Provided by: openvpn_2.2.1-8ubuntu1_amd64 bug


       openvpn - secure IP tunnel daemon.


       openvpn [ options ... ]


       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:

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


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

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

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

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

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


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

       --help Show options.

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

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

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

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

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

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

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

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

              For examples of configuration files, see

              Here is an example configuration file:

                  # Sample OpenVPN configuration file for
                  # using a pre-shared static key.
                  # '#' or ';' may be used to delimit comments.

                  # Use a dynamic tun device.
                  dev tun

                  # Our remote peer
                  remote mypeer.mydomain

                  # is our local VPN endpoint
                  # is our remote VPN endpoint

                  # Our pre-shared static key
                  secret static.key

   Tunnel Options:
       --mode m
              Set OpenVPN major mode.  By default, OpenVPN runs in point-to-point  mode  ("p2p").
              OpenVPN 2.0 introduces a new mode ("server") which implements a multi-client server

       --local host
              Local host name or IP address for bind.  If specified, OpenVPN will  bind  to  this
              address only.  If unspecified, OpenVPN will bind to all interfaces.

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

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

              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  --ping
              and --ping-restart options.

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

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

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

              If host is a DNS name which resolves to multiple IP addresses, one will be randomly
              chosen, providing a sort of basic load-balancing and failover capability.

              Add a random string (6 characters) to first DNS label of hostname  to  prevent  DNS
              caching.    For   example,   ""   would   be   modified   to   "<random-

              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 <connection> and </connection>.

              An OpenVPN client will try each connection profile sequentially until it achieves a
              successful connection.

              --remote-random can be used to initially "scramble" the connection list.

              Here is an example of connection profile usage:

                  dev tun

                  remote 1194 udp

                  remote 443 tcp

                  remote 443 tcp
                  http-proxy 8080

                  remote 443 tcp
                  http-proxy 8080

                  pkcs12 client.p12
                  ns-cert-type server
                  verb 3

              First we try to connect to a server at using UDP.  If that fails,
              we then try to connect to using TCP.  If that also fails, then try
              connecting through an HTTP proxy at to using TCP.
              Finally,  try  to  connect  through  the same proxy to a server at
              using TCP.

              The following OpenVPN options may be used inside of a <connection> block:

              bind, connect-retry, connect-retry-max, connect-timeout, float,  http-proxy,  http-
              proxy-option,  http-proxy-retry,  http-proxy-timeout,  local,  lport, nobind, port,
              proto, remote, rport, socks-proxy, and socks-proxy-retry.

              A defaulting mechanism exists for specifying options to apply to  all  <connection>
              profiles.   If  any  of  the  above  options (with the exception of remote ) appear
              outside of a <connection> block, but in a configuration file which has one or  more
              <connection>  blocks, the option setting will be used as a default for <connection>
              blocks which follow it in the configuration file.

              For example, suppose the nobind option were placed in the sample configuration file
              above,  near  the top of the file, before the first <connection> block.  The effect
              would be as if nobind were declared in all <connection> blocks below it.

       --proto-force p
              When iterating through connection profiles, only consider profiles using protocol p

              When  multiple  --remote address/ports are specified, or if connection profiles are
              being used, initially randomize the order of the list as  a  kind  of  basic  load-
              balancing measure.

       --proto p
              Use  protocol  p  for communicating with remote host.  p can be udp, tcp-client, or

              The default protocol is udp when --proto is not specified.

              For UDP operation, --proto udp should be specified on both peers.

              For TCP operation, one peer must use --proto tcp-server  and  the  other  must  use
              --proto  tcp-client.   A peer started with tcp-server will wait indefinitely for an
              incoming connection.  A peer started with tcp-client will attempt to  connect,  and
              if that fails, will sleep for 5 seconds (adjustable via the --connect-retry option)
              and try again infinite or up to N retries (adjustable via  the  --connect-retry-max
              option).   Both  TCP  client  and  server will simulate a SIGUSR1 restart signal if
              either side resets the connection.

              OpenVPN is designed to operate optimally over UDP, but TCP capability  is  provided
              for  situations where UDP cannot be used.  In comparison with UDP, TCP will usually
              be somewhat less efficient and less robust when used over unreliable  or  congested

              This article outlines some of problems with tunneling IP over TCP:


              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

       --connect-retry n
              For --proto tcp-client, take n as the number of seconds to wait between  connection
              retries (default=5).

       --connect-timeout n
              For --proto tcp-client, set connection timeout to n seconds (default=10).

       --connect-retry-max n
              For  --proto  tcp-client,  take  n  as  the number of retries of connection attempt

              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.

              Show sensed HTTP or SOCKS proxy settings. Currently, only Windows  clients  support
              this option.

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

              auth-method should be one of "none", "basic", or "ntlm".

              HTTP  Digest authentication is supported as well, but only via the auto or auto-nct
              flags (below).

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

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

              Retry indefinitely on HTTP proxy errors.  If an HTTP proxy error occurs, simulate a
              SIGUSR1 reset.

       --http-proxy-timeout n
              Set proxy timeout to n seconds, default=5.

       --http-proxy-option type [parm]
              Set extended HTTP proxy options.  Repeat to set multiple options.

              VERSION version -- Set HTTP version number to version (default=1.0).

              AGENT user-agent -- Set HTTP "User-Agent" string to user-agent.

       --socks-proxy server [port]
              Connect  to  remote  host  through  a  Socks5 proxy at address server and port port

              Retry indefinitely on Socks proxy errors.  If a Socks proxy error occurs,  simulate
              a SIGUSR1 reset.

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

              Set n to "infinite" to retry indefinitely.

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

              Allow  remote peer to change its IP address and/or port number, such as due to DHCP
              (this is the default if  --remote  is  not  used).   --float  when  specified  with
              --remote  allows  an  OpenVPN  session  to  initially  connect to a peer at a known
              address, however if packets arrive from a new address and pass  all  authentication
              tests,  the  new address will take control of the session.  This is useful when you
              are connecting to a peer which holds a dynamic address such as a  dial-in  user  or
              DHCP client.

              Essentially,  --float  tells  OpenVPN  to  accept  authenticated  packets  from any
              address, not only the address which was specified in the --remote option.

       --ipchange cmd
              Execute shell command cmd when our remote ip-address is initially authenticated  or

              Execute as:

              cmd ip_address port_number

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

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

              Note that cmd can be a shell command with multiple arguments,  in  which  case  all
              OpenVPN-generated  arguments  will be appended to 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 /etc/hosts file with the current address of the peer.  The script will  be
              run every time the remote peer changes its IP address.

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

       --port port
              TCP/UDP port number 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.

       --lport port
              TCP/UDP port number for bind.

       --rport port
              TCP/UDP port number for remote.

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

              Do  not  bind to local address and port.  The IP stack will allocate a dynamic port
              for returning packets.  Since the value of the dynamic port could not be  known  in
              advance  by a peer, this option is only suitable for peers which will be initiating
              connections by using the --remote option.

       --dev tunX | tapX | null
              TUN/TAP virtual network device ( 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

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

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

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

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

              mode can be one of:

              net30  --  Use  a point-to-point topology, by allocating one /30 subnet per client.
              This is designed to  allow  point-to-point  semantics  when  some  or  all  of  the
              connecting clients might be Windows systems.  This is the default on OpenVPN 2.0.

              p2p  -- Use a point-to-point topology where the remote endpoint of the client's tun
              interface always points to the local endpoint of the server's tun interface.   This
              mode  allocates  a  single IP address per connecting client.  Only use when none of
              the connecting clients are Windows systems.  This mode is  functionally  equivalent
              to  the  --ifconfig-pool-linear  directive which is available in OpenVPN 2.0 and is
              now deprecated.

              subnet -- Use a subnet rather than a point-to-point topology by configuring the tun
              interface  with a local IP address and subnet mask, similar to the topology used in
              --dev tap and ethernet bridging mode.  This mode allocates a single IP address  per
              connecting  client  and  works  on Windows as well.  Only available when server and
              clients are OpenVPN 2.1 or higher, or OpenVPN 2.0.x which has been manually patched
              with  the --topology directive code.  When used on Windows, requires version 8.2 or
              higher of the TAP-Win32 driver.  When used on *nix, requires that  the  tun  driver
              supports an ifconfig(8) command which sets a subnet instead of a remote endpoint IP

              This option exists in OpenVPN 2.1 or higher.

