBnone\fP to disable Diffie Hellman key exchange (and +use ECDH only). Note that this requires peers to be using an SSL library +that supports ECDH TLS cipher suites (e.g. OpenSSL 1.0.1+, or +mbed TLS 2.0+). +.sp +Use \fBopenssl dhparam \-out dh2048.pem 2048\fP to generate 2048\-bit DH +parameters. Diffie Hellman parameters may be considered public. +.TP +.BI \-\-ecdh\-curve \ name +Specify the curve to use for elliptic curve Diffie Hellman. Available +curves can be listed with \fB\-\-show\-curves\fP\&. The specified curve will +only be used for ECDH TLS\-ciphers. +.sp +This option is not supported in mbed TLS builds of OpenVPN. +.TP +.BI \-\-extra\-certs \ file +Specify a \fBfile\fP containing one or more PEM certs (concatenated +together) that complete the local certificate chain. +.sp +This option is useful for "split" CAs, where the CA for server certs is +different than the CA for client certs. Putting certs in this file +allows them to be used to complete the local certificate chain without +trusting them to verify the peer\-submitted certificate, as would be the +case if the certs were placed in the \fBca\fP file. +.TP +.BI \-\-hand\-window \ n +Handshake Window \-\- the TLS\-based key exchange must finalize within +\fBn\fP seconds of handshake initiation by any peer (default \fB60\fP +seconds). If the handshake fails we will attempt to reset our connection +with our peer and try again. Even in the event of handshake failure we +will still use our expiring key for up to \fB\-\-tran\-window\fP seconds to +maintain continuity of transmission of tunnel data. +.TP +.BI \-\-key \ file +Local peer\(aqs private key in .pem format. Use the private key which was +generated when you built your peer\(aqs certificate (see \fB\-\-cert file\fP +above). +.TP +.BI \-\-pkcs12 \ file +Specify a PKCS #12 file containing local private key, local certificate, +and root CA certificate. This option can be used instead of \fB\-\-ca\fP, +\fB\-\-cert\fP, and \fB\-\-key\fP\&. Not available with mbed TLS. +.TP +.BI \-\-remote\-cert\-eku \ oid +Require that peer certificate was signed with an explicit \fIextended key +usage\fP\&. +.sp +This is a useful security option for clients, to ensure that the host +they connect to is a designated server. +.sp +The extended key usage should be encoded in \fIoid notation\fP, or \fIOpenSSL +symbolic representation\fP\&. +.TP +.BI \-\-remote\-cert\-ku \ key\-usage +Require that peer certificate was signed with an explicit +\fBkey\-usage\fP\&. +.sp +If present in the certificate, the \fBkeyUsage\fP value is validated by +the TLS library during the TLS handshake. Specifying this option without +arguments requires this extension to be present (so the TLS library will +verify it). +.sp +If \fBkey\-usage\fP is a list of usage bits, the \fBkeyUsage\fP field +must have \fIat least\fP the same bits set as the bits in \fIone of\fP the values +supplied in the \fBkey\-usage\fP list. +.sp +The \fBkey\-usage\fP values in the list must be encoded in hex, e.g. +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +remote\-cert\-ku a0 +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-remote\-cert\-tls \ type +Require that peer certificate was signed with an explicit \fIkey usage\fP +and \fIextended key usage\fP based on RFC3280 TLS rules. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +remote\-cert\-tls server +remote\-cert\-tls client +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +This is a useful security option for clients, to ensure that the host +they connect to is a designated server. Or the other way around; for a +server to verify that only hosts with a client certificate can connect. +.sp +The \fB\-\-remote\-cert\-tls client\fP option is equivalent to +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +remote\-cert\-ku +remote\-cert\-eku "TLS Web Client Authentication" +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The \fB\-\-remote\-cert\-tls server\fP option is equivalent to +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +remote\-cert\-ku +remote\-cert\-eku "TLS Web Server Authentication" +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +This is an important security precaution to protect against a +man\-in\-the\-middle attack where an authorized client attempts to connect +to another client by impersonating the server. The attack is easily +prevented by having clients verify the server certificate using any one +of \fB\-\-remote\-cert\-tls\fP, \fB\-\-verify\-x509\-name\fP, or \fB\-\-tls\-verify\fP\&. +.TP +.BI \-\-tls\-auth \ args +Add an additional layer of HMAC authentication on top of the TLS control +channel to mitigate DoS attacks and attacks on the TLS stack. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +tls\-auth file +tls\-auth file 0 +tls\-auth file 1 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +In a nutshell, \fB\-\-tls\-auth\fP enables a kind of "HMAC firewall" on +OpenVPN\(aqs TCP/UDP port, where TLS control channel packets bearing an +incorrect HMAC signature can be dropped immediately without response. +.sp +\fBfile\fP (required) is a file in OpenVPN static key format which can be +generated by \fB\-\-genkey\fP\&. +.sp +Older versions (up to OpenVPN 2.3) supported a freeform passphrase file. +This is no longer supported in newer versions (v2.4+). +.sp +See the \fB\-\-secret\fP option for more information on the optional +\fBdirection\fP parameter. +.sp +\fB\-\-tls\-auth\fP is recommended when you are running OpenVPN in a mode +where it is listening for packets from any IP address, such as when +\fB\-\-remote\fP is not specified, or \fB\-\-remote\fP is specified with +\fB\-\-float\fP\&. +.sp +The rationale for this feature is as follows. TLS requires a +multi\-packet exchange before it is able to authenticate a peer. During +this time before authentication, OpenVPN is allocating resources (memory +and CPU) to this potential peer. The potential peer is also exposing +many parts of OpenVPN and the OpenSSL library to the packets it is +sending. Most successful network attacks today seek to either exploit +bugs in programs (such as buffer overflow attacks) or force a program to +consume so many resources that it becomes unusable. Of course the first +line of defense is always to produce clean, well\-audited code. OpenVPN +has been written with buffer overflow attack prevention as a top +priority. But as history has shown, many of the most widely used network +applications have, from time to time, fallen to buffer overflow attacks. +.sp +So as a second line of defense, OpenVPN offers this special layer of +authentication on top of the TLS control channel so that every packet on +the control channel is authenticated by an HMAC signature and a unique +ID for replay protection. This signature will also help protect against +DoS (Denial of Service) attacks. An important rule of thumb in reducing +vulnerability to DoS attacks is to minimize the amount of resources a +potential, but as yet unauthenticated, client is able to consume. +.sp +\fB\-\-tls\-auth\fP does this by signing every TLS control channel packet +with an HMAC signature, including packets which are sent before the TLS +level has had a chance to authenticate the peer. The result is that +packets without the correct signature can be dropped immediately upon +reception, before they have a chance to consume additional system +resources such as by initiating a TLS handshake. \fB\-\-tls\-auth\fP can be +strengthened by adding the \fB\-\-replay\-persist\fP option which will keep +OpenVPN\(aqs replay protection state in a file so that it is not lost +across restarts. +.sp +It should be emphasized that this feature is optional and that the key +file used with \fB\-\-tls\-auth\fP gives a peer nothing more than the power +to initiate a TLS handshake. It is not used to encrypt or authenticate +any tunnel data. +.sp +Use \fB\-\-tls\-crypt\fP instead if you want to use the key file to not only +authenticate, but also encrypt the TLS control channel. +.TP +.BI \-\-tls\-groups \ list +A list of allowable groups/curves in order of preference. +.sp +Set the allowed elliptic curves/groups for the TLS session. +These groups are allowed to be used in signatures and key exchange. +.sp +mbedTLS currently allows all known curves per default. +.sp +OpenSSL 1.1+ restricts the list per default to +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +"X25519:secp256r1:X448:secp521r1:secp384r1". +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +If you use certificates that use non\-standard curves, you +might need to add them here. If you do not force the ecdh curve +by using \fB\-\-ecdh\-curve\fP, the groups for ecdh will also be picked +from this list. +.sp +OpenVPN maps the curve name \fIsecp256r1\fP to \fIprime256v1\fP to allow +specifying the same tls\-groups option for mbedTLS and OpenSSL. +.sp +Warning: this option not only affects elliptic curve certificates +but also the key exchange in TLS 1.3 and using this option improperly +will disable TLS 1.3. +.TP +.BI \-\-tls\-cert\-profile \ profile +Set the allowed cryptographic algorithms for certificates according to +\fBprofile\fP\&. +.sp +The following profiles are supported: +.INDENT 7.0 +.TP +.B \fBlegacy\fP (default) +SHA1 and newer, RSA 2048\-bit+, any elliptic curve. +.TP +.B \fBpreferred\fP +SHA2 and newer, RSA 2048\-bit+, any elliptic curve. +.TP +.B \fBsuiteb\fP +SHA256/SHA384, ECDSA with P\-256 or P\-384. +.UNINDENT +.sp +This option is only fully supported for mbed TLS builds. OpenSSL builds +use the following approximation: +.INDENT 7.0 +.TP +.B \fBlegacy\fP (default) +sets "security level 1" +.TP +.B \fBpreferred\fP +sets "security level 2" +.TP +.B \fBsuiteb\fP +sets "security level 3" and \fB\-\-tls\-cipher "SUITEB128"\fP\&. +.UNINDENT +.sp +OpenVPN will migrate to \(aqpreferred\(aq as default in the future. Please +ensure that your keys already comply. +.UNINDENT +.INDENT 0.0 +.TP +.B \fIWARNING:\fP \fB\-\-tls\-ciphers\fP, \fB\-\-tls\-ciphersuites\fP and \fBtls\-groups\fP +These options are expert features, which \- if used correctly \- can +improve the security of your VPN connection. But it is also easy to +unwittingly use them to carefully align a gun with your foot, or just +break your connection. Use with care! +.UNINDENT +.INDENT 0.0 +.TP +.BI \-\-tls\-cipher \ l +A list \fBl\fP of allowable TLS ciphers delimited by a colon ("\fB:\fP"). +.sp +These setting can be used to ensure that certain cipher suites are used +(or not used) for the TLS connection. OpenVPN uses TLS to secure the +control channel, over which the keys that are used to protect the actual +VPN traffic are exchanged. +.sp +The supplied list of ciphers is (after potential OpenSSL/IANA name +translation) simply supplied to the crypto library. Please see the +OpenSSL and/or mbed TLS documentation for details on the cipher list +interpretation. +.sp +For OpenSSL, the \fB\-\-tls\-cipher\fP is used for TLS 1.2 and below. +.sp +Use \fB\-\-show\-tls\fP to see a list of TLS ciphers supported by your crypto +library. +.sp +The default for \fB\-\-tls\-cipher\fP is to use mbed TLS\(aqs default cipher list +when using mbed TLS or +\fBDEFAULT:!EXP:!LOW:!MEDIUM:!kDH:!kECDH:!DSS:!PSK:!SRP:!kRSA\fP when +using OpenSSL. +.sp +The default for \fI\-\-tls\-ciphersuites\fP is to use the crypto library\(aqs +default. +.TP +.BI \-\-tls\-ciphersuites \ l +Same as \fB\-\-tls\-cipher\fP but for TLS 1.3 and up. mbed TLS has no +TLS 1.3 support yet and only the \fB\-\-tls\-cipher\fP setting is used. +.TP +.B \-\-tls\-client +Enable TLS and assume client role during TLS handshake. +.TP +.BI \-\-tls\-crypt \ keyfile +Encrypt and authenticate all control channel packets with the key from +\fBkeyfile\fP\&. (See \fB\-\-tls\-auth\fP for more background.) +.sp +Encrypting (and authenticating) control channel packets: +.INDENT 7.0 +.IP \(bu 2 +provides more privacy by hiding the certificate used for the TLS +connection, +.IP \(bu 2 +makes it harder to identify OpenVPN traffic as such, +.IP \(bu 2 +provides "poor\-man\(aqs" post\-quantum security, against attackers who will +never know the pre\-shared key (i.e. no forward secrecy). +.UNINDENT +.sp +In contrast to \fB\-\-tls\-auth\fP, \fB\-\-tls\-crypt\fP does \fInot\fP require the +user to set \fB\-\-key\-direction\fP\&. +.sp +\fBSecurity Considerations\fP +.sp +All peers use the same \fB\-\-tls\-crypt\fP pre\-shared group key to +authenticate and encrypt control channel messages. To ensure that IV +collisions remain unlikely, this key should not be used to encrypt more +than 2^48 client\-to\-server or 2^48 server\-to\-client control channel +messages. A typical initial negotiation is about 10 packets in each +direction. Assuming both initial negotiation and renegotiations are at +most 2^16 (65536) packets (to be conservative), and (re)negotiations +happen each minute for each user (24/7), this limits the tls\-crypt key +lifetime to 8171 years divided by the number of users. So a setup with +1000 users should rotate the key at least once each eight years. (And a +setup with 8000 users each year.) +.sp +If IV collisions were to occur, this could result in the security of +\fB\-\-tls\-crypt\fP degrading to the same security as using \fB\-\-tls\-auth\fP\&. +That is, the control channel still benefits from the extra protection +against active man\-in\-the\-middle\-attacks and DoS attacks, but may no +longer offer extra privacy and post\-quantum security on top of what TLS +itself offers. +.sp +For large setups or setups where clients are not trusted, consider using +\fB\-\-tls\-crypt\-v2\fP instead. That uses per\-client unique keys, and +thereby improves the bounds to \(aqrotate a client key at least once per +8000 years\(aq. +.TP +.BI \-\-tls\-crypt\-v2 \ keyfile +Use client\-specific tls\-crypt keys. +.sp +For clients, \fBkeyfile\fP is a client\-specific tls\-crypt key. Such a key +can be generated using the \fB\-\-genkey tls\-crypt\-v2\-client\fP option. +.sp +For servers, \fBkeyfile\fP is used to unwrap client\-specific keys supplied +by the client during connection setup. This key must be the same as the +key used to generate the client\-specific key (see \fB\-\-genkey +tls\-crypt\-v2\-client\fP). +.sp +On servers, this option can be used together with the \fB\-\-tls\-auth\fP or +\fB\-\-tls\-crypt\fP option. In that case, the server will detect whether the +client is using client\-specific keys, and automatically select the right +mode. +.TP +.BI \-\-tls\-crypt\-v2\-verify \ cmd +Run command \fBcmd\fP to verify the metadata of the client\-specific +tls\-crypt\-v2 key of a connecting client. This allows server +administrators to reject client connections, before exposing the TLS +stack (including the notoriously dangerous X.509 and ASN.1 stacks) to +the connecting client. +.sp +OpenVPN supplies the following environment variables to the command: +.INDENT 7.0 +.IP \(bu 2 +\fBscript_type\fP is set to \fBtls\-crypt\-v2\-verify\fP +.IP \(bu 2 +\fBmetadata_type\fP is set to \fB0\fP if the metadata was user +supplied, or \fB1\fP if it\(aqs a 64\-bit unix timestamp representing +the key creation time. +.IP \(bu 2 +\fBmetadata_file\fP contains the filename of a temporary file that +contains the client metadata. +.UNINDENT +.sp +The command can reject the connection by exiting with a non\-zero exit +code. +.TP +.B \-\-tls\-exit +Exit on TLS negotiation failure. +.TP +.BI \-\-tls\-export\-cert \ directory +Store the certificates the clients use upon connection to this +directory. This will be done before \fB\-\-tls\-verify\fP is called. The +certificates will use a temporary name and will be deleted when the +tls\-verify script returns. The file name used for the certificate is +available via the \fBpeer_cert\fP environment variable. +.TP +.B \-\-tls\-server +Enable TLS and assume server role during TLS handshake. Note that +OpenVPN is designed as a peer\-to\-peer application. The designation of +client or server is only for the purpose of negotiating the TLS control +channel. +.TP +.BI \-\-tls\-timeout \ n +Packet retransmit timeout on TLS control channel if no acknowledgment +from remote within \fBn\fP seconds (default \fB2\fP). When OpenVPN sends +a control packet to its peer, it will expect to receive an +acknowledgement within \fBn\fP seconds or it will retransmit the packet, +subject to a TCP\-like exponential backoff algorithm. This parameter only +applies to control channel packets. Data channel packets (which carry +encrypted tunnel data) are never acknowledged, sequenced, or +retransmitted by OpenVPN because the higher level network protocols +running on top of the tunnel such as TCP expect this role to be left to +them. +.TP +.BI \-\-tls\-version\-min \ args +Sets the minimum TLS version we will accept from the peer (default is +"1.0"). +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +tls\-version\-min version [\(aqor\-highest\(aq] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Examples for version include \fB1.0\fP, \fB1.1\fP, or \fB1.2\fP\&. If +\fBor\-highest\fP is specified and version is not recognized, we will +only accept the highest TLS version supported by the local SSL +implementation. +.TP +.BI \-\-tls\-version\-max \ version +Set the maximum TLS version we will use (default is the highest version +supported). Examples for version include \fB1.0\fP, \fB1.1\fP, or +\fB1.2\fP\&. +.TP +.BI \-\-verify\-hash \ args +Specify SHA1 or SHA256 fingerprint for level\-1 cert. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +verify\-hash hash [algo] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The level\-1 cert is the CA (or intermediate cert) that signs the leaf +certificate, and is one removed from the leaf certificate in the +direction of the root. When accepting a connection from a peer, the +level\-1 cert fingerprint must match \fBhash\fP or certificate verification +will fail. Hash is specified as XX:XX:... For example: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +AD:B0:95:D8:09:C8:36:45:12:A9:89:C8:90:09:CB:13:72:A6:AD:16 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The \fBalgo\fP flag can be either \fBSHA1\fP or \fBSHA256\fP\&. If not +provided, it defaults to \fBSHA1\fP\&. +.TP +.BI \-\-verify\-x509\-name \ args +Accept connections only if a host\(aqs X.509 name is equal to \fBname.\fP The +remote host must also pass all other tests of verification. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +verify\-x509 name type +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Which X.509 name is compared to \fBname\fP depends on the setting of type. +\fBtype\fP can be \fBsubject\fP to match the complete subject DN +(default), \fBname\fP to match a subject RDN or \fBname\-prefix\fP to +match a subject RDN prefix. Which RDN is verified as name depends on the +\fB\-\-x509\-username\-field\fP option. But it defaults to the common name +(CN), e.g. a certificate with a subject DN +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +C=KG, ST=NA, L=Bishkek, CN=Server\-1 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +would be matched by: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +verify\-x509\-name \(aqC=KG, ST=NA, L=Bishkek, CN=Server\-1\(aq +verify\-x509\-name Server\-1 name +verify\-x509\-name Server\- name\-prefix +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The last example is useful if you want a client to only accept +connections to \fBServer\-1\fP, \fBServer\-2\fP, etc. +.sp +\fB\-\-verify\-x509\-name\fP is a useful replacement for the \fB\-\-tls\-verify\fP +option to verify the remote host, because \fB\-\-verify\-x509\-name\fP works +in a \fB\-\-chroot\fP environment without any dependencies. +.sp +Using a name prefix is a useful alternative to managing a CRL +(Certificate Revocation List) on the client, since it allows the client +to refuse all certificates except for those associated with designated +servers. +.INDENT 7.0 +.TP +.B \fINOTE:\fP +Test against a name prefix only when you are using OpenVPN +with a custom CA certificate that is under your control. Never use +this option with type \fBname\-prefix\fP when your client +certificates are signed by a third party, such as a commercial +web CA. +.UNINDENT +.TP +.BI \-\-x509\-track \ attribute +Save peer X509 \fBattribute\fP value in environment for use by plugins and +management interface. Prepend a \fB+\fP to \fBattribute\fP to save values +from full cert chain. Values will be encoded as +\fBX509__=\fP\&. Multiple \fB\-\-x509\-track\fP +options can be defined to track multiple attributes. +.TP +.BI \-\-x509\-username\-field \ args +Field in the X.509 certificate subject to be used as the username +(default \fBCN\fP). +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +x509\-username\-field [ext:]fieldname +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Typically, this option is specified with \fBfieldname\fP as +either of the following: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +x509\-username\-field emailAddress +x509\-username\-field ext:subjectAltName +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The first example uses the value of the \fBemailAddress\fP attribute +in the certificate\(aqs Subject field as the username. The second example +uses the \fBext:\fP prefix to signify that the X.509 extension +\fBfieldname\fP \fBsubjectAltName\fP be searched for an rfc822Name +(email) field to be used as the username. In cases where there are +multiple email addresses in \fBext:fieldname\fP, the last occurrence +is chosen. +.sp +When this option is used, the \fB\-\-verify\-x509\-name\fP option will match +against the chosen \fBfieldname\fP instead of the Common Name. +.sp +Only the \fBsubjectAltName\fP and \fBissuerAltName\fP X.509 +extensions are supported. +.sp +\fBPlease note:\fP This option has a feature which will convert an +all\-lowercase \fBfieldname\fP to uppercase characters, e.g., +\fBou\fP \-> \fBOU\fP\&. A mixed\-case \fBfieldname\fP or one having the +\fBext:\fP prefix will be left as\-is. This automatic upcasing feature is +deprecated and will be removed in a future release. +.UNINDENT +.SS PKCS#11 / SmartCard options +.INDENT 0.0 +.TP +.BI \-\-pkcs11\-cert\-private \ args +Set if access to certificate object should be performed after login. +Every provider has its own setting. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +pkcs11\-cert\-private 0 +pkcs11\-cert\-private 1 +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-pkcs11\-id \ name +Specify the serialized certificate id to be used. The id can be gotten +by the standalone \fB\-\-show\-pkcs11\-ids\fP option. +.TP +.B \-\-pkcs11\-id\-management +Acquire PKCS#11 id from management interface. In this case a +\fBNEED\-STR \(aqpkcs11\-id\-request\(aq\fP real\-time message will be triggered, +application may use pkcs11\-id\-count command to retrieve available number of +certificates, and pkcs11\-id\-get command to retrieve certificate id and +certificate body. +.TP +.BI \-\-pkcs11\-pin\-cache \ seconds +Specify how many seconds the PIN can be cached, the default is until the +token is removed. +.TP +.BI \-\-pkcs11\-private\-mode \ mode +Specify which method to use in order to perform private key operations. +A different mode can be specified for each provider. Mode is encoded as +hex number, and can be a mask one of the following: +.sp +\fB0\fP (default) Try to determine automatically. +.sp +\fB1\fP Use sign. +.sp +\fB2\fP Use sign recover. +.sp +\fB4\fP Use decrypt. +.sp +\fB8\fP Use unwrap. +.TP +.BI \-\-pkcs11\-protected\-authentication \ args +Use PKCS#11 protected authentication path, useful for biometric and +external keypad devices. Every provider has its own setting. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +pkcs11\-protected\-authentication 0 +pkcs11\-protected\-authentication 1 +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-pkcs11\-providers \ provider +Specify an RSA Security Inc. PKCS #11 Cryptographic Token Interface +(Cryptoki) providers to load. This option can be used instead of +\fB\-\-cert\fP, \fB\-\-key\fP and \fB\-\-pkcs12\fP\&. +.sp +If p11\-kit is present on the system, its \fBp11\-kit\-proxy.so\fP module +will be loaded by default if either the \fB\-\-pkcs11\-id\fP or +\fB\-\-pkcs11\-id\-management\fP options are specified without +\fB\-\-pkcs11\-provider\fP being given. +.TP +.BI \-\-show\-pkcs11\-ids \ args +(Standalone) Show PKCS#11 token object list. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +show\-pkcs11 [provider] [cert_private] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Specify \fBcert_private\fP as \fB1\fP if certificates are stored as +private objects. +.sp +If \fIp11\-kit\fP is present on the system, the \fBprovider\fP argument is +optional; if omitted the default \fBp11\-kit\-proxy.so\fP module will be +queried. +.sp +\fB\-\-verb\fP option can be used BEFORE this option to produce debugging +information. +.UNINDENT +.SH DATA CHANNEL CIPHER NEGOTIATION +.sp +OpenVPN 2.4 and higher have the capability to negotiate the data cipher that +is used to encrypt data packets. This section describes the mechanism in more detail and the +different backwards compatibility mechanism with older server and clients. +.SS OpenVPN 2.5 and higher behaviour +.sp +When both client and server are at least running OpenVPN 2.5, that the order of +the ciphers of the server\(aqs \fB\-\-data\-ciphers\fP is used to pick the the data cipher. +That means that the first cipher in that list that is also in the client\(aqs +\fB\-\-data\-ciphers\fP list is chosen. If no common cipher is found the client is rejected +with a AUTH_FAILED message (as seen in client log): +.INDENT 0.0 +.INDENT 3.5 +AUTH: Received control message: AUTH_FAILED,Data channel cipher negotiation failed (no shared cipher) +.UNINDENT +.UNINDENT +.sp +OpenVPN 2.5 will only allow the ciphers specified in \fB\-\-data\-ciphers\fP\&. To ensure +backwards compatibility also if a cipher is specified using the \fB\-\-cipher\fP option +it is automatically added to this list. If both options are unset the default is +\fBAES\-256\-GCM:AES\-128\-GCM\fP\&. +.SS OpenVPN 2.4 clients +.sp +The negotiation support in OpenVPN 2.4 was the first iteration of the implementation +and still had some quirks. Its main goal was "upgrade to AES\-256\-GCM when possible". +An OpenVPN 2.4 client that is built against a crypto library that supports AES in GCM +mode and does not have \fB\-\-ncp\-disable\fP will always announce support for +\fIAES\-256\-GCM\fP and \fIAES\-128\-GCM\fP to a server by sending \fBIV_NCP=2\fP\&. +.sp +This only causes a problem if \fB\-\-ncp\-ciphers\fP option has been changed from the +default of \fBAES\-256\-GCM:AES\-128\-GCM\fP to a value that does not include +these two ciphers. When a OpenVPN servers try to use \fIAES\-256\-GCM\fP or +\fIAES\-128\-GCM\fP the connection will then fail. It is therefore recommended to +always have the \fIAES\-256\-GCM\fP and \fIAES\-128\-GCM\fP ciphers to the \fB\-\-ncp\-ciphers\fP +options to avoid this behaviour. +.SS OpenVPN 3 clients +.sp +Clients based on the OpenVPN 3.x library (\fI\%https://github.com/openvpn/openvpn3/\fP) +do not have a configurable \fB\-\-ncp\-ciphers\fP or \fB\-\-data\-ciphers\fP option. Instead +these clients will announce support for all their supported AEAD ciphers +(\fIAES\-256\-GCM\fP, \fIAES\-128\-GCM\fP and in newer versions also \fIChacha20\-Poly1305\fP). +.sp +To support OpenVPN 3.x based clients at least one of these ciphers needs to be +included in the server\(aqs \fB\-\-data\-ciphers\fP option. +.SS OpenVPN 2.3 and older clients (and clients with \fB\-\-ncp\-disable\fP) +.sp +When a client without cipher negotiation support connects to a server the +cipher specified with the \fB\-\-cipher\fP option in the client configuration +must be included in the \fB\-\-data\-ciphers\fP option of the server to allow +the client to connect. Otherwise the client will be sent the \fBAUTH_FAILED\fP +message that indicates no shared cipher. +.sp +If the client is 2.3 or older and has been configured with the +\fB\-\-enable\-small\fP \fB\&./configure\fP argument, using +\fBdata\-ciphers\-fallback cipher\fP in the server config file with the explicit +cipher used by the client is necessary. +.SS OpenVPN 2.4 server +.sp +When a client indicates support for \fIAES\-128\-GCM\fP and \fIAES\-256\-GCM\fP +(with \fBIV_NCP=2\fP) an OpenVPN 2.4 server will send the first +cipher of the \fB\-\-ncp\-ciphers\fP to the OpenVPN client regardless of what +the cipher is. To emulate the behaviour of an OpenVPN 2.4 client as close +as possible and have compatibility to a setup that depends on this quirk, +adding \fIAES\-128\-GCM\fP and \fIAES\-256\-GCM\fP to the client\(aqs \fB\-\-data\-ciphers\fP +option is required. OpenVPN 2.5+ will only announce the \fBIV_NCP=2\fP flag if +those ciphers are present. +.SS OpenVPN 2.3 and older servers (and servers with \fB\-\-ncp\-disable\fP) +.sp +The cipher used by the server must be included in \fB\-\-data\-ciphers\fP to +allow the client connecting to a server without cipher negotiation +support. +(For compatibility OpenVPN 2.5 will also accept the cipher set with +\fB\-\-cipher\fP) +.sp +If the server is 2.3 or older and has been configured with the +\fB\-\-enable\-small\fP \fB\&./configure\fP argument, adding +\fBdata\-ciphers\-fallback cipher\fP to the client config with the explicit +cipher used by the server is necessary. +.SS Blowfish in CBC mode (BF\-CBC) deprecation +.sp +The \fB\-\-cipher\fP option defaulted to \fBBF\-CBC\fP in OpenVPN 2.4 and older +version. The default was never changed to ensure backwards compatibility. +In OpenVPN 2.5 this behaviour has now been changed so that if the \fB\-\-cipher\fP +is not explicitly set it does not allow the weak \fBBF\-CBC\fP cipher any more +and needs to explicitly added as \fB\-\-cipher BFC\-CBC\fP or added to +\fB\-\-data\-ciphers\fP\&. +.sp +We strongly recommend to switching away from BF\-CBC to a +more secure cipher as soon as possible instead. +.SH NETWORK CONFIGURATION +.sp +OpenVPN consists of two sides of network configuration. One side is the +\fIlink\fP between the local and remote side, the other side is the \fIvirtual +network adapter\fP (tun/tap device). +.SS Link Options +.sp +This link options section covers options related to the connection between +the local and the remote host. +.INDENT 0.0 +.TP +.BI \-\-bind \ keywords +Bind to local address and port. This is the default unless any of +\fB\-\-proto tcp\-client\fP , \fB\-\-http\-proxy\fP or \fB\-\-socks\-proxy\fP are used. +.sp +If the optional \fBipv6only\fP keyword is present OpenVPN will bind only +to IPv6 (as opposed to IPv6 and IPv4) when a IPv6 socket is opened. +.TP +.B \-\-float +Allow remote peer to change its IP address and/or port number, such as +due to DHCP (this is the default if \fB\-\-remote\fP is not used). +\fB\-\-float\fP when specified with \fB\-\-remote\fP allows an OpenVPN session +to initially connect to a peer at a known address, however if packets +arrive from a new address and pass all authentication tests, the new +address will take control of the session. This is useful when you are +connecting to a peer which holds a dynamic address such as a dial\-in +user or DHCP client. +.sp +Essentially, \fB\-\-float\fP tells OpenVPN to accept authenticated packets +from any address, not only the address which was specified in the +\fB\-\-remote\fP option. +.TP +.BI \-\-fragment \ max +Enable internal datagram fragmentation so that no UDP datagrams are sent +which are larger than \fBmax\fP bytes. +.sp +The \fBmax\fP parameter is interpreted in the same way as the +\fB\-\-link\-mtu\fP parameter, i.e. the UDP packet size after encapsulation +overhead has been added in, but not including the UDP header itself. +.sp +The \fB\-\-fragment\fP option only makes sense when you are using the UDP +protocol (\fB\-\-proto udp\fP). +.sp +\fB\-\-fragment\fP adds 4 bytes of overhead per datagram. +.sp +See the \fB\-\-mssfix\fP option below for an important related option to +\fB\-\-fragment\fP\&. +.sp +It should also be noted that this option is not meant to replace UDP +fragmentation at the IP stack level. It is only meant as a last resort +when path MTU discovery is broken. Using this option is less efficient +than fixing path MTU discovery for your IP link and using native IP +fragmentation instead. +.sp +Having said that, there are circumstances where using OpenVPN\(aqs internal +fragmentation capability may be your only option, such as tunneling a +UDP multicast stream which requires fragmentation. +.TP +.BI \-\-keepalive \ args +A helper directive designed to simplify the expression of \fB\-\-ping\fP and +\fB\-\-ping\-restart\fP\&. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +keepalive interval timeout +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +This option can be used on both client and server side, but it is enough +to add this on the server side as it will push appropriate \fB\-\-ping\fP +and \fB\-\-ping\-restart\fP options to the client. If used on both server and +client, the values pushed from server will override the client local +values. +.sp +The \fBtimeout\fP argument will be twice as long on the server side. This +ensures that a timeout is detected on client side before the server side +drops the connection. +.sp +For example, \fB\-\-keepalive 10 60\fP expands as follows: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +if mode server: + ping 10 # Argument: interval + ping\-restart 120 # Argument: timeout*2 + push "ping 10" # Argument: interval + push "ping\-restart 60" # Argument: timeout +else + ping 10 # Argument: interval + ping\-restart 60 # Argument: timeout +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-link\-mtu \ n +Sets an upper bound on the size of UDP packets which are sent between +OpenVPN peers. \fIIt\(aqs best not to set this parameter unless you know what +you\(aqre doing.\fP +.TP +.BI \-\-local \ host +Local host name or IP address for bind. If specified, OpenVPN will bind +to this address only. If unspecified, OpenVPN will bind to all +interfaces. +.TP +.BI \-\-lport \ port +Set local TCP/UDP port number or name. Cannot be used together with +\fB\-\-nobind\fP option. +.TP +.BI \-\-mark \ value +Mark encrypted packets being sent with value. The mark value can be +matched in policy routing and packetfilter rules. This option is only +supported in Linux and does nothing on other operating systems. +.TP +.BI \-\-mode \ m +Set OpenVPN major mode. By default, OpenVPN runs in point\-to\-point mode +(\fBp2p\fP). OpenVPN 2.0 introduces a new mode (\fBserver\fP) which +implements a multi\-client server capability. +.TP +.BI \-\-mssfix \ max +Announce to TCP sessions running over the tunnel that they should limit +their send packet sizes such that after OpenVPN has encapsulated them, +the resulting UDP packet size that OpenVPN sends to its peer will not +exceed \fBmax\fP bytes. The default value is \fB1450\fP\&. +.sp +The \fBmax\fP parameter is interpreted in the same way as the +\fB\-\-link\-mtu\fP parameter, i.e. the UDP packet size after encapsulation +overhead has been added in, but not including the UDP header itself. +Resulting packet would be at most 28 bytes larger for IPv4 and 48 bytes +for IPv6 (20/40 bytes for IP header and 8 bytes for UDP header). Default +value of 1450 allows IPv4 packets to be transmitted over a link with MTU +1473 or higher without IP level fragmentation. +.sp +The \fB\-\-mssfix\fP option only makes sense when you are using the UDP +protocol for OpenVPN peer\-to\-peer communication, i.e. \fB\-\-proto udp\fP\&. +.sp +\fB\-\-mssfix\fP and \fB\-\-fragment\fP can be ideally used together, where +\fB\-\-mssfix\fP will try to keep TCP from needing packet fragmentation in +the first place, and if big packets come through anyhow (from protocols +other than TCP), \fB\-\-fragment\fP will internally fragment them. +.sp +Both \fB\-\-fragment\fP and \fB\-\-mssfix\fP are designed to work around cases +where Path MTU discovery is broken on the network path between OpenVPN +peers. +.sp +The usual symptom of such a breakdown is an OpenVPN connection which +successfully starts, but then stalls during active usage. +.sp +If \fB\-\-fragment\fP and \fB\-\-mssfix\fP are used together, \fB\-\-mssfix\fP will +take its default \fBmax\fP parameter from the \fB\-\-fragment max\fP option. +.sp +Therefore, one could lower the maximum UDP packet size to 1300 (a good +first try for solving MTU\-related connection problems) with the +following options: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +\-\-tun\-mtu 1500 \-\-fragment 1300 \-\-mssfix +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-mtu\-disc \ type +Should we do Path MTU discovery on TCP/UDP channel? Only supported on +OSes such as Linux that supports the necessary system call to set. +.sp +Valid types: +.sp +\fBno\fP Never send DF (Don\(aqt Fragment) frames +.sp +\fBmaybe\fP Use per\-route hints +.sp +\fByes\fP Always DF (Don\(aqt Fragment) +.TP +.B \-\-mtu\-test +To empirically measure MTU on connection startup, add the \fB\-\-mtu\-test\fP +option to your configuration. OpenVPN will send ping packets of various +sizes to the remote peer and measure the largest packets which were +successfully received. The \fB\-\-mtu\-test\fP process normally takes about 3 +minutes to complete. +.TP +.B \-\-nobind +Do not bind to local address and port. The IP stack will allocate a +dynamic port for returning packets. Since the value of the dynamic port +could not be known in advance by a peer, this option is only suitable +for peers which will be initiating connections by using the \-\-remote +option. +.TP +.B \-\-passtos +Set the TOS field of the tunnel packet to what the payload\(aqs TOS is. +.TP +.BI \-\-ping \ n +Ping remote over the TCP/UDP control channel if no packets have been +sent for at least \fBn\fP seconds (specify \fB\-\-ping\fP on both peers to +cause ping packets to be sent in both directions since OpenVPN ping +packets are not echoed like IP ping packets). When used in one of +OpenVPN\(aqs secure modes (where \fB\-\-secret\fP, \fB\-\-tls\-server\fP or +\fB\-\-tls\-client\fP is specified), the ping packet will be +cryptographically secure. +.sp +This option has two intended uses: +.INDENT 7.0 +.IP 1. 3 +Compatibility with stateful firewalls. The periodic ping will ensure +that a stateful firewall rule which allows OpenVPN UDP packets to +pass will not time out. +.IP 2. 3 +To provide a basis for the remote to test the existence of its peer +using the \fB\-\-ping\-exit\fP option. +.UNINDENT +.TP +.BI \-\-ping\-exit \ n +Causes OpenVPN to exit after \fBn\fP seconds pass without reception of a +ping or other packet from remote. This option can be combined with +\fB\-\-inactive\fP, \fB\-\-ping\fP and \fB\-\-ping\-exit\fP to create a two\-tiered +inactivity disconnect. +.sp +For example, +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +openvpn [options...] \-\-inactive 3600 \-\-ping 10 \-\-ping\-exit 60 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +when used on both peers will cause OpenVPN to exit within 60 seconds if +its peer disconnects, but will exit after one hour if no actual tunnel +data is exchanged. +.TP +.BI \-\-ping\-restart \ n +Similar to \fB\-\-ping\-exit\fP, but trigger a \fBSIGUSR1\fP restart after +\fBn\fP seconds pass without reception of a ping or other packet from +remote. +.sp +This option is useful in cases where the remote peer has a dynamic IP +address and a low\-TTL DNS name is used to track the IP address using a +service such as \fI\%http://dyndns.org/\fP + a dynamic DNS client such as +\fBddclient\fP\&. +.sp +If the peer cannot be reached, a restart will be triggered, causing the +hostname used with \fB\-\-remote\fP to be re\-resolved (if \fB\-\-resolv\-retry\fP +is also specified). +.sp +In server mode, \fB\-\-ping\-restart\fP, \fB\-\-inactive\fP or any other type of +internally generated signal will always be applied to individual client +instance objects, never to whole server itself. Note also in server mode +that any internally generated signal which would normally cause a +restart, will cause the deletion of the client instance object instead. +.sp +In client mode, the \fB\-\-ping\-restart\fP parameter is set to 120 seconds +by default. This default will hold until the client pulls a replacement +value from the server, based on the \fB\-\-keepalive\fP setting in the +server configuration. To disable the 120 second default, set +\fB\-\-ping\-restart 0\fP on the client. +.sp +See the signals section below for more information on \fBSIGUSR1\fP\&. +.sp +Note that the behavior of \fBSIGUSR1\fP can be modified by the +\fB\-\-persist\-tun\fP, \fB\-\-persist\-key\fP, \fB\-\-persist\-local\-ip\fP and +\fB\-\-persist\-remote\-ip\fP options. +.sp +Also note that \fB\-\-ping\-exit\fP and \fB\-\-ping\-restart\fP are mutually +exclusive and cannot be used together. +.TP +.B \-\-ping\-timer\-rem +Run the \fB\-\-ping\-exit\fP / \fB\-\-ping\-restart\fP timer only if we have a +remote address. Use this option if you are starting the daemon in listen +mode (i.e. without an explicit \fB\-\-remote\fP peer), and you don\(aqt want to +start clocking timeouts until a remote peer connects. +.TP +.BI \-\-proto \ p +Use protocol \fBp\fP for communicating with remote host. \fBp\fP can be +\fBudp\fP, \fBtcp\-client\fP, or \fBtcp\-server\fP\&. +.sp +The default protocol is \fBudp\fP when \fB\-\-proto\fP is not specified. +.sp +For UDP operation, \fB\-\-proto udp\fP should be specified on both peers. +.sp +For TCP operation, one peer must use \fB\-\-proto tcp\-server\fP and the +other must use \fB\-\-proto tcp\-client\fP\&. A peer started with +\fBtcp\-server\fP will wait indefinitely for an incoming connection. A peer +started with \fBtcp\-client\fP will attempt to connect, and if that fails, +will sleep for 5 seconds (adjustable via the \fB\-\-connect\-retry\fP option) +and try again infinite or up to N retries (adjustable via the +\fB\-\-connect\-retry\-max\fP option). Both TCP client and server will +simulate a SIGUSR1 restart signal if either side resets the connection. +.sp +OpenVPN is designed to operate optimally over UDP, but TCP capability is +provided for situations where UDP cannot be used. In comparison with +UDP, TCP will usually be somewhat less efficient and less robust when +used over unreliable or congested networks. +.sp +This article outlines some of problems with tunneling IP over TCP: +\fI\%http://sites.inka.de/sites/bigred/devel/tcp\-tcp.html\fP +.sp +There are certain cases, however, where using TCP may be advantageous +from a security and robustness perspective, such as tunneling non\-IP or +application\-level UDP protocols, or tunneling protocols which don\(aqt +possess a built\-in reliability layer. +.TP +.BI \-\-port \ port +TCP/UDP port number or port name for both local and remote (sets both +\fB\-\-lport\fP and \fB\-\-rport\fP options to given port). The current default +of 1194 represents the official IANA port number assignment for OpenVPN +and has been used since version 2.0\-beta17. Previous versions used port +5000 as the default. +.TP +.BI \-\-rport \ port +Set TCP/UDP port number or name used by the \fB\-\-remote\fP option. The +port can also be set directly using the \fB\-\-remote\fP option. +.TP +.BI \-\-replay\-window \ args +Modify the replay protection sliding\-window size and time window. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +replay\-window n [t] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Use a replay protection sliding\-window of size \fBn\fP and a time window +of \fBt\fP seconds. +.sp +By default \fBn\fP is 64 (the IPSec default) and \fBt\fP is 15 seconds. +.sp +This option is only relevant in UDP mode, i.e. when either \fB\-\-proto +udp\fP is specified, or no \fB\-\-proto\fP option is specified. +.sp +When OpenVPN tunnels IP packets over UDP, there is the possibility that +packets might be dropped or delivered out of order. Because OpenVPN, +like IPSec, is emulating the physical network layer, it will accept an +out\-of\-order packet sequence, and will deliver such packets in the same +order they were received to the TCP/IP protocol stack, provided they +satisfy several constraints. +.INDENT 7.0 +.IP a. 3 +The packet cannot be a replay (unless \fB\-\-no\-replay\fP is +specified, which disables replay protection altogether). +.IP b. 3 +If a packet arrives out of order, it will only be accepted if +the difference between its sequence number and the highest sequence +number received so far is less than \fBn\fP\&. +.IP c. 3 +If a packet arrives out of order, it will only be accepted if it +arrives no later than \fBt\fP seconds after any packet containing a higher +sequence number. +.UNINDENT +.sp +If you are using a network link with a large pipeline (meaning that the +product of bandwidth and latency is high), you may want to use a larger +value for \fBn\fP\&. Satellite links in particular often require this. +.sp +If you run OpenVPN at \fB\-\-verb 4\fP, you will see the message +"Replay\-window backtrack occurred [x]" every time the maximum sequence +number backtrack seen thus far increases. This can be used to calibrate +\fBn\fP\&. +.sp +There is some controversy on the appropriate method of handling packet +reordering at the security layer. +.sp +Namely, to what extent should the security layer protect the +encapsulated protocol from attacks which masquerade as the kinds of +normal packet loss and reordering that occur over IP networks? +.sp +The IPSec and OpenVPN approach is to allow packet reordering within a +certain fixed sequence number window. +.sp +OpenVPN adds to the IPSec model by limiting the window size in time as +well as sequence space. +.sp +OpenVPN also adds TCP transport as an option (not offered by IPSec) in +which case OpenVPN can adopt a very strict attitude towards message +deletion and reordering: Don\(aqt allow it. Since TCP guarantees +reliability, any packet loss or reordering event can be assumed to be an +attack. +.sp +In this sense, it could be argued that TCP tunnel transport is preferred +when tunneling non\-IP or UDP application protocols which might be +vulnerable to a message deletion or reordering attack which falls within +the normal operational parameters of IP networks. +.sp +So I would make the statement that one should never tunnel a non\-IP +protocol or UDP application protocol over UDP, if the protocol might be +vulnerable to a message deletion or reordering attack that falls within +the normal operating parameters of what is to be expected from the +physical IP layer. The problem is easily fixed by simply using TCP as +the VPN transport layer. +.TP +.BI \-\-replay\-persist \ file +Persist replay\-protection state across sessions using \fBfile\fP to save +and reload the state. +.sp +This option will strengthen protection against replay attacks, +especially when you are using OpenVPN in a dynamic context (such as with +\fB\-\-inetd\fP) when OpenVPN sessions are frequently started and stopped. +.sp +This option will keep a disk copy of the current replay protection state +(i.e. the most recent packet timestamp and sequence number received from +the remote peer), so that if an OpenVPN session is stopped and +restarted, it will reject any replays of packets which were already +received by the prior session. +.sp +This option only makes sense when replay protection is enabled (the +default) and you are using either \fB\-\-secret\fP (shared\-secret key mode) +or TLS mode with \fB\-\-tls\-auth\fP\&. +.TP +.BI \-\-socket\-flags \ flags +Apply the given flags to the OpenVPN transport socket. Currently, only +\fBTCP_NODELAY\fP is supported. +.sp +The \fBTCP_NODELAY\fP socket flag is useful in TCP mode, and causes the +kernel to send tunnel packets immediately over the TCP connection without +trying to group several smaller packets into a larger packet. This can +result in a considerably improvement in latency. +.sp +This option is pushable from server to client, and should be used on +both client and server for maximum effect. +.TP +.B \-\-tcp\-nodelay +This macro sets the \fBTCP_NODELAY\fP socket flag on the server as well +as pushes it to connecting clients. The \fBTCP_NODELAY\fP flag disables +the Nagle algorithm on TCP sockets causing packets to be transmitted +immediately with low latency, rather than waiting a short period of time +in order to aggregate several packets into a larger containing packet. +In VPN applications over TCP, \fBTCP_NODELAY\fP is generally a good +latency optimization. +.sp +The macro expands as follows: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +if mode server: + socket\-flags TCP_NODELAY + push "socket\-flags TCP_NODELAY" +.ft P +.fi +.UNINDENT +.UNINDENT +.UNINDENT +.SS Virtual Network Adapter (VPN interface) +.sp +Options in this section relates to configuration of the virtual tun/tap +network interface, including setting the VPN IP address and network +routing. +.INDENT 0.0 +.TP +.BI \-\-bind\-dev \ device +(Linux only) Set \fBdevice\fP to bind the server socket to a +\fI\%Virtual Routing and Forwarding\fP device +.TP +.B \-\-block\-ipv6 +On the client, instead of sending IPv6 packets over the VPN tunnel, all +IPv6 packets are answered with an ICMPv6 no route host message. On the +server, all IPv6 packets from clients are answered with an ICMPv6 no +route to host message. This options is intended for cases when IPv6 +should be blocked and other options are not available. \fB\-\-block\-ipv6\fP +will use the remote IPv6 as source address of the ICMPv6 packets if set, +otherwise will use \fBfe80::7\fP as source address. +.sp +For this option to make sense you actually have to route traffic to the +tun interface. The following example config block would send all IPv6 +traffic to OpenVPN and answer all requests with no route to host, +effectively blocking IPv6. +.INDENT 7.0 +.TP +.B \fBClient config\fP +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +\-\-ifconfig\-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1 +\-\-redirect\-gateway ipv6 +\-\-block\-ipv6 +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.B \fBServer config\fP +Push a "valid" ipv6 config to the client and block on the server +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +\-\-push "ifconfig\-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1" +\-\-push "redirect\-gateway ipv6" +\-\-block\-ipv6 +.ft P +.fi +.UNINDENT +.UNINDENT +.UNINDENT +.TP +.BI \-\-dev \ device +TUN/TAP virtual network device which can be \fBtunX\fP, \fBtapX\fP, +\fBnull\fP or an arbitrary name string (\fBX\fP can be omitted for +a dynamic device.) +.sp +See examples section below for an example on setting up a TUN device. +.sp +You must use either tun devices on both ends of the connection or tap +devices on both ends. You cannot mix them, as they represent different +underlying network layers: +.INDENT 7.0 +.TP +.B \fBtun\fP +devices encapsulate IPv4 or IPv6 (OSI Layer 3) +.TP +.B \fBtap\fP +devices encapsulate Ethernet 802.3 (OSI Layer 2). +.UNINDENT +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +dev tun2 +dev tap4 +dev ovpn +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +When the device name starts with \fBtun\fP or \fBtap\fP, the device +type is extracted automatically. Otherwise the \fB\-\-dev\-type\fP option +needs to be added as well. +.TP +.BI \-\-dev\-node \ node +Explicitly set the device node rather than using \fB/dev/net/tun\fP, +\fB/dev/tun\fP, \fB/dev/tap\fP, etc. If OpenVPN cannot figure out +whether \fBnode\fP is a TUN or TAP device based on the name, you should +also specify \fB\-\-dev\-type tun\fP or \fB\-\-dev\-type tap\fP\&. +.sp +Under Mac OS X this option can be used to specify the default tun +implementation. Using \fB\-\-dev\-node utun\fP forces usage of the native +Darwin tun kernel support. Use \fB\-\-dev\-node utunN\fP to select a specific +utun instance. To force using the \fBtun.kext\fP (\fB/dev/tunX\fP) +use \fB\-\-dev\-node tun\fP\&. When not specifying a \fB\-\-dev\-node\fP option +openvpn will first try to open utun, and fall back to tun.kext. +.sp +On Windows systems, select the TAP\-Win32 adapter which is named \fBnode\fP +in the Network Connections Control Panel or the raw GUID of the adapter +enclosed by braces. The \fB\-\-show\-adapters\fP option under Windows can +also be used to enumerate all available TAP\-Win32 adapters and will show +both the network connections control panel name and the GUID for each +TAP\-Win32 adapter. +.TP +.BI \-\-dev\-type \ device\-type +Which device type are we using? \fBdevice\-type\fP should be \fBtun\fP +(OSI Layer 3) or \fBtap\fP (OSI Layer 2). Use this option only if +the TUN/TAP device used with \fB\-\-dev\fP does not begin with \fBtun\fP +or \fBtap\fP\&. +.TP +.BI \-\-dhcp\-option \ args +Set additional network parameters on supported platforms. May be specified +on the client or pushed from the server. On Windows these options are +handled by the \fBtap\-windows6\fP driver by default or directly by OpenVPN +if dhcp is disabled or the \fBwintun\fP driver is in use. The +\fBOpenVPN for Android\fP client also handles them internally. +.sp +On all other platforms these options are only saved in the client\(aqs +environment under the name \fBforeign_options_{n}\fP before the +\fB\-\-up\fP script is called. A plugin or an \fB\-\-up\fP script must be used to +pick up and interpret these as required. Many Linux distributions include +such scripts and some third\-party user interfaces such as tunnelblick also +come with scripts that process these options. