.\"  OpenVPN -- An application to securely tunnel IP networks
 .\"             over a single TCP/UDP port, with support for SSL/TLS-based
 .\"             session authentication and key exchange,
 .\"             packet encryption, packet authentication, and
 .\"             packet compression.
 .\"

 .\"  Copyright (C) 2002-2009 OpenVPN Technologies, Inc. <sales@openvpn.net>

 .\"
 .\"  This program is free software; you can redistribute it and/or modify
 .\"  it under the terms of the GNU General Public License version 2
 .\"  as published by the Free Software Foundation.
 .\"
 .\"  This program is distributed in the hope that it will be useful,
 .\"  but WITHOUT ANY WARRANTY; without even the implied warranty of
 .\"  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 .\"  GNU General Public License for more details.
 .\"
 .\"  You should have received a copy of the GNU General Public License
 .\"  along with this program (see the file COPYING included with this
 .\"  distribution); if not, write to the Free Software Foundation, Inc.,
 .\"  59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 .\"
 .\" Manual page for openvpn

 .\

 .\" SH section heading
 .\" SS subsection heading
 .\" LP paragraph
 .\" IP indented paragraph
 .\" TP hanging label

 .\
 .\" .nf -- no formatting
 .\" .fi -- resume formatting
 .\" .ft 3 -- boldface
 .\" .ft -- normal face
 .\" .in +|-{n} -- indent
 .\"

 .TH openvpn 8 "17 November 2008"

 .\"*********************************************************
 .SH NAME
 openvpn \- secure IP tunnel daemon.
 .\"*********************************************************
 .SH SYNOPSIS

 .ft 3
 openvpn [ options ... ]
 .ft

 .\"*********************************************************
 .SH INTRODUCTION
 .LP
 OpenVPN is an open source VPN daemon by James Yonan.
 Because OpenVPN tries to
 be a universal VPN tool offering a great deal of flexibility,
 there are a lot of options on this manual page.
 If you're new to OpenVPN, you might want to skip ahead to the
 examples section where you will see how to construct simple
 VPNs on the command line without even needing a configuration file.
 
 Also note that there's more documentation and examples on
 the OpenVPN web site:
 .I http://openvpn.net/
 
 And if you would like to see a shorter version of this manual,
 see the openvpn usage message which can be obtained by
 running
 .B openvpn
 without any parameters.
 .\"*********************************************************
 .SH DESCRIPTION
 .LP
 OpenVPN is a robust and highly flexible VPN daemon.
 OpenVPN supports SSL/TLS security, ethernet bridging,
 TCP or UDP tunnel transport through proxies or NAT,
 support for dynamic IP addresses and DHCP,
 scalability to hundreds or thousands of users,
 and portability to most major OS platforms.
 
 OpenVPN is tightly bound to the OpenSSL library, and derives much
 of its crypto capabilities from it.
 
 OpenVPN supports
 conventional encryption
 using a pre-shared secret key
 .B (Static Key mode)
 or
 public key security
 .B (SSL/TLS mode)
 using client & server certificates.
 OpenVPN also
 supports non-encrypted TCP/UDP tunnels.  
 
 OpenVPN is designed to work with the
 .B TUN/TAP
 virtual networking interface that exists on most platforms.
 
 Overall, OpenVPN aims to offer many of the key features of IPSec but
 with a relatively lightweight footprint.
 .\"*********************************************************
 .SH OPTIONS
 OpenVPN allows any option to be placed either on the command line
 or in a configuration file.  Though all command line options are preceded
 by a double-leading-dash ("--"), this prefix can be removed when
 an option is placed in a configuration file.
 .\"*********************************************************
 .TP
 .B --help
 Show options.
 .\"*********************************************************
 .TP
 .B --config file
 Load additional config options from
 .B file
 where each line corresponds to one command line option,
 but with the leading '--' removed.
 
 If
 .B --config file
 is the only option to the openvpn command,
 the
 .B --config
 can be removed, and the command can be given as
 .B openvpn file
 
 Note that
 configuration files can be nested to a reasonable depth.
 

 Double quotation or single quotation characters ("", '')
 can be used to enclose single parameters containing whitespace,

 and "#" or ";" characters in the first column
 can be used to denote comments.
 
 Note that OpenVPN 2.0 and higher performs backslash-based shell

 escaping for characters not in single quotations,
 so the following mappings should be observed:

 
 .nf

 .ft 3
 .in +4

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

 .in -4

 .ft
 .fi
 
 For example on Windows, use double backslashes to
 represent pathnames:
 
 .nf

 .ft 3
 .in +4

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

 .in -4

 .ft
 .fi
 
 For examples of configuration files,
 see
 .I http://openvpn.net/examples.html
 
 Here is an example configuration file:

 .nf

 .ft 3
 .in +4

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

 .in -4

 .ft
 .fi
 .\"*********************************************************
 .SS Tunnel Options:
 .TP
 .B --mode m
 Set OpenVPN major mode.  By default, OpenVPN runs in
 point-to-point mode ("p2p").  OpenVPN 2.0 introduces
 a new mode ("server") which implements a multi-client
 server capability.
 .\"*********************************************************
 .TP
 .B --local host

 Local host name or IP address for bind.

 If specified, OpenVPN will bind to this address only.
 If unspecified, OpenVPN will bind to all interfaces.
 .\"*********************************************************
 .TP

 .B --remote host [port] [proto]

 Remote host name or IP address.  On the client, multiple

 .B --remote
 options may be specified for redundancy, each referring

 to a different OpenVPN server.  Specifying multiple
 .B --remote
 options for this purpose is a special case of the more
 general connection-profile feature.  See the
 .B <connection>
 documentation below.

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

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

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

 Note that since UDP is connectionless, connection failure

 is defined by the
 .B --ping
 and
 .B --ping-restart
 options.
 

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

 If
 .B --remote
 is unspecified, OpenVPN will listen
 for packets from any IP address, but will not act on those packets unless
 they pass all authentication tests.  This requirement for authentication
 is binding on all potential peers, even those from known and supposedly
 trusted IP addresses (it is very easy to forge a source IP address on
 a UDP packet).
 
 When used in TCP mode, 
 .B --remote
 will act as a filter, rejecting connections from any host which does
 not match
 .B host.
 
 If
 .B host
 is a DNS name which resolves to multiple IP addresses,
 one will be randomly
 chosen, providing a sort of basic load-balancing and
 failover capability.
 .\"*********************************************************
 .TP

 .B <connection>
 Define a client connection
 profile.  Client connection profiles are groups of OpenVPN options that
 describe how to connect to a given OpenVPN server.  Client connection
 profiles are specified within an OpenVPN configuration file, and
 each profile is bracketed by
 .B <connection>
 and
 .B </connection>.
 
 An OpenVPN client will try each connection profile sequentially
 until it achieves a successful connection.  
 
 .B --remote-random
 can be used to initially "scramble" the connection
 list.
 
 Here is an example of connection profile usage:
 
 .nf

 .ft 3
 .in +4

 client
 dev tun
 
 <connection>
 remote 198.19.34.56 1194 udp
 </connection>
 
 <connection>
 remote 198.19.34.56 443 tcp
 </connection>
 
 <connection>
 remote 198.19.34.56 443 tcp
 http-proxy 192.168.0.8 8080
 http-proxy-retry
 </connection>
 
 <connection>
 remote 198.19.36.99 443 tcp
 http-proxy 192.168.0.8 8080
 http-proxy-retry
 </connection>
 
 persist-key
 persist-tun
 pkcs12 client.p12
 ns-cert-type server
 verb 3

 .in -4

 .ft
 .fi
 
 First we try to connect to a server at 198.19.34.56:1194 using UDP.
 If that fails, we then try to connect to 198.19.34.56:443 using TCP.
 If that also fails, then try connecting through an HTTP proxy at 
 192.168.0.8:8080 to 198.19.34.56:443 using TCP.  Finally, try to
 connect through the same proxy to a server at 198.19.36.99:443
 using TCP.
 
 The following OpenVPN options may be used inside of
 a
 .B <connection>
 block:
 
 .B bind,
 .B connect-retry,
 .B connect-retry-max,
 .B connect-timeout,
 .B float,
 .B http-proxy,
 .B http-proxy-option,
 .B http-proxy-retry,
 .B http-proxy-timeout,
 .B local,
 .B lport,
 .B nobind,
 .B port,
 .B proto,
 .B remote,
 .B rport,
 .B socks-proxy, and
 .B socks-proxy-retry.
 
 A defaulting mechanism exists for specifying options to apply to
 all
 .B <connection>
 profiles.  If any of the above options (with the exception of
 .B remote
 ) appear outside of a
 .B <connection>
 block, but in a configuration file which has one or more
 .B <connection>
 blocks, the option setting will be used as a default for
 .B <connection>
 blocks which follow it in the configuration file.
 
 For example, suppose the
 .B nobind
 option were placed in the sample configuration file above, near
 the top of the file, before the first
 .B <connection>
 block.  The effect would be as if
 .B nobind
 were declared in all
 .B <connection>
 blocks below it.
 
 .\"*********************************************************
 .TP

 .B --remote-random
 When multiple
 .B --remote

 address/ports are specified, or if connection profiles are being
 used, initially randomize the order of the list

 as a kind of basic load-balancing measure.
 .\"*********************************************************
 .TP
 .B --proto p
 Use protocol
 .B p
 for communicating with remote host.
 .B p
 can be
 .B udp,
 .B tcp-client,
 or
 .B tcp-server.
 
 The default protocol is
 .B udp
 when
 .B --proto
 is not specified.
 
 For UDP operation,
 .B --proto udp
 should be specified on both peers.
 
 For TCP operation, one peer must use
 .B --proto tcp-server
 and the other must use
 .B --proto tcp-client.
 A peer started with
 .B tcp-server
 will wait indefinitely for an incoming connection.  A peer
 started with
 .B tcp-client
 will attempt to connect, and if that fails, will sleep for 5
 seconds (adjustable via the
 .B --connect-retry

 option) and try again infinite or up to N retries (adjustable via the
 .B --connect-retry-max
 option).  Both TCP client and server will simulate

 a SIGUSR1 restart signal if either side resets the connection.
 
 OpenVPN is designed to operate optimally over UDP, but TCP capability is provided
 for situations where UDP cannot be used.
 In comparison with UDP, TCP will usually be
 somewhat less efficient and less robust when used over unreliable or congested
 networks.
 
 This article outlines some of problems with tunneling IP over TCP:
 
 .I http://sites.inka.de/sites/bigred/devel/tcp-tcp.html
 
 There are certain cases, however, where using TCP may be advantageous from
 a security and robustness perspective, such as tunneling non-IP or
 application-level UDP protocols, or tunneling protocols which don't
 possess a built-in reliability layer.
 .\"*********************************************************
 .TP
 .B --connect-retry n
 For
 .B --proto tcp-client,
 take
 .B n
 as the
 number of seconds to wait
 between connection retries (default=5).
 .\"*********************************************************
 .TP

 .B --connect-retry-max n
 For
 .B --proto tcp-client,
 take
 .B n
 as the
 number of retries of connection attempt (default=infinite).
 .\"*********************************************************
 .TP

 .B --auto-proxy
 Try to sense HTTP or SOCKS proxy settings automatically.
 If no settings are present, a direct connection will be attempted.
 If both HTTP and SOCKS settings are present, HTTP will be preferred.
 If the HTTP proxy server requires a password, it will be queried from
 stdin or the management interface.  If the underlying OS doesn't support an API for
 returning proxy settings, a direct connection will be attempted.
 Currently, only Windows clients support this option via the
 InternetQueryOption API.
 This option exists in OpenVPN 2.1 or higher.
 .\"*********************************************************
 .TP
 .B --http-proxy server port [authfile|'auto'] [auth-method]

 Connect to remote host through an HTTP proxy at address
 .B server
 and port
 .B port.
 If HTTP Proxy-Authenticate is required,
 .B authfile
 is a file containing a username and password on 2 lines, or
 "stdin" to prompt from console.
 
 .B auth-method

 should be one of "none", "basic", or "ntlm".
 
 The
 .B auto
 flag causes OpenVPN to automatically determine the
 .B auth-method
 and query stdin or the management interface for
 username/password credentials, if required.  This flag
 exists on OpenVPN 2.1 or higher.

 .\"*********************************************************
 .TP
 .B --http-proxy-retry
 Retry indefinitely on HTTP proxy errors.  If an HTTP proxy error
 occurs, simulate a SIGUSR1 reset.
 .\"*********************************************************
 .TP
 .B --http-proxy-timeout n
 Set proxy timeout to
 .B n
 seconds, default=5.
 .\"*********************************************************
 .TP
 .B --http-proxy-option type [parm]
 Set extended HTTP proxy options.
 Repeat to set multiple options.
 
 .B VERSION version --
 Set HTTP version number to
 .B version
 (default=1.0).
 
 .B AGENT user-agent --
 Set HTTP "User-Agent" string to
 .B user-agent.
 .\"*********************************************************
 .TP
 .B --socks-proxy server [port]
 Connect to remote host through a Socks5 proxy at address
 .B server
 and port
 .B port
 (default=1080).
 .\"*********************************************************
 .TP
 .B --socks-proxy-retry
 Retry indefinitely on Socks proxy errors.  If a Socks proxy error
 occurs, simulate a SIGUSR1 reset.
 .\"*********************************************************
 .TP
 .B --resolv-retry n
 If hostname resolve fails for
 .B --remote,
 retry resolve for
 .B n
 seconds before failing.
 
 Set
 .B n
 to "infinite" to retry indefinitely.
 
 By default,
 .B --resolv-retry infinite
 is enabled.  You can disable by setting n=0.
 .\"*********************************************************
 .TP
 .B --float
 Allow remote peer to change its IP address and/or port number, such as due to
 DHCP (this is the default if
 .B --remote
 is not used).
 .B --float
 when specified with
 .B --remote
 allows an OpenVPN session to initially connect to a peer
 at a known address, however if packets arrive from a new
 address and pass all authentication tests, the new address
 will take control of the session.  This is useful when
 you are connecting to a peer which holds a dynamic address
 such as a dial-in user or DHCP client.
 
 Essentially,
 .B --float
 tells OpenVPN to accept authenticated packets
 from any address, not only the address which was specified in the
 .B --remote
 option.
 .\"*********************************************************
 .TP
 .B --ipchange cmd
 Execute shell command
 .B cmd
 when our remote ip-address is initially authenticated or
 changes.
 
 Execute as:
 
 .B cmd ip_address port_number
 
 Don't use
 .B --ipchange
 in
 .B --mode server
 mode.  Use a
 .B --client-connect
 script instead.
 
 See the "Environmental Variables" section below for
 additional parameters passed as environmental variables.
 
 Note that
 .B cmd
 can be a shell command with multiple arguments, in which
 case all OpenVPN-generated arguments will be appended
 to
 .B cmd
 to build a command line which will be passed to the script.
 
 If you are running in a dynamic IP address environment where
 the IP addresses of either peer could change without notice,
 you can use this script, for example, to edit the
 .I /etc/hosts
 file with the current address of the peer.  The script will
 be run every time the remote peer changes its IP address.
 
 Similarly if
 .I our
 IP address changes due to DHCP, we should configure
 our IP address change script (see man page for
 .BR dhcpcd (8)
 ) to deliver a
 .B SIGHUP
 or
 .B SIGUSR1
 signal to OpenVPN.  OpenVPN will then
 reestablish a connection with its most recently authenticated
 peer on its new IP address.
 .\"*********************************************************
 .TP
 .B --port port
 TCP/UDP port number for both local and remote.  The current
 default of 1194 represents the official IANA port number
 assignment for OpenVPN and has been used since version 2.0-beta17.
 Previous versions used port 5000 as the default.
 .\"*********************************************************
 .TP
 .B --lport port

 TCP/UDP port number for bind.

 .\"*********************************************************
 .TP
 .B --rport port
 TCP/UDP port number for remote.
 .\"*********************************************************
 .TP

 .B --bind
 Bind to local address and port. This is the default unless any of 
 .B --proto tcp-client
 ,
 .B --http-proxy
 or
 .B --socks-proxy
 are used.
 .\"*********************************************************
 .TP

 .B --nobind
 Do not bind to local address and port.  The IP stack will allocate
 a dynamic port for returning packets.  Since the value of the dynamic port
 could not be known in advance by a peer, this option is only suitable for
 peers which will be initiating connections by using the
 .B --remote
 option.
 .\"*********************************************************
 .TP
 .B --dev tunX | tapX | null
 TUN/TAP virtual network device (
 .B X
 can be omitted for a dynamic device.)
 
 See examples section below
 for an example on setting up a TUN device.
 
 You must use either tun devices on both ends of the connection
 or tap devices on both ends.  You cannot mix them, as they

 represent different underlying network layers.

 
 .B tun

 devices encapsulate IPv4 or IPv6 (OSI Layer 3) while

 .B tap

 devices encapsulate Ethernet 802.3 (OSI Layer 2).

 .\"*********************************************************
 .TP
 .B --dev-type device-type
 Which device type are we using?
 .B device-type
 should be
 .B tun

 (OSI Layer 3)

 or

 .B tap
 (OSI Layer 2).

 Use this option only if the TUN/TAP device used with
 .B --dev
 does not begin with
 .B tun
 or
 .B tap.
 .\"*********************************************************
 .TP

 .B --topology mode
 Configure virtual addressing topology when running in
 .B --dev tun
 mode.  This directive has no meaning in
 .B --dev tap
 mode, which always uses a
 .B subnet
 topology.
 
 If you set this directive on the server, the
 .B --server
 and
 .B --server-bridge
 directives will automatically push your chosen topology setting to clients
 as well.  This directive can also be manually pushed to clients.  Like the
 .B --dev
 directive, this directive must always be compatible between client and server.
 
 .B mode
 can be one of:
 
 .B net30 --
 Use a point-to-point topology, by allocating one /30 subnet per client.
 This is designed to allow point-to-point semantics when some
 or all of the connecting clients might be Windows systems.  This is the
 default on OpenVPN 2.0.
 
 .B p2p --
 Use a point-to-point topology where the remote endpoint of the client's
 tun interface always points to the local endpoint of the server's tun interface.
 This mode allocates a single IP address per connecting client.
 Only use
 when none of the connecting clients are Windows systems.  This mode
 is functionally equivalent to the
 .B --ifconfig-pool-linear
 directive which is available in OpenVPN 2.0 and is now deprecated.
 
 .B subnet --
 Use a subnet rather than a point-to-point topology by
 configuring the tun interface with a local IP address and subnet mask,
 similar to the topology used in
 .B --dev tap
 and ethernet bridging mode.
 This mode allocates a single IP address per connecting client and works on
 Windows as well.  Only available when server and clients are OpenVPN 2.1 or
 higher, or OpenVPN 2.0.x which has been manually patched with the
 .B --topology
 directive code.  When used on Windows, requires version 8.2 or higher
 of the TAP-Win32 driver.  When used on *nix, requires that the tun
 driver supports an
 .BR ifconfig (8)
 command which sets a subnet instead of a remote endpoint IP address.

 
 This option exists in OpenVPN 2.1 or higher.

 .\"*********************************************************
 .TP

 .B --tun-ipv6
 Build a tun link capable of forwarding IPv6 traffic.
 Should be used in conjunction with
 .B --dev tun
 or
 .B --dev tunX.
 A warning will be displayed
 if no specific IPv6 TUN support for your OS has been compiled into OpenVPN.
 .\"*********************************************************
 .TP
 .B --dev-node node
 Explicitly set the device node rather than using
 /dev/net/tun, /dev/tun, /dev/tap, etc.  If OpenVPN
 cannot figure out whether
 .B node
 is a TUN or TAP device based on the name, you should
 also specify
 .B --dev-type tun
 or
 .B --dev-type tap.
 
