Provided by: openvpn_2.3.10-1ubuntu2_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, the first address
              returned by the system getaddrinfo() function will be used  (no  DNS  randomization
              inside OpenVPN 2.3.x, and it will not try multiple addresses).

              Prepend  a  random  string  (6 bytes, 12 hex characters) to 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,  explicit-exit-notify,
              float,  fragment,  http-proxy,  http-proxy-option,  http-proxy-retry,   http-proxy-
              timeout,  link-mtu,  local,  lport,  mssfix, mtu-disc, nobind, port, proto, remote,
              rport, socks-proxy, socks-proxy-retry, tun-mtu and tun-mtu-extra.

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

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

       --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

              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] [authfile]
              Connect  to  remote  host  through  a  Socks5 proxy at address server and port port
              (default=1080).  authfile (optional) is a file containing a username  and  password
              on 2 lines, or "stdin" to prompt from console.

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

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

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

              cmd ip_address port_number

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

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

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

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

       --port port
              TCP/UDP  port  number or port name for both local and remote (sets both --lport and
              --rport options to given  port).   The  current  default  of  1194  represents  the
              official  IANA  port  number assignment for OpenVPN and has been used since version
              2.0-beta17.  Previous versions used port 5000 as the default.

       --lport port
              Set local TCP/UDP port number or name.   Cannot  be  used  together  with  --nobind

       --rport port
              Set  TCP/UDP  port number or name used by the --remote option. The port can also be
              set directly using the --remote option.

       --bind 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.

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

              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.

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

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

       --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 in point-to-point mode, rn is the IP  address  of  the  remote  VPN
              endpoint.   For  TAP devices, or TUN devices used with --topology subnet, rn is the
              subnet mask of the virtual network segment which is being created or connected to.

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

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

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

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

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

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

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

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

       --route-pre-down cmd
              Run command cmd before routes are removed upon disconnection.

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

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

              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
              routes, block-outside-dns and dhcp options like DNS servers.

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

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

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

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

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

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

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

              This option performs three steps:

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

              (2) Delete the default gateway route.

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

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

              Option flags:

              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

              autolocal -- Try to automatically determine whether to enable local flag above.

              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).

              block-local -- Block access to local LAN when the tunnel is active, except for  the
              LAN  gateway itself.  This is accomplished by routing the local LAN (except for the
              LAN gateway address) into the tunnel.

       --link-mtu n
              Sets an upper bound on the size of UDP  packets  which  are  sent  between  OpenVPN
              peers.  It's best not to set this parameter unless you know what you're doing.

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

       --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.  Defaults to operation system default.

       --rcvbuf size
              Set the TCP/UDP socket receive buffer size.  Defaults to operation system default.

       --mark value
              Mark  encrypted  packets  being  sent  with value. The mark value can be matched in
              policy routing and packetfilter rules. This option is only supported in  Linux  and
              does nothing on other operating systems.

       --socket-flags flags...
              Apply the given flags to the OpenVPN transport socket.  Currently, only 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.
              Note that this will only work if mode is set to p2p.  If  you  want  to  limit  the
              bandwidth in both directions, use this option on both peers.

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

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

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

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

       --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.

              The server timeout is set twice the value of the  second  argument.   This  ensures
              that  a  timeout  is  detected  on  client  side  before  the server side drops the

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

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

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

              For --dev tun execute as:

              cmd tun_dev tun_mtu link_mtu ifconfig_local_ip ifconfig_remote_ip [ init |  restart

              For --dev tap execute as:

              cmd tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask [ init | restart ]

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

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

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

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

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

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

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

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

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

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

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

              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.

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

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

              See also --ignore-unknown-option

       --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.

       --ignore-unknown-option opt1 opt2 opt3 ... optN
              When one of options opt1 ... optN is encountered  in  the  configuration  file  the
              configuration  file  parsing does not fail if this OpenVPN version does not support
              the option. Multiple --ignore-unknown-option options can  be  given  to  support  a
              larger number of options to ignore.

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

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

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

              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).

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

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

              To run scripts in Windows in earlier OpenVPN versions you needed to  either  add  a
              full  path  to  the script interpreter which can parse the script or use the system
              flag to run these scripts.  As of OpenVPN v2.3 it is now a  strict  requirement  to
              have  full path to the script interpreter when running non-executables files.  This
              is not needed for executable files, such as .exe, .com, .bat or  .cmd  files.   For
              example, if you have a Visual Basic script, you must use this syntax now:

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

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

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

              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

              Note: if OpenVPN is built using the PolarSSL SSL library, --chroot will  only  work
              if  a  /dev/urandom device node is available inside the chroot directory dir.  This
              is due to the way  PolarSSL  works  (it  wants  to  open  /dev/urandom  every  time
              randomness is needed, not just once at startup) and nothing OpenVPN can influence.