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +dhcp\-options type [parm] +.ft P +.fi +.UNINDENT +.UNINDENT +.INDENT 7.0 +.TP +.B \fBDOMAIN\fP \fBname\fP +Set Connection\-specific DNS Suffix to \fBname\fP\&. +.TP +.B \fBDOMAIN\-SEARCH\fP \fBname\fP +Add \fBname\fP to the domain search list. +Repeat this option to add more entries. Up to +10 domains are supported. +.TP +.B \fBDNS\fP \fBaddress\fP +Set primary domain name server IPv4 or IPv6 address. +Repeat this option to set secondary DNS server addresses. +.sp +Note: DNS IPv6 servers are currently set using netsh (the existing +DHCP code can only do IPv4 DHCP, and that protocol only permits +IPv4 addresses anywhere). The option will be put into the +environment, so an \fB\-\-up\fP script could act upon it if needed. +.TP +.B \fBWINS\fP \fBaddress\fP +Set primary WINS server address (NetBIOS over TCP/IP Name Server). +Repeat this option to set secondary WINS server addresses. +.TP +.B \fBNBDD\fP \fBaddress\fP +Set primary NBDD server address (NetBIOS over TCP/IP Datagram +Distribution Server). Repeat this option to set secondary NBDD +server addresses. +.TP +.B \fBNTP\fP \fBaddress\fP +Set primary NTP server address (Network Time Protocol). +Repeat this option to set secondary NTP server addresses. +.TP +.B \fBNBT\fP \fBtype\fP +Set NetBIOS over TCP/IP Node type. Possible options: +.INDENT 7.0 +.TP +.B \fB1\fP +b\-node (broadcasts) +.TP +.B \fB2\fP +p\-node (point\-to\-point name queries to a WINS server) +.TP +.B \fB4\fP +m\-node (broadcast then query name server) +.TP +.B \fB8\fP +h\-node (query name server, then broadcast). +.UNINDENT +.TP +.B \fBNBS\fP \fBscope\-id\fP +Set NetBIOS over TCP/IP Scope. A NetBIOS Scope ID provides an +extended naming service for the NetBIOS over TCP/IP (Known as NBT) +module. The primary purpose of a NetBIOS scope ID is to isolate +NetBIOS traffic on a single network to only those nodes with the +same NetBIOS scope ID. The NetBIOS scope ID is a character string +that is appended to the NetBIOS name. The NetBIOS scope ID on two +hosts must match, or the two hosts will not be able to communicate. +The NetBIOS Scope ID also allows computers to use the same computer +name, as they have different scope IDs. The Scope ID becomes a part +of the NetBIOS name, making the name unique. (This description of +NetBIOS scopes courtesy of \fI\%NeonSurge@abyss.com\fP) +.TP +.B \fBDISABLE\-NBT\fP +Disable Netbios\-over\-TCP/IP. +.UNINDENT +.TP +.BI \-\-ifconfig \ args +Set TUN/TAP adapter parameters. It requires the \fIIP address\fP of the local +VPN endpoint. For TUN devices in point\-to\-point mode, the next argument +must be the VPN IP address of the remote VPN endpoint. For TAP devices, +or TUN devices used with \fB\-\-topology subnet\fP, the second argument +is the subnet mask of the virtual network segment which is being created +or connected to. +.sp +For TUN devices, which facilitate virtual point\-to\-point IP connections +(when used in \fB\-\-topology net30\fP or \fBp2p\fP mode), the proper usage of +\fB\-\-ifconfig\fP is to use two private IP addresses which are not a member +of any existing subnet which is in use. The IP addresses may be +consecutive and should have their order reversed on the remote peer. +After the VPN is established, by pinging \fBrn\fP, you will be pinging +across the VPN. +.sp +For TAP devices, which provide the ability to create virtual ethernet +segments, or TUN devices in \fB\-\-topology subnet\fP mode (which create +virtual "multipoint networks"), \fB\-\-ifconfig\fP is used to set an IP +address and subnet mask just as a physical ethernet adapter would be +similarly configured. If you are attempting to connect to a remote +ethernet bridge, the IP address and subnet should be set to values which +would be valid on the the bridged ethernet segment (note also that DHCP +can be used for the same purpose). +.sp +This option, while primarily a proxy for the \fBifconfig\fP(8) command, +is designed to simplify TUN/TAP tunnel configuration by providing a +standard interface to the different ifconfig implementations on +different platforms. +.sp +\fB\-\-ifconfig\fP parameters which are IP addresses can also be specified +as a DNS or /etc/hosts file resolvable name. +.sp +For TAP devices, \fB\-\-ifconfig\fP should not be used if the TAP interface +will be getting an IP address lease from a DHCP server. +.sp +Examples: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +# tun device in net30/p2p mode +ifconfig 10.8.0.2 10.8.0.1 + +# tun/tap device in subnet mode +ifconfig 10.8.0.2 255.255.255.0 +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-ifconfig\-ipv6 \ args +Configure an IPv6 address on the \fItun\fP device. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +ifconfig\-ipv6 ipv6addr/bits [ipv6remote] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The \fBipv6addr/bits\fP argument is the IPv6 address to use. The +second parameter is used as route target for \fB\-\-route\-ipv6\fP if no +gateway is specified. +.sp +The \fB\-\-topology\fP option has no influence with \fB\-\-ifconfig\-ipv6\fP +.TP +.B \-\-ifconfig\-noexec +Don\(aqt actually execute ifconfig/netsh commands, instead pass +\fB\-\-ifconfig\fP parameters to scripts using environmental variables. +.TP +.B \-\-ifconfig\-nowarn +Don\(aqt output an options consistency check warning if the \fB\-\-ifconfig\fP +option on this side of the connection doesn\(aqt match the remote side. +This is useful when you want to retain the overall benefits of the +options consistency check (also see \fB\-\-disable\-occ\fP option) while only +disabling the ifconfig component of the check. +.sp +For example, if you have a configuration where the local host uses +\fB\-\-ifconfig\fP but the remote host does not, use \fB\-\-ifconfig\-nowarn\fP +on the local host. +.sp +This option will also silence warnings about potential address conflicts +which occasionally annoy more experienced users by triggering "false +positive" warnings. +.TP +.BI \-\-lladdr \ address +Specify the link layer address, more commonly known as the MAC address. +Only applied to TAP devices. +.TP +.B \-\-persist\-tun +Don\(aqt close and reopen TUN/TAP device or run up/down scripts across +\fBSIGUSR1\fP or \fB\-\-ping\-restart\fP restarts. +.sp +\fBSIGUSR1\fP is a restart signal similar to \fBSIGHUP\fP, but which +offers finer\-grained control over reset options. +.TP +.BI \-\-redirect\-gateway \ flags +Automatically execute routing commands to cause all outgoing IP traffic +to be redirected over the VPN. This is a client\-side option. +.sp +This option performs three steps: +.INDENT 7.0 +.IP 1. 3 +Create a static route for the \fB\-\-remote\fP address which +forwards to the pre\-existing default gateway. This is done so that +\fB(3)\fP will not create a routing loop. +.IP 2. 3 +Delete the default gateway route. +.IP 3. 3 +Set the new default gateway to be the VPN endpoint address +(derived either from \fB\-\-route\-gateway\fP or the second parameter to +\fB\-\-ifconfig\fP when \fB\-\-dev tun\fP is specified). +.UNINDENT +.sp +When the tunnel is torn down, all of the above steps are reversed so +that the original default route is restored. +.sp +Option flags: +.INDENT 7.0 +.TP +.B \fBlocal\fP +Add the \fBlocal\fP flag if both OpenVPN peers are directly +connected via a common subnet, such as with wireless. The +\fBlocal\fP flag will cause step \fB(1)\fP above to be omitted. +.TP +.B \fBautolocal\fP +Try to automatically determine whether to enable \fBlocal\fP +flag above. +.TP +.B \fBdef1\fP +Use this flag to override the default gateway by using +\fB0.0.0.0/1\fP and \fB128.0.0.0/1\fP rather than +\fB0.0.0.0/0\fP\&. This has the benefit of overriding but not +wiping out the original default gateway. +.TP +.B \fBbypass\-dhcp\fP +Add a direct route to the DHCP server (if it is non\-local) which +bypasses the tunnel (Available on Windows clients, may not be +available on non\-Windows clients). +.TP +.B \fBbypass\-dns\fP +Add a direct route to the DNS server(s) (if they are non\-local) +which bypasses the tunnel (Available on Windows clients, may +not be available on non\-Windows clients). +.TP +.B \fBblock\-local\fP +Block access to local LAN when the tunnel is active, except for +the LAN gateway itself. This is accomplished by routing the local +LAN (except for the LAN gateway address) into the tunnel. +.TP +.B \fBipv6\fP +Redirect IPv6 routing into the tunnel. This works similar to +the \fBdef1\fP flag, that is, more specific IPv6 routes are added +(\fB2000::/4\fP, \fB3000::/4\fP), covering the whole IPv6 +unicast space. +.TP +.B \fB!ipv4\fP +Do not redirect IPv4 traffic \- typically used in the flag pair +\fBipv6 !ipv4\fP to redirect IPv6\-only. +.UNINDENT +.TP +.BI \-\-redirect\-private \ flags +Like \fB\-\-redirect\-gateway\fP, but omit actually changing the default gateway. +Useful when pushing private subnets. +.TP +.BI \-\-route \ args +Add route to routing table after connection is established. Multiple +routes can be specified. Routes will be automatically torn down in +reverse order prior to TUN/TAP device close. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +route network/IP +route network/IP netmask +route network/IP netmask gateway +route network/IP netmask gateway metric +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +This option is intended as a convenience proxy for the \fBroute\fP(8) +shell command, while at the same time providing portable semantics +across OpenVPN\(aqs platform space. +.INDENT 7.0 +.TP +.B \fBnetmask\fP +defaults to \fB255.255.255.255\fP when not given +.TP +.B \fBgateway\fP +default taken from \fB\-\-route\-gateway\fP or the second +parameter to \fB\-\-ifconfig\fP when \fB\-\-dev tun\fP is specified. +.TP +.B \fBmetric\fP +default taken from \fB\-\-route\-metric\fP if set, otherwise \fB0\fP\&. +.UNINDENT +.sp +The default can be specified by leaving an option blank or setting it to +\fBdefault\fP\&. +.sp +The \fBnetwork\fP and \fBgateway\fP parameters can also be specified as a +DNS or \fB/etc/hosts\fP file resolvable name, or as one of three special +keywords: +.INDENT 7.0 +.TP +.B \fBvpn_gateway\fP +The remote VPN endpoint address (derived either from +\fB\-\-route\-gateway\fP or the second parameter to \fB\-\-ifconfig\fP +when \fB\-\-dev tun\fP is specified). +.TP +.B \fBnet_gateway\fP +The pre\-existing IP default gateway, read from the +routing table (not supported on all OSes). +.TP +.B \fBremote_host\fP +The \fB\-\-remote\fP address if OpenVPN is being run in +client mode, and is undefined in server mode. +.UNINDENT +.TP +.BI \-\-route\-delay \ args +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +route\-delay +route\-delay n +route\-delay n m +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Delay \fBn\fP seconds (default \fB0\fP) after connection establishment, +before adding routes. If \fBn\fP is \fB0\fP, routes will be added +immediately upon connection establishment. If \fB\-\-route\-delay\fP is +omitted, routes will be added immediately after TUN/TAP device open and +\fB\-\-up\fP script execution, before any \fB\-\-user\fP or \fB\-\-group\fP privilege +downgrade (or \fB\-\-chroot\fP execution.) +.sp +This option is designed to be useful in scenarios where DHCP is used to +set tap adapter addresses. The delay will give the DHCP handshake time +to complete before routes are added. +.sp +On Windows, \fB\-\-route\-delay\fP tries to be more intelligent by waiting +\fBw\fP seconds (default \fB30\fP by default) for the TAP\-Win32 adapter +to come up before adding routes. +.TP +.BI \-\-route\-ipv6 \ args +Setup IPv6 routing in the system to send the specified IPv6 network into +OpenVPN\(aqs \fItun\fP\&. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +route\-ipv6 ipv6addr/bits [gateway] [metric] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The gateway parameter is only used for IPv6 routes across \fItap\fP devices, +and if missing, the \fBipv6remote\fP field from \fB\-\-ifconfig\-ipv6\fP or +\fB\-\-route\-ipv6\-gateway\fP is used. +.TP +.BI \-\-route\-gateway \ arg +Specify a default \fIgateway\fP for use with \fB\-\-route\fP\&. +.sp +If \fBdhcp\fP is specified as the parameter, the gateway address will +be extracted from a DHCP negotiation with the OpenVPN server\-side LAN. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +route\-gateway gateway +route\-gateway dhcp +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.BI \-\-route\-ipv6\-gateway \ gw +Specify a default gateway \fBgw\fP for use with \fB\-\-route\-ipv6\fP\&. +.TP +.BI \-\-route\-metric \ m +Specify a default metric \fBm\fP for use with \fB\-\-route\fP\&. +.TP +.B \-\-route\-noexec +Don\(aqt add or remove routes automatically. Instead pass routes to +\fB\-\-route\-up\fP script using environmental variables. +.TP +.B \-\-route\-nopull +When used with \fB\-\-client\fP or \fB\-\-pull\fP, accept options pushed by +server EXCEPT for routes, block\-outside\-dns and dhcp options like DNS +servers. +.sp +When used on the client, this option effectively bars the server from +adding routes to the client\(aqs routing table, however note that this +option still allows the server to set the TCP/IP properties of the +client\(aqs TUN/TAP interface. +.TP +.BI \-\-topology \ mode +Configure virtual addressing topology when running in \fB\-\-dev tun\fP +mode. This directive has no meaning in \fB\-\-dev tap\fP mode, which always +uses a \fBsubnet\fP topology. +.sp +If you set this directive on the server, the \fB\-\-server\fP and +\fB\-\-server\-bridge\fP directives will automatically push your chosen +topology setting to clients as well. This directive can also be manually +pushed to clients. Like the \fB\-\-dev\fP directive, this directive must +always be compatible between client and server. +.sp +\fBmode\fP can be one of: +.INDENT 7.0 +.TP +.B \fBnet30\fP +Use a point\-to\-point topology, by allocating one /30 subnet +per client. This is designed to allow point\-to\-point semantics when some +or all of the connecting clients might be Windows systems. This is the +default on OpenVPN 2.0. +.TP +.B \fBp2p\fP +Use a point\-to\-point topology where the remote endpoint of +the client\(aqs tun interface always points to the local endpoint of the +server\(aqs tun interface. This mode allocates a single IP address per +connecting client. Only use when none of the connecting clients are +Windows systems. +.TP +.B \fBsubnet\fP +Use a subnet rather than a point\-to\-point topology by +configuring the tun interface with a local IP address and subnet mask, +similar to the topology used in \fB\-\-dev tap\fP and ethernet bridging +mode. This mode allocates a single IP address per connecting client and +works on Windows as well. Only available when server and clients are +OpenVPN 2.1 or higher, or OpenVPN 2.0.x which has been manually patched +with the \fB\-\-topology\fP directive code. When used on Windows, requires +version 8.2 or higher of the TAP\-Win32 driver. When used on *nix, +requires that the tun driver supports an \fBifconfig\fP(8) command which +sets a subnet instead of a remote endpoint IP address. +.UNINDENT +.sp +\fINote:\fP Using \fB\-\-topology subnet\fP changes the interpretation of the +arguments of \fB\-\-ifconfig\fP to mean "address netmask", no longer "local +remote". +.TP +.BI \-\-tun\-mtu \ n +Take the TUN device MTU to be \fBn\fP and derive the link MTU from it +(default \fB1500\fP). In most cases, you will probably want to leave +this parameter set to its default value. +.sp +The MTU (Maximum Transmission Units) is the maximum datagram size in +bytes that can be sent unfragmented over a particular network path. +OpenVPN requires that packets on the control and data channels be sent +unfragmented. +.sp +MTU problems often manifest themselves as connections which hang during +periods of active usage. +.sp +It\(aqs best to use the \fB\-\-fragment\fP and/or \fB\-\-mssfix\fP options to deal +with MTU sizing issues. +.TP +.BI \-\-tun\-mtu\-extra \ n +Assume that the TUN/TAP device might return as many as \fBn\fP bytes more +than the \fB\-\-tun\-mtu\fP size on read. This parameter defaults to 0, which +is sufficient for most TUN devices. TAP devices may introduce additional +overhead in excess of the MTU size, and a setting of 32 is the default +when TAP devices are used. This parameter only controls internal OpenVPN +buffer sizing, so there is no transmission overhead associated with +using a larger value. +.UNINDENT +.SS TUN/TAP standalone operations +.sp +These two standalone operations will require \fB\-\-dev\fP and optionally +\fB\-\-user\fP and/or \fB\-\-group\fP\&. +.INDENT 0.0 +.TP +.B \-\-mktun +(Standalone) Create a persistent tunnel on platforms which support them +such as Linux. Normally TUN/TAP tunnels exist only for the period of +time that an application has them open. This option takes advantage of +the TUN/TAP driver\(aqs ability to build persistent tunnels that live +through multiple instantiations of OpenVPN and die only when they are +deleted or the machine is rebooted. +.sp +One of the advantages of persistent tunnels is that they eliminate the +need for separate \fB\-\-up\fP and \fB\-\-down\fP scripts to run the appropriate +\fBifconfig\fP(8) and \fBroute\fP(8) commands. These commands can be +placed in the the same shell script which starts or terminates an +OpenVPN session. +.sp +Another advantage is that open connections through the TUN/TAP\-based +tunnel will not be reset if the OpenVPN peer restarts. This can be +useful to provide uninterrupted connectivity through the tunnel in the +event of a DHCP reset of the peer\(aqs public IP address (see the +\fB\-\-ipchange\fP option above). +.sp +One disadvantage of persistent tunnels is that it is harder to +automatically configure their MTU value (see \fB\-\-link\-mtu\fP and +\fB\-\-tun\-mtu\fP above). +.sp +On some platforms such as Windows, TAP\-Win32 tunnels are persistent by +default. +.TP +.B \-\-rmtun +(Standalone) Remove a persistent tunnel. +.UNINDENT +.SS Virtual Routing and Forwarding +.sp +Options in this section relates to configuration of virtual routing and +forwarding in combination with the underlying operating system. +.sp +As of today this is only supported on Linux, a kernel >= 4.9 is +recommended. +.sp +This could come in handy when for example the external network should be +only used as a means to connect to some VPN endpoints and all regular +traffic should only be routed through any tunnel(s). This could be +achieved by setting up a VRF and configuring the interface connected to +the external network to be part of the VRF. The examples below will cover +this setup. +.sp +Another option would be to put the tun/tap interface into a VRF. This could +be done by an up\-script which uses the \fBip link set\fP command shown +below. +.SS VRF setup with iproute2 +.sp +Create VRF \fBvrf_external\fP and map it to routing table \fB1023\fP +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +ip link add vrf_external type vrf table 1023 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Move \fBeth0\fP into \fBvrf_external\fP +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +ip link set master vrf_external dev eth0 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Any prefixes configured on \fBeth0\fP will be moved from the :code\(gamain\(ga +routing table into routing table \fI1023\fP +.SS VRF setup with ifupdown +.sp +For Debian based Distributions \fBifupdown2\fP provides an almost drop\-in +replacement for \fBifupdown\fP including VRFs and other features. +A configuration for an interface \fBeth0\fP being part of VRF +code:\fIvrf_external\fP could look like this: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +auto eth0 +iface eth0 + address 192.0.2.42/24 + address 2001:db8:08:15::42/64 + gateway 192.0.2.1 + gateway 2001:db8:08:15::1 + vrf vrf_external + +auto vrf_external +iface vrf_external + vrf\-table 1023 +.ft P +.fi +.UNINDENT +.UNINDENT +.SS OpenVPN configuration +.sp +The OpenVPN configuration needs to contain this line: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +bind\-dev vrf_external +.ft P +.fi +.UNINDENT +.UNINDENT +.SS Further reading +.sp +Wikipedia has nice page one VRFs: \fI\%https://en.wikipedia.org/wiki/Virtual_routing_and_forwarding\fP +.sp +This talk from the Network Track of FrOSCon 2018 provides an overview about +advanced layer 2 and layer 3 features of Linux +.INDENT 0.0 +.INDENT 3.5 +.INDENT 0.0 +.IP \(bu 2 +Slides: \fI\%https://www.slideshare.net/BarbarossaTM/l2l3\-fr\-fortgeschrittene\-helle\-und\-dunkle\-magie\-im\-linuxnetzwerkstack\fP +.IP \(bu 2 +Video (german): \fI\%https://media.ccc.de/v/froscon2018\-2247\-l2_l3_fur_fortgeschrittene_\-_helle_und_dunkle_magie_im_linux\-netzwerkstack\fP +.UNINDENT +.UNINDENT +.UNINDENT +.SH SCRIPTING INTEGRATION +.sp +OpenVPN can execute external scripts in various phases of the lifetime of +the OpenVPN process. +.SS Script Order of Execution +.INDENT 0.0 +.IP 1. 4 +\fB\-\-up\fP +.sp +Executed after TCP/UDP socket bind and TUN/TAP open. +.IP 2. 4 +\fB\-\-tls\-verify\fP +.sp +Executed when we have a still untrusted remote peer. +.IP 3. 4 +\fB\-\-ipchange\fP +.sp +Executed after connection authentication, or remote IP address change. +.IP 4. 4 +\fB\-\-client\-connect\fP +.sp +Executed in \fB\-\-mode server\fP mode immediately after client +authentication. +.IP 5. 4 +\fB\-\-route\-up\fP +.sp +Executed after connection authentication, either immediately after, or +some number of seconds after as defined by the \fB\-\-route\-delay\fP option. +.IP 6. 4 +\fB\-\-route\-pre\-down\fP +.sp +Executed right before the routes are removed. +.IP 7. 4 +\fB\-\-client\-disconnect\fP +.sp +Executed in \fB\-\-mode server\fP mode on client instance shutdown. +.IP 8. 4 +\fB\-\-down\fP +.sp +Executed after TCP/UDP and TUN/TAP close. +.IP 9. 4 +\fB\-\-learn\-address\fP +.sp +Executed in \fB\-\-mode server\fP mode whenever an IPv4 address/route or MAC +address is added to OpenVPN\(aqs internal routing table. +.IP 10. 4 +\fB\-\-auth\-user\-pass\-verify\fP +.sp +Executed in \fB\-\-mode server\fP mode on new client connections, when the +client is still untrusted. +.UNINDENT +.SS SCRIPT HOOKS +.INDENT 0.0 +.TP +.BI \-\-auth\-user\-pass\-verify \ args +Require the client to provide a username/password (possibly in addition +to a client certificate) for authentication. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +auth\-user\-pass\-verify cmd method +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +OpenVPN will run command \fBcmd\fP to validate the username/password +provided by the client. +.sp +\fBcmd\fP consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single\- or +double\-quoted and/or escaped using a backslash, and should be separated +by one or more spaces. +.sp +If \fBmethod\fP is set to \fBvia\-env\fP, OpenVPN will call \fBscript\fP +with the environmental variables \fBusername\fP and \fBpassword\fP +set to the username/password strings provided by the client. \fIBeware\fP +that this method is insecure on some platforms which make the environment +of a process publicly visible to other unprivileged processes. +.sp +If \fBmethod\fP is set to \fBvia\-file\fP, OpenVPN will write the username +and password to the first two lines of a temporary file. The filename +will be passed as an argument to \fBscript\fP, and the file will be +automatically deleted by OpenVPN after the script returns. The location +of the temporary file is controlled by the \fB\-\-tmp\-dir\fP option, and +will default to the current directory if unspecified. For security, +consider setting \fB\-\-tmp\-dir\fP to a volatile storage medium such as +\fB/dev/shm\fP (if available) to prevent the username/password file +from touching the hard drive. +.sp +The script should examine the username and password, returning a success +exit code (\fB0\fP) if the client\(aqs authentication request is to be +accepted, or a failure code (\fB1\fP) to reject the client. +.sp +This directive is designed to enable a plugin\-style interface for +extending OpenVPN\(aqs authentication capabilities. +.sp +To protect against a client passing a maliciously formed username or +password string, the username string must consist only of these +characters: alphanumeric, underbar (\(aq\fB_\fP\(aq), dash (\(aq\fB\-\fP\(aq), +dot (\(aq\fB\&.\fP\(aq), or at (\(aq\fB@\fP\(aq). The password string can consist +of any printable characters except for CR or LF. Any illegal characters +in either the username or password string will be converted to +underbar (\(aq\fB_\fP\(aq). +.sp +Care must be taken by any user\-defined scripts to avoid creating a +security vulnerability in the way that these strings are handled. Never +use these strings in such a way that they might be escaped or evaluated +by a shell interpreter. +.sp +For a sample script that performs PAM authentication, see +\fBsample\-scripts/auth\-pam.pl\fP in the OpenVPN source distribution. +.TP +.BI \-\-client\-connect \ cmd +Run command \fBcmd\fP on client connection. +.sp +\fBcmd\fP consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single\- or +double\-quoted and/or escaped using a backslash, and should be separated +by one or more spaces. +.sp +The command is passed the common name and IP address of the +just\-authenticated client as environmental variables (see environmental +variable section below). The command is also passed the pathname of a +freshly created temporary file as the last argument (after any arguments +specified in \fBcmd\fP ), to be used by the command to pass dynamically +generated config file directives back to OpenVPN. +.sp +If the script wants to generate a dynamic config file to be applied on +the server when the client connects, it should write it to the file +named by the last argument. +.sp +See the \fB\-\-client\-config\-dir\fP option below for options which can be +legally used in a dynamically generated config file. +.sp +Note that the return value of \fBscript\fP is significant. If \fBscript\fP +returns a non\-zero error status, it will cause the client to be +disconnected. +.sp +If a \fB\-\-client\-connect\fP wants to defer the generating of the +configuration then the script needs to use the +\fBclient_connect_deferred_file\fP and +\fBclient_connect_config_file\fP environment variables, and write +status accordingly into these files. See the \fI\%Environmental Variables\fP +section for more details. +.TP +.BI \-\-client\-disconnect \ cmd +Like \fB\-\-client\-connect\fP but called on client instance shutdown. Will +not be called unless the \fB\-\-client\-connect\fP script and plugins (if +defined) were previously called on this instance with successful (0) +status returns. +.sp +The exception to this rule is if the \fB\-\-client\-disconnect\fP command or +plugins are cascaded, and at least one client\-connect function +succeeded, then ALL of the client\-disconnect functions for scripts and +plugins will be called on client instance object deletion, even in cases +where some of the related client\-connect functions returned an error +status. +.sp +The \fB\-\-client\-disconnect\fP command is passed the same pathname as the +corresponding \fB\-\-client\-connect\fP command as its last argument (after +any arguments specified in \fBcmd\fP). +.TP +.BI \-\-down \ cmd +Run command \fBcmd\fP after TUN/TAP device close (post \fB\-\-user\fP UID +change and/or \fB\-\-chroot\fP ). \fBcmd\fP consists of a path to script (or +executable program), optionally followed by arguments. The path and +arguments may be single\- or double\-quoted and/or escaped using a +backslash, and should be separated by one or more spaces. +.sp +Called with the same parameters and environmental variables as the +\fB\-\-up\fP option above. +.sp +Note that if you reduce privileges by using \fB\-\-user\fP and/or +\fB\-\-group\fP, your \fB\-\-down\fP script will also run at reduced privilege. +.TP +.B \-\-down\-pre +Call \fB\-\-down\fP cmd/script before, rather than after, TUN/TAP close. +.TP +.BI \-\-ipchange \ cmd +Run command \fBcmd\fP when our remote ip\-address is initially +authenticated or changes. +.sp +\fBcmd\fP consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single\- or +double\-quoted and/or escaped using a backslash, and should be separated +by one or more spaces. +.sp +When \fBcmd\fP is executed two arguments are appended after any arguments +specified in \fBcmd\fP , as follows: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +cmd ip address port number +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Don\(aqt use \fB\-\-ipchange\fP in \fB\-\-mode server\fP mode. Use a +\fB\-\-client\-connect\fP script instead. +.sp +See the \fI\%Environmental Variables\fP section below for additional +parameters passed as environmental variables. +.sp +If you are running in a dynamic IP address environment where the IP +addresses of either peer could change without notice, you can use this +script, for example, to edit the \fB/etc/hosts\fP file with the current +address of the peer. The script will be run every time the remote peer +changes its IP address. +.sp +Similarly if \fIour\fP IP address changes due to DHCP, we should configure +our IP address change script (see man page for \fBdhcpcd\fP(8)) to +deliver a \fBSIGHUP\fP or \fBSIGUSR1\fP signal to OpenVPN. OpenVPN will +then re\-establish a connection with its most recently authenticated +peer on its new IP address. +.TP +.BI \-\-learn\-address \ cmd +Run command \fBcmd\fP to validate client virtual addresses or routes. +.sp +\fBcmd\fP consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single\- or +double\-quoted and/or escaped using a backslash, and should be separated +by one or more spaces. +.sp +Three arguments will be appended to any arguments in \fBcmd\fP as follows: +.INDENT 7.0 +.TP +.B \fB$1\fP \- [operation] +\fB"add"\fP, \fB"update"\fP, or \fB"delete"\fP based on whether +or not the address is being added to, modified, or deleted from +OpenVPN\(aqs internal routing table. +.TP +.B \fB$2\fP \- [address] +The address being learned or unlearned. This can be an IPv4 address +such as \fB"198.162.10.14"\fP, an IPv4 subnet such as +\fB"198.162.10.0/24"\fP, or an ethernet MAC address (when +\fB\-\-dev tap\fP is being used) such as \fB"00:FF:01:02:03:04"\fP\&. +.TP +.B \fB$3\fP \- [common name] +The common name on the certificate associated with the client linked +to this address. Only present for \fB"add"\fP or \fB"update"\fP +operations, not \fB"delete"\fP\&. +.UNINDENT +.sp +On \fB"add"\fP or \fB"update"\fP methods, if the script returns +a failure code (non\-zero), OpenVPN will reject the address and will not +modify its internal routing table. +.sp +Normally, the \fBcmd\fP script will use the information provided above to +set appropriate firewall entries on the VPN TUN/TAP interface. Since +OpenVPN provides the association between virtual IP or MAC address and +the client\(aqs authenticated common name, it allows a user\-defined script +to configure firewall access policies with regard to the client\(aqs +high\-level common name, rather than the low level client virtual +addresses. +.TP +.BI \-\-route\-up \ cmd +Run command \fBcmd\fP after routes are added, subject to \fB\-\-route\-delay\fP\&. +.sp +\fBcmd\fP consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single\- or +double\-quoted and/or escaped using a backslash, and should be separated +by one or more spaces. +.sp +See the \fI\%Environmental Variables\fP section below for additional +parameters passed as environmental variables. +.TP +.BI \-\-route\-pre\-down \ cmd +Run command \fBcmd\fP before routes are removed upon disconnection. +.sp +\fBcmd\fP consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single\- or +double\-quoted and/or escaped using a backslash, and should be separated +by one or more spaces. +.sp +See the \fI\%Environmental Variables\fP section below for additional +parameters passed as environmental variables. +.TP +.BI \-\-setenv \ args +Set a custom environmental variable \fBname=value\fP to pass to script. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +setenv name value +setenv FORWARD_COMPATIBLE 1 +setenv opt config_option +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +By setting \fBFORWARD_COMPATIBLE\fP to \fB1\fP, the config file +syntax checking is relaxed so that unknown directives will trigger a +warning but not a fatal error, on the assumption that a given unknown +directive might be valid in future OpenVPN versions. +.sp +This option should be used with caution, as there are good security +reasons for having OpenVPN fail if it detects problems in a config file. +Having said that, there are valid reasons for wanting new software +features to gracefully degrade when encountered by older software +versions. +.sp +It is also possible to tag a single directive so as not to trigger a +fatal error if the directive isn\(aqt recognized. To do this, prepend the +following before the directive: \fBsetenv opt\fP +.sp +Versions prior to OpenVPN 2.3.3 will always ignore options set with the +\fBsetenv opt\fP directive. +.sp +See also \fB\-\-ignore\-unknown\-option\fP +.TP +.BI \-\-setenv\-safe \ args +Set a custom environmental variable \fBOPENVPN_name\fP to \fBvalue\fP +to pass to scripts. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +setenv\-safe name value +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +This directive is designed to be pushed by the server to clients, and +the prepending of \fBOPENVPN_\fP to the environmental variable is a +safety precaution to prevent a \fBLD_PRELOAD\fP style attack from a +malicious or compromised server. +.TP +.BI \-\-tls\-verify \ cmd +Run command \fBcmd\fP to verify the X509 name of a pending TLS connection +that has otherwise passed all other tests of certification (except for +revocation via \fB\-\-crl\-verify\fP directive; the revocation test occurs +after the \fB\-\-tls\-verify\fP test). +.sp +\fBcmd\fP should return \fB0\fP to allow the TLS handshake to proceed, +or \fB1\fP to fail. +.sp +\fBcmd\fP consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single\- or +double\-quoted and/or escaped using a backslash, and should be separated +by one or more spaces. +.sp +When \fBcmd\fP is executed two arguments are appended after any arguments +specified in \fBcmd\fP, as follows: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +cmd certificate_depth subject +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +These arguments are, respectively, the current certificate depth and the +X509 subject distinguished name (dn) of the peer. +.sp +This feature is useful if the peer you want to trust has a certificate +which was signed by a certificate authority who also signed many other +certificates, where you don\(aqt necessarily want to trust all of them, but +rather be selective about which peer certificate you will accept. This +feature allows you to write a script which will test the X509 name on a +certificate and decide whether or not it should be accepted. For a +simple perl script which will test the common name field on the +certificate, see the file \fBverify\-cn\fP in the OpenVPN distribution. +.sp +See the \fI\%Environmental Variables\fP section below for additional +parameters passed as environmental variables. +.TP +.BI \-\-up \ cmd +Run command \fBcmd\fP after successful TUN/TAP device open (pre \fB\-\-user\fP +UID change). +.sp +\fBcmd\fP consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single\- or +double\-quoted and/or escaped using a backslash, and should be separated +by one or more spaces. +.sp +The up command is useful for specifying route commands which route IP +traffic destined for private subnets which exist at the other end of the +VPN connection into the tunnel. +.sp +For \fB\-\-dev tun\fP execute as: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +cmd tun_dev tun_mtu link_mtu ifconfig_local_ip ifconfig_remote_ip [init | restart] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +For \fB\-\-dev tap\fP execute as: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +cmd tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask [init | restart] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +See the \fI\%Environmental Variables\fP section below for additional +parameters passed as environmental variables. +.sp +Note that if \fBcmd\fP includes arguments, all OpenVPN\-generated arguments +will be appended to them to build an argument list with which the +executable will be called. +.sp +Typically, \fBcmd\fP will run a script to add routes to the tunnel. +.sp +Normally the up script is called after the TUN/TAP device is opened. In +this context, the last command line parameter passed to the script will +be \fIinit.\fP If the \fB\-\-up\-restart\fP option is also used, the up script +will be called for restarts as well. A restart is considered to be a +partial reinitialization of OpenVPN where the TUN/TAP instance is +preserved (the \fB\-\-persist\-tun\fP option will enable such preservation). +A restart can be generated by a SIGUSR1 signal, a \fB\-\-ping\-restart\fP +timeout, or a connection reset when the TCP protocol is enabled with the +\fB\-\-proto\fP option. If a restart occurs, and \fB\-\-up\-restart\fP has been +specified, the up script will be called with \fIrestart\fP as the last +parameter. +.INDENT 7.0 +.TP +.B \fINOTE:\fP +On restart, OpenVPN will not pass the full set of environment +variables to the script. Namely, everything related to routing and +gateways will not be passed, as nothing needs to be done anyway \- all +the routing setup is already in place. Additionally, the up\-restart +script will run with the downgraded UID/GID settings (if configured). +.UNINDENT +.sp +The following standalone example shows how the \fB\-\-up\fP script can be +called in both an initialization and restart context. (\fINOTE:\fP for +security reasons, don\(aqt run the following example unless UDP port 9999 +is blocked by your firewall. Also, the example will run indefinitely, so +you should abort with control\-c). +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +openvpn \-\-dev tun \-\-port 9999 \-\-verb 4 \-\-ping\-restart 10 \e + \-\-up \(aqecho up\(aq \-\-down \(aqecho down\(aq \-\-persist\-tun \e + \-\-up\-restart +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Note that OpenVPN also provides the \fB\-\-ifconfig\fP option to +automatically ifconfig the TUN device, eliminating the need to define an +\fB\-\-up\fP script, unless you also want to configure routes in the +\fB\-\-up\fP script. +.sp +If \fB\-\-ifconfig\fP is also specified, OpenVPN will pass the ifconfig +local and remote endpoints on the command line to the \fB\-\-up\fP script so +that they can be used to configure routes such as: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +route add \-net 10.0.0.0 netmask 255.255.255.0 gw $5 +.ft P +.fi +.UNINDENT +.UNINDENT +.TP +.B \-\-up\-delay +Delay TUN/TAP open and possible \fB\-\-up\fP script execution until after +TCP/UDP connection establishment with peer. +.sp +In \fB\-\-proto udp\fP mode, this option normally requires the use of +\fB\-\-ping\fP to allow connection initiation to be sensed in the absence of +tunnel data, since UDP is a "connectionless" protocol. +.sp +On Windows, this option will delay the TAP\-Win32 media state +transitioning to "connected" until connection establishment, i.e. the +receipt of the first authenticated packet from the peer. +.TP +.B \-\-up\-restart +Enable the \fB\-\-up\fP and \fB\-\-down\fP scripts to be called for restarts as +well as initial program start. This option is described more fully above +in the \fB\-\-up\fP option documentation. +.UNINDENT +.SS String Types and Remapping +.sp +In certain cases, OpenVPN will perform remapping of characters in +strings. Essentially, any characters outside the set of permitted +characters for each string type will be converted to underbar (\(aq_\(aq). +.INDENT 0.0 +.TP +.B \fIQ: Why is string remapping necessary?\fP +It\(aqs an important security feature to prevent the malicious +coding of strings from untrusted sources to be passed as parameters to +scripts, saved in the environment, used as a common name, translated to +a filename, etc. +.TP +.B \fIQ: Can string remapping be disabled?\fP +Yes, by using the \fB\-\-no\-name\-remapping\fP option, however this +should be considered an advanced option. +.UNINDENT +.sp +Here is a brief rundown of OpenVPN\(aqs current string types and the +permitted character class for each string: +.INDENT 0.0 +.TP +.B \fIX509 Names\fP +Alphanumeric, underbar (\(aq_\(aq), dash (\(aq\-\(aq), dot (\(aq.\(aq), at +(\(aq@\(aq), colon (\(aq:\(aq), slash (\(aq/\(aq), and equal (\(aq=\(aq). Alphanumeric is +defined as a character which will cause the C library isalnum() function +to return true. +.TP +.B \fICommon Names\fP +Alphanumeric, underbar (\(aq_\(aq), dash (\(aq\-\(aq), dot (\(aq.\(aq), and at (\(aq@\(aq). +.TP +.B \fI\-\-auth\-user\-pass username\fP +Same as Common Name, with one exception: +starting with OpenVPN 2.0.1, the username is passed to the +\fBOPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY\fP plugin in its raw form, +without string remapping. +.TP +.B \fI\-\-auth\-user\-pass password\fP +Any "printable" character except CR or LF. Printable is defined to be +a character which will cause the C library isprint() function to +return true. +.TP +.B \fI\-\-client\-config\-dir filename as derived from common name or\(gausername\fP +Alphanumeric, underbar (\(aq_\(aq), dash (\(aq\-\(aq), and dot (\(aq.