 On Windows systems, select the TAP-Win32 adapter which
 is named
 .B node
 in the Network Connections Control Panel or the
 raw GUID of the adapter enclosed by braces.
 The
 .B --show-adapters
 option under Windows can also be used
 to enumerate all available TAP-Win32
 adapters and will show both the network
 connections control panel name and the GUID for
 each TAP-Win32 adapter.

 .TP
 .B --lladdr address
 Specify the link layer address, more commonly known as the MAC address.
 Only applied to TAP devices.

 .\"*********************************************************
 .TP

 .B --iproute cmd
 Set alternate command to execute instead of default iproute2 command.
 May be used in order to execute OpenVPN in unprivileged environment.
 .\"*********************************************************
 .TP

 .B --ifconfig l rn
 Set TUN/TAP adapter parameters. 
 .B l
 is the IP address of the local VPN endpoint.
 For TUN devices,
 .B rn
 is the IP address of the remote VPN endpoint.
 For TAP devices,
 .B rn
 is the subnet mask of the virtual ethernet segment
 which is being created or connected to.
 
 For TUN devices, which facilitate virtual
 point-to-point IP connections,
 the proper usage of
 .B --ifconfig
 is to use two private IP addresses
 which are not a member of any
 existing subnet which is in use.
 The IP addresses may be consecutive
 and should have their order reversed
 on the remote peer.  After the VPN
 is established, by pinging
 .B rn,
 you will be pinging across the VPN.
 
 For TAP devices, which provide
 the ability to create virtual
 ethernet segments,
 .B --ifconfig
 is used to set an IP address and
 subnet mask just as a physical
 ethernet adapter would be
 similarly configured.  If you are
 attempting to connect to a remote
 ethernet bridge, the IP address
 and subnet should be set to values
 which would be valid on the
 the bridged ethernet segment (note
 also that DHCP can be used for the
 same purpose).
 
 This option, while primarily a proxy for the
 .BR ifconfig (8)
 command, is designed to simplify TUN/TAP
 tunnel configuration by providing a
 standard interface to the different
 ifconfig implementations on different
 platforms.
 
 .B --ifconfig
 parameters which are IP addresses can
 also be specified as a DNS or /etc/hosts
 file resolvable name.
 
 For TAP devices,
 .B --ifconfig
 should not be used if the TAP interface will be
 getting an IP address lease from a DHCP
 server.
 .\"*********************************************************
 .TP
 .B --ifconfig-noexec
 Don't actually execute ifconfig/netsh commands, instead
 pass
 .B --ifconfig
 parameters to scripts using environmental variables.
 .\"*********************************************************
 .TP
 .B --ifconfig-nowarn
 Don't output an options consistency check warning
 if the
 .B --ifconfig
 option on this side of the
 connection doesn't match the remote side.  This is useful
 when you want to retain the overall benefits of the
 options consistency check (also see
 .B --disable-occ
 option) while only disabling the ifconfig component of
 the check.
 
 For example,
 if you have a configuration where the local host uses
 .B --ifconfig
 but the remote host does not, use
 .B --ifconfig-nowarn
 on the local host.
 
 This option will also silence warnings about potential
 address conflicts which occasionally annoy more experienced
 users by triggering "false positive" warnings.
 .\"*********************************************************
 .TP
 .B --route network/IP [netmask] [gateway] [metric]
 Add route to routing table after connection is established.
 Multiple routes can be specified.  Routes will be
 automatically torn down in reverse order prior to
 TUN/TAP device close.
 
 This option is intended as
 a convenience proxy for the
 .BR route (8)
 shell command,
 while at the same time providing portable semantics
 across OpenVPN's platform space.
 
 .B netmask
 default -- 255.255.255.255
 
 .B gateway
 default -- taken from
 .B --route-gateway
 or the second parameter to
 .B --ifconfig
 when
 .B --dev tun
 is specified.
 

 .B metric
 default -- taken from
 .B --route-metric
 otherwise 0.
 

 The default can be specified by leaving an option blank or setting
 it to "default".
 
 The
 .B network
 and
 .B gateway
 parameters can
 also be specified as a DNS or /etc/hosts
 file resolvable name, or as one of three special keywords:
 
 .B vpn_gateway
 -- The remote VPN endpoint address
 (derived either from
 .B --route-gateway
 or the second parameter to
 .B --ifconfig
 when
 .B --dev tun
 is specified).
 
 .B net_gateway
 -- The pre-existing IP default gateway, read from the routing
 table (not supported on all OSes).
 
 .B remote_host
 -- The
 .B --remote
 address if OpenVPN is being run in client mode, and is undefined in server mode.
 .\"*********************************************************
 .TP

 .B --route-gateway gw|'dhcp'

 Specify a default gateway
 .B gw
 for use with
 .B --route.

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

 .TP
 .B --route-metric m
 Specify a default metric
 .B m
 for use with
 .B --route.

 .\"*********************************************************
 .TP
 .B --route-delay [n] [w]
 Delay
 .B n
 seconds (default=0) after connection
 establishment, before adding routes. If
 .B n
 is 0, routes will be added immediately upon connection
 establishment.  If
 .B --route-delay
 is omitted, routes will be added immediately after TUN/TAP device
 open and
 .B --up
 script execution, before any
 .B --user
 or 
 .B --group
 privilege downgrade (or
 .B --chroot
 execution.)
 
 This option is designed to be useful in scenarios where DHCP is
 used to set
 tap adapter addresses.  The delay will give the DHCP handshake
 time to complete before routes are added.
 
 On Windows,
 .B --route-delay
 tries to be more intelligent by waiting
 .B w
 seconds (w=30 by default)
 for the TAP-Win32 adapter to come up before adding routes.
 .\"*********************************************************
 .TP
 .B --route-up cmd
 Execute shell command
 .B cmd
 after routes are added, subject to
 .B --route-delay.
 
 See the "Environmental Variables" section below for
 additional parameters passed as environmental variables.
 
 Note that
 .B cmd
 can be a shell command with multiple arguments.
 .\"*********************************************************
 .TP
 .B --route-noexec
 Don't add or remove routes automatically.  Instead pass routes to
 .B --route-up
 script using environmental variables.
 .\"*********************************************************
 .TP

 .B --route-nopull
 When used with
 .B --client
 or
 .B --pull,
 accept options pushed by server EXCEPT for routes.
 
 When used on the client, this option effectively bars the
 server from adding routes to the client's routing table,
 however note that this option still allows the server
 to set the TCP/IP properties of the client's TUN/TAP interface.
 .\"*********************************************************
 .TP

 .B --allow-pull-fqdn
 Allow client to pull DNS names from server (rather than being limited
 to IP address) for
 .B --ifconfig,
 .B --route,
 and
 .B --route-gateway.
 .\"*********************************************************
 .TP

 .B --redirect-gateway flags...

 (Experimental) Automatically execute routing commands to cause all outgoing IP traffic
 to be redirected over the VPN.
 
 This option performs three steps:
 
 .B (1)
 Create a static route for the
 .B --remote
 address which forwards to the pre-existing default gateway.
 This is done so that
 .B (3)
 will not create a routing loop.
 
 .B (2)
 Delete the default gateway route.
 
 .B (3)
 Set the new default gateway to be the VPN endpoint address (derived either from
 .B --route-gateway
 or the second parameter to
 .B --ifconfig
 when
 .B --dev tun
 is specified).
 
 When the tunnel is torn down, all of the above steps are reversed so
 that the original default route is restored.
 

 Option flags:
 
 .B local --

 Add the
 .B local
 flag if both OpenVPN servers are directly connected via a common subnet,
 such as with wireless.  The
 .B local
 flag will cause step
 .B 1
 above to be omitted.
 

 .B def1 --
 Use this flag to override

 the default gateway by using 0.0.0.0/1 and 128.0.0.0/1
 rather than 0.0.0.0/0.  This has the benefit of overriding
 but not wiping out the original default gateway. 
 

 .B bypass-dhcp --
 Add a direct route to the DHCP server (if it is non-local) which
 bypasses the tunnel
 (Available on Windows clients, may not be available
 on non-Windows clients).
 
 .B bypass-dns --
 Add a direct route to the DNS server(s) (if they are non-local) which
 bypasses the tunnel
 (Available on Windows clients, may not be available
 on non-Windows clients).
 

 Using the def1 flag is highly recommended.

 .\"*********************************************************
 .TP
 .B --link-mtu n
 Sets an upper bound on the size of UDP packets which are sent
 between OpenVPN peers.  It's best not to set this parameter unless
 you know what you're doing.
 .\"*********************************************************
 .TP
 .B --tun-mtu n
 Take the TUN device MTU to be
 .B n
 and derive the link MTU
 from it (default=1500).  In most cases, you will probably want to
 leave this parameter set to its default value.
 
 The MTU (Maximum Transmission Units) is
 the maximum datagram size in bytes that can be sent unfragmented
 over a particular network path.  OpenVPN requires that packets
 on the control or data channels be sent unfragmented.
 
 MTU problems often manifest themselves as connections which
 hang during periods of active usage.
 
 It's best to use the
 .B --fragment
 and/or
 .B --mssfix
 options to deal with MTU sizing issues.
 .\"*********************************************************
 .TP
 .B --tun-mtu-extra n
 Assume that the TUN/TAP device might return as many as
 .B n
 bytes more than the
 .B --tun-mtu
 size on read.  This parameter defaults to 0, which is sufficient for
 most TUN devices.  TAP devices may introduce additional overhead in excess
 of the MTU size, and a setting of 32 is the default when TAP devices are used.
 This parameter only controls internal OpenVPN buffer sizing,
 so there is no transmission overhead associated with using a larger value.
 .\"*********************************************************
 .TP
 .B --mtu-disc type
 Should we do Path MTU discovery on TCP/UDP channel?  Only supported on OSes such
 as Linux that supports the necessary system call to set.
 
 .B 'no'
 -- Never send DF (Don't Fragment) frames
 .br
 .B 'maybe'
 -- Use per-route hints
 .br
 .B 'yes'
 -- Always DF (Don't Fragment)
 .br
 .\"*********************************************************
 .TP
 .B --mtu-test
 To empirically measure MTU on connection startup,
 add the
 .B --mtu-test
 option to your configuration.
 OpenVPN will send ping packets of various sizes
 to the remote peer and measure the largest packets
 which were successfully received.  The
 .B --mtu-test
 process normally takes about 3 minutes to complete.
 .\"*********************************************************
 .TP
 .B --fragment max
 Enable internal datagram fragmentation so
 that no UDP datagrams are sent which
 are larger than
 .B max
 bytes.
 
 The
 .B max
 parameter is interpreted in the same way as the
 .B --link-mtu
 parameter, i.e. the UDP packet size after encapsulation
 overhead has been added in, but not including
 the UDP header itself.
 
 The
 .B --fragment
 option only makes sense when you are using the UDP protocol (
 .B --proto udp
 ).
 
 .B --fragment
 adds 4 bytes of overhead per datagram.
 
 See the
 .B --mssfix
 option below for an important related option to
 .B --fragment.
 
 It should also be noted that this option is not meant to replace
 UDP fragmentation at the IP stack level.  It is only meant as a
 last resort when path MTU discovery is broken.  Using this option
 is less efficient than fixing path MTU discovery for your IP link and
 using native IP fragmentation instead.
 
 Having said that, there are circumstances where using OpenVPN's
 internal fragmentation capability may be your only option, such
 as tunneling a UDP multicast stream which requires fragmentation.
 .\"*********************************************************
 .TP
 .B --mssfix max
 Announce to TCP sessions running over the tunnel that they should limit
 their send packet sizes such that after OpenVPN has encapsulated them,
 the resulting UDP packet size that OpenVPN sends to its peer will not
 exceed
 .B max
 bytes.
 
 The
 .B max
 parameter is interpreted in the same way as the
 .B --link-mtu
 parameter, i.e. the UDP packet size after encapsulation
 overhead has been added in, but not including
 the UDP header itself.
 
 The
 .B --mssfix
 option only makes sense when you are using the UDP protocol
 for OpenVPN peer-to-peer communication, i.e.
 .B --proto udp.
 
 .B --mssfix
 and
 .B --fragment
 can be ideally used together, where
 .B --mssfix
 will try to keep TCP from needing
 packet fragmentation in the first place,
 and if big packets come through anyhow
 (from protocols other than TCP),
 .B --fragment
 will internally fragment them.
 
 Both
 .B --fragment
 and
 .B --mssfix
 are designed to work around cases where Path MTU discovery
 is broken on the network path between OpenVPN peers.
 
 The usual symptom of such a breakdown is an OpenVPN
 connection which successfully starts, but then stalls
 during active usage.
 
 If
 .B --fragment
 and
 .B --mssfix
 are used together,
 .B --mssfix
 will take its default
 .B max
 parameter from the
 .B --fragment max
 option.
 
 Therefore, one could lower the maximum UDP packet size
 to 1300 (a good first try for solving MTU-related
 connection problems) with the following options:
 
 .B --tun-mtu 1500 --fragment 1300 --mssfix
 .\"*********************************************************
 .TP
 .B --sndbuf size
 Set the TCP/UDP socket send buffer size.
 Currently defaults to 65536 bytes.
 .\"*********************************************************
 .TP
 .B --rcvbuf size
 Set the TCP/UDP socket receive buffer size.
 Currently defaults to 65536 bytes.
 .\"*********************************************************
 .TP

 .B --socket-flags flags...
 Apply the given flags to the OpenVPN transport socket.
 Currently, only
 .B TCP_NODELAY
 is supported.
 
 The
 .B TCP_NODELAY
 socket flag is useful in TCP mode, and causes the kernel
 to send tunnel packets immediately over the TCP connection without
 trying to group several smaller packets into a larger packet.
 This can result in a considerably improvement in latency.
 
 This option is pushable from server to client, and should be used
 on both client and server for maximum effect.
 .\"*********************************************************
 .TP

 .B --txqueuelen n
 (Linux only) Set the TX queue length on the TUN/TAP interface.
 Currently defaults to 100.
 .\"*********************************************************
 .TP
 .B --shaper n
 Limit bandwidth of outgoing tunnel data to
 .B n
 bytes per second on the TCP/UDP port.
 If you want to limit the bandwidth
 in both directions, use this option on both peers.
 
 OpenVPN uses the following algorithm to implement
 traffic shaping: Given a shaper rate of
 .I n
 bytes per second, after a datagram write of
 .I b
 bytes is queued on the TCP/UDP port, wait a minimum of
 .I (b / n)
 seconds before queuing the next write.
 
 It should be noted that OpenVPN supports multiple
 tunnels between the same two peers, allowing you
 to construct full-speed and reduced bandwidth tunnels
 at the same time,
 routing low-priority data such as off-site backups
 over the reduced bandwidth tunnel, and other data
 over the full-speed tunnel.
 
 Also note that for low bandwidth tunnels
 (under 1000 bytes per second), you should probably
 use lower MTU values as well (see above), otherwise
 the packet latency will grow so large as to trigger
 timeouts in the TLS layer and TCP connections running
 over the tunnel.
 
 OpenVPN allows
 .B n
 to be between 100 bytes/sec and 100 Mbytes/sec.
 .\"*********************************************************
 .TP

 .B --inactive n [bytes]
 Causes OpenVPN to exit after

 .B n
 seconds of inactivity on the TUN/TAP device.  The time length
 of inactivity is measured since the last incoming tunnel packet.

 
 If the optional
 .B bytes
 parameter is included,
 exit after n seconds of activity on tun/tap device
 produces a combined in/out byte count that is less than
 .B bytes.

 .\"*********************************************************
 .TP
 .B --ping n
 Ping remote over the TCP/UDP control channel
 if no packets have been sent for at least
 .B n
 seconds (specify
 .B --ping
 on both peers to cause ping packets to be sent in both directions since
 OpenVPN ping packets are not echoed like IP ping packets).
 When used in one of OpenVPN's secure modes (where
 .B --secret, --tls-server,
 or
 .B --tls-client
 is specified), the ping packet
 will be cryptographically secure.
 
 This option has two intended uses:
 
 (1) Compatibility
 with stateful firewalls.  The periodic ping will ensure that
 a stateful firewall rule which allows OpenVPN UDP packets to
 pass will not time out.
 
 (2) To provide a basis for the remote to test the existence
 of its peer using the
 .B --ping-exit
 option.
 .\"*********************************************************
 .TP
 .B --ping-exit n
 Causes OpenVPN to exit after
 .B n
 seconds pass without reception of a ping
 or other packet from remote.
 This option can be combined with
 .B --inactive, --ping,
 and
 .B --ping-exit
 to create a two-tiered inactivity disconnect.
 
 For example,
 
 .B openvpn [options...] --inactive 3600 --ping 10 --ping-exit 60
 
 when used on both peers will cause OpenVPN to exit within 60
 seconds if its peer disconnects, but will exit after one
 hour if no actual tunnel data is exchanged.
 .\"*********************************************************
 .TP
 .B --ping-restart n
 Similar to
 .B --ping-exit,
 but trigger a
 .B SIGUSR1
 restart after
 .B n
 seconds pass without reception of a ping
 or other packet from remote.
 
 This option is useful in cases
 where the remote peer has a dynamic IP address and
 a low-TTL DNS name is used to track the IP address using
 a service such as
 .I http://dyndns.org/
 + a dynamic DNS client such
 as
 .B ddclient.
 
 If the peer cannot be reached, a restart will be triggered, causing
 the hostname used with
 .B --remote
 to be re-resolved (if
 .B --resolv-retry
 is also specified).
 
 In server mode,
 .B --ping-restart, --inactive,
 or any other type of internally generated signal will always be
 applied to
 individual client instance objects, never to whole server itself.
 Note also in server mode that any internally generated signal
 which would normally cause a restart, will cause the deletion
 of the client instance object instead.
 
 In client mode, the
 .B --ping-restart
 parameter is set to 120 seconds by default.  This default will
 hold until the client pulls a replacement value from the server, based on
 the
 .B --keepalive
 setting in the server configuration.
 To disable the 120 second default, set
 .B --ping-restart 0
 on the client.
 
 See the signals section below for more information
 on
 .B SIGUSR1.
 
 Note that the behavior of
 .B SIGUSR1
 can be modified by the
 .B --persist-tun, --persist-key, --persist-local-ip,
 and
 .B --persist-remote-ip
 options.
 
 Also note that
 .B --ping-exit
 and
 .B --ping-restart
 are mutually exclusive and cannot be used together.
 .\"*********************************************************
 .TP
 .B --keepalive n m
 A helper directive designed to simplify the expression of
 .B --ping
 and
 .B --ping-restart
 in server mode configurations.
 
 For example,
 .B --keepalive 10 60
 expands as follows:
 
 .nf

 .ft 3
 .in +4

  if mode server:
    ping 10
    ping-restart 120
    push "ping 10"
    push "ping-restart 60"
  else
    ping 10
    ping-restart 60

 .in -4

 .ft
 .fi
 .\"*********************************************************
 .TP
 .B --ping-timer-rem
 Run the
 .B --ping-exit
 /
 .B --ping-restart
 timer only if we have a remote address.  Use this option if you are
 starting the daemon in listen mode (i.e. without an explicit
 .B --remote
 peer), and you don't want to start clocking timeouts until a remote
 peer connects.
 .\"*********************************************************
 .TP
 .B --persist-tun
 Don't close and reopen TUN/TAP device or run up/down scripts
 across
 .B SIGUSR1
 or
 .B --ping-restart
 restarts.
 
 .B SIGUSR1
 is a restart signal similar to
 .B SIGHUP,
 but which offers finer-grained control over
 reset options.
 .\"*********************************************************
 .TP
 .B --persist-key
 Don't re-read key files across
 .B SIGUSR1
 or
 .B --ping-restart.
 
 This option can be combined with
 .B --user nobody
 to allow restarts triggered by the
 .B SIGUSR1
 signal.
 Normally if you drop root privileges in OpenVPN,
 the daemon cannot be restarted since it will now be unable to re-read protected
 key files.
 