              Build a tun link capable of forwarding IPv6 traffic.  Should be used in conjunction
              with  --dev tun or --dev tunX.  A warning will be displayed if no specific IPv6 TUN
              support for your OS has been compiled into OpenVPN.

              See below for further IPv6-related configuration options.

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

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

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

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

       --ifconfig l rn
              Set TUN/TAP adapter parameters.  l is the IP address of  the  local  VPN  endpoint.
              For TUN devices, rn is the IP address of the remote VPN endpoint.  For TAP devices,
              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 --ifconfig is to use two private IP addresses which are not  a  member  of
              any  existing  subnet  which  is  in  use.  The IP addresses may be consecutive and
              should have their order reversed on the remote peer.  After the VPN is established,
              by pinging rn, you will be pinging across the VPN.

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

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

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

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

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

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

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

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

       --route 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  route(8)  shell  command,
              while  at  the  same  time  providing  portable semantics across OpenVPN's platform

              netmask default --

              gateway default -- taken from --route-gateway or the second parameter to --ifconfig
              when --dev tun is specified.

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

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

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

              vpn_gateway -- The remote VPN endpoint address (derived either from --route-gateway
              or the second parameter to --ifconfig when --dev tun is specified).

              net_gateway  --  The  pre-existing  IP default gateway, read from the routing table
              (not supported on all OSes).

              remote_host -- The --remote address if OpenVPN is being run in client mode, and  is
              undefined in server mode.

       --max-routes n
              Allow  a  maximum  number of n --route options to be specified, either in the local
              configuration file, or pulled from an OpenVPN server.  By default, n=100.

       --route-gateway gw|'dhcp'
              Specify a default gateway gw for use with --route.

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

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

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

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

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

       --route-up cmd
              Execute shell command cmd after routes are added, subject to --route-delay.

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

              Note that cmd can be a shell command with multiple arguments.

              Don't add or remove routes automatically.  Instead pass routes to --route-up script
              using environmental variables.

              When used with --client or --pull, accept  options  pushed  by  server  EXCEPT  for

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

              Allow  client  to  pull  DNS  names  from  server  (rather than being limited to IP
              address) for --ifconfig, --route, and --route-gateway.

       --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:

              (1)  Create  a  static  route  for  the --remote address which forwards to the pre-
              existing default gateway.  This is done so that (3) will not create a routing loop.

              (2) Delete the default gateway route.

              (3) Set the new default gateway to be the VPN endpoint address (derived either from
              --route-gateway or the second parameter to --ifconfig when --dev tun is specified).

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

              Option flags:

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

              def1 -- Use this flag to override  the  default  gateway  by  using  and
      rather  than   This  has the benefit of overriding but not
              wiping out the original default gateway.

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

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

              Using the def1 flag is highly recommended.

       --redirect-private [flags]
              Like --redirect-gateway, but omit actually changing the  default  gateway.   Useful
              when pushing private subnets.

       --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.

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

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

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

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

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

       --mtu-disc type
              Should we do Path MTU discovery on TCP/UDP channel?  Only supported on OSes such as
              Linux that supports the necessary system call to set.

              'no' -- Never send DF (Don't Fragment) frames
              'maybe' -- Use per-route hints
              'yes' -- Always DF (Don't Fragment)

              To empirically measure MTU on connection startup, add the --mtu-test option to your
              configuration.   OpenVPN will send ping packets of various sizes to the remote peer
              and measure the largest packets which were successfully received.   The  --mtu-test
              process normally takes about 3 minutes to complete.

       --fragment max
              Enable  internal datagram fragmentation so that no UDP datagrams are sent which are
              larger than max bytes.

              The max parameter is interpreted in the same way as the --link-mtu parameter,  i.e.
              the  UDP  packet  size  after  encapsulation  overhead  has  been added in, but not
              including the UDP header itself.

              The --fragment option only makes sense when  you  are  using  the  UDP  protocol  (
              --proto udp ).

              --fragment adds 4 bytes of overhead per datagram.

              See the --mssfix option below for an important related option to --fragment.

              It  should also be noted that this option is not meant to replace UDP fragmentation
              at the IP stack level.  It is only meant as a last resort when path  MTU  discovery
              is  broken.  Using this option is less efficient than fixing path MTU discovery for
              your IP link and using native IP fragmentation instead.

              Having  said  that,  there  are  circumstances  where  using   OpenVPN's   internal
              fragmentation capability may be your only option, such as tunneling a UDP multicast
              stream which requires fragmentation.

       --mssfix max
              Announce to TCP sessions running over the tunnel that they should limit their  send
              packet  sizes  such  that  after  OpenVPN  has encapsulated them, the resulting UDP
              packet size that OpenVPN sends to its peer will not exceed max bytes.  The  default
              value is 1450.

              The  max parameter is interpreted in the same way as the --link-mtu parameter, i.e.
              the UDP packet size after  encapsulation  overhead  has  been  added  in,  but  not
              including the UDP header itself.

              The  --mssfix  option  only  makes  sense  when  you are using the UDP protocol for
              OpenVPN peer-to-peer communication, i.e.  --proto udp.

              --mssfix and --fragment can be ideally used together, where --mssfix  will  try  to
              keep  TCP  from needing packet fragmentation in the first place, and if big packets
              come through anyhow (from protocols other than  TCP),  --fragment  will  internally
              fragment them.

              Both  --fragment  and  --mssfix  are  designed  to work around cases where Path MTU
              discovery is broken on the network path between OpenVPN peers.

              The usual symptom of such a breakdown is an OpenVPN connection  which  successfully
              starts, but then stalls during active usage.

              If  --fragment  and  --mssfix are used together, --mssfix will take its default max
              parameter from the --fragment max option.

              Therefore, one could lower the maximum UDP packet size to 1300 (a  good  first  try
              for solving MTU-related connection problems) with the following options:

              --tun-mtu 1500 --fragment 1300 --mssfix

       --sndbuf size
              Set the TCP/UDP socket send buffer size.  Currently defaults to 65536 bytes.

       --rcvbuf size
              Set the TCP/UDP socket receive buffer size.  Currently defaults to 65536 bytes.

       --socket-flags flags...
              Apply the given flags to the OpenVPN transport socket.  Currently, only TCP_NODELAY
              is supported.

              The TCP_NODELAY socket flag is useful in TCP mode, and causes the  kernel  to  send
              tunnel  packets immediately over the TCP connection without trying to group several
              smaller  packets  into  a  larger  packet.   This  can  result  in  a  considerably
              improvement in latency.

              This  option  is  pushable from server to client, and should be used on both client
              and server for maximum effect.

       --txqueuelen n
              (Linux only) Set the TX queue length on the TUN/TAP interface.  Currently  defaults
              to 100.

       --shaper n
              Limit  bandwidth of outgoing tunnel data to n bytes per second on the TCP/UDP port.
              If you want to limit the bandwidth in both directions,  use  this  option  on  both

              OpenVPN  uses  the following algorithm to implement traffic shaping: Given a shaper
              rate of n bytes per second, after a datagram write of b  bytes  is  queued  on  the
              TCP/UDP port, wait a minimum of (b / n) seconds before queuing the next write.

              It  should  be  noted  that  OpenVPN supports multiple tunnels between the same two
              peers, allowing you to construct full-speed and reduced bandwidth  tunnels  at  the
              same  time,  routing  low-priority  data  such as off-site backups over the reduced
              bandwidth tunnel, and other data over the full-speed tunnel.

              Also note that for low bandwidth tunnels (under 1000 bytes per second), you  should
              probably  use  lower  MTU  values as well (see above), otherwise the packet latency
              will grow so large as to trigger timeouts in the  TLS  layer  and  TCP  connections
              running over the tunnel.

              OpenVPN allows n to be between 100 bytes/sec and 100 Mbytes/sec.

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

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

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

       --ping n
              Ping  remote  over  the TCP/UDP control channel if no packets have been sent for at
              least n seconds (specify --ping on both peers to cause ping packets to be  sent  in
              both  directions  since  OpenVPN ping packets are not echoed like IP ping packets).
              When used in one of OpenVPN's secure modes (where --secret, --tls-server, or --tls-
              client is specified), the ping packet will be cryptographically secure.