\(aq) except for "." +or ".." as standalone strings. As of v2.0.1\-rc6, the at (\(aq@\(aq) character +has been added as well for compatibility with the common name character +class. +.TP +.B \fIEnvironmental variable names\fP +Alphanumeric or underbar (\(aq_\(aq). +.TP +.B \fIEnvironmental variable values\fP +Any printable character. +.UNINDENT +.sp +For all cases, characters in a string which are not members of the legal +character class for that string type will be remapped to underbar +(\(aq_\(aq). +.SS Environmental Variables +.sp +Once set, a variable is persisted indefinitely until it is reset by a +new value or a restart, +.sp +As of OpenVPN 2.0\-beta12, in server mode, environmental variables set by +OpenVPN are scoped according to the client objects they are associated +with, so there should not be any issues with scripts having access to +stale, previously set variables which refer to different client +instances. +.INDENT 0.0 +.TP +.B \fBbytes_received\fP +Total number of bytes received from client during VPN session. Set prior +to execution of the \fB\-\-client\-disconnect\fP script. +.TP +.B \fBbytes_sent\fP +Total number of bytes sent to client during VPN session. Set prior to +execution of the \fB\-\-client\-disconnect\fP script. +.TP +.B \fBclient_connect_config_file\fP +The path to the configuration file that should be written to by the +\fB\-\-client\-connect\fP script (optional, if per\-session configuration +is desired). This is the same file name as passed via command line +argument on the call to the \fB\-\-client\-connect\fP script. +.TP +.B \fBclient_connect_deferred_file\fP +This file can be optionally written to in order to to communicate a +status code of the \fB\-\-client\-connect\fP script or plgin. Only the +first character in the file is relevant. It must be either \fB1\fP +to indicate normal script execution, \fB0\fP indicates an error (in +the same way that a non zero exit status does) or \fB2\fP to indicate +that the script deferred returning the config file. +.sp +For deferred (background) handling, the script or plugin MUST write +\fB2\fP to the file to indicate the deferral and then return with +exit code \fB0\fP to signal \fBdeferred handler started OK\fP\&. +.sp +A background process or similar must then take care of writing the +configuration to the file indicated by the +\fBclient_connect_config_file\fP environment variable and when +finished, write the a \fB1\fP to this file (or \fB0\fP in case of +an error). +.sp +The absence of any character in the file when the script finishes +executing is interpreted the same as \fB1\fP\&. This allows scripts +that are not written to support the defer mechanism to be used +unmodified. +.TP +.B \fBcommon_name\fP +The X509 common name of an authenticated client. Set prior to execution +of \fB\-\-client\-connect\fP, \fB\-\-client\-disconnect\fP and +\fB\-\-auth\-user\-pass\-verify\fP scripts. +.TP +.B \fBconfig\fP +Name of first \fB\-\-config\fP file. Set on program initiation and reset on +SIGHUP. +.TP +.B \fBdaemon\fP +Set to "1" if the \fB\-\-daemon\fP directive is specified, or "0" otherwise. +Set on program initiation and reset on SIGHUP. +.TP +.B \fBdaemon_log_redirect\fP +Set to "1" if the \fB\-\-log\fP or \fB\-\-log\-append\fP directives are +specified, or "0" otherwise. Set on program initiation and reset on +SIGHUP. +.TP +.B \fBdev\fP +The actual name of the TUN/TAP device, including a unit number if it +exists. Set prior to \fB\-\-up\fP or \fB\-\-down\fP script execution. +.TP +.B \fBdev_idx\fP +On Windows, the device index of the TUN/TAP adapter (to be used in +netsh.exe calls which sometimes just do not work right with interface +names). Set prior to \fB\-\-up\fP or \fB\-\-down\fP script execution. +.TP +.B \fBforeign_option_{n}\fP +An option pushed via \fB\-\-push\fP to a client which does not natively +support it, such as \fB\-\-dhcp\-option\fP on a non\-Windows system, will be +recorded to this environmental variable sequence prior to \fB\-\-up\fP +script execution. +.TP +.B \fBifconfig_broadcast\fP +The broadcast address for the virtual ethernet segment which is derived +from the \fB\-\-ifconfig\fP option when \fB\-\-dev tap\fP is used. Set prior to +OpenVPN calling the \fBifconfig\fP or \fBnetsh\fP (windows version +of ifconfig) commands which normally occurs prior to \fB\-\-up\fP script +execution. +.TP +.B \fBifconfig_ipv6_local\fP +The local VPN endpoint IPv6 address specified in the +\fB\-\-ifconfig\-ipv6\fP option (first parameter). Set prior to OpenVPN +calling the \fBifconfig\fP or code:\fInetsh\fP (windows version of +ifconfig) commands which normally occurs prior to \fB\-\-up\fP script +execution. +.TP +.B \fBifconfig_ipv6_netbits\fP +The prefix length of the IPv6 network on the VPN interface. Derived +from the /nnn parameter of the IPv6 address in the \fB\-\-ifconfig\-ipv6\fP +option (first parameter). Set prior to OpenVPN calling the +\fBifconfig\fP or \fBnetsh\fP (windows version of ifconfig) +commands which normally occurs prior to \fB\-\-up\fP script execution. +.TP +.B \fBifconfig_ipv6_remote\fP +The remote VPN endpoint IPv6 address specified in the +\fB\-\-ifconfig\-ipv6\fP option (second parameter). Set prior to OpenVPN +calling the \fBifconfig\fP or \fBnetsh\fP (windows version of +ifconfig) commands which normally occurs prior to \fB\-\-up\fP script +execution. +.TP +.B \fBifconfig_local\fP +The local VPN endpoint IP address specified in the \fB\-\-ifconfig\fP +option (first parameter). Set prior to OpenVPN calling the +\fBifconfig\fP or \fBnetsh\fP (windows version of ifconfig) +commands which normally occurs prior to \fB\-\-up\fP script execution. +.TP +.B \fBifconfig_remote\fP +The remote VPN endpoint IP address specified in the \fB\-\-ifconfig\fP +option (second parameter) when \fB\-\-dev tun\fP is used. Set prior to +OpenVPN calling the \fBifconfig\fP or \fBnetsh\fP (windows version +of ifconfig) commands which normally occurs prior to \fB\-\-up\fP script +execution. +.TP +.B \fBifconfig_netmask\fP +The subnet mask of the virtual ethernet segment that is specified as +the second parameter to \fB\-\-ifconfig\fP when \fB\-\-dev tap\fP is being +used. Set prior to OpenVPN calling the \fBifconfig\fP or +\fBnetsh\fP (windows version of ifconfig) commands which normally +occurs prior to \fB\-\-up\fP script execution. +.TP +.B \fBifconfig_pool_local_ip\fP +The local virtual IP address for the TUN/TAP tunnel taken from an +\fB\-\-ifconfig\-push\fP directive if specified, or otherwise from the +ifconfig pool (controlled by the \fB\-\-ifconfig\-pool\fP config file +directive). Only set for \fB\-\-dev tun\fP tunnels. This option is set on +the server prior to execution of the \fB\-\-client\-connect\fP and +\fB\-\-client\-disconnect\fP scripts. +.TP +.B \fBifconfig_pool_netmask\fP +The virtual IP netmask for the TUN/TAP tunnel taken from an +\fB\-\-ifconfig\-push\fP directive if specified, or otherwise from the +ifconfig pool (controlled by the \fB\-\-ifconfig\-pool\fP config file +directive). Only set for \fB\-\-dev tap\fP tunnels. This option is set on +the server prior to execution of the \fB\-\-client\-connect\fP and +\fB\-\-client\-disconnect\fP scripts. +.TP +.B \fBifconfig_pool_remote_ip\fP +The remote virtual IP address for the TUN/TAP tunnel taken from an +\fB\-\-ifconfig\-push\fP directive if specified, or otherwise from the +ifconfig pool (controlled by the \fB\-\-ifconfig\-pool\fP config file +directive). This option is set on the server prior to execution of the +\fB\-\-client\-connect\fP and \fB\-\-client\-disconnect\fP scripts. +.TP +.B \fBlink_mtu\fP +The maximum packet size (not including the IP header) of tunnel data in +UDP tunnel transport mode. Set prior to \fB\-\-up\fP or \fB\-\-down\fP script +execution. +.TP +.B \fBlocal\fP +The \fB\-\-local\fP parameter. Set on program initiation and reset on +SIGHUP. +.TP +.B \fBlocal_port\fP +The local port number or name, specified by \fB\-\-port\fP or \fB\-\-lport\fP\&. +Set on program initiation and reset on SIGHUP. +.TP +.B \fBpassword\fP +The password provided by a connecting client. Set prior to +\fB\-\-auth\-user\-pass\-verify\fP script execution only when the \fBvia\-env\fP +modifier is specified, and deleted from the environment after the script +returns. +.TP +.B \fBproto\fP +The \fB\-\-proto\fP parameter. Set on program initiation and reset on +SIGHUP. +.TP +.B \fBremote_{n}\fP +The \fB\-\-remote\fP parameter. Set on program initiation and reset on +SIGHUP. +.TP +.B \fBremote_port_{n}\fP +The remote port number, specified by \fB\-\-port\fP or \fB\-\-rport\fP\&. Set on +program initiation and reset on SIGHUP. +.TP +.B \fBroute_net_gateway\fP +The pre\-existing default IP gateway in the system routing table. Set +prior to \fB\-\-up\fP script execution. +.TP +.B \fBroute_vpn_gateway\fP +The default gateway used by \fB\-\-route\fP options, as specified in either +the \fB\-\-route\-gateway\fP option or the second parameter to +\fB\-\-ifconfig\fP when \fB\-\-dev tun\fP is specified. Set prior to \fB\-\-up\fP +script execution. +.TP +.B \fBroute_{parm}_{n}\fP +A set of variables which define each route to be added, and are set +prior to \fB\-\-up\fP script execution. +.sp +\fBparm\fP will be one of \fBnetwork\fP, \fBnetmask"\fP, +\fBgateway\fP, or \fBmetric\fP\&. +.sp +\fBn\fP is the OpenVPN route number, starting from 1. +.sp +If the network or gateway are resolvable DNS names, their IP address +translations will be recorded rather than their names as denoted on the +command line or configuration file. +.TP +.B \fBroute_ipv6_{parm}_{n}\fP +A set of variables which define each IPv6 route to be added, and are +set prior to \fB\-\-up\fP script execution. +.sp +\fBparm\fP will be one of \fBnetwork\fP or \fBgateway\fP +(\fBnetmask\fP is contained as \fB/nnn\fP in the +\fBroute_ipv6_network_{n}\fP, unlike IPv4 where it is passed in a +separate environment variable). +.sp +\fBn\fP is the OpenVPN route number, starting from 1. +.sp +If the network or gateway are resolvable DNS names, their IP address +translations will be recorded rather than their names as denoted on the +command line or configuration file. +.TP +.B \fBpeer_cert\fP +Temporary file name containing the client certificate upon connection. +Useful in conjunction with \fB\-\-tls\-verify\fP\&. +.TP +.B \fBscript_context\fP +Set to "init" or "restart" prior to up/down script execution. For more +information, see documentation for \fB\-\-up\fP\&. +.TP +.B \fBscript_type\fP +Prior to execution of any script, this variable is set to the type of +script being run. It can be one of the following: \fBup\fP, +\fBdown\fP, \fBipchange\fP, \fBroute\-up\fP, \fBtls\-verify\fP, +\fBauth\-user\-pass\-verify\fP, \fBclient\-connect\fP, +\fBclient\-disconnect\fP or \fBlearn\-address\fP\&. Set prior to +execution of any script. +.TP +.B \fBsignal\fP +The reason for exit or restart. Can be one of \fBsigusr1\fP, +\fBsighup\fP, \fBsigterm\fP, \fBsigint\fP, \fBinactive\fP +(controlled by \fB\-\-inactive\fP option), \fBping\-exit\fP (controlled +by \fB\-\-ping\-exit\fP option), \fBping\-restart\fP (controlled by +\fB\-\-ping\-restart\fP option), \fBconnection\-reset\fP (triggered on TCP +connection reset), \fBerror\fP or \fBunknown\fP (unknown signal). +This variable is set just prior to down script execution. +.TP +.B \fBtime_ascii\fP +Client connection timestamp, formatted as a human\-readable time string. +Set prior to execution of the \fB\-\-client\-connect\fP script. +.TP +.B \fBtime_duration\fP +The duration (in seconds) of the client session which is now +disconnecting. Set prior to execution of the \fB\-\-client\-disconnect\fP +script. +.TP +.B \fBtime_unix\fP +Client connection timestamp, formatted as a unix integer date/time +value. Set prior to execution of the \fB\-\-client\-connect\fP script. +.TP +.B \fBtls_digest_{n}\fP / \fBtls_digest_sha256_{n}\fP +Contains the certificate SHA1 / SHA256 fingerprint, where \fBn\fP is the +verification level. Only set for TLS connections. Set prior to execution +of \fB\-\-tls\-verify\fP script. +.TP +.B \fBtls_id_{n}\fP +A series of certificate fields from the remote peer, where \fBn\fP is the +verification level. Only set for TLS connections. Set prior to execution +of \fB\-\-tls\-verify\fP script. +.TP +.B \fBtls_serial_{n}\fP +The serial number of the certificate from the remote peer, where \fBn\fP +is the verification level. Only set for TLS connections. Set prior to +execution of \fB\-\-tls\-verify\fP script. This is in the form of a decimal +string like "933971680", which is suitable for doing serial\-based OCSP +queries (with OpenSSL, do not prepend "0x" to the string) If something +goes wrong while reading the value from the certificate it will be an +empty string, so your code should check that. See the +\fBcontrib/OCSP_check/OCSP_check.sh\fP script for an example. +.TP +.B \fBtls_serial_hex_{n}\fP +Like \fBtls_serial_{n}\fP, but in hex form (e.g. +\fB12:34:56:78:9A\fP). +.TP +.B \fBtun_mtu\fP +The MTU of the TUN/TAP device. Set prior to \fB\-\-up\fP or \fB\-\-down\fP +script execution. +.TP +.B \fBtrusted_ip\fP / \fBtrusted_ip6\fP) +Actual IP address of connecting client or peer which has been +authenticated. Set prior to execution of \fB\-\-ipchange\fP, +\fB\-\-client\-connect\fP and \fB\-\-client\-disconnect\fP scripts. If using ipv6 +endpoints (udp6, tcp6), \fBtrusted_ip6\fP will be set instead. +.TP +.B \fBtrusted_port\fP +Actual port number of connecting client or peer which has been +authenticated. Set prior to execution of \fB\-\-ipchange\fP, +\fB\-\-client\-connect\fP and \fB\-\-client\-disconnect\fP scripts. +.TP +.B \fBuntrusted_ip\fP / \fBuntrusted_ip6\fP +Actual IP address of connecting client or peer which has not been +authenticated yet. Sometimes used to \fInmap\fP the connecting host in a +\fB\-\-tls\-verify\fP script to ensure it is firewalled properly. Set prior +to execution of \fB\-\-tls\-verify\fP and \fB\-\-auth\-user\-pass\-verify\fP +scripts. If using ipv6 endpoints (udp6, tcp6), \fBuntrusted_ip6\fP +will be set instead. +.TP +.B \fBuntrusted_port\fP +Actual port number of connecting client or peer which has not been +authenticated yet. Set prior to execution of \fB\-\-tls\-verify\fP and +\fB\-\-auth\-user\-pass\-verify\fP scripts. +.TP +.B \fBusername\fP +The username provided by a connecting client. Set prior to +\fB\-\-auth\-user\-pass\-verify\fP script execution only when the +\fBvia\-env\fP modifier is specified. +.TP +.B \fBX509_{n}_{subject_field}\fP +An X509 subject field from the remote peer certificate, where \fBn\fP is +the verification level. Only set for TLS connections. Set prior to +execution of \fB\-\-tls\-verify\fP script. This variable is similar to +\fBtls_id_{n}\fP except the component X509 subject fields are broken +out, and no string remapping occurs on these field values (except for +remapping of control characters to "\fB_\fP"). For example, the +following variables would be set on the OpenVPN server using the sample +client certificate in sample\-keys (client.crt). Note that the +verification level is 0 for the client certificate and 1 for the CA +certificate. +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +X509_0_emailAddress=me@myhost.mydomain +X509_0_CN=Test\-Client +X509_0_O=OpenVPN\-TEST +X509_0_ST=NA +X509_0_C=KG +X509_1_emailAddress=me@myhost.mydomain +X509_1_O=OpenVPN\-TEST +X509_1_L=BISHKEK +X509_1_ST=NA +X509_1_C=KG +.ft P +.fi +.UNINDENT +.UNINDENT +.UNINDENT +.SS Management Interface Options +.sp +OpenVPN provides a feature rich socket based management interface for both +server and client mode operations. +.INDENT 0.0 +.TP +.BI \-\-management \ args +Enable a management server on a \fBsocket\-name\fP Unix socket on those +platforms supporting it, or on a designated TCP port. +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +management socket\-name unix # +management socket\-name unix pw\-file # (recommended) +management IP port # (INSECURE) +management IP port pw\-file # +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +\fBpw\-file\fP, if specified, is a password file where the password must +be on first line. Instead of a filename it can use the keyword stdin +which will prompt the user for a password to use when OpenVPN is +starting. +.sp +For unix sockets, the default behaviour is to create a unix domain +socket that may be connected to by any process. Use the +\fB\-\-management\-client\-user\fP and \fB\-\-management\-client\-group\fP +directives to restrict access. +.sp +The management interface provides a special mode where the TCP +management link can operate over the tunnel itself. To enable this mode, +set IP to \fBtunnel\fP\&. Tunnel mode will cause the management interface to +listen for a TCP connection on the local VPN address of the TUN/TAP +interface. +.sp +\fB*BEWARE*\fP of enabling the management interface over TCP. In these cases +you should \fIALWAYS\fP make use of \fBpw\-file\fP to password protect the +management interface. Any user who can connect to this TCP \fBIP:port\fP +will be able to manage and control (and interfere with) the OpenVPN +process. It is also strongly recommended to set IP to 127.0.0.1 +(localhost) to restrict accessibility of the management server to local +clients. +.sp +While the management port is designed for programmatic control of +OpenVPN by other applications, it is possible to telnet to the port, +using a telnet client in "raw" mode. Once connected, type \fBhelp\fP +for a list of commands. +.sp +For detailed documentation on the management interface, see the +\fImanagement\-notes.txt\fP file in the management folder of the OpenVPN +source distribution. +.TP +.B \-\-management\-client +Management interface will connect as a TCP/unix domain client to +\fBIP:port\fP specified by \fB\-\-management\fP rather than listen as a TCP +server or on a unix domain socket. +.sp +If the client connection fails to connect or is disconnected, a SIGTERM +signal will be generated causing OpenVPN to quit. +.TP +.B \-\-management\-client\-auth +Gives management interface client the responsibility to authenticate +clients after their client certificate has been verified. See +\fBmanagement\-notes.txt\fP in OpenVPN distribution for detailed notes. +.TP +.BI \-\-management\-client\-group \ g +When the management interface is listening on a unix domain socket, only +allow connections from group \fBg\fP\&. +.TP +.B \-\-management\-client\-pf +Management interface clients must specify a packet filter file for each +connecting client. See \fBmanagement\-notes.txt\fP in OpenVPN +distribution for detailed notes. +.TP +.BI \-\-management\-client\-user \ u +When the management interface is listening on a unix domain socket, only +allow connections from user \fBu\fP\&. +.TP +.BI \-\-management\-external\-cert \ certificate\-hint +Allows usage for external certificate instead of \fB\-\-cert\fP option +(client\-only). \fBcertificate\-hint\fP is an arbitrary string which is +passed to a management interface client as an argument of +\fINEED\-CERTIFICATE\fP notification. Requires \fB\-\-management\-external\-key\fP\&. +.TP +.BI \-\-management\-external\-key \ args +Allows usage for external private key file instead of \fB\-\-key\fP option +(client\-only). +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +management\-external\-key +management\-external\-key nopadding +management\-external\-key pkcs1 +management\-external\-key nopadding pkcs1 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The optional parameters \fBnopadding\fP and \fBpkcs1\fP signal +support for different padding algorithms. See +\fBdoc/mangement\-notes.txt\fP for a complete description of this +feature. +.TP +.B \-\-management\-forget\-disconnect +Make OpenVPN forget passwords when management session disconnects. +.sp +This directive does not affect the \fB\-\-http\-proxy\fP username/password. +It is always cached. +.TP +.B \-\-management\-hold +Start OpenVPN in a hibernating state, until a client of the management +interface explicitly starts it with the \fBhold release\fP command. +.TP +.BI \-\-management\-log\-cache \ n +Cache the most recent \fBn\fP lines of log file history for usage by the +management channel. +.TP +.B \-\-management\-query\-passwords +Query management channel for private key password and +\fB\-\-auth\-user\-pass\fP username/password. Only query the management +channel for inputs which ordinarily would have been queried from the +console. +.TP +.B \-\-management\-query\-proxy +Query management channel for proxy server information for a specific +\fB\-\-remote\fP (client\-only). +.TP +.B \-\-management\-query\-remote +Allow management interface to override \fB\-\-remote\fP directives +(client\-only). +.TP +.B \-\-management\-signal +Send SIGUSR1 signal to OpenVPN if management session disconnects. This +is useful when you wish to disconnect an OpenVPN session on user logoff. +For \fB\-\-management\-client\fP this option is not needed since a disconnect +will always generate a \fBSIGTERM\fP\&. +.TP +.B \-\-management\-up\-down +Report tunnel up/down events to management interface. +.UNINDENT +.SS Plug\-in Interface Options +.sp +OpenVPN can be extended by loading external plug\-in modules at runtime. These +plug\-ins must be prebuilt and adhere to the OpenVPN Plug\-In API. +.INDENT 0.0 +.TP +.BI \-\-plugin \ args +Loads an OpenVPN plug\-in module. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +plugin module\-name +plugin module\-name "arguments" +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The \fBmodule\-name\fP needs to be the first +argument, indicating the plug\-in to load. The second argument is an +optional init string which will be passed directly to the plug\-in. +If the init consists of multiple arguments it must be enclosed in +double\-quotes ("). Multiple plugin modules may be loaded into one +OpenVPN process. +.sp +The \fBmodule\-name\fP argument can be just a filename or a filename +with a relative or absolute path. The format of the filename and path +defines if the plug\-in will be loaded from a default plug\-in directory +or outside this directory. +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +\-\-plugin path Effective directory used +===================== ============================= + myplug.so DEFAULT_DIR/myplug.so + subdir/myplug.so DEFAULT_DIR/subdir/myplug.so + ./subdir/myplug.so CWD/subdir/myplug.so + /usr/lib/my/plug.so /usr/lib/my/plug.so +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +\fBDEFAULT_DIR\fP is replaced by the default plug\-in directory, which is +configured at the build time of OpenVPN. \fBCWD\fP is the current directory +where OpenVPN was started or the directory OpenVPN have switched into +via the \fB\-\-cd\fP option before the \fB\-\-plugin\fP option. +.sp +For more information and examples on how to build OpenVPN plug\-in +modules, see the README file in the \fBplugin\fP folder of the OpenVPN +source distribution. +.sp +If you are using an RPM install of OpenVPN, see +\fB/usr/share/openvpn/plugin\fP\&. The documentation is in \fBdoc\fP and +the actual plugin modules are in \fBlib\fP\&. +.sp +Multiple plugin modules can be cascaded, and modules can be used in +tandem with scripts. The modules will be called by OpenVPN in the order +that they are declared in the config file. If both a plugin and script +are configured for the same callback, the script will be called last. If +the return code of the module/script controls an authentication function +(such as tls\-verify, auth\-user\-pass\-verify, or client\-connect), then +every module and script must return success (\fB0\fP) in order for the +connection to be authenticated. +.UNINDENT +.SS Windows\-Specific Options +.INDENT 0.0 +.TP +.BI \-\-allow\-nonadmin \ TAP\-adapter +(Standalone) Set \fBTAP\-adapter\fP to allow access from non\-administrative +accounts. If \fBTAP\-adapter\fP is omitted, all TAP adapters on the system +will be configured to allow non\-admin access. The non\-admin access +setting will only persist for the length of time that the TAP\-Win32 +device object and driver remain loaded, and will need to be re\-enabled +after a reboot, or if the driver is unloaded and reloaded. This +directive can only be used by an administrator. +.TP +.B \-\-block\-outside\-dns +Block DNS servers on other network adapters to prevent DNS leaks. This +option prevents any application from accessing TCP or UDP port 53 except +one inside the tunnel. It uses Windows Filtering Platform (WFP) and +works on Windows Vista or later. +.sp +This option is considered unknown on non\-Windows platforms and +unsupported on Windows XP, resulting in fatal error. You may want to use +\fB\-\-setenv opt\fP or \fB\-\-ignore\-unknown\-option\fP (not suitable for +Windows XP) to ignore said error. Note that pushing unknown options from +server does not trigger fatal errors. +.TP +.BI \-\-cryptoapicert \ select\-string +\fI(Windows/OpenSSL Only)\fP Load the certificate and private key from the +Windows Certificate System Store. +.sp +Use this option instead of \fB\-\-cert\fP and \fB\-\-key\fP\&. +.sp +This makes it possible to use any smart card, supported by Windows, but +also any kind of certificate, residing in the Cert Store, where you have +access to the private key. This option has been tested with a couple of +different smart cards (GemSAFE, Cryptoflex, and Swedish Post Office eID) +on the client side, and also an imported PKCS12 software certificate on +the server side. +.sp +To select a certificate, based on a substring search in the +certificate\(aqs subject: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +cryptoapicert "SUBJ:Peter Runestig" +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +To select a certificate, based on certificate\(aqs thumbprint: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +cryptoapicert "THUMB:f6 49 24 41 01 b4 ..." +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The thumbprint hex string can easily be copy\-and\-pasted from the Windows +Certificate Store GUI. +.TP +.B \-\-dhcp\-release +Ask Windows to release the TAP adapter lease on shutdown. This option +has no effect now, as it is enabled by default starting with +OpenVPN 2.4.1. +.TP +.B \-\-dhcp\-renew +Ask Windows to renew the TAP adapter lease on startup. This option is +normally unnecessary, as Windows automatically triggers a DHCP +renegotiation on the TAP adapter when it comes up, however if you set +the TAP\-Win32 adapter Media Status property to "Always Connected", you +may need this flag. +.TP +.BI \-\-ip\-win32 \ method +When using \fB\-\-ifconfig\fP on Windows, set the TAP\-Win32 adapter IP +address and netmask using \fBmethod\fP\&. Don\(aqt use this option unless you +are also using \fB\-\-ifconfig\fP\&. +.INDENT 7.0 +.TP +.B \fBmanual\fP +Don\(aqt set the IP address or netmask automatically. Instead +output a message to the console telling the user to configure the +adapter manually and indicating the IP/netmask which OpenVPN +expects the adapter to be set to. +.TP +.B \fBdynamic [offset] [lease\-time]\fP +Automatically set the IP address and netmask by replying to DHCP +query messages generated by the kernel. This mode is probably the +"cleanest" solution for setting the TCP/IP properties since it +uses the well\-known DHCP protocol. There are, however, two +prerequisites for using this mode: +.INDENT 7.0 +.IP 1. 3 +The TCP/IP properties for the TAP\-Win32 adapter must be set +to "Obtain an IP address automatically", and +.IP 2. 3 +OpenVPN needs to claim an IP address in the subnet for use +as the virtual DHCP server address. +.UNINDENT +.sp +By default in \fB\-\-dev tap\fP mode, OpenVPN will take the normally +unused first address in the subnet. For example, if your subnet is +\fB192.168.4.0 netmask 255.255.255.0\fP, then OpenVPN will take +the IP address \fB192.168.4.0\fP to use as the virtual DHCP +server address. In \fB\-\-dev tun\fP mode, OpenVPN will cause the DHCP +server to masquerade as if it were coming from the remote endpoint. +.sp +The optional offset parameter is an integer which is > \fB\-256\fP +and < \fB256\fP and which defaults to \-1. If offset is positive, +the DHCP server will masquerade as the IP address at network +address + offset. If offset is negative, the DHCP server will +masquerade as the IP address at broadcast address + offset. +.sp +The Windows \fBipconfig /all\fP command can be used to show what +Windows thinks the DHCP server address is. OpenVPN will "claim" +this address, so make sure to use a free address. Having said that, +different OpenVPN instantiations, including different ends of +the same connection, can share the same virtual DHCP server +address. +.sp +The \fBlease\-time\fP parameter controls the lease time of the DHCP +assignment given to the TAP\-Win32 adapter, and is denoted in +seconds. Normally a very long lease time is preferred because it +prevents routes involving the TAP\-Win32 adapter from being lost +when the system goes to sleep. The default lease time is one year. +.TP +.B \fBnetsh\fP +Automatically set the IP address and netmask using the Windows +command\-line "netsh" command. This method appears to work correctly +on Windows XP but not Windows 2000. +.TP +.B \fBipapi\fP +Automatically set the IP address and netmask using the Windows IP +Helper API. This approach does not have ideal semantics, though +testing has indicated that it works okay in practice. If you use +this option, it is best to leave the TCP/IP properties for the +TAP\-Win32 adapter in their default state, i.e. "Obtain an IP +address automatically." +.TP +.B \fBadaptive\fP (Default) +Try \fBdynamic\fP method initially and fail over to \fBnetsh\fP +if the DHCP negotiation with the TAP\-Win32 adapter does not succeed +in 20 seconds. Such failures have been known to occur when certain +third\-party firewall packages installed on the client machine block +the DHCP negotiation used by the TAP\-Win32 adapter. Note that if +the \fBnetsh\fP failover occurs, the TAP\-Win32 adapter TCP/IP +properties will be reset from DHCP to static, and this will cause +future OpenVPN startups using the \fBadaptive\fP mode to use +\fBnetsh\fP immediately, rather than trying \fBdynamic\fP first. +.sp +To "unstick" the \fBadaptive\fP mode from using \fBnetsh\fP, +run OpenVPN at least once using the \fBdynamic\fP mode to restore +the TAP\-Win32 adapter TCP/IP properties to a DHCP configuration. +.UNINDENT +.TP +.B \-\-pause\-exit +Put up a "press any key to continue" message on the console prior to +OpenVPN program exit. This option is automatically used by the Windows +explorer when OpenVPN is run on a configuration file using the +right\-click explorer menu. +.TP +.B \-\-register\-dns +Run \fBipconfig /flushdns\fP and \fBipconfig /registerdns\fP on +connection initiation. This is known to kick Windows into recognizing +pushed DNS servers. +.TP +.BI \-\-route\-method \ m +Which method \fBm\fP to use for adding routes on Windows? +.INDENT 7.0 +.TP +.B \fBadaptive\fP (default) +Try IP helper API first. If that fails, fall back to the route.exe +shell command. +.TP +.B \fBipapi\fP +Use IP helper API. +.TP +.B \fBexe\fP +Call the route.exe shell command. +.UNINDENT +.TP +.BI \-\-service \ args +Should be used when OpenVPN is being automatically executed by another +program in such a context that no interaction with the user via display +or keyboard is possible. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +service exit\-event [0|1] +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +In general, end\-users should never need to explicitly use this option, +as it is automatically added by the OpenVPN service wrapper when a given +OpenVPN configuration is being run as a service. +.sp +\fBexit\-event\fP is the name of a Windows global event object, and OpenVPN +will continuously monitor the state of this event object and exit when +it becomes signaled. +.sp +The second parameter indicates the initial state of \fBexit\-event\fP and +normally defaults to 0. +.sp +Multiple OpenVPN processes can be simultaneously executed with the same +\fBexit\-event\fP parameter. In any case, the controlling process can +signal \fBexit\-event\fP, causing all such OpenVPN processes to exit. +.sp +When executing an OpenVPN process using the \fB\-\-service\fP directive, +OpenVPN will probably not have a console window to output status/error +messages, therefore it is useful to use \fB\-\-log\fP or \fB\-\-log\-append\fP to +write these messages to a file. +.TP +.B \-\-show\-adapters +(Standalone) Show available TAP\-Win32 adapters which can be selected +using the \fB\-\-dev\-node\fP option. On non\-Windows systems, the +\fBifconfig\fP(8) command provides similar functionality. +.TP +.B \-\-show\-net +(Standalone) Show OpenVPN\(aqs view of the system routing table and network +adapter list. +.TP +.B \-\-show\-net\-up +Output OpenVPN\(aqs view of the system routing table and network adapter +list to the syslog or log file after the TUN/TAP adapter has been +brought up and any routes have been added. +.TP +.B \-\-show\-valid\-subnets +(Standalone) Show valid subnets for \fB\-\-dev tun\fP emulation. Since the +TAP\-Win32 driver exports an ethernet interface to Windows, and since TUN +devices are point\-to\-point in nature, it is necessary for the TAP\-Win32 +driver to impose certain constraints on TUN endpoint address selection. +.sp +Namely, the point\-to\-point endpoints used in TUN device emulation must +be the middle two addresses of a /30 subnet (netmask 255.255.255.252). +.TP +.BI \-\-tap\-sleep \ n +Cause OpenVPN to sleep for \fBn\fP seconds immediately after the TAP\-Win32 +adapter state is set to "connected". +.sp +This option is intended to be used to troubleshoot problems with the +\fB\-\-ifconfig\fP and \fB\-\-ip\-win32\fP options, and is used to give the +TAP\-Win32 adapter time to come up before Windows IP Helper API +operations are applied to it. +.TP +.BI \-\-win\-sys \ path +Set the Windows system directory pathname to use when looking for system +executables such as \fBroute.exe\fP and \fBnetsh.exe\fP\&. By default, if this +directive is not specified, OpenVPN will use the SystemRoot environment +variable. +.sp +This option has changed behaviour since OpenVPN 2.3. Earlier you had to +define \fB\-\-win\-sys env\fP to use the SystemRoot environment variable, +otherwise it defaulted to \fBC:\e\eWINDOWS\fP\&. It is not needed to use +the \fBenv\fP keyword any more, and it will just be ignored. A warning is +logged when this is found in the configuration file. +.TP +.BI \-\-windows\-driver \ drv +Specifies which tun driver to use. Values are \fBtap\-windows6\fP +(default) and \fBwintun\fP\&. This is a Windows\-only option. +\fBwintun\fP" requires \fB\-\-dev tun\fP and the OpenVPN process to run +elevated, or be invoked using the Interactive Service. +.UNINDENT +.SS Standalone Debug Options +.INDENT 0.0 +.TP +.BI \-\-show\-gateway \ args +(Standalone) Show current IPv4 and IPv6 default gateway and interface +towards the gateway (if the protocol in question is enabled). +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +\-\-show\-gateway +\-\-show\-gateway IPv6\-target +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +If an IPv6 target address is passed as argument, the IPv6 route for this +host is reported. +.UNINDENT +.SS Advanced Expert Options +.sp +These are options only required when special tweaking is needed, often +used when debugging or testing out special usage scenarios. +.INDENT 0.0 +.TP +.BI \-\-hash\-size \ args +Set the size of the real address hash table to \fBr\fP and the virtual +address table to \fBv\fP\&. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +hash\-size r v +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +By default, both tables are sized at 256 buckets. +.TP +.BI \-\-bcast\-buffers \ n +Allocate \fBn\fP buffers for broadcast datagrams (default \fB256\fP). +.TP +.B \-\-persist\-local\-ip +Preserve initially resolved local IP address and port number across +\fBSIGUSR1\fP or \fB\-\-ping\-restart\fP restarts. +.TP +.B \-\-persist\-remote\-ip +Preserve most recently authenticated remote IP address and port number +across \fBSIGUSR1\fP or \fB\-\-ping\-restart\fP restarts. +.TP +.BI \-\-prng \ args +\fI(Advanced)\fP Change the PRNG (Pseudo\-random number generator) parameters +.sp +Valid syntaxes: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +prng alg +prng alg nsl +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Changes the PRNG to use digest algorithm \fBalg\fP (default \fBsha1\fP), +and set \fBnsl\fP (default \fB16\fP) to the size in bytes of the nonce +secret length (between 16 and 64). +.sp +Set \fBalg\fP to \fBnone\fP to disable the PRNG and use the OpenSSL +RAND_bytes function instead for all of OpenVPN\(aqs pseudo\-random number +needs. +.TP +.BI \-\-rcvbuf \ size +Set the TCP/UDP socket receive buffer size. Defaults to operating system +default. +.TP +.BI \-\-shaper \ n +Limit bandwidth of outgoing tunnel data to \fBn\fP bytes per second on the +TCP/UDP port. Note that this will only work if mode is set to +\fBp2p\fP\&. If you want to limit the bandwidth in both directions, use +this option on both peers. +.sp +OpenVPN uses the following algorithm to implement traffic shaping: Given +a shaper rate of \fBn\fP bytes per second, after a datagram write of \fBb\fP +bytes is queued on the TCP/UDP port, wait a minimum of \fB(b / n)\fP +seconds before queuing the next write. +.sp +It should be noted that OpenVPN supports multiple tunnels between the +same two peers, allowing you to construct full\-speed and reduced +bandwidth tunnels at the same time, routing low\-priority data such as +off\-site backups over the reduced bandwidth tunnel, and other data over +the full\-speed tunnel. +.sp +Also note that for low bandwidth tunnels (under 1000 bytes per second), +you should probably use lower MTU values as well (see above), otherwise +the packet latency will grow so large as to trigger timeouts in the TLS +layer and TCP connections running over the tunnel. +.sp +OpenVPN allows \fBn\fP to be between 100 bytes/sec and 100 Mbytes/sec. +.TP +.BI \-\-sndbuf \ size +Set the TCP/UDP socket send buffer size. Defaults to operating system +default. +.TP +.BI \-\-tcp\-queue\-limit \ n +Maximum number of output packets queued before TCP (default \fB64\fP). +.sp +When OpenVPN is tunneling data from a TUN/TAP device to a remote client +over a TCP connection, it is possible that the TUN/TAP device might +produce data at a faster rate than the TCP connection can support. When +the number of output packets queued before sending to the TCP socket +reaches this limit for a given client connection, OpenVPN will start to +drop outgoing packets directed at this client. +.TP +.BI \-\-txqueuelen \ n +\fI(Linux only)\fP Set the TX queue length on the TUN/TAP interface. +Currently defaults to operating system default. +.UNINDENT +.SH UNSUPPORTED OPTIONS +.sp +Options listed in this section have been removed from OpenVPN and are no +longer supported +.INDENT 0.0 +.TP +.B \-\-client\-cert\-not\-required +Removed in OpenVPN 2.5. This should be replaxed with +\fB\-\-verify\-client\-cert none\fP\&. +.TP +.B \-\-ifconfig\-pool\-linear +Removed in OpenVPN 2.5. This should be replaced with \fB\-\-topology p2p\fP\&. +.TP +.B \-\-key\-method +Removed in OpenVPN 2.5. This option should not be used, as using the old +\fBkey\-method\fP weakens the VPN tunnel security. The old \fBkey\-method\fP +was also only needed when the remote side was older than OpenVPN 2.0. +.TP +.B \-\-no\-iv +Removed in OpenVPN 2.5. This option should not be used as it weakens the +VPN tunnel security. This has been a NOOP option since OpenVPN 2.4. +.TP +.B \-\-no\-replay +Removed in OpenVPN 2.5. This option should not be used as it weakens the +VPN tunnel security. +.TP +.B \-\-ns\-cert\-type +Removed in OpenVPN 2.5. The \fBnsCertType\fP field is no longer supported +in recent SSL/TLS libraries. If your certificates does not include \fIkey +usage\fP and \fIextended key usage\fP fields, they must be upgraded and the +\fB\-\-remote\-cert\-tls\fP option should be used instead. +.UNINDENT +.SH CONNECTION PROFILES +.sp +Client configuration files may contain multiple remote servers which +it will attempt to connect against. But there are some configuration +options which are related to specific \fB\-\-remote\fP options. For these +use cases, connection profiles are the solution. +.sp +By enacpulating the \fB\-\-remote\fP option and related options within +\fB\fP and \fB\fP, these options are handled as a +group. +.sp +An OpenVPN client will try each connection profile sequentially until it +achieves a successful connection. +.sp +\fB\-\-remote\-random\fP can be used to initially "scramble" the connection +list. +.sp +Here is an example of connection profile usage: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +client +dev tun + + +remote 198.19.34.56 1194 udp + + + +remote 198.19.34.56 443 tcp + + + +remote 198.19.34.56 443 tcp +http\-proxy 192.168.0.8 8080 + + + +remote 198.19.36.99 443 tcp +http\-proxy 192.168.0.8 8080 + + +persist\-key +persist\-tun +pkcs12 client.p12 +remote\-cert\-tls server +verb 3 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +First we try to connect to a server at 198.19.34.56:1194 using UDP. If +that fails, we then try to connect to 198.19.34.56:443 using TCP. If +that also fails, then try connecting through an HTTP proxy at +192.168.0.8:8080 to 198.19.34.56:443 using TCP. Finally, try to connect +through the same proxy to a server at 198.19.36.99:443 using TCP. +.sp +The following OpenVPN options may be used inside of a \fB\fP +block: +.sp +\fBbind\fP, \fBconnect\-retry\fP, \fBconnect\-retry\-max\fP, \fBconnect\-timeout\fP, +\fBexplicit\-exit\-notify\fP, \fBfloat\fP, \fBfragment\fP, \fBhttp\-proxy\fP, +\fBhttp\-proxy\-option\fP, \fBkey\-direction\fP, \fBlink\-mtu\fP, \fBlocal\fP, +\fBlport\fP, \fBmssfix\fP, \fBmtu\-disc\fP, \fBnobind\fP, \fBport\fP, \fBproto\fP, +\fBremote\fP, \fBrport\fP, \fBsocks\-proxy\fP, \fBtls\-auth\fP, \fBtls\-crypt\fP, +\fBtun\-mtu and\fP, \fBtun\-mtu\-extra\fP\&. +.sp +A defaulting mechanism exists for specifying options to apply to all +\fB\fP profiles. If any of the above options (with the +exception of \fBremote\fP ) appear outside of a \fB\fP block, +but in a configuration file which has one or more \fB\fP +blocks, the option setting will be used as a default for +\fB\fP blocks which follow it in the configuration file. +.sp +For example, suppose the \fBnobind\fP option were placed in the sample +configuration file above, near the top of the file, before the first +\fB\fP block. The effect would be as if \fBnobind\fP were +declared in all \fB\fP blocks below it. +.SH INLINE FILE SUPPORT +.sp +OpenVPN allows including files in the main configuration for the \fB\-\-ca\fP, +\fB\-\-cert\fP, \fB\-\-dh\fP, \fB\-\-extra\-certs\fP, \fB\-\-key\fP, \fB\-\-pkcs12\fP, +\fB\-\-secret\fP, \fB\-\-crl\-verify\fP, \fB\-\-http\-proxy\-user\-pass\fP, \fB\-\-tls\-auth\fP, +\fB\-\-auth\-gen\-token\-secret\fP, \fB\-\-tls\-crypt\fP and \fB\-\-tls\-crypt\-v2\fP +options. +.sp +Each inline file started by the line \fB\fP +.sp +Here is an example of an inline file usage +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C + +\-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\- +[...] +\-\-\-\-\-END CERTIFICATE\-\-\-\-\- + +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +When using the inline file feature with \fB\-\-pkcs12\fP the inline file has +to be base64 encoded. Encoding of a .p12 file into base64 can be done +for example with OpenSSL by running \fBopenssl base64 \-in input.p12\fP +.SH SIGNALS +.INDENT 0.0 +.TP +.B \fBSIGHUP\fP +Cause OpenVPN to close all TUN/TAP and network connections, restart, +re\-read the configuration file (if any), and reopen TUN/TAP and network +connections. +.TP +.B \fBSIGUSR1\fP +Like \fBSIGHUP\(ga\fP, except don\(aqt re\-read configuration file, and +possibly don\(aqt close and reopen TUN/TAP device, re\-read key files, +preserve local IP address/port, or preserve most recently authenticated +remote IP address/port based on \fB\-\-persist\-tun\fP, \fB\-\-persist\-key\fP, +\fB\-\-persist\-local\-ip\fP and \fB\-\-persist\-remote\-ip\fP options respectively +(see above). +.sp +This signal may also be internally generated by a timeout condition, +governed by the \fB\-\-ping\-restart\fP option. +.sp +This signal, when combined with \fB\-\-persist\-remote\-ip\fP, may be sent +when the underlying parameters of the host\(aqs network interface change +such as when the host is a DHCP client and is assigned a new IP address. +See \fB\-\-ipchange\fP for more information. +.TP +.B \fBSIGUSR2\fP +Causes OpenVPN to display its current statistics (to the syslog file if +\fB\-\-daemon\fP is used, or stdout otherwise). +.TP +.B \fBSIGINT\fP, \fBSIGTERM\fP +Causes OpenVPN to exit gracefully. +.UNINDENT +.SH EXAMPLES +.sp +Prior to running these examples, you should have OpenVPN installed on +two machines with network connectivity between them. If you have not yet +installed OpenVPN, consult the INSTALL file included in the OpenVPN +distribution. +.SS Firewall Setup: +.sp +If firewalls exist between the two machines, they should be set to +forward the port OpenVPN is configured to use, in both directions. +The default for OpenVPN is 1194/udp. If you do not have control +over the firewalls between the two machines, you may still be able to +use OpenVPN by adding \fB\-\-ping 15\fP to each of the \fBopenvpn\fP commands +used below in the examples (this will cause each peer to send out a UDP +ping to its remote peer once every 15 seconds which will cause many +stateful firewalls to forward packets in both directions without an +explicit firewall rule). +.sp +Please see your operating system guides for how to configure the firewall +on your systems. +.SS VPN Address Setup: +.sp +For purposes of our example, our two machines will be called +\fBbob.example.com\fP and \fBalice.example.com\fP\&. If you are constructing a +VPN over the internet, then replace \fBbob.example.com\fP and +\fBalice.example.com\fP with the internet hostname or IP address that each +machine will use to contact the other over the internet. +.sp +Now we will choose the tunnel endpoints. Tunnel endpoints are private IP +addresses that only have meaning in the context of the VPN. Each machine +will use the tunnel endpoint of the other machine to access it over the +VPN. In our example, the tunnel endpoint for bob.example.com will be +10.4.0.1 and for alice.example.com, 10.4.0.2. +.sp +Once the VPN is established, you have essentially created a secure +alternate path between the two hosts which is addressed by using the +tunnel endpoints. You can control which network traffic passes between +the hosts (a) over the VPN or (b) independently of the VPN, by choosing +whether to use (a) the VPN endpoint address or (b) the public internet +address, to access the remote host. For example if you are on +bob.example.com and you wish to connect to \fBalice.example.com\fP via +\fBssh\fP without using the VPN (since \fBssh\fP has its own built\-in security) +you would use the command \fBssh alice.example.com\fP\&. However in the same +scenario, you could also use the command \fBtelnet 10.4.0.2\fP to create a +telnet session with alice.example.com over the VPN, that would use the +VPN to secure the session rather than \fBssh\fP\&. +.sp +You can use any address you wish for the tunnel endpoints but make sure +that they are private addresses (such as those that begin with 10 or +192.168) and that they are not part of any existing subnet on the +networks of either peer, unless you are bridging. If you use an address +that is part of your local subnet for either of the tunnel endpoints, +you will get a weird feedback loop. +.SS Example 1: A simple tunnel without security +.sp +On bob: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +openvpn \-\-remote alice.example.com \-\-dev tun1 \e + \-\-ifconfig 10.4.0.1 10.4.0.2 \-\-verb 9 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +On alice: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +openvpn \-\-remote bob.example.com \-\-dev tun1 \e + \-\-ifconfig 10.4.0.2 10.4.0.1 \-\-verb 9 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Now verify the tunnel is working by pinging across the tunnel. +.sp +On bob: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +ping 10.4.0.2 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +On alice: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +ping 10.4.0.1 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +The \fB\-\-verb 9\fP option will produce verbose output, similar to the +\fBtcpdump\fP(8) program. Omit the \fB\-\-verb 9\fP option to have OpenVPN run +quietly. +.SS Example 2: A tunnel with static\-key security (i.e. using a pre\-shared secret) +.sp +First build a static key on bob. +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +openvpn \-\-genkey \-\-secret key +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +This command will build a key file called \fBkey\fP (in ascii format). Now +copy \fBkey\fP to \fBalice.example.com\fP over a secure medium such as by using +the \fBscp\fP(1) program. +.sp +On bob: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +openvpn \-\-remote alice.example.com \-\-dev tun1 \e + \-\-ifconfig 10.4.0.1 10.4.0.2 \-\-verb 5 \e + \-\-secret key +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +On alice: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +openvpn \-\-remote bob.example.com \-\-dev tun1 \e + \-\-ifconfig 10.4.0.2 10.4.0.1 \-\-verb 5 \e + \-\-secret key +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Now verify the tunnel is working by pinging across the tunnel. +.sp +On bob: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +ping 10.4.0.2 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +On alice: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +ping 10.4.0.1 +.ft P +.fi +.UNINDENT +.UNINDENT +.SS Example 3: A tunnel with full TLS\-based security +.sp +For this test, we will designate \fBbob\fP as the TLS client and \fBalice\fP +as the TLS server. +.INDENT 0.0 +.TP +.B \fINote:\fP +The client or server designation only has +meaning for the TLS subsystem. It has no bearing on OpenVPN\(aqs +peer\-to\-peer, UDP\-based communication model.* +.UNINDENT +.sp +First, build a separate certificate/key pair for both bob and alice (see +above where \fB\-\-cert\fP is discussed for more info). Then construct +Diffie Hellman parameters (see above where \fB\-\-dh\fP is discussed for +more info). You can also use the included test files \fBclient.crt\fP, +\fBclient.key\fP, \fBserver.crt\fP, \fBserver.key\fP and +\fBca.crt\fP\&. The \fB\&.crt\fP files are certificates/public\-keys, the +\fB\&.key\fP files are private keys, and \fBca.crt\fP is a certification +authority who has signed both \fBclient.crt\fP and \fBserver.crt\fP\&. +For Diffie Hellman parameters you can use the included file +\fBdh2048.pem\fP\&. +.INDENT 0.0 +.TP +.B \fIWARNING:\fP +All client, server, and certificate authority certificates +and keys included in the OpenVPN distribution are totally +insecure and should be used for testing only. +.UNINDENT +.sp +On bob: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +openvpn \-\-remote alice.example.com \-\-dev tun1 \e + \-\-ifconfig 10.4.0.1 10.4.0.2 \e + \-\-tls\-client \-\-ca ca.crt \e + \-\-cert client.crt \-\-key client.key \e + \-\-reneg\-sec 60 \-\-verb 5 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +On alice: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +openvpn \-\-remote bob.example.com \-\-dev tun1 \e + \-\-ifconfig 10.4.0.2 10.4.0.1 \e + \-\-tls\-server \-\-dh dh1024.pem \-\-ca ca.crt \e + \-\-cert server.crt \-\-key server.key \e + \-\-reneg\-sec 60 \-\-verb 5 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Now verify the tunnel is working by pinging across the tunnel. +.sp +On bob: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +ping 10.4.0.2 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +On alice: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +ping 10.4.0.1 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Notice the \fB\-\-reneg\-sec 60\fP option we used above. That tells OpenVPN +to renegotiate the data channel keys every minute. Since we used +\fB\-\-verb 5\fP above, you will see status information on each new key +negotiation. +.sp +For production operations, a key renegotiation interval of 60 seconds is +probably too frequent. Omit the \fB\-\-reneg\-sec 60\fP option to use +OpenVPN\(aqs default key renegotiation interval of one hour. +.SS Routing: +.sp +Assuming you can ping across the tunnel, the next step is to route a +real subnet over the secure tunnel. Suppose that bob and alice have two +network interfaces each, one connected to the internet, and the other to +a private network. Our goal is to securely connect both private +networks. We will assume that bob\(aqs private subnet is \fI10.0.0.0/24\fP and +alice\(aqs is \fI10.0.1.0/24\fP\&. +.sp +First, ensure that IP forwarding is enabled on both peers. On Linux, +enable routing: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +echo 1 > /proc/sys/net/ipv4/ip_forward +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +This setting is not persistent. Please see your operating systems +documentation how to properly configure IP forwarding, which is also +persistent through system boots. +.sp +If your system is configured with a firewall. Please see your operating +systems guide on how to configure the firewall. You typically want to +allow traffic coming from and going to the tun/tap adapter OpenVPN is +configured to use. +.sp +On bob: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +route add \-net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +On alice: +.INDENT 0.0 +.INDENT 3.5 +.sp +.nf +.ft C +route add \-net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1 +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Now any machine on the \fI10.0.0.0/24\fP subnet can access any machine on the +\fI10.0.1.0/24\fP subnet over the secure tunnel (or vice versa). +.sp +In a production environment, you could put the route command(s) in a +script and execute with the \fB\-\-up\fP option. +.SH FAQ +.sp +\fI\%https://community.openvpn.net/openvpn/wiki/FAQ\fP +.SH HOWTO +.sp +For a more comprehensive guide to setting up OpenVPN in a production +setting, see the OpenVPN HOWTO at +\fI\%https://openvpn.net/community\-resources/how\-to/\fP +.SH PROTOCOL +.sp +For a description of OpenVPN\(aqs underlying protocol, see +\fI\%https://openvpn.net/community\-resources/openvpn\-protocol/\fP +.SH WEB +.sp +OpenVPN\(aqs web site is at \fI\%https://openvpn.net/\fP +.sp +Go here to download the latest version of OpenVPN, subscribe to the +mailing lists, read the mailing list archives, or browse the SVN +repository. +.SH BUGS +.sp +Report all bugs to the OpenVPN team \fI\%info@openvpn.net\fP +.SH SEE ALSO +.sp +\fBdhcpcd\fP(8), +\fBifconfig\fP(8), +\fBopenssl\fP(1), +\fBroute\fP(8), +\fBscp\fP(1) +\fBssh\fP(1) +.SH NOTES +.sp +This product includes software developed by the OpenSSL Project +(\fI\%https://www.openssl.org/\fP) +.sp +For more information on the TLS protocol, see +\fI\%http://www.ietf.org/rfc/rfc2246.txt\fP +.sp +For more information on the LZO real\-time compression library see +\fI\%https://www.oberhumer.com/opensource/lzo/\fP +.SH COPYRIGHT +.sp +Copyright (C) 2002\-2020 OpenVPN Inc This program is free software; you +can redistribute it and/or modify it under the terms of the GNU General +Public License version 2 as published by the Free Software Foundation. +.SH AUTHORS +.sp +James Yonan \fI\%james@openvpn.net\fP +.\" Generated by docutils manpage writer. +. diff --git a/doc/openvpn.8.html b/doc/openvpn.8.html new file mode 100644 index 0000000..d6b2719 --- /dev/null +++ b/doc/openvpn.8.html @@ -0,0 +1,6023 @@ + + + + + + +openvpn + + + +
+