 This option solves the problem by persisting keys across
 .B SIGUSR1
 resets, so they don't need to be re-read.
 .\"*********************************************************
 .TP
 .B --persist-local-ip
 Preserve initially resolved local IP address and port number
 across
 .B SIGUSR1
 or
 .B --ping-restart
 restarts.
 .\"*********************************************************
 .TP
 .B --persist-remote-ip
 Preserve most recently authenticated remote IP address and port number
 across
 .B SIGUSR1
 or
 .B --ping-restart
 restarts.
 .\"*********************************************************
 .TP
 .B --mlock
 Disable paging by calling the POSIX mlockall function.
 Requires that OpenVPN be initially run as root (though
 OpenVPN can subsequently downgrade its UID using the
 .B --user
 option).
 
 Using this option ensures that key material and tunnel
 data are never written to disk due to virtual
 memory paging operations which occur under most
 modern operating systems.  It ensures that even if an
 attacker was able to crack the box running OpenVPN, he
 would not be able to scan the system swap file to
 recover previously used
 ephemeral keys, which are used for a period of time
 governed by the
 .B --reneg
 options (see below), then are discarded.
 
 The downside
 of using
 .B --mlock
 is that it will reduce the amount of physical
 memory available to other applications.
 .\"*********************************************************
 .TP
 .B --up cmd
 Shell command to run after successful TUN/TAP device open
 (pre
 .B --user
 UID change).  The up script is useful for specifying route
 commands which route IP traffic destined for
 private subnets which exist at the other
 end of the VPN connection into the tunnel.
 
 For
 .B --dev tun
 execute as:
 
 .B cmd tun_dev tun_mtu link_mtu ifconfig_local_ip ifconfig_remote_ip [ init | restart ]
 
 For
 .B --dev tap
 execute as:
 
 .B cmd tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask [ init | restart ]
 
 See the "Environmental Variables" section below for
 additional parameters passed as environmental variables.
 
 Note that
 .B cmd
 can be a shell command with multiple arguments, in which
 case all OpenVPN-generated arguments will be appended
 to
 .B cmd
 to build a command line which will be passed to the shell.
 
 Typically,
 .B cmd
 will run a script to add routes to the tunnel.
 
 Normally the up script is called after the TUN/TAP device is opened.
 In this context, the last command line parameter passed to the script
 will be
 .I init.
 If the
 .B --up-restart
 option is also used, the up script will be called for restarts as
 well.  A restart is considered to be a partial reinitialization
 of OpenVPN where the TUN/TAP instance is preserved (the
 .B --persist-tun
 option will enable such preservation).  A restart
 can be generated by a SIGUSR1 signal, a
 .B --ping-restart
 timeout, or a connection reset when the TCP protocol is enabled
 with the
 .B --proto
 option.  If a restart occurs, and
 .B --up-restart
 has been specified, the up script will be called with
 .I restart
 as the last parameter.
 
 The following standalone example shows how the
 .B --up
 script can be called in both an initialization and restart context.
 (NOTE: for security reasons, don't run the following example unless UDP port
 9999 is blocked by your firewall.  Also, the example will run indefinitely,
 so you should abort with control-c).
 
 .B openvpn --dev tun --port 9999 --verb 4 --ping-restart 10 --up 'echo up' --down 'echo down' --persist-tun --up-restart
 
 Note that OpenVPN also provides the
 .B --ifconfig
 option to automatically ifconfig the TUN device,
 eliminating the need to define an
 .B --up
 script, unless you also want to configure routes
 in the
 .B --up
 script.
 
 If
 .B --ifconfig
 is also specified, OpenVPN will pass the ifconfig local
 and remote endpoints on the command line to the
 .B --up
 script so that they can be used to configure routes such as:
 
 .B route add -net 10.0.0.0 netmask 255.255.255.0 gw $5
 .\"*********************************************************
 .TP
 .B --up-delay
 Delay TUN/TAP open and possible
 .B --up
 script execution
 until after TCP/UDP connection establishment with peer.
 
 In
 .B --proto udp
 mode, this option normally requires the use of
 .B --ping
 to allow connection initiation to be sensed in the absence
 of tunnel data, since UDP is a "connectionless" protocol.
 
 On Windows, this option will delay the TAP-Win32 media state
 transitioning to "connected" until connection establishment,
 i.e. the receipt of the first authenticated packet from the peer.
 .\"*********************************************************
 .TP
 .B --down cmd
 Shell command to run after TUN/TAP device close
 (post
 .B --user
 UID change and/or
 .B --chroot
 ).  Called with the same parameters and environmental
 variables as the
 .B --up
 option above.
 
 Note that if you reduce privileges by using
 .B --user
 and/or
 .B --group,
 your
 .B --down
 script will also run at reduced privilege.
 .\"*********************************************************
 .TP
 .B --down-pre
 Call
 .B --down
 cmd/script before, rather than after, TUN/TAP close.
 .\"*********************************************************
 .TP
 .B --up-restart
 Enable the
 .B --up
 and
 .B --down
 scripts to be called for restarts as well as initial program start.
 This option is described more fully above in the
 .B --up
 option documentation.
 .\"*********************************************************
 .TP
 .B --setenv name value
 Set a custom environmental variable
 .B name=value
 to pass to script.
 .\"*********************************************************
 .TP

 .B --setenv FORWARD_COMPATIBLE 1
 Relax config file syntax checking so that unknown directives
 will trigger a warning but not a fatal error,
 on the assumption that a given unknown directive might be valid
 in future OpenVPN versions.
 
 This option should be used with caution, as there are good security
 reasons for having OpenVPN fail if it detects problems in a
 config file.  Having said that, there are valid reasons for wanting
 new software features to gracefully degrade when encountered by
 older software versions.
 .\"*********************************************************
 .TP

 .B --setenv-safe name value
 Set a custom environmental variable
 .B OPENVPN_name=value
 to pass to script.
 
 This directive is designed to be pushed by the server to clients,
 and the prepending of "OPENVPN_" to the environmental variable
 is a safety precaution to prevent a LD_PRELOAD style attack
 from a malicious or compromised server.
 .\"*********************************************************
 .TP

 .B --script-security level [method]

 This directive offers policy-level control over OpenVPN's usage of external programs

 and scripts.  Lower
 .B level
 values are more restrictive, higher values are more permissive.  Settings for

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

 
 The
 .B method
 parameter indicates how OpenVPN should call external commands and scripts.
 Settings for
 .B method:
 
 .B execve --
 (default) Use execve() function on Unix family OSes and CreateProcess() on Windows.
 .br
 .B system --
 Use system() function (deprecated and less safe since the external program command
 line is subject to shell expansion).
 
 The
 .B --script-security
 option was introduced in OpenVPN 2.1_rc9.  For configuration file compatibility
 with previous OpenVPN versions, use:
 .B --script-security 3 system

 .\"*********************************************************
 .TP

 .B --disable-occ
 Don't output a warning message if option inconsistencies are detected between
 peers.  An example of an option inconsistency would be where one peer uses
 .B --dev tun
 while the other peer uses
 .B --dev tap.
 
 Use of this option is discouraged, but is provided as
 a temporary fix in situations where a recent version of OpenVPN must
 connect to an old version.
 .\"*********************************************************
 .TP
 .B --user user
 Change the user ID of the OpenVPN process to
 .B user
 after initialization, dropping privileges in the process.
 This option is useful to protect the system
 in the event that some hostile party was able to gain control of
 an OpenVPN session.  Though OpenVPN's security features make
 this unlikely, it is provided as a second line of defense.
 
 By setting
 .B user
 to
 .I nobody
 or somebody similarly unprivileged, the hostile party would be
 limited in what damage they could cause.  Of course once
 you take away privileges, you cannot return them
 to an OpenVPN session.  This means, for example, that if
 you want to reset an OpenVPN daemon with a
 .B SIGUSR1
 signal
 (for example in response
 to a DHCP reset), you should make use of one or more of the
 .B --persist
 options to ensure that OpenVPN doesn't need to execute any privileged
 operations in order to restart (such as re-reading key files
 or running
 .BR ifconfig
 on the TUN device).
 .\"*********************************************************
 .TP
 .B --group group
 Similar to the
 .B --user
 option,
 this option changes the group ID of the OpenVPN process to
 .B group
 after initialization.
 .\"*********************************************************
 .TP
 .B --cd dir
 Change directory to
 .B dir
 prior to reading any files such as
 configuration files, key files, scripts, etc.
 .B dir
 should be an absolute path, with a leading "/",
 and without any references
 to the current directory such as "." or "..".
 
 This option is useful when you are running
 OpenVPN in 
 .B --daemon
 mode, and you want to consolidate all of
 your OpenVPN control files in one location.
 .\"*********************************************************
 .TP
 .B --chroot dir
 Chroot to
 .B dir
 after initialization.  
 .B --chroot
 essentially redefines
 .B dir
 as being the top
 level directory tree (/).  OpenVPN will therefore
 be unable to access any files outside this tree.
 This can be desirable from a security standpoint.
 
 Since the chroot operation is delayed until after
 initialization, most OpenVPN options that reference
 files will operate in a pre-chroot context.
 
 In many cases, the
 .B dir
 parameter can point to an empty directory, however
 complications can result when scripts or restarts
 are executed after the chroot operation.
 .\"*********************************************************
 .TP
 .B --daemon [progname]
 Become a daemon after all initialization functions are completed.
 This option will cause all message and error output to
 be sent to the syslog file (such as /var/log/messages),
 except for the output of shell scripts and
 ifconfig commands,
 which will go to /dev/null unless otherwise redirected.
 The syslog redirection occurs immediately at the point
 that
 .B --daemon
 is parsed on the command line even though
 the daemonization point occurs later.  If one of the
 .B --log
 options is present, it will supercede syslog
 redirection.
 
 The optional
 .B progname
 parameter will cause OpenVPN to report its program name
 to the system logger as
 .B progname.
 This can be useful in linking OpenVPN messages
 in the syslog file with specific tunnels.
 When unspecified,
 .B progname
 defaults to "openvpn".
 
 When OpenVPN is run with the
 .B --daemon
 option, it will try to delay daemonization until the majority of initialization
 functions which are capable of generating fatal errors are complete.  This means
 that initialization scripts can test the return status of the
 openvpn command for a fairly reliable indication of whether the command
 has correctly initialized and entered the packet forwarding event loop.
 
 In OpenVPN, the vast majority of errors which occur after initialization are non-fatal.
 .\"*********************************************************
 .TP
 .B --syslog [progname]
 Direct log output to system logger, but do not become a daemon.
 See
 .B --daemon
 directive above for description of
 .B progname
 parameter.
 .\"*********************************************************
 .TP
 .B --passtos
 Set the TOS field of the tunnel packet to what the payload's TOS is.
 .\"*********************************************************
 .TP
 .B --inetd [wait|nowait] [progname]
 Use this option when OpenVPN is being run from the inetd or
 .BR xinetd(8)
 server.
 
 The
 .B wait/nowait
 option must match what is specified in the inetd/xinetd
 config file.  The
 .B nowait
 mode can only be used with
 .B --proto tcp-server.
 The default is
 .B wait.
 The
 .B nowait
 mode can be used to instantiate the OpenVPN daemon as a classic TCP server,
 where client connection requests are serviced on a single
 port number.  For additional information on this kind of configuration,
 see the OpenVPN FAQ:
 .I http://openvpn.net/faq.html#oneport
 
 This option precludes the use of
 .B --daemon, --local,
 or
 .B --remote.
 Note that this option causes message and error output to be handled in the same
 way as the
 .B --daemon
 option.  The optional
 .B progname
 parameter is also handled exactly as in
 .B --daemon.
 
 Also note that in
 .B wait
 mode, each OpenVPN tunnel requires a separate TCP/UDP port and
 a separate inetd or xinetd entry.  See the OpenVPN 1.x HOWTO for an example
 on using OpenVPN with xinetd:
 .I http://openvpn.net/1xhowto.html
 .\"*********************************************************
 .TP
 .B --log file
 Output logging messages to
 .B file,
 including output to stdout/stderr which
 is generated by called scripts.
 If
 .B file
 already exists it will be truncated.
 This option takes effect
 immediately when it is parsed in the command line
 and will supercede syslog output if
 .B --daemon
 or
 .B --inetd
 is also specified.
 This option is persistent over the entire course of
 an OpenVPN instantiation and will not be reset by SIGHUP,
 SIGUSR1, or
 .B --ping-restart.
 
 Note that on Windows, when OpenVPN is started as a service,
 logging occurs by default without the need to specify
 this option.
 .\"*********************************************************
 .TP
 .B --log-append file
 Append logging messages to
 .B file.
 If
 .B file
 does not exist, it will be created.
 This option behaves exactly like
 .B --log
 except that it appends to rather
 than truncating the log file.
 .\"*********************************************************
 .TP
 .B --suppress-timestamps
 Avoid writing timestamps to log messages, even when they
 otherwise would be prepended. In particular, this applies to
 log messages sent to stdout.
 .\"*********************************************************
 .TP
 .B --writepid file
 Write OpenVPN's main process ID to
 .B file.
 .\"*********************************************************
 .TP
 .B --nice n
 Change process priority after initialization
 (
 .B n
 greater than 0 is lower priority,
 .B n
 less than zero is higher priority).
 .\"*********************************************************
 .\".TP
 .\".B --nice-work n
 .\"Change priority of background TLS work thread.  The TLS thread
 .\"feature is enabled when OpenVPN is built
 .\"with pthread support, and you are running OpenVPN
 .\"in TLS mode (i.e. with
 .\".B --tls-client
 .\"or
 .\".B --tls-server
 .\"specified).
 .\"
 .\"Using a TLS thread offloads the CPU-intensive process of SSL/TLS-based
 .\"key exchange to a background thread so that it does not become
 .\"a latency bottleneck in the tunnel packet forwarding process.
 .\"
 .\"The parameter
 .\".B n
 .\"is interpreted exactly as with the
 .\".B --nice
 .\"option above, but in relation to the work thread rather
 .\"than the main thread.
 .\"*********************************************************
 .TP
 .B --fast-io
 (Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding
 a call to poll/epoll/select prior to the write operation.  The purpose
 of such a call would normally be to block until the device
 or socket is ready to accept the write.  Such blocking is unnecessary
 on some platforms which don't support write blocking on UDP sockets
 or TUN/TAP devices.  In such cases, one can optimize the event loop
 by avoiding the poll/epoll/select call, improving CPU efficiency
 by 5% to 10%.
 
 This option can only be used on non-Windows systems, when
 .B --proto udp
 is specified, and when
 .B --shaper
 is NOT specified.
 .\"*********************************************************
 .TP
 .B --echo [parms...]
 Echo
 .B parms
 to log output.
 
 Designed to be used to send messages to a controlling application
 which is receiving the OpenVPN log output.
 .\"*********************************************************
 .TP
 .B --remap-usr1 signal
 Control whether internally or externally
 generated SIGUSR1 signals are remapped to
 SIGHUP (restart without persisting state) or
 SIGTERM (exit).
 
 .B signal
 can be set to "SIGHUP" or "SIGTERM".  By default, no remapping
 occurs.
 .\"*********************************************************
 .TP
 .B --verb n
 Set output verbosity to
 .B n
 (default=1).  Each level shows all info from the previous levels.
 Level 3 is recommended if you want a good summary
 of what's happening without being swamped by output.
 
 .B 0 --
 No output except fatal errors.
 .br
 .B 1 to 4 --
 Normal usage range.
 .br
 .B 5 --
 Output
 .B R
 and
 .B W
 characters to the console for each packet read and write, uppercase is
 used for TCP/UDP packets and lowercase is used for TUN/TAP packets.
 .br
 .B 6 to 11 --
 Debug info range (see errlevel.h for additional
 information on debug levels).
 .\"*********************************************************
 .TP
 .B --status file [n]
 Write operational status to
 .B file
 every
 .B n
 seconds.
 
 Status can also be written to the syslog by sending a
 .B SIGUSR2
 signal.
 .\"*********************************************************
 .TP
 .B --status-version [n]
 Choose the status file format version number.  Currently
 .B n

 can be 1, 2, or 3 and defaults to 1.

 .\"*********************************************************
 .TP
 .B --mute n
 Log at most
 .B n
 consecutive messages in the same category.  This is useful to
 limit repetitive logging of similar message types.
 .\"*********************************************************
 .TP

 .B --comp-lzo [mode]

 Use fast LZO compression -- may add up to 1 byte per
 packet for incompressible data.

 .B mode
 may be "yes", "no", or "adaptive" (default).
 
 In a server mode setup, it is possible to selectively turn
 compression on or off for individual clients.
 
 First, make sure the client-side config file enables selective
 compression by having at least one
 .B --comp-lzo
 directive, such as
 .B --comp-lzo no.
 This will turn off compression by default,
 but allow a future directive push from the server to
 dynamically change the
 on/off/adaptive setting.
 
 Next in a
 .B --client-config-dir
 file, specify the compression setting for the client,
 for example:
 
 .nf

 .ft 3
 .in +4

 comp-lzo yes
 push "comp-lzo yes"

 .in -4

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

 .\"*********************************************************
 .TP
 .B --comp-noadapt
 When used in conjunction with
 .B --comp-lzo,
 this option will disable OpenVPN's adaptive compression algorithm.
 Normally, adaptive compression is enabled with
 .B --comp-lzo.
 
 Adaptive compression tries to optimize the case where you have
 compression enabled, but you are sending predominantly uncompressible
 (or pre-compressed) packets over the tunnel, such as an FTP or rsync transfer
 of a large, compressed file.  With adaptive compression,
 OpenVPN will periodically sample the compression process to measure its
 efficiency.  If the data being sent over the tunnel is already compressed,
 the compression efficiency will be very low, triggering openvpn to disable
 compression for a period of time until the next re-sample test.
 .\"*********************************************************
 .TP
 .B --management IP port [pw-file]
 Enable a TCP server on
 .B IP:port
 to handle daemon management functions.
 .B pw-file,
 if specified,
 is a password file (password on first line)
 or "stdin" to prompt from standard input.  The password
 provided will set the password which TCP clients will need
 to provide in order to access management functions.
 

 The management interface can also listen on a unix domain socket,
 for those platforms that support it.  To use a unix domain socket, specify
 the unix socket pathname in place of
 .B IP
 and set
 .B port
 to 'unix'.  While the default behavior is to create a unix domain socket
 that may be connected to by any process, the
 .B --management-client-user
 and
 .B --management-client-group
 directives can be used 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
 .B IP
 = "tunnel".  Tunnel mode will cause the management interface
 to listen for a TCP connection on the local VPN address of the
 TUN/TAP interface.
 
 While the management port is designed for programmatic control
 of OpenVPN by other applications, it is possible to telnet
 to the port, using a telnet client in "raw" mode.  Once connected,
 type "help" for a list of commands.
 
 For detailed documentation on the management interface, see
 the management-notes.txt file in the
 .B management
 folder of
 the OpenVPN source distribution.
 
 It is strongly recommended that
 .B IP
 be set to 127.0.0.1
 (localhost) to restrict accessibility of the management
 server to local clients. 
 .\"*********************************************************
 .TP
 .B --management-query-passwords
 Query management channel for private key password and
 .B --auth-user-pass
 username/password.  Only query the management channel
 for inputs which ordinarily would have been queried from the
 console.
 .\"*********************************************************
 .TP

 .B --management-forget-disconnect
 Make OpenVPN forget passwords when management session
 disconnects.
 