              This option has two intended uses:

              (1)  Compatibility  with  stateful firewalls.  The periodic ping will ensure that a
              stateful firewall rule which allows OpenVPN UDP packets to pass will not time out.

              (2) To provide a basis for the remote to test the existence of its peer  using  the
              --ping-exit option.

       --ping-exit n
              Causes  OpenVPN  to  exit after n seconds pass without reception of a ping or other
              packet from remote.  This option can  be  combined  with  --inactive,  --ping,  and
              --ping-exit to create a two-tiered inactivity disconnect.

              For example,

              openvpn [options...] --inactive 3600 --ping 10 --ping-exit 60

              when  used  on  both peers will cause OpenVPN to exit within 60 seconds if its peer
              disconnects, but will exit after one hour if no actual tunnel data is exchanged.

       --ping-restart n
              Similar to --ping-exit, but trigger a SIGUSR1 restart after n seconds pass  without
              reception of a ping or other packet from remote.

              This option is useful in cases where the remote peer has a dynamic IP address and a
              low-TTL DNS name is  used  to  track  the  IP  address  using  a  service  such  as
     + a dynamic DNS client such as ddclient.

              If  the  peer  cannot be reached, a restart will be triggered, causing the hostname
              used with --remote to be re-resolved (if --resolv-retry is also specified).

              In server mode,  --ping-restart,  --inactive,  or  any  other  type  of  internally
              generated  signal  will  always  be  applied to individual client instance objects,
              never to whole server itself.   Note  also  in  server  mode  that  any  internally
              generated  signal  which would normally cause a restart, will cause the deletion of
              the client instance object instead.

              In client mode, the --ping-restart parameter is set  to  120  seconds  by  default.
              This  default will hold until the client pulls a replacement value from the server,
              based on the --keepalive setting in the server configuration.  To disable  the  120
              second default, set --ping-restart 0 on the client.

              See the signals section below for more information on SIGUSR1.

              Note  that the behavior of SIGUSR1 can be modified by the --persist-tun, --persist-
              key, --persist-local-ip, and --persist-remote-ip options.

              Also note that --ping-exit and --ping-restart are mutually exclusive and cannot  be
              used together.

       --keepalive n m
              A helper directive designed to simplify the expression of --ping and --ping-restart
              in server mode configurations.

              For example, --keepalive 10 60 expands as follows:

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

              Run the --ping-exit / --ping-restart timer only if we have a remote  address.   Use
              this option if you are starting the daemon in listen mode (i.e. without an explicit
              --remote peer), and you don't want to start clocking timeouts until a  remote  peer

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

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

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

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

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

              Preserve initially resolved local IP address and  port  number  across  SIGUSR1  or
              --ping-restart restarts.

              Preserve  most  recently  authenticated  remote  IP  address and port number across
              SIGUSR1 or --ping-restart restarts.

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

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

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

       --up cmd
              Shell command to run after successful TUN/TAP device open (pre --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 --dev tun execute as:

              cmd  tun_dev tun_mtu link_mtu ifconfig_local_ip ifconfig_remote_ip [ init | restart

              For --dev tap execute as:

              cmd tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask [ init | restart ]

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

              Note  that  cmd  can  be a shell command with multiple arguments, in which case all
              OpenVPN-generated arguments will be appended to cmd to build a command  line  which
              will be passed to the shell.

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

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

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

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

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

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

              route add -net netmask gw $5

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

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

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

       --down cmd
              Shell command to run after TUN/TAP device close  (post  --user  UID  change  and/or
              --chroot  ).   Called  with  the same parameters and environmental variables as the
              --up option above.

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

              Call --down cmd/script before, rather than after, TUN/TAP close.

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

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

       --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.

       --setenv-safe name value
              Set a custom environmental variable 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.

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

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

              The method parameter indicates  how  OpenVPN  should  call  external  commands  and
              scripts.  Settings for method:

              execve  --  (default) Use execve() function on Unix family OSes and CreateProcess()
              on Windows.
              system -- Use system() function  (deprecated  and  less  safe  since  the  external
              program command line is subject to shell expansion).

              The  --script-security option was introduced in OpenVPN 2.1_rc9.  For configuration
              file compatibility with previous OpenVPN versions, use: --script-security 3 system

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

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

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

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

       --group group
              Similar to the --user option, this option changes  the  group  ID  of  the  OpenVPN
              process to group after initialization.

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

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

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

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

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

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

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

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

       --daemon [progname]
              Become a daemon after all initialization functions are completed.  This option will
              cause  all  message  and  error  output  to  be  sent  to  the syslog file (such as
              /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 --daemon is parsed on the  command  line  even
              though  the  daemonization  point  occurs  later.   If  one of the --log options is
              present, it will supercede syslog redirection.

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

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

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

       --syslog [progname]
              Direct log output to system logger, but do  not  become  a  daemon.   See  --daemon
              directive above for description of progname parameter.

              Set the TOS field of the tunnel packet to what the payload's TOS is.

       --inetd [wait|nowait] [progname]
              Use this option when OpenVPN is being run from the inetd or xinetd(8) server.

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

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

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

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

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

       --log-append file
              Append logging messages to file.  If file does not exist, it will be created.  This
              option behaves exactly like --log except that it appends to rather than  truncating
              the log file.

              Avoid  writing  timestamps  to  log  messages,  even  when  they otherwise would be
              prepended. In particular, this applies to log messages sent to stdout.

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

       --nice n
              Change process priority after initialization ( n greater than 0 is lower  priority,
              n less than zero is higher priority).

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

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

              Configure  a multi-homed UDP server.  This option can be used when OpenVPN has been
              configured to listen on all interfaces, and will attempt to bind client sessions to
              the interface on which packets are being received, so that outgoing packets will be
              sent out of the same interface.  Note that this option is  only  relevant  for  UDP
              servers and currently is only implemented on Linux.

              Note:  clients  connecting  to  a --multihome server should always use the --nobind

       --echo [parms...]
              Echo parms to log output.

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

       --remap-usr1 signal
              Control  whether internally or externally generated SIGUSR1 signals are remapped to
              SIGHUP (restart without persisting state) or SIGTERM (exit).

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

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

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

       --status file [n]
              Write operational status to file every n seconds.

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

       --status-version [n]
              Choose the status file format version number.  Currently n can be 1, 2,  or  3  and
              defaults to 1.

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

       --comp-lzo [mode]
              Use fast LZO compression -- may add up to 1  byte  per  packet  for  incompressible
              data.  mode may be "yes", "no", or "adaptive" (default).

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

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

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

                  comp-lzo yes
                  push "comp-lzo yes"

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

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

              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.

       --management IP port [pw-file]
              Enable  a TCP server on IP:port to handle daemon management functions.  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 IP and set port to 'unix'.  While the default behavior  is  to
              create  a  unix  domain  socket  that  may  be  connected  to  by  any process, the
              --management-client-user and --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 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 management folder of the OpenVPN source distribution.

              It  is  strongly  recommended  that  IP be set to (localhost) to restrict
              accessibility of the management server to local clients.

              Management interface  will  connect  as  a  TCP  client  to  IP:port  specified  by
              --management rather than listen as a TCP server.

              Query   management   channel   for   private   key  password  and  --auth-user-pass
              username/password.  Only query the management channel for inputs  which  ordinarily
              would have been queried from the console.

              Make OpenVPN forget passwords when management session disconnects.

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

              Start OpenVPN in a hibernating state, until a client of  the  management  interface
              explicitly starts it with the hold release command.

              Send  SIGUSR1  signal to OpenVPN if management session disconnects.  This is useful
              when you wish to disconnect an OpenVPN session on user logoff.

       --management-log-cache n
              Cache the most recent n lines of log file  history  for  usage  by  the  management

              Gives  management interface client the responsibility to authenticate clients after
              their client certificate has been verified.  See  management-notes.txt  in  OpenVPN
              distribution for detailed notes.

              Management  interface clients must specify a packet filter file for each connecting
              client.  See management-notes.txt in OpenVPN distribution for detailed notes.

       --management-client-user u
              When the management interface is listening on a  unix  domain  socket,  only  allow
              connections from user u.