openvpn

+

Secure IP tunnel daemon

+ +++ + + + + + +
Manual section:8
Manual group:System Manager's Manual
+
+

SYNOPSIS

+
+
openvpn [ options ... ]
+
openvpn --help
+
+
+
+

INTRODUCTION

+

OpenVPN is an open source VPN daemon by James Yonan. Because OpenVPN +tries to be a universal VPN tool offering a great deal of flexibility, +there are a lot of options on this manual page. If you're new to +OpenVPN, you might want to skip ahead to the examples section where you +will see how to construct simple VPNs on the command line without even +needing a configuration file.

+

Also note that there's more documentation and examples on the OpenVPN +web site: https://openvpn.net/

+

And if you would like to see a shorter version of this manual, see the +openvpn usage message which can be obtained by running openvpn +without any parameters.

+
+
+

DESCRIPTION

+

OpenVPN is a robust and highly flexible VPN daemon. OpenVPN supports +SSL/TLS security, ethernet bridging, TCP or UDP tunnel transport through +proxies or NAT, support for dynamic IP addresses and DHCP, scalability +to hundreds or thousands of users, and portability to most major OS +platforms.

+

OpenVPN is tightly bound to the OpenSSL library, and derives much of its +crypto capabilities from it.

+

OpenVPN supports conventional encryption using a pre-shared secret key +(Static Key mode) or public key security (SSL/TLS mode) using +client & server certificates. OpenVPN also supports non-encrypted +TCP/UDP tunnels.

+

OpenVPN is designed to work with the TUN/TAP virtual networking +interface that exists on most platforms.

+

Overall, OpenVPN aims to offer many of the key features of IPSec but +with a relatively lightweight footprint.

+
+
+

OPTIONS

+

OpenVPN allows any option to be placed either on the command line or in +a configuration file. Though all command line options are preceded by a +double-leading-dash ("--"), this prefix can be removed when an option is +placed in a configuration file.

+
+

Generic Options

+

This section covers generic options which are accessible regardless of +which mode OpenVPN is configured as.

+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+--helpShow options.
+--auth-nocache

Don't cache --askpass or --auth-user-pass username/passwords in +virtual memory.

+

If specified, this directive will cause OpenVPN to immediately forget +username/password inputs after they are used. As a result, when OpenVPN +needs a username/password, it will prompt for input from stdin, which +may be multiple times during the duration of an OpenVPN session.

+

When using --auth-nocache in combination with a user/password file +and --chroot or --daemon, make sure to use an absolute path.

+

This directive does not affect the --http-proxy username/password. +It is always cached.

+
+--cd dir

Change directory to dir prior to reading any files such as +configuration files, key files, scripts, etc. dir should be an +absolute path, with a leading "/", and without any references to the +current directory such as . or ...

+

This option is useful when you are running OpenVPN in --daemon mode, +and you want to consolidate all of your OpenVPN control files in one +location.

+
+--chroot dir

Chroot to dir after initialization. --chroot essentially +redefines dir as being the top level directory tree (/). OpenVPN +will therefore be unable to access any files outside this tree. This can +be desirable from a security standpoint.

+

Since the chroot operation is delayed until after initialization, most +OpenVPN options that reference files will operate in a pre-chroot +context.

+

In many cases, the dir parameter can point to an empty directory, +however complications can result when scripts or restarts are executed +after the chroot operation.

+

Note: The SSL library will probably need /dev/urandom to be available +inside the chroot directory dir. This is because SSL libraries +occasionally need to collect fresh random. Newer linux kernels and some +BSDs implement a getrandom() or getentropy() syscall that removes the +need for /dev/urandom to be available.

+
+--config file

Load additional config options from file where each line corresponds +to one command line option, but with the leading '--' removed.

+

If --config file is the only option to the openvpn command, the +--config can be removed, and the command can be given as openvpn +file

+

Note that configuration files can be nested to a reasonable depth.

+

Double quotation or single quotation characters ("", '') can be used to +enclose single parameters containing whitespace, and "#" or ";" +characters in the first column can be used to denote comments.

+

Note that OpenVPN 2.0 and higher performs backslash-based shell escaping +for characters not in single quotations, so the following mappings +should be observed:

+
+\\       Maps to a single backslash character (\).
+\"       Pass a literal doublequote character ("), don't
+         interpret it as enclosing a parameter.
+\[SPACE] Pass a literal space or tab character, don't
+         interpret it as a parameter delimiter.
+
+

For example on Windows, use double backslashes to represent pathnames:

+
+secret "c:\\OpenVPN\\secret.key"
+
+

For examples of configuration files, see +https://openvpn.net/community-resources/how-to/

+

Here is an example configuration file:

+
+#
+# Sample OpenVPN configuration file for
+# using a pre-shared static key.
+#
+# '#' or ';' may be used to delimit comments.
+
+# Use a dynamic tun device.
+dev tun
+
+# Our remote peer
+remote mypeer.mydomain
+
+# 10.1.0.1 is our local VPN endpoint
+# 10.1.0.2 is our remote VPN endpoint
+ifconfig 10.1.0.1 10.1.0.2
+
+# Our pre-shared static key
+secret static.key
+
+
+--daemon progname
 

Become a daemon after all initialization functions are completed. This +option will cause all message and error output to be sent to the syslog +file (such as /var/log/messages), except for the output of +scripts and ifconfig commands, which will go to /dev/null unless +otherwise redirected. The syslog redirection occurs immediately at the +point that --daemon is parsed on the command line even though the +daemonization point occurs later. If one of the --log options is +present, it will supersede syslog redirection.

+

The optional progname parameter will cause OpenVPN to report its +program name to the system logger as progname. This can be useful in +linking OpenVPN messages in the syslog file with specific tunnels. When +unspecified, progname defaults to "openvpn".

+

When OpenVPN is run with the --daemon option, it will try to delay +daemonization until the majority of initialization functions which are +capable of generating fatal errors are complete. This means that +initialization scripts can test the return status of the openvpn command +for a fairly reliable indication of whether the command has correctly +initialized and entered the packet forwarding event loop.

+

In OpenVPN, the vast majority of errors which occur after initialization +are non-fatal.

+

Note: as soon as OpenVPN has daemonized, it can not ask for usernames, +passwords, or key pass phrases anymore. This has certain consequences, +namely that using a password-protected private key will fail unless the +--askpass option is used to tell OpenVPN to ask for the pass phrase +(this requirement is new in v2.3.7, and is a consequence of calling +daemon() before initializing the crypto layer).

+

Further, using --daemon together with --auth-user-pass (entered +on console) and --auth-nocache will fail as soon as key +renegotiation (and reauthentication) occurs.

+
+--disable-occ

Don't output a warning message if option inconsistencies are detected +between peers. An example of an option inconsistency would be where one +peer uses --dev tun while the other peer uses --dev tap.

+

Use of this option is discouraged, but is provided as a temporary fix in +situations where a recent version of OpenVPN must connect to an old +version.

+
+--engine engine-name
 

Enable OpenSSL hardware-based crypto engine functionality.

+

If engine-name is specified, use a specific crypto engine. Use the +--show-engines standalone option to list the crypto engines which +are supported by OpenSSL.

+
+--fast-io

(Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a call to +poll/epoll/select prior to the write operation. The purpose of such a +call would normally be to block until the device or socket is ready to +accept the write. Such blocking is unnecessary on some platforms which +don't support write blocking on UDP sockets or TUN/TAP devices. In such +cases, one can optimize the event loop by avoiding the poll/epoll/select +call, improving CPU efficiency by 5% to 10%.

+

This option can only be used on non-Windows systems, when --proto +udp is specified, and when --shaper is NOT specified.

+
+--group groupSimilar to the --user option, this option changes the group ID of +the OpenVPN process to group after initialization.
+--ignore-unknown-option args
 

Valid syntax:

+
+ignore-unknown-options opt1 opt2 opt3 ... optN
+
+

When one of options opt1 ... optN is encountered in the configuration +file the configuration file parsing does not fail if this OpenVPN version +does not support the option. Multiple --ignore-unknown-option options +can be given to support a larger number of options to ignore.

+

This option should be used with caution, as there are good security +reasons for having OpenVPN fail if it detects problems in a config file. +Having said that, there are valid reasons for wanting new software +features to gracefully degrade when encountered by older software +versions.

+

--ignore-unknown-option is available since OpenVPN 2.3.3.

+
+--iproute cmdSet alternate command to execute instead of default iproute2 command. +May be used in order to execute OpenVPN in unprivileged environment.
+--keying-material-exporter args
 

Save Exported Keying Material [RFC5705] of len bytes (must be between 16 +and 4095 bytes) using label in environment +(exported_keying_material) for use by plugins in +OPENVPN_PLUGIN_TLS_FINAL callback.

+

Valid syntax:

+
+keying-material-exporter label len
+
+

Note that exporter labels have the potential to collide with existing +PRF labels. In order to prevent this, labels MUST begin with +EXPORTER.

+
+--mlock

Disable paging by calling the POSIX mlockall function. Requires that +OpenVPN be initially run as root (though OpenVPN can subsequently +downgrade its UID using the --user option).

+

Using this option ensures that key material and tunnel data are never +written to disk due to virtual memory paging operations which occur +under most modern operating systems. It ensures that even if an attacker +was able to crack the box running OpenVPN, he would not be able to scan +the system swap file to recover previously used ephemeral keys, which +are used for a period of time governed by the --reneg options (see +below), then are discarded.

+

The downside of using --mlock is that it will reduce the amount of +physical memory available to other applications.

+
+--nice nChange process priority after initialization (n greater than 0 is +lower priority, n less than zero is higher priority).
+--persist-key

Don't re-read key files across SIGUSR1 or --ping-restart.

+

This option can be combined with --user nobody to allow restarts +triggered by the SIGUSR1 signal. Normally if you drop root +privileges in OpenVPN, the daemon cannot be restarted since it will now +be unable to re-read protected key files.

+

This option solves the problem by persisting keys across SIGUSR1 +resets, so they don't need to be re-read.

+
+--remap-usr1 signal
 

Control whether internally or externally generated SIGUSR1 signals +are remapped to SIGHUP (restart without persisting state) or +SIGTERM (exit).

+

signal can be set to SIGHUP or SIGTERM. By default, +no remapping occurs.

+
+--script-security level
 

This directive offers policy-level control over OpenVPN's usage of +external programs and scripts. Lower level values are more +restrictive, higher values are more permissive. Settings for level:

+
+
0
+
Strictly no calling of external programs.
+
1
+
(Default) Only call built-in executables such as ifconfig, +ip, route, or netsh.
+
2
+
Allow calling of built-in executables and user-defined +scripts.
+
3
+
Allow passwords to be passed to scripts via environmental +variables (potentially unsafe).
+
+

OpenVPN releases before v2.3 also supported a method flag which +indicated how OpenVPN should call external commands and scripts. This +could be either execve or system. As of OpenVPN 2.3, this +flag is no longer accepted. In most *nix environments the execve() +approach has been used without any issues.

+

Some directives such as --up allow options to be passed to the +external script. In these cases make sure the script name does not +contain any spaces or the configuration parser will choke because it +can't determine where the script name ends and script options start.

+

To run scripts in Windows in earlier OpenVPN versions you needed to +either add a full path to the script interpreter which can parse the +script or use the system flag to run these scripts. As of OpenVPN +2.3 it is now a strict requirement to have full path to the script +interpreter when running non-executables files. This is not needed for +executable files, such as .exe, .com, .bat or .cmd files. For example, +if you have a Visual Basic script, you must use this syntax now:

+
+--up 'C:\\Windows\\System32\\wscript.exe C:\\Program\ Files\\OpenVPN\\config\\my-up-script.vbs'
+
+

Please note the single quote marks and the escaping of the backslashes +(\) and the space character.

+

The reason the support for the system flag was removed is due to +the security implications with shell expansions when executing scripts +via the system() call.

+
+--setcon context
 

Apply SELinux context after initialization. This essentially +provides the ability to restrict OpenVPN's rights to only network I/O +operations, thanks to SELinux. This goes further than --user and +--chroot in that those two, while being great security features, +unfortunately do not protect against privilege escalation by +exploitation of a vulnerable system call. You can of course combine all +three, but please note that since setcon requires access to /proc you +will have to provide it inside the chroot directory (e.g. with mount +--bind).

+

Since the setcon operation is delayed until after initialization, +OpenVPN can be restricted to just network-related system calls, whereas +by applying the context before startup (such as the OpenVPN one provided +in the SELinux Reference Policies) you will have to allow many things +required only during initialization.

+

Like with chroot, complications can result when scripts or restarts are +executed after the setcon operation, which is why you should really +consider using the --persist-key and --persist-tun options.

+
+--status args

Write operational status to file every n seconds.

+

Valid syntaxes:

+
+status file
+status file n
+
+

Status can also be written to the syslog by sending a SIGUSR2 +signal.

+

With multi-client capability enabled on a server, the status file +includes a list of clients and a routing table. The output format can be +controlled by the --status-version option in that case.

+

For clients or instances running in point-to-point mode, it will contain +the traffic statistics.

+
+--status-version n
 

Set the status file format version number to n.

+

This only affects the status file on servers with multi-client +capability enabled. Valid status version values:

+
+
1
+
Traditional format (default). The client list contains the +following fields comma-separated: Common Name, Real Address, Bytes +Received, Bytes Sent, Connected Since.
+
2
+
A more reliable format for external processing. Compared to +version 1, the client list contains some additional fields: +Virtual Address, Virtual IPv6 Address, Username, Client ID, Peer ID, +Data Channel Cipher. Future versions may extend the number of fields.
+
3
+
Identical to 2, but fields are tab-separated.
+
+
+--test-crypto

Do a self-test of OpenVPN's crypto options by encrypting and decrypting +test packets using the data channel encryption options specified above. +This option does not require a peer to function, and therefore can be +specified without --dev or --remote.

+

The typical usage of --test-crypto would be something like this:

+
+openvpn --test-crypto --secret key
+
+

or

+
+openvpn --test-crypto --secret key --verb 9
+
+

This option is very useful to test OpenVPN after it has been ported to a +new platform, or to isolate problems in the compiler, OpenSSL crypto +library, or OpenVPN's crypto code. Since it is a self-test mode, +problems with encryption and authentication can be debugged +independently of network and tunnel issues.

+
+--tmp-dir dir

Specify a directory dir for temporary files. This directory will be +used by openvpn processes and script to communicate temporary data with +openvpn main process. Note that the directory must be writable by the +OpenVPN process after it has dropped it's root privileges.

+

This directory will be used by in the following cases:

+
    +
  • --client-connect scripts and OPENVPN_PLUGIN_CLIENT_CONNECT +plug-in hook to dynamically generate client-specific configuration +client_connect_config_file and return success/failure via +client_connect_deferred_file when using deferred client connect +method
    • +
  • OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY plug-in hooks returns +success/failure via auth_control_file when using deferred auth +method
    • +
  • OPENVPN_PLUGIN_ENABLE_PF plugin hook to pass filtering rules +via pf_file
    • +
+
+--use-prediction-resistance
 

Enable prediction resistance on mbed TLS's RNG.

+

Enabling prediction resistance causes the RNG to reseed in each call for +random. Reseeding this often can quickly deplete the kernel entropy +pool.

+

If you need this option, please consider running a daemon that adds +entropy to the kernel pool.

+
+--user user

Change the user ID of the OpenVPN process to user after +initialization, dropping privileges in the process. This option is +useful to protect the system in the event that some hostile party was +able to gain control of an OpenVPN session. Though OpenVPN's security +features make this unlikely, it is provided as a second line of defense.

+

By setting user to nobody or somebody similarly unprivileged, +the hostile party would be limited in what damage they could cause. Of +course once you take away privileges, you cannot return them to an +OpenVPN session. This means, for example, that if you want to reset an +OpenVPN daemon with a SIGUSR1 signal (for example in response to +a DHCP reset), you should make use of one or more of the --persist +options to ensure that OpenVPN doesn't need to execute any privileged +operations in order to restart (such as re-reading key files or running +ifconfig on the TUN device).

+
+--writepid file
 Write OpenVPN's main process ID to file.
+
+
+

Log options

+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+--echo parms

Echo parms to log output.

+

Designed to be used to send messages to a controlling application which +is receiving the OpenVPN log output.

+
+--errors-to-stderr
 Output errors to stderr instead of stdout unless log output is +redirected by one of the --log options.
+--log file

Output logging messages to file, including output to stdout/stderr +which is generated by called scripts. If file already exists it will +be truncated. This option takes effect immediately when it is parsed in +the command line and will supersede syslog output if --daemon or +--inetd is also specified. This option is persistent over the entire +course of an OpenVPN instantiation and will not be reset by +SIGHUP, SIGUSR1, or --ping-restart.

+

Note that on Windows, when OpenVPN is started as a service, logging +occurs by default without the need to specify this option.

+
+--log-append file
 Append logging messages to file. If file does not exist, it will +be created. This option behaves exactly like --log except that it +appends to rather than truncating the log file.
+--machine-readable-output
 Always write timestamps and message flags to log messages, even when +they otherwise would not be prefixed. In particular, this applies to log +messages sent to stdout.
+--mute nLog at most n consecutive messages in the same category. This is +useful to limit repetitive logging of similar message types.
+--mute-replay-warnings
 Silence the output of replay warnings, which are a common false alarm on +WiFi networks. This option preserves the security of the replay +protection code without the verbosity associated with warnings about +duplicate packets.
+--suppress-timestamps
 Avoid writing timestamps to log messages, even when they otherwise would +be prepended. In particular, this applies to log messages sent to +stdout.
+--syslog progname
 Direct log output to system logger, but do not become a daemon. See +--daemon directive above for description of progname parameter.
+--verb n

Set output verbosity to n (default 1). Each level shows all +info from the previous levels. Level 3 is recommended if you want +a good summary of what's happening without being swamped by output.

+
+
0
+
No output except fatal errors.
+
1 to 4
+
Normal usage range.
+
5
+
Outputs R and W characters to the console for +each packet read and write, uppercase is used for TCP/UDP +packets and lowercase is used for TUN/TAP packets.
+
6 to 11
+
Debug info range (see errlevel.h in the source code for +additional information on debug levels).
+
+
+
+
+

Protocol options

+

Options in this section affect features available in the OpenVPN wire +protocol. Many of these options also define the encryption options +of the data channel in the OpenVPN wire protocol. These options must be +configured in a compatible way between both the local and remote side.

+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+--allow-compression mode
 

As described in the --compress option, compression is a potentially +dangerous option. This option allows controlling the behaviour of +OpenVPN when compression is used and allowed.

+

Valid syntaxes:

+
+allow-compression
+allow-compression mode
+
+

The mode argument can be one of the following values:

+
+
asym (default)
+
OpenVPN will only decompress downlink packets but not compress +uplink packets. This also allows migrating to disable compression +when changing both server and client configurations to remove +compression at the same time is not a feasible option.
+
no
+
OpenVPN will refuse any non-stub compression.
+
yes
+
OpenVPN will send and receive compressed packets.
+
+
+--auth alg

Authenticate data channel packets and (if enabled) tls-auth control +channel packets with HMAC using message digest algorithm alg. (The +default is SHA1 ). HMAC is a commonly used message authentication +algorithm (MAC) that uses a data string, a secure hash algorithm and a +key to produce a digital signature.

+

The OpenVPN data channel protocol uses encrypt-then-mac (i.e. first +encrypt a packet then HMAC the resulting ciphertext), which prevents +padding oracle attacks.

+

If an AEAD cipher mode (e.g. GCM) is chosen then the specified --auth +algorithm is ignored for the data channel and the authentication method +of the AEAD cipher is used instead. Note that alg still specifies +the digest used for tls-auth.

+

In static-key encryption mode, the HMAC key is included in the key file +generated by --genkey. In TLS mode, the HMAC key is dynamically +generated and shared between peers via the TLS control channel. If +OpenVPN receives a packet with a bad HMAC it will drop the packet. HMAC +usually adds 16 or 20 bytes per packet. Set alg=none to disable +authentication.

+

For more information on HMAC see +http://www.cs.ucsd.edu/users/mihir/papers/hmac.html

+
+--cipher alg

This option is deprecated for server-client mode. --data-ciphers +or possibly --data-ciphers-fallback` should be used instead.

+

Encrypt data channel packets with cipher algorithm alg.

+

The default is BF-CBC, an abbreviation for Blowfish in Cipher +Block Chaining mode. When cipher negotiation (NCP) is allowed, +OpenVPN 2.4 and newer on both client and server side will automatically +upgrade to AES-256-GCM. See --data-ciphers and +--ncp-disable for more details on NCP.

+

Using BF-CBC is no longer recommended, because of its 64-bit +block size. This small block size allows attacks based on collisions, as +demonstrated by SWEET32. See +https://community.openvpn.net/openvpn/wiki/SWEET32 +for details. Due to this, support for BF-CBC, DES, +CAST5, IDEA and RC2 ciphers will be removed in +OpenVPN 2.6.

+

To see other ciphers that are available with OpenVPN, use the +--show-ciphers option.

+

Set alg to none to disable encryption.

+
+--compress algorithm
 

DEPRECATED Enable a compression algorithm. Compression is generally +not recommended. VPN tunnels which use compression are susceptible to +the VORALCE attack vector.

+

The algorithm parameter may be lzo, lz4, +lz4-v2, stub, stub-v2 or empty. +LZO and LZ4 are different compression algorithms, with LZ4 generally +offering the best performance with least CPU usage.

+

The lz4-v2 and stub-v2 variants implement a better +framing that does not add overhead when packets cannot be compressed. All +other variants always add one extra framing byte compared to no +compression framing.

+

If the algorithm parameter is stub, stub-v2 or empty, +compression will be turned off, but the packet framing for compression +will still be enabled, allowing a different setting to be pushed later. +Additionally, stub and stub-v2 wil disable announcing +lzo and lz4 compression support via IV_ variables to the +server.

+

Note: the stub (or empty) option is NOT compatible with the older +option --comp-lzo no.

+

*Security Considerations*

+

Compression and encryption is a tricky combination. If an attacker knows +or is able to control (parts of) the plain-text of packets that contain +secrets, the attacker might be able to extract the secret if compression +is enabled. See e.g. the CRIME and BREACH attacks on TLS and +VORACLE on VPNs which also leverage to break encryption. If you are not +entirely sure that the above does not apply to your traffic, you are +advised to not enable compression.

+
+--comp-lzo mode
 

DEPRECATED Enable LZO compression algorithm. Compression is +generally not recommended. VPN tunnels which uses compression are +suspectible to the VORALCE attack vector.

+

Use LZO compression -- may add up to 1 byte per packet for incompressible +data. mode may be yes, no, or adaptive +(default).

+

In a server mode setup, it is possible to selectively turn compression +on or off for individual clients.

+

First, make sure the client-side config file enables selective +compression by having at least one --comp-lzo directive, such as +--comp-lzo no. This will turn off compression by default, but allow +a future directive push from the server to dynamically change the +on/off/adaptive setting.

+

Next in a --client-config-dir file, specify the compression setting +for the client, for example:

+
+comp-lzo yes
+push "comp-lzo yes"
+
+

The first line sets the comp-lzo setting for the server side of the +link, the second sets the client side.

+
+--comp-noadapt

DEPRECATED When used in conjunction with --comp-lzo, this option +will disable OpenVPN's adaptive compression algorithm. Normally, adaptive +compression is enabled with --comp-lzo.

+

Adaptive compression tries to optimize the case where you have +compression enabled, but you are sending predominantly incompressible +(or pre-compressed) packets over the tunnel, such as an FTP or rsync +transfer of a large, compressed file. With adaptive compression, OpenVPN +will periodically sample the compression process to measure its +efficiency. If the data being sent over the tunnel is already +compressed, the compression efficiency will be very low, triggering +openvpn to disable compression for a period of time until the next +re-sample test.

+
+--key-direction
 Alternative way of specifying the optional direction parameter for the +--tls-auth and --secret options. Useful when using inline files +(See section on inline files).
+--keysize n

DEPRECATED This option will be removed in OpenVPN 2.6.

+

Size of cipher key in bits (optional). If unspecified, defaults to +cipher-specific default. The --show-ciphers option (see below) shows +all available OpenSSL ciphers, their default key sizes, and whether the +key size can be changed. Use care in changing a cipher's default key +size. Many ciphers have not been extensively cryptanalyzed with +non-standard key lengths, and a larger key may offer no real guarantee +of greater security, or may even reduce security.

+
+--data-ciphers cipher-list
 

Restrict the allowed ciphers to be negotiated to the ciphers in +cipher-list. cipher-list is a colon-separated list of ciphers, +and defaults to AES-256-GCM:AES-128-GCM.

+

For servers, the first cipher from cipher-list that is also +supported by the client will be pushed to clients that support cipher +negotiation.

+

Cipher negotiation is enabled in client-server mode only. I.e. if +--mode is set to 'server' (server-side, implied by setting +--server ), or if --pull is specified (client-side, implied by +setting --client).

+

If no common cipher is found during cipher negotiation, the connection +is terminated. To support old clients/old servers that do not provide any +cipher negotiation support see --data-ciphers-fallback.

+

Additionally, to allow for more smooth transition, if NCP is enabled, +OpenVPN will inherit the cipher of the peer if that cipher is different +from the local --cipher setting, but the peer cipher is one of the +ciphers specified in --data-ciphers. E.g. a non-NCP client (<=v2.3, +or with --ncp-disabled set) connecting to a NCP server (v2.4+) with +--cipher BF-CBC and --data-ciphers AES-256-GCM:AES-256-CBC set can +either specify --cipher BF-CBC or --cipher AES-256-CBC and both +will work.

+

Note for using NCP with an OpenVPN 2.4 peer: This list must include the +AES-256-GCM and AES-128-GCM ciphers.

+

This list is restricted to be 127 chars long after conversion to OpenVPN +ciphers.

+

This option was called --ncp-ciphers in OpenVPN 2.4 but has been renamed +to --data-ciphers in OpenVPN 2.5 to more accurately reflect its meaning.

+
+--data-ciphers-fallback alg
 

Configure a cipher that is used to fall back to if we could not determine +which cipher the peer is willing to use.

+

This option should only be needed to +connect to peers that are running OpenVPN 2.3 and older version, and +have been configured with --enable-small +(typically used on routers or other embedded devices).

+
+--ncp-disableDEPRECATED Disable "Negotiable Crypto Parameters". This completely +disables cipher negotiation.
+--secret args

Enable Static Key encryption mode (non-TLS). Use pre-shared secret +file which was generated with --genkey.

+

Valid syntaxes:

+
+secret file
+secret file direction
+
+

The optional direction parameter enables the use of 4 distinct keys +(HMAC-send, cipher-encrypt, HMAC-receive, cipher-decrypt), so that each +data flow direction has a different set of HMAC and cipher keys. This +has a number of desirable security properties including eliminating +certain kinds of DoS and message replay attacks.

+

When the direction parameter is omitted, 2 keys are used +bidirectionally, one for HMAC and the other for encryption/decryption.

+

The direction parameter should always be complementary on either +side of the connection, i.e. one side should use 0 and the other +should use 1, or both sides should omit it altogether.

+

The direction parameter requires that file contains a 2048 bit +key. While pre-1.5 versions of OpenVPN generate 1024 bit key files, any +version of OpenVPN which supports the direction parameter, will also +support 2048 bit key file generation using the --genkey option.

+

Static key encryption mode has certain advantages, the primary being +ease of configuration.

+

There are no certificates or certificate authorities or complicated +negotiation handshakes and protocols. The only requirement is that you +have a pre-existing secure channel with your peer (such as ssh) to +initially copy the key. This requirement, along with the fact that your +key never changes unless you manually generate a new one, makes it +somewhat less secure than TLS mode (see below). If an attacker manages +to steal your key, everything that was ever encrypted with it is +compromised. Contrast that to the perfect forward secrecy features of +TLS mode (using Diffie Hellman key exchange), where even if an attacker +was able to steal your private key, he would gain no information to help +him decrypt past sessions.

+

Another advantageous aspect of Static Key encryption mode is that it is +a handshake-free protocol without any distinguishing signature or +feature (such as a header or protocol handshake sequence) that would +mark the ciphertext packets as being generated by OpenVPN. Anyone +eavesdropping on the wire would see nothing but random-looking data.

+
+--tran-window n
 Transition window -- our old key can live this many seconds after a new +a key renegotiation begins (default 3600 seconds). This feature +allows for a graceful transition from old to new key, and removes the key +renegotiation sequence from the critical path of tunnel data forwarding.
+
+
+

Client Options

+

The client options are used when connecting to an OpenVPN server configured +to use --server, --server-bridge, or --mode server in its +configuration.

+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+--allow-pull-fqdn
 Allow client to pull DNS names from server (rather than being limited to +IP address) for --ifconfig, --route, and --route-gateway.
+--allow-recursive-routing
 When this option is set, OpenVPN will not drop incoming tun packets with +same destination as host.
+--auth-token token
 

This is not an option to be used directly in any configuration files, +but rather push this option from a --client-connect script or a +--plugin which hooks into the OPENVPN_PLUGIN_CLIENT_CONNECT +or OPENVPN_PLUGIN_CLIENT_CONNECT_V2 calls. This option provides a +possibility to replace the clients password with an authentication token +during the lifetime of the OpenVPN client.

+

Whenever the connection is renegotiated and the +--auth-user-pass-verify script or --plugin making use of the +OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY hook is triggered, it will +pass over this token as the password instead of the password the user +provided. The authentication token can only be reset by a full reconnect +where the server can push new options to the client. The password the +user entered is never preserved once an authentication token has been +set. If the OpenVPN server side rejects the authentication token then +the client will receive an AUTH_FAILED and disconnect.

+

The purpose of this is to enable two factor authentication methods, such +as HOTP or TOTP, to be used without needing to retrieve a new OTP code +each time the connection is renegotiated. Another use case is to cache +authentication data on the client without needing to have the users +password cached in memory during the life time of the session.

+

To make use of this feature, the --client-connect script or +--plugin needs to put

+
+push "auth-token UNIQUE_TOKEN_VALUE"
+
+

into the file/buffer for dynamic configuration data. This will then make +the OpenVPN server to push this value to the client, which replaces the +local password with the UNIQUE_TOKEN_VALUE.

+

Newer clients (2.4.7+) will fall back to the original password method +after a failed auth. Older clients will keep using the token value and +react according to --auth-retry

+
+--auth-user-pass
 

Authenticate with server using username/password.

+

Valid syntaxes:

+
+auth-user-pass
+auth-user-pass up
+
+

If up is present, it must be a file containing username/password on 2 +lines. If the password line is missing, OpenVPN will prompt for one.

+

If up is omitted, username/password will be prompted from the +console.

+

The server configuration must specify an --auth-user-pass-verify +script to verify the username/password provided by the client.

+
+--auth-retry type
 

Controls how OpenVPN responds to username/password verification errors +such as the client-side response to an AUTH_FAILED message from +the server or verification failure of the private key password.

+

Normally used to prevent auth errors from being fatal on the client +side, and to permit username/password requeries in case of error.

+

An AUTH_FAILED message is generated by the server if the client +fails --auth-user-pass authentication, or if the server-side +--client-connect script returns an error status when the client +tries to connect.

+

type can be one of:

+
+
none
+
Client will exit with a fatal error (this is the default).
+
nointeract
+
Client will retry the connection without requerying +for an --auth-user-pass username/password. Use this option for +unattended clients.
+
interact
+
Client will requery for an --auth-user-pass +username/password and/or private key password before attempting a +reconnection.
+
+

Note that while this option cannot be pushed, it can be controlled from +the management interface.

+
+--client

A helper directive designed to simplify the configuration of OpenVPN's +client mode. This directive is equivalent to:

+
+pull
+tls-client
+
+
+--client-nat args
 

This pushable client option sets up a stateless one-to-one NAT rule on +packet addresses (not ports), and is useful in cases where routes or +ifconfig settings pushed to the client would create an IP numbering +conflict.

+

Examples:

+
+client-nat snat 192.168.0.0/255.255.0.0
+client-nat dnat 10.64.0.0/255.255.0.0
+
+

network/netmask (for example 192.168.0.0/255.255.0.0) defines +the local view of a resource from the client perspective, while +alias/netmask (for example 10.64.0.0/255.255.0.0) defines the +remote view from the server perspective.

+

Use snat (source NAT) for resources owned by the client and +dnat (destination NAT) for remote resources.

+

Set --verb 6 for debugging info showing the transformation of +src/dest addresses in packets.

+
+--connect-retry n
 Wait n seconds between connection attempts (default 5). +Repeated reconnection attempts are slowed down after 5 retries per +remote by doubling the wait time after each unsuccessful attempt. An +optional argument max specifies the maximum value of wait time in +seconds at which it gets capped (default 300).
+--connect-retry-max n
 n specifies the number of times each --remote or +<connection> entry is tried. Specifying n as 1 would try +each entry exactly once. A successful connection resets the counter. +(default unlimited).
+--connect-timeout n
 See --server-poll-timeout.
+--explicit-exit-notify n
 

In UDP client mode or point-to-point mode, send server/peer an exit +notification if tunnel is restarted or OpenVPN process is exited. In +client mode, on exit/restart, this option will tell the server to +immediately close its client instance object rather than waiting for a +timeout.

+

The n parameter (default 1 if not present) controls the +maximum number of attempts that the client will try to resend the exit +notification message.

+

In UDP server mode, send RESTART control channel command to +connected clients. The n parameter (default 1 if not present) +controls client behavior. With n = 1 client will attempt to +reconnect to the same server, with n = 2 client will advance +to the next server.

+

OpenVPN will not send any exit notifications unless this option is +enabled.

+
+--inactive args
 

Causes OpenVPN to exit after n seconds of inactivity on the TUN/TAP +device. The time length of inactivity is measured since the last +incoming or outgoing tunnel packet. The default value is 0 seconds, +which disables this feature.

+

Valid syntaxes:

+
+inactive n
+inactive n bytes
+
+

If the optional bytes parameter is included, exit if less than +bytes of combined in/out traffic are produced on the tun/tap device +in n seconds.

+

In any case, OpenVPN's internal ping packets (which are just keepalives) +and TLS control packets are not considered "activity", nor are they +counted as traffic, as they are used internally by OpenVPN and are not +an indication of actual user activity.

+
+--proto-force p
 When iterating through connection profiles, only consider profiles using +protocol p (tcp | udp).
+--pull

This option must be used on a client which is connecting to a +multi-client server. It indicates to OpenVPN that it should accept +options pushed by the server, provided they are part of the legal set of +pushable options (note that the --pull option is implied by +--client ).

+

In particular, --pull allows the server to push routes to the +client, so you should not use --pull or --client in situations +where you don't trust the server to have control over the client's +routing table.

+
+--pull-filter args
 

Filter options on the client pushed by the server to the client.

+

Valid syntaxes:

+
+pull-filter accept text
+pull-filter ignore text
+pull-filter reject text
+
+

Filter options received from the server if the option starts with +text. The action flag accept allows the option, +ignore removes it and reject flags an error and triggers +a SIGUSR1 restart. The filters may be specified multiple times, +and each filter is applied in the order it is specified. The filtering of +each option stops as soon as a match is found. Unmatched options are accepted +by default.

+

Prefix comparison is used to match text against the received option so +that

+
+pull-filter ignore "route"
+
+

would remove all pushed options starting with route which would +include, for example, route-gateway. Enclose text in quotes to +embed spaces.

+
+pull-filter accept "route 192.168.1."
+pull-filter ignore "route "
+
+

would remove all routes that do not start with 192.168.1.

+

Note that reject may result in a repeated cycle of failure and +reconnect, unless multiple remotes are specified and connection to the +next remote succeeds. To silently ignore an option pushed by the server, +use ignore.

+
+--remote args

Remote host name or IP address. It supports two additional optional +arguments: port and proto. On the client, multiple --remote +options may be specified for redundancy, each referring to a different +OpenVPN server. Specifying multiple --remote options for this +purpose is a special case of the more general connection-profile +feature. See the <connection> documentation below.

+

The OpenVPN client will try to connect to a server at host:port in +the order specified by the list of --remote options.

+

Examples:

+
+remote server.example.net
+remote server.example.net 1194
+remote server.example.net tcp
+
+

proto indicates the protocol to use when connecting with the remote, +and may be tcp or udp.

+

For forcing IPv4 or IPv6 connection suffix tcp or udp with 4/6 like +udp4/udp6/tcp4/tcp6.

+

The client will move on to the next host in the list, in the event of +connection failure. Note that at any given time, the OpenVPN client will +at most be connected to one server.

+

Note that since UDP is connectionless, connection failure is defined by +the --ping and --ping-restart options.

+

Note the following corner case: If you use multiple --remote +options, AND you are dropping root privileges on the client with +--user and/or --group AND the client is running a non-Windows +OS, if the client needs to switch to a different server, and that server +pushes back different TUN/TAP or route settings, the client may lack the +necessary privileges to close and reopen the TUN/TAP interface. This +could cause the client to exit with a fatal error.

+

If --remote is unspecified, OpenVPN will listen for packets from any +IP address, but will not act on those packets unless they pass all +authentication tests. This requirement for authentication is binding on +all potential peers, even those from known and supposedly trusted IP +addresses (it is very easy to forge a source IP address on a UDP +packet).

+

When used in TCP mode, --remote will act as a filter, rejecting +connections from any host which does not match host.

+

If host is a DNS name which resolves to multiple IP addresses, +OpenVPN will try them in the order that the system getaddrinfo() +presents them, so priorization and DNS randomization is done by the +system library. Unless an IP version is forced by the protocol +specification (4/6 suffix), OpenVPN will try both IPv4 and IPv6 +addresses, in the order getaddrinfo() returns them.

+
+--remote-random
 When multiple --remote address/ports are specified, or if connection +profiles are being used, initially randomize the order of the list as a +kind of basic load-balancing measure.
+--remote-random-hostname
 Prepend a random string (6 bytes, 12 hex characters) to hostname to +prevent DNS caching. For example, "foo.bar.gov" would be modified to +"<random-chars>.foo.bar.gov".
+--resolv-retry n
 

If hostname resolve fails for --remote, retry resolve for n +seconds before failing.

+

Set n to "infinite" to retry indefinitely.

+

By default, --resolv-retry infinite is enabled. You can disable by +setting n=0.

+
+--single-session
 

After initially connecting to a remote peer, disallow any new +connections. Using this option means that a remote peer cannot connect, +disconnect, and then reconnect.

+

If the daemon is reset by a signal or --ping-restart, it will allow +one new connection.

+

--single-session can be used with --ping-exit or --inactive +to create a single dynamic session that will exit when finished.

+
+--server-poll-timeout n
 When connecting to a remote server do not wait for more than n +seconds for a response before trying the next server. The default value +is 120s. This timeout includes proxy and TCP connect timeouts.
+--static-challenge args
 

Enable static challenge/response protocol

+

Valid syntax:

+
+static-challenge text echo
+
+

The text challenge text is presented to the user which describes what +information is requested. The echo flag indicates if the user's +input should be echoed on the screen. Valid echo values are +0 or 1.

+

See management-notes.txt in the OpenVPN distribution for a description of +the OpenVPN challenge/response protocol.