 This directive does not affect the
 .B --http-proxy
 username/password.  It is always cached.
 .\"*********************************************************
 .TP

 .B --management-hold
 Start OpenVPN in a hibernating state, until a client
 of the management interface explicitly starts it
 with the
 .B hold release
 command.
 .\"*********************************************************
 .TP

 .B --management-signal
 Send SIGUSR1 signal to OpenVPN if management session disconnects.
 This is useful when you wish to disconnect an OpenVPN session on
 user logoff.
 .\"*********************************************************
 .TP

 .B --management-log-cache n
 Cache the most recent
 .B n
 lines of log file history for usage
 by the management channel.
 .\"*********************************************************
 .TP

 .B --management-client-auth
 Gives management interface client the responsibility
 to authenticate clients after their client certificate
 has been verified.  See management-notes.txt in OpenVPN
 distribution for detailed notes.
 .\"*********************************************************
 .TP
 .B --management-client-pf
 Management interface clients must specify a packet
 filter file for each connecting client.  See management-notes.txt
 in OpenVPN distribution for detailed notes.
 .\"*********************************************************
 .TP

 .B --management-client-user u
 When the management interface is listening on a unix domain socket,
 only allow connections from user
 .B u.
 .\"*********************************************************
 .TP
 .B --management-client-group g
 When the management interface is listening on a unix domain socket,
 only allow connections from group
 .B g.
 .\"*********************************************************
 .TP

 .B --plugin module-pathname [init-string]
 Load plug-in module from the file
 .B module-pathname,
 passing
 .B init-string
 as an argument
 to the module initialization function.  Multiple
 plugin modules may be loaded into one OpenVPN
 process.
 
 For more information and examples on how to build OpenVPN
 plug-in modules, see the README file in the
 .B plugin
 folder of the OpenVPN source distribution.
 
 If you are using an RPM install of OpenVPN, see
 /usr/share/openvpn/plugin.  The documentation is
 in
 .B doc
 and the actual plugin modules are in
 .B lib.
 
 Multiple plugin modules can be cascaded, and modules can be
 used in tandem with scripts.  The modules will be called by
 OpenVPN in the order that they are declared in the config
 file.  If both a plugin and script are configured for the same
 callback, the script will be called last.  If the
 return code of the module/script controls an authentication
 function (such as tls-verify, auth-user-pass-verify, or
 client-connect), then
 every module and script must return success (0) in order for
 the connection to be authenticated.
 .\"*********************************************************
 .SS Server Mode
 Starting with OpenVPN 2.0, a multi-client TCP/UDP server mode
 is supported, and can be enabled with the
 .B --mode server
 option.  In server mode, OpenVPN will listen on a single
 port for incoming client connections.  All client
 connections will be routed through a single tun or tap
 interface.  This mode is designed for scalability and should
 be able to support hundreds or even thousands of clients
 on sufficiently fast hardware.  SSL/TLS authentication must
 be used in this mode.
 .\"*********************************************************
 .TP
 .B --server network netmask
 A helper directive designed to simplify the configuration
 of OpenVPN's server mode.  This directive will set up an
 OpenVPN server which will allocate addresses to clients
 out of the given network/netmask.  The server itself
 will take the ".1" address of the given network
 for use as the server-side endpoint of the local
 TUN/TAP interface.
 
 For example,
 .B --server 10.8.0.0 255.255.255.0
 expands as follows:
 
 .nf

 .ft 3
 .in +4

  mode server
  tls-server

  push "topology [topology]"

  if dev tun AND (topology == net30 OR topology == p2p):

    ifconfig 10.8.0.1 10.8.0.2
    if !nopool:
      ifconfig-pool 10.8.0.4 10.8.0.251

    route 10.8.0.0 255.255.255.0
    if client-to-client:
      push "route 10.8.0.0 255.255.255.0"

    else if topology == net30:

      push "route 10.8.0.1"
 

  if dev tap OR (dev tun AND topology == subnet):

    ifconfig 10.8.0.1 255.255.255.0

    if !nopool:
      ifconfig-pool 10.8.0.2 10.8.0.254 255.255.255.0

    push "route-gateway 10.8.0.1"

 .in -4

 .ft
 .fi
 
 Don't use
 .B --server
 if you are ethernet bridging.  Use
 .B --server-bridge
 instead.
 .\"*********************************************************
 .TP

 .B --server-bridge gateway netmask pool-start-IP pool-end-IP
 .TP
 .B --server-bridge ['nogw']

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

 If
 .B --server-bridge
 is used without any parameters, it will enable a DHCP-proxy
 mode, where connecting OpenVPN clients will receive an IP
 address for their TAP adapter from the DHCP server running
 on the OpenVPN server-side LAN.
 Note that only clients that support
 the binding of a DHCP client with the TAP adapter (such as

 Windows) can support this mode.  The optional 
 .B nogw
 flag (advanced) indicates that gateway information should not be
 pushed to the client.

 To configure ethernet bridging, you 
 must first use your OS's bridging capability
 to bridge the TAP interface with the ethernet
 NIC interface.  For example, on Linux this is done
 with the
 .B brctl
 tool, and with Windows XP it is done in the Network
 Connections Panel by selecting the ethernet and
 TAP adapters and right-clicking on "Bridge Connections".
 
 Next you you must manually set the
 IP/netmask on the bridge interface.  The
 .B gateway
 and
 .B netmask
 parameters to
 .B --server-bridge
 can be set to either the IP/netmask of the
 bridge interface, or the IP/netmask of the
 default gateway/router on the bridged
 subnet.
 
 Finally, set aside a IP range in the bridged
 subnet,
 denoted by
 .B pool-start-IP
 and
 .B pool-end-IP,
 for OpenVPN to allocate to connecting
 clients.
 
 For example,
 .B server-bridge 10.8.0.4 255.255.255.0 10.8.0.128 10.8.0.254
 expands as follows:
 
 .nf

 .ft 3
 .in +4

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

 .in -4

 .ft
 .fi

 
 In another example,
 .B --server-bridge
 (without parameters) expands as follows:
 
 .nf

 .ft 3
 .in +4

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

 .in -4
 .ft
 .fi
 
 Or
 .B --server-bridge nogw
 expands as follows:
 
 .nf
 .ft 3
 .in +4
 mode server
 tls-server
 .in -4

 .ft
 .fi

 .\"*********************************************************
 .TP
 .B --push "option"
 Push a config file option back to the client for remote
 execution.  Note that
 .B
 option
 must be enclosed in double quotes ("").  The client must specify
 .B --pull
 in its config file.  The set of options which can be
 pushed is limited by both feasibility and security.
 Some options such as those which would execute scripts
 are banned, since they would effectively allow a compromised
 server to execute arbitrary code on the client.
 Other options such as TLS or MTU parameters
 cannot be pushed because the client needs to know
 them before the connection to the server can be initiated.
 
 This is a partial list of options which can currently be pushed:
 .B --route, --route-gateway, --route-delay, --redirect-gateway,
 .B --ip-win32, --dhcp-option,
 .B --inactive, --ping, --ping-exit, --ping-restart,
 .B --setenv,

 .B --persist-key, --persist-tun, --echo,
 .B --comp-lzo,
 .B --socket-flags,
 .B --sndbuf, --rcvbuf

 .\"*********************************************************
 .TP
 .B --push-reset
 Don't inherit the global push list for a specific client instance.
 Specify this option in a client-specific context such
 as with a
 .B --client-config-dir
 configuration file.  This option will ignore
 .B --push
 options at the global config file level.
 .\"*********************************************************
 .TP
 .B --disable
 Disable a particular client (based on the common name)
 from connecting.  Don't use this option to disable a client
 due to key or password compromise.  Use a CRL (certificate
 revocation list) instead (see the
 .B --crl-verify
 option).
 
 This option must be associated with a specific client instance,
 which means that it must be specified either in a client
 instance config file using
 .B --client-config-dir
 or dynamically generated using a
 .B --client-connect
 script.
 .\"*********************************************************
 .TP
 .B --ifconfig-pool start-IP end-IP [netmask]
 Set aside a pool of subnets to be
 dynamically allocated to connecting clients, similar
 to a DHCP server.  For tun-style
 tunnels, each client will be given a /30 subnet (for
 interoperability with Windows clients).  For tap-style
 tunnels, individual addresses will be allocated, and the
 optional
 .B netmask
 parameter will also be pushed to clients.
 
 .\"*********************************************************
 .TP
 .B --ifconfig-pool-persist file [seconds]
 Persist/unpersist ifconfig-pool
 data to
 .B file,
 at
 .B seconds
 intervals (default=600), as well as on program startup and
 shutdown.
 
 The goal of this option is to provide a long-term association
 between clients (denoted by their common name) and the virtual
 IP address assigned to them from the ifconfig-pool.
 Maintaining a long-term
 association is good for clients because it allows them
 to effectively use the
 .B --persist-tun
 option.
 
 .B file
 is a comma-delimited ASCII file, formatted as
 <Common-Name>,<IP-address>.
 
 If
 .B seconds
 = 0,
 .B file
 will be treated as read-only.  This is useful if
 you would like to treat
 .B file
 as a configuration file.
 
 Note that the entries in this file are treated by OpenVPN as
 suggestions only, based on past associations between
 a common name and IP address.  They do not guarantee that the given common
 name will always receive the given IP address.  If you want guaranteed
 assignment, use
 .B --ifconfig-push
 .\"*********************************************************
 .TP
 .B --ifconfig-pool-linear
 Modifies the
 .B --ifconfig-pool
 directive to
 allocate individual TUN interface addresses for
 clients rather than /30 subnets.  NOTE:  This option
 is incompatible with Windows clients.

 
 This option is deprecated, and should be replaced with
 .B --topology p2p
 which is functionally equivalent.

 .\"*********************************************************
 .TP
 .B --ifconfig-push local remote-netmask
 Push virtual IP endpoints for client tunnel,
 overriding the --ifconfig-pool dynamic allocation.
 
 The parameters
 .B local
 and
 .B remote-netmask
 are set according to the
 .B --ifconfig
 directive which you want to execute on the client machine to
 configure the remote end of the tunnel.  Note that the parameters
 .B local
 and
 .B remote-netmask
 are from the perspective of the client, not the server.  They may be
 DNS names rather than IP addresses, in which case they will be resolved
 on the server at the time of client connection.
 
 This option must be associated with a specific client instance,
 which means that it must be specified either in a client
 instance config file using
 .B --client-config-dir
 or dynamically generated using a
 .B --client-connect
 script.
 
 Remember also to include a
 .B --route
 directive in the main OpenVPN config file which encloses
 .B local,
 so that the kernel will know to route it
 to the server's TUN/TAP interface.
 
 OpenVPN's internal client IP address selection algorithm works as
 follows:
 
 .B 1
 -- Use
 .B --client-connect script
 generated file for static IP (first choice).
 .br
 .B 2
 -- Use 
 .B --client-config-dir
 file for static IP (next choice).
 .br
 .B 3
 -- Use
 .B --ifconfig-pool
 allocation for dynamic IP (last choice).
 .br
 .\"*********************************************************
 .TP
 .B --iroute network [netmask]
 Generate an internal route to a specific
 client. The
 .B netmask
 parameter, if omitted, defaults to 255.255.255.255.
 
 This directive can be used to route a fixed subnet from
 the server to a particular client, regardless
 of where the client is connecting from.  Remember
 that you must also add the route to the system
 routing table as well (such as by using the
 .B --route
 directive).  The reason why two routes are needed
 is that the
 .B --route
 directive routes the packet from the kernel
 to OpenVPN.  Once in OpenVPN, the
 .B --iroute
 directive routes to the specific client.
 
 This option must be specified either in a client
 instance config file using
 .B --client-config-dir
 or dynamically generated using a
 .B --client-connect
 script.
 
 The
 .B --iroute
 directive also has an important interaction with
 .B --push
 "route ...".
 .B --iroute
 essentially defines a subnet which is owned by a
 particular client (we will call this client A).
 If you would like other clients to be able to reach A's
 subnet, you can use
 .B --push
 "route ..."
 together with
 .B --client-to-client
 to effect this.  In order for all clients to see
 A's subnet, OpenVPN must push this route to all clients
 EXCEPT for A, since the subnet is already owned by A.
 OpenVPN accomplishes this by not
 not pushing a route to a client
 if it matches one of the client's iroutes.
 .\"*********************************************************
 .TP
 .B --client-to-client
 Because the OpenVPN server mode handles multiple clients
 through a single tun or tap interface, it is effectively
 a router.  The
 .B --client-to-client
 flag tells OpenVPN to internally route client-to-client
 traffic rather than pushing all client-originating traffic
 to the TUN/TAP interface.
 
 When this option is used, each client will "see" the other
 clients which are currently connected.  Otherwise, each
 client will only see the server.  Don't use this option
 if you want to firewall tunnel traffic using
 custom, per-client rules.
 .\"*********************************************************
 .TP
 .B --duplicate-cn
 Allow multiple clients with the same common name to concurrently connect.
 In the absence of this option, OpenVPN will disconnect a client instance
 upon connection of a new client having the same common name.
 .\"*********************************************************
 .TP
 .B --client-connect script
 Run
 .B script
 on client connection.  The script is passed the common name
 and IP address of the just-authenticated client
 as environmental variables (see environmental variable section
 below).  The script is also passed
 the pathname of a not-yet-created temporary file as $1
 (i.e. the first command line argument), to be used by the script
 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 $1.
 
 See the
 .B --client-config-dir
 option below for options which
 can be legally used in a dynamically generated config file.
 
 Note that the return value of
 .B script
 is significant.  If
 .B script
 returns a non-zero error status, it will cause the client
 to be disconnected.
 .\"*********************************************************
 .TP
 .B --client-disconnect
 Like
 .B --client-connect
 but called on client instance shutdown.  Will not be called
 unless the
 .B --client-connect
 script and plugins (if defined)
 were previously called on this instance with
 successful (0) status returns.
 
 The exception to this rule is if the
 .B --client-disconnect
 script 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.
 .B 
 .\"*********************************************************
 .TP
 .B --client-config-dir dir
 Specify a directory
 .B dir
 for custom client config files.  After
 a connecting client has been authenticated, OpenVPN will
 look in this directory for a file having the same name
 as the client's X509 common name.  If a matching file
 exists, it will be opened and parsed for client-specific
 configuration options.  If no matching file is found, OpenVPN
 will instead try to open and parse a default file called
 "DEFAULT", which may be provided but is not required.
 
 This file can specify a fixed IP address for a given
 client using
 .B --ifconfig-push,
 as well as fixed subnets owned by the client using
 .B --iroute.
 
 One of the useful properties of this option is that it
 allows client configuration files to be conveniently
 created, edited, or removed while the server is live,
 without needing to restart the server.
 
 The following
 options are legal in a client-specific context:
 .B --push, --push-reset, --iroute, --ifconfig-push,
 and
 .B --config.
 .\"*********************************************************
 .TP
 .B --ccd-exclusive
 Require, as a
 condition of authentication, that a connecting client has a
 .B --client-config-dir
 file.
 .\"*********************************************************
 .TP
 .B --tmp-dir dir
 Specify a directory
 .B dir
 for temporary files.  This directory will be used by
 .B --client-connect
 scripts to dynamically generate client-specific
 configuration files.
 .\"*********************************************************
 .TP
 .B --hash-size r v
 Set the size of the real address hash table to
 .B r
 and the virtual address table to
 .B v.
 By default, both tables are sized at 256 buckets.
 .\"*********************************************************
 .TP
 .B --bcast-buffers n
 Allocate
 .B n
 buffers for broadcast datagrams (default=256).
 .\"*********************************************************
 .TP
 .B --tcp-queue-limit n

 Maximum number of output packets queued before TCP (default=64).

 
 When OpenVPN is tunneling data from a TUN/TAP device to a
 remote client over a TCP connection, it is possible that the TUN/TAP device
 might produce data at a faster rate than the TCP connection

 can support.  When the number of output packets queued before sending to
 the TCP socket reaches this limit for a given client connection,

 OpenVPN will start to drop outgoing packets directed
 at this client.
 .\"*********************************************************
 .TP

 .B --tcp-nodelay
 This macro sets the TCP_NODELAY socket flag on the server
 as well as pushes it to connecting clients.  The TCP_NODELAY
 flag disables the Nagle algorithm on TCP sockets causing
 packets to be transmitted immediately with low latency,
 rather than waiting a short period of time in order
 to aggregate several packets into a larger containing
 packet.  In VPN applications over TCP, TCP_NODELAY
 is generally a good latency optimization.
 
 The macro expands as follows:
 
 .nf

 .ft 3
 .in +4

  if mode server:
    socket-flags TCP_NODELAY
    push "socket-flags TCP_NODELAY"

 .in -4

 .ft
 .fi
 .\"*********************************************************
 .TP

 .B --max-clients n
 Limit server to a maximum of
 .B n
 concurrent clients.
 .\"*********************************************************
 .TP
 .B --max-routes-per-client n
 Allow a maximum of
 .B n
 internal routes per client (default=256).
 This is designed to
 help contain DoS attacks where an authenticated client floods the
 server with packets appearing to come from many unique MAC addresses,
 forcing the server to deplete
 virtual memory as its internal routing table expands.
 This directive can be used in a
 .B --client-config-dir
 file or auto-generated by a
 .B --client-connect
 script to override the global value for a particular client.
 
 Note that this
 directive affects OpenVPN's internal routing table, not the
 kernel routing table.
 .\"*********************************************************
 .TP
 .B --connect-freq n sec
 Allow a maximum of
 .B n
 new connections per
 .B sec 
 seconds from clients.  This is designed to contain DoS attacks which flood
 the server with connection requests using certificates which
 will ultimately fail to authenticate.
 
 This is an imperfect solution however, because in a real
 DoS scenario, legitimate connections might also be refused.
 
 For the best protection against DoS attacks in server mode,
 use
 .B --proto udp
 and
 .B --tls-auth.
 .\"*********************************************************
 .TP
 .B --learn-address cmd
 Run script or shell command
 .B cmd
 to validate client virtual addresses or routes.
 
 .B cmd
 will be executed with 3 parameters:
 
 .B [1] operation --
 "add", "update", or "delete" based on whether or not
 the address is being added to, modified, or deleted from
 OpenVPN's internal routing table.
 .br
 .B [2] address --
 The address being learned or unlearned.  This can be
 an IPv4 address such as "198.162.10.14", an IPv4 subnet
 such as "198.162.10.0/24", or an ethernet MAC address (when
 .B --dev tap
 is being used) such as "00:FF:01:02:03:04".
 .br
 .B [3] common name --
 The common name on the certificate associated with the
 client linked to this address.  Only present for "add"
 or "update" operations, not "delete".
 
 On "add" or "update" methods, if the script returns
 a failure code (non-zero), OpenVPN will reject the address
 and will not modify its internal routing table.
 
 Normally, the
 .B cmd
 script will use the information provided above to set
 appropriate firewall entries on the VPN TUN/TAP interface.
 Since OpenVPN provides the association between virtual IP
 or MAC address and the client's authenticated common name,
 it allows a user-defined script to configure firewall access
 policies with regard to the client's high-level common name,
 rather than the low level client virtual addresses.
 .\"*********************************************************
 .TP
 .B --auth-user-pass-verify script method
 Require the client to provide a username/password (possibly
 in addition to a client certificate) for authentication.
 
 OpenVPN will execute
 .B script
 as a shell command to validate the username/password
 provided by the client.
 
 If
 .B method
 is set to "via-env", OpenVPN will call
 .B script
 with the environmental variables
 .B username
 and
 .B password
 set to the username/password strings provided by the client.
 Be aware that this method is insecure on some platforms which
 make the environment of a process publicly visible to other
 unprivileged processes.
 
 If
 .B method
 is set to "via-file", OpenVPN will write the username and
 password to the first two lines of a temporary file.  The filename
 will be passed as an argument to
 .B script,
 and the file will be automatically deleted by OpenVPN after
 the script returns.  The location of the temporary file is
 controlled by the
 .B --tmp-dir
 option, and will default to the current directory if unspecified.
 For security, consider setting 
 .B --tmp-dir
 to a volatile storage medium such as
 .B /dev/shm
 (if available) to prevent the username/password file from touching the hard drive.
 
 The script should examine the username
 and password,
 returning a success exit code (0) if the
 client's authentication request is to be accepted, or a failure
 code (1) to reject the client.
 