       --management-client-group g
              When  the  management  interface  is  listening on a unix domain socket, only allow
              connections from group g.

       --plugin module-pathname [init-string]
              Load plug-in module from  the  file  module-pathname,  passing  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 plugin folder of the OpenVPN source distribution.

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

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

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

       --server 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, --server expands as follows:

                   mode server
                   push "topology [topology]"

                   if dev tun AND (topology == net30 OR topology == p2p):
                     if !nopool:
                     if client-to-client:
                       push "route"
                     else if topology == net30:
                       push "route"

                   if dev tap OR (dev tun AND topology == subnet):
                     if !nopool:
                     push "route-gateway"

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

       --server-bridge gateway netmask pool-start-IP pool-end-IP

       --server-bridge ['nogw']

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

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

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

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

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

              For  example, server-bridge expands as

                  mode server

                  push "route-gateway"

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

                  mode server

                  push "route-gateway dhcp"

              Or --server-bridge nogw expands as follows:

                  mode server

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

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

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

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

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

       --ifconfig-pool 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  netmask  parameter  will
              also be pushed to clients.

       --ifconfig-pool-persist file [seconds]
              Persist/unpersist  ifconfig-pool  data to file, at 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 --persist-tun option.

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

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

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

              Modifies  the  --ifconfig-pool  directive  to  allocate  individual  TUN  interface
              addresses for clients rather than /30 subnets.  NOTE:  This option is  incompatible
              with Windows clients.

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

       --ifconfig-push local remote-netmask
              Push virtual IP endpoints for client tunnel, overriding the --ifconfig-pool dynamic

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

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

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

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

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

       --iroute network [netmask]
              Generate an internal route to a specific client. The netmask parameter, if omitted,
              defaults to

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

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

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

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

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

              Allow  multiple  clients with the same common name to concurrently connect.  In the
              absence of this option, OpenVPN will disconnect a client instance  upon  connection
              of a new client having the same common name.

       --client-connect script
              Run  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
              freshly 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

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

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

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

              The  exception  to  this  rule  is if the --client-disconnect 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.

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

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

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

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

              Require, as a condition of authentication, that a connecting client has a --client-
              config-dir file.

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

              This directory will be used by in the following cases:

              * --client-connect scripts to dynamically  generate  client-specific  configuration

              *  OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY  plugin  hook to return success/failure via
              auth_control_file when using deferred auth method

              * OPENVPN_PLUGIN_ENABLE_PF plugin hook to pass filtering rules via pf_file

       --hash-size r v
              Set the size of the real address hash table to r and the virtual address  table  to
              v.  By default, both tables are sized at 256 buckets.

       --bcast-buffers n
              Allocate n buffers for broadcast datagrams (default=256).

       --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.

              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:

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

       --max-clients n
              Limit server to a maximum of n concurrent clients.

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

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

       --connect-freq n sec
              Allow a maximum of n new  connections  per  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 --proto udp and

       --learn-address cmd
              Run script or shell command cmd to validate client virtual addresses or routes.

              cmd will be executed with 3 parameters:

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

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

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

       --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 script as a shell command to  validate  the  username/password
              provided by the client.

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

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

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

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

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

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

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

              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 --disable-occ NOT be used.

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

              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 --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 --auth-user-pass-verify
              script, then OpenVPN will perform double authentication.   The  client  certificate
              verification  AND  the --auth-user-pass-verify script will need to succeed in order
              for a client to be authenticated and accepted onto the VPN.

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

              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 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!

       --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  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.

   Client Mode
       Use client mode when connecting to an OpenVPN server which has --server,  --server-bridge,
       or --mode server in it's configuration.

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


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

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

       --auth-user-pass [up]
              Authenticate  with  server  using  username/password.   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 win/

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

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

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

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

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

              type can be one of:

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

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

       --server-poll-timeout n
              when  polling possible remote servers to connect to in a round-robin fashion, spend
              no more than n seconds waiting for a response before trying the next server.

       --explicit-exit-notify [n]
              In UDP client mode or point-to-point mode, send server/peer an exit notification if
              tunnel is restarted or OpenVPN process is exited.  In client mode, on exit/restart,
              this option will tell the server to immediately close its  client  instance  object
              rather  than  waiting  for  a  timeout.   The  n parameter (default=1) controls the
              maximum number of attempts that the client will try to resend the exit notification
              message.   OpenVPN  will  not  send  any  exit  notifications unless this option is

   Data Channel Encryption Options:
       These options are  meaningful  for  both  Static  &  TLS-negotiated  key  modes  (must  be
       compatible between peers).

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

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

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

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

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

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

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

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

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

              OpenVPN's usage of HMAC is to first encrypt  a  packet,  then  HMAC  the  resulting

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

              For            more           information           on           HMAC           see

       --cipher alg
              Encrypt packets with cipher algorithm alg.  The default is 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

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

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

              Set alg=none to disable encryption.

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

       --prng alg [nsl]
              (Advanced) For PRNG (Pseudo-random number  generator),  use  digest  algorithm  alg
              (default=sha1),  and  set nsl (default=16) to the size in bytes of the nonce secret
              length (between 16 and 64).

              Set alg=none to disable the PRNG and use the OpenSSL  RAND_bytes  function  instead
              for all of OpenVPN's pseudo-random number needs.

       --engine [engine-name]
              Enable OpenSSL hardware-based crypto engine functionality.

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

              (Advanced) Disable OpenVPN's protection against replay  attacks.   Don't  use  this
              option unless you are prepared to make a tradeoff of greater efficiency in exchange
              for less security.

              OpenVPN provides datagram replay protection by default.

              Replay protection is  accomplished  by  tagging  each  outgoing  datagram  with  an
              identifier  that  is guaranteed to be unique for the key being used.  The peer that
              receives the datagram will check for the uniqueness  of  the  identifier.   If  the
              identifier  was  already  received  in  a  previous datagram, OpenVPN will drop the
              packet.  Replay protection is important to defeat  attacks  such  as  a  SYN  flood
              attack,  where  the  attacker  listens  in  the  wire,  intercepts a TCP SYN packet
              (identifying it by the context in which it occurs in relation  to  other  packets),
              then floods the receiving peer with copies of this packet.

              OpenVPN's replay protection is implemented in slightly different ways, depending on
              the key management mode you have selected.

              In Static Key mode or when using an CFB or OFB mode cipher, OpenVPN uses a  64  bit
              unique identifier that combines a time stamp with an incrementing sequence number.

              When  using TLS mode for key exchange and a CBC cipher mode, OpenVPN uses only a 32
              bit sequence  number  without  a  time  stamp,  since  OpenVPN  can  guarantee  the
              uniqueness  of  this  value  for  each key.  As in IPSec, if the sequence number is
              close to wrapping back to zero, OpenVPN will trigger a new key exchange.

              To check for replays, OpenVPN uses the sliding window algorithm used by IPSec.

       --replay-window n [t]
              Use a replay protection sliding-window of size n and a time window of t seconds.

              By default n is 64 (the IPSec default) and t is 15 seconds.

              This option is only relevant  in  UDP  mode,  i.e.   when  either  --proto  udp  is
              specified, or no --proto option is specified.

              When  OpenVPN  tunnels  IP  packets over UDP, there is the possibility that packets
              might be dropped or delivered out  of  order.   Because  OpenVPN,  like  IPSec,  is
              emulating  the  physical  network  layer,  it  will  accept  an out-of-order packet
              sequence, and will deliver such packets in the same order they were received to the
              TCP/IP protocol stack, provided they satisfy several constraints.

              (a)  The packet cannot be a replay (unless --no-replay is specified, which disables
              replay protection altogether).

              (b) If a packet arrives out of order, it will only be accepted  if  the  difference
              between its sequence number and the highest sequence number received so far is less
              than n.

              (c) If a packet arrives out of order, it will only be accepted  if  it  arrives  no
              later than t seconds after any packet containing a higher sequence number.

              If  you are using a network link with a large pipeline (meaning that the product of
              bandwidth and latency is high),  you  may  want  to  use  a  larger  value  for  n.
              Satellite links in particular often require this.

              If  you  run OpenVPN at --verb 4, you will see the message "Replay-window backtrack
              occurred [x]" every time the  maximum  sequence  number  backtrack  seen  thus  far
              increases.  This can be used to calibrate n.