+
+ +++ + + + + + + + + + + + + + +
+--show-proxy-settings
 Show sensed HTTP or SOCKS proxy settings. Currently, only Windows +clients support this option.
+--http-proxy args
 

Connect to remote host through an HTTP proxy. This requires at least an +address server and port argument. If HTTP Proxy-Authenticate +is required, a file name to an authfile file containing a username +and password on 2 lines can be given, or stdin to prompt from +console. Its content can also be specified in the config file with the +--http-proxy-user-pass option. (See section on inline files)

+

The last optional argument is an auth-method which should be one +of none, basic, or ntlm.

+

HTTP Digest authentication is supported as well, but only via the +auto or auto-nct flags (below). This must replace +the authfile argument.

+

The auto flag causes OpenVPN to automatically determine the +auth-method and query stdin or the management interface for +username/password credentials, if required. This flag exists on OpenVPN +2.1 or higher.

+

The auto-nct flag (no clear-text auth) instructs OpenVPN to +automatically determine the authentication method, but to reject weak +authentication protocols such as HTTP Basic Authentication.

+

Examples:

+
+http-proxy proxy.example.net 3128
+http-proxy proxy.example.net 3128 authfile.txt
+http-proxy proxy.example.net 3128 stdin
+http-proxy proxy.example.net 3128 auto basic
+http-proxy proxy.example.net 3128 auto-nct ntlm
+
+
+--http-proxy-option args
 

Set extended HTTP proxy options. Requires an option type as argument +and an optional parameter to the type. Repeat to set multiple +options.

+
+
VERSION version
+
Set HTTP version number to version (default 1.0).
+
AGENT user-agent
+
Set HTTP "User-Agent" string to user-agent.
+
CUSTOM-HEADER name content
+
Adds the custom Header with name as name and content as +the content of the custom HTTP header.
+
+

Examples:

+
+http-proxy-option VERSION 1.1
+http-proxy-option AGENT OpenVPN/2.4
+http-proxy-option X-Proxy-Flag some-flags
+
+
+--socks-proxy args
 Connect to remote host through a Socks5 proxy. A required server +argument is needed. Optionally a port (default 1080) and +authfile can be given. The authfile is a file containing a +username and password on 2 lines, or stdin can be used to +prompt from console.
+
+
+

Server Options

+

Starting with OpenVPN 2.0, a multi-client TCP/UDP server mode is +supported, and can be enabled with the --mode server option. In +server mode, OpenVPN will listen on a single port for incoming client +connections. All client connections will be routed through a single tun +or tap interface. This mode is designed for scalability and should be +able to support hundreds or even thousands of clients on sufficiently +fast hardware. SSL/TLS authentication must be used in this mode.

+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+--auth-gen-token args
 

Returns an authentication token to successfully authenticated clients.

+

Valid syntax:

+
+auth-gen-token [lifetime] [external-auth]
+
+

After successful user/password authentication, the OpenVPN server will +with this option generate a temporary authentication token and push that +to the client. On the following renegotiations, the OpenVPN client will pass +this token instead of the users password. On the server side the server +will do the token authentication internally and it will NOT do any +additional authentications against configured external user/password +authentication mechanisms.

+

The tokens implemented by this mechanism include an initial timestamp and +a renew timestamp and are secured by HMAC.

+

The lifetime argument defines how long the generated token is valid. +The lifetime is defined in seconds. If lifetime is not set or it is set +to 0, the token will never expire.

+

The token will expire either after the configured lifetime of the +token is reached or after not being renewed for more than 2 * +reneg-sec seconds. Clients will be sent renewed tokens on every TLS +renogiation to keep the client's token updated. This is done to +invalidate a token if a client is disconnected for a sufficently long +time, while at the same time permitting much longer token lifetimes for +active clients.

+

This feature is useful for environments which are configured to use One +Time Passwords (OTP) as part of the user/password authentications and +that authentication mechanism does not implement any auth-token support.

+

When the external-auth keyword is present the normal +authentication method will always be called even if auth-token succeeds. +Normally other authentications method are skipped if auth-token +verification suceeds or fails.

+

This option postpones this decision to the external authentication +methods and checks the validity of the account and do other checks.

+

In this mode the environment will have a session_id variable that +holds the session id from auth-gen-token. Also an environment variable +session_state is present. This variable indicates whether the +auth-token has succeeded or not. It can have the following values:

+
+
Initial
+
No token from client.
+
Authenticated
+
Token is valid and not expired.
+
Expired
+
Token is valid but has expired.
+
Invalid
+
Token is invalid (failed HMAC or wrong length)
+
AuthenticatedEmptyUser / ExpiredEmptyUser
+
The token is not valid with the username sent from the client but +would be valid (or expired) if we assume an empty username was +used instead. These two cases are a workaround for behaviour in +OpenVPN 3. If this workaround is not needed these two cases should +be handled in the same way as Invalid.
+
+

Warning: Use this feature only if you want your authentication +method called on every verification. Since the external authentication +is called it needs to also indicate a success or failure of the +authentication. It is strongly recommended to return an authentication +failure in the case of the Invalid/Expired auth-token with the +external-auth option unless the client could authenticate in another +acceptable way (e.g. client certificate), otherwise returning success +will lead to authentication bypass (as does returning success on a wrong +password from a script).

+
+--auth-gen-token-secret file
 Specifies a file that holds a secret for the HMAC used in +--auth-gen-token If file is not present OpenVPN will generate a +random secret on startup. This file should be used if auth-token should +validate after restarting a server or if client should be able to roam +between multiple OpenVPN servers with their auth-token.
+--auth-user-pass-optional
 Allow connections by clients that do not specify a username/password. +Normally, when --auth-user-pass-verify or +--management-client-auth are specified (or an authentication plugin +module), the OpenVPN server daemon will require connecting clients to +specify a username and password. This option makes the submission of a +username/password by clients optional, passing the responsibility to the +user-defined authentication module/script to accept or deny the client +based on other factors (such as the setting of X509 certificate fields). +When this option is used, and a connecting client does not submit a +username/password, the user-defined authentication module/script will +see the username and password as being set to empty strings (""). The +authentication module/script MUST have logic to detect this condition +and respond accordingly.
+--ccd-exclusive
 Require, as a condition of authentication, that a connecting client has +a --client-config-dir file.
+--client-config-dir dir
 

Specify a directory dir for custom client config files. After a +connecting client has been authenticated, OpenVPN will look in this +directory for a file having the same name as the client's X509 common +name. If a matching file exists, it will be opened and parsed for +client-specific configuration options. If no matching file is found, +OpenVPN will instead try to open and parse a default file called +"DEFAULT", which may be provided but is not required. Note that the +configuration files must be readable by the OpenVPN process after it has +dropped it's root privileges.

+

This file can specify a fixed IP address for a given client using +--ifconfig-push, as well as fixed subnets owned by the client using +--iroute.

+

One of the useful properties of this option is that it allows client +configuration files to be conveniently created, edited, or removed while +the server is live, without needing to restart the server.

+

The following options are legal in a client-specific context: --push, +--push-reset, --push-remove, --iroute, --ifconfig-push, +--vlan-pvid and --config.

+
+--client-to-client
 

Because the OpenVPN server mode handles multiple clients through a +single tun or tap interface, it is effectively a router. The +--client-to-client flag tells OpenVPN to internally route +client-to-client traffic rather than pushing all client-originating +traffic to the TUN/TAP interface.

+

When this option is used, each client will "see" the other clients which +are currently connected. Otherwise, each client will only see the +server. Don't use this option if you want to firewall tunnel traffic +using custom, per-client rules.

+
+--disable

Disable a particular client (based on the common name) from connecting. +Don't use this option to disable a client due to key or password +compromise. Use a CRL (certificate revocation list) instead (see the +--crl-verify option).

+

This option must be associated with a specific client instance, which +means that it must be specified either in a client instance config file +using --client-config-dir or dynamically generated using a +--client-connect script.

+
+--connect-freq args
 

Allow a maximum of n new connections per sec seconds from +clients.

+

Valid syntax:

+
+connect-freq n sec
+
+

This is designed to contain DoS attacks which flood the server +with connection requests using certificates which will ultimately fail +to authenticate.

+

This is an imperfect solution however, because in a real DoS scenario, +legitimate connections might also be refused.

+

For the best protection against DoS attacks in server mode, use +--proto udp and either --tls-auth or --tls-crypt.

+
+--duplicate-cnAllow multiple clients with the same common name to concurrently +connect. In the absence of this option, OpenVPN will disconnect a client +instance upon connection of a new client having the same common name.
+--ifconfig-pool args
 

Set aside a pool of subnets to be dynamically allocated to connecting +clients, similar to a DHCP server.

+

Valid syntax:

+
+ifconfig-pool start-IP end-IP [netmask]
+
+

For tun-style tunnels, each client +will be given a /30 subnet (for interoperability with Windows clients). +For tap-style tunnels, individual addresses will be allocated, and the +optional netmask parameter will also be pushed to clients.

+
+--ifconfig-ipv6-pool args
 

Specify an IPv6 address pool for dynamic assignment to clients.

+

Valid args:

+
+ifconfig-ipv6-pool ipv6addr/bits
+
+

The pool starts at ipv6addr and matches the offset determined from +the start of the IPv4 pool.

+
+--ifconfig-pool-persist args
 

Persist/unpersist ifconfig-pool data to file, at seconds +intervals (default 600), as well as on program startup and shutdown.

+

Valid syntax:

+
+ifconfig-pool-persist file [seconds]
+
+

The goal of this option is to provide a long-term association between +clients (denoted by their common name) and the virtual IP address +assigned to them from the ifconfig-pool. Maintaining a long-term +association is good for clients because it allows them to effectively +use the --persist-tun option.

+

file is a comma-delimited ASCII file, formatted as +<Common-Name>,<IP-address>.

+

If seconds = 0, file will be treated as read-only. This +is useful if you would like to treat file as a configuration file.

+

Note that the entries in this file are treated by OpenVPN as +suggestions only, based on past associations between a common name and +IP address. They do not guarantee that the given common name will always +receive the given IP address. If you want guaranteed assignment, use +--ifconfig-push

+
+--ifconfig-push args
 

Push virtual IP endpoints for client tunnel, overriding the +--ifconfig-pool dynamic allocation.

+

Valid syntax:

+
+ifconfig-push local remote-netmask [alias]
+
+

The parameters local and remote-netmask are set according to the +--ifconfig directive which you want to execute on the client machine +to configure the remote end of the tunnel. Note that the parameters +local and remote-netmask are from the perspective of the client, +not the server. They may be DNS names rather than IP addresses, in which +case they will be resolved on the server at the time of client +connection.

+

The optional alias parameter may be used in cases where NAT causes +the client view of its local endpoint to differ from the server view. In +this case local/remote-netmask will refer to the server view while +alias/remote-netmask will refer to the client view.

+

This option must be associated with a specific client instance, which +means that it must be specified either in a client instance config file +using --client-config-dir or dynamically generated using a +--client-connect script.

+

Remember also to include a --route directive in the main OpenVPN +config file which encloses local, so that the kernel will know to +route it to the server's TUN/TAP interface.

+

OpenVPN's internal client IP address selection algorithm works as +follows:

+
    +
  1. Use --client-connect script generated file for static IP +(first choice).
    2. +
  2. Use --client-config-dir file for static IP (next choice).
    3. +
  3. Use --ifconfig-pool allocation for dynamic IP (last +choice).
    4. +
+
+--ifconfig-ipv6-push args
 

for --client-config-dir per-client static IPv6 interface +configuration, see --client-config-dir and --ifconfig-push for +more details.

+

Valid syntax:

+
+ifconfig-ipv6-push ipv6addr/bits ipv6remote
+
+
+--inetd args

Valid syntaxes:

+
+inetd
+inetd wait
+inetd nowait
+inetd wait progname
+
+

Use this option when OpenVPN is being run from the inetd or xinetd(8) +server.

+

The wait and nowait option must match what is specified +in the inetd/xinetd config file. The nowait mode can only be used +with --proto tcp-server The default is wait. The +nowait mode can be used to instantiate the OpenVPN daemon as a +classic TCP server, where client connection requests are serviced on a +single port number. For additional information on this kind of +configuration, see the OpenVPN FAQ: +https://community.openvpn.net/openvpn/wiki/325-openvpn-as-a--forking-tcp-server-which-can-service-multiple-clients-over-a-single-tcp-port

+

This option precludes the use of --daemon, --local or +--remote. Note that this option causes message and error output to +be handled in the same way as the --daemon option. The optional +progname parameter is also handled exactly as in --daemon.

+

Also note that in wait mode, each OpenVPN tunnel requires a separate +TCP/UDP port and a separate inetd or xinetd entry. See the OpenVPN 1.x +HOWTO for an example on using OpenVPN with xinetd: +https://openvpn.net/community-resources/1xhowto/

+
+--multihome

Configure a multi-homed UDP server. This option needs to be used when a +server has more than one IP address (e.g. multiple interfaces, or +secondary IP addresses), and is not using --local to force binding +to one specific address only. This option will add some extra lookups to +the packet path to ensure that the UDP reply packets are always sent +from the address that the client is talking to. This is not supported on +all platforms, and it adds more processing, so it's not enabled by +default.

+
+
Notes:
+
    +
  • This option is only relevant for UDP servers.
    • +
  • If you do an IPv6+IPv4 dual-stack bind on a Linux machine with +multiple IPv4 address, connections to IPv4 addresses will not +work right on kernels before 3.15, due to missing kernel +support for the IPv4-mapped case (some distributions have +ported this to earlier kernel versions, though).
    • +
+
+
+
+--iroute args

Generate an internal route to a specific client. The netmask +parameter, if omitted, defaults to 255.255.255.255.

+

Valid syntax:

+
+iroute network [netmask]
+
+

This directive can be used to route a fixed subnet from the server to a +particular client, regardless of where the client is connecting from. +Remember that you must also add the route to the system routing table as +well (such as by using the --route directive). The reason why two +routes are needed is that the --route directive routes the packet +from the kernel to OpenVPN. Once in OpenVPN, the --iroute directive +routes to the specific client.

+

This option must be specified either in a client instance config file +using --client-config-dir or dynamically generated using a +--client-connect script.

+

The --iroute directive also has an important interaction with +--push "route ...". --iroute essentially defines a subnet which +is owned by a particular client (we will call this client A). If you +would like other clients to be able to reach A's subnet, you can use +--push "route ..." together with --client-to-client to effect +this. In order for all clients to see A's subnet, OpenVPN must push +this route to all clients EXCEPT for A, since the subnet is already +owned by A. OpenVPN accomplishes this by not not pushing a route to +a client if it matches one of the client's iroutes.

+
+--iroute-ipv6 args
 

for --client-config-dir per-client static IPv6 route configuration, +see --iroute for more details how to setup and use this, and how +--iroute and --route interact.

+

Valid syntax:

+
+iroute-ipv6 ipv6addr/bits
+
+
+--max-clients n
 Limit server to a maximum of n concurrent clients.
+--max-routes-per-client n
 

Allow a maximum of n internal routes per client (default +256). This is designed to help contain DoS attacks where an +authenticated client floods the server with packets appearing to come +from many unique MAC addresses, forcing the server to deplete virtual +memory as its internal routing table expands. This directive can be used +in a --client-config-dir file or auto-generated by a +--client-connect script to override the global value for a particular +client.

+

Note that this directive affects OpenVPN's internal routing table, not +the kernel routing table.

+
+--opt-verify

Clients that connect with options that are incompatible with those of the +server will be disconnected.

+

Options that will be compared for compatibility include dev-type, +link-mtu, tun-mtu, proto, ifconfig, +comp-lzo, fragment, keydir, cipher, +auth, keysize, secret, no-replay, +tls-auth, key-method, tls-server +and tls-client.

+

This option requires that --disable-occ NOT be used.

+
+--port-share args
 

Share OpenVPN TCP with another service

+

Valid syntax:

+
+port-share host port [dir]
+
+

When run in TCP server mode, share the OpenVPN port with another +application, such as an HTTPS server. If OpenVPN senses a connection to +its port which is using a non-OpenVPN protocol, it will proxy the +connection to the server at host:port. Currently only designed to +work with HTTP/HTTPS, though it would be theoretically possible to +extend to other protocols such as ssh.

+

dir specifies an optional directory where a temporary file with name +N containing content C will be dynamically generated for each proxy +connection, where N is the source IP:port of the client connection and C +is the source IP:port of the connection to the proxy receiver. This +directory can be used as a dictionary by the proxy receiver to determine +the origin of the connection. Each generated file will be automatically +deleted when the proxied connection is torn down.

+

Not implemented on Windows.

+
+--push option

Push a config file option back to the client for remote execution. Note +that option must be enclosed in double quotes (""). The +client must specify --pull in its config file. The set of options +which can be pushed is limited by both feasibility and security. Some +options such as those which would execute scripts are banned, since they +would effectively allow a compromised server to execute arbitrary code +on the client. Other options such as TLS or MTU parameters cannot be +pushed because the client needs to know them before the connection to the +server can be initiated.

+

This is a partial list of options which can currently be pushed: +--route, --route-gateway, --route-delay, +--redirect-gateway, --ip-win32, --dhcp-option, +--inactive, --ping, --ping-exit, --ping-restart, +--setenv, --auth-token, --persist-key, --persist-tun, +--echo, --comp-lzo, --socket-flags, --sndbuf, +--rcvbuf

+
+--push-peer-info
 

Push additional information about the client to server. The following +data is always pushed to the server:

+
+
IV_VER=<version>
+
The client OpenVPN version
+
IV_PLAT=[linux|solaris|openbsd|mac|netbsd|freebsd|win]
+
The client OS platform
+
IV_LZO_STUB=1
+
If client was built with LZO stub capability
+
IV_LZ4=1
+
If the client supports LZ4 compressions.
+
IV_PROTO
+

Details about protocol extensions that the peer supports. The +variable is a bitfield and the bits are defined as follows +(starting a bit 0 for the first (unused) bit:

+
    +
  • bit 1: The peer supports peer-id floating mechanism
    • +
  • bit 2: The client expects a push-reply and the server may +send this reply without waiting for a push-request first.
    • +
+
+
IV_NCP=2
+
Negotiable ciphers, client supports --cipher pushed by +the server, a value of 2 or greater indicates client supports +AES-GCM-128 and AES-GCM-256.
+
IV_CIPHERS=<ncp-ciphers>
+
The client announces the list of supported ciphers configured with the +--data-ciphers option to the server.
+
IV_GUI_VER=<gui_id> <version>
+
The UI version of a UI if one is running, for example +de.blinkt.openvpn 0.5.47 for the Android app.
+
+

When --push-peer-info is enabled the additional information consists +of the following data:

+
+
IV_HWADDR=<mac address>
+
The MAC address of clients default gateway
+
IV_SSL=<version string>
+
The ssl version used by the client, e.g. +OpenSSL 1.0.2f 28 Jan 2016.
+
IV_PLAT_VER=x.y
+
The version of the operating system, e.g. 6.1 for Windows 7.
+
UV_<name>=<value>
+
Client environment variables whose names start with +UV_
+
+
+--push-remove opt
 

Selectively remove all --push options matching "opt" from the option +list for a client. opt is matched as a substring against the whole +option string to-be-pushed to the client, so --push-remove route +would remove all --push route ... and --push route-ipv6 ... +statements, while --push-remove "route-ipv6 2001:" would only remove +IPv6 routes for 2001:... networks.

+

--push-remove can only be used in a client-specific context, like in +a --client-config-dir file, or --client-connect script or plugin +-- similar to --push-reset, just more selective.

+

NOTE: to change an option, --push-remove can be used to first +remove the old value, and then add a new --push option with the new +value.

+

NOTE 2: due to implementation details, 'ifconfig' and 'ifconfig-ipv6' +can only be removed with an exact match on the option ( +push-remove ifconfig), no substring matching and no matching on +the IPv4/IPv6 address argument is possible.

+
+--push-resetDon't inherit the global push list for a specific client instance. +Specify this option in a client-specific context such as with a +--client-config-dir configuration file. This option will ignore +--push options at the global config file level.
+--server args

A helper directive designed to simplify the configuration of OpenVPN's +server mode. This directive will set up an OpenVPN server which will +allocate addresses to clients out of the given network/netmask. The +server itself will take the .1 address of the given network for +use as the server-side endpoint of the local TUN/TAP interface. If the +optional nopool flag is given, no dynamic IP address pool will +prepared for VPN clients.

+

Valid syntax:

+
+server network netmask [nopool]
+
+

For example, --server 10.8.0.0 255.255.255.0 expands as follows:

+
+mode server
+tls-server
+push "topology [topology]"
+
+if dev tun AND (topology == net30 OR topology == p2p):
+  ifconfig 10.8.0.1 10.8.0.2
+  if !nopool:
+    ifconfig-pool 10.8.0.4 10.8.0.251
+  route 10.8.0.0 255.255.255.0
+  if client-to-client:
+    push "route 10.8.0.0 255.255.255.0"
+  else if topology == net30:
+    push "route 10.8.0.1"
+
+if dev tap OR (dev tun AND topology == subnet):
+  ifconfig 10.8.0.1 255.255.255.0
+  if !nopool:
+    ifconfig-pool 10.8.0.2 10.8.0.253 255.255.255.0
+  push "route-gateway 10.8.0.1"
+  if route-gateway unset:
+    route-gateway 10.8.0.2
+
+

Don't use --server if you are ethernet bridging. Use +--server-bridge instead.

+
+--server-bridge args
 

A helper directive similar to --server which is designed to simplify +the configuration of OpenVPN's server mode in ethernet bridging +configurations.

+

Valid syntaxes:

+
+server-bridge gateway netmask pool-start-IP pool-end-IP
+server-bridge [nogw]
+
+

If --server-bridge is used without any parameters, it will enable a +DHCP-proxy mode, where connecting OpenVPN clients will receive an IP +address for their TAP adapter from the DHCP server running on the +OpenVPN server-side LAN. Note that only clients that support the binding +of a DHCP client with the TAP adapter (such as Windows) can support this +mode. The optional nogw flag (advanced) indicates that gateway +information should not be pushed to the client.

+

To configure ethernet bridging, you must first use your OS's bridging +capability to bridge the TAP interface with the ethernet NIC interface. +For example, on Linux this is done with the brctl tool, and with +Windows XP it is done in the Network Connections Panel by selecting the +ethernet and TAP adapters and right-clicking on "Bridge Connections".

+

Next you you must manually set the IP/netmask on the bridge interface. +The gateway and netmask parameters to --server-bridge can be +set to either the IP/netmask of the bridge interface, or the IP/netmask +of the default gateway/router on the bridged subnet.

+

Finally, set aside a IP range in the bridged subnet, denoted by +pool-start-IP and pool-end-IP, for OpenVPN to allocate to +connecting clients.

+

For example, server-bridge 10.8.0.4 255.255.255.0 10.8.0.128 +10.8.0.254 expands as follows:

+
+mode server
+tls-server
+
+ifconfig-pool 10.8.0.128 10.8.0.254 255.255.255.0
+push "route-gateway 10.8.0.4"
+
+

In another example, --server-bridge (without parameters) expands as +follows:

+
+mode server
+tls-server
+
+push "route-gateway dhcp"
+
+

Or --server-bridge nogw expands as follows:

+
+mode server
+tls-server
+
+
+--stale-routes-check args
 

Remove routes which haven't had activity for n seconds (i.e. the ageing +time). This check is run every t seconds (i.e. check interval).

+

Valid syntax:

+
+stale-routes-check n [t]
+
+

If t is not present it defaults to n.

+

This option helps to keep the dynamic routing table small. See also +--max-routes-per-client

+
+--username-as-common-name
 For --auth-user-pass-verify authentication, use the authenticated +username as the common name, rather than the common name from the client +cert.
+--verify-client-cert mode
 

Specify whether the client is required to supply a valid certificate.

+

Possible mode options are:

+
+
none
+

A client certificate is not required. the client needs to +authenticate using username/password only. Be aware that using this +directive is less secure than requiring certificates from all +clients.

+

If you use this directive, the entire responsibility of authentication +will rest on your --auth-user-pass-verify script, so keep in mind +that bugs in your script could potentially compromise the security of +your VPN.

+

--verify-client-cert none is functionally equivalent to +--client-cert-not-required.

+
+
optional
+

A client may present a certificate but it is not required to do so. +When using this directive, you should also use a +--auth-user-pass-verify script to ensure that clients are +authenticated using a certificate, a username and password, or +possibly even both.

+

Again, the entire responsibility of authentication will rest on your +--auth-user-pass-verify script, so keep in mind that bugs in your +script could potentially compromise the security of your VPN.

+
+
require
+
This is the default option. A client is required to present a +certificate, otherwise VPN access is refused.
+
+

If you don't use this directive (or use --verify-client-cert require) +but you also specify an --auth-user-pass-verify script, then OpenVPN +will perform double authentication. The client certificate verification +AND the --auth-user-pass-verify script will need to succeed in order +for a client to be authenticated and accepted onto the VPN.

+
+--vlan-tagging

Server-only option. Turns the OpenVPN server instance into a switch that +understands VLAN-tagging, based on IEEE 802.1Q.

+

The server TAP device and each of the connecting clients is seen as a +port of the switch. All client ports are in untagged mode and the server +TAP device is VLAN-tagged, untagged or accepts both, depending on the +--vlan-accept setting.

+

Ethernet frames with a prepended 802.1Q tag are called "tagged". If the +VLAN Identifier (VID) field in such a tag is non-zero, the frame is +called "VLAN-tagged". If the VID is zero, but the Priority Control Point +(PCP) field is non-zero, the frame is called "prio-tagged". If there is +no 802.1Q tag, the frame is "untagged".

+

Using the --vlan-pvid v option once per client (see +--client-config-dir), each port can be associated with a certain VID. +Packets can only be forwarded between ports having the same VID. +Therefore, clients with differing VIDs are completely separated from +one-another, even if --client-to-client is activated.

+

The packet filtering takes place in the OpenVPN server. Clients should +not have any VLAN tagging configuration applied.

+

The --vlan-tagging option is off by default. While turned off, +OpenVPN accepts any Ethernet frame and does not perform any special +processing for VLAN-tagged packets.

+

This option can only be activated in --dev tap mode.

+
+--vlan-accept args
 

Configure the VLAN tagging policy for the server TAP device.

+

Valid syntax:

+
+vlan-accept  all|tagged|untagged
+
+

The following modes are available:

+
+
tagged
+
Admit only VLAN-tagged frames. Only VLAN-tagged packets are accepted, +while untagged or priority-tagged packets are dropped when entering +the server TAP device.
+
untagged
+
Admit only untagged and prio-tagged frames. VLAN-tagged packets are +not accepted, while untagged or priority-tagged packets entering the +server TAP device are tagged with the value configured for the global +--vlan-pvid setting.
+
all (default)
+
Admit all frames. All packets are admitted and then treated like +untagged or tagged mode respectively.
+
Note:
+
Some vendors refer to switch ports running in tagged mode +as "trunk ports" and switch ports running in untagged mode +as "access ports".
+
+

Packets forwarded from clients to the server are VLAN-tagged with the +originating client's PVID, unless the VID matches the global +--vlan-pvid, in which case the tag is removed.

+

If no PVID is configured for a given client (see --vlan-pvid) packets +are tagged with 1 by default.

+
+--vlan-pvid v

Specifies which VLAN identifier a "port" is associated with. Only valid +when --vlan-tagging is speficied.

+

In the client context, the setting specifies which VLAN ID a client is +associated with. In the global context, the VLAN ID of the server TAP +device is set. The latter only makes sense for --vlan-accept +untagged and --vlan-accept all modes.

+

Valid values for v go from 1 through to 4094. The +global value defaults to 1. If no --vlan-pvid is specified in +the client context, the global value is inherited.

+

In some switch implementations, the PVID is also referred to as "Native +VLAN".

+
+
+
+
+

Encryption Options

+
+

SSL Library information

+ +++ + + + + + + + + + + + +
+--show-ciphers(Standalone) Show all cipher algorithms to use with the --cipher +option.
+--show-digests(Standalone) Show all message digest algorithms to use with the +--auth option.
+--show-tls

(Standalone) Show all TLS ciphers supported by the crypto library. +OpenVPN uses TLS to secure the control channel, over which the keys that +are used to protect the actual VPN traffic are exchanged. The TLS +ciphers will be sorted from highest preference (most secure) to lowest.

+

Be aware that whether a cipher suite in this list can actually work +depends on the specific setup of both peers (e.g. both peers must +support the cipher, and an ECDSA cipher suite will not work if you are +using an RSA certificate, etc.).

+
+--show-engines(Standalone) Show currently available hardware-based crypto acceleration +engines supported by the OpenSSL library.
+--show-groups(Standalone) Show all available elliptic curves/groups to use with the +--ecdh-curve and tls-groups options.
+
+
+

Generating key material

+ +++ + + + +
+--genkey args

(Standalone) Generate a key to be used of the type keytype. if keyfile +is left out or empty the key will be output on stdout. See the following +sections for the different keytypes.

+

Valid syntax:

+
+--genkey keytype keyfile
+
+

Valid keytype arguments are:

+

secret Standard OpenVPN shared secret keys

+

tls-crypt Alias for secret

+

tls-auth Alias for secret

+

auth-token Key used for --auth-gen-token-key

+

tls-crypt-v2-server TLS Crypt v2 server key

+

tls-crypt-v2-client TLS Crypt v2 client key

+

Examples:

+
+$ openvpn --genkey secret shared.key
+$ openvpn --genkey tls-crypt shared.key
+$ openvpn --genkey tls-auth shared.key
+$ openvpn --genkey tls-crypt-v2-server v2crypt-server.key
+$ openvpn --tls-crypt-v2 v2crypt-server.key --genkey tls-crypt-v2-client v2crypt-client-1.key
+
+
    +

  • Generating Shared Secret Keys +Generate a shared secret, for use with the --secret, --tls-auth +or --tls-crypt options.

    +

    Syntax:

    +
    +$ openvpn --genkey secret|tls-crypt|tls-auth keyfile
+
    +

    The key is saved in keyfile. All three variants (--secret, +tls-crypt and tls-auth) generate the same type of key. The +aliases are added for convenience.

    +

    If using this for --secret, this file must be shared with the peer +over a pre-existing secure channel such as scp(1).

    +
    • +

  • Generating TLS Crypt v2 Server key +Generate a --tls-crypt-v2 key to be used by an OpenVPN server. +The key is stored in keyfile.

    +

    Syntax:

    +
    +--genkey tls-crypt-v2-server keyfile
+
    +
    • +

  • Generating TLS Crypt v2 Client key +Generate a --tls-crypt-v2 key to be used by OpenVPN clients. The +key is stored in keyfile.

    +

    Syntax

    +
    +--genkey tls-crypt-v2-client keyfile [metadata]
+
    +

    If supplied, include the supplied metadata in the wrapped client +key. This metadata must be supplied in base64-encoded form. The +metadata must be at most 735 bytes long (980 bytes in base64).

    +

    If no metadata is supplied, OpenVPN will use a 64-bit unix timestamp +representing the current time in UTC, encoded in network order, as +metadata for the generated key.

    +

    A tls-crypt-v2 client key is wrapped using a server key. To generate a +client key, the user must therefore supply the server key using the +--tls-crypt-v2 option.

    +

    Servers can use --tls-crypt-v2-verify to specify a metadata +verification command.

    +
    • +

  • Generate Authentication Token key +Generate a new secret that can be used with --auth-gen-token-secret

    +

    Syntax:

    +
    +--genkey auth-token [keyfile]
+
    +
    +
    Note:
    +

    This file should be kept secret to the server as anyone that has +access to this file will be able to generate auth tokens that the +OpenVPN server will accept as valid.

    +
    +
    +
    • +
+
+
+
+

Data Channel Renegotiation

+

When running OpenVPN in client/server mode, the data channel will use a +separate ephemeral encryption key which is rotated at regular intervals.

+ +++ + + + + + + + + + +
+--reneg-bytes n
 

Renegotiate data channel key after n bytes sent or received +(disabled by default with an exception, see below). OpenVPN allows the +lifetime of a key to be expressed as a number of bytes +encrypted/decrypted, a number of packets, or a number of seconds. A key +renegotiation will be forced if any of these three criteria are met by +either peer.

+

If using ciphers with cipher block sizes less than 128-bits, +--reneg-bytes is set to 64MB by default, unless it is explicitly +disabled by setting the value to 0, but this is +HIGHLY DISCOURAGED as this is designed to add some protection against +the SWEET32 attack vector. For more information see the --cipher +option.

+
+--reneg-pkts nRenegotiate data channel key after n packets sent and received +(disabled by default).
+--reneg-sec args
 

Renegotiate data channel key after at most max seconds +(default 3600) and at least min seconds (default is 90% of +max for servers, and equal to max for clients).

+
+reneg-sec max [min]
+
+

The effective --reneg-sec value used is per session +pseudo-uniform-randomized between min and max.

+

With the default value of 3600 this results in an effective per +session value in the range of 3240..:code:3600 seconds for +servers, or just 3600 for clients.

+

When using dual-factor authentication, note that this default value may +cause the end user to be challenged to reauthorize once per hour.

+

Also, keep in mind that this option can be used on both the client and +server, and whichever uses the lower value will be the one to trigger +the renegotiation. A common mistake is to set --reneg-sec to a +higher value on either the client or server, while the other side of the +connection is still using the default value of 3600 seconds, +meaning that the renegotiation will still occur once per 3600 +seconds. The solution is to increase --reneg-sec on both the client and +server, or set it to 0 on one side of the connection (to +disable), and to your chosen value on the other side.

+
+
+
+

TLS Mode Options

+

TLS mode is the most powerful crypto mode of OpenVPN in both security +and flexibility. TLS mode works by establishing control and data +channels which are multiplexed over a single TCP/UDP port. OpenVPN +initiates a TLS session over the control channel and uses it to exchange +cipher and HMAC keys to protect the data channel. TLS mode uses a robust +reliability layer over the UDP connection for all control channel +communication, while the data channel, over which encrypted tunnel data +passes, is forwarded without any mediation. The result is the best of +both worlds: a fast data channel that forwards over UDP with only the +overhead of encrypt, decrypt, and HMAC functions, and a control channel +that provides all of the security features of TLS, including +certificate-based authentication and Diffie Hellman forward secrecy.

+

To use TLS mode, each peer that runs OpenVPN should have its own local +certificate/key pair (--cert and --key), signed by the root +certificate which is specified in --ca.

+

When two OpenVPN peers connect, each presents its local certificate to +the other. Each peer will then check that its partner peer presented a +certificate which was signed by the master root certificate as specified +in --ca.

+

If that check on both peers succeeds, then the TLS negotiation will +succeed, both OpenVPN peers will exchange temporary session keys, and +the tunnel will begin passing data.

+

The OpenVPN project provides a set of scripts for managing RSA +certificates and keys: https://github.com/OpenVPN/easy-rsa

+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+--askpass file

Get certificate password from console or file before we daemonize.

+

Valid syntaxes:

+
+askpass
+askpass file
+
+

For the extremely security conscious, it is possible to protect your +private key with a password. Of course this means that every time the +OpenVPN daemon is started you must be there to type the password. The +--askpass option allows you to start OpenVPN from the command line. +It will query you for a password before it daemonizes. To protect a +private key with a password you should omit the -nodes option when +you use the openssl command line tool to manage certificates and +private keys.

+

If file is specified, read the password from the first line of +file. Keep in mind that storing your password in a file to a certain +extent invalidates the extra security provided by using an encrypted +key.

+
+--ca file

Certificate authority (CA) file in .pem format, also referred to as the +root certificate. This file can have multiple certificates in .pem +format, concatenated together. You can construct your own certificate +authority certificate and private key by using a command such as:

+
+openssl req -nodes -new -x509 -keyout ca.key -out ca.crt
+
+

Then edit your openssl.cnf file and edit the certificate variable to +point to your new root certificate ca.crt.

+

For testing purposes only, the OpenVPN distribution includes a sample CA +certificate (ca.crt). Of course you should never use the test +certificates and test keys distributed with OpenVPN in a production +environment, since by virtue of the fact that they are distributed with +OpenVPN, they are totally insecure.

+
+--capath dir

Directory containing trusted certificates (CAs and CRLs). Not available +with mbed TLS.

+

CAs in the capath directory are expected to be named <hash>.<n>. CRLs +are expected to be named <hash>.r<n>. See the -CApath option of +openssl verify, and the -hash option of openssl x509, +openssl crl and X509_LOOKUP_hash_dir()(3) +for more information.

+

Similar to the --crl-verify option, CRLs are not mandatory - +OpenVPN will log the usual warning in the logs if the relevant CRL is +missing, but the connection will be allowed.

+
+--cert file

Local peer's signed certificate in .pem format -- must be signed by a +certificate authority whose certificate is in --ca file. Each peer +in an OpenVPN link running in TLS mode should have its own certificate +and private key file. In addition, each certificate should have been +signed by the key of a certificate authority whose public key resides in +the --ca certificate authority file. You can easily make your own +certificate authority (see above) or pay money to use a commercial +service such as thawte.com (in which case you will be helping to finance +the world's second space tourist :). To generate a certificate, you can +use a command such as:

+
+openssl req -nodes -new -keyout mycert.key -out mycert.csr
+
+

If your certificate authority private key lives on another machine, copy +the certificate signing request (mycert.csr) to this other machine (this +can be done over an insecure channel such as email). Now sign the +certificate with a command such as:

+
+openssl ca -out mycert.crt -in mycert.csr
+
+

Now copy the certificate (mycert.crt) back to the peer which initially +generated the .csr file (this can be over a public medium). Note that +the openssl ca command reads the location of the certificate +authority key from its configuration file such as +/usr/share/ssl/openssl.cnf -- note also that for certificate +authority functions, you must set up the files index.txt (may be +empty) and serial (initialize to 01).

+
+--crl-verify args
 

Check peer certificate against a Certificate Revocation List.

+

Valid syntax:

+
+crl-verify file/directory flag
+
+

Examples:

+
+crl-verify crl-file.pem
+crl-verify /etc/openvpn/crls dir
+
+

A CRL (certificate revocation list) is used when a particular key is +compromised but when the overall PKI is still intact.

+

Suppose you had a PKI consisting of a CA, root certificate, and a number +of client certificates. Suppose a laptop computer containing a client +key and certificate was stolen. By adding the stolen certificate to the +CRL file, you could reject any connection which attempts to use it, +while preserving the overall integrity of the PKI.

+

The only time when it would be necessary to rebuild the entire PKI from +scratch would be if the root certificate key itself was compromised.

+

The option is not mandatory - if the relevant CRL is missing, OpenVPN +will log a warning in the logs - e.g.

+
+VERIFY WARNING: depth=0, unable to get certificate CRL
+
+

but the connection will be allowed. If the optional dir flag +is specified, enable a different mode where the crl-verify is +pointed at a directory containing files named as revoked serial numbers +(the files may be empty, the contents are never read). If a client +requests a connection, where the client certificate serial number +(decimal string) is the name of a file present in the directory, it will +be rejected.

+
+
Note:
+
As the crl file (or directory) is read every time a peer +connects, if you are dropping root privileges with +--user, make sure that this user has sufficient +privileges to read the file.
+
+
+--dh file

File containing Diffie Hellman parameters in .pem format (required for +--tls-server only).

+

Set file to none to disable Diffie Hellman key exchange (and +use ECDH only). Note that this requires peers to be using an SSL library +that supports ECDH TLS cipher suites (e.g. OpenSSL 1.0.1+, or +mbed TLS 2.0+).

+

Use openssl dhparam -out dh2048.pem 2048 to generate 2048-bit DH +parameters. Diffie Hellman parameters may be considered public.

+
+--ecdh-curve name
 

Specify the curve to use for elliptic curve Diffie Hellman. Available +curves can be listed with --show-curves. The specified curve will +only be used for ECDH TLS-ciphers.

+

This option is not supported in mbed TLS builds of OpenVPN.

+
+--extra-certs file
 

Specify a file containing one or more PEM certs (concatenated +together) that complete the local certificate chain.

+

This option is useful for "split" CAs, where the CA for server certs is +different than the CA for client certs. Putting certs in this file +allows them to be used to complete the local certificate chain without +trusting them to verify the peer-submitted certificate, as would be the +case if the certs were placed in the ca file.

+
+--hand-window n
 Handshake Window -- the TLS-based key exchange must finalize within +n seconds of handshake initiation by any peer (default 60 +seconds). If the handshake fails we will attempt to reset our connection +with our peer and try again. Even in the event of handshake failure we +will still use our expiring key for up to --tran-window seconds to +maintain continuity of transmission of tunnel data.
+--key fileLocal peer's private key in .pem format. Use the private key which was +generated when you built your peer's certificate (see --cert file +above).
+--pkcs12 fileSpecify a PKCS #12 file containing local private key, local certificate, +and root CA certificate. This option can be used instead of --ca, +--cert, and --key. Not available with mbed TLS.
+--remote-cert-eku oid
 

Require that peer certificate was signed with an explicit extended key +usage.

+

This is a useful security option for clients, to ensure that the host +they connect to is a designated server.

+

The extended key usage should be encoded in oid notation, or OpenSSL +symbolic representation.

+
+--remote-cert-ku key-usage
 

Require that peer certificate was signed with an explicit +key-usage.

+

If present in the certificate, the keyUsage value is validated by +the TLS library during the TLS handshake. Specifying this option without +arguments requires this extension to be present (so the TLS library will +verify it).

+

If key-usage is a list of usage bits, the keyUsage field +must have at least the same bits set as the bits in one of the values +supplied in the key-usage list.

+

The key-usage values in the list must be encoded in hex, e.g.

+
+remote-cert-ku a0
+
+
+--remote-cert-tls type
 

Require that peer certificate was signed with an explicit key usage +and extended key usage based on RFC3280 TLS rules.

+

Valid syntaxes:

+
+remote-cert-tls server
+remote-cert-tls client
+
+

This is a useful security option for clients, to ensure that the host +they connect to is a designated server. Or the other way around; for a +server to verify that only hosts with a client certificate can connect.

+

The --remote-cert-tls client option is equivalent to

+
+remote-cert-ku
+remote-cert-eku "TLS Web Client Authentication"
+
+

The --remote-cert-tls server option is equivalent to

+
+remote-cert-ku
+remote-cert-eku "TLS Web Server Authentication"
+
+

This is an important security precaution to protect against a +man-in-the-middle attack where an authorized client attempts to connect +to another client by impersonating the server. The attack is easily +prevented by having clients verify the server certificate using any one +of --remote-cert-tls, --verify-x509-name, or --tls-verify.

+
+--tls-auth args
 

Add an additional layer of HMAC authentication on top of the TLS control +channel to mitigate DoS attacks and attacks on the TLS stack.

+

Valid syntaxes:

+
+tls-auth file
+tls-auth file 0
+tls-auth file 1
+
+

In a nutshell, --tls-auth enables a kind of "HMAC firewall" on +OpenVPN's TCP/UDP port, where TLS control channel packets bearing an +incorrect HMAC signature can be dropped immediately without response.

+

file (required) is a file in OpenVPN static key format which can be +generated by --genkey.

+

Older versions (up to OpenVPN 2.3) supported a freeform passphrase file. +This is no longer supported in newer versions (v2.4+).

+

See the --secret option for more information on the optional +direction parameter.

+

--tls-auth is recommended when you are running OpenVPN in a mode +where it is listening for packets from any IP address, such as when +--remote is not specified, or --remote is specified with +--float.

+

The rationale for this feature is as follows. TLS requires a +multi-packet exchange before it is able to authenticate a peer. During +this time before authentication, OpenVPN is allocating resources (memory +and CPU) to this potential peer. The potential peer is also exposing +many parts of OpenVPN and the OpenSSL library to the packets it is +sending. Most successful network attacks today seek to either exploit +bugs in programs (such as buffer overflow attacks) or force a program to +consume so many resources that it becomes unusable. Of course the first +line of defense is always to produce clean, well-audited code. OpenVPN +has been written with buffer overflow attack prevention as a top +priority. But as history has shown, many of the most widely used network +applications have, from time to time, fallen to buffer overflow attacks.

+

So as a second line of defense, OpenVPN offers this special layer of +authentication on top of the TLS control channel so that every packet on +the control channel is authenticated by an HMAC signature and a unique +ID for replay protection. This signature will also help protect against +DoS (Denial of Service) attacks. An important rule of thumb in reducing +vulnerability to DoS attacks is to minimize the amount of resources a +potential, but as yet unauthenticated, client is able to consume.

+

--tls-auth does this by signing every TLS control channel packet +with an HMAC signature, including packets which are sent before the TLS +level has had a chance to authenticate the peer. The result is that +packets without the correct signature can be dropped immediately upon +reception, before they have a chance to consume additional system +resources such as by initiating a TLS handshake. --tls-auth can be +strengthened by adding the --replay-persist option which will keep +OpenVPN's replay protection state in a file so that it is not lost +across restarts.

+

It should be emphasized that this feature is optional and that the key +file used with --tls-auth gives a peer nothing more than the power +to initiate a TLS handshake. It is not used to encrypt or authenticate +any tunnel data.

+

Use --tls-crypt instead if you want to use the key file to not only +authenticate, but also encrypt the TLS control channel.

+
+--tls-groups list
 

A list of allowable groups/curves in order of preference.

+

Set the allowed elliptic curves/groups for the TLS session. +These groups are allowed to be used in signatures and key exchange.

+

mbedTLS currently allows all known curves per default.

+

OpenSSL 1.1+ restricts the list per default to

+
+"X25519:secp256r1:X448:secp521r1:secp384r1".
+
+

If you use certificates that use non-standard curves, you +might need to add them here. If you do not force the ecdh curve +by using --ecdh-curve, the groups for ecdh will also be picked +from this list.

+

OpenVPN maps the curve name secp256r1 to prime256v1 to allow +specifying the same tls-groups option for mbedTLS and OpenSSL.

+

Warning: this option not only affects elliptic curve certificates +but also the key exchange in TLS 1.3 and using this option improperly +will disable TLS 1.3.

+
+--tls-cert-profile profile
 

Set the allowed cryptographic algorithms for certificates according to +profile.

