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

   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

          Note that configuration files can  be  nested  to  a  reasonable

          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

          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

              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 capability.

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

   --remote 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

          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-chars>".

          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 ('tcp'|'udp').

          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 tcp-server.

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

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

          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

          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

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

          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

          VERSION  version  --  Set  HTTP  version   number   to   version

          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 option.

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

   --bind 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

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

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

          tun devices encapsulate IPv4 or IPv6 (OSI  Layer  3)  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 address.

          This option exists in OpenVPN 2.1 or higher.

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

          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

          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

          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 space.

          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

          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

   --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 packets.

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

          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 omitted.

          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

          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 value.

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

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

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

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

   --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

          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

   --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. Resulting packet would be at  most  28  bytes
          larger for IPv4 and 48 bytes for IPv6 (20/40 bytes for IP header
          and 8 bytes for UDP header). Default value of 1450  allows  IPv4
          packets  to  be  transmitted over a link with MTU 1473 or higher
          without IP level fragmentation.

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

          --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

          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

   --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

          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 connection.

          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 called.

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

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

          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"

          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

   --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

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

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

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

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

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

          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

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

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

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

          See also --ignore-unknown-option

   --setenv-safe 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

          0 -- Strictly no calling of external programs.
          1 -- (Default) Only call built-in executables such as  ifconfig,
          ip, route, or netsh.
          2  --  Allow  calling  of  built-in executables and user-defined
          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 device).

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

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

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

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

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

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

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

   --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-fatal.

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

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

          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

   --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 --daemon.

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

   --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

   --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 default.

          Note: this option is only relevant for UDP servers.

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

   --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

          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 levels).

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

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

   --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"

          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 --comp-lzo.

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

   --management 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 (client-only).

          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

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

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

          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

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

          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 follows:

              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

          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

          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-

          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 allocation.

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

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

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

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

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

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

   --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

          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 argument.

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

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

   --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 files.

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

          * 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

   --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 --max-routes-per-client

   --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 --tls-auth.

   --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

          [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 "delete".

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

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

   --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 client.

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

          If method is set to "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

          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/ 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 characters.

          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

          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 necessary.

   --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 option.

          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

          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
          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 enabled.

   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

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

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

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

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

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

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

          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 ciphertext.

          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

          For       more       information      on      blowfish,      see

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

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

          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

   --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

          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 state.

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

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

          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

          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

   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

          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

   --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

          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 file.

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

   --tls-version-min 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

   --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

   --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 removed.

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

   --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 process.

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

   --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 care!

          The default for --tls-cipher is to use PolarSSL's default cipher
          list          when          using          PolarSSL           or
          "DEFAULT:!EXP:!LOW:!MEDIUM:!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

   --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 default).

   --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 reconnect.

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

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

          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

          (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

          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

          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

          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

          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

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

   --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 Server

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

          --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

   --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

          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 --tls-verify.

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

          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 representation.

   --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

          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

          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 --tls-verify.

   --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 PKI.

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

          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

          (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

   --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

          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

          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

   --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 later.

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

          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 signaled.

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

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

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

          (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

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

   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

          --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

          Executed  in  --mode  server  mode  immediately   after   client

          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 untrusted.

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

   Q: Why is string remapping necessary?

   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 true.

   --client-config-dir  filename  as derived from common name or username:
   Alphanumeric, underbar ('_'), dash ('-'), and dot ('.') except for  "."
   or ".." as standalone strings.  As of 2.0.1-rc6, the at ('@') character
   has been added as well for compatibility with the common name character

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

   Environmental variable values: Any printable character.

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

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

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

          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

          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

          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

          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

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

          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

          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 variable).

          n is the OpenVPN route number, starting from 1.

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

          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

          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

          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 script.

          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 scripts.

   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

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

   Here is an example of an inline file usage

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

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

          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

   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 information.

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

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

          iptables -A INPUT -i tun+ -j ACCEPT

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

   VPN Address Setup:
   For   purposes  of  our  example,  our  two  machines  will  be  called 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 ssh.

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

   Example 1: A simple tunnel without security
   On bob:

          openvpn   --remote   --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

   Example  2:  A  tunnel  with  static-key  security (i.e. using a pre-shared
   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)

   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 as:

          iptables -A INPUT -i tun+ -j ACCEPT

   to allow input packets from tun devices,

          iptables -A FORWARD -i tun+ -j ACCEPT

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

          iptables -A INPUT -i tap+ -j ACCEPT

   to allow input packets from tap devices, and

          iptables -A FORWARD -i tap+ -j ACCEPT

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

   These rules are secure if  you  use  packet  authentication,  since  no
   incoming packets will arrive on a TUN or TAP virtual device unless they
   first pass an HMAC authentication test.



   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


   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)


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.