              There  is  some controversy on the appropriate method of handling packet reordering
              at the security layer.

              Namely, to what extent should the security layer protect the encapsulated  protocol
              from  attacks  which  masquerade  as the kinds of normal packet loss and reordering
              that occur over IP networks?

              The IPSec and OpenVPN approach is to allow packet reordering within a certain fixed
              sequence number window.

              OpenVPN  adds  to  the  IPSec  model by limiting the window size in time as well as
              sequence space.

              OpenVPN also adds TCP transport as an option (not offered by IPSec) in  which  case
              OpenVPN  can  adopt a very strict attitude towards message deletion and reordering:
              Don't allow it.  Since TCP guarantees reliability, any packet  loss  or  reordering
              event can be assumed to be an attack.

              In  this  sense,  it  could  be  argued that TCP tunnel transport is preferred when
              tunneling non-IP or UDP application  protocols  which  might  be  vulnerable  to  a
              message  deletion  or  reordering  attack which falls within the normal operational
              parameters of IP networks.

              So I would make the statement that one should never tunnel a non-IP protocol or UDP
              application  protocol  over  UDP,  if the protocol might be vulnerable to a message
              deletion or reordering attack that falls within the normal operating parameters  of
              what  is to be expected from the physical IP layer.  The problem is easily fixed by
              simply using TCP as the VPN transport layer.

              Silence the output of replay warnings, which are  a  common  false  alarm  on  WiFi
              networks.  This option preserves the security of the replay protection code without
              the verbosity associated with warnings about duplicate packets.

       --replay-persist file
              Persist replay-protection state across sessions using file to save and  reload  the

              This  option will strengthen protection against replay attacks, especially when you
              are using OpenVPN in a dynamic context (such as with --inetd) when OpenVPN sessions
              are frequently started and stopped.

              This  option will keep a disk copy of the current replay protection state (i.e. the
              most recent packet timestamp and sequence number received from the remote peer), so
              that  if an OpenVPN session is stopped and restarted, it will reject any replays of
              packets which were already received by the prior session.

              This option only makes sense when replay protection is enabled  (the  default)  and
              you are using either --secret (shared-secret key mode) or TLS mode with --tls-auth.

              (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.

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

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

              openvpn --test-crypto --secret key


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

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

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

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

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

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

       The OpenVPN distribution contains a set of scripts for managing RSA certificates  &  keys,
       located in the easy-rsa subdirectory.

       The easy-rsa package is also rendered in web form here:

              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.

              Enable TLS and assume client role during TLS handshake.

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

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

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

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

       --capath dir
              Directory containing trusted certificates (CAs and CRLs).  Available  with  OpenSSL
              version >= 0.9.7 dev.

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

              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.

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

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

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

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

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

       --key file
              Local  peer's  private key in .pem format.  Use the private key which was generated
              when you built your peer's certificate (see -cert file above).

       --pkcs12 file
              Specify a PKCS #12 file containing local private key, local certificate,  and  root
              CA certificate.  This option can be used instead of --ca, --cert, and --key.

       --pkcs11-cert-private [0|1]...
              Set  if  access  to  certificate  object  should  be  performed after login.  Every
              provider has its own setting.

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

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

       --pkcs11-pin-cache seconds
              Specify how many seconds the PIN can be cached, the default is until the  token  is

       --pkcs11-protected-authentication [0|1]...
              Use PKCS#11 protected authentication path, useful for biometric and external keypad
              devices.  Every provider has its own setting.

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

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

              0 (default) -- Try to determind automatically.
              1 -- Use sign.
              2 -- Use sign recover.
              4 -- Use decrypt.
              8 -- Use unwrap.

       --cryptoapicert select-string
              Load  the  certificate  and  private  key from the Windows Certificate System Store
              (Windows Only).

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

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

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

              cryptoapicert "SUBJ:Peter Runestig"

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

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

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

       --key-method m
              Use data channel key negotiation method m.  The key method must match on both sides
              of the connection.

              After OpenVPN negotiates a TLS session, a new set of keys for protecting the tunnel
              data channel is generated and exchanged over the TLS session.

              In  method  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 --key-method parameter  has  no  effect  on  this

              (2) After the TLS connection is established, the tunnel session keys are separately
              negotiated over the existing secure TLS channel.  Here, --key-method determines the
              derivation of the tunnel session keys.

       --tls-cipher l
              A  list  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 --show-tls  to
              see a list of supported TLS ciphers.

       --tls-timeout n
              Packet  retransmit  timeout on TLS control channel if no acknowledgment from remote
              within n seconds (default=2).  When OpenVPN sends a control packet to its peer,  it
              will  expect  to  receive an acknowledgement within n seconds or it will retransmit
              the packet, subject to a TCP-like exponential backoff  algorithm.   This  parameter
              only  applies  to  control  channel  packets.   Data  channel  packets (which carry
              encrypted tunnel data) are  never  acknowledged,  sequenced,  or  retransmitted  by
              OpenVPN  because  the  higher  level network protocols running on top of the tunnel
              such as TCP expect this role to be left to them.

       --reneg-bytes n
              Renegotiate data channel key after 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.

       --reneg-pkts n
              Renegotiate  data  channel  key  after  n  packets  sent  and received (disabled by

       --reneg-sec n
              Renegotiate data channel key after 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  --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.

       --hand-window n
              Handshake Window -- the TLS-based key exchange must finalize within  n  seconds  of
              handshake initiation by any peer (default = 60 seconds).  If the handshake fails we
              will attempt to reset our connection with our peer and  try  again.   Even  in  the
              event  of  handshake  failure  we will still use our expiring key for up to --tran-
              window seconds to maintain continuity of transmission of tunnel data.

       --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.

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

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

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

              Exit on TLS negotiation failure.

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

              file (required) is a key file which can be in one of two formats:

              (1) An OpenVPN static  key  file  generated  by  --genkey  (required  if  direction
              parameter is used).

              (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 md5sum(1) or 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 --secret option for more information on the optional direction parameter.

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

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

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

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

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

       --askpass [file]
              Get certificate password from console or 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 --askpass option allows you to
              start OpenVPN from the command line.  It will query you for a  password  before  it
              daemonizes.   To  protect  a private key with a password you should omit the -nodes
              option when you use the openssl  command  line  tool  to  manage  certificates  and
              private keys.

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

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

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

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

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

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

              Note  that  cmd  is  a command line and as such may (if enclosed in quotes) contain
              whitespace separated arguments.  The first word of cmd  is  the  shell  command  to
              execute  and  the  remaining  words  are  its  arguments.  When cmd is executed two
              arguments are appended, as follows:

              cmd certificate_depth X509_NAME_oneline

              These arguments are, respectively, the  current  certificate  depth  and  the  X509
              common name (cn) of the peer.

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

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

       --tls-export-cert directory
              Store the certificates the clients uses upon connection  to  this  directory.  This
              will  be done before --tls-verify is called.  The certificates will use a temporary
              name and will be deleted when the tls-verify script returns.  The  file  name  used
              for the certificate is available via the peer_cert environment variable.

       --x509-username-field fieldname
              Field  in  x509 certificate subject to be used as username (default=CN).  Fieldname
              will be uppercased before matching. When this  option  is  used,  the  --tls-remote
              option will match against the chosen fieldname instead of the CN.

       --tls-remote name
              Accept  connections  only  from a host with X509 name or common name equal to name.
              The remote host must also pass all other tests of verification.

              NOTE: Because tls-remote may test against a  common  name  prefix,  only  use  this
              option  when  you are using OpenVPN with a custom CA certificate that is under your
              control.  Never use this option when your client certificates are signed by a third
              party, such as a commercial web CA.

              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 --tls-remote

              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.

              --tls-remote  is  a  useful  replacement  for the --tls-verify option to verify the
              remote host, because --tls-remote works in a --chroot environment too.

       --ns-cert-type client|server
              Require that peer certificate was signed with an explicit 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 nsCertType field set to "server".

              If  the  server certificate's nsCertType field is set to "server", then the clients
              can verify this with --ns-cert-type server.

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

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

       --remote-cert-eku oid
              Require that peer certificate was signed with an explicit extended key usage.