+

The following profiles are supported:

+
+
legacy (default)
+
SHA1 and newer, RSA 2048-bit+, any elliptic curve.
+
preferred
+
SHA2 and newer, RSA 2048-bit+, any elliptic curve.
+
suiteb
+
SHA256/SHA384, ECDSA with P-256 or P-384.
+
+

This option is only fully supported for mbed TLS builds. OpenSSL builds +use the following approximation:

+
+
legacy (default)
+
sets "security level 1"
+
preferred
+
sets "security level 2"
+
suiteb
+
sets "security level 3" and --tls-cipher "SUITEB128".
+
+

OpenVPN will migrate to 'preferred' as default in the future. Please +ensure that your keys already comply.

+
+
+
WARNING: --tls-ciphers, --tls-ciphersuites and tls-groups
+
These options are expert features, which - if used correctly - can +improve the security of your VPN connection. But it is also easy to +unwittingly use them to carefully align a gun with your foot, or just +break your connection. Use with care!
+
+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+--tls-cipher l

A list l of allowable TLS ciphers delimited by a colon (":").

+

These setting can be used to ensure that certain cipher suites are used +(or not used) for the TLS connection. OpenVPN uses TLS to secure the +control channel, over which the keys that are used to protect the actual +VPN traffic are exchanged.

+

The supplied list of ciphers is (after potential OpenSSL/IANA name +translation) simply supplied to the crypto library. Please see the +OpenSSL and/or mbed TLS documentation for details on the cipher list +interpretation.

+

For OpenSSL, the --tls-cipher is used for TLS 1.2 and below.

+

Use --show-tls to see a list of TLS ciphers supported by your crypto +library.

+

The default for --tls-cipher is to use mbed TLS's default cipher list +when using mbed TLS or +DEFAULT:!EXP:!LOW:!MEDIUM:!kDH:!kECDH:!DSS:!PSK:!SRP:!kRSA when +using OpenSSL.

+

The default for --tls-ciphersuites is to use the crypto library's +default.

+
+--tls-ciphersuites l
 Same as --tls-cipher but for TLS 1.3 and up. mbed TLS has no +TLS 1.3 support yet and only the --tls-cipher setting is used.
+--tls-clientEnable TLS and assume client role during TLS handshake.
+--tls-crypt keyfile
 

Encrypt and authenticate all control channel packets with the key from +keyfile. (See --tls-auth for more background.)

+

Encrypting (and authenticating) control channel packets:

+
    +
  • provides more privacy by hiding the certificate used for the TLS +connection,
    • +
  • makes it harder to identify OpenVPN traffic as such,
    • +
  • provides "poor-man's" post-quantum security, against attackers who will +never know the pre-shared key (i.e. no forward secrecy).
    • +
+

In contrast to --tls-auth, --tls-crypt does not require the +user to set --key-direction.

+

Security Considerations

+

All peers use the same --tls-crypt pre-shared group key to +authenticate and encrypt control channel messages. To ensure that IV +collisions remain unlikely, this key should not be used to encrypt more +than 2^48 client-to-server or 2^48 server-to-client control channel +messages. A typical initial negotiation is about 10 packets in each +direction. Assuming both initial negotiation and renegotiations are at +most 2^16 (65536) packets (to be conservative), and (re)negotiations +happen each minute for each user (24/7), this limits the tls-crypt key +lifetime to 8171 years divided by the number of users. So a setup with +1000 users should rotate the key at least once each eight years. (And a +setup with 8000 users each year.)

+

If IV collisions were to occur, this could result in the security of +--tls-crypt degrading to the same security as using --tls-auth. +That is, the control channel still benefits from the extra protection +against active man-in-the-middle-attacks and DoS attacks, but may no +longer offer extra privacy and post-quantum security on top of what TLS +itself offers.

+

For large setups or setups where clients are not trusted, consider using +--tls-crypt-v2 instead. That uses per-client unique keys, and +thereby improves the bounds to 'rotate a client key at least once per +8000 years'.

+
+--tls-crypt-v2 keyfile
 

Use client-specific tls-crypt keys.

+

For clients, keyfile is a client-specific tls-crypt key. Such a key +can be generated using the --genkey tls-crypt-v2-client option.

+

For servers, keyfile is used to unwrap client-specific keys supplied +by the client during connection setup. This key must be the same as the +key used to generate the client-specific key (see --genkey +tls-crypt-v2-client).

+

On servers, this option can be used together with the --tls-auth or +--tls-crypt option. In that case, the server will detect whether the +client is using client-specific keys, and automatically select the right +mode.

+
+--tls-crypt-v2-verify cmd
 

Run command cmd to verify the metadata of the client-specific +tls-crypt-v2 key of a connecting client. This allows server +administrators to reject client connections, before exposing the TLS +stack (including the notoriously dangerous X.509 and ASN.1 stacks) to +the connecting client.

+

OpenVPN supplies the following environment variables to the command:

+
    +
  • script_type is set to tls-crypt-v2-verify
    • +
  • metadata_type is set to 0 if the metadata was user +supplied, or 1 if it's a 64-bit unix timestamp representing +the key creation time.
    • +
  • metadata_file contains the filename of a temporary file that +contains the client metadata.
    • +
+

The command can reject the connection by exiting with a non-zero exit +code.

+
+--tls-exitExit on TLS negotiation failure.
+--tls-export-cert directory
 Store the certificates the clients use upon connection to this +directory. This will be done before --tls-verify is called. The +certificates will use a temporary name and will be deleted when the +tls-verify script returns. The file name used for the certificate is +available via the peer_cert environment variable.
+--tls-serverEnable TLS and assume server role during TLS handshake. Note that +OpenVPN is designed as a peer-to-peer application. The designation of +client or server is only for the purpose of negotiating the TLS control +channel.
+--tls-timeout n
 Packet retransmit timeout on TLS control channel if no acknowledgment +from remote within n seconds (default 2). When OpenVPN sends +a control packet to its peer, it will expect to receive an +acknowledgement within n seconds or it will retransmit the packet, +subject to a TCP-like exponential backoff algorithm. This parameter only +applies to control channel packets. Data channel packets (which carry +encrypted tunnel data) are never acknowledged, sequenced, or +retransmitted by OpenVPN because the higher level network protocols +running on top of the tunnel such as TCP expect this role to be left to +them.
+--tls-version-min args
 

Sets the minimum TLS version we will accept from the peer (default is +"1.0").

+

Valid syntax:

+
+tls-version-min version ['or-highest']
+
+

Examples for version include 1.0, 1.1, or 1.2. If +or-highest is specified and version is not recognized, we will +only accept the highest TLS version supported by the local SSL +implementation.

+
+--tls-version-max version
 Set the maximum TLS version we will use (default is the highest version +supported). Examples for version include 1.0, 1.1, or +1.2.
+--verify-hash args
 

Specify SHA1 or SHA256 fingerprint for level-1 cert.

+

Valid syntax:

+
+verify-hash hash [algo]
+
+

The level-1 cert is the CA (or intermediate cert) that signs the leaf +certificate, and is one removed from the leaf certificate in the +direction of the root. When accepting a connection from a peer, the +level-1 cert fingerprint must match hash or certificate verification +will fail. Hash is specified as XX:XX:... For example:

+
+AD:B0:95:D8:09:C8:36:45:12:A9:89:C8:90:09:CB:13:72:A6:AD:16
+
+

The algo flag can be either SHA1 or SHA256. If not +provided, it defaults to SHA1.

+
+--verify-x509-name args
 

Accept connections only if a host's X.509 name is equal to name. The +remote host must also pass all other tests of verification.

+

Valid syntax:

+
+verify-x509 name type
+
+

Which X.509 name is compared to name depends on the setting of type. +type can be subject to match the complete subject DN +(default), name to match a subject RDN or name-prefix to +match a subject RDN prefix. Which RDN is verified as name depends on the +--x509-username-field option. But it defaults to the common name +(CN), e.g. a certificate with a subject DN

+
+C=KG, ST=NA, L=Bishkek, CN=Server-1
+
+

would be matched by:

+
+verify-x509-name 'C=KG, ST=NA, L=Bishkek, CN=Server-1'
+verify-x509-name Server-1 name
+verify-x509-name Server- name-prefix
+
+

The last example is useful if you want a client to only accept +connections to Server-1, Server-2, etc.

+

--verify-x509-name is a useful replacement for the --tls-verify +option to verify the remote host, because --verify-x509-name works +in a --chroot environment without any dependencies.

+

Using a name prefix is a useful alternative to managing a CRL +(Certificate Revocation List) on the client, since it allows the client +to refuse all certificates except for those associated with designated +servers.

+
+
NOTE:
+
Test against a name prefix only when you are using OpenVPN +with a custom CA certificate that is under your control. Never use +this option with type name-prefix when your client +certificates are signed by a third party, such as a commercial +web CA.
+
+
+--x509-track attribute
 Save peer X509 attribute value in environment for use by plugins and +management interface. Prepend a + to attribute to save values +from full cert chain. Values will be encoded as +X509_<depth>_<attribute>=<value>. Multiple --x509-track +options can be defined to track multiple attributes.
+--x509-username-field args
 

Field in the X.509 certificate subject to be used as the username +(default CN).

+

Valid syntax:

+
+x509-username-field [ext:]fieldname
+
+

Typically, this option is specified with fieldname as +either of the following:

+
+x509-username-field emailAddress
+x509-username-field ext:subjectAltName
+
+

The first example uses the value of the emailAddress attribute +in the certificate's Subject field as the username. The second example +uses the ext: prefix to signify that the X.509 extension +fieldname subjectAltName be searched for an rfc822Name +(email) field to be used as the username. In cases where there are +multiple email addresses in ext:fieldname, the last occurrence +is chosen.

+

When this option is used, the --verify-x509-name option will match +against the chosen fieldname instead of the Common Name.

+

Only the subjectAltName and issuerAltName X.509 +extensions are supported.

+

Please note: This option has a feature which will convert an +all-lowercase fieldname to uppercase characters, e.g., +ou -> OU. A mixed-case fieldname or one having the +ext: prefix will be left as-is. This automatic upcasing feature is +deprecated and will be removed in a future release.

+
+
+
+

PKCS#11 / SmartCard options

+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + +
+--pkcs11-cert-private args
 

Set if access to certificate object should be performed after login. +Every provider has its own setting.

+

Valid syntaxes:

+
+pkcs11-cert-private 0
+pkcs11-cert-private 1
+
+
+--pkcs11-id name
 Specify the serialized certificate id to be used. The id can be gotten +by the standalone --show-pkcs11-ids option.
+--pkcs11-id-management
 Acquire PKCS#11 id from management interface. In this case a +NEED-STR 'pkcs11-id-request' real-time message will be triggered, +application may use pkcs11-id-count command to retrieve available number of +certificates, and pkcs11-id-get command to retrieve certificate id and +certificate body.
+--pkcs11-pin-cache seconds
 Specify how many seconds the PIN can be cached, the default is until the +token is removed.
+--pkcs11-private-mode mode
 

Specify which method to use in order to perform private key operations. +A different mode can be specified for each provider. Mode is encoded as +hex number, and can be a mask one of the following:

+

0 (default) Try to determine automatically.

+

1 Use sign.

+

2 Use sign recover.

+

4 Use decrypt.

+

8 Use unwrap.

+
+--pkcs11-protected-authentication args
 

Use PKCS#11 protected authentication path, useful for biometric and +external keypad devices. Every provider has its own setting.

+

Valid syntaxes:

+
+pkcs11-protected-authentication 0
+pkcs11-protected-authentication 1
+
+
+--pkcs11-providers provider
 

Specify an RSA Security Inc. PKCS #11 Cryptographic Token Interface +(Cryptoki) providers to load. This option can be used instead of +--cert, --key and --pkcs12.

+

If p11-kit is present on the system, its p11-kit-proxy.so module +will be loaded by default if either the --pkcs11-id or +--pkcs11-id-management options are specified without +--pkcs11-provider being given.

+
+--show-pkcs11-ids args
 

(Standalone) Show PKCS#11 token object list.

+

Valid syntax:

+
+show-pkcs11 [provider] [cert_private]
+
+

Specify cert_private as 1 if certificates are stored as +private objects.

+

If p11-kit is present on the system, the provider argument is +optional; if omitted the default p11-kit-proxy.so module will be +queried.

+

--verb option can be used BEFORE this option to produce debugging +information.

+
+
+
+
+

Data channel cipher negotiation

+

OpenVPN 2.4 and higher have the capability to negotiate the data cipher that +is used to encrypt data packets. This section describes the mechanism in more detail and the +different backwards compatibility mechanism with older server and clients.

+
+

OpenVPN 2.5 and higher behaviour

+

When both client and server are at least running OpenVPN 2.5, that the order of +the ciphers of the server's --data-ciphers is used to pick the the data cipher. +That means that the first cipher in that list that is also in the client's +--data-ciphers list is chosen. If no common cipher is found the client is rejected +with a AUTH_FAILED message (as seen in client log):

+
+AUTH: Received control message: AUTH_FAILED,Data channel cipher negotiation failed (no shared cipher)
+

OpenVPN 2.5 will only allow the ciphers specified in --data-ciphers. To ensure +backwards compatibility also if a cipher is specified using the --cipher option +it is automatically added to this list. If both options are unset the default is +AES-256-GCM:AES-128-GCM.

+
+
+

OpenVPN 2.4 clients

+

The negotiation support in OpenVPN 2.4 was the first iteration of the implementation +and still had some quirks. Its main goal was "upgrade to AES-256-GCM when possible". +An OpenVPN 2.4 client that is built against a crypto library that supports AES in GCM +mode and does not have --ncp-disable will always announce support for +AES-256-GCM and AES-128-GCM to a server by sending IV_NCP=2.

+

This only causes a problem if --ncp-ciphers option has been changed from the +default of AES-256-GCM:AES-128-GCM to a value that does not include +these two ciphers. When a OpenVPN servers try to use AES-256-GCM or +AES-128-GCM the connection will then fail. It is therefore recommended to +always have the AES-256-GCM and AES-128-GCM ciphers to the --ncp-ciphers +options to avoid this behaviour.

+
+
+

OpenVPN 3 clients

+

Clients based on the OpenVPN 3.x library (https://github.com/openvpn/openvpn3/) +do not have a configurable --ncp-ciphers or --data-ciphers option. Instead +these clients will announce support for all their supported AEAD ciphers +(AES-256-GCM, AES-128-GCM and in newer versions also Chacha20-Poly1305).

+

To support OpenVPN 3.x based clients at least one of these ciphers needs to be +included in the server's --data-ciphers option.

+
+
+

OpenVPN 2.3 and older clients (and clients with --ncp-disable)

+

When a client without cipher negotiation support connects to a server the +cipher specified with the --cipher option in the client configuration +must be included in the --data-ciphers option of the server to allow +the client to connect. Otherwise the client will be sent the AUTH_FAILED +message that indicates no shared cipher.

+

If the client is 2.3 or older and has been configured with the +--enable-small ./configure argument, using +data-ciphers-fallback cipher in the server config file with the explicit +cipher used by the client is necessary.

+
+
+

OpenVPN 2.4 server

+

When a client indicates support for AES-128-GCM and AES-256-GCM +(with IV_NCP=2) an OpenVPN 2.4 server will send the first +cipher of the --ncp-ciphers to the OpenVPN client regardless of what +the cipher is. To emulate the behaviour of an OpenVPN 2.4 client as close +as possible and have compatibility to a setup that depends on this quirk, +adding AES-128-GCM and AES-256-GCM to the client's --data-ciphers +option is required. OpenVPN 2.5+ will only announce the IV_NCP=2 flag if +those ciphers are present.

+
+
+

OpenVPN 2.3 and older servers (and servers with --ncp-disable)

+

The cipher used by the server must be included in --data-ciphers to +allow the client connecting to a server without cipher negotiation +support. +(For compatibility OpenVPN 2.5 will also accept the cipher set with +--cipher)

+

If the server is 2.3 or older and has been configured with the +--enable-small ./configure argument, adding +data-ciphers-fallback cipher to the client config with the explicit +cipher used by the server is necessary.

+
+
+

Blowfish in CBC mode (BF-CBC) deprecation

+

The --cipher option defaulted to BF-CBC in OpenVPN 2.4 and older +version. The default was never changed to ensure backwards compatibility. +In OpenVPN 2.5 this behaviour has now been changed so that if the --cipher +is not explicitly set it does not allow the weak BF-CBC cipher any more +and needs to explicitly added as --cipher BFC-CBC or added to +--data-ciphers.

+

We strongly recommend to switching away from BF-CBC to a +more secure cipher as soon as possible instead.

+
+
+
+

NETWORK CONFIGURATION

+

OpenVPN consists of two sides of network configuration. One side is the +link between the local and remote side, the other side is the virtual +network adapter (tun/tap device).

+ +
+

Virtual Network Adapter (VPN interface)

+

Options in this section relates to configuration of the virtual tun/tap +network interface, including setting the VPN IP address and network +routing.

+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+--bind-dev device
 (Linux only) Set device to bind the server socket to a +Virtual Routing and Forwarding device
+--block-ipv6

On the client, instead of sending IPv6 packets over the VPN tunnel, all +IPv6 packets are answered with an ICMPv6 no route host message. On the +server, all IPv6 packets from clients are answered with an ICMPv6 no +route to host message. This options is intended for cases when IPv6 +should be blocked and other options are not available. --block-ipv6 +will use the remote IPv6 as source address of the ICMPv6 packets if set, +otherwise will use fe80::7 as source address.

+

For this option to make sense you actually have to route traffic to the +tun interface. The following example config block would send all IPv6 +traffic to OpenVPN and answer all requests with no route to host, +effectively blocking IPv6.

+
+
Client config
+
+--ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1
+--redirect-gateway ipv6
+--block-ipv6
+
+
+
Server config
+

Push a "valid" ipv6 config to the client and block on the server

+
+--push "ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1"
+--push "redirect-gateway ipv6"
+--block-ipv6
+
+
+
+
+--dev device

TUN/TAP virtual network device which can be tunX, tapX, +null or an arbitrary name string (X can be omitted for +a dynamic device.)

+

See examples section below for an example on setting up a TUN device.

+

You must use either tun devices on both ends of the connection or tap +devices on both ends. You cannot mix them, as they represent different +underlying network layers:

+
+
tun
+
devices encapsulate IPv4 or IPv6 (OSI Layer 3)
+
tap
+
devices encapsulate Ethernet 802.3 (OSI Layer 2).
+
+

Valid syntaxes:

+
+dev tun2
+dev tap4
+dev ovpn
+
+

When the device name starts with tun or tap, the device +type is extracted automatically. Otherwise the --dev-type option +needs to be added as well.

+
+--dev-node node
 

Explicitly set the device node rather than using /dev/net/tun, +/dev/tun, /dev/tap, etc. If OpenVPN cannot figure out +whether node is a TUN or TAP device based on the name, you should +also specify --dev-type tun or --dev-type tap.

+

Under Mac OS X this option can be used to specify the default tun +implementation. Using --dev-node utun forces usage of the native +Darwin tun kernel support. Use --dev-node utunN to select a specific +utun instance. To force using the tun.kext (/dev/tunX) +use --dev-node tun. When not specifying a --dev-node option +openvpn will first try to open utun, and fall back to tun.kext.

+

On Windows systems, select the TAP-Win32 adapter which is named node +in the Network Connections Control Panel or the raw GUID of the adapter +enclosed by braces. The --show-adapters option under Windows can +also be used to enumerate all available TAP-Win32 adapters and will show +both the network connections control panel name and the GUID for each +TAP-Win32 adapter.

+
+--dev-type device-type
 Which device type are we using? device-type should be tun +(OSI Layer 3) or tap (OSI Layer 2). Use this option only if +the TUN/TAP device used with --dev does not begin with tun +or tap.
+--dhcp-option args
 

Set additional network parameters on supported platforms. May be specified +on the client or pushed from the server. On Windows these options are +handled by the tap-windows6 driver by default or directly by OpenVPN +if dhcp is disabled or the wintun driver is in use. The +OpenVPN for Android client also handles them internally.

+

On all other platforms these options are only saved in the client's +environment under the name foreign_options_{n} before the +--up script is called. A plugin or an --up script must be used to +pick up and interpret these as required. Many Linux distributions include +such scripts and some third-party user interfaces such as tunnelblick also +come with scripts that process these options.

+

Valid syntax:

+
+dhcp-options type [parm]
+
+
+
DOMAIN name
+
Set Connection-specific DNS Suffix to name.
+
DOMAIN-SEARCH name
+
Add name to the domain search list. +Repeat this option to add more entries. Up to +10 domains are supported.
+
DNS address
+

Set primary domain name server IPv4 or IPv6 address. +Repeat this option to set secondary DNS server addresses.

+

Note: DNS IPv6 servers are currently set using netsh (the existing +DHCP code can only do IPv4 DHCP, and that protocol only permits +IPv4 addresses anywhere). The option will be put into the +environment, so an --up script could act upon it if needed.

+
+
WINS address
+
Set primary WINS server address (NetBIOS over TCP/IP Name Server). +Repeat this option to set secondary WINS server addresses.
+
NBDD address
+
Set primary NBDD server address (NetBIOS over TCP/IP Datagram +Distribution Server). Repeat this option to set secondary NBDD +server addresses.
+
NTP address
+
Set primary NTP server address (Network Time Protocol). +Repeat this option to set secondary NTP server addresses.
+
NBT type
+

Set NetBIOS over TCP/IP Node type. Possible options:

+
+
1
+
b-node (broadcasts)
+
2
+
p-node (point-to-point name queries to a WINS server)
+
4
+
m-node (broadcast then query name server)
+
8
+
h-node (query name server, then broadcast).
+
+
+
NBS scope-id
+
Set NetBIOS over TCP/IP Scope. A NetBIOS Scope ID provides an +extended naming service for the NetBIOS over TCP/IP (Known as NBT) +module. The primary purpose of a NetBIOS scope ID is to isolate +NetBIOS traffic on a single network to only those nodes with the +same NetBIOS scope ID. The NetBIOS scope ID is a character string +that is appended to the NetBIOS name. The NetBIOS scope ID on two +hosts must match, or the two hosts will not be able to communicate. +The NetBIOS Scope ID also allows computers to use the same computer +name, as they have different scope IDs. The Scope ID becomes a part +of the NetBIOS name, making the name unique. (This description of +NetBIOS scopes courtesy of NeonSurge@abyss.com)
+
DISABLE-NBT
+
Disable Netbios-over-TCP/IP.
+
+
+--ifconfig args
 

Set TUN/TAP adapter parameters. It requires the IP address of the local +VPN endpoint. For TUN devices in point-to-point mode, the next argument +must be the VPN IP address of the remote VPN endpoint. For TAP devices, +or TUN devices used with --topology subnet, the second argument +is the subnet mask of the virtual network segment which is being created +or connected to.

+

For TUN devices, which facilitate virtual point-to-point IP connections +(when used in --topology net30 or p2p mode), the proper usage of +--ifconfig is to use two private IP addresses which are not a member +of any existing subnet which is in use. The IP addresses may be +consecutive and should have their order reversed on the remote peer. +After the VPN is established, by pinging rn, you will be pinging +across the VPN.

+

For TAP devices, which provide the ability to create virtual ethernet +segments, or TUN devices in --topology subnet mode (which create +virtual "multipoint networks"), --ifconfig is used to set an IP +address and subnet mask just as a physical ethernet adapter would be +similarly configured. If you are attempting to connect to a remote +ethernet bridge, the IP address and subnet should be set to values which +would be valid on the the bridged ethernet segment (note also that DHCP +can be used for the same purpose).

+

This option, while primarily a proxy for the ifconfig(8) command, +is designed to simplify TUN/TAP tunnel configuration by providing a +standard interface to the different ifconfig implementations on +different platforms.

+

--ifconfig parameters which are IP addresses can also be specified +as a DNS or /etc/hosts file resolvable name.

+

For TAP devices, --ifconfig should not be used if the TAP interface +will be getting an IP address lease from a DHCP server.

+

Examples:

+
+# tun device in net30/p2p mode
+ifconfig 10.8.0.2 10.8.0.1
+
+# tun/tap device in subnet mode
+ifconfig 10.8.0.2 255.255.255.0
+
+
+--ifconfig-ipv6 args
 

Configure an IPv6 address on the tun device.

+

Valid syntax:

+
+ifconfig-ipv6 ipv6addr/bits [ipv6remote]
+
+

The ipv6addr/bits argument is the IPv6 address to use. The +second parameter is used as route target for --route-ipv6 if no +gateway is specified.

+

The --topology option has no influence with --ifconfig-ipv6

+
+--ifconfig-noexec
 Don't actually execute ifconfig/netsh commands, instead pass +--ifconfig parameters to scripts using environmental variables.
+--ifconfig-nowarn
 

Don't output an options consistency check warning if the --ifconfig +option on this side of the connection doesn't match the remote side. +This is useful when you want to retain the overall benefits of the +options consistency check (also see --disable-occ option) while only +disabling the ifconfig component of the check.

+

For example, if you have a configuration where the local host uses +--ifconfig but the remote host does not, use --ifconfig-nowarn +on the local host.

+

This option will also silence warnings about potential address conflicts +which occasionally annoy more experienced users by triggering "false +positive" warnings.

+
+--lladdr address
 Specify the link layer address, more commonly known as the MAC address. +Only applied to TAP devices.
+--persist-tun

Don't close and reopen TUN/TAP device or run up/down scripts across +SIGUSR1 or --ping-restart restarts.

+

SIGUSR1 is a restart signal similar to SIGHUP, but which +offers finer-grained control over reset options.

+
+--redirect-gateway flags
 

Automatically execute routing commands to cause all outgoing IP traffic +to be redirected over the VPN. This is a client-side option.

+

This option performs three steps:

+
    +
  1. Create a static route for the --remote address which +forwards to the pre-existing default gateway. This is done so that +(3) will not create a routing loop.
    2. +
  2. Delete the default gateway route.
    3. +
  3. Set the new default gateway to be the VPN endpoint address +(derived either from --route-gateway or the second parameter to +--ifconfig when --dev tun is specified).
    4. +
+

When the tunnel is torn down, all of the above steps are reversed so +that the original default route is restored.

+

Option flags:

+
+
local
+
Add the local flag if both OpenVPN peers are directly +connected via a common subnet, such as with wireless. The +local flag will cause step (1) above to be omitted.
+
autolocal
+
Try to automatically determine whether to enable local +flag above.
+
def1
+
Use this flag to override the default gateway by using +0.0.0.0/1 and 128.0.0.0/1 rather than +0.0.0.0/0. This has the benefit of overriding but not +wiping out the original default gateway.
+
bypass-dhcp
+
Add a direct route to the DHCP server (if it is non-local) which +bypasses the tunnel (Available on Windows clients, may not be +available on non-Windows clients).
+
bypass-dns
+
Add a direct route to the DNS server(s) (if they are non-local) +which bypasses the tunnel (Available on Windows clients, may +not be available on non-Windows clients).
+
block-local
+
Block access to local LAN when the tunnel is active, except for +the LAN gateway itself. This is accomplished by routing the local +LAN (except for the LAN gateway address) into the tunnel.
+
ipv6
+
Redirect IPv6 routing into the tunnel. This works similar to +the def1 flag, that is, more specific IPv6 routes are added +(2000::/4, 3000::/4), covering the whole IPv6 +unicast space.
+
!ipv4
+
Do not redirect IPv4 traffic - typically used in the flag pair +ipv6 !ipv4 to redirect IPv6-only.
+
+
+--redirect-private flags
 Like --redirect-gateway, but omit actually changing the default gateway. +Useful when pushing private subnets.
+--route args

Add route to routing table after connection is established. Multiple +routes can be specified. Routes will be automatically torn down in +reverse order prior to TUN/TAP device close.

+

Valid syntaxes:

+
+route network/IP
+route network/IP netmask
+route network/IP netmask gateway
+route network/IP netmask gateway metric
+
+

This option is intended as a convenience proxy for the route(8) +shell command, while at the same time providing portable semantics +across OpenVPN's platform space.

+
+
netmask
+
defaults to 255.255.255.255 when not given
+
gateway
+
default taken from --route-gateway or the second +parameter to --ifconfig when --dev tun is specified.
+
metric
+
default taken from --route-metric if set, otherwise 0.
+
+

The default can be specified by leaving an option blank or setting it to +default.

+

The network and gateway parameters can also be specified as a +DNS or /etc/hosts file resolvable name, or as one of three special +keywords:

+
+
vpn_gateway
+
The remote VPN endpoint address (derived either from +--route-gateway or the second parameter to --ifconfig +when --dev tun is specified).
+
net_gateway
+
The pre-existing IP default gateway, read from the +routing table (not supported on all OSes).
+
remote_host
+
The --remote address if OpenVPN is being run in +client mode, and is undefined in server mode.
+
+
+--route-delay args
 

Valid syntaxes:

+
+route-delay
+route-delay n
+route-delay n m
+
+

Delay n seconds (default 0) after connection establishment, +before adding routes. If n is 0, routes will be added +immediately upon connection establishment. If --route-delay is +omitted, routes will be added immediately after TUN/TAP device open and +--up script execution, before any --user or --group privilege +downgrade (or --chroot execution.)

+

This option is designed to be useful in scenarios where DHCP is used to +set tap adapter addresses. The delay will give the DHCP handshake time +to complete before routes are added.

+

On Windows, --route-delay tries to be more intelligent by waiting +w seconds (default 30 by default) for the TAP-Win32 adapter +to come up before adding routes.

+
+--route-ipv6 args
 

Setup IPv6 routing in the system to send the specified IPv6 network into +OpenVPN's tun.

+

Valid syntax:

+
+route-ipv6 ipv6addr/bits [gateway] [metric]
+
+

The gateway parameter is only used for IPv6 routes across tap devices, +and if missing, the ipv6remote field from --ifconfig-ipv6 or +--route-ipv6-gateway is used.

+
+--route-gateway arg
 

Specify a default gateway for use with --route.

+

If dhcp is specified as the parameter, the gateway address will +be extracted from a DHCP negotiation with the OpenVPN server-side LAN.

+

Valid syntaxes:

+
+route-gateway gateway
+route-gateway dhcp
+
+
+--route-ipv6-gateway gw
 Specify a default gateway gw for use with --route-ipv6.
+--route-metric m
 Specify a default metric m for use with --route.
+--route-noexecDon't add or remove routes automatically. Instead pass routes to +--route-up script using environmental variables.
+--route-nopull

When used with --client or --pull, accept options pushed by +server EXCEPT for routes, block-outside-dns and dhcp options like DNS +servers.

+

When used on the client, this option effectively bars the server from +adding routes to the client's routing table, however note that this +option still allows the server to set the TCP/IP properties of the +client's TUN/TAP interface.

+
+--topology mode
 

Configure virtual addressing topology when running in --dev tun +mode. This directive has no meaning in --dev tap mode, which always +uses a subnet topology.

+

If you set this directive on the server, the --server and +--server-bridge directives will automatically push your chosen +topology setting to clients as well. This directive can also be manually +pushed to clients. Like the --dev directive, this directive must +always be compatible between client and server.

+

mode can be one of:

+
+
net30
+
Use a point-to-point topology, by allocating one /30 subnet +per client. This is designed to allow point-to-point semantics when some +or all of the connecting clients might be Windows systems. This is the +default on OpenVPN 2.0.
+
p2p
+
Use a point-to-point topology where the remote endpoint of +the client's tun interface always points to the local endpoint of the +server's tun interface. This mode allocates a single IP address per +connecting client. Only use when none of the connecting clients are +Windows systems.
+
subnet
+
Use a subnet rather than a point-to-point topology by +configuring the tun interface with a local IP address and subnet mask, +similar to the topology used in --dev tap and ethernet bridging +mode. This mode allocates a single IP address per connecting client and +works on Windows as well. Only available when server and clients are +OpenVPN 2.1 or higher, or OpenVPN 2.0.x which has been manually patched +with the --topology directive code. When used on Windows, requires +version 8.2 or higher of the TAP-Win32 driver. When used on *nix, +requires that the tun driver supports an ifconfig(8) command which +sets a subnet instead of a remote endpoint IP address.
+
+

Note: Using --topology subnet changes the interpretation of the +arguments of --ifconfig to mean "address netmask", no longer "local +remote".

+
+--tun-mtu n

Take the TUN device MTU to be n and derive the link MTU from it +(default 1500). In most cases, you will probably want to leave +this parameter set to its default value.

+

The MTU (Maximum Transmission Units) is the maximum datagram size in +bytes that can be sent unfragmented over a particular network path. +OpenVPN requires that packets on the control and data channels be sent +unfragmented.

+

MTU problems often manifest themselves as connections which hang during +periods of active usage.

+

It's best to use the --fragment and/or --mssfix options to deal +with MTU sizing issues.

+
+--tun-mtu-extra n
 Assume that the TUN/TAP device might return as many as n bytes more +than the --tun-mtu size on read. This parameter defaults to 0, which +is sufficient for most TUN devices. TAP devices may introduce additional +overhead in excess of the MTU size, and a setting of 32 is the default +when TAP devices are used. This parameter only controls internal OpenVPN +buffer sizing, so there is no transmission overhead associated with +using a larger value.
+
+
+

TUN/TAP standalone operations

+

These two standalone operations will require --dev and optionally +--user and/or --group.

+ +++ + + + + + +
+--mktun

(Standalone) Create a persistent tunnel on platforms which support them +such as Linux. Normally TUN/TAP tunnels exist only for the period of +time that an application has them open. This option takes advantage of +the TUN/TAP driver's ability to build persistent tunnels that live +through multiple instantiations of OpenVPN and die only when they are +deleted or the machine is rebooted.

+

One of the advantages of persistent tunnels is that they eliminate the +need for separate --up and --down scripts to run the appropriate +ifconfig(8) and route(8) commands. These commands can be +placed in the the same shell script which starts or terminates an +OpenVPN session.

+

Another advantage is that open connections through the TUN/TAP-based +tunnel will not be reset if the OpenVPN peer restarts. This can be +useful to provide uninterrupted connectivity through the tunnel in the +event of a DHCP reset of the peer's public IP address (see the +--ipchange option above).

+

One disadvantage of persistent tunnels is that it is harder to +automatically configure their MTU value (see --link-mtu and +--tun-mtu above).

+

On some platforms such as Windows, TAP-Win32 tunnels are persistent by +default.

+
+--rmtun(Standalone) Remove a persistent tunnel.
+
+
+

Virtual Routing and Forwarding

+

Options in this section relates to configuration of virtual routing and +forwarding in combination with the underlying operating system.

+

As of today this is only supported on Linux, a kernel >= 4.9 is +recommended.

+

This could come in handy when for example the external network should be +only used as a means to connect to some VPN endpoints and all regular +traffic should only be routed through any tunnel(s). This could be +achieved by setting up a VRF and configuring the interface connected to +the external network to be part of the VRF. The examples below will cover +this setup.

+

Another option would be to put the tun/tap interface into a VRF. This could +be done by an up-script which uses the ip link set command shown +below.

+
+

VRF setup with iproute2

+

Create VRF vrf_external and map it to routing table 1023

+
+ip link add vrf_external type vrf table 1023
+
+

Move eth0 into vrf_external

+
+ip link set master vrf_external dev eth0
+
+

Any prefixes configured on eth0 will be moved from the :code`main` +routing table into routing table 1023

+
+
+

VRF setup with ifupdown

+

For Debian based Distributions ifupdown2 provides an almost drop-in +replacement for ifupdown including VRFs and other features. +A configuration for an interface eth0 being part of VRF +code:vrf_external could look like this:

+
+auto eth0
+iface eth0
+    address 192.0.2.42/24
+    address 2001:db8:08:15::42/64
+    gateway 192.0.2.1
+    gateway 2001:db8:08:15::1
+    vrf vrf_external
+
+auto vrf_external
+iface vrf_external
+    vrf-table 1023
+
+
+
+

OpenVPN configuration

+

The OpenVPN configuration needs to contain this line:

+
+bind-dev vrf_external
+
+
+
+

Further reading

+

Wikipedia has nice page one VRFs: https://en.wikipedia.org/wiki/Virtual_routing_and_forwarding

+

This talk from the Network Track of FrOSCon 2018 provides an overview about +advanced layer 2 and layer 3 features of Linux

+
+ +
+
+
+
+
+

SCRIPTING INTEGRATION

+

OpenVPN can execute external scripts in various phases of the lifetime of +the OpenVPN process.

+
+

Script Order of Execution

+
    +

  1. --up

    +

    Executed after TCP/UDP socket bind and TUN/TAP open.

    +
    2. +

  2. --tls-verify

    +

    Executed when we have a still untrusted remote peer.

    +
    3. +

  3. --ipchange

    +

    Executed after connection authentication, or remote IP address change.

    +
    4. +

  4. --client-connect

    +

    Executed in --mode server mode immediately after client +authentication.

    +
    5. +

  5. --route-up

    +

    Executed after connection authentication, either immediately after, or +some number of seconds after as defined by the --route-delay option.

    +
    6. +

  6. --route-pre-down

    +

    Executed right before the routes are removed.

    +
    7. +

  7. --client-disconnect

    +

    Executed in --mode server mode on client instance shutdown.

    +
    8. +

  8. --down

    +

    Executed after TCP/UDP and TUN/TAP close.

    +
    9. +

  9. --learn-address

    +

    Executed in --mode server mode whenever an IPv4 address/route or MAC +address is added to OpenVPN's internal routing table.

    +
    10. +

  10. --auth-user-pass-verify

    +

    Executed in --mode server mode on new client connections, when the +client is still untrusted.

    +
    11. +
+
+
+

SCRIPT HOOKS

+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+--auth-user-pass-verify args
 

Require the client to provide a username/password (possibly in addition +to a client certificate) for authentication.

+

Valid syntax:

+
+auth-user-pass-verify cmd method
+
+

OpenVPN will run command cmd to validate the username/password +provided by the client.

+

cmd consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single- or +double-quoted and/or escaped using a backslash, and should be separated +by one or more spaces.

+

If method is set to via-env, OpenVPN will call script +with the environmental variables username and password +set to the username/password strings provided by the client. Beware +that this method is insecure on some platforms which make the environment +of a process publicly visible to other unprivileged processes.

+

If method is set to via-file, OpenVPN will write the username +and password to the first two lines of a temporary file. The filename +will be passed as an argument to script, and the file will be +automatically deleted by OpenVPN after the script returns. The location +of the temporary file is controlled by the --tmp-dir option, and +will default to the current directory if unspecified. For security, +consider setting --tmp-dir to a volatile storage medium such as +/dev/shm (if available) to prevent the username/password file +from touching the hard drive.

+

The script should examine the username and password, returning a success +exit code (0) if the client's authentication request is to be +accepted, or a failure code (1) to reject the client.

+

This directive is designed to enable a plugin-style interface for +extending OpenVPN's authentication capabilities.

+

To protect against a client passing a maliciously formed username or +password string, the username string must consist only of these +characters: alphanumeric, underbar ('_'), dash ('-'), +dot ('.'), or at ('@'). The password string can consist +of any printable characters except for CR or LF. Any illegal characters +in either the username or password string will be converted to +underbar ('_').

+

Care must be taken by any user-defined scripts to avoid creating a +security vulnerability in the way that these strings are handled. Never +use these strings in such a way that they might be escaped or evaluated +by a shell interpreter.

+

For a sample script that performs PAM authentication, see +sample-scripts/auth-pam.pl in the OpenVPN source distribution.

+
+--client-connect cmd
 

Run command cmd on client connection.

+

cmd consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single- or +double-quoted and/or escaped using a backslash, and should be separated +by one or more spaces.

+

The command is passed the common name and IP address of the +just-authenticated client as environmental variables (see environmental +variable section below). The command is also passed the pathname of a +freshly created temporary file as the last argument (after any arguments +specified in cmd ), to be used by the command to pass dynamically +generated config file directives back to OpenVPN.

+

If the script wants to generate a dynamic config file to be applied on +the server when the client connects, it should write it to the file +named by the last argument.

+

See the --client-config-dir option below for options which can be +legally used in a dynamically generated config file.

+

Note that the return value of script is significant. If script +returns a non-zero error status, it will cause the client to be +disconnected.

+

If a --client-connect wants to defer the generating of the +configuration then the script needs to use the +client_connect_deferred_file and +client_connect_config_file environment variables, and write +status accordingly into these files. See the Environmental Variables +section for more details.

+
+--client-disconnect cmd
 

Like --client-connect but called on client instance shutdown. Will +not be called unless the --client-connect script and plugins (if +defined) were previously called on this instance with successful (0) +status returns.

+

The exception to this rule is if the --client-disconnect command or +plugins are cascaded, and at least one client-connect function +succeeded, then ALL of the client-disconnect functions for scripts and +plugins will be called on client instance object deletion, even in cases +where some of the related client-connect functions returned an error +status.

+

The --client-disconnect command is passed the same pathname as the +corresponding --client-connect command as its last argument (after +any arguments specified in cmd).

+
+--down cmd

Run command cmd after TUN/TAP device close (post --user UID +change and/or --chroot ). cmd consists of a path to script (or +executable program), optionally followed by arguments. The path and +arguments may be single- or double-quoted and/or escaped using a +backslash, and should be separated by one or more spaces.

+

Called with the same parameters and environmental variables as the +--up option above.

+

Note that if you reduce privileges by using --user and/or +--group, your --down script will also run at reduced privilege.

+
+--down-preCall --down cmd/script before, rather than after, TUN/TAP close.
+--ipchange cmd

Run command cmd when our remote ip-address is initially +authenticated or changes.

+

cmd consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single- or +double-quoted and/or escaped using a backslash, and should be separated +by one or more spaces.

+

When cmd is executed two arguments are appended after any arguments +specified in cmd , as follows:

+
+cmd ip address port number
+
+

Don't use --ipchange in --mode server mode. Use a +--client-connect script instead.

+

See the Environmental Variables section below for additional +parameters passed as environmental variables.

+

If you are running in a dynamic IP address environment where the IP +addresses of either peer could change without notice, you can use this +script, for example, to edit the /etc/hosts file with the current +address of the peer. The script will be run every time the remote peer +changes its IP address.

+

Similarly if our IP address changes due to DHCP, we should configure +our IP address change script (see man page for dhcpcd(8)) to +deliver a SIGHUP or SIGUSR1 signal to OpenVPN. OpenVPN will +then re-establish a connection with its most recently authenticated +peer on its new IP address.

+
+--learn-address cmd
 

Run command cmd to validate client virtual addresses or routes.

+

cmd consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single- or +double-quoted and/or escaped using a backslash, and should be separated +by one or more spaces.

+

Three arguments will be appended to any arguments in cmd as follows:

+
+
$1 - [operation]
+
"add", "update", or "delete" based on whether +or not the address is being added to, modified, or deleted from +OpenVPN's internal routing table.
+
$2 - [address]
+
The address being learned or unlearned. This can be an IPv4 address +such as "198.162.10.14", an IPv4 subnet such as +"198.162.10.0/24", or an ethernet MAC address (when +--dev tap is being used) such as "00:FF:01:02:03:04".
+
$3 - [common name]
+
The common name on the certificate associated with the client linked +to this address. Only present for "add" or "update" +operations, not "delete".
+
+

On "add" or "update" methods, if the script returns +a failure code (non-zero), OpenVPN will reject the address and will not +modify its internal routing table.

+

Normally, the cmd script will use the information provided above to +set appropriate firewall entries on the VPN TUN/TAP interface. Since +OpenVPN provides the association between virtual IP or MAC address and +the client's authenticated common name, it allows a user-defined script +to configure firewall access policies with regard to the client's +high-level common name, rather than the low level client virtual +addresses.

+
+--route-up cmd

Run command cmd after routes are added, subject to --route-delay.

+

cmd consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single- or +double-quoted and/or escaped using a backslash, and should be separated +by one or more spaces.

+

See the Environmental Variables section below for additional +parameters passed as environmental variables.

+
+--route-pre-down cmd
 

Run command cmd before routes are removed upon disconnection.

+

cmd consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single- or +double-quoted and/or escaped using a backslash, and should be separated +by one or more spaces.

+

See the Environmental Variables section below for additional +parameters passed as environmental variables.

+
+--setenv args

Set a custom environmental variable name=value to pass to script.

+

Valid syntaxes:

+
+setenv name value
+setenv FORWARD_COMPATIBLE 1
+setenv opt config_option
+
+

By setting FORWARD_COMPATIBLE to 1, the config file +syntax checking is relaxed so that unknown directives will trigger a +warning but not a fatal error, on the assumption that a given unknown +directive might be valid in future OpenVPN versions.

+

This option should be used with caution, as there are good security +reasons for having OpenVPN fail if it detects problems in a config file. +Having said that, there are valid reasons for wanting new software +features to gracefully degrade when encountered by older software +versions.

+

It is also possible to tag a single directive so as not to trigger a +fatal error if the directive isn't recognized. To do this, prepend the +following before the directive: setenv opt

+

Versions prior to OpenVPN 2.3.3 will always ignore options set with the +setenv opt directive.

+

See also --ignore-unknown-option

+
+--setenv-safe args
 

Set a custom environmental variable OPENVPN_name to value +to pass to scripts.

+

Valid syntaxes:

+
+setenv-safe name value
+
+

This directive is designed to be pushed by the server to clients, and +the prepending of OPENVPN_ to the environmental variable is a +safety precaution to prevent a LD_PRELOAD style attack from a +malicious or compromised server.

+
+--tls-verify cmd
 

Run command cmd to verify the X509 name of a pending TLS connection +that has otherwise passed all other tests of certification (except for +revocation via --crl-verify directive; the revocation test occurs +after the --tls-verify test).

+

cmd should return 0 to allow the TLS handshake to proceed, +or 1 to fail.

+

cmd consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single- or +double-quoted and/or escaped using a backslash, and should be separated +by one or more spaces.

+

When cmd is executed two arguments are appended after any arguments +specified in cmd, as follows:

+
+cmd certificate_depth subject
+
+

These arguments are, respectively, the current certificate depth and the +X509 subject distinguished name (dn) of the peer.

+

This feature is useful if the peer you want to trust has a certificate +which was signed by a certificate authority who also signed many other +certificates, where you don't necessarily want to trust all of them, but +rather be selective about which peer certificate you will accept. This +feature allows you to write a script which will test the X509 name on a +certificate and decide whether or not it should be accepted. For a +simple perl script which will test the common name field on the +certificate, see the file verify-cn in the OpenVPN distribution.

+

See the Environmental Variables section below for additional +parameters passed as environmental variables.

+
+--up cmd

Run command cmd after successful TUN/TAP device open (pre --user +UID change).

+

cmd consists of a path to a script (or executable program), optionally +followed by arguments. The path and arguments may be single- or +double-quoted and/or escaped using a backslash, and should be separated +by one or more spaces.