 This directive is designed to enable a plugin-style interface
 for extending OpenVPN's authentication capabilities.
 
 To protect against a client passing a maliciously formed
 username or password string, the username string must
 consist only of these characters: alphanumeric, underbar
 ('_'), dash ('-'), dot ('.'), or at ('@').  The password
 string can consist of any printable characters except for
 CR or LF.  Any illegal characters in either the username
 or password string will be converted to underbar ('_').
 
 Care must be taken by any user-defined scripts to avoid
 creating a security vulnerability in the way that these
 strings are handled.  Never use these strings in such a way
 that they might be escaped or evaluated by a shell interpreter.
 
 For a sample script that performs PAM authentication, see
 .B sample-scripts/auth-pam.pl
 in the OpenVPN source distribution.
 .\"*********************************************************
 .TP

 .B --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, tun-ipv6, ifconfig,
 comp-lzo, fragment, keydir, cipher, auth, keysize, secret,
 no-replay, no-iv, tls-auth, key-method, tls-server, and tls-client.
 
 This option requires that
 .B --disable-occ
 NOT be used.
 .\"*********************************************************
 .TP

 .B --auth-user-pass-optional
 Allow connections by clients that do not specify a username/password.
 Normally, when
 .B --auth-user-pass-verify
 or
 .B --management-client-auth
 is specified (or an authentication plugin module), the
 OpenVPN server daemon will require connecting clients to specify a
 username and password.  This option makes the submission of a username/password
 by clients optional, passing the responsibility to the user-defined authentication
 module/script to accept or deny the client based on other factors
 (such as the setting of X509 certificate fields).  When this option is used,
 and a connecting client does not submit a username/password, the user-defined
 authentication module/script will see the username and password as being set
 to empty strings ("").  The authentication module/script MUST have logic
 to detect this condition and respond accordingly.
 .\"*********************************************************
 .TP

 .B --client-cert-not-required
 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.
 
 If you use this directive, the
 entire responsibility of authentication will rest on your
 .B --auth-user-pass-verify
 script, so keep in mind that bugs in your script
 could potentially compromise the security of your VPN.
 
 If you don't use this directive, but you also specify an
 .B --auth-user-pass-verify
 script, then OpenVPN will perform double authentication.  The
 client certificate verification AND the
 .B --auth-user-pass-verify
 script will need to succeed in order for a client to be
 authenticated and accepted onto the VPN.
 .\"*********************************************************
 .TP
 .B --username-as-common-name
 For
 .B --auth-user-pass-verify
 authentication, use
 the authenticated username as the common name,
 rather than the common name from the client cert.
 .\"*********************************************************

 .TP

 .B --no-name-remapping
 Allow Common Name, X509 Subject, and username strings to include
 any printable character including space, but excluding control
 characters such as tab, newline, and carriage-return.
 
 By default, OpenVPN will remap
 any character other than alphanumeric, underbar ('_'), dash
 ('-'), dot ('.'), and slash ('/') to underbar ('_').  The X509
 Subject string as returned by the
 .B tls_id
 environmental variable, can additionally contain colon (':') or
 equal ('=').
 
 While name remapping is performed for security reasons to reduce
 the possibility of introducing string expansion security vulnerabilities
 in user-defined authentication
 scripts, this option is provided for those cases where it is desirable to
 disable the remapping feature.  Don't use this option unless you 
 know what you are doing!
 .\"*********************************************************
 .TP

 .B --port-share host port
 When run in TCP server mode, share the OpenVPN port with
 another application, such as an HTTPS server.  If OpenVPN
 senses a connection to its port which is using a non-OpenVPN
 protocol, it will proxy the connection to the server at
 .B host:port.

 Currently only designed to work with HTTP/HTTPS,

 though it would be theoretically possible to extend to
 other protocols such as ssh.
 

 Not implemented on Windows.

 .\"*********************************************************

 .SS Client Mode
 Use client mode when connecting to an OpenVPN server
 which has
 .B --server, --server-bridge,
 or
 .B --mode server
 in it's configuration.
 .\"*********************************************************
 .TP
 .B --client
 A helper directive designed to simplify the configuration
 of OpenVPN's client mode.  This directive is equivalent to:
 
 .nf

 .ft 3
 .in +4

  pull
  tls-client

 .in -4

 .ft
 .fi
 .\"*********************************************************
 .TP
 .B --pull
 This option must be used on a client which is connecting
 to a multi-client server.  It indicates to OpenVPN that it
 should accept options pushed by the server, provided they

 are part of the legal set of pushable options (note that the
 .B --pull
 option is implied by
 .B --client
 ).
 
 In particular,
 .B --pull
 allows the server to push routes to the client, so you should
 not use
 .B --pull
 or
 .B --client
 in situations where you don't trust the server to have control
 over the client's routing table.

 .\"*********************************************************
 .TP
 .B --auth-user-pass [up]
 Authenticate with server using username/password.
 .B up
 is a file containing username/password on 2 lines (Note: OpenVPN
 will only read passwords from a file if it has been built
 with the --enable-password-save configure option, or on Windows
 by defining ENABLE_PASSWORD_SAVE in config-win32.h).
 
 If
 .B up
 is omitted, username/password will be prompted from the
 console.
 
 The server configuration must specify an
 .B --auth-user-pass-verify
 script to verify the username/password provided by
 the client.
 .\"*********************************************************
 .TP
 .B --auth-retry type
 Controls how OpenVPN responds to username/password verification
 errors such as the client-side response to an AUTH_FAILED message from the server
 or verification failure of the private key password.
 
 Normally used to prevent auth errors from being fatal
 on the client side, and to permit username/password requeries in case
 of error.
 
 An AUTH_FAILED message is generated by the server if the client
 fails
 .B --auth-user-pass
 authentication, or if the server-side
 .B --client-connect
 script returns an error status when the client
 tries to connect.
 
 .B type
 can be one of:
 
 .B none --
 Client will exit with a fatal error (this is the default).
 .br
 .B nointeract --
 Client will retry the connection without requerying for an
 .B --auth-user-pass
 username/password.  Use this option for unattended clients.
 .br
 .B interact --
 Client will requery for an
 .B --auth-user-pass
 username/password and/or private key password before attempting a reconnection.
 
 Note that while this option cannot be pushed, it can be controlled
 from the management interface.
 .\"*********************************************************
 .TP
 .B --explicit-exit-notify [n]
 In UDP client mode or point-to-point mode, send server/peer an exit notification
 if tunnel is restarted or OpenVPN process is exited.  In client mode, on
 exit/restart, this
 option will tell the server to immediately close its client instance object
 rather than waiting for a timeout.  The
 .B n
 parameter (default=1) controls the maximum number of retries that the client
 will attempt to resend the exit notification message.
 .\"*********************************************************
 .SS Data Channel Encryption Options:
 These options are meaningful for both Static & TLS-negotiated key modes
 (must be compatible between peers).
 .\"*********************************************************
 .TP
 .B --secret file [direction]
 Enable Static Key encryption mode (non-TLS).
 Use pre-shared secret
 .B file
 which was generated with
 .B --genkey.
 
 The optional
 .B direction
 parameter enables the use of 4 distinct keys
 (HMAC-send, cipher-encrypt, HMAC-receive, cipher-decrypt), so that
 each data flow direction has a different set of HMAC and cipher keys.
 This has a number of desirable security properties including
 eliminating certain kinds of DoS and message replay attacks.
 
 When the
 .B direction
 parameter is omitted, 2 keys are used bidirectionally, one for HMAC
 and the other for encryption/decryption.
 
 The
 .B direction
 parameter should always be complementary on either side of the connection,
 i.e. one side should use "0" and the other should use "1", or both sides
 should omit it altogether.
 
 The
 .B direction
 parameter requires that
 .B file
 contains a 2048 bit key.  While pre-1.5 versions of OpenVPN
 generate 1024 bit key files, any version of OpenVPN which
 supports the
 .B direction
 parameter, will also support 2048 bit key file generation
 using the
 .B --genkey
 option.
 
 Static key encryption mode has certain advantages,
 the primary being ease of configuration.
 
 There are no certificates
 or certificate authorities or complicated negotiation handshakes and protocols.
 The only requirement is that you have a pre-existing secure channel with
 your peer (such as
 .B ssh
 ) to initially copy the key.  This requirement, along with the
 fact that your key never changes unless you manually generate a new one,
 makes it somewhat less secure than TLS mode (see below).  If an attacker
 manages to steal your key, everything that was ever encrypted with
 it is compromised.  Contrast that to the perfect forward secrecy features of
 TLS mode (using Diffie Hellman key exchange), where even if an attacker
 was able to steal your private key, he would gain no information to help
 him decrypt past sessions.
 
 Another advantageous aspect of Static Key encryption mode is that
 it is a handshake-free protocol 
 without any distinguishing signature or feature
 (such as a header or protocol handshake sequence) 
 that would mark the ciphertext packets as being
 generated by OpenVPN.  Anyone eavesdropping on the wire
 would see nothing
 but random-looking data.
 .\"*********************************************************
 .TP
 .B --auth alg
 Authenticate packets with HMAC using message
 digest algorithm
 .B alg.
 (The default is
 .B SHA1
 ).
 HMAC is a commonly used message authentication algorithm (MAC) that uses
 a data string, a secure hash algorithm, and a key, to produce
 a digital signature.
 
 OpenVPN's usage of HMAC is to first encrypt a packet, then HMAC the resulting ciphertext.
 
 In static-key encryption mode, the HMAC key
 is included in the key file generated by
 .B --genkey.
 In TLS mode, the HMAC key is dynamically generated and shared
 between peers via the TLS control channel.  If OpenVPN receives a packet with
 a bad HMAC it will drop the packet.
 HMAC usually adds 16 or 20 bytes per packet.
 Set
 .B alg=none
 to disable authentication.
 
 For more information on HMAC see
 .I http://www.cs.ucsd.edu/users/mihir/papers/hmac.html
 .\"*********************************************************
 .TP
 .B --cipher alg
 Encrypt packets with cipher algorithm
 .B alg.
 The default is
 .B BF-CBC,
 an abbreviation for Blowfish in Cipher Block Chaining mode.
 Blowfish has the advantages of being fast, very secure, and allowing key sizes
 of up to 448 bits.  Blowfish is designed to be used in situations where
 keys are changed infrequently.
 
 For more information on blowfish, see
 .I http://www.counterpane.com/blowfish.html
 
 To see other ciphers that are available with
 OpenVPN, use the
 .B --show-ciphers
 option.
 

 OpenVPN supports the CBC, CFB, and OFB cipher modes,
 however CBC is recommended and CFB and OFB should
 be considered advanced modes.

 
 Set
 .B alg=none
 to disable encryption.
 .\"*********************************************************
 .TP
 .B --keysize n
 Size of cipher key in bits (optional).
 If unspecified, defaults to cipher-specific default.  The
 .B --show-ciphers
 option (see below) shows all available OpenSSL ciphers,
 their default key sizes, and whether the key size can
 be changed.  Use care in changing a cipher's default
 key size.  Many ciphers have not been extensively
 cryptanalyzed with non-standard key lengths, and a
 larger key may offer no real guarantee of greater
 security, or may even reduce security.
 .\"*********************************************************
 .TP

 .B --prng alg [nsl]
 (Advanced) For PRNG (Pseudo-random number generator),
 use digest algorithm
 .B alg
 (default=sha1), and set
 .B nsl
 (default=16)
 to the size in bytes of the nonce secret length (between 16 and 64).
 
 Set
 .B alg=none
 to disable the PRNG and use the OpenSSL RAND_bytes function
 instead for all of OpenVPN's pseudo-random number needs.
 .\"*********************************************************
 .TP

 .B --engine [engine-name]
 Enable OpenSSL hardware-based crypto engine functionality.
 
 If
 .B engine-name
 is specified,
 use a specific crypto engine.  Use the
 .B --show-engines
 standalone option to list the crypto engines which are
 supported by OpenSSL.
 .\"*********************************************************
 .TP
 .B --no-replay

 (Advanced) Disable OpenVPN's protection against replay attacks.

 Don't use this option unless you are prepared to make
 a tradeoff of greater efficiency in exchange for less
 security.
 
 OpenVPN provides datagram replay protection by default.
 
 Replay protection is accomplished
 by tagging each outgoing datagram with an identifier
 that is guaranteed to be unique for the key being used.
 The peer that receives the datagram will check for
 the uniqueness of the identifier.  If the identifier
 was already received in a previous datagram, OpenVPN
 will drop the packet.  Replay protection is important
 to defeat attacks such as a SYN flood attack, where
 the attacker listens in the wire, intercepts a TCP
 SYN packet (identifying it by the context in which
 it occurs in relation to other packets), then floods
 the receiving peer with copies of this packet.
 
 OpenVPN's replay protection is implemented in slightly
 different ways, depending on the key management mode
 you have selected.
 
 In Static Key mode
 or when using an CFB or OFB mode cipher, OpenVPN uses a
 64 bit unique identifier that combines a time stamp with
 an incrementing sequence number.
 
 When using TLS mode for key exchange and a CBC cipher
 mode, OpenVPN uses only a 32 bit sequence number without
 a time stamp, since OpenVPN can guarantee the uniqueness
 of this value for each key.  As in IPSec, if the sequence number is
 close to wrapping back to zero, OpenVPN will trigger
 a new key exchange.
 
 To check for replays, OpenVPN uses
 the
 .I sliding window
 algorithm used
 by IPSec.
 .\"*********************************************************
 .TP
 .B --replay-window n [t]
 Use a replay protection sliding-window of size
 .B n
 and a time window of
 .B t
 seconds.
 
 By default
 .B n
 is 64 (the IPSec default) and
 .B t
 is 15 seconds.
 
 This option is only relevant in UDP mode, i.e.
 when either
 .B --proto udp
 is specifed, or no
 .B --proto
 option is specified.
 
 When OpenVPN tunnels IP packets over UDP, there is the possibility that
 packets might be dropped or delivered out of order.  Because OpenVPN, like IPSec,
 is emulating the physical network layer,
 it will accept an out-of-order packet sequence, and
 will deliver such packets in the same order they were received to
 the TCP/IP protocol stack, provided they satisfy several constraints.
 
 .B (a)
 The packet cannot be a replay (unless
 .B --no-replay
 is specified, which disables replay protection altogether).
 
 .B (b)
 If a packet arrives out of order, it will only be accepted if the difference
 between its sequence number and the highest sequence number received
 so far is less than
 .B n.
 
 .B (c)
 If a packet arrives out of order, it will only be accepted if it arrives no later
 than
 .B t
 seconds after any packet containing a higher sequence number.
 
 If you are using a network link with a large pipeline (meaning that
 the product of bandwidth and latency is high), you may want to use
 a larger value for
 .B n.
 Satellite links in particular often require this.
 
 If you run OpenVPN at
 .B --verb 4,
 you will see the message "Replay-window backtrack occurred [x]"
 every time the maximum sequence number backtrack seen thus far
 increases.  This can be used to calibrate
 .B n.
 
 There is some controversy on the appropriate method of handling packet
 reordering at the security layer.
 
 Namely, to what extent should the
 security layer protect the encapsulated protocol from attacks which masquerade
 as the kinds of normal packet loss and reordering that occur over IP networks?
 
 The IPSec and OpenVPN approach is to allow packet reordering within a certain
 fixed sequence number window.
 
 OpenVPN adds to the IPSec model by limiting the window size in time as well as
 sequence space.
 
 OpenVPN also adds TCP transport as an option (not offered by IPSec) in which
 case OpenVPN can adopt a very strict attitude towards message deletion and
 reordering:  Don't allow it.  Since TCP guarantees reliability, any packet
 loss or reordering event can be assumed to be an attack.
 
 In this sense, it could be argued that TCP tunnel transport is preferred when
 tunneling non-IP or UDP application protocols which might be vulnerable to a
 message deletion or reordering attack which falls within the normal
 operational parameters of IP networks.
 
 So I would make the statement that one should never tunnel a non-IP protocol
 or UDP application protocol over UDP, if the protocol might be vulnerable to a
 message deletion or reordering attack that falls within the normal operating
 parameters of what is to be expected from the physical IP layer.  The problem
 is easily fixed by simply using TCP as the VPN transport layer.
 .\"*********************************************************
 .TP
 .B --mute-replay-warnings
 Silence the output of replay warnings, which are a common
 false alarm on WiFi networks.  This option preserves
 the security of the replay protection code without
 the verbosity associated with warnings about duplicate
 packets.
 .\"*********************************************************
 .TP
 .B --replay-persist file
 Persist replay-protection state across sessions using
 .B file
 to save and reload the state.
 
 This option will strengthen protection against replay attacks,
 especially when you are using OpenVPN in a dynamic context (such
 as with
 .B --inetd)
 when OpenVPN sessions are frequently started and stopped. 
 
 This option will keep a disk copy of the current replay protection
 state (i.e. the most recent packet timestamp and sequence number
 received from the remote peer), so that if an OpenVPN session
 is stopped and restarted, it will reject any replays of packets
 which were already received by the prior session.
 
 This option only makes sense when replay protection is enabled
 (the default) and you are using either
 .B --secret
 (shared-secret key mode) or TLS mode with
 .B --tls-auth.
 .\"*********************************************************
 .TP
 .B --no-iv

 (Advanced) Disable OpenVPN's use of IV (cipher initialization vector).

 Don't use this option unless you are prepared to make
 a tradeoff of greater efficiency in exchange for less
 security.
 
 OpenVPN uses an IV by default, and requires it for CFB and
 OFB cipher modes (which are totally insecure without it).
 Using an IV is important for security when multiple
 messages are being encrypted/decrypted with the same key.
 
 IV is implemented differently depending on the cipher mode used.
 
 In CBC mode, OpenVPN uses a pseudo-random IV for each packet.
 
 In CFB/OFB mode, OpenVPN uses a unique sequence number and time stamp
 as the IV.  In fact, in CFB/OFB mode, OpenVPN uses a datagram
 space-saving optimization that uses the unique identifier for
 datagram replay protection as the IV.
 .\"*********************************************************
 .TP
 .B --test-crypto
 Do a self-test of OpenVPN's crypto options by encrypting and
 decrypting test packets using the data channel encryption options
 specified above.  This option does not require a peer to function,
 and therefore can be specified without
 .B --dev
 or
 .B --remote.
 
 The typical usage of
 .B --test-crypto
 would be something like this:
 
 .B openvpn --test-crypto --secret key
 
 or
 
 .B openvpn --test-crypto --secret key --verb 9
 
 This option is very useful to test OpenVPN after it has been ported to
 a new platform, or to isolate problems in the compiler, OpenSSL
 crypto library, or OpenVPN's crypto code.  Since it is a self-test mode,
 problems with encryption and authentication can be debugged independently
 of network and tunnel issues.
 .\"*********************************************************
 .SS TLS Mode Options:
 TLS mode is the most powerful crypto mode of OpenVPN in both security and flexibility.
 TLS mode works by establishing control and
 data channels which are multiplexed over a single TCP/UDP port.  OpenVPN initiates
 a TLS session over the control channel and uses it to exchange cipher
 and HMAC keys to protect the data channel.  TLS mode uses a robust reliability
 layer over the UDP connection for all control channel communication, while
 the data channel, over which encrypted tunnel data passes, is forwarded without
 any mediation.  The result is the best of both worlds: a fast data channel
 that forwards over UDP with only the overhead of encrypt,
 decrypt, and HMAC functions,
 and a control channel that provides all of the security features of TLS,
 including certificate-based authentication and Diffie Hellman forward secrecy.
 
 To use TLS mode, each peer that runs OpenVPN should have its own local
 certificate/key pair (
 .B --cert
 and
 .B --key
 ), signed by the root certificate which is specified
 in
 .B --ca.
 
 When two OpenVPN peers connect, each presents its local certificate to the
 other.  Each peer will then check that its partner peer presented a
 certificate which was signed by the master root certificate as specified in
 .B --ca.
 