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

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

       --remote-cert-tls client|server
              Require  that  peer  certificate was signed with an explicit key usage and 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  --remote-cert-tls  client  option  is  equivalent to --remote-cert-ku 80 08 88
              --remote-cert-eku "TLS Web Client Authentication"

              The key usage is digitalSignature and/or keyAgreement.

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

       --crl-verify crl
              Check peer certificate against the file 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

              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.

   SSL Library information:
              (Standalone) Show all cipher algorithms to use with the --cipher option.

              (Standalone) Show all message digest algorithms to use with the --auth option.

              (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.

              (Standalone) Show currently available hardware-based  crypto  acceleration  engines
              supported by the OpenSSL library.

   Generate a random key:
       Used only for non-TLS static key encryption mode.

              (Standalone)  Generate a random key to be used as a shared secret, for use with the
              --secret option.  This file must be shared with the peer over a pre-existing secure
              channel such as scp(1)

       --secret file
              Write key to file.

   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.

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

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

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

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

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

              (Standalone) Remove a persistent tunnel.

       --dev tunX | tapX
              TUN/TAP device

       --user user
              Optional user to be owner of this tunnel.

       --group group
              Optional group to be owner of this tunnel.

   Windows-Specific Options:
       --win-sys path|'env'
              Set  the  Windows  system  directory  pathname  to  use  when  looking  for  system
              executables such as route.exe and netsh.exe.  By default, if this directive is  not
              specified, the pathname will be set to "C:\WINDOWS"

              The  special  string  'env'  indicates  that  the  pathname should be read from the
              SystemRoot environmental variable.

       --ip-win32 method
              When using --ifconfig on Windows, set the TAP-Win32 adapter IP address and  netmask
              using method.  Don't use this option unless you are also using --ifconfig.

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

              dynamic  [offset]  [lease-time]  -- Automatically set the IP address and netmask by
              replying to DHCP query messages generated by the kernel.  This mode is probably the
              "cleanest"  solution for setting the TCP/IP properties since it uses the well-known
              DHCP protocol.  There are, however, two prerequisites for using this mode: (1)  The
              TCP/IP  properties  for  the TAP-Win32 adapter must be set to "Obtain an IP address
              automatically," and (2) OpenVPN needs to claim an IP address in the subnet for  use
              as  the  virtual  DHCP  server address.  By default in --dev tap mode, OpenVPN will
              take the normally unused first address in the subnet.  For example, if your  subnet
              is  netmask,  then  OpenVPN  will  take  the IP address
     to use as the virtual DHCP server address.  In --dev tun mode,  OpenVPN
              will  cause  the  DHCP  server  to  masquerade as if it were coming from the remote
              endpoint.  The optional offset parameter is an integer which is > -256  and  <  256
              and which defaults to 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
              ipconfig /all command can be used to show  what  Windows  thinks  the  DHCP  server
              address is.  OpenVPN will "claim" this address, so make sure to use a free address.
              Having said that, different OpenVPN instantiations, including different ends of the
              same  connection,  can  share the same virtual DHCP server address.  The lease-time
              parameter controls the lease time of the DHCP assignment  given  to  the  TAP-Win32
              adapter,  and  is denoted in seconds.  Normally a very long lease time is preferred
              because it prevents routes involving the TAP-Win32 adapter from being lost when the
              system goes to sleep.  The default lease time is one year.

              netsh  --  Automatically  set the IP address and netmask using the Windows command-
              line "netsh" command.  This method appears to work correctly on Windows XP but  not
              Windows 2000.

              ipapi  --  Automatically set the IP address and netmask using the Windows IP Helper
              API.  This approach does not have ideal semantics,  though  testing  has  indicated
              that  it  works  okay in practice.  If you use this option, it is best to leave the
              TCP/IP properties for the TAP-Win32 adapter in their default state, i.e. "Obtain an
              IP address automatically."

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

       --route-method m
              Which method m to use for adding routes on Windows?

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

       --dhcp-option type [parm]
              Set  extended  TAP-Win32 TCP/IP properties, must be used with --ip-win32 dynamic or
              --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.

              DOMAIN name -- Set Connection-specific DNS Suffix.

              DNS addr -- Set primary domain name server address.   Repeat  this  option  to  set
              secondary DNS server addresses.

              WINS  addr  --  Set  primary WINS server address (NetBIOS over TCP/IP Name Server).
              Repeat this option to set secondary WINS server addresses.

              NBDD addr --  Set  primary  NBDD  server  address  (NetBIOS  over  TCP/IP  Datagram
              Distribution Server) Repeat this option to set secondary NBDD server addresses.

              NTP  addr  --  Set primary NTP server address (Network Time Protocol).  Repeat this
              option to set secondary NTP server addresses.

              NBT type -- Set NetBIOS over TCP/IP  Node  type.   Possible  options:  1  =  b-node
              (broadcasts), 2 = p-node (point-to-point name queries to a WINS server), 4 = m-node
              (broadcast then query name server),  and  8  =  h-node  (query  name  server,  then

              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

              DISABLE-NBT -- Disable Netbios-over-TCP/IP.

              Note that if --dhcp-option is pushed via --push to a non-windows client, the option
              will be saved in the client's environment before the up script is called, under the
              name "foreign_option_{n}".

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

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

              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.

              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.

              Ask Windows to release the TAP adapter lease on shutdown.  This option has the same
              caveats as --dhcp-renew above.

              Run net  stop  dnscache,  net  start  dnscache,  ipconfig  /flushdns  and  ipconfig
              /registerdns  on  connection  initiation.   This  is  known  to  kick  Windows into
              recognizing pushed DNS servers.

              Put up a "press any key to continue"  message  on  the  console  prior  to  OpenVPN
              program  exit.   This  option  is  automatically  used by the Windows explorer when
              OpenVPN is run on a configuration file using the right-click explorer menu.

       --service 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.

              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

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

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

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

              (Standalone)  Show  available  TAP-Win32  adapters  which can be selected using the
              --dev-node option.   On  non-Windows  systems,  the  ifconfig(8)  command  provides
              similar functionality.

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

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

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

              (Standalone) Show OpenVPN's view of the system routing table  and  network  adapter

   PKCS#11 Standalone Options:
       --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.

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

   IPv6 Related Options
       The following options exist to support IPv6 tunneling in  peer-to-peer  and  client-server
       mode.   As of now, this is just very basic documentation of the IPv6-related options. More
       documentation can be found on

       --ifconfig-ipv6 ipv6addr/bits ipv6remote
              configure IPv6 address ipv6addr/bits on the ``tun'' device.  The  second  parameter
              is used as route target for --route-ipv6 if no gateway is specified.

       --route-ipv6 ipv6addr/bits [gateway] [metric]
              setup  IPv6 routing in the system to send the specified IPv6 network into OpenVPN's
              ``tun'' device

       --server-ipv6 ipv6addr/bits
              convenience-function to enable a number of IPv6 related  options  at  once,  namely
              --ifconfig-ipv6,  --ifconfig-ipv6-pool,  --tun-ipv6  and  --push  tun-ipv6  Is only
              accepted if ``--mode server'' or ``--server'' is set.

       --ifconfig-ipv6-pool ipv6addr/bits
              Specify an IPv6 address pool for dynamic assignment to clients.  The pool starts at
              ipv6addr  and  increments  by  +1  for  every  new client (linear mode).  The /bits
              setting controls the size of the pool.

       --ifconfig-ipv6-push ipv6addr/bits ipv6remote
              for ccd/ per-client static IPv6 interface  configuration,  see  --client-config-dir
              and --ifconfig-push for more details.

       --iroute-ipv6 ipv6addr/bits
              for  ccd/ per-client static IPv6 route configuration, see --iroute for more details
              how to setup and use this, and how --iroute and --route interact.


       OpenVPN exports a series of environmental variables for use by user-defined scripts.

   Script Order of Execution
       --up   Executed after TCP/UDP socket bind and TUN/TAP open.

              Executed when we have a still untrusted remote peer.

              Executed after connection authentication, or remote IP address change.

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

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

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

       --down Executed after TCP/UDP and TUN/TAP close.

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

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

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

       Q: Why is string remapping necessary?

       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.

       Q: Can string remapping be disabled?

       A:  Yes,  by  using  the  --no-name-remapping option, however this should be considered an
       advanced option.