+

The up command is useful for specifying route commands which route IP +traffic destined for private subnets which exist at the other end of the +VPN connection into the tunnel.

+

For --dev tun execute as:

+
+cmd tun_dev tun_mtu link_mtu ifconfig_local_ip ifconfig_remote_ip [init | restart]
+
+

For --dev tap execute as:

+
+cmd tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask [init | restart]
+
+

See the Environmental Variables section below for additional +parameters passed as environmental variables.

+

Note that if cmd includes arguments, all OpenVPN-generated arguments +will be appended to them to build an argument list with which the +executable will be called.

+

Typically, cmd will run a script to add routes to the tunnel.

+

Normally the up script is called after the TUN/TAP device is opened. In +this context, the last command line parameter passed to the script will +be init. If the --up-restart option is also used, the up script +will be called for restarts as well. A restart is considered to be a +partial reinitialization of OpenVPN where the TUN/TAP instance is +preserved (the --persist-tun option will enable such preservation). +A restart can be generated by a SIGUSR1 signal, a --ping-restart +timeout, or a connection reset when the TCP protocol is enabled with the +--proto option. If a restart occurs, and --up-restart has been +specified, the up script will be called with restart as the last +parameter.

+
+
NOTE:
+
On restart, OpenVPN will not pass the full set of environment +variables to the script. Namely, everything related to routing and +gateways will not be passed, as nothing needs to be done anyway - all +the routing setup is already in place. Additionally, the up-restart +script will run with the downgraded UID/GID settings (if configured).
+
+

The following standalone example shows how the --up script can be +called in both an initialization and restart context. (NOTE: for +security reasons, don't run the following example unless UDP port 9999 +is blocked by your firewall. Also, the example will run indefinitely, so +you should abort with control-c).

+
+openvpn --dev tun --port 9999 --verb 4 --ping-restart 10 \
+        --up 'echo up' --down 'echo down' --persist-tun  \
+        --up-restart
+
+

Note that OpenVPN also provides the --ifconfig option to +automatically ifconfig the TUN device, eliminating the need to define an +--up script, unless you also want to configure routes in the +--up script.

+

If --ifconfig is also specified, OpenVPN will pass the ifconfig +local and remote endpoints on the command line to the --up script so +that they can be used to configure routes such as:

+
+route add -net 10.0.0.0 netmask 255.255.255.0 gw $5
+
+
+--up-delay

Delay TUN/TAP open and possible --up script execution until after +TCP/UDP connection establishment with peer.

+

In --proto udp mode, this option normally requires the use of +--ping to allow connection initiation to be sensed in the absence of +tunnel data, since UDP is a "connectionless" protocol.

+

On Windows, this option will delay the TAP-Win32 media state +transitioning to "connected" until connection establishment, i.e. the +receipt of the first authenticated packet from the peer.

+
+--up-restartEnable the --up and --down scripts to be called for restarts as +well as initial program start. This option is described more fully above +in the --up option documentation.
+
+
+

String Types and Remapping

+

In certain cases, OpenVPN will perform remapping of characters in +strings. Essentially, any characters outside the set of permitted +characters for each string type will be converted to underbar ('_').

+
+
Q: Why is string remapping necessary?
+
It's an important security feature to prevent the malicious +coding of strings from untrusted sources to be passed as parameters to +scripts, saved in the environment, used as a common name, translated to +a filename, etc.
+
Q: Can string remapping be disabled?
+
Yes, by using the --no-name-remapping option, however this +should be considered an advanced option.
+
+

Here is a brief rundown of OpenVPN's current string types and the +permitted character class for each string:

+
+
X509 Names
+
Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), at +('@'), colon (':'), slash ('/'), and equal ('='). Alphanumeric is +defined as a character which will cause the C library isalnum() function +to return true.
+
Common Names
+
Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), and at ('@').
+
--auth-user-pass username
+
Same as Common Name, with one exception: +starting with OpenVPN 2.0.1, the username is passed to the +OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY plugin in its raw form, +without string remapping.
+
--auth-user-pass password
+
Any "printable" character except CR or LF. Printable is defined to be +a character which will cause the C library isprint() function to +return true.
+
--client-config-dir filename as derived from common name or`username
+
Alphanumeric, underbar ('_'), dash ('-'), and dot ('.') except for "." +or ".." as standalone strings. As of v2.0.1-rc6, the at ('@') character +has been added as well for compatibility with the common name character +class.
+
Environmental variable names
+
Alphanumeric or underbar ('_').
+
Environmental variable values
+
Any printable character.
+
+

For all cases, characters in a string which are not members of the legal +character class for that string type will be remapped to underbar +('_').

+
+
+

Environmental Variables

+

Once set, a variable is persisted indefinitely until it is reset by a +new value or a restart,

+

As of OpenVPN 2.0-beta12, in server mode, environmental variables set by +OpenVPN are scoped according to the client objects they are associated +with, so there should not be any issues with scripts having access to +stale, previously set variables which refer to different client +instances.

+
+
bytes_received
+
Total number of bytes received from client during VPN session. Set prior +to execution of the --client-disconnect script.
+
bytes_sent
+
Total number of bytes sent to client during VPN session. Set prior to +execution of the --client-disconnect script.
+
client_connect_config_file
+
The path to the configuration file that should be written to by the +--client-connect script (optional, if per-session configuration +is desired). This is the same file name as passed via command line +argument on the call to the --client-connect script.
+
client_connect_deferred_file
+

This file can be optionally written to in order to to communicate a +status code of the --client-connect script or plgin. Only the +first character in the file is relevant. It must be either 1 +to indicate normal script execution, 0 indicates an error (in +the same way that a non zero exit status does) or 2 to indicate +that the script deferred returning the config file.

+

For deferred (background) handling, the script or plugin MUST write +2 to the file to indicate the deferral and then return with +exit code 0 to signal deferred handler started OK.

+

A background process or similar must then take care of writing the +configuration to the file indicated by the +client_connect_config_file environment variable and when +finished, write the a 1 to this file (or 0 in case of +an error).

+

The absence of any character in the file when the script finishes +executing is interpreted the same as 1. This allows scripts +that are not written to support the defer mechanism to be used +unmodified.

+
+
common_name
+
The X509 common name of an authenticated client. Set prior to execution +of --client-connect, --client-disconnect and +--auth-user-pass-verify scripts.
+
config
+
Name of first --config file. Set on program initiation and reset on +SIGHUP.
+
daemon
+
Set to "1" if the --daemon directive is specified, or "0" otherwise. +Set on program initiation and reset on SIGHUP.
+
daemon_log_redirect
+
Set to "1" if the --log or --log-append directives are +specified, or "0" otherwise. Set on program initiation and reset on +SIGHUP.
+
dev
+
The actual name of the TUN/TAP device, including a unit number if it +exists. Set prior to --up or --down script execution.
+
dev_idx
+
On Windows, the device index of the TUN/TAP adapter (to be used in +netsh.exe calls which sometimes just do not work right with interface +names). Set prior to --up or --down script execution.
+
foreign_option_{n}
+
An option pushed via --push to a client which does not natively +support it, such as --dhcp-option on a non-Windows system, will be +recorded to this environmental variable sequence prior to --up +script execution.
+
ifconfig_broadcast
+
The broadcast address for the virtual ethernet segment which is derived +from the --ifconfig option when --dev tap is used. Set prior to +OpenVPN calling the ifconfig or netsh (windows version +of ifconfig) commands which normally occurs prior to --up script +execution.
+
ifconfig_ipv6_local
+
The local VPN endpoint IPv6 address specified in the +--ifconfig-ipv6 option (first parameter). Set prior to OpenVPN +calling the ifconfig or code:netsh (windows version of +ifconfig) commands which normally occurs prior to --up script +execution.
+
ifconfig_ipv6_netbits
+
The prefix length of the IPv6 network on the VPN interface. Derived +from the /nnn parameter of the IPv6 address in the --ifconfig-ipv6 +option (first parameter). Set prior to OpenVPN calling the +ifconfig or netsh (windows version of ifconfig) +commands which normally occurs prior to --up script execution.
+
ifconfig_ipv6_remote
+
The remote VPN endpoint IPv6 address specified in the +--ifconfig-ipv6 option (second parameter). Set prior to OpenVPN +calling the ifconfig or netsh (windows version of +ifconfig) commands which normally occurs prior to --up script +execution.
+
ifconfig_local
+
The local VPN endpoint IP address specified in the --ifconfig +option (first parameter). Set prior to OpenVPN calling the +ifconfig or netsh (windows version of ifconfig) +commands which normally occurs prior to --up script execution.
+
ifconfig_remote
+
The remote VPN endpoint IP address specified in the --ifconfig +option (second parameter) when --dev tun is used. Set prior to +OpenVPN calling the ifconfig or netsh (windows version +of ifconfig) commands which normally occurs prior to --up script +execution.
+
ifconfig_netmask
+
The subnet mask of the virtual ethernet segment that is specified as +the second parameter to --ifconfig when --dev tap is being +used. Set prior to OpenVPN calling the ifconfig or +netsh (windows version of ifconfig) commands which normally +occurs prior to --up script execution.
+
ifconfig_pool_local_ip
+
The local virtual IP address for the TUN/TAP tunnel taken from an +--ifconfig-push directive if specified, or otherwise from the +ifconfig pool (controlled by the --ifconfig-pool config file +directive). Only set for --dev tun tunnels. This option is set on +the server prior to execution of the --client-connect and +--client-disconnect scripts.
+
ifconfig_pool_netmask
+
The virtual IP netmask for the TUN/TAP tunnel taken from an +--ifconfig-push directive if specified, or otherwise from the +ifconfig pool (controlled by the --ifconfig-pool config file +directive). Only set for --dev tap tunnels. This option is set on +the server prior to execution of the --client-connect and +--client-disconnect scripts.
+
ifconfig_pool_remote_ip
+
The remote virtual IP address for the TUN/TAP tunnel taken from an +--ifconfig-push directive if specified, or otherwise from the +ifconfig pool (controlled by the --ifconfig-pool config file +directive). This option is set on the server prior to execution of the +--client-connect and --client-disconnect scripts.
+
link_mtu
+
The maximum packet size (not including the IP header) of tunnel data in +UDP tunnel transport mode. Set prior to --up or --down script +execution.
+
local
+
The --local parameter. Set on program initiation and reset on +SIGHUP.
+
local_port
+
The local port number or name, specified by --port or --lport. +Set on program initiation and reset on SIGHUP.
+
password
+
The password provided by a connecting client. Set prior to +--auth-user-pass-verify script execution only when the via-env +modifier is specified, and deleted from the environment after the script +returns.
+
proto
+
The --proto parameter. Set on program initiation and reset on +SIGHUP.
+
remote_{n}
+
The --remote parameter. Set on program initiation and reset on +SIGHUP.
+
remote_port_{n}
+
The remote port number, specified by --port or --rport. Set on +program initiation and reset on SIGHUP.
+
route_net_gateway
+
The pre-existing default IP gateway in the system routing table. Set +prior to --up script execution.
+
route_vpn_gateway
+
The default gateway used by --route options, as specified in either +the --route-gateway option or the second parameter to +--ifconfig when --dev tun is specified. Set prior to --up +script execution.
+
route_{parm}_{n}
+

A set of variables which define each route to be added, and are set +prior to --up script execution.

+

parm will be one of network, netmask", +gateway, or metric.

+

n is the OpenVPN route number, starting from 1.

+

If the network or gateway are resolvable DNS names, their IP address +translations will be recorded rather than their names as denoted on the +command line or configuration file.

+
+
route_ipv6_{parm}_{n}
+

A set of variables which define each IPv6 route to be added, and are +set prior to --up script execution.

+

parm will be one of network or gateway +(netmask is contained as /nnn in the +route_ipv6_network_{n}, unlike IPv4 where it is passed in a +separate environment variable).

+

n is the OpenVPN route number, starting from 1.

+

If the network or gateway are resolvable DNS names, their IP address +translations will be recorded rather than their names as denoted on the +command line or configuration file.

+
+
peer_cert
+
Temporary file name containing the client certificate upon connection. +Useful in conjunction with --tls-verify.
+
script_context
+
Set to "init" or "restart" prior to up/down script execution. For more +information, see documentation for --up.
+
script_type
+
Prior to execution of any script, this variable is set to the type of +script being run. It can be one of the following: up, +down, ipchange, route-up, tls-verify, +auth-user-pass-verify, client-connect, +client-disconnect or learn-address. Set prior to +execution of any script.
+
signal
+
The reason for exit or restart. Can be one of sigusr1, +sighup, sigterm, sigint, inactive +(controlled by --inactive option), ping-exit (controlled +by --ping-exit option), ping-restart (controlled by +--ping-restart option), connection-reset (triggered on TCP +connection reset), error or unknown (unknown signal). +This variable is set just prior to down script execution.
+
time_ascii
+
Client connection timestamp, formatted as a human-readable time string. +Set prior to execution of the --client-connect script.
+
time_duration
+
The duration (in seconds) of the client session which is now +disconnecting. Set prior to execution of the --client-disconnect +script.
+
time_unix
+
Client connection timestamp, formatted as a unix integer date/time +value. Set prior to execution of the --client-connect script.
+
tls_digest_{n} / tls_digest_sha256_{n}
+
Contains the certificate SHA1 / SHA256 fingerprint, where n is the +verification level. Only set for TLS connections. Set prior to execution +of --tls-verify script.
+
tls_id_{n}
+
A series of certificate fields from the remote peer, where n is the +verification level. Only set for TLS connections. Set prior to execution +of --tls-verify script.
+
tls_serial_{n}
+
The serial number of the certificate from the remote peer, where n +is the verification level. Only set for TLS connections. Set prior to +execution of --tls-verify script. This is in the form of a decimal +string like "933971680", which is suitable for doing serial-based OCSP +queries (with OpenSSL, do not prepend "0x" to the string) If something +goes wrong while reading the value from the certificate it will be an +empty string, so your code should check that. See the +contrib/OCSP_check/OCSP_check.sh script for an example.
+
tls_serial_hex_{n}
+
Like tls_serial_{n}, but in hex form (e.g. +12:34:56:78:9A).
+
tun_mtu
+
The MTU of the TUN/TAP device. Set prior to --up or --down +script execution.
+
trusted_ip / trusted_ip6)
+
Actual IP address of connecting client or peer which has been +authenticated. Set prior to execution of --ipchange, +--client-connect and --client-disconnect scripts. If using ipv6 +endpoints (udp6, tcp6), trusted_ip6 will be set instead.
+
trusted_port
+
Actual port number of connecting client or peer which has been +authenticated. Set prior to execution of --ipchange, +--client-connect and --client-disconnect scripts.
+
untrusted_ip / untrusted_ip6
+
Actual IP address of connecting client or peer which has not been +authenticated yet. Sometimes used to nmap the connecting host in a +--tls-verify script to ensure it is firewalled properly. Set prior +to execution of --tls-verify and --auth-user-pass-verify +scripts. If using ipv6 endpoints (udp6, tcp6), untrusted_ip6 +will be set instead.
+
untrusted_port
+
Actual port number of connecting client or peer which has not been +authenticated yet. Set prior to execution of --tls-verify and +--auth-user-pass-verify scripts.
+
username
+
The username provided by a connecting client. Set prior to +--auth-user-pass-verify script execution only when the +via-env modifier is specified.
+
X509_{n}_{subject_field}
+

An X509 subject field from the remote peer certificate, where n is +the verification level. Only set for TLS connections. Set prior to +execution of --tls-verify script. This variable is similar to +tls_id_{n} except the component X509 subject fields are broken +out, and no string remapping occurs on these field values (except for +remapping of control characters to "_"). For example, the +following variables would be set on the OpenVPN server using the sample +client certificate in sample-keys (client.crt). Note that the +verification level is 0 for the client certificate and 1 for the CA +certificate.

+
+X509_0_emailAddress=me@myhost.mydomain
+X509_0_CN=Test-Client
+X509_0_O=OpenVPN-TEST
+X509_0_ST=NA
+X509_0_C=KG
+X509_1_emailAddress=me@myhost.mydomain
+X509_1_O=OpenVPN-TEST
+X509_1_L=BISHKEK
+X509_1_ST=NA
+X509_1_C=KG
+
+
+
+
+
+

Management Interface Options

+

OpenVPN provides a feature rich socket based management interface for both +server and client mode operations.

+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+--management args
 

Enable a management server on a socket-name Unix socket on those +platforms supporting it, or on a designated TCP port.

+

Valid syntaxes:

+
+management socket-name unix          #
+management socket-name unix pw-file  # (recommended)
+management IP port                   # (INSECURE)
+management IP port pw-file           #
+
+

pw-file, if specified, is a password file where the password must +be on first line. Instead of a filename it can use the keyword stdin +which will prompt the user for a password to use when OpenVPN is +starting.

+

For unix sockets, the default behaviour is to create a unix domain +socket that may be connected to by any process. Use the +--management-client-user and --management-client-group +directives to restrict access.

+

The management interface provides a special mode where the TCP +management link can operate over the tunnel itself. To enable this mode, +set IP to tunnel. Tunnel mode will cause the management interface to +listen for a TCP connection on the local VPN address of the TUN/TAP +interface.

+

*BEWARE* of enabling the management interface over TCP. In these cases +you should ALWAYS make use of pw-file to password protect the +management interface. Any user who can connect to this TCP IP:port +will be able to manage and control (and interfere with) the OpenVPN +process. It is also strongly recommended to set IP to 127.0.0.1 +(localhost) to restrict accessibility of the management server to local +clients.

+

While the management port is designed for programmatic control of +OpenVPN by other applications, it is possible to telnet to the port, +using a telnet client in "raw" mode. Once connected, type help +for a list of commands.

+

For detailed documentation on the management interface, see the +management-notes.txt file in the management folder of the OpenVPN +source distribution.

+
+--management-client
 

Management interface will connect as a TCP/unix domain client to +IP:port specified by --management rather than listen as a TCP +server or on a unix domain socket.

+

If the client connection fails to connect or is disconnected, a SIGTERM +signal will be generated causing OpenVPN to quit.

+
+--management-client-auth
 Gives management interface client the responsibility to authenticate +clients after their client certificate has been verified. See +management-notes.txt in OpenVPN distribution for detailed notes.
+--management-client-group g
 When the management interface is listening on a unix domain socket, only +allow connections from group g.
+--management-client-pf
 Management interface clients must specify a packet filter file for each +connecting client. See management-notes.txt in OpenVPN +distribution for detailed notes.
+--management-client-user u
 When the management interface is listening on a unix domain socket, only +allow connections from user u.
+--management-external-cert certificate-hint
 Allows usage for external certificate instead of --cert option +(client-only). certificate-hint is an arbitrary string which is +passed to a management interface client as an argument of +NEED-CERTIFICATE notification. Requires --management-external-key.
+--management-external-key args
 

Allows usage for external private key file instead of --key option +(client-only).

+

Valid syntaxes:

+
+management-external-key
+management-external-key nopadding
+management-external-key pkcs1
+management-external-key nopadding pkcs1
+
+

The optional parameters nopadding and pkcs1 signal +support for different padding algorithms. See +doc/mangement-notes.txt for a complete description of this +feature.

+
+--management-forget-disconnect
 

Make OpenVPN forget passwords when management session disconnects.

+

This directive does not affect the --http-proxy username/password. +It is always cached.

+
+--management-hold
 Start OpenVPN in a hibernating state, until a client of the management +interface explicitly starts it with the hold release command.
+--management-log-cache n
 Cache the most recent n lines of log file history for usage by the +management channel.
+--management-query-passwords
 Query management channel for private key password and +--auth-user-pass username/password. Only query the management +channel for inputs which ordinarily would have been queried from the +console.
+--management-query-proxy
 Query management channel for proxy server information for a specific +--remote (client-only).
+--management-query-remote
 Allow management interface to override --remote directives +(client-only).
+--management-signal
 Send SIGUSR1 signal to OpenVPN if management session disconnects. This +is useful when you wish to disconnect an OpenVPN session on user logoff. +For --management-client this option is not needed since a disconnect +will always generate a SIGTERM.
+--management-up-down
 Report tunnel up/down events to management interface.
+
+
+

Plug-in Interface Options

+

OpenVPN can be extended by loading external plug-in modules at runtime. These +plug-ins must be prebuilt and adhere to the OpenVPN Plug-In API.

+ +++ + + + +
+--plugin args

Loads an OpenVPN plug-in module.

+

Valid syntax:

+
+plugin module-name
+plugin module-name "arguments"
+
+

The module-name needs to be the first +argument, indicating the plug-in to load. The second argument is an +optional init string which will be passed directly to the plug-in. +If the init consists of multiple arguments it must be enclosed in +double-quotes ("). Multiple plugin modules may be loaded into one +OpenVPN process.

+

The module-name argument can be just a filename or a filename +with a relative or absolute path. The format of the filename and path +defines if the plug-in will be loaded from a default plug-in directory +or outside this directory.

+
+--plugin path         Effective directory used
+===================== =============================
+ myplug.so            DEFAULT_DIR/myplug.so
+ subdir/myplug.so     DEFAULT_DIR/subdir/myplug.so
+ ./subdir/myplug.so   CWD/subdir/myplug.so
+ /usr/lib/my/plug.so  /usr/lib/my/plug.so
+
+

DEFAULT_DIR is replaced by the default plug-in directory, which is +configured at the build time of OpenVPN. CWD is the current directory +where OpenVPN was started or the directory OpenVPN have switched into +via the --cd option before the --plugin option.

+

For more information and examples on how to build OpenVPN plug-in +modules, see the README file in the plugin folder of the OpenVPN +source distribution.

+

If you are using an RPM install of OpenVPN, see +/usr/share/openvpn/plugin. The documentation is in doc and +the actual plugin modules are in lib.

+

Multiple plugin modules can be cascaded, and modules can be used in +tandem with scripts. The modules will be called by OpenVPN in the order +that they are declared in the config file. If both a plugin and script +are configured for the same callback, the script will be called last. If +the return code of the module/script controls an authentication function +(such as tls-verify, auth-user-pass-verify, or client-connect), then +every module and script must return success (0) in order for the +connection to be authenticated.

+
+
+
+

Windows-Specific Options

+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+--allow-nonadmin TAP-adapter
 (Standalone) Set TAP-adapter to allow access from non-administrative +accounts. If TAP-adapter is omitted, all TAP adapters on the system +will be configured to allow non-admin access. The non-admin access +setting will only persist for the length of time that the TAP-Win32 +device object and driver remain loaded, and will need to be re-enabled +after a reboot, or if the driver is unloaded and reloaded. This +directive can only be used by an administrator.
+--block-outside-dns
 

Block DNS servers on other network adapters to prevent DNS leaks. This +option prevents any application from accessing TCP or UDP port 53 except +one inside the tunnel. It uses Windows Filtering Platform (WFP) and +works on Windows Vista or later.

+

This option is considered unknown on non-Windows platforms and +unsupported on Windows XP, resulting in fatal error. You may want to use +--setenv opt or --ignore-unknown-option (not suitable for +Windows XP) to ignore said error. Note that pushing unknown options from +server does not trigger fatal errors.

+
+--cryptoapicert select-string
 

(Windows/OpenSSL Only) Load the certificate and private key from the +Windows Certificate System Store.

+

Use this option instead of --cert and --key.

+

This makes it possible to use any smart card, supported by Windows, but +also any kind of certificate, residing in the Cert Store, where you have +access to the private key. This option has been tested with a couple of +different smart cards (GemSAFE, Cryptoflex, and Swedish Post Office eID) +on the client side, and also an imported PKCS12 software certificate on +the server side.

+

To select a certificate, based on a substring search in the +certificate's subject:

+
+cryptoapicert "SUBJ:Peter Runestig"
+
+

To select a certificate, based on certificate's thumbprint:

+
+cryptoapicert "THUMB:f6 49 24 41 01 b4 ..."
+
+

The thumbprint hex string can easily be copy-and-pasted from the Windows +Certificate Store GUI.

+
+--dhcp-releaseAsk Windows to release the TAP adapter lease on shutdown. This option +has no effect now, as it is enabled by default starting with +OpenVPN 2.4.1.
+--dhcp-renewAsk Windows to renew the TAP adapter lease on startup. This option is +normally unnecessary, as Windows automatically triggers a DHCP +renegotiation on the TAP adapter when it comes up, however if you set +the TAP-Win32 adapter Media Status property to "Always Connected", you +may need this flag.
+--ip-win32 method
 

When using --ifconfig on Windows, set the TAP-Win32 adapter IP +address and netmask using method. Don't use this option unless you +are also using --ifconfig.

+
+
manual
+
Don't set the IP address or netmask automatically. Instead +output a message to the console telling the user to configure the +adapter manually and indicating the IP/netmask which OpenVPN +expects the adapter to be set to.
+
dynamic [offset] [lease-time]
+

Automatically set the IP address and netmask by replying to DHCP +query messages generated by the kernel. This mode is probably the +"cleanest" solution for setting the TCP/IP properties since it +uses the well-known DHCP protocol. There are, however, two +prerequisites for using this mode:

+
    +
  1. The TCP/IP properties for the TAP-Win32 adapter must be set +to "Obtain an IP address automatically", and
    2. +
  2. OpenVPN needs to claim an IP address in the subnet for use +as the virtual DHCP server address.
    3. +
+

By default in --dev tap mode, OpenVPN will take the normally +unused first address in the subnet. For example, if your subnet is +192.168.4.0 netmask 255.255.255.0, then OpenVPN will take +the IP address 192.168.4.0 to use as the virtual DHCP +server address. In --dev tun mode, OpenVPN will cause the DHCP +server to masquerade as if it were coming from the remote endpoint.

+

The optional offset parameter is an integer which is > -256 +and < 256 and which defaults to -1. If offset is positive, +the DHCP server will masquerade as the IP address at network +address + offset. If offset is negative, the DHCP server will +masquerade as the IP address at broadcast address + offset.

+

The Windows ipconfig /all command can be used to show what +Windows thinks the DHCP server address is. OpenVPN will "claim" +this address, so make sure to use a free address. Having said that, +different OpenVPN instantiations, including different ends of +the same connection, can share the same virtual DHCP server +address.

+

The lease-time parameter controls the lease time of the DHCP +assignment given to the TAP-Win32 adapter, and is denoted in +seconds. Normally a very long lease time is preferred because it +prevents routes involving the TAP-Win32 adapter from being lost +when the system goes to sleep. The default lease time is one year.

+
+
netsh
+
Automatically set the IP address and netmask using the Windows +command-line "netsh" command. This method appears to work correctly +on Windows XP but not Windows 2000.
+
ipapi
+
Automatically set the IP address and netmask using the Windows IP +Helper API. This approach does not have ideal semantics, though +testing has indicated that it works okay in practice. If you use +this option, it is best to leave the TCP/IP properties for the +TAP-Win32 adapter in their default state, i.e. "Obtain an IP +address automatically."
+
adaptive (Default)
+

Try dynamic method initially and fail over to netsh +if the DHCP negotiation with the TAP-Win32 adapter does not succeed +in 20 seconds. Such failures have been known to occur when certain +third-party firewall packages installed on the client machine block +the DHCP negotiation used by the TAP-Win32 adapter. Note that if +the netsh failover occurs, the TAP-Win32 adapter TCP/IP +properties will be reset from DHCP to static, and this will cause +future OpenVPN startups using the adaptive mode to use +netsh immediately, rather than trying dynamic first.

+

To "unstick" the adaptive mode from using netsh, +run OpenVPN at least once using the dynamic mode to restore +the TAP-Win32 adapter TCP/IP properties to a DHCP configuration.

+
+
+
+--pause-exitPut up a "press any key to continue" message on the console prior to +OpenVPN program exit. This option is automatically used by the Windows +explorer when OpenVPN is run on a configuration file using the +right-click explorer menu.
+--register-dnsRun ipconfig /flushdns and ipconfig /registerdns on +connection initiation. This is known to kick Windows into recognizing +pushed DNS servers.
+--route-method m
 

Which method m to use for adding routes on Windows?

+
+
adaptive (default)
+
Try IP helper API first. If that fails, fall back to the route.exe +shell command.
+
ipapi
+
Use IP helper API.
+
exe
+
Call the route.exe shell command.
+
+
+--service args

Should be used when OpenVPN is being automatically executed by another +program in such a context that no interaction with the user via display +or keyboard is possible.

+

Valid syntax:

+
+service exit-event [0|1]
+
+

In general, end-users should never need to explicitly use this option, +as it is automatically added by the OpenVPN service wrapper when a given +OpenVPN configuration is being run as a service.

+

exit-event is the name of a Windows global event object, and OpenVPN +will continuously monitor the state of this event object and exit when +it becomes signaled.

+

The second parameter indicates the initial state of exit-event and +normally defaults to 0.

+

Multiple OpenVPN processes can be simultaneously executed with the same +exit-event parameter. In any case, the controlling process can +signal exit-event, causing all such OpenVPN processes to exit.

+

When executing an OpenVPN process using the --service directive, +OpenVPN will probably not have a console window to output status/error +messages, therefore it is useful to use --log or --log-append to +write these messages to a file.

+
+--show-adapters
 (Standalone) Show available TAP-Win32 adapters which can be selected +using the --dev-node option. On non-Windows systems, the +ifconfig(8) command provides similar functionality.
+--show-net(Standalone) Show OpenVPN's view of the system routing table and network +adapter list.
+--show-net-upOutput OpenVPN's view of the system routing table and network adapter +list to the syslog or log file after the TUN/TAP adapter has been +brought up and any routes have been added.
+--show-valid-subnets
 

(Standalone) Show valid subnets for --dev tun emulation. Since the +TAP-Win32 driver exports an ethernet interface to Windows, and since TUN +devices are point-to-point in nature, it is necessary for the TAP-Win32 +driver to impose certain constraints on TUN endpoint address selection.

+

Namely, the point-to-point endpoints used in TUN device emulation must +be the middle two addresses of a /30 subnet (netmask 255.255.255.252).

+
+--tap-sleep n

Cause OpenVPN to sleep for n seconds immediately after the TAP-Win32 +adapter state is set to "connected".

+

This option is intended to be used to troubleshoot problems with the +--ifconfig and --ip-win32 options, and is used to give the +TAP-Win32 adapter time to come up before Windows IP Helper API +operations are applied to it.

+
+--win-sys path

Set the Windows system directory pathname to use when looking for system +executables such as route.exe and netsh.exe. By default, if this +directive is not specified, OpenVPN will use the SystemRoot environment +variable.

+

This option has changed behaviour since OpenVPN 2.3. Earlier you had to +define --win-sys env to use the SystemRoot environment variable, +otherwise it defaulted to C:\\WINDOWS. It is not needed to use +the env keyword any more, and it will just be ignored. A warning is +logged when this is found in the configuration file.

+
+--windows-driver drv
 Specifies which tun driver to use. Values are tap-windows6 +(default) and wintun. This is a Windows-only option. +wintun" requires --dev tun and the OpenVPN process to run +elevated, or be invoked using the Interactive Service.
+
+
+

Standalone Debug Options

+ +++ + + + + +
+--show-gateway args
 

(Standalone) Show current IPv4 and IPv6 default gateway and interface +towards the gateway (if the protocol in question is enabled).

+

Valid syntax:

+
+--show-gateway
+--show-gateway IPv6-target
+
+

If an IPv6 target address is passed as argument, the IPv6 route for this +host is reported.

+
+
+
+

Advanced Expert Options

+

These are options only required when special tweaking is needed, often +used when debugging or testing out special usage scenarios.

+ +++ + + + + + + + + + + + + + + + + + + + + + + + + + + +
+--hash-size args
 

Set the size of the real address hash table to r and the virtual +address table to v.

+

Valid syntax:

+
+hash-size r v
+
+

By default, both tables are sized at 256 buckets.

+
+--bcast-buffers n
 Allocate n buffers for broadcast datagrams (default 256).
+--persist-local-ip
 Preserve initially resolved local IP address and port number across +SIGUSR1 or --ping-restart restarts.
+--persist-remote-ip
 Preserve most recently authenticated remote IP address and port number +across SIGUSR1 or --ping-restart restarts.
+--prng args

(Advanced) Change the PRNG (Pseudo-random number generator) parameters

+

Valid syntaxes:

+
+prng alg
+prng alg nsl
+
+

Changes the PRNG to use digest algorithm alg (default sha1), +and set nsl (default 16) to the size in bytes of the nonce +secret length (between 16 and 64).

+

Set alg to none to disable the PRNG and use the OpenSSL +RAND_bytes function instead for all of OpenVPN's pseudo-random number +needs.

+
+--rcvbuf sizeSet the TCP/UDP socket receive buffer size. Defaults to operating system +default.
+--shaper n

Limit bandwidth of outgoing tunnel data to n bytes per second on the +TCP/UDP port. Note that this will only work if mode is set to +p2p. If you want to limit the bandwidth in both directions, use +this option on both peers.

+

OpenVPN uses the following algorithm to implement traffic shaping: Given +a shaper rate of n bytes per second, after a datagram write of b +bytes is queued on the TCP/UDP port, wait a minimum of (b / n) +seconds before queuing the next write.

+

It should be noted that OpenVPN supports multiple tunnels between the +same two peers, allowing you to construct full-speed and reduced +bandwidth tunnels at the same time, routing low-priority data such as +off-site backups over the reduced bandwidth tunnel, and other data over +the full-speed tunnel.

+

Also note that for low bandwidth tunnels (under 1000 bytes per second), +you should probably use lower MTU values as well (see above), otherwise +the packet latency will grow so large as to trigger timeouts in the TLS +layer and TCP connections running over the tunnel.

+

OpenVPN allows n to be between 100 bytes/sec and 100 Mbytes/sec.

+
+--sndbuf sizeSet the TCP/UDP socket send buffer size. Defaults to operating system +default.
+--tcp-queue-limit n
 

Maximum number of output packets queued before TCP (default 64).

+

When OpenVPN is tunneling data from a TUN/TAP device to a remote client +over a TCP connection, it is possible that the TUN/TAP device might +produce data at a faster rate than the TCP connection can support. When +the number of output packets queued before sending to the TCP socket +reaches this limit for a given client connection, OpenVPN will start to +drop outgoing packets directed at this client.

+
+--txqueuelen n(Linux only) Set the TX queue length on the TUN/TAP interface. +Currently defaults to operating system default.
+
+
+
+

UNSUPPORTED OPTIONS

+

Options listed in this section have been removed from OpenVPN and are no +longer supported

+ +++ + + + + + + + + + + + + + + + +
+--client-cert-not-required
 Removed in OpenVPN 2.5. This should be replaxed with +--verify-client-cert none.
+--ifconfig-pool-linear
 Removed in OpenVPN 2.5. This should be replaced with --topology p2p.
+--key-methodRemoved in OpenVPN 2.5. This option should not be used, as using the old +key-method weakens the VPN tunnel security. The old key-method +was also only needed when the remote side was older than OpenVPN 2.0.
+--no-ivRemoved in OpenVPN 2.5. This option should not be used as it weakens the +VPN tunnel security. This has been a NOOP option since OpenVPN 2.4.
+--no-replayRemoved in OpenVPN 2.5. This option should not be used as it weakens the +VPN tunnel security.
+--ns-cert-typeRemoved in OpenVPN 2.5. The nsCertType field is no longer supported +in recent SSL/TLS libraries. If your certificates does not include key +usage and extended key usage fields, they must be upgraded and the +--remote-cert-tls option should be used instead.
+
+
+

CONNECTION PROFILES

+

Client configuration files may contain multiple remote servers which +it will attempt to connect against. But there are some configuration +options which are related to specific --remote options. For these +use cases, connection profiles are the solution.

+

By enacpulating the --remote option and related options within +<connection> and </connection>, these options are handled as a +group.

+

An OpenVPN client will try each connection profile sequentially until it +achieves a successful connection.

+

--remote-random can be used to initially "scramble" the connection +list.

+

Here is an example of connection profile usage:

+
+client
+dev tun
+
+<connection>
+remote 198.19.34.56 1194 udp
+</connection>
+
+<connection>
+remote 198.19.34.56 443 tcp
+</connection>
+
+<connection>
+remote 198.19.34.56 443 tcp
+http-proxy 192.168.0.8 8080
+</connection>
+
+<connection>
+remote 198.19.36.99 443 tcp
+http-proxy 192.168.0.8 8080
+</connection>
+
+persist-key
+persist-tun
+pkcs12 client.p12
+remote-cert-tls server
+verb 3
+
+

First we try to connect to a server at 198.19.34.56:1194 using UDP. If +that fails, we then try to connect to 198.19.34.56:443 using TCP. If +that also fails, then try connecting through an HTTP proxy at +192.168.0.8:8080 to 198.19.34.56:443 using TCP. Finally, try to connect +through the same proxy to a server at 198.19.36.99:443 using TCP.

+

The following OpenVPN options may be used inside of a <connection> +block:

+

bind, connect-retry, connect-retry-max, connect-timeout, +explicit-exit-notify, float, fragment, http-proxy, +http-proxy-option, key-direction, link-mtu, local, +lport, mssfix, mtu-disc, nobind, port, proto, +remote, rport, socks-proxy, tls-auth, tls-crypt, +tun-mtu and, tun-mtu-extra.

+

A defaulting mechanism exists for specifying options to apply to all +<connection> profiles. If any of the above options (with the +exception of remote ) appear outside of a <connection> block, +but in a configuration file which has one or more <connection> +blocks, the option setting will be used as a default for +<connection> blocks which follow it in the configuration file.

+

For example, suppose the nobind option were placed in the sample +configuration file above, near the top of the file, before the first +<connection> block. The effect would be as if nobind were +declared in all <connection> blocks below it.

+
+
+

INLINE FILE SUPPORT

+

OpenVPN allows including files in the main configuration for the --ca, +--cert, --dh, --extra-certs, --key, --pkcs12, +--secret, --crl-verify, --http-proxy-user-pass, --tls-auth, +--auth-gen-token-secret, --tls-crypt and --tls-crypt-v2 +options.

+

Each inline file started by the line <option> and ended by the line +</option>

+

Here is an example of an inline file usage

+
+<cert>
+-----BEGIN CERTIFICATE-----
+[...]
+-----END CERTIFICATE-----
+</cert>
+
+

When using the inline file feature with --pkcs12 the inline file has +to be base64 encoded. Encoding of a .p12 file into base64 can be done +for example with OpenSSL by running openssl base64 -in input.p12

+
+
+

SIGNALS

+
+
SIGHUP
+
Cause OpenVPN to close all TUN/TAP and network connections, restart, +re-read the configuration file (if any), and reopen TUN/TAP and network +connections.
+
SIGUSR1
+

Like SIGHUP`, except don't re-read configuration file, and +possibly don't close and reopen TUN/TAP device, re-read key files, +preserve local IP address/port, or preserve most recently authenticated +remote IP address/port based on --persist-tun, --persist-key, +--persist-local-ip and --persist-remote-ip options respectively +(see above).

+

This signal may also be internally generated by a timeout condition, +governed by the --ping-restart option.

+

This signal, when combined with --persist-remote-ip, may be sent +when the underlying parameters of the host's network interface change +such as when the host is a DHCP client and is assigned a new IP address. +See --ipchange for more information.

+
+
SIGUSR2
+
Causes OpenVPN to display its current statistics (to the syslog file if +--daemon is used, or stdout otherwise).
+
SIGINT, SIGTERM
+
Causes OpenVPN to exit gracefully.
+
+
+
+

EXAMPLES

+

Prior to running these examples, you should have OpenVPN installed on +two machines with network connectivity between them. If you have not yet +installed OpenVPN, consult the INSTALL file included in the OpenVPN +distribution.

+
+

Firewall Setup:

+

If firewalls exist between the two machines, they should be set to +forward the port OpenVPN is configured to use, in both directions. +The default for OpenVPN is 1194/udp. If you do not have control +over the firewalls between the two machines, you may still be able to +use OpenVPN by adding --ping 15 to each of the openvpn commands +used below in the examples (this will cause each peer to send out a UDP +ping to its remote peer once every 15 seconds which will cause many +stateful firewalls to forward packets in both directions without an +explicit firewall rule).

+

Please see your operating system guides for how to configure the firewall +on your systems.

+
+
+

VPN Address Setup:

+

For purposes of our example, our two machines will be called +bob.example.com and alice.example.com. If you are constructing a +VPN over the internet, then replace bob.example.com and +alice.example.com with the internet hostname or IP address that each +machine will use to contact the other over the internet.

+

Now we will choose the tunnel endpoints. Tunnel endpoints are private IP +addresses that only have meaning in the context of the VPN. Each machine +will use the tunnel endpoint of the other machine to access it over the +VPN. In our example, the tunnel endpoint for bob.example.com will be +10.4.0.1 and for alice.example.com, 10.4.0.2.

+

Once the VPN is established, you have essentially created a secure +alternate path between the two hosts which is addressed by using the +tunnel endpoints. You can control which network traffic passes between +the hosts (a) over the VPN or (b) independently of the VPN, by choosing +whether to use (a) the VPN endpoint address or (b) the public internet +address, to access the remote host. For example if you are on +bob.example.com and you wish to connect to alice.example.com via +ssh without using the VPN (since ssh has its own built-in security) +you would use the command ssh alice.example.com. However in the same +scenario, you could also use the command telnet 10.4.0.2 to create a +telnet session with alice.example.com over the VPN, that would use the +VPN to secure the session rather than ssh.

+

You can use any address you wish for the tunnel endpoints but make sure +that they are private addresses (such as those that begin with 10 or +192.168) and that they are not part of any existing subnet on the +networks of either peer, unless you are bridging. If you use an address +that is part of your local subnet for either of the tunnel endpoints, +you will get a weird feedback loop.

+
+
+

Example 1: A simple tunnel without security

+

On bob:

+
+openvpn --remote alice.example.com --dev tun1 \
+         --ifconfig 10.4.0.1 10.4.0.2 --verb 9
+
+

On alice:

+
+openvpn --remote bob.example.com --dev tun1 \
+         --ifconfig 10.4.0.2 10.4.0.1 --verb 9
+
+

Now verify the tunnel is working by pinging across the tunnel.

+

On bob:

+
+ping 10.4.0.2
+
+

On alice:

+
+ping 10.4.0.1
+
+

The --verb 9 option will produce verbose output, similar to the +tcpdump(8) program. Omit the --verb 9 option to have OpenVPN run +quietly.

+
+
+

Example 2: A tunnel with static-key security (i.e. using a pre-shared secret)

+

First build a static key on bob.

+
+openvpn --genkey --secret key
+
+

This command will build a key file called key (in ascii format). Now +copy key to alice.example.com over a secure medium such as by using +the scp(1) program.

+

On bob:

+
+openvpn --remote alice.example.com --dev tun1  \
+         --ifconfig 10.4.0.1 10.4.0.2 --verb 5 \
+         --secret key
+
+

On alice:

+
+openvpn --remote bob.example.com --dev tun1   \
+        --ifconfig 10.4.0.2 10.4.0.1 --verb 5 \
+        --secret key
+
+

Now verify the tunnel is working by pinging across the tunnel.

+

On bob:

+
+ping 10.4.0.2
+
+

On alice:

+
+ping 10.4.0.1
+
+
+
+

Example 3: A tunnel with full TLS-based security

+

For this test, we will designate bob as the TLS client and alice +as the TLS server.

+
+
Note:
+
The client or server designation only has +meaning for the TLS subsystem. It has no bearing on OpenVPN's +peer-to-peer, UDP-based communication model.*
+
+

First, build a separate certificate/key pair for both bob and alice (see +above where --cert is discussed for more info). Then construct +Diffie Hellman parameters (see above where --dh is discussed for +more info). You can also use the included test files client.crt, +client.key, server.crt, server.key and +ca.crt. The .crt files are certificates/public-keys, the +.key files are private keys, and ca.crt is a certification +authority who has signed both client.crt and server.crt. +For Diffie Hellman parameters you can use the included file +dh2048.pem.

+
+
WARNING:
+
All client, server, and certificate authority certificates +and keys included in the OpenVPN distribution are totally +insecure and should be used for testing only.
+
+

On bob:

+
+openvpn --remote alice.example.com --dev tun1    \
+        --ifconfig 10.4.0.1 10.4.0.2             \
+        --tls-client --ca ca.crt                 \
+        --cert client.crt --key client.key       \
+        --reneg-sec 60 --verb 5
+
+

On alice:

+
+openvpn --remote bob.example.com --dev tun1      \
+        --ifconfig 10.4.0.2 10.4.0.1             \
+        --tls-server --dh dh1024.pem --ca ca.crt \
+        --cert server.crt --key server.key       \
+        --reneg-sec 60 --verb 5
+
+

Now verify the tunnel is working by pinging across the tunnel.

+

On bob:

+
+ping 10.4.0.2
+
+

On alice:

+
+ping 10.4.0.1
+
+

Notice the --reneg-sec 60 option we used above. That tells OpenVPN +to renegotiate the data channel keys every minute. Since we used +--verb 5 above, you will see status information on each new key +negotiation.

+

For production operations, a key renegotiation interval of 60 seconds is +probably too frequent. Omit the --reneg-sec 60 option to use +OpenVPN's default key renegotiation interval of one hour.

+
+
+

Routing:

+

Assuming you can ping across the tunnel, the next step is to route a +real subnet over the secure tunnel. Suppose that bob and alice have two +network interfaces each, one connected to the internet, and the other to +a private network. Our goal is to securely connect both private +networks. We will assume that bob's private subnet is 10.0.0.0/24 and +alice's is 10.0.1.0/24.

+

First, ensure that IP forwarding is enabled on both peers. On Linux, +enable routing:

+
+echo 1 > /proc/sys/net/ipv4/ip_forward
+
+

This setting is not persistent. Please see your operating systems +documentation how to properly configure IP forwarding, which is also +persistent through system boots.

+

If your system is configured with a firewall. Please see your operating +systems guide on how to configure the firewall. You typically want to +allow traffic coming from and going to the tun/tap adapter OpenVPN is +configured to use.

+

On bob:

+
+route add -net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2
+
+

On alice:

+
+route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1
+
+

Now any machine on the 10.0.0.0/24 subnet can access any machine on the +10.0.1.0/24 subnet over the secure tunnel (or vice versa).

+

In a production environment, you could put the route command(s) in a +script and execute with the --up option.