       --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 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-

              Note: as soon as OpenVPN has daemonized, it can not ask for  usernames,  passwords,
              or  key  pass  phrases anymore.  This has certain consequences, namely that using a
              password-protected private key will fail unless the --askpass  option  is  used  to
              tell OpenVPN to ask for the pass phrase (this requirement is new in 2.3.7, and is a
              consequence of calling daemon() before initializing the crypto layer).

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

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

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

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

              Note: this option is only relevant for UDP servers.

              Note 2: if you do an IPv6+IPv4 dual-stack bind on a  Linux  machine  with  multiple
              IPv4  address,  connections to IPv4 addresses will not work right on kernels before
              3.15, due to missing kernel support for the IPv4-mapped  case  (some  distributions
              have ported this to earlier kernel versions, though).

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

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

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

              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.

              Query  management  channel  for  proxy  server  information for a specific --remote

              Allow  management  interface  to  override   --remote   directives   (client-only).
              --management-external-key  Allows  usage  for  external private key file instead of
              --key option (client-only).

              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.  For
              --management-client this option is  not  needed  since  a  disconnect  will  always
              generate a SIGTERM.

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

              Report tunnel up/down events to management interface.

              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 ['nopool']
              A helper directive designed to simplify the configuration of OpenVPN's server mode.
              This  directive  will  set  up  an  OpenVPN server which will allocate addresses to
              clients out of the given network/netmask.  The server itself  will  take  the  ".1"
              address  of  the  given  network  for  use as the server-side endpoint of the local
              TUN/TAP interface.

              For example, --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"
                     if route-gateway unset:

              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.

              Push additional information about the client to server.  The additional information
              consists of the following data:

              IV_VER=<version> -- the client OpenVPN version

              IV_PLAT=[linux|solaris|openbsd|mac|netbsd|freebsd|win] -- the client OS platform

              IV_HWADDR=<mac address> -- the MAC address of clients default gateway

              IV_LZO_STUB=1 -- if client was built with LZO stub capability

              UV_<name>=<value> -- client environment variables whose names start with "UV_"

              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 [alias]
              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

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

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

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

              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 cmd
              Run command cmd on client connection.

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

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

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

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

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

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

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

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

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

              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.

       --stale-routes-check n [t]
              Remove routes haven't had activity for n seconds (i.e. the ageing time).

              This check is ran every t seconds (i.e. check interval).

              If t is not present it defaults to n

              This   option   helps   to   keep  the  dynamic  routing  table  small.   See  also

       --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 command cmd to validate client virtual addresses or routes.

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

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

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

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

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

              If  method  is  set  to  "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.

       --compat-names [no-remapping] (DEPRECATED)
              Until OpenVPN v2.3 the format of the X.509 Subject fields was formatted like this:

              /C=US/L=Somewhere/CN=John Doe/

              In  addition  the old behaviour was to remap any character other than alphanumeric,
              underscore ('_'), dash ('-'), dot ('.'), and slash ('/') to underscore ('_').   The
              X.509  Subject  string  as  returned  by  the  tls_id environmental variable, could
              additionally contain colon (':') or equal ('=').

              When using the --compat-names option, this old formatting and remapping will be re-
              enabled  again.   This  is  purely implemented for compatibility reasons when using
              older plug-ins or scripts which  does  not  handle  the  new  formatting  or  UTF-8

              In  OpenVPN  v2.3  the  formatting of these fields changed into a more standardised
              format.  It now looks like:

              C=US, L=Somewhere, CN=John Doe,

              The new default format in OpenVPN v2.3 also does not  do  the  character  remapping
              which  happened  earlier.   This  new  format  enables  proper  support  for  UTF-8
              characters in the usernames, X.509 Subject fields and Common Name variables and  it
              complies to the RFC 2253, UTF-8 String Representation of Distinguished Names.

              The  no-remapping  mode  flag  can  be  used  with  the --compat-names option to be
              compatible  with  the  now  deprecated  --no-name-remapping  option.   It  is  only
              available at the server. When this mode flag is used, the Common Name, Subject, and
              username strings are allowed to include any printable  character  including  space,
              but  excluding  control  characters  such as tab, newline, and carriage-return. no-
              remapping is only available on the server side.

