diff --git a/doc/openvpn.8.rst b/doc/openvpn.8.rst new file mode 100644 index 00000000..4627a7d3 --- /dev/null +++ b/doc/openvpn.8.rst @@ -0,0 +1,5882 @@ +========= + 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. + +--help + + Show options. + +--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 + + +Tunnel Options: +--------------- + +--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. + +--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. + +--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-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". + +```` + 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 + ```` and ````. + + 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. + +--proto-force p + When iterating through connection profiles, only consider profiles using + protocol ``p`` (:code:`tcp` \| :code:`udp`). + +--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. + +--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. + +--connect-retry args + 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 one would try each + entry exactly once. A successful connection resets the counter. + (default *unlimited*). + +--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. + +--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. + +--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. + +--ipchange cmd + Run command ``cmd`` when our remote ip-address is initially + authenticated or changes. + + ``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 ``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 reestablish a connection with its most recently authenticated + peer on its new IP address. + +--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. + +--lport port + Set local TCP/UDP port number or name. Cannot be used together with + ``--nobind`` option. + +--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. + +--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. + +--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. + +--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). + +--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`. + +--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. This mode is functionally equivalent to the + ``--ifconfig-pool-linear`` directive which is available in OpenVPN 2.0, + is deprecated and will be removed in OpenVPN 2.5 + + :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. + + This option exists in OpenVPN 2.1 or higher. + + *Note:* Using ``--topology subnet`` changes the interpretation of the + arguments of ``--ifconfig`` to mean "address netmask", no longer "local + remote". + +--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. + +--lladdr address + Specify the link layer address, more commonly known as the MAC address. + Only applied to TAP devices. + +--iproute cmd + Set alternate command to execute instead of default ``iproute2`` command. + May be used in order to execute OpenVPN in unprivileged environment. + +--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-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. + +--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-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-metric m + Specify a default metric ``m`` for use with ``--route``. + +--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-up cmd + Run command ``cmd`` after routes are added, subject to ``--route-delay``. + + ``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. + +--route-pre-down cmd + Run command ``cmd`` before routes are removed upon disconnection. + + ``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. + +--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. + +--allow-pull-fqdn + Allow client to pull DNS names from server (rather than being limited to + IP address) for ``--ifconfig``, ``--route``, and ``--route-gateway``. + +--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. + +--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. + +--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.* + +--redirect-private flags + Like ``--redirect-gateway``, but omit actually changing the default gateway. + Useful when pushing private subnets. + +--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 + +--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 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 ``--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. + +--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. + +--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. + +--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 + +--sndbuf size + Set the TCP/UDP socket send buffer size. Defaults to operation system + default. + +--rcvbuf size + Set the TCP/UDP socket receive buffer size. Defaults to operation system + default. + +--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. + +--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. + +--txqueuelen n + *(Linux only)* Set the TX queue length on the TUN/TAP interface. + Currently defaults to 100. + +--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. + +--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. + +--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. + +--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 + +--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. + +--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. + +--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. + +--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. + +--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. + +--up cmd + Run command ``cmd`` after successful TUN/TAP device open (pre ``--user`` + UID change). + + ``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 ``--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. + +--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. + +--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. + +--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. + +--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. + +--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. + +--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. + +--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). + +--group group + Similar to the ``--user`` option, this option changes the group ID of + the OpenVPN process to ``group`` after initialization. + +--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. + +--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. + +--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. + +--syslog progname + Direct log output to system logger, but do not become a daemon. See + ``--daemon`` directive above for description of ``progname`` parameter. + +--errors-to-stderr + Output errors to stderr instead of stdout unless log output is + redirected by one of the ``--log`` options. + +--passtos + Set the TOS field of the tunnel packet to what the payload's TOS is. + +--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/ + +--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. + +--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. + +--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. + +--writepid file + Write OpenVPN's main process ID to ``file``. + +--nice n + Change process priority after initialization (``n`` greater than 0 is + lower priority, ``n`` less than zero is higher priority). + +--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. + +--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). + +--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. + +--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. + +--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). + +--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. + +--mute n + Log at most ``n`` consecutive messages in the same category. This is + useful to limit repetitive logging of similar message types. + +--compress algorithm + Enable a compression algorithm. + + The ``algorithm`` parameter may be :code:`lzo`, :code:`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 :code:`lzo` (which + is identical to the older option ``--comp-lzo yes``). + + If the ``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. + + ***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. + +--comp-lzo mode + *DEPRECATED* This option will be removed in a future OpenVPN release. + Use the newer ``--compress`` instead. + + 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 + 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. + +--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-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-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-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-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-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-log-cache n + Cache the most recent ``n`` lines of log file history for usage by the + management channel. + +--management-up-down + Report tunnel up/down events to management