+
+
+ +
+

HOWTO

+

For a more comprehensive guide to setting up OpenVPN in a production +setting, see the OpenVPN HOWTO at +https://openvpn.net/community-resources/how-to/

+
+
+

PROTOCOL

+

For a description of OpenVPN's underlying protocol, see +https://openvpn.net/community-resources/openvpn-protocol/

+
+
+

WEB

+

OpenVPN's web site is at https://openvpn.net/

+

Go here to download the latest version of OpenVPN, subscribe to the +mailing lists, read the mailing list archives, or browse the SVN +repository.

+
+
+

BUGS

+

Report all bugs to the OpenVPN team info@openvpn.net

+
+
+

SEE ALSO

+

dhcpcd(8), +ifconfig(8), +openssl(1), +route(8), +scp(1) +ssh(1)

+
+
+

NOTES

+

This product includes software developed by the OpenSSL Project +(https://www.openssl.org/)

+

For more information on the TLS protocol, see +http://www.ietf.org/rfc/rfc2246.txt

+

For more information on the LZO real-time compression library see +https://www.oberhumer.com/opensource/lzo/

+
+ +
+

AUTHORS

+

James Yonan james@openvpn.net

+
+
+ + diff --git a/doc/tls-crypt-v2.txt b/doc/tls-crypt-v2.txt deleted file mode 100644 index 3798791..0000000 --- a/doc/tls-crypt-v2.txt +++ /dev/null @@ -1,189 +0,0 @@ -Client-specific tls-crypt keys (--tls-crypt-v2) -=============================================== - -This document describes the ``--tls-crypt-v2`` option, which enables OpenVPN -to use client-specific ``--tls-crypt`` keys. - -Rationale ---------- - -``--tls-auth`` and ``tls-crypt`` use a pre-shared group key, which is shared -among all clients and servers in an OpenVPN deployment. If any client or -server is compromised, the attacker will have access to this shared key, and it -will no longer provide any security. To reduce the risk of losing pre-shared -keys, ``tls-crypt-v2`` adds the ability to supply each client with a unique -tls-crypt key. This allows large organisations and VPN providers to profit -from the same DoS and TLS stack protection that small deployments can already -achieve using ``tls-auth`` or ``tls-crypt``. - -Also, for ``tls-crypt``, even if all these peers succeed in keeping the key -secret, the key lifetime is limited to roughly 8000 years, divided by the -number of clients (see the ``--tls-crypt`` section of the man page). Using -client-specific keys, we lift this lifetime requirement to roughly 8000 years -for each client key (which "Should Be Enough For Everybody (tm)"). - - -Introduction ------------- - -``tls-crypt-v2`` uses an encrypted cookie mechanism to introduce -client-specific tls-crypt keys without introducing a lot of server-side state. -The client-specific key is encrypted using a server key. The server key is the -same for all servers in a group. When a client connects, it first sends the -encrypted key to the server, such that the server can decrypt the key and all -messages can thereafter be encrypted using the client-specific key. - -A wrapped (encrypted and authenticated) client-specific key can also contain -metadata. The metadata is wrapped together with the key, and can be used to -allow servers to identify clients and/or key validity. This allows the server -to abort the connection immediately after receiving the first packet, rather -than performing an entire TLS handshake. Aborting the connection this early -greatly improves the DoS resilience and reduces attack surface against -malicious clients that have the ``tls-crypt`` or ``tls-auth`` key. This is -particularly relevant for large deployments (think lost key or disgruntled -employee) and VPN providers (clients are not trusted). - -To allow for a smooth transition, ``tls-crypt-v2`` is designed such that a -server can enable both ``tls-crypt-v2`` and either ``tls-crypt`` or -``tls-auth``. This is achieved by introducing a P_CONTROL_HARD_RESET_CLIENT_V3 -opcode, that indicates that the client wants to use ``tls-crypt-v2`` for the -current connection. - -For an exact specification and more details, read the Implementation section. - - -Implementation --------------- - -When setting up a tls-crypt-v2 group (similar to generating a tls-crypt or -tls-auth key previously): - -1. Generate a tls-crypt-v2 server key using OpenVPN's ``--tls-crypt-v2-genkey server``. - This key contains 2 512-bit keys, of which we use: - - * the first 256 bits of key 1 as AES-256-CTR encryption key ``Ke`` - * the first 256 bits of key 2 as HMAC-SHA-256 authentication key ``Ka`` - - This format is similar to the format for regular ``tls-crypt``/``tls-auth`` - and data channel keys, which allows us to reuse code. - -2. Add the tls-crypt-v2 server key to all server configs - (``tls-crypt-v2 /path/to/server.key``) - - -When provisioning a client, create a client-specific tls-crypt key: - -1. Generate 2048 bits client-specific key ``Kc`` using OpenVPN's ``--tls-crypt-v2-genkey client`` - -2. Optionally generate metadata - - The first byte of the metadata determines the type. The initial - implementation supports the following types: - - 0x00 (USER): User-defined free-form data. - 0x01 (TIMESTAMP): 64-bit network order unix timestamp of key generation. - - The timestamp can be used to reject too-old tls-crypt-v2 client keys. - - User metadata could for example contain the users certificate serial, such - that the incoming connection can be verified against a CRL. - - If no metadata is supplied during key generation, openvpn defaults to the - TIMESTAMP metadata type. - -3. Create a wrapped client key ``WKc``, using the same nonce-misuse-resistant - SIV construction we use for tls-crypt: - - ``len = len(WKc)`` (16 bit, network byte order) - - ``T = HMAC-SHA256(Ka, len || Kc || metadata)`` - - ``IV = 128 most significant bits of T`` - - ``WKc = T || AES-256-CTR(Ke, IV, Kc || metadata) || len`` - - Note that the length of ``WKc`` can be computed before composing ``WKc``, - because the length of each component is known (and AES-256-CTR does not add - any padding). - -4. Create a tls-crypt-v2 client key: PEM-encode ``Kc || WKc`` and store in a - file, using the header ``-----BEGIN OpenVPN tls-crypt-v2 client key-----`` - and the footer ``-----END OpenVPN tls-crypt-v2 client key-----``. (The PEM - format is simple, and following PEM allows us to use the crypto lib function - for en/decoding.) - -5. Add the tls-crypt-v2 client key to the client config - (``tls-crypt-v2 /path/to/client-specific.key``) - - -When setting up the openvpn connection: - -1. The client reads the tls-crypt-v2 key from its config, and: - - 1. loads ``Kc`` as its tls-crypt key, - 2. stores ``WKc`` in memory for sending to the server. - -2. To start the connection, the client creates a P_CONTROL_HARD_RESET_CLIENT_V3 - message, wraps it with tls-crypt using ``Kc`` as the key, and appends - ``WKc``. (``WKc`` must not be encrypted, to prevent a chicken-and-egg - problem.) - -3. The server receives the P_CONTROL_HARD_RESET_CLIENT_V3 message, and - - 1. reads the WKc length field from the end of the message, and extracts WKc - from the message - 2. unwraps ``WKc`` - 3. uses unwrapped ``Kc`` to verify the remaining - P_CONTROL_HARD_RESET_CLIENT_V3 message's (encryption and) authentication. - - The message is dropped and no error response is sent when either 3.1, 3.2 or - 3.3 fails (DoS protection). - -4. Server optionally checks metadata using a --tls-crypt-v2-verify script - - This allows early abort of connection, *before* we expose any of the - notoriously dangerous TLS, X.509 and ASN.1 parsers and thereby reduces the - attack surface of the server. - - The metadata is checked *after* the OpenVPN three-way handshake has - completed, to prevent DoS attacks. (That is, once the client has proved to - the server that it possesses Kc, by authenticating a packet that contains the - session ID picked by the server.) - - A server should not send back any error messages if metadata verification - fails, to reduce attack surface and maximize DoS resilience. - -6. Client and server use ``Kc`` for (un)wrapping any following control channel - messages. - - -Considerations --------------- - -To allow for a smooth transition, the server implementation allows -``tls-crypt`` or ``tls-auth`` to be used simultaneously with ``tls-crypt-v2``. -This specification does not allow simultaneously using ``tls-crypt-v2`` and -connections without any control channel wrapping, because that would break DoS -resilience. - -WKc includes a length field, so we leave the option for future extension of the -P_CONTROL_HEAD_RESET_CLIENT_V3 message open. (E.g. add payload to the reset to -indicate low-level protocol features.) - -``tls-crypt-v2`` uses fixed crypto algorithms, because: - - * The crypto is used before we can do any negotiation, so the algorithms have - to be predefined. - * The crypto primitives are chosen conservatively, making problems with these - primitives unlikely. - * Making anything configurable adds complexity, both in implementation and - usage. We should not add any more complexity than is absolutely necessary. - -Potential ``tls-crypt-v2`` risks: - - * Slightly more work on first connection (``WKc`` unwrap + hard reset unwrap) - than with ``tls-crypt`` (hard reset unwrap) or ``tls-auth`` (hard reset auth). - * Flexible metadata allow mistakes - (So we should make it easy to do it right. Provide tooling to create client - keys based on cert serial + CA fingerprint, provide script that uses CRL (if - available) to drop revoked keys.) -- cgit v1.2.3 From 5246174f27866c0e9e22844d998f3c97cac54050 Mon Sep 17 00:00:00 2001 From: Bernhard Schmidt Date: Wed, 30 Sep 2020 21:10:50 +0200 Subject: New upstream version 2.5~rc2 --- doc/man-sections/advanced-options.rst | 7 +- doc/man-sections/client-options.rst | 60 ++++++++------ doc/man-sections/generic-options.rst | 7 ++ doc/man-sections/script-options.rst | 5 +- doc/man-sections/server-options.rst | 36 ++++++++- doc/man-sections/vpn-network-options.rst | 4 + doc/openvpn.8 | 133 +++++++++++++++++++++++-------- doc/openvpn.8.html | 126 ++++++++++++++++++++--------- 8 files changed, 271 insertions(+), 107 deletions(-) (limited to 'doc') diff --git a/doc/man-sections/advanced-options.rst b/doc/man-sections/advanced-options.rst index 9b96e40..bedc884 100644 --- a/doc/man-sections/advanced-options.rst +++ b/doc/man-sections/advanced-options.rst @@ -11,8 +11,11 @@ Standalone Debug Options --show-gateway --show-gateway IPv6-target - If an IPv6 target address is passed as argument, the IPv6 route for this - host is reported. + For IPv6 this queries the route towards ::/128, or the specified IPv6 + target address if passed as argument. + For IPv4 on Linux, Windows, MacOS and BSD it looks for a 0.0.0.0/0 route. + If there are more specific routes, the result will not always be matching + the route of the IPv4 packets to the VPN gateway. Advanced Expert Options diff --git a/doc/man-sections/client-options.rst b/doc/man-sections/client-options.rst index ec1e3b1..af21fbc 100644 --- a/doc/man-sections/client-options.rst +++ b/doc/man-sections/client-options.rst @@ -244,43 +244,51 @@ configuration. use :code:`ignore`. --remote args - Remote host name or IP address. It supports two additional optional - arguments: ``port`` and ``proto``. On the client, multiple ``--remote`` - options may be specified for redundancy, each referring to a different - OpenVPN server. Specifying multiple ``--remote`` options for this - purpose is a special case of the more general connection-profile - feature. See the ```` documentation below. + Remote host name or IP address, port and protocol. - The OpenVPN client will try to connect to a server at ``host:port`` in - the order specified by the list of ``--remote`` options. - - Examples: + Valid syntaxes: :: - remote server.example.net - remote server.example.net 1194 - remote server.example.net tcp + remote host + remote host port + remote host port proto - ``proto`` indicates the protocol to use when connecting with the remote, - and may be :code:`tcp` or :code:`udp`. + The ``port`` and ``proto`` arguments are optional. The OpenVPN client + will try to connect to a server at ``host:port``. The ``proto`` argument + indicates the protocol to use when connecting with the remote, and may be + :code:`tcp` or :code:`udp`. To enforce IPv4 or IPv6 connections add a + :code:`4` or :code:`6` suffix; like :code:`udp4` / :code:`udp6` + / :code:`tcp4` / :code:`tcp6`. - For forcing IPv4 or IPv6 connection suffix tcp or udp with 4/6 like - udp4/udp6/tcp4/tcp6. + On the client, multiple ``--remote`` options may be specified for + redundancy, each referring to a different OpenVPN server, in the order + specified by the list of ``--remote`` options. Specifying multiple + ``--remote`` options for this purpose is a special case of the more + general connection-profile feature. See the ```` + documentation below. The client will move on to the next host in the list, in the event of connection failure. Note that at any given time, the OpenVPN client will at most be connected to one server. - Note that since UDP is connectionless, connection failure is defined by - the ``--ping`` and ``--ping-restart`` options. + Examples: + :: - Note the following corner case: If you use multiple ``--remote`` - options, AND you are dropping root privileges on the client with - ``--user`` and/or ``--group`` AND the client is running a non-Windows - OS, if the client needs to switch to a different server, and that server - pushes back different TUN/TAP or route settings, the client may lack the - necessary privileges to close and reopen the TUN/TAP interface. This - could cause the client to exit with a fatal error. + remote server1.example.net + remote server1.example.net 1194 + remote server2.example.net 1194 tcp + + *Note:* + Since UDP is connectionless, connection failure is defined by + the ``--ping`` and ``--ping-restart`` options. + + Also, if you use multiple ``--remote`` options, AND you are dropping + root privileges on the client with ``--user`` and/or ``--group`` AND + the client is running a non-Windows OS, if the client needs to switch + to a different server, and that server pushes back different TUN/TAP + or route settings, the client may lack the necessary privileges to + close and reopen the TUN/TAP interface. This could cause the client + to exit with a fatal error. If ``--remote`` is unspecified, OpenVPN will listen for packets from any IP address, but will not act on those packets unless they pass all diff --git a/doc/man-sections/generic-options.rst b/doc/man-sections/generic-options.rst index a07fe7e..d5f0883 100644 --- a/doc/man-sections/generic-options.rst +++ b/doc/man-sections/generic-options.rst @@ -230,6 +230,13 @@ which mode OpenVPN is configured as. The downside of using ``--mlock`` is that it will reduce the amount of physical memory available to other applications. + The limit on how much memory can be locked and how that limit + is enforced are OS-dependent. On Linux the default limit that an + unprivileged process may lock (RLIMIT_MEMLOCK) is low, and if + privileges are dropped later, future memory allocations will very + likely fail. The limit can be increased using ulimit or systemd + directives depending on how OpenVPN is started. + --nice n Change process priority after initialization (``n`` greater than 0 is lower priority, ``n`` less than zero is higher priority). diff --git a/doc/man-sections/script-options.rst b/doc/man-sections/script-options.rst index b4bbf52..a4df673 100644 --- a/doc/man-sections/script-options.rst +++ b/doc/man-sections/script-options.rst @@ -157,9 +157,8 @@ SCRIPT HOOKS where some of the related client-connect functions returned an error status. - The ``--client-disconnect`` command is passed the same pathname as the - corresponding ``--client-connect`` command as its last argument (after - any arguments specified in ``cmd``). + The ``--client-disconnect`` command is not passed any extra arguments + (only those arguments specified in cmd, if any). --down cmd Run command ``cmd`` after TUN/TAP device close (post ``--user`` UID diff --git a/doc/man-sections/server-options.rst b/doc/man-sections/server-options.rst index f1f0667..5a68945 100644 --- a/doc/man-sections/server-options.rst +++ b/doc/man-sections/server-options.rst @@ -204,7 +204,8 @@ fast hardware. SSL/TLS authentication must be used in this mode. ifconfig-ipv6-pool ipv6addr/bits The pool starts at ``ipv6addr`` and matches the offset determined from - the start of the IPv4 pool. + the start of the IPv4 pool. If the host part of the given IPv6 + address is ``0``, the pool starts at ``ipv6addr`` +1. --ifconfig-pool-persist args Persist/unpersist ifconfig-pool data to ``file``, at ``seconds`` @@ -530,6 +531,14 @@ fast hardware. SSL/TLS authentication must be used in this mode. ``--client-config-dir`` configuration file. This option will ignore ``--push`` options at the global config file level. + *NOTE*: ``--push-reset`` is very thorough: it will remove almost + all options from the list of to-be-pushed options. In many cases, + some of these options will need to be re-configured afterwards - + specifically, ``--topology subnet`` and ``--route-gateway`` will get + lost and this will break client configs in many cases. Thus, for most + purposes, ``--push-remove`` is better suited to selectively remove + push options for individual clients. + --server args A helper directive designed to simplify the configuration of OpenVPN's server mode. This directive will set up an OpenVPN server which will @@ -631,6 +640,19 @@ fast hardware. SSL/TLS authentication must be used in this mode. mode server tls-server +--server-ipv6 args + Convenience-function to enable a number of IPv6 related options at once, + namely ``--ifconfig-ipv6``, ``--ifconfig-ipv6-pool`` and + ``--push tun-ipv6``. + + Valid syntax: + :: + + server-ipv6 ipv6addr/bits + + Pushing of the ``--tun-ipv6`` directive is done for older clients which + require an explicit ``--tun-ipv6`` in their configuration. + --stale-routes-check args Remove routes which haven't had activity for ``n`` seconds (i.e. the ageing time). This check is run every ``t`` seconds (i.e. check interval). @@ -646,9 +668,15 @@ fast hardware. SSL/TLS authentication must be used in this mode. ``--max-routes-per-client`` --username-as-common-name - For ``--auth-user-pass-verify`` authentication, use the authenticated - username as the common name, rather than the common name from the client - cert. + Use the authenticated username as the common-name, rather than the + common-name from the client certificate. Requires that some form of + ``--auth-user-pass`` verification is in effect. As the replacement happens + after ``--auth-user-pass`` verification, the verification script or + plugin will still receive the common-name from the certificate. + + The common_name environment variable passed to scripts and plugins invoked + after authentication (e.g, client-connect script) and file names parsed in + client-config directory will match the username. --verify-client-cert mode Specify whether the client is required to supply a valid certificate. diff --git a/doc/man-sections/vpn-network-options.rst b/doc/man-sections/vpn-network-options.rst index 825dd1c..2668278 100644 --- a/doc/man-sections/vpn-network-options.rst +++ b/doc/man-sections/vpn-network-options.rst @@ -114,6 +114,10 @@ routing. :code:`DOMAIN` ``name`` Set Connection-specific DNS Suffix to :code:`name`. + :code:`ADAPTER_DOMAIN_SUFFIX` ``name`` + Alias to :code:`DOMAIN`. This is a compatibility option, it + should not be used in new deployments. + :code:`DOMAIN-SEARCH` ``name`` Add :code:`name` to the domain search list. Repeat this option to add more entries. Up to diff --git a/doc/openvpn.8 b/doc/openvpn.8 index b914f32..5056e03 100644 --- a/doc/openvpn.8 +++ b/doc/openvpn.8 @@ -343,6 +343,13 @@ below), then are discarded. .sp The downside of using \fB\-\-mlock\fP is that it will reduce the amount of physical memory available to other applications. +.sp +The limit on how much memory can be locked and how that limit +is enforced are OS\-dependent. On Linux the default limit that an +unprivileged process may lock (RLIMIT_MEMLOCK) is low, and if +privileges are dropped later, future memory allocations will very +likely fail. The limit can be increased using ulimit or systemd +directives depending on how OpenVPN is started. .TP .BI \-\-nice \ n Change process priority after initialization (\fBn\fP greater than 0 is @@ -1268,50 +1275,67 @@ next remote succeeds. To silently ignore an option pushed by the server, use \fBignore\fP\&. .TP .BI \-\-remote \ args -Remote host name or IP address. It supports two additional optional -arguments: \fBport\fP and \fBproto\fP\&. On the client, multiple \fB\-\-remote\fP -options may be specified for redundancy, each referring to a different -OpenVPN server. Specifying multiple \fB\-\-remote\fP options for this -purpose is a special case of the more general connection\-profile -feature. See the \fB\fP documentation below. -.sp -The OpenVPN client will try to connect to a server at \fBhost:port\fP in -the order specified by the list of \fB\-\-remote\fP options. +Remote host name or IP address, port and protocol. .sp -Examples: +Valid syntaxes: .INDENT 7.0 .INDENT 3.5 .sp .nf .ft C -remote server.example.net -remote server.example.net 1194 -remote server.example.net tcp +remote host +remote host port +remote host port proto .ft P .fi .UNINDENT .UNINDENT .sp -\fBproto\fP indicates the protocol to use when connecting with the remote, -and may be \fBtcp\fP or \fBudp\fP\&. +The \fBport\fP and \fBproto\fP arguments are optional. The OpenVPN client +will try to connect to a server at \fBhost:port\fP\&. The \fBproto\fP argument +indicates the protocol to use when connecting with the remote, and may be +\fBtcp\fP or \fBudp\fP\&. To enforce IPv4 or IPv6 connections add a +\fB4\fP or \fB6\fP suffix; like \fBudp4\fP / \fBudp6\fP +/ \fBtcp4\fP / \fBtcp6\fP\&. .sp -For forcing IPv4 or IPv6 connection suffix tcp or udp with 4/6 like -udp4/udp6/tcp4/tcp6. +On the client, multiple \fB\-\-remote\fP options may be specified for +redundancy, each referring to a different OpenVPN server, in the order +specified by the list of \fB\-\-remote\fP options. Specifying multiple +\fB\-\-remote\fP options for this purpose is a special case of the more +general connection\-profile feature. See the \fB\fP +documentation below. .sp The client will move on to the next host in the list, in the event of connection failure. Note that at any given time, the OpenVPN client will at most be connected to one server. .sp -Note that since UDP is connectionless, connection failure is defined by +Examples: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +remote server1.example.net +remote server1.example.net 1194 +remote server2.example.net 1194 tcp +.ft P +.fi +.UNINDENT +.UNINDENT +.INDENT 7.0 +.TP +.B \fINote:\fP +Since UDP is connectionless, connection failure is defined by the \fB\-\-ping\fP and \fB\-\-ping\-restart\fP options. .sp -Note the following corner case: If you use multiple \fB\-\-remote\fP -options, AND you are dropping root privileges on the client with -\fB\-\-user\fP and/or \fB\-\-group\fP AND the client is running a non\-Windows -OS, if the client needs to switch to a different server, and that server -pushes back different TUN/TAP or route settings, the client may lack the -necessary privileges to close and reopen the TUN/TAP interface. This -could cause the client to exit with a fatal error. +Also, if you use multiple \fB\-\-remote\fP options, AND you are dropping +root privileges on the client with \fB\-\-user\fP and/or \fB\-\-group\fP AND +the client is running a non\-Windows OS, if the client needs to switch +to a different server, and that server pushes back different TUN/TAP +or route settings, the client may lack the necessary privileges to +close and reopen the TUN/TAP interface. This could cause the client +to exit with a fatal error. +.UNINDENT .sp If \fB\-\-remote\fP is unspecified, OpenVPN will listen for packets from any IP address, but will not act on those packets unless they pass all @@ -1709,7 +1733,8 @@ ifconfig\-ipv6\-pool ipv6addr/bits .UNINDENT .sp The pool starts at \fBipv6addr\fP and matches the offset determined from -the start of the IPv4 pool. +the start of the IPv4 pool. If the host part of the given IPv6 +address is \fB0\fP, the pool starts at \fBipv6addr\fP +1. .TP .BI \-\-ifconfig\-pool\-persist \ args Persist/unpersist ifconfig\-pool data to \fBfile\fP, at \fBseconds\fP @@ -2098,6 +2123,14 @@ Don\(aqt inherit the global push list for a specific client instance. Specify this option in a client\-specific context such as with a \fB\-\-client\-config\-dir\fP configuration file. This option will ignore \fB\-\-push\fP options at the global config file level. +.sp +\fINOTE\fP: \fB\-\-push\-reset\fP is very thorough: it will remove almost +all options from the list of to\-be\-pushed options. In many cases, +some of these options will need to be re\-configured afterwards \- +specifically, \fB\-\-topology subnet\fP and \fB\-\-route\-gateway\fP will get +lost and this will break client configs in many cases. Thus, for most +purposes, \fB\-\-push\-remove\fP is better suited to selectively remove +push options for individual clients. .TP .BI \-\-server \ args A helper directive designed to simplify the configuration of OpenVPN\(aqs @@ -2242,6 +2275,26 @@ tls\-server .UNINDENT .UNINDENT .TP +.BI \-\-server\-ipv6 \ args +Convenience\-function to enable a number of IPv6 related options at once, +namely \fB\-\-ifconfig\-ipv6\fP, \fB\-\-ifconfig\-ipv6\-pool\fP and +\fB\-\-push tun\-ipv6\fP\&. +.sp +Valid syntax: +.INDENT 7.0 +.INDENT 3.5 +.sp +.nf +.ft C +server\-ipv6 ipv6addr/bits +.ft P +.fi +.UNINDENT +.UNINDENT +.sp +Pushing of the \fB\-\-tun\-ipv6\fP directive is done for older clients which +require an explicit \fB\-\-tun\-ipv6\fP in their configuration. +.TP .BI \-\-stale\-routes\-check \ args Remove routes which haven\(aqt had activity for \fBn\fP seconds (i.e. the ageing time). This check is run every \fBt\fP seconds (i.e. check interval). @@ -2264,9 +2317,15 @@ This option helps to keep the dynamic routing table small. See also \fB\-\-max\-routes\-per\-client\fP .TP .B \-\-username\-as\-common\-name -For \fB\-\-auth\-user\-pass\-verify\fP authentication, use the authenticated -username as the common name, rather than the common name from the client -cert. +Use the authenticated username as the common\-name, rather than the +common\-name from the client certificate. Requires that some form of +\fB\-\-auth\-user\-pass\fP verification is in effect. As the replacement happens +after \fB\-\-auth\-user\-pass\fP verification, the verification script or +plugin will still receive the common\-name from the certificate. +.sp +The common_name environment variable passed to scripts and plugins invoked +after authentication (e.g, client\-connect script) and file names parsed in +client\-config directory will match the username. .TP .BI \-\-verify\-client\-cert \ mode Specify whether the client is required to supply a valid certificate. @@ -4271,6 +4330,10 @@ dhcp\-options type [parm] .B \fBDOMAIN\fP \fBname\fP Set Connection\-specific DNS Suffix to \fBname\fP\&. .TP +.B \fBADAPTER_DOMAIN_SUFFIX\fP \fBname\fP +Alias to \fBDOMAIN\fP\&. This is a compatibility option, it +should not be used in new deployments. +.TP .B \fBDOMAIN\-SEARCH\fP \fBname\fP Add \fBname\fP to the domain search list. Repeat this option to add more entries. Up to @@ -5020,9 +5083,8 @@ plugins will be called on client instance object deletion, even in cases where some of the related client\-connect functions returned an error status. .sp -The \fB\-\-client\-disconnect\fP command is passed the same pathname as the -corresponding \fB\-\-client\-connect\fP command as its last argument (after -any arguments specified in \fBcmd\fP). +The \fB\-\-client\-disconnect\fP command is not passed any extra arguments +(only those arguments specified in cmd, if any). .TP .BI \-\-down \ cmd Run command \fBcmd\fP after TUN/TAP device close (post \fB\-\-user\fP UID @@ -6283,8 +6345,11 @@ Valid syntax: .UNINDENT .UNINDENT .sp -If an IPv6 target address is passed as argument, the IPv6 route for this -host is reported. +For IPv6 this queries the route towards ::/128, or the specified IPv6 +target address if passed as argument. +For IPv4 on Linux, Windows, MacOS and BSD it looks for a 0.0.0.0/0 route. +If there are more specific routes, the result will not always be matching +the route of the IPv4 packets to the VPN gateway. .UNINDENT .SS Advanced Expert Options .sp diff --git a/doc/openvpn.8.html b/doc/openvpn.8.html index d6b2719..f5d6f26 100644 --- a/doc/openvpn.8.html +++ b/doc/openvpn.8.html @@ -3,7 +3,7 @@ - + openvpn + + +
+

openvpn examples

+

Secure IP tunnel daemon

+ +++ + + + + + +
Manual section:5
Manual group:Configuration files
+
+

INTRODUCTION

+

This man page gives a few simple examples to create OpenVPN setups and configuration files.

+
+
+

EXAMPLES

+

Prior to running these examples, you should have OpenVPN installed on +two machines with network connectivity between them. If you have not yet +installed OpenVPN, consult the INSTALL file included in the OpenVPN +distribution.

+
+

Firewall Setup:

+

If firewalls exist between the two machines, they should be set to +forward the port OpenVPN is configured to use, in both directions. +The default for OpenVPN is 1194/udp. If you do not have control +over the firewalls between the two machines, you may still be able to +use OpenVPN by adding --ping 15 to each of the openvpn commands +used below in the examples (this will cause each peer to send out a UDP +ping to its remote peer once every 15 seconds which will cause many +stateful firewalls to forward packets in both directions without an +explicit firewall rule).

+

Please see your operating system guides for how to configure the firewall +on your systems.

+
+
+

VPN Address Setup:

+

For purposes of our example, our two machines will be called +bob.example.com and alice.example.com. If you are constructing a +VPN over the internet, then replace bob.example.com and +alice.example.com with the internet hostname or IP address that each +machine will use to contact the other over the internet.

+

Now we will choose the tunnel endpoints. Tunnel endpoints are private IP +addresses that only have meaning in the context of the VPN. Each machine +will use the tunnel endpoint of the other machine to access it over the +VPN. In our example, the tunnel endpoint for bob.example.com will be +10.4.0.1 and for alice.example.com, 10.4.0.2.

+

Once the VPN is established, you have essentially created a secure +alternate path between the two hosts which is addressed by using the +tunnel endpoints. You can control which network traffic passes between +the hosts (a) over the VPN or (b) independently of the VPN, by choosing +whether to use (a) the VPN endpoint address or (b) the public internet +address, to access the remote host. For example if you are on +bob.example.com and you wish to connect to alice.example.com via +ssh without using the VPN (since ssh has its own built-in security) +you would use the command ssh alice.example.com. However in the same +scenario, you could also use the command telnet 10.4.0.2 to create a +telnet session with alice.example.com over the VPN, that would use the +VPN to secure the session rather than ssh.

+

You can use any address you wish for the tunnel endpoints but make sure +that they are private addresses (such as those that begin with 10 or +192.168) and that they are not part of any existing subnet on the +networks of either peer, unless you are bridging. If you use an address +that is part of your local subnet for either of the tunnel endpoints, +you will get a weird feedback loop.

+
+
+

Example 1: A simple tunnel without security

+

On bob:

+
+openvpn --remote alice.example.com --dev tun1 \
+         --ifconfig 10.4.0.1 10.4.0.2 --verb 9
+
+

On alice:

+
+openvpn --remote bob.example.com --dev tun1 \
+         --ifconfig 10.4.0.2 10.4.0.1 --verb 9
+
+

Now verify the tunnel is working by pinging across the tunnel.

+

On bob:

+
+ping 10.4.0.2
+
+

On alice:

+
+ping 10.4.0.1
+
+

The --verb 9 option will produce verbose output, similar to the +tcpdump(8) program. Omit the --verb 9 option to have OpenVPN run +quietly.

+
+
+

Example 2: A tunnel with static-key security (i.e. using a pre-shared secret)

+

First build a static key on bob.

+
+openvpn --genkey --secret key
+
+

This command will build a key file called key (in ascii format). Now +copy key to alice.example.com over a secure medium such as by using +the scp(1) program.

+

On bob:

+
+openvpn --remote alice.example.com --dev tun1  \
+         --ifconfig 10.4.0.1 10.4.0.2 --verb 5 \
+         --secret key
+
+

On alice:

+
+openvpn --remote bob.example.com --dev tun1   \
+        --ifconfig 10.4.0.2 10.4.0.1 --verb 5 \
+        --secret key
+
+

Now verify the tunnel is working by pinging across the tunnel.

+

On bob:

+
+ping 10.4.0.2
+
+

On alice:

+
+ping 10.4.0.1
+
+
+
+

Example 3: A tunnel with full TLS-based security

+

For this test, we will designate bob as the TLS client and alice +as the TLS server.

+
+
Note:
+
The client or server designation only has +meaning for the TLS subsystem. It has no bearing on OpenVPN's +peer-to-peer, UDP-based communication model.*
+
+

First, build a separate certificate/key pair for both bob and alice (see +above where --cert is discussed for more info). Then construct +Diffie Hellman parameters (see above where --dh is discussed for +more info). You can also use the included test files client.crt, +client.key, server.crt, server.key and +ca.crt. The .crt files are certificates/public-keys, the +.key files are private keys, and ca.crt is a certification +authority who has signed both client.crt and server.crt. +For Diffie Hellman parameters you can use the included file +dh2048.pem.

+
+
WARNING:
+
All client, server, and certificate authority certificates +and keys included in the OpenVPN distribution are totally +insecure and should be used for testing only.
+
+

On bob:

+
+openvpn --remote alice.example.com --dev tun1    \
+        --ifconfig 10.4.0.1 10.4.0.2             \
+        --tls-client --ca ca.crt                 \
+        --cert client.crt --key client.key       \
+        --reneg-sec 60 --verb 5
+
+

On alice:

+
+openvpn --remote bob.example.com --dev tun1      \
+        --ifconfig 10.4.0.2 10.4.0.1             \
+        --tls-server --dh dh1024.pem --ca ca.crt \
+        --cert server.crt --key server.key       \
+        --reneg-sec 60 --verb 5
+
+

Now verify the tunnel is working by pinging across the tunnel.

+

On bob:

+
+ping 10.4.0.2
+
+

On alice:

+
+ping 10.4.0.1
+
+

Notice the --reneg-sec 60 option we used above. That tells OpenVPN +to renegotiate the data channel keys every minute. Since we used +--verb 5 above, you will see status information on each new key +negotiation.

+

For production operations, a key renegotiation interval of 60 seconds is +probably too frequent. Omit the --reneg-sec 60 option to use +OpenVPN's default key renegotiation interval of one hour.

+
+
+

Routing:

+

Assuming you can ping across the tunnel, the next step is to route a +real subnet over the secure tunnel. Suppose that bob and alice have two +network interfaces each, one connected to the internet, and the other to +a private network. Our goal is to securely connect both private +networks. We will assume that bob's private subnet is 10.0.0.0/24 and +alice's is 10.0.1.0/24.

+

First, ensure that IP forwarding is enabled on both peers. On Linux, +enable routing:

+
+echo 1 > /proc/sys/net/ipv4/ip_forward
+
+

This setting is not persistent. Please see your operating systems +documentation how to properly configure IP forwarding, which is also +persistent through system boots.

+

If your system is configured with a firewall. Please see your operating +systems guide on how to configure the firewall. You typically want to +allow traffic coming from and going to the tun/tap adapter OpenVPN is +configured to use.

+

On bob:

+
+route add -net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2
+
+

On alice:

+
+route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1
+
+

Now any machine on the 10.0.0.0/24 subnet can access any machine on the +10.0.1.0/24 subnet over the secure tunnel (or vice versa).

+

In a production environment, you could put the route command(s) in a +script and execute with the --up option.

+
+
+
+ + diff --git a/doc/openvpn-examples.5.rst b/doc/openvpn-examples.5.rst new file mode 100644 index 0000000..988b602 --- /dev/null +++ b/doc/openvpn-examples.5.rst @@ -0,0 +1,17 @@ +=============================== + openvpn examples +=============================== +------------------------- + Secure IP tunnel daemon +------------------------- + +:Manual section: 5 +:Manual group: Configuration files + + +INTRODUCTION +============ + +This man page gives a few simple examples to create OpenVPN setups and configuration files. + +.. include:: man-sections/examples.rst diff --git a/doc/openvpn.8 b/doc/openvpn.8 index 57d94ea..ceb6348 100644 --- a/doc/openvpn.8 +++ b/doc/openvpn.8 @@ -1031,6 +1031,14 @@ Newer clients (2.4.7+) will fall back to the original password method after a failed auth. Older clients will keep using the token value and react according to \fB\-\-auth\-retry\fP .TP +.BI \-\-auth\-token\-user \ base64username +Companion option to \fB\-\-auth\-token\fP\&. This options allows to override +the username used by the client when reauthenticating with the \fBauth\-token\fP\&. +It also allows to use \fB\-\-auth\-token\fP in setups that normally do not use +username and password. +.sp +The username has to be base64 encoded. +.TP .B \-\-auth\-user\-pass Authenticate with server using username/password. .sp @@ -2076,14 +2084,24 @@ The client announces the list of supported ciphers configured with the .B \fBIV_GUI_VER= \fP The UI version of a UI if one is running, for example \fBde.blinkt.openvpn 0.5.47\fP for the Android app. +.TP +.B \fBIV_SSO=[crtext,][openurl,][proxy_url]\fP +Additional authentication methods supported by the client. +This may be set by the client UI/GUI using \fB\-\-setenv\fP .UNINDENT .sp When \fB\-\-push\-peer\-info\fP is enabled the additional information consists of the following data: .INDENT 7.0 .TP -.B \fBIV_HWADDR=\fP -The MAC address of clients default gateway +.B \fBIV_HWADDR=\fP +This is intended to be a unique and persistent ID of the client. +The string value can be any readable ASCII string up to 64 bytes. +OpenVPN 2.x and some other implementations use the MAC address of +the client\(aqs interface used to reach the default gateway. If this +string is generated by the client, it should be consistent and +preserved across independent session and preferably +re\-installations and upgrades. .TP .B \fBIV_SSL=\fP The ssl version used by the client, e.g. @@ -6637,343 +6655,6 @@ Causes OpenVPN to display its current statistics (to the syslog file if .B \fBSIGINT\fP, \fBSIGTERM\fP Causes OpenVPN to exit gracefully. .UNINDENT -.SH EXAMPLES -.sp -Prior to running these examples, you should have OpenVPN installed on -two machines with network connectivity between them. If you have not yet -installed OpenVPN, consult the INSTALL file included in the OpenVPN -distribution. -.SS Firewall Setup: -.sp -If firewalls exist between the two machines, they should be set to -forward the port OpenVPN is configured to use, in both directions. -The default for OpenVPN is 1194/udp. If you do not have control -over the firewalls between the two machines, you may still be able to -use OpenVPN by adding \fB\-\-ping 15\fP to each of the \fBopenvpn\fP commands -used below in the examples (this will cause each peer to send out a UDP -ping to its remote peer once every 15 seconds which will cause many -stateful firewalls to forward packets in both directions without an -explicit firewall rule). -.sp -Please see your operating system guides for how to configure the firewall -on your systems. -.SS VPN Address Setup: -.sp -For purposes of our example, our two machines will be called -\fBbob.example.com\fP and \fBalice.example.com\fP\&. If you are constructing a -VPN over the internet, then replace \fBbob.example.com\fP and -\fBalice.example.com\fP with the internet hostname or IP address that each -machine will use to contact the other over the internet. -.sp -Now we will choose the tunnel endpoints. Tunnel endpoints are private IP -addresses that only have meaning in the context of the VPN. Each machine -will use the tunnel endpoint of the other machine to access it over the -VPN. In our example, the tunnel endpoint for bob.example.com will be -10.4.0.1 and for alice.example.com, 10.4.0.2. -.sp -Once the VPN is established, you have essentially created a secure -alternate path between the two hosts which is addressed by using the -tunnel endpoints. You can control which network traffic passes between -the hosts (a) over the VPN or (b) independently of the VPN, by choosing -whether to use (a) the VPN endpoint address or (b) the public internet -address, to access the remote host. For example if you are on -bob.example.com and you wish to connect to \fBalice.example.com\fP via -\fBssh\fP without using the VPN (since \fBssh\fP has its own built\-in security) -you would use the command \fBssh alice.example.com\fP\&. However in the same -scenario, you could also use the command \fBtelnet 10.4.0.2\fP to create a -telnet session with alice.example.com over the VPN, that would use the -VPN to secure the session rather than \fBssh\fP\&. -.sp -You can use any address you wish for the tunnel endpoints but make sure -that they are private addresses (such as those that begin with 10 or -192.168) and that they are not part of any existing subnet on the -networks of either peer, unless you are bridging. If you use an address -that is part of your local subnet for either of the tunnel endpoints, -you will get a weird feedback loop. -.SS Example 1: A simple tunnel without security -.sp -On bob: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -openvpn \-\-remote alice.example.com \-\-dev tun1 \e - \-\-ifconfig 10.4.0.1 10.4.0.2 \-\-verb 9 -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -On alice: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -openvpn \-\-remote bob.example.com \-\-dev tun1 \e - \-\-ifconfig 10.4.0.2 10.4.0.1 \-\-verb 9 -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -Now verify the tunnel is working by pinging across the tunnel. -.sp -On bob: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -ping 10.4.0.2 -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -On alice: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -ping 10.4.0.1 -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -The \fB\-\-verb 9\fP option will produce verbose output, similar to the -\fBtcpdump\fP(8) program. Omit the \fB\-\-verb 9\fP option to have OpenVPN run -quietly. -.SS Example 2: A tunnel with static\-key security (i.e. using a pre\-shared secret) -.sp -First build a static key on bob. -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -openvpn \-\-genkey \-\-secret key -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -This command will build a key file called \fBkey\fP (in ascii format). Now -copy \fBkey\fP to \fBalice.example.com\fP over a secure medium such as by using -the \fBscp\fP(1) program. -.sp -On bob: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -openvpn \-\-remote alice.example.com \-\-dev tun1 \e - \-\-ifconfig 10.4.0.1 10.4.0.2 \-\-verb 5 \e - \-\-secret key -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -On alice: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -openvpn \-\-remote bob.example.com \-\-dev tun1 \e - \-\-ifconfig 10.4.0.2 10.4.0.1 \-\-verb 5 \e - \-\-secret key -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -Now verify the tunnel is working by pinging across the tunnel. -.sp -On bob: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -ping 10.4.0.2 -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -On alice: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -ping 10.4.0.1 -.ft P -.fi -.UNINDENT -.UNINDENT -.SS Example 3: A tunnel with full TLS\-based security -.sp -For this test, we will designate \fBbob\fP as the TLS client and \fBalice\fP -as the TLS server. -.INDENT 0.0 -.TP -.B \fINote:\fP -The client or server designation only has -meaning for the TLS subsystem. It has no bearing on OpenVPN\(aqs -peer\-to\-peer, UDP\-based communication model.* -.UNINDENT -.sp -First, build a separate certificate/key pair for both bob and alice (see -above where \fB\-\-cert\fP is discussed for more info). Then construct -Diffie Hellman parameters (see above where \fB\-\-dh\fP is discussed for -more info). You can also use the included test files \fBclient.crt\fP, -\fBclient.key\fP, \fBserver.crt\fP, \fBserver.key\fP and -\fBca.crt\fP\&. The \fB\&.crt\fP files are certificates/public\-keys, the -\fB\&.key\fP files are private keys, and \fBca.crt\fP is a certification -authority who has signed both \fBclient.crt\fP and \fBserver.crt\fP\&. -For Diffie Hellman parameters you can use the included file -\fBdh2048.pem\fP\&. -.INDENT 0.0 -.TP -.B \fIWARNING:\fP -All client, server, and certificate authority certificates -and keys included in the OpenVPN distribution are totally -insecure and should be used for testing only. -.UNINDENT -.sp -On bob: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -openvpn \-\-remote alice.example.com \-\-dev tun1 \e - \-\-ifconfig 10.4.0.1 10.4.0.2 \e - \-\-tls\-client \-\-ca ca.crt \e - \-\-cert client.crt \-\-key client.key \e - \-\-reneg\-sec 60 \-\-verb 5 -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -On alice: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -openvpn \-\-remote bob.example.com \-\-dev tun1 \e - \-\-ifconfig 10.4.0.2 10.4.0.1 \e - \-\-tls\-server \-\-dh dh1024.pem \-\-ca ca.crt \e - \-\-cert server.crt \-\-key server.key \e - \-\-reneg\-sec 60 \-\-verb 5 -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -Now verify the tunnel is working by pinging across the tunnel. -.sp -On bob: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -ping 10.4.0.2 -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -On alice: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -ping 10.4.0.1 -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -Notice the \fB\-\-reneg\-sec 60\fP option we used above. That tells OpenVPN -to renegotiate the data channel keys every minute. Since we used -\fB\-\-verb 5\fP above, you will see status information on each new key -negotiation. -.sp -For production operations, a key renegotiation interval of 60 seconds is -probably too frequent. Omit the \fB\-\-reneg\-sec 60\fP option to use -OpenVPN\(aqs default key renegotiation interval of one hour. -.SS Routing: -.sp -Assuming you can ping across the tunnel, the next step is to route a -real subnet over the secure tunnel. Suppose that bob and alice have two -network interfaces each, one connected to the internet, and the other to -a private network. Our goal is to securely connect both private -networks. We will assume that bob\(aqs private subnet is \fI10.0.0.0/24\fP and -alice\(aqs is \fI10.0.1.0/24\fP\&. -.sp -First, ensure that IP forwarding is enabled on both peers. On Linux, -enable routing: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -echo 1 > /proc/sys/net/ipv4/ip_forward -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -This setting is not persistent. Please see your operating systems -documentation how to properly configure IP forwarding, which is also -persistent through system boots. -.sp -If your system is configured with a firewall. Please see your operating -systems guide on how to configure the firewall. You typically want to -allow traffic coming from and going to the tun/tap adapter OpenVPN is -configured to use. -.sp -On bob: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -route add \-net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2 -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -On alice: -.INDENT 0.0 -.INDENT 3.5 -.sp -.nf -.ft C -route add \-net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1 -.ft P -.fi -.UNINDENT -.UNINDENT -.sp -Now any machine on the \fI10.0.0.0/24\fP subnet can access any machine on the -\fI10.0.1.0/24\fP subnet over the secure tunnel (or vice versa). -.sp -In a production environment, you could put the route command(s) in a -script and execute with the \fB\-\-up\fP option. .SH FAQ .sp \fI\%https://community.openvpn.net/openvpn/wiki/FAQ\fP @@ -6998,6 +6679,7 @@ repository. Report all bugs to the OpenVPN team \fI\%info@openvpn.net\fP .SH SEE ALSO .sp +\fBopenvpn\-examples\fP(5), \fBdhcpcd\fP(8), \fBifconfig\fP(8), \fBopenssl\fP(1), diff --git a/doc/openvpn.8.html b/doc/openvpn.8.html index 6ca509d..1c0c65e 100644 --- a/doc/openvpn.8.html +++ b/doc/openvpn.8.html @@ -3,7 +3,7 @@ - + openvpn