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

       X509  Names:  Alphanumeric,  underbar ('_'), dash ('-'), dot ('.'), at ('@'), colon (':'),
       slash ('/'), and equal ('=').  Alphanumeric is defined as a character which will cause the
       C library isalnum() function to return true.

       Common Names: Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), and at ('@').

       --auth-user-pass  username: Same as Common Name, with one exception: starting with OpenVPN
       2.0.1, the username is passed to the OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY  plugin  in  its
       raw form, without string remapping.

       --auth-user-pass  password:  Any  "printable"  character  except  CR  or LF.  Printable is
       defined to be a character which will cause the C  library  isprint()  function  to  return

       --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.

       Environmental variable names: Alphanumeric or underbar ('_').

       Environmental variable values: Any printable character.

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

   Environmental Variables
       Once  set,  a  variable  is  persisted  indefinitely until it is reset by a new value or a

       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.

              Total  number  of  bytes  received  from  client  during VPN session.  Set prior to
              execution of the --client-disconnect script.

              Total number of bytes sent to client during VPN session.  Set prior to execution of
              the --client-disconnect script.

              The  X509  common  name  of  an  authenticated  client.   Set prior to execution of
              --client-connect, --client-disconnect, and --auth-user-pass-verify scripts.

       config Name of first --config file.  Set on program initiation and reset on SIGHUP.

       daemon Set to "1" if the --daemon directive  is  specified,  or  "0"  otherwise.   Set  on
              program initiation and reset on SIGHUP.

              Set to "1" if the --log or --log-append directives are specified, or "0" otherwise.
              Set on program initiation and reset on SIGHUP.

       dev    The actual name of the TUN/TAP device, including a unit number if it  exists.   Set
              prior to --up or --down script execution.

              An option pushed via --push to a client which does not natively support it, such as
              --dhcp-option on a non-Windows system,  will  be  recorded  to  this  environmental
              variable sequence prior to --up script execution.

              The  broadcast  address  for the virtual ethernet segment which is derived from the
              --ifconfig option when --dev tap  is  used.   Set  prior  to  OpenVPN  calling  the
              ifconfig  or  netsh  (windows  version  of ifconfig) commands which normally occurs
              prior to --up script execution.

              The local VPN endpoint  IP  address  specified  in  the  --ifconfig  option  (first
              parameter).  Set prior to OpenVPN calling the ifconfig or netsh (windows version of
              ifconfig) commands which normally occurs prior to --up script execution.

              The remote VPN endpoint IP address  specified  in  the  --ifconfig  option  (second
              parameter)  when  --dev  tun is used.  Set prior to OpenVPN calling the ifconfig or
              netsh (windows version of ifconfig) commands which normally occurs  prior  to  --up
              script execution.

              The  subnet  mask  of  the virtual ethernet segment that is specified as the second
              parameter to --ifconfig when --dev tap is being used.  Set prior to OpenVPN calling
              the  ifconfig or netsh (windows version of ifconfig) commands which normally occurs
              prior to --up script execution.

              The local virtual IP address for the TUN/TAP tunnel taken from  an  --ifconfig-push
              directive  if  specified,  or  otherwise  from the ifconfig pool (controlled by the
              --ifconfig-pool config file directive).  Only set  for  --dev  tun  tunnels.   This
              option  is  set  on  the  server  prior  to  execution  of the --client-connect and
              --client-disconnect scripts.

              The virtual IP netmask  for  the  TUN/TAP  tunnel  taken  from  an  --ifconfig-push
              directive  if  specified,  or  otherwise  from the ifconfig pool (controlled by the
              --ifconfig-pool config file directive).  Only set  for  --dev  tap  tunnels.   This
              option  is  set  on  the  server  prior  to  execution  of the --client-connect and
              --client-disconnect scripts.

              The remote virtual IP address for the TUN/TAP tunnel taken from an  --ifconfig-push
              directive  if  specified,  or  otherwise  from the ifconfig pool (controlled by the
              --ifconfig-pool config file directive).  This option is set on the server prior  to
              execution of the --client-connect and --client-disconnect scripts.

              The  maximum packet size (not including the IP header) of tunnel data in UDP tunnel
              transport mode.  Set prior to --up or --down script execution.

       local  The --local parameter.  Set on program initiation and reset on SIGHUP.

              The local port number, specified by --port or --lport.  Set on  program  initiation
              and reset on SIGHUP.

              The password provided by a connecting client.  Set prior to --auth-user-pass-verify
              script execution only when the via-env modifier is specified, and deleted from  the
              environment after the script returns.

       proto  The --proto parameter.  Set on program initiation and reset on SIGHUP.

              The --remote parameter.  Set on program initiation and reset on SIGHUP.

              The  remote port number, specified by --port or --rport.  Set on program initiation
              and reset on SIGHUP.

              The pre-existing default IP gateway in the system routing table.  Set prior to --up
              script execution.

              The  default  gateway  used by --route options, as specified in either the --route-
              gateway option or the second parameter to --ifconfig when --dev tun  is  specified.
              Set prior to --up script execution.

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

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

              n is the OpenVPN route number, starting from 1.

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

              Temporary file name containing the client certificate upon connection.   Useful  in
              conjunction with --tls-verify

              Set   to  "init"  or  "restart"  prior  to  up/down  script  execution.   For  more
              information, see documentation for --up.

              Prior to execution of any script, this variable is set to the type of script  being
              run.   It  can  be  one of the following: up, down, ipchange, route-up, tls-verify,
              auth-user-pass-verify, client-connect, client-disconnect, or learn-address.

       signal The reason for exit or restart.  Can be one of sigusr1,  sighup,  sigterm,  sigint,
              inactive  (controlled  by  --inactive option), ping-exit (controlled by --ping-exit
              option),  ping-restart  (controlled  by  --ping-restart  option),  connection-reset
              (triggered  on  TCP  connection  reset),  error, or unknown (unknown signal).  This
              variable is set just prior to down script execution.

              Client connection timestamp, formatted as a human-readable time string.  Set  prior
              to execution of the --client-connect script.

              The  duration  (in  seconds) of the client session which is now disconnecting.  Set
              prior to execution of the --client-disconnect script.

              Client connection timestamp, formatted as a  unix  integer  date/time  value.   Set
              prior to execution of the --client-connect script.

              A  series  of  certificate fields from the remote peer, where n is the verification
              level.  Only set for TLS connections.   Set  prior  to  execution  of  --tls-verify

              The  serial  number  of  the  certificate  from  the  remote  peer,  where n is the
              verification level.  Only set for TLS  connections.   Set  prior  to  execution  of
              --tls-verify  script. This is in the form of a hex string like "37AB46E0", which is
              suitable for doing serial-based OCSP queries (with OpenSSL,  you  have  to  prepend
              "0x"  to  the  string).  If  something  goes wrong while reading the value from the
              certificate it will be an empty string, so your code should check  that.   See  the
              contrib/OCSP_check/ script for an example.

              The MTU of the TUN/TAP device.  Set prior to --up or --down script execution.

       trusted_ip (or trusted_ip6)
              Actual  IP  address of connecting client or peer which has been authenticated.  Set
              prior  to  execution  of  --ipchange,  --client-connect,  and   --client-disconnect
              scripts.  If using ipv6 endpoints (udp6, tcp6), trusted_ip6 will be set instead.

              Actual  port number of connecting client or peer which has been authenticated.  Set
              prior  to  execution  of  --ipchange,  --client-connect,  and   --client-disconnect

       untrusted_ip (or untrusted_ip6)
              Actual  IP  address  of  connecting client or peer which has not been authenticated
              yet.  Sometimes used to nmap the connecting host in a --tls-verify script to ensure
              it is firewalled properly.  Set prior to execution of --tls-verify and --auth-user-
              pass-verify scripts.  If using ipv6 endpoints (udp6, tcp6), untrusted_ip6  will  be
              set instead.

              Actual  port  number  of connecting client or peer which has not been authenticated
              yet.  Set prior to execution of --tls-verify and --auth-user-pass-verify scripts.

              The username provided by a connecting client.  Set prior to --auth-user-pass-verify
              script execution only when the via-env modifier is specified.

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



       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.