interface. + +--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-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-client-group g + When the management interface is listening on a unix domain socket, only + allow connections from group ``g``. + +--plugin args + Loads a given plug-in module. The ``module-name`` need 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. + +--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`. + + +Server Mode +----------- + +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. + +--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 + +--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-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. + +--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-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=2` + If the client supports peer-id floating mechanism + + :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 pushes the list of configured ciphers with the + ``--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_` + +--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. + +--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-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-pool-linear + **DEPRECATED** This option will be removed in OpenVPN 2.5 + + Modifies the ``--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 ``--topology + p2p`` which is functionally equivalent. + +--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). + +--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. + +--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. + +--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. + +--client-connect cmd + Run command ``cmd`` on client connection. + + ``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 ``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. + +--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``). + +--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``. + +--ccd-exclusive + Require, as a condition of authentication, that a connecting client has + a ``--client-config-dir`` file. + +--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 to dynamically generate client-specific + configuration files. + + * :code:`OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY` plugin hook to return + success/failure via ``auth_control_file`` when using deferred auth + method + + * :code:`OPENVPN_PLUGIN_ENABLE_PF` plugin hook to pass filtering rules + via ``pf_file`` + +--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`). + +--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. + +--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" + +--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. + +--stale-routes-check args + Remove routes haven't had activity for ``n`` seconds (i.e. the ageing + time). This check is ran 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`` + +--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``. + +--learn-address cmd + Run command ``cmd`` to validate client virtual addresses or routes. + + ``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 ``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. + +--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 cmd method + + OpenVPN will run command ``cmd`` to validate the username/password + provided by the client. + + ``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 ``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. + +--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 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 a 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 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. + + 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 check the validity of the account and do other checks. + + In this mode the environment will have a session\_id variable that hold + the session id from auth-gen-token. Also a environment variable + session\_state is present. This variable tells 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 send 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 hold 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 + valid after restarting a server or if client should be able to roam + between multiple OpenVPN server with their auth-token. + +--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 ``--disable-occ`` NOT be used. + +--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`` 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. + +--client-cert-not-required + **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. + + **Please note:** This is replaced by ``--verify-client-cert`` which + allows for more flexibility. The option ``--verify-client-cert none`` is + functionally equivalent to ``--client-cert-not-required`` + +--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 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 ``--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 topresent 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. + +--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. + +--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. + +--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. + + The 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". + + +Client Mode +----------- + +Use client mode when connecting to an OpenVPN server which has +``--server``, ``--server-bridge``, or ``--mode server`` in its +configuration. + +--client + A helper directive designed to simplify the configuration of OpenVPN's + client mode. This directive is equivalent to: + :: + + pull + tls-client + +--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`. + +--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: + + :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. + +--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. + +--server-poll-timeout n + When connecting to a remote server do not wait for more than **n** + seconds waiting for a response before trying the next server. The + default value is 120s. This timeout includes proxy and TCP connect + timeouts. + +--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. + +--allow-recursive-routing + When this option is set, OpenVPN will not drop incoming tun packets with + same destination as host. + + +Data Channel Encryption Options +------------------------------- + +These options are meaningful for both Static & TLS-negotiated key modes +(must be compatible between peers). + +--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. + +--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). + +--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, 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 + 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 ``--ncp-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. + +--ncp-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 both peers support and do not disable NCP, the negotiated cipher will + override the cipher specified by ``--cipher``. + + 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 ``--ncp-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 ``--ncp-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 a 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. + +--ncp-disable + Disable "Negotiable Crypto Parameters". This completely disables cipher + negotiation. + +--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. + +--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. + +--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. + +--no-replay + **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 *sliding window* algorithm used + by IPSec. + +--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. + +--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. + +--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``. + +--no-iv + **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. + +--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. + +--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. + + +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 + +--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-client + Enable TLS and assume client role during TLS handshake. + +--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. + + Similarly 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. + +--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. + +--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`). + +--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. + +--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). + +--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`. + +--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. + +--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`. + +--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-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 a 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. + +--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. + +--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. + +--key-method m + **DEPRECATED** This