 If that check on both peers succeeds, then the TLS negotiation
 will succeed, both OpenVPN
 peers will exchange temporary session keys, and the tunnel will begin
 passing data.
 
 The OpenVPN distribution contains a set of scripts for
 managing RSA certificates & keys,
 located in the
 .I easy-rsa
 subdirectory.
 
 The easy-rsa package is also rendered in web form here:
 .I http://openvpn.net/easyrsa.html
 .\"*********************************************************
 .TP
 .B --tls-server
 Enable TLS and assume server role during TLS handshake.  Note that
 OpenVPN is designed as a peer-to-peer application.  The designation
 of client or server is only for the purpose of negotiating the TLS
 control channel.
 .\"*********************************************************
 .TP
 .B --tls-client
 Enable TLS and assume client role during TLS handshake.
 .\"*********************************************************
 .TP
 .B --ca file
 Certificate authority (CA) file in .pem format, also referred to as the
 .I root
 certificate.  This file can have multiple
 certificates in .pem format, concatenated together.  You can construct your own
 certificate authority certificate and private key by using a command such as:
 

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

 
 Then edit your openssl.cnf file and edit the
 .B certificate
 variable to point to your new root certificate

 .B ca.crt.

 
 For testing purposes only, the OpenVPN distribution includes a sample

 CA certificate (ca.crt).

 Of course you should never use
 the test certificates and test keys distributed with OpenVPN in a
 production environment, since by virtue of the fact that
 they are distributed with OpenVPN, they are totally insecure.
 .\"*********************************************************
 .TP
 .B --dh file
 File containing Diffie Hellman parameters
 in .pem format (required for
 .B --tls-server
 only). Use
 
 .B openssl dhparam -out dh1024.pem 1024
 
 to generate your own, or use the existing dh1024.pem file
 included with the OpenVPN distribution.  Diffie Hellman parameters
 may be considered public.
 .\"*********************************************************
 .TP
 .B --cert file
 Local peer's signed certificate in .pem format -- must be signed
 by a certificate authority whose certificate is in
 .B --ca file.
 Each peer in an OpenVPN link running in TLS mode should have its own
 certificate and private key file.  In addition, each certificate should
 have been signed by the key of a certificate
 authority whose public key resides in the
 .B --ca
 certificate authority file.
 You can easily make your own certificate authority (see above) or pay money
 to use a commercial service such as thawte.com (in which case you will be
 helping to finance the world's second space tourist :).
 To generate a certificate,
 you can use a command such as:
 
 .B openssl req -nodes -new -keyout mycert.key -out mycert.csr
 
 If your certificate authority private key lives on another machine, copy
 the certificate signing request (mycert.csr) to this other machine (this can
 be done over an insecure channel such as email).  Now sign the certificate
 with a command such as:
 
 .B openssl ca -out mycert.crt -in mycert.csr
 
 Now copy the certificate (mycert.crt)
 back to the peer which initially generated the .csr file (this
 can be over a public medium).
 Note that the
 .B openssl ca
 command reads the location of the certificate authority key from its
 configuration file such as
 .B /usr/share/ssl/openssl.cnf
 -- note also
 that for certificate authority functions, you must set up the files
 .B index.txt
 (may be empty) and
 .B serial
 (initialize to
 .B 
 01
 ).
 .\"*********************************************************
 .TP
 .B --key file
 Local peer's private key in .pem format.  Use the private key which was generated
 when you built your peer's certificate (see
 .B -cert file
 above).
 .\"*********************************************************
 .TP
 .B --pkcs12 file
 Specify a PKCS #12 file containing local private key,
 local certificate, and root CA certificate.
 This option can be used instead of
 .B --ca, --cert,
 and
 .B --key.
 .\"*********************************************************
 .TP

 .B --pkcs11-cert-private [0|1]...
 Set if access to certificate object should be performed after login.
 Every provider has its own setting.
 .\"*********************************************************
 .TP
 .B --pkcs11-id name

 Specify the serialized certificate id to be used. The id can be gotten
 by the standalone
 .B --show-pkcs11-ids
 option.

 .\"*********************************************************
 .TP

 .B --pkcs11-id-management
 Acquire PKCS#11 id from management interface. In this case a NEED-STR 'pkcs11-id-request'
 real-time message will be triggered, application may use pkcs11-id-count command to
 retrieve available number of certificates, and pkcs11-id-get command to retrieve certificate
 id and certificate body.
 .\"*********************************************************
 .TP

 .B --pkcs11-pin-cache seconds
 Specify how many seconds the PIN can be cached, the default is until the token is removed.
 .\"*********************************************************
 .TP
 .B --pkcs11-protected-authentication [0|1]...
 Use PKCS#11 protected authentication path, useful for biometric and external
 keypad devices.
 Every provider has its own setting.
 .\"*********************************************************
 .TP

 .B --pkcs11-providers provider...
 Specify a RSA Security Inc. PKCS #11 Cryptographic Token Interface (Cryptoki) providers
 to load.
 This option can be used instead of
 .B --cert, --key,
 and
 .B --pkcs12.
 .\"*********************************************************
 .TP

 .B --pkcs11-private-mode mode...
 Specify which method to use in order to perform private key operations.
 A different mode can be specified for each provider.
 Mode is encoded as hex number, and can be a mask one of the following:

 .B 0

 (default) -- Try to determind automatically.
 .br

 .B 1
 -- Use sign.

 .br

 .B 2
 -- Use sign recover.

 .br

 .B 4
 -- Use decrypt.

 .br

 .B 8
 -- Use unwrap.

 .br
 .\"*********************************************************
 .TP

 .B --cryptoapicert select-string
 Load the certificate and private key from the
 Windows Certificate System Store (Windows Only).
 
 Use this option instead of
 .B --cert
 and
 .B --key.
 
 This makes
 it possible to use any smart card, supported by Windows, but also any
 kind of certificate, residing in the Cert Store, where you have access to
 the private key.  This option has been tested with a couple of different
 smart cards (GemSAFE, Cryptoflex, and Swedish Post Office eID) on the
 client side, and also an imported PKCS12 software certificate on the
 server side.
 
 To select a certificate, based on a substring search in the
 certificate's subject:
 
 .B cryptoapicert
 "SUBJ:Peter Runestig"
 
 To select a certificate, based on certificate's thumbprint:
 
 .B cryptoapicert
 "THUMB:f6 49 24 41 01 b4 ..."
 
 The thumbprint hex string can easily be copy-and-pasted from the Windows
 Certificate Store GUI.
 
 .\"*********************************************************
 .TP
 .B --key-method m
 Use data channel key negotiation method
 .B m.
 The key method must match on both sides of the connection.
 
 After OpenVPN negotiates a TLS session, a new set of keys
 for protecting the tunnel data channel is generated and
 exchanged over the TLS session.
 
 In method 1 (the default for OpenVPN 1.x), both sides generate
 random encrypt and HMAC-send keys which are forwarded to
 the other host over the TLS channel.
 
 In method 2, (the default for OpenVPN 2.0)
 the client generates a random key.  Both client
 and server also generate some random seed material.  All key source
 material is exchanged over the TLS channel. The actual
 keys are generated using the TLS PRF function, taking source
 entropy from both client and server.  Method 2 is designed to
 closely parallel the key generation process used by TLS 1.0.
 
 Note that in TLS mode, two separate levels 
 of keying occur:
 
 (1) The TLS connection is initially negotiated, with both sides
 of the connection producing certificates and verifying the certificate
 (or other authentication info provided) of
 the other side.  The
 .B --key-method
 parameter has no effect on this process.
 
 (2) After the TLS connection is established, the tunnel session keys are
 separately negotiated over the existing secure TLS channel.  Here,
 .B --key-method
 determines the derivation of the tunnel session keys.
 .\"*********************************************************
 .TP
 .B --tls-cipher l
 A list
 .B l
 of allowable TLS ciphers delimited by a colon (":").
 If you require a high level of security,
 you may want to set this parameter manually, to prevent a
 version rollback attack where a man-in-the-middle attacker tries
 to force two peers to negotiate to the lowest level
 of security they both support.
 Use
 .B --show-tls
 to see a list of supported TLS ciphers.
 .\"*********************************************************
 .TP
 .B --tls-timeout n
 Packet retransmit timeout on TLS control channel
 if no acknowledgment from remote within
 .B n
 seconds (default=2).  When OpenVPN sends a control
 packet to its peer, it will expect to receive an
 acknowledgement within
 .B n
 seconds or it will retransmit the packet, subject
 to a TCP-like exponential backoff algorithm.  This parameter
 only applies to control channel packets.  Data channel
 packets (which carry encrypted tunnel data) are never
 acknowledged, sequenced, or retransmitted by OpenVPN because
 the higher level network protocols running on top of the tunnel
 such as TCP expect this role to be left to them.
 .\"*********************************************************
 .TP
 .B --reneg-bytes n
 Renegotiate data channel key after
 .B n
 bytes sent or received (disabled by default).
 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.
 .\"*********************************************************
 .TP
 .B --reneg-pkts n
 Renegotiate data channel key after
 .B n
 packets sent and received (disabled by default).
 .\"*********************************************************
 .TP
 .B --reneg-sec n
 Renegotiate data channel key after
 .B n
 seconds (default=3600).

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

 .\"*********************************************************
 .TP
 .B --hand-window n
 Handshake Window -- the TLS-based key exchange must finalize within
 .B n
 seconds
 of handshake initiation by any peer (default = 60 seconds).
 If the handshake fails
 we will attempt to reset our connection with our peer and try again.
 Even in the event of handshake failure we will still use
 our expiring key for up to
 .B --tran-window
 seconds to maintain continuity of transmission of tunnel
 data.
 .\"*********************************************************
 .TP
 .B --tran-window n
 Transition window -- our old key can live this many seconds
 after a new a key renegotiation begins (default = 3600 seconds).
 This feature allows for a graceful transition from old to new
 key, and removes the key renegotiation sequence from the critical
 path of tunnel data forwarding.
 .\"*********************************************************
 .TP
 .B --single-session
 After initially connecting to a remote peer, disallow any new connections.
 Using this
 option means that a remote peer cannot connect, disconnect, and then
 reconnect.
 
 If the daemon is reset by a signal or
 .B --ping-restart,
 it will allow one new connection.
 
 .B --single-session
 can be used with
 .B --ping-exit
 or
 .B --inactive
 to create a single dynamic session that will exit when finished.
 .\"*********************************************************
 .TP
 .B --tls-exit
 Exit on TLS negotiation failure.
 .\"*********************************************************
 .TP
 .B --tls-auth file [direction]
 Add an additional layer of HMAC authentication on top of the TLS
 control channel to protect against DoS attacks.
 
 In a nutshell,
 .B --tls-auth
 enables a kind of "HMAC firewall" on OpenVPN's TCP/UDP port,
 where TLS control channel packets
 bearing an incorrect HMAC signature can be dropped immediately without
 response.
 
 .B file
 (required) is a key file which can be in one of two formats:
 
 .B (1)
 An OpenVPN static key file generated by
 .B --genkey
 (required if
 .B direction
 parameter is used).
 
 .B (2)
 A freeform passphrase file.  In this case the HMAC key will
 be derived by taking a secure hash of this file, similar to
 the
 .BR md5sum (1)
 or
 .BR sha1sum (1)
 commands.
 
 OpenVPN will first try format (1), and if the file fails to parse as
 a static key file, format (2) will be used.
 
 See the
 .B --secret
 option for more information on the optional
 .B direction
 parameter.
 
 .B --tls-auth
 is recommended when you are running OpenVPN in a mode where
 it is listening for packets from any IP address, such as when
 .B --remote
 is not specified, or
 .B --remote
 is specified with
 .B --float.
 
 The rationale for
 this feature is as follows.  TLS requires a multi-packet exchange
 before it is able to authenticate a peer.  During this time
 before authentication, OpenVPN is allocating resources (memory
 and CPU) to this potential peer.  The potential peer is also
 exposing many parts of OpenVPN and the OpenSSL library to the packets
 it is sending.  Most successful network attacks today seek
 to either exploit bugs in programs (such as buffer overflow attacks) or
 force a program to consume so many resources that it becomes unusable.
 Of course the first line of defense is always to produce clean,
 well-audited code.  OpenVPN has been written with buffer overflow
 attack prevention as a top priority.
 But as history has shown, many of the most widely used
 network applications have, from time to time,
 fallen to buffer overflow attacks.
 
 So as a second line of defense, OpenVPN offers
 this special layer of authentication on top of the TLS control channel so that
 every packet on the control channel is authenticated by an
 HMAC signature and a unique ID for replay protection.
 This signature will also help protect against DoS (Denial of Service) attacks.
 An important rule of thumb in reducing vulnerability to DoS attacks is to
 minimize the amount of resources a potential, but as yet unauthenticated,
 client is able to consume.
 
 .B --tls-auth
 does this by signing every TLS control channel packet with an HMAC signature,
 including packets which are sent before the TLS level has had a chance
 to authenticate the peer.
 The result is that packets without
 the correct signature can be dropped immediately upon reception,
 before they have a chance to consume additional system resources
 such as by initiating a TLS handshake.
 .B --tls-auth
 can be strengthened by adding the
 .B --replay-persist
 option which will keep OpenVPN's replay protection state
 in a file so that it is not lost across restarts.
 
 It should be emphasized that this feature is optional and that the
 passphrase/key file used with
 .B --tls-auth
 gives a peer nothing more than the power to initiate a TLS
 handshake.  It is not used to encrypt or authenticate any tunnel data.
 .\"*********************************************************
 .TP
 .B --askpass [file]
 Get certificate password from console or
 .B file
 before we daemonize.
 
 For the extremely
 security conscious, it is possible to protect your private key with
 a password.  Of course this means that every time the OpenVPN
 daemon is started you must be there to type the password.  The
 .B --askpass
 option allows you to start OpenVPN from the command line.  It will
 query you for a password before it daemonizes.  To protect a private
 key with a password you should omit the
 .B -nodes
 option when you use the
 .B openssl
 command line tool to manage certificates and private keys.
 
 If
 .B file
 is specified, read the password from the first line of
 .B file.
 Keep in mind that storing your password in a file
 to a certain extent invalidates the extra security provided by
 using an encrypted key (Note: OpenVPN
 will only read passwords from a file if it has been built
 with the --enable-password-save configure option, or on Windows
 by defining ENABLE_PASSWORD_SAVE in config-win32.h).
 .\"*********************************************************
 .TP
 .B --auth-nocache
 Don't cache
 .B --askpass
 or
 .B --auth-user-pass
 username/passwords in virtual memory.
 
 If specified, this directive will cause OpenVPN to immediately
 forget username/password inputs after they are used.  As a result,
 when OpenVPN needs a username/password, it will prompt for input
 from stdin, which may be multiple times during the duration of an
 OpenVPN session.
 
 This directive does not affect the
 .B --http-proxy
 username/password.  It is always cached.
 .\"*********************************************************
 .TP
 .B --tls-verify cmd
 Execute shell command
 .B cmd
 to verify the X509 name of a
 pending TLS connection that has otherwise passed all other
 tests of certification (except for revocation via
 .B --crl-verify
 directive; the revocation test occurs after the
 .B --tls-verify
 test).
 
 .B cmd
 should return 0 to allow the TLS handshake to proceed, or 1 to fail.
 .B cmd
 is executed as
 
 .B cmd certificate_depth X509_NAME_oneline
 
 This feature is useful if the peer you want to trust has a certificate
 which was signed by a certificate authority who also signed many
 other certificates, where you don't necessarily want to trust all of them,
 but rather be selective about which
 peer certificate you will accept.  This feature allows you to write a script
 which will test the X509 name on a certificate and decide whether or
 not it should be accepted.  For a simple perl script which will test
 the common name field on the certificate, see the file
 .B verify-cn
 in the OpenVPN distribution.
 
 See the "Environmental Variables" section below for
 additional parameters passed as environmental variables.
 
 Note that
 .B cmd
 can be a shell command with multiple arguments, in which
 case all OpenVPN-generated arguments will be appended
 to
 .B cmd
 to build a command line which will be passed to the script.
 .\"*********************************************************
 .TP
 .B --tls-remote name
 Accept connections only from a host with X509 name
 or common name equal to
 .B name.
 The remote host must also pass all other tests
 of verification.
 
 Name can also be a common name prefix, for example if you
 want a client to only accept connections to "Server-1",
 "Server-2", etc., you can simply use
 .B --tls-remote Server
 
 Using a common name prefix is a useful alternative to managing
 a CRL (Certificate Revocation List) on the client, since it allows the client
 to refuse all certificates except for those associated
 with designated servers.
 
 .B --tls-remote
 is a useful replacement for the
 .B --tls-verify
 option to verify the remote host, because
 .B --tls-remote
 works in a
 .B --chroot
 environment too.
 .\"*********************************************************
 .TP
 .B --ns-cert-type client|server
 Require that peer certificate was signed with an explicit
 .B nsCertType
 designation of "client" or "server".
 
 This is a useful security option for clients, to ensure that
 the host they connect with is a designated server.
 
 See the easy-rsa/build-key-server script for an example
 of how to generate a certificate with the
 .B nsCertType
 field set to "server".
 
 If the server certificate's nsCertType field is set
 to "server", then the clients can verify this with
 .B --ns-cert-type server.
 
 This is an important security precaution to protect against
 a man-in-the-middle attack where an authorized client
 attempts to connect to another client by impersonating the server.
 The attack is easily prevented by having clients verify
 the server certificate using any one of
 .B --ns-cert-type, --tls-remote,
 or
 .B --tls-verify.
 .\"*********************************************************
 .TP

 .B --remote-cert-ku v...
 Require that peer certificate was signed with an explicit
 .B key usage.
 

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

 
 The key usage should be encoded in hex, more than one key
 usage can be specified.
 .\"*********************************************************
 .TP
 .B --remote-cert-eku oid
 Require that peer certificate was signed with an explicit
 .B extended key usage.
 

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

 
 The extended key usage should be encoded in oid notation, or
 OpenSSL symbolic representation.
 .\"*********************************************************
 .TP
 .B --remote-cert-tls client|server
 Require that peer certificate was signed with an explicit
 .B key usage
 and
 .B extended key usage

 based on RFC3280 TLS rules.

 
 This is a useful security option for clients, to ensure that

 the host they connect to is a designated server.

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

 .B
 --remote-cert-ku 80 08 88 --remote-cert-eku "TLS Web Client Authentication"

 The key usage is digitalSignature and/or keyAgreement.
 

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

 .B

 --remote-cert-ku a0 88 --remote-cert-eku "TLS Web Server Authentication"
 
 The key usage is digitalSignature and ( keyEncipherment or keyAgreement ).

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

 .B --crl-verify crl
 Check peer certificate against the file
 .B crl
 in PEM format.
 
 A CRL (certificate revocation list) is used when a particular key is
 compromised but when the overall PKI is still intact.
 
 Suppose you had a PKI consisting of a CA, root certificate, and a number of
 client certificates.  Suppose a laptop computer containing a client key and
 certificate was stolen.  By adding the stolen certificate to the CRL file,
 you could reject any connection which attempts to use it, while preserving the
 overall integrity of the PKI.
 