              Please note: This option is immediately deprecated.  It is only implemented to make
              the  transition to the new formatting less intrusive.  It will be removed either in
              OpenVPN v2.4 or v2.5.  So please make sure you use  the  --verify-x509-name  option
              instead  of  --tls-remote  as  soon  as  possible  and  update  your  scripts where

       --no-name-remapping (DEPRECATED)
              The --no-name-remapping option is an  alias  for  --compat-names no-remapping.   It
              ensures  compatibility  with  server  configurations  using the --no-name-remapping

              Please note: This option is now deprecated.  It will be removed either  in  OpenVPN
              v2.4  or  v2.5.   So  please  make  sure  you support the new X.509 name formatting
              described with the --compat-names option as soon as possible.

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

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

              Not implemented on Windows.

   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. If the password line is missing, OpenVPN will prompt
              for one.

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

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

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

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

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

              type can be one of:

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

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

       --static-challenge t e
              Enable  static  challenge/response  protocol using challenge text t, with echo flag
              given by e (0|1).

              The echo flag indicates whether or not the user's response to the challenge  should
              be echoed.

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

       --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.  As
              this only makes sense in client-to-server setups, it cannot be  used  in  point-to-
              point setups using --secret symmetrical key mode.

       --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.

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

       --auth alg
              Authenticate 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 data channel 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.

              Enable prediction resistance on PolarSSL's RNG.

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

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

              Note that this option only works with PolarSSL versions greater than 1.1.

              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.  Not available with PolarSSL.

              When  using  the --capath option, you are required to supply valid CRLs for the CAs
              too.  CAs in the capath directory are expected to be named  <hash>.<n>.   CRLs  are
              expected  to  be named <hash>.r<n>.  See the -CApath option of openssl verify , and
              the -hash option of openssl x509 and openssl crl for more information.

       --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 ).

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

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

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

       --tls-version-min version ['or-highest']
              Enable TLS version negotiation, and set the minimum TLS version we will accept from
              the  peer (default is "1.0").  Examples for version include "1.0", "1.1", or "1.2".
              If 'or-highest' is specified and version is not recognized, we will only accept the
              highest TLS version supported by the local SSL implementation.

              Also see --tls-version-max below, for information on compatibility.

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

              If and only if this is set to 1.0, and OpenSSL is used (not PolarSSL), then OpenVPN
              will  set  up OpenSSL to use a fixed TLSv1 handshake. All other configurations will
              autonegotiate in the given limits, and the choice of handshake versions is left  to
              the SSL implementation.

       --pkcs12 file
              Specify  a  PKCS #12 file containing local private key, local certificate, and root
              CA certificate.  This option can be used instead of --ca, --cert, and  --key.   Not
              available with PolarSSL.

       --verify-hash hash
              Specify  SHA1  fingerprint  for  level-1  cert.   The  level-1  cert  is the CA (or
              intermediate cert) that signs the leaf certificate, and is  one  removed  from  the
              leaf  certificate in the direction of the root.  When accepting a connection from a
              peer, the level-1 cert fingerprint must match hash or certificate verification will
              fail.       Hash      is      specified      as     XX:XX:...      For     example:

       --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.

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

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

              0 (default) -- Try to determine 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/OpenSSL 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 (":").

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

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

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

              Warning!  --tls-cipher is an expert feature, which - if used correcly - can improve
              the  security of your VPN connection.  But it is also easy to unwittingly use it to
              carefully align a gun with your foot, or just  break  your  connection.   Use  with

              The  default  for  --tls-cipher is to use PolarSSL's default cipher list when using
              PolarSSL or "DEFAULT:!EXP:!PSK:!SRP:!kRSA" when using OpenSSL.

       --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) DEPRECATED 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. This option is deprecated and will stop working in OpenVPN 2.4
              and newer releases.

              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.

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

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

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

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

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

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

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

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

              cmd certificate_depth subject

              These arguments are, respectively, the  current  certificate  depth  and  the  X509
              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 [ext:]fieldname
              Field  in  the  X.509  certificate subject to be used as the username (default=CN).
              Typically, this option is specified with fieldname as either of the following:

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

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

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

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

       --tls-remote name (DEPRECATED)
              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.

              Please  also  note:  This  option  is now deprecated.  It will be removed either in
              OpenVPN v2.4 or v2.5.   So  please  make  sure  you  support  the  new  X.509  name
              formatting described with the --compat-names option as soon as possible by updating
              your configurations to use --verify-x509-name instead.

       --verify-x509-name name type
              Accept connections only if a host's X.509 name is equal to name.  The  remote  host
              must also pass all other tests of verification.

              Which  X.509  name is compared to name depends on the setting of type.  type can be
              "subject" to match the complete subject DN (default), "name" to match a subject RDN
              or  "name-prefix"  to  match  a  subject RDN prefix.  Which RDN is verified as name
              depends on the --x509-username-field option. But it defaults  to  the  common  name
              (CN),  e.g.  a  certificate with a subject DN "C=KG, ST=NA, L=Bishkek, CN=Server-1"
              would be matched by:

              --verify-x509-name 'C=KG, ST=NA,  L=Bishkek,  CN=Server-1'  and  --verify-x509-name
              Server-1 name or you could use --verify-x509-name Server- name-prefix if you want a
              client to only accept connections to "Server-1", "Server-2", etc.