              Like  SIGHUP, except don't re-read configuration file, and possibly don't close and
              reopen TUN/TAP device, re-read  key  files,  preserve  local  IP  address/port,  or
              preserve most recently authenticated remote IP address/port based on --persist-tun,
              --persist-key, --persist-local-ip,  and  --persist-remote-ip  options  respectively
              (see above).

              This  signal  may  also be internally generated by a timeout condition, governed by
              the --ping-restart option.

              This  signal,  when  combined  with  --persist-remote-ip,  may  be  sent  when  the
              underlying  parameters of the host's network interface change such as when the host
              is a DHCP client and is assigned a new IP address.  See --ipchange above  for  more

              Causes OpenVPN to display its current statistics (to the syslog file if --daemon is
              used, or stdout otherwise).

              Causes OpenVPN to exit gracefully.


       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: mknod /dev/net/tun c 10 200

       Load driver: modprobe tun


       Prior  to  running  these examples, you should have OpenVPN installed on two machines with
       network connectivity between them.  If you have not yet  installed  OpenVPN,  consult  the
       INSTALL file included in the OpenVPN distribution.

   TUN/TAP Setup:
       If you are using Linux 2.4 or higher, make the tun device node and load the tun module:

              mknod /dev/net/tun c 10 200

              modprobe tun

       If  you  installed  from  RPM, the mknod step may be omitted, because the RPM install does
       that for you.

       Only Linux 2.4 and newer are supported.

       For other platforms, consult the INSTALL file at for  more

   Firewall Setup:
       If  firewalls  exist between the two machines, they should be set to forward UDP port 1194
       in both directions.  If you do not  have  control  over  the  firewalls  between  the  two
       machines,  you may still be able to use OpenVPN by adding --ping 15 to each of the openvpn
       commands used below in the examples (this will cause each peer to send out a UDP  ping  to
       its  remote peer once every 15 seconds which will cause many stateful firewalls to forward
       packets in both directions without an explicit firewall rule).

       If you are using a Linux iptables-based firewall, you may  need  to  enter  the  following
       command to allow incoming packets on the TUN device:

              iptables -A INPUT -i tun+ -j ACCEPT

       See the firewalls section below for more information on configuring firewalls for use with

   VPN Address Setup:
       For purposes of our example, our two machines will be called and   If  you
       are  constructing  a  VPN  over  the  internet,  then  replace and with the
       internet hostname or IP address that each machine will use to contact the other  over  the

       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 will be and for,

       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  and  you  wish  to
       connect to via ssh without using the VPN (since ssh has its own built-in security)
       you would use the command ssh  However in the same scenario, you could  also  use
       the  command  telnet  to create a telnet session with over the VPN, that
       would use the VPN to secure the session rather than ssh.

       You can use any address you wish for the tunnel endpoints but  make  sure  that  they  are
       private addresses (such as those that begin with 10 or 192.168) and that they are not part
       of any existing subnet on the networks of either peer, unless you are  bridging.   If  you
       use  an  address that is part of your local subnet for either of the tunnel endpoints, you
       will get a weird feedback loop.

   Example 1: A simple tunnel without security
       On may:

              openvpn --remote --dev tun1 --ifconfig --verb 9

       On june:

              openvpn --remote --dev tun1 --ifconfig --verb 9

       Now verify the tunnel is working by pinging across the tunnel.

       On may:


       On june:


       The --verb 9 option will produce verbose output, similar to the tcpdump(8) program.   Omit
       the --verb 9 option to have OpenVPN run quietly.

   Example 2: A tunnel with static-key security (i.e. using a pre-shared secret)
       First build a static key on may.

              openvpn --genkey --secret key

       This  command  will build a random key file called key (in ascii format).  Now copy key to
       june over a secure medium such as by using the scp(1) program.

       On may:

              openvpn --remote --dev tun1 --ifconfig --verb 5  --secret

       On june:

              openvpn  --remote --dev tun1 --ifconfig --verb 5 --secret

       Now verify the tunnel is working by pinging across the tunnel.

       On may:


       On june:


   Example 3: A tunnel with full TLS-based security
       For this test, we will designate may as the TLS client and june as the TLS  server.   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 --cert
       is  discussed  for  more info).  Then construct Diffie Hellman parameters (see above where
       --dh is discussed for more info).  You can also use the included  test  files  client.crt,
       client.key,  server.crt,  server.key  and ca.crt.  The .crt files are certificates/public-
       keys, the .key files are private keys, and ca.crt is a  certification  authority  who  has
       signed  both  client.crt  and  server.crt.   For Diffie Hellman parameters you can use the
       included file dh1024.pem.   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.

       On may:

              openvpn --remote --dev tun1 --ifconfig --tls-client  --ca
              ca.crt --cert client.crt --key client.key --reneg-sec 60 --verb 5

       On june:

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

       Now verify the tunnel is working by pinging across the tunnel.

       On may:


       On june:


       Notice the --reneg-sec 60 option we used above.  That tells  OpenVPN  to  renegotiate  the
       data  channel  keys  every  minute.   Since  we  used  --verb 5 above, you will see status
       information on each new key negotiation.

       For production operations, a key renegotiation interval of  60  seconds  is  probably  too
       frequent.   Omit  the  --reneg-sec  60  option  to use OpenVPN's default key renegotiation
       interval of one hour.

       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 and june's is

       First, ensure that IP forwarding is enabled on both peers.  On Linux, enable routing:

              echo 1 > /proc/sys/net/ipv4/ip_forward

       and enable TUN packet forwarding through the firewall:

              iptables -A FORWARD -i tun+ -j ACCEPT

       On may:

              route add -net netmask gw

       On june:

              route add -net netmask gw

       Now any machine on the subnet can access any machine on the 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 --up option.


       OpenVPN's usage of a single UDP port makes it fairly firewall-friendly.  You should add an
       entry to your firewall rules to allow incoming OpenVPN packets.  On Linux 2.4+:

              iptables -A INPUT -p udp -s --dport 1194 -j ACCEPT

       This  will  allow  incoming  packets on UDP port 1194 (OpenVPN's default UDP port) from an
       OpenVPN peer at

       If you are using HMAC-based packet authentication (the default in any of OpenVPN's  secure
       modes),  having  the  firewall  filter on source address can be considered optional, since
       HMAC packet authentication is a much more secure method of verifying the authenticity of a
       packet source.  In that case:

              iptables -A INPUT -p udp --dport 1194 -j ACCEPT

       would be adequate and would not render the host inflexible with respect to its peer having
       a dynamic IP address.

       OpenVPN also works well on stateful firewalls.  In some cases, you may not need to add any
       static  rules  to the firewall list if you are using a stateful firewall that knows how to
       track UDP connections.  If you specify --ping n, OpenVPN will  be  guaranteed  to  send  a
       packet to its peer at least once every n seconds.  If n is less than the stateful firewall
       connection timeout, you can maintain an OpenVPN connection indefinitely  without  explicit
       firewall rules.

       You should also add firewall rules to allow incoming IP traffic on TUN or TAP devices such

              iptables -A INPUT -i tun+ -j ACCEPT

       to allow input packets from tun devices,

              iptables -A FORWARD -i tun+ -j ACCEPT

       to allow input packets from tun devices to be  forwarded  to  other  hosts  on  the  local

              iptables -A INPUT -i tap+ -j ACCEPT

       to allow input packets from tap devices, and

              iptables -A FORWARD -i tap+ -j ACCEPT

       to  allow  input  packets  from  tap  devices  to be forwarded to other hosts on the local

       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.



       For  a  more  comprehensive  guide  to setting up OpenVPN in a production setting, see the
       OpenVPN HOWTO at


       For a description of OpenVPN's underlying protocol, see


       OpenVPN's web site is at

       Go here to download the latest version of OpenVPN, subscribe to the  mailing  lists,  read
       the mailing list archives, or browse the SVN repository.


       Report all bugs to the OpenVPN team <>.


       dhcpcd(8), ifconfig(8), openssl(1), route(8), scp(1) ssh(1)


       This  product includes software developed by the OpenSSL Project (

       For more information on the TLS protocol, see

       For   more   information    on    the    LZO    real-time    compression    library    see


       Copyright  (C) 2002-2010 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.


       James Yonan <>

                                         17 November 2008                              openvpn(8)