 The only time when it would be necessary to rebuild the entire PKI from scratch would be
 if the root certificate key itself was compromised.
 .\"*********************************************************
 .SS SSL Library information:
 .\"*********************************************************
 .TP
 .B --show-ciphers
 (Standalone)
 Show all cipher algorithms to use with the
 .B --cipher
 option.
 .\"*********************************************************
 .TP
 .B --show-digests
 (Standalone)
 Show all message digest algorithms to use with the
 .B --auth
 option.
 .\"*********************************************************
 .TP
 .B --show-tls
 (Standalone)
 Show all TLS ciphers (TLS used only as a control channel).  The TLS
 ciphers will be sorted from highest preference (most secure) to
 lowest.
 .\"*********************************************************
 .TP
 .B --show-engines
 (Standalone)
 Show currently available hardware-based crypto acceleration
 engines supported by the OpenSSL library.
 .\"*********************************************************
 .SS Generate a random key:
 Used only for non-TLS static key encryption mode.
 .\"*********************************************************
 .TP
 .B --genkey
 (Standalone)
 Generate a random key to be used as a shared secret,
 for use with the
 .B --secret
 option.  This file must be shared with the
 peer over a pre-existing secure channel such as
 .BR scp (1)
 .
 .\"*********************************************************
 .TP
 .B --secret file
 Write key to
 .B file.
 .\"*********************************************************
 .SS TUN/TAP persistent tunnel config mode:
 Available with linux 2.4.7+.  These options comprise a standalone mode
 of OpenVPN which can be used to create and delete persistent tunnels.
 .\"*********************************************************
 .TP
 .B --mktun
 (Standalone)
 Create a persistent tunnel on platforms which support them such
 as Linux.  Normally TUN/TAP tunnels exist only for
 the period of time that an application has them open.  This option
 takes advantage of the TUN/TAP driver's ability to build persistent
 tunnels that live through multiple instantiations of OpenVPN and die
 only when they are deleted or the machine is rebooted.
 
 One of the advantages of persistent tunnels is that they eliminate the
 need for separate
 .B --up
 and
 .B --down
 scripts to run the appropriate
 .BR ifconfig (8)
 and
 .BR route (8)
 commands.  These commands can be placed in the the same shell script
 which starts or terminates an OpenVPN session.
 
 Another advantage is that open connections through the TUN/TAP-based tunnel
 will not be reset if the OpenVPN peer restarts.  This can be useful to
 provide uninterrupted connectivity through the tunnel in the event of a DHCP
 reset of the peer's public IP address (see the
 .B --ipchange
 option above).
 
 One disadvantage of persistent tunnels is that it is harder to automatically
 configure their MTU value (see
 .B --link-mtu
 and
 .B --tun-mtu
 above).
 
 On some platforms such as Windows, TAP-Win32 tunnels are persistent by
 default.
 .\"*********************************************************
 .TP
 .B --rmtun
 (Standalone)
 Remove a persistent tunnel.
 .\"*********************************************************
 .TP
 .B --dev tunX | tapX
 TUN/TAP device
 .\"*********************************************************

 .TP
 .B --user user
 Optional user to be owner of this tunnel.
 .\"*********************************************************
 .TP
 .B --group group
 Optional group to be owner of this tunnel.
 .\"*********************************************************

 .SS Windows-Specific Options:
 .\"*********************************************************
 .TP

 .B --win-sys path|'env'
 Set the Windows system directory pathname to use when looking for system
 executables such as
 .B route.exe
 and
 .B netsh.exe.
 By default, if this directive is
 not specified, the pathname will be set to "C:\\WINDOWS"
 
 The special string
 .B 'env'
 indicates that the pathname should be read from the
 .B SystemRoot
 environmental variable.
 .\"*********************************************************
 .TP

 .B --ip-win32 method
 When using
 .B --ifconfig
 on Windows, set the TAP-Win32 adapter
 IP address and netmask using
 .B method.
 Don't use this option unless you are also using
 .B --ifconfig.
 
 .B manual --
 Don't set the IP address or netmask automatically.
 Instead output a message
 to the console telling the user to configure the
 adapter manually and indicating the IP/netmask which
 OpenVPN expects the adapter to be set to.
 
 .B dynamic [offset] [lease-time] --

 Automatically set the IP address and netmask by replying to

 DHCP query messages generated by the kernel.  This mode is
 probably the "cleanest" solution
 for setting the TCP/IP properties since it uses the well-known
 DHCP protocol.  There are, however, two prerequisites for using
 this mode: (1) The TCP/IP properties for the TAP-Win32
 adapter must be set to "Obtain an IP address automatically," and
 (2) OpenVPN needs to claim an IP address in the subnet for use
 as the virtual DHCP server address.  By default in
 .B --dev tap
 mode, OpenVPN will
 take the normally unused first address in the subnet.  For example,
 if your subnet is 192.168.4.0 netmask 255.255.255.0, then
 OpenVPN will take the IP address 192.168.4.0 to use as the
 virtual DHCP server address.  In
 .B --dev tun
 mode, OpenVPN will cause the DHCP server to masquerade as if it were
 coming from the remote endpoint.  The optional offset parameter is
 an integer which is > -256 and < 256 and which defaults to 0.
 If offset is positive, the DHCP server will masquerade as the IP
 address at network address + offset.
 If offset is negative, the DHCP server will masquerade as the IP
 address at broadcast address + offset.  The Windows
 .B ipconfig /all
 command can be used to show what Windows thinks the DHCP server
 address is.  OpenVPN will "claim" this address, so make sure to
 use a free address.  Having said that, different OpenVPN instantiations,
 including different ends of the same connection, can share the same
 virtual DHCP server address.  The
 .B lease-time
 parameter controls the lease time of the DHCP assignment given to
 the TAP-Win32 adapter, and is denoted in seconds.
 Normally a very long lease time is preferred
 because it prevents routes involving the TAP-Win32 adapter from
 being lost when the system goes to sleep.  The default
 lease time is one year.
 
 .B netsh --
 Automatically set the IP address and netmask using
 the Windows command-line "netsh"
 command.  This method appears to work correctly on
 Windows XP but not Windows 2000.
 
 .B ipapi --
 Automatically set the IP address and netmask using the
 Windows IP Helper API.  This approach
 does not have ideal semantics, though testing has indicated
 that it works okay in practice.  If you use this option,
 it is best to leave the TCP/IP properties for the TAP-Win32
 adapter in their default state, i.e. "Obtain an IP address
 automatically."

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

 .\"*********************************************************
 .TP
 .B --route-method m
 Which method
 .B m
 to use for adding routes on Windows?
 

 .B adaptive
 (default) -- Try IP helper API first.  If that fails, fall
 back to the route.exe shell command.
 .br

 .B ipapi

 -- Use IP helper API.

 .br
 .B exe
 -- Call the route.exe shell command.
 .\"*********************************************************
 .TP
 .B --dhcp-option type [parm]
 Set extended TAP-Win32 TCP/IP properties, must
 be used with

 .B --ip-win32 dynamic
 or
 .B --ip-win32 adaptive.

 This option can be used to set additional TCP/IP properties
 on the TAP-Win32 adapter, and is particularly useful for
 configuring an OpenVPN client to access a Samba server
 across the VPN.
 
 .B DOMAIN name --
 Set Connection-specific DNS Suffix.
 
 .B DNS addr --
 Set primary domain name server address.  Repeat
 this option to set secondary DNS server addresses.
 
 .B WINS addr --
 Set primary WINS server address (NetBIOS over TCP/IP Name Server).
 Repeat this option to set secondary WINS server addresses.
 
 .B NBDD addr --
 Set primary NBDD server address (NetBIOS over TCP/IP Datagram Distribution Server)
 Repeat this option
 to set secondary NBDD server addresses.
 
 .B NTP addr --
 Set primary NTP server address (Network Time Protocol).
 Repeat this option
 to set secondary NTP server addresses.
 
 .B NBT type --
 Set NetBIOS over TCP/IP Node type.  Possible options:
 .B 1
 = b-node (broadcasts),
 .B 2
 = p-node (point-to-point
 name queries to a WINS server),
 .B 4
 = m-node (broadcast
 then query name server), and
 .B 8
 = h-node (query name server, then broadcast).
 
 .B NBS scope-id --
 Set NetBIOS over TCP/IP Scope. A NetBIOS Scope ID provides an extended
 naming service for the NetBIOS over TCP/IP (Known as NBT) module. The
 primary purpose of a NetBIOS scope ID is to isolate NetBIOS traffic on
 a single network to only those nodes with the same NetBIOS scope ID.
 The NetBIOS scope ID is a character string that is appended to the NetBIOS
 name. The NetBIOS scope ID on two hosts must match, or the two hosts
 will not be able to communicate. The NetBIOS Scope ID also allows
 computers to use the same computer name, as they have different
 scope IDs. The Scope ID becomes a part of the NetBIOS name, making the name unique.
 (This description of NetBIOS scopes courtesy of NeonSurge@abyss.com)
 
 .B DISABLE-NBT --
 Disable Netbios-over-TCP/IP.
 
 Note that if
 .B --dhcp-option
 is pushed via
 .B --push
 to a non-windows client, the option will be saved in the client's
 environment before the up script is called, under
 the name "foreign_option_{n}".
 .\"*********************************************************
 .TP
 .B --tap-sleep n
 Cause OpenVPN to sleep for
 .B n
 seconds immediately after the TAP-Win32 adapter state
 is set to "connected".
 
 This option is intended to be used to troubleshoot problems
 with the
 .B --ifconfig
 and
 .B --ip-win32
 options, and is used to give
 the TAP-Win32 adapter time to come up before
 Windows IP Helper API operations are applied to it.
 .\"*********************************************************
 .TP
 .B --show-net-up
 Output OpenVPN's view of the system routing table and network
 adapter list to the syslog or log file after the TUN/TAP adapter
 has been brought up and any routes have been added.
 .\"*********************************************************
 .TP
 .B --dhcp-renew
 Ask Windows to renew the TAP adapter lease on startup.
 This option is normally unnecessary, as Windows automatically
 triggers a DHCP renegotiation on the TAP adapter when it
 comes up, however if you set the TAP-Win32 adapter
 Media Status property to "Always Connected", you may need this
 flag.
 .\"*********************************************************
 .TP
 .B --dhcp-release
 Ask Windows to release the TAP adapter lease on shutdown.
 This option has the same caveats as
 .B --dhcp-renew
 above.
 .\"*********************************************************
 .TP
 .B --pause-exit
 Put up a "press any key to continue" message on the console prior
 to OpenVPN program exit.  This option is automatically used by the
 Windows explorer when OpenVPN is run on a configuration
 file using the right-click explorer menu.
 .\"*********************************************************
 .TP
 .B --service exit-event [0|1]
 Should be used when OpenVPN is being automatically executed by another
 program in such
 a context that no interaction with the user via display or keyboard
 is possible.  In general, end-users should never need to explicitly
 use this option, as it is automatically added by the OpenVPN service wrapper
 when a given OpenVPN configuration is being run as a service.
 
 .B exit-event
 is the name of a Windows global event object, and OpenVPN will continuously
 monitor the state of this event object and exit when it becomes signaled.
 
 The second parameter indicates the initial state of
 .B exit-event
 and normally defaults to 0.
 
 Multiple OpenVPN processes can be simultaneously executed with the same
 .B exit-event
 parameter.  In any case, the controlling process can signal
 .B exit-event,
 causing all such OpenVPN processes to exit.
 
 When executing an OpenVPN process using the
 .B --service
 directive, OpenVPN will probably not have a console
 window to output status/error
 messages, therefore it is useful to use
 .B --log
 or
 .B --log-append
 to write these messages to a file.
 .\"*********************************************************
 .TP
 .B --show-adapters
 (Standalone)
 Show available TAP-Win32 adapters which can be selected using the
 .B --dev-node
 option.  On non-Windows systems, the
 .BR ifconfig (8)
 command provides similar functionality.
 .\"*********************************************************
 .TP

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

 .B --show-valid-subnets
 (Standalone)
 Show valid subnets for
 .B --dev tun
 emulation.  Since the TAP-Win32 driver
 exports an ethernet interface to Windows, and since TUN devices are
 point-to-point in nature, it is necessary for the TAP-Win32 driver
 to impose certain constraints on TUN endpoint address selection.
 
 Namely, the point-to-point endpoints used in TUN device emulation
 must be the middle two addresses of a /30 subnet (netmask 255.255.255.252).
 .\"*********************************************************
 .TP
 .B --show-net
 (Standalone)
 Show OpenVPN's view of the system routing table and network
 adapter list.
 .\"*********************************************************

 .SS PKCS#11 Standalone Options:
 .\"*********************************************************
 .TP

 .B --show-pkcs11-ids provider [cert_private]

 (Standalone)

 Show PKCS#11 token object list. Specify cert_private as 1
 if certificates are stored as private objects.
 
 .B --verb
 option can be used BEFORE this option to produce debugging information.

 .\"*********************************************************

 .SH SCRIPTING AND ENVIRONMENTAL VARIABLES
 OpenVPN exports a series
 of environmental variables for use by user-defined scripts.
 .\"*********************************************************
 .SS Script Order of Execution
 .\"*********************************************************
 .TP
 .B --up
 Executed after TCP/UDP socket bind and TUN/TAP open.
 .\"*********************************************************
 .TP
 .B --tls-verify
 Executed when we have a still untrusted remote peer.
 .\"*********************************************************
 .TP
 .B --ipchange
 Executed after connection authentication, or remote IP address change.
 .\"*********************************************************
 .TP
 .B --client-connect
 Executed in
 .B --mode server
 mode immediately after client authentication.
 .\"*********************************************************
 .TP
 .B --route-up
 Executed after connection authentication, either
 immediately after, or some number of seconds after
 as defined by the
 .B --route-delay
 option.
 .\"*********************************************************
 .TP
 .B --client-disconnect
 Executed in
 .B --mode server
 mode on client instance shutdown.
 .\"*********************************************************
 .TP
 .B --down
 Executed after TCP/UDP and TUN/TAP close.
 .\"*********************************************************
 .TP
 .B --learn-address
 Executed in
 .B --mode server
 mode whenever an IPv4 address/route or MAC address is added to OpenVPN's
 internal routing table.
 .\"*********************************************************
 .TP
 .B --auth-user-pass-verify
 Executed in
 .B --mode server
 mode on new client connections, when the client is
 still untrusted.
 .\"*********************************************************
 .SS String Types and Remapping
 In certain cases, OpenVPN will perform remapping of characters
 in strings.  Essentially, any characters outside the set of
 permitted characters for each string type will be converted
 to underbar ('_').
 
 .B Q:
 Why is string remapping necessary?
 
 .B A:
 It's an important security feature to prevent the malicious coding of
 strings from untrusted sources to be passed as parameters to scripts,
 saved in the environment, used as a common name, translated to a filename,
 etc.
 

 .B Q:
 Can string remapping be disabled?
 
 .B A:
 Yes, by using the
 .B --no-name-remapping
 option, however this should be considered an advanced option.
 

 Here is a brief rundown of OpenVPN's current string types and the 
 permitted character class for each string:
 
 .B X509 Names:
 Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), at 
 ('@'), colon (':'), slash ('/'), and equal ('=').  Alphanumeric is defined 
 as a character which will cause the C library isalnum() function to return 
 true.
 
 .B Common Names:
 Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), and at                
 ('@').
 
 .B --auth-user-pass username:
 Same as Common Name, with one exception: starting with OpenVPN 2.0.1,
 the username is passed to the OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY plugin in its raw form,
 without string remapping.
 
 .B --auth-user-pass password:
 Any "printable" character except CR or LF.  
 Printable is defined to be a character which will cause the C library 
 isprint() function to return true.
 
 .B --client-config-dir filename as derived from common name or username:
 Alphanumeric, underbar ('_'), dash ('-'), and dot ('.') except for "." or 
 ".." as standalone strings.  As of 2.0.1-rc6, the at ('@') character has
 been added as well for compatibility with the common name character class.
 
 .B Environmental variable names:
 Alphanumeric or underbar ('_').
 
 .B Environmental variable values:
 Any printable character.
 
 For all cases, characters in a string which are not members of the legal 
 character class for that string type will be remapped to underbar ('_').
 .\"*********************************************************
 .SS Environmental Variables
 Once set, a variable is persisted
 indefinitely until it is reset by a new value or a restart,
 
 As of OpenVPN 2.0-beta12, in server mode, environmental
 variables set by OpenVPN
 are scoped according to the client objects
 they are
 associated with, so there should not be any issues with
 scripts having access to stale, previously set variables
 which refer to different client instances.
 .\"*********************************************************
 .TP
 .B bytes_received
 Total number of bytes received from client during VPN session.
 Set prior to execution of the
 .B --client-disconnect
 script.
 .\"*********************************************************
 .TP
 .B bytes_sent
 Total number of bytes sent to client during VPN session.
 Set prior to execution of the
 .B --client-disconnect
 script.
 .\"*********************************************************
 .TP
 .B common_name
 The X509 common name of an authenticated client.
 Set prior to execution of
 .B --client-connect, --client-disconnect,
 and
 .B --auth-user-pass-verify
 scripts.
 .\"*********************************************************
 .TP
 .B config
 Name of first
 .B --config
 file.
 Set on program initiation and reset on SIGHUP.
 .\"*********************************************************
 .TP
 .B daemon
 Set to "1" if the
 .B --daemon
 directive is specified, or "0" otherwise.
 Set on program initiation and reset on SIGHUP.
 .\"*********************************************************
 .TP
 .B daemon_log_redirect
 Set to "1" if the
 .B --log
 or
 .B --log-append
 directives are specified, or "0" otherwise.
 Set on program initiation and reset on SIGHUP.
 .\"*********************************************************
 .TP
 .B dev
 The actual name of the TUN/TAP device, including
 a unit number if it exists.
 Set prior to
 .B --up
 or
 .B --down
 script execution.
 .\"*********************************************************
 .TP
 .B foreign_option_{n}
 An option pushed via
 .B --push
 to a client which does not natively support it,
 such as
 .B --dhcp-option
 on a non-Windows system, will be recorded to this
 environmental variable sequence prior to
 .B --up
 script execution.
 .\"*********************************************************
 .TP
 .B ifconfig_broadcast
 The broadcast address for the virtual
 ethernet segment which is derived from the
 .B --ifconfig
 option when
 .B --dev tap
 is used.
 Set prior to OpenVPN calling the
 .I ifconfig
 or
 .I netsh
 (windows version of ifconfig) commands which
 normally occurs prior to
 .B --up
 script execution.
 .\"*********************************************************
 .TP
 .B ifconfig_local
 The local VPN endpoint IP address specified in the
 .B --ifconfig
 option (first parameter).
 Set prior to OpenVPN calling the
 .I ifconfig
 or
 .I netsh
 (windows version of ifconfig) commands which
 normally occurs prior to
 .B --up
 script execution.
 .\"*********************************************************
 .TP
 .B ifconfig_remote
 The remote VPN endpoint IP address specified in the
 .B --ifconfig
 option (second parameter) when
 .B --dev tun
 is used.
 Set prior to OpenVPN calling the
 .I ifconfig
 or
 .I netsh
 (windows version of ifconfig) commands which
 normally occurs prior to
 .B --up
 script execution.
 .\"*********************************************************
 .TP
 .B ifconfig_netmask
 The subnet mask of the virtual ethernet segment
 that is specified as the second parameter to
 .B --ifconfig
 when
 .B --dev tap
 is being used.
 Set prior to OpenVPN calling the
 .I ifconfig
 or
 .I netsh
 (windows version of ifconfig) commands which
 normally occurs prior to
 .B --up
 script execution.
 .\"*********************************************************
 .TP
 .B ifconfig_pool_local_ip
 The local
 virtual IP address for the TUN/TAP tunnel taken from an
 .B --ifconfig-push
 directive if specified, or otherwise from
 the ifconfig pool (controlled by the
 .B --ifconfig-pool
 config file directive).
 Only set for
 .B --dev tun
 tunnels.
 This option is set on the server prior to execution
 of the
 .B --client-connect
 and
 .B --client-disconnect
 scripts.
 .\"*********************************************************
 .TP
 .B ifconfig_pool_netmask
 The
 virtual IP netmask for the TUN/TAP tunnel taken from an
 .B --ifconfig-push
 directive if specified, or otherwise from
 the ifconfig pool (controlled by the
 .B --ifconfig-pool
 config file directive).
 Only set for
 .B --dev tap
 tunnels.
 This option is set on the server prior to execution
 of the
 .B --client-connect
 and
 .B --client-disconnect
 scripts.
 .\"*********************************************************
 .TP
 .B ifconfig_pool_remote_ip
 The remote
 virtual IP address for the TUN/TAP tunnel taken from an
 .B --ifconfig-push
 directive if specified, or otherwise from
 the ifconfig pool (controlled by the
 .B --ifconfig-pool
 config file directive).
 This option is set on the server prior to execution
 of the
 .B --client-connect
 and
 .B --client-disconnect
 scripts.
 .\"*********************************************************
 .TP
 .B link_mtu
 The maximum packet size (not including the IP header)
 of tunnel data in UDP tunnel transport mode.
 Set prior to
 .B --up
 or
 .B --down
 script execution.
 .\"*********************************************************
 .TP
 .B local
 The
 .B --local
 parameter.
 Set on program initiation and reset on SIGHUP.
 .\"*********************************************************
 .TP
 .B local_port
 The local port number, specified by
 .B --port
 or
 .B --lport.
 Set on program initiation and reset on SIGHUP.
 .\"*********************************************************
 .TP
 .B password
 The password provided by a connecting client.
 Set prior to
 .B --auth-user-pass-verify
 script execution only when the
 .B via-env
 modifier is specified, and deleted from the environment
 after the script returns.
 .\"*********************************************************
 .TP
 .B proto
 The
 .B --proto
 parameter.
 Set on program initiation and reset on SIGHUP.
 .\"*********************************************************
 .TP
 .B remote_{n}
 The
 .B --remote
 parameter.
 Set on program initiation and reset on SIGHUP.
 .\"*********************************************************
 .TP
 .B remote_port_{n}
 The remote port number, specified by
 .B --port
 or
 .B --rport.
 Set on program initiation and reset on SIGHUP.
 .\"*********************************************************
 .TP
 .B route_net_gateway
 The pre-existing default IP gateway in the system routing
 table.
 Set prior to
 .B --up
 script execution.
 .\"*********************************************************
 .TP
 .B route_vpn_gateway
 The default gateway used by
 .B --route
 options, as specified in either the
 .B --route-gateway
 option or the second parameter to
 .B --ifconfig
 when
 .B --dev tun
 is specified.
 Set prior to
 .B --up
 script execution.
 .\"*********************************************************
 .TP
 .B route_{parm}_{n}
 A set of variables which define each route to be added, and
 are set prior to
 .B --up
 script execution.
 