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

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

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

       --x509-track attribute
              Save  peer  X509  attribute  value in environment for use by plugins and management
              interface.  Prepend a '+' to attribute to save values from full cert chain.  Values
              will be encoded as X509_<depth>_<attribute>=<value>.  Multiple --x509-track options
              can be defined to track multiple attributes.  Not available with PolarSSL.

       --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, --verify-x509-name, or

       --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,  --verify-x509-name,  or

       --crl-verify crl ['dir']
              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.

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

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

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

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

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

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

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

              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.

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

              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.

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

              --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.    All  options  are  modeled  after  their  IPv4  counterparts,  so  more  detailed
       explanations given there apply here as well (except for --topology , which has  no  effect
       on IPv6).

       --ifconfig-ipv6 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.  Due to implementation details, the pool
              size must be between /64 and /112.

       --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 right before the routes are removed.

              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.

              On  Windows, the device index of the TUN/TAP adapter (to be used in netsh.exe calls
              which sometimes just do not work right with interface names).  Set prior to --up or
              --down script execution.

              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 IPv6 address specified in the --ifconfig-ipv6 option  (first
              parameter).  Set prior to OpenVPN calling the ifconfig or netsh (windows version of
              ifconfig) commands which normally occurs prior to --up script execution.

              The prefix length of the IPv6 network on the VPN interface.  Derived from the  /nnn
              parameter of the IPv6 address in the --ifconfig-ipv6 option (first parameter).  Set
              prior to OpenVPN calling the  ifconfig  or  netsh  (windows  version  of  ifconfig)
              commands which normally occurs prior to --up script execution.

              The  remote  VPN  endpoint  IPv6  address  specified  in the --ifconfig-ipv6 option
              (second parameter).  Set prior to OpenVPN calling the ifconfig  or  netsh  (windows
              version of ifconfig) commands which normally occurs prior to --up script execution.

              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.

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

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

              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.   Set
              prior to execution of any script.

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

              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.

              Contains the certificate  SHA1  fingerprint/digest  hash  value,  where  n  is  the
              verification  level.   Only  set  for  TLS  connections.  Set prior to execution of
              --tls-verify 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  decimal  string  like  "933971680",
              which is suitable for doing serial-based OCSP queries (with OpenSSL, do not prepend
              "0x" to the string) If something goes  wrong  while  reading  the  value  from  the
              certificate  it  will  be an empty string, so your code should check that.  See the
              contrib/OCSP_check/ script for an example.

              Like tls_serial_{n}, but in hex form (e.g. "12:34:56:78:9A").

              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.



       OpenVPN  allows  including  files  in  the  main configuration for the --ca, --cert, --dh,
       --extra-certs, --key, --pkcs12, --secret and --tls-auth options.

       Each inline file started by the line <option> and ended by the line </option>

       Here is an example of an inline file usage

           -----BEGIN CERTIFICATE-----
           -----END CERTIFICATE-----

       When using the inline file feature with --pkcs12 the inline file has to be base64 encoded.
       Encoding  of  a  .p12  file  into  base64  can be done for example with OpenSSL by running
       openssl base64 -in input.p12


       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 internet.

       Now  we  will choose the tunnel endpoints.  Tunnel endpoints are private IP addresses that
       only have meaning in the context of the VPN.  Each machine will use the tunnel endpoint of
       the  other  machine  to  access  it over the VPN.  In our example, the tunnel endpoint for 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

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

   Example 1: A simple tunnel without security
       On bob:

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

       On alice:

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

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

       On bob:


       On alice:


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

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

              openvpn --genkey --secret key

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

       On bob:

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

       On alice:

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

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

       On bob:


       On alice:


   Example 3: A tunnel with full TLS-based security
       For  this test, we will designate bob as the TLS client and alice as the TLS server.  Note
       that client or server designation only has meaning  for  the  TLS  subsystem.  It  has  no
       bearing on OpenVPN's peer-to-peer, UDP-based communication model.

       First,  build  a  separate  certificate/key  pair  for both bob and alice (see above where
       --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 bob:

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

       On alice:

              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 bob:


       On alice:


       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 bob and alice have two network interfaces each, one connected
       to the internet, and the other to a private network.  Our goal is to securely connect both
       private  networks.  We will assume that bob's private subnet is and alice'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 bob:

              route add -net netmask gw

       On alice:

              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 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)