option will be removed in OpenVPN 2.5 + + Use data channel key negotiation method ``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 :code:`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 :code:`1` is **deprecated in OpenVPN 2.4**, + and **will be removed in OpenVPN 2.5**. + + In method :code:`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 :code:`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 + ``--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, + ``--key-method`` determines the derivation of the tunnel session keys. + + +*WARNING:* ``--tls-ciphers`` and ``--tls-ciphersuites`` + 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-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. + +--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. + +--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. + +--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. + +--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. + +--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. + +--tls-exit + Exit on TLS negotiation failure. + +--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-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. + +--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. + +--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. + +--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 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 ``--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`` + +--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 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. + +--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. + +--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. + +--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. + +--ns-cert-type args + **DEPRECATED** This option will be removed in OpenVPN 2.5. Use the more + modern equivalent ``--remote-cert-tls`` instead. This option will be + removed in OpenVPN 2.5. + + Valid syntax: + :: + + ns-cert-type client | server + + Require that peer certificate was signed with an explicit ``nsCertType`` + designation of :code:`client` or :code:`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 ``nsCertType`` field set to "server". + + If the server certificate's nsCertType field is set to :code:`server`, + then the clients can verify this with :code:`--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 ``--ns-cert-type``, ``--verify-x509-name`` or ``--tls-verify``. + +--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-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-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``. + +--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. + + +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-curves + (Standalone) Show all available elliptic curves to use with the + ``--ecdh-curve`` option. + + +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 tp 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 + access to this file will be to generate auth tokens that the OpenVPN + server will accept as valid. + + +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. + +--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. + +--dev name + Designate the TUN/TAP device name to use + + 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. + +--user user + Optional user to be owner of this tunnel. + +--group group + Optional group to be owner of this tunnel. + + +Windows-Specific Options +------------------------- + +--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 have changed behaviour in 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. + +--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. + +--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. + +--dhcp-option args + Set extended TAP-Win32 TCP/IP properties, must be used with + :code:`--ip-win32 dynamic` or :code:`--ip-win32 adaptive`. + + Valid syntax: + :: + + dhcp-options type [parm] + + 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. + + :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. + + Note that if ``--dhcp-option`` is pushed via ``--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}". + +--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. + +--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. + +--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. + +--windows-driver drv + Specifies which tun driver to use. Values are :code:`tap-windows6` + (default) and :code:`wintun`. This is Windows-only option. + :code:`wintun`" requires ``--dev tun`` and the OpenVPN process to run + elevated, or be invoked using the Interactive Service. + +--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. + +--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. + +--register-dns + Run :code:`ipconfig /flushdns` and :code:`ipconfig /registerdns` on + connection initiation. This is known to kick Windows into recognizing + pushed DNS servers. + +--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. + +--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. + +--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. + +--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). + +--show-net + (Standalone) Show OpenVPN's view of the system routing table and network + adapter list. + + +PKCS#11 Standalone Options +-------------------------- + +--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. + + +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. + + +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 **--topology** , which has no effect on IPv6). + +--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. + +--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-ipv6-gateway gw + Specify a default gateway ``gw`` for use with ``--route-ipv6``. + +--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 + + This is only accepted if ``--mode server`` or ``--server`` is set. + Pushing of the ``--tun-ipv6`` directive is done for older clients which + require an explicit ``--tun-ipv6`` in their configuration. + +--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-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 + +--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 + + + +SCRIPTING AND ENVIRONMENTAL VARIABLES +===================================== + +OpenVPN exports a series of environmental variables for use by +user-defined scripts. + + +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. + + +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. + +: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:`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 + + + +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` + + + +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`` above 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. + + + +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: :code:`mknod /dev/net/tun c 10 200` + +Load driver: :code:`modprobe tun**` + + + +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. + + +TUN/TAP Setup: +-------------- + +If you are using Linux 2.4 or higher, make the tun device node and load +the tun module: + +:: + + mknod /dev/net/tun c 10 200 + modprobe tun + +If you installed from RPM, the ``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 +https://openvpn.net/community-resources/the-standard-install-file-included-in-the-source-distribution/ +for more information. + + +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 ``--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). + +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: + +:code:`iptables -A INPUT -i tun+ -j ACCEPT` + +See the firewalls section below for more information on configuring +firewalls for use with OpenVPN. + + +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 + +and enable TUN packet forwarding through the firewall: +:: + + iptables -A FORWARD -i tun+ -j ACCEPT + +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. + + +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+: +:: + + iptables -A INPUT -p udp -s 1.2.3.4 --dport 1194 -j ACCEPT + +This will allow incoming packets on UDP port :code:`1194` (OpenVPN's +default UDP port) from an OpenVPN peer at :code:`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: +:: + + iptables -A INPUT -p udp --dport 1194 -j ACCEPT + +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 ``--ping n``, OpenVPN will be guaranteed to send a packet to its +peer at least once every ``n`` seconds. If ``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: +:: + + iptables -A INPUT -i tun+ -j ACCEPT + +to allow input packets from tun devices, +:: + + iptables -A FORWARD -i tun+ -j ACCEPT + +to allow input packets from tun devices to be forwarded to other hosts +on the local network, +:: + + iptables -A INPUT -i tap+ -j ACCEPT + +to allow input packets from tap devices, and +:: + + iptables -A FORWARD -i tap+ -j ACCEPT + +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.   + + + +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