 .B parm
 will be one of "network", "netmask", "gateway", or "metric".
 
 .B n
 is the OpenVPN route number, starting from 1.
 
 If the network or gateway are resolvable DNS names,
 their IP address translations will be recorded rather
 than their names as denoted on the command line
 or configuration file.
 .\"*********************************************************
 .TP
 .B script_context
 Set to "init" or "restart" prior to up/down script execution.
 For more information, see
 documentation for
 .B --up.
 .\"*********************************************************
 .TP
 .B script_type
 One of
 .B up, down, ipchange, route-up, tls-verify, auth-user-pass-verify,
 .B client-connect, client-disconnect, 
 or
 .B learn-address.
 Set prior to execution of any script.
 .\"*********************************************************
 .TP
 .B signal
 The reason for exit or restart.  Can be one of
 .B sigusr1, sighup, sigterm, sigint, inactive
 (controlled by
 .B --inactive
 option),
 .B ping-exit
 (controlled by
 .B --ping-exit
 option),
 .B ping-restart
 (controlled by
 .B --ping-restart
 option),
 .B connection-reset
 (triggered on TCP connection reset),
 .B error,
 or
 .B unknown
 (unknown signal).  This variable is set just prior to down script execution.
 .\"*********************************************************
 .TP

 .B time_ascii
 Client connection timestamp, formatted as a human-readable
 time string.
 Set prior to execution of the
 .B --client-connect
 script.
 .\"*********************************************************
 .TP
 .B time_duration
 The duration (in seconds) of the client session which is now
 disconnecting.
 Set prior to execution of the
 .B --client-disconnect
 script.
 .\"*********************************************************
 .TP
 .B time_unix
 Client connection timestamp, formatted as a unix integer
 date/time value.
 Set prior to execution of the
 .B --client-connect
 script.
 .\"*********************************************************
 .TP

 .B tls_id_{n}
 A series of certificate fields from the remote peer,
 where
 .B n
 is the verification level.  Only set for TLS connections.  Set prior
 to execution of
 .B --tls-verify
 script.
 .\"*********************************************************
 .TP
 .B tls_serial_{n}
 The serial number of the certificate from the remote peer,
 where
 .B n
 is the verification level.  Only set for TLS connections.  Set prior
 to execution of
 .B --tls-verify
 script.
 .\"*********************************************************
 .TP
 .B tun_mtu
 The MTU of the TUN/TAP device.
 Set prior to
 .B --up
 or
 .B --down
 script execution.
 .\"*********************************************************
 .TP
 .B trusted_ip
 Actual IP address of connecting client or peer which has been authenticated.
 Set prior to execution of
 .B --ipchange, --client-connect,
 and
 .B --client-disconnect
 scripts.
 .\"*********************************************************
 .TP
 .B trusted_port
 Actual port number of connecting client or peer which has been authenticated.
 Set prior to execution of
 .B --ipchange, --client-connect,
 and
 .B --client-disconnect
 scripts.
 .\"*********************************************************
 .TP
 .B untrusted_ip
 Actual IP address of connecting client or peer which has not been authenticated
 yet.  Sometimes used to
 .B nmap
 the connecting host in a
 .B --tls-verify
 script to ensure it is firewalled properly.
 Set prior to execution of
 .B --tls-verify
 and
 .B --auth-user-pass-verify
 scripts.
 .\"*********************************************************
 .TP
 .B untrusted_port
 Actual port number of connecting client or peer which has not been authenticated
 yet.
 Set prior to execution of
 .B --tls-verify
 and
 .B --auth-user-pass-verify
 scripts.
 .\"*********************************************************
 .TP
 .B username
 The username provided by a connecting client.
 Set prior to
 .B --auth-user-pass-verify
 script execution only when the
 .B via-env
 modifier is specified.
 .\"*********************************************************

 .TP
 .B X509_{n}_{subject_field}
 An X509 subject field from the remote peer certificate,
 where
 .B n
 is the verification level.  Only set for TLS connections.  Set prior
 to execution of
 .B --tls-verify
 script.  This variable is similar to
 .B tls_id_{n}
 except the component X509 subject fields are broken out, and
 no string remapping occurs on these field values (except for remapping
 of control characters to "_").
 For example, the following variables would be set on the
 OpenVPN server using the sample client certificate
 in sample-keys (client.crt).
 Note that the verification level is 0 for the client certificate
 and 1 for the CA certificate.

 .nf

 .ft 3
 .in +4

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

 .in -4

 .ft
 .fi
 .\"*********************************************************

 .SH SIGNALS
 .TP
 .B SIGHUP
 Cause OpenVPN to close all TUN/TAP and
 network connections,
 restart, re-read the configuration file (if any),
 and reopen TUN/TAP and network connections.
 .\"*********************************************************
 .TP
 .B SIGUSR1
 Like 
 .B SIGHUP,
 except don't re-read configuration file, and possibly don't close and reopen TUN/TAP
 device, re-read key files, preserve local IP address/port, or preserve most recently authenticated
 remote IP address/port based on
 .B --persist-tun, --persist-key, --persist-local-ip,
 and
 .B --persist-remote-ip
 options respectively (see above).
 
 This signal may also be internally generated by a timeout condition, governed
 by the
 .B --ping-restart
 option.
 
 This signal, when combined with
 .B --persist-remote-ip,
 may be
 sent when the underlying parameters of the host's network interface change
 such as when the host is a DHCP client and is assigned a new IP address.
 See
 .B --ipchange
 above for more information.
 .\"*********************************************************
 .TP
 .B SIGUSR2
 Causes OpenVPN to display its current statistics (to the syslog
 file if
 .B --daemon
 is used, or stdout otherwise).
 .\"*********************************************************
 .TP
 .B SIGINT, SIGTERM
 Causes OpenVPN to exit gracefully.
 .\"*********************************************************
 .SH TUN/TAP DRIVER SETUP
 If you are running Linux 2.4.7 or higher, you probably have the TUN/TAP driver
 already installed.  If so, there are still a few things you need to do:
 
 Make device:
 .B mknod /dev/net/tun c 10 200
 
 Load driver:
 .B modprobe tun
 
 If you have Linux 2.2 or earlier, you should obtain version 1.1 of the
 TUN/TAP driver from
 .I http://vtun.sourceforge.net/tun/
 and follow the installation instructions.
 .\"*********************************************************
 .SH EXAMPLES
 Prior to running these examples, you should have OpenVPN installed on two
 machines with network connectivity between them.  If you have not
 yet installed OpenVPN, consult the INSTALL file included in the OpenVPN
 distribution.
 .\"*********************************************************
 .SS TUN/TAP Setup:
 If you are using Linux 2.4 or higher,
 make the tun device node and load the tun module:
 .IP
 .B mknod /dev/net/tun c 10 200
 .LP
 .IP
 .B modprobe tun
 .LP
 If you installed from RPM, the
 .B mknod
 step may be omitted, because the RPM install does that for you.
 
 If you have Linux 2.2, you should obtain version 1.1 of the
 TUN/TAP driver from
 .I http://vtun.sourceforge.net/tun/
 and follow the installation instructions.
 
 For other platforms, consult the INSTALL file at
 .I http://openvpn.net/install.html
 for more information.
 .\"*********************************************************
 .SS Firewall Setup:
 If firewalls exist between
 the two machines, they should be set to forward UDP port 1194
 in both directions.  If you do not have control over the firewalls
 between the two machines, you may still be able to use OpenVPN by adding
 .B --ping 15
 to each of the
 .B openvpn
 commands used below in the examples (this will cause each peer to send out
 a UDP ping to its remote peer once every 15 seconds which will cause many
 stateful firewalls to forward packets in both directions
 without an explicit firewall rule).
 
 If you are using a Linux iptables-based firewall, you may need to enter
 the following command to allow incoming packets on the TUN device:
 .IP
 .B iptables -A INPUT -i tun+ -j ACCEPT
 .LP
 See the firewalls section below for more information on configuring firewalls
 for use with OpenVPN.
 .\"*********************************************************
 .SS VPN Address Setup:
 For purposes
 of our example, our two machines will be called
 .B may.kg
 and
 .B june.kg.
 If you are constructing a VPN over the internet, then replace
 .B may.kg
 and
 .B june.kg
 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 may.kg
 will be 10.4.0.1 and for june.kg, 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 may.kg and you wish to connect to june.kg
 via
 .B ssh
 without using the VPN (since
 .B ssh
 has its own built-in security) you would use the command
 .B ssh june.kg.
 However in the same scenario, you could also use the command
 .B telnet 10.4.0.2
 to create a telnet session with june.kg over the VPN, that would
 use the VPN to secure the session rather than
 .B ssh.
 
 You can use any address you wish for the
 tunnel endpoints
 but make sure that they are private addresses
 (such as those that begin with 10 or 192.168) and that they are
 not part of any existing subnet on the networks of
 either peer, unless you are bridging.  If you use an address that is part of
 your local subnet for either of the tunnel endpoints,
 you will get a weird feedback loop.
 .\"*********************************************************
 .SS Example 1: A simple tunnel without security
 .LP
 On may:
 .IP
 .B openvpn --remote june.kg --dev tun1 --ifconfig 10.4.0.1 10.4.0.2 --verb 9
 .LP
 On june:
 .IP
 .B openvpn --remote may.kg --dev tun1 --ifconfig 10.4.0.2 10.4.0.1 --verb 9
 .LP
 Now verify the tunnel is working by pinging across the tunnel.
 .LP
 On may:
 .IP
 .B ping 10.4.0.2
 .LP
 On june:
 .IP
 .B ping 10.4.0.1
 .LP
 The
 .B --verb 9
 option will produce verbose output, similar to the
 .BR tcpdump (8)
 program.  Omit the
 .B --verb 9
 option to have OpenVPN run quietly.
 .\"*********************************************************
 .SS Example 2: A tunnel with static-key security (i.e. using a pre-shared secret)
 First build a static key on may.
 .IP
 .B openvpn --genkey --secret key
 .LP
 This command will build a random key file called
 .B key
 (in ascii format).
 Now copy
 .B key
 to june over a secure medium such as by
 using the
 .BR scp (1)
 program.
 .LP
 On may:
 .IP
 .B openvpn --remote june.kg --dev tun1 --ifconfig 10.4.0.1 10.4.0.2 --verb 5 --secret key
 .LP
 On june:
 .IP
 .B openvpn --remote may.kg --dev tun1 --ifconfig 10.4.0.2 10.4.0.1 --verb 5 --secret key
 .LP
 Now verify the tunnel is working by pinging across the tunnel.
 .LP
 On may:
 .IP
 .B ping 10.4.0.2
 .LP
 On june:
 .IP
 .B ping 10.4.0.1
 .\"*********************************************************
 .SS Example 3: A tunnel with full TLS-based security
 For this test, we will designate
 .B may
 as the TLS client and
 .B june
 as the TLS server.
 .I Note that client or server designation only has meaning for the TLS subsystem.  It has no bearing on OpenVPN's peer-to-peer, UDP-based communication model.
 
 First, build a separate certificate/key pair
 for both may and june (see above where
 .B --cert
 is discussed for more info).  Then construct
 Diffie Hellman parameters (see above where
 .B --dh
 is discussed for more info).  You can also use the
 included test files client.crt, client.key,

 server.crt, server.key and ca.crt.

 The .crt files are certificates/public-keys, the .key

 files are private keys, and ca.crt is a certification

 authority who has signed both
 client.crt and server.crt.  For Diffie Hellman
 parameters you can use the included file dh1024.pem.
 .I Note that all client, server, and certificate authority certificates and keys included in the OpenVPN distribution are totally insecure and should be used for testing only.
 .LP
 On may:
 .IP

 .B openvpn --remote june.kg --dev tun1 --ifconfig 10.4.0.1 10.4.0.2 --tls-client --ca ca.crt --cert client.crt --key client.key --reneg-sec 60 --verb 5

 .LP
 On june:
 .IP

 .B openvpn --remote may.kg --dev tun1 --ifconfig 10.4.0.2 10.4.0.1 --tls-server --dh dh1024.pem --ca ca.crt --cert server.crt --key server.key --reneg-sec 60 --verb 5

 .LP
 Now verify the tunnel is working by pinging across the tunnel.
 .LP
 On may:
 .IP
 .B ping 10.4.0.2
 .LP
 On june:
 .IP
 .B ping 10.4.0.1
 .LP
 Notice the
 .B --reneg-sec 60
 option we used above.  That tells OpenVPN to renegotiate
 the data channel keys every minute.
 Since we used
 .B --verb 5
 above, you will see status information on each new key negotiation.
 
 For production operations, a key renegotiation interval of 60 seconds
 is probably too frequent.  Omit the
 .B --reneg-sec 60
 option to use OpenVPN's default key renegotiation interval of one hour.
 .\"*********************************************************
 .SS Routing:
 Assuming you can ping across the tunnel,
 the next step is to route a real subnet over
 the secure tunnel.  Suppose that may and june 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 may's private subnet
 is 10.0.0.0/24 and june's is 10.0.1.0/24.
 .LP
 First, ensure that IP forwarding is enabled on both peers.
 On Linux, enable routing:
 .IP
 .B echo 1 > /proc/sys/net/ipv4/ip_forward
 .LP
 and enable TUN packet forwarding through the firewall:
 .IP
 .B iptables -A FORWARD -i tun+ -j ACCEPT
 .LP
 On may:
 .IP
 .B route add -net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2
 .LP
 On june:
 .IP
 .B route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1
 .LP
 Now any machine on the 10.0.0.0/24 subnet can
 access any machine on the 10.0.1.0/24 subnet
 over the secure tunnel (or vice versa).
 
 In a production environment, you could put the route command(s)
 in a shell script and execute with the
 .B --up
 option.
 .\"*********************************************************
 .SH FIREWALLS
 OpenVPN's usage of a single UDP port makes it fairly firewall-friendly.
 You should add an entry to your firewall rules to allow incoming OpenVPN
 packets.  On Linux 2.4+:
 .IP
 .B iptables -A INPUT -p udp -s 1.2.3.4 --dport 1194 -j ACCEPT
 .LP
 This will allow incoming packets on UDP port 1194 (OpenVPN's default UDP port)
 from an OpenVPN peer at 1.2.3.4.
 
 If you are using HMAC-based packet authentication (the default in any of
 OpenVPN's secure modes), having the firewall filter on source
 address can be considered optional, since HMAC packet authentication
 is a much more secure method of verifying the authenticity of
 a packet source.  In that case:
 .IP
 .B iptables -A INPUT -p udp --dport 1194 -j ACCEPT
 .LP
 would be adequate and would not render the host inflexible with
 respect to its peer having a dynamic IP address.
 
 OpenVPN also works well on stateful firewalls.  In some cases, you may
 not need to add any static rules to the firewall list if you are
 using a stateful firewall that knows how to track UDP connections.
 If you specify
 .B --ping n,
 OpenVPN will be guaranteed
 to send a packet to its peer at least once every
 .B n
 seconds.  If
 .B n
 is less than the stateful firewall connection timeout, you can
 maintain an OpenVPN connection indefinitely without explicit
 firewall rules.
 
 You should also add firewall rules to allow incoming IP traffic on
 TUN or TAP devices such as:
 .IP
 .B iptables -A INPUT -i tun+ -j ACCEPT
 .LP
 to allow input packets from tun devices,
 .IP
 .B iptables -A FORWARD -i tun+ -j ACCEPT
 .LP
 to allow input packets from tun devices to be forwarded to
 other hosts on the local network,
 .IP
 .B iptables -A INPUT -i tap+ -j ACCEPT
 .LP
 to allow input packets from tap devices, and
 .IP
 .B iptables -A FORWARD -i tap+ -j ACCEPT
 .LP
 to allow input packets from tap devices to be forwarded to
 other hosts on the local network.
 
 These rules are secure if you use packet authentication,
 since no incoming packets will arrive on a TUN or TAP
 virtual device
 unless they first pass an HMAC authentication test.
 .\"*********************************************************
 .SH FAQ
 .I http://openvpn.net/faq.html
 .\"*********************************************************
 .SH HOWTO
 For a more comprehensive guide to setting up OpenVPN
 in a production setting, see the OpenVPN HOWTO at
 .I http://openvpn.net/howto.html
 .\"*********************************************************
 .SH PROTOCOL
 For a description of OpenVPN's underlying protocol,
 see 
 .I http://openvpn.net/security.html
 .\"*********************************************************
 .SH WEB
 OpenVPN's web site is at
 .I http://openvpn.net/
 
 Go here to download the latest version of OpenVPN, subscribe
 to the mailing lists, read the mailing list

 archives, or browse the SVN repository.

 .\"*********************************************************
 .SH BUGS

 Report all bugs to the OpenVPN team <info@openvpn.net>.

 .\"*********************************************************
 .SH "SEE ALSO"
 .BR dhcpcd (8),
 .BR ifconfig (8),
 .BR openssl (1),
 .BR route (8),
 .BR scp (1)
 .BR ssh (1)
 .\"*********************************************************
 .SH NOTES 
 .LP
 This product includes software developed by the
 OpenSSL Project (
 .I http://www.openssl.org/
 )
 
 For more information on the TLS protocol, see
 .I http://www.ietf.org/rfc/rfc2246.txt
 
 For more information on the LZO real-time compression library see
 .I http://www.oberhumer.com/opensource/lzo/
 .\"*********************************************************
 .SH COPYRIGHT

 Copyright (C) 2002-2009 OpenVPN Technologies, Inc. This program is free software;

 you can redistribute it and/or modify
 it under the terms of the GNU General Public License version 2
 as published by the Free Software Foundation.
 .\"*********************************************************
 .SH AUTHORS
 James Yonan <jim@yonan.net>