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       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 ("), dont
                           interpret it as enclosing a parameter.
                  \[SPACE] Pass a literal space or tab character, dont
                           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,
              one will be randomly chosen, providing a  sort  of  basic  load-
              balancing and failover capability.

              Define  a client connection profile.  Client connection profiles
              are groups of OpenVPN options that describe how to connect to  a
              given  OpenVPN server.  Client connection profiles are specified
              within an  OpenVPN  configuration  file,  and  each  profile  is
              bracketed by <connection> and </connection>.

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

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

              Here is an example of connection profile usage:

                  dev tun

                  remote 1194 udp

                  remote 443 tcp

                  remote 443 tcp
                  http-proxy 8080

                  remote 443 tcp
                  http-proxy 8080

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

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

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

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

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

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

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

              Try to sense HTTP or SOCKS proxy settings automatically.  If  no
              settings are present, a direct connection will be attempted.  If
              both  HTTP  and  SOCKS  settings  are  present,  HTTP  will   be
              preferred.   If  the  HTTP  proxy server requires a password, it
              will be queried from stdin or the management interface.  If  the
              underlying  OS  doesn’t  support  an  API  for  returning  proxy
              settings, a direct connection  will  be  attempted.   Currently,
              only    Windows    clients   support   this   option   via   the
              InternetQueryOption API.  This option exists in OpenVPN  2.1  or

       --http-proxy server port [authfile|auto] [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".

              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.

              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]
              Connect  to remote host through a Socks5 proxy at address server
              and port port (default=1080).

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

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

              Set n to "infinite" to retry indefinitely.

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

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

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

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

              Execute as:

              cmd ip_address port_number

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

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

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

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

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

       --port port
              TCP/UDP port number for both  local  and  remote.   The  current
              default  of  1194  represents  the  official  IANA  port  number
              assignment  for  OpenVPN  and  has  been  used   since   version
              2.0-beta17.  Previous versions used port 5000 as the default.

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

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

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

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

       --dev tunX | tapX | null
              TUN/TAP  virtual network device ( X can be omitted for a dynamic

              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.

              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.

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

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

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

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

       --ifconfig l rn
              Set  TUN/TAP  adapter  parameters.   l  is the IP address of the
              local VPN endpoint.  For TUN devices, rn is the  IP  address  of
              the remote VPN endpoint.  For TAP devices, rn is the subnet mask
              of the virtual  ethernet  segment  which  is  being  created  or
              connected to.

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

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

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

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

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

              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
              Execute shell command cmd after routes  are  added,  subject  to

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

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

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

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

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

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

       --redirect-gateway flags...
              (Experimental)  Automatically  execute routing commands to cause
              all outgoing IP traffic to be redirected over the VPN.

              This option performs three steps:

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

              (2) Delete the default gateway route.

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

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

              Option flags:

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

              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).

              Using the def1 flag is highly recommended.

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

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

              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 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

              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.  Currently defaults  to
              65536 bytes.

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

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

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

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

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

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

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

       --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.

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

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

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

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

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

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

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

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

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

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

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

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

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

       --up cmd
              Shell  command  to run after successful TUN/TAP device open (pre
              --user UID change).  The up  script  is  useful  for  specifying
              route  commands  which  route  IP  traffic  destined for private
              subnets which exist at the other end of the VPN connection  into
              the tunnel.

              For --dev tun execute as:

              cmd      tun_dev      tun_mtu     link_mtu     ifconfig_local_ip
              ifconfig_remote_ip [ init | restart ]

              For --dev tap execute as:

              cmd tap_dev tap_mtu link_mtu ifconfig_local_ip  ifconfig_netmask
              [ init | restart ]

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

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

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

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

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

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

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

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

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

       --setenv FORWARD_COMPATIBLE 1
              Relax config file syntax checking  so  that  unknown  directives
              will  trigger a warning but not a fatal error, on the assumption
              that a given unknown directive might be valid in future  OpenVPN

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

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

              This directive is  designed  to  be  pushed  by  the  server  to
              clients,  and  the prepending of "OPENVPN_" to the environmental
              variable is a safety precaution to prevent  a  LD_PRELOAD  style
              attack from a malicious or compromised server.

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

              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).

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

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

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

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

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

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

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

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

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

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

       --daemon [progname]
              Become   a   daemon   after  all  initialization  functions  are
              completed.  This option will cause all message and error  output
              to  be  sent  to  the  syslog  file (such as /var/log/messages),
              except for the output of shell scripts  and  ifconfig  commands,
              which  will  go  to  /dev/null unless otherwise redirected.  The
              syslog redirection occurs immediately at the point that --daemon
              is  parsed  on  the  command  line even though the daemonization
              point occurs later.  If one of the --log options is present,  it
              will supercede syslog redirection.

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

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

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

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

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

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

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

       --management IP port [pw-file]
              Enable a TCP server  on  IP:port  to  handle  daemon  management
              functions.   pw-file, if specified, is a password file (password
              on first line) or "stdin" to prompt from  standard  input.   The
              password  provided  will set the password which TCP clients will
              need to provide in order to access management functions.

              The management interface  can  also  listen  on  a  unix  domain
              socket,  for  those  platforms  that  support it.  To use a unix
              domain socket, specify the unix socket pathname in place  of  IP
              and set port to ’unix’.  While the default behavior is to create
              a unix domain socket that may be connected to  by  any  process,
              the   --management-client-user   and   --management-client-group
              directives can be used to restrict access.

              The management interface provides a special mode where  the  TCP
              management  link  can operate over the tunnel itself.  To enable
              this mode, set IP  =  "tunnel".   Tunnel  mode  will  cause  the
              management interface to listen for a TCP connection on the local
              VPN address of the TUN/TAP interface.

              While the management port is designed for  programmatic  control
              of  OpenVPN  by  other applications, it is possible to telnet to
              the port, using a telnet client in "raw" mode.  Once  connected,
              type "help" for a list of commands.

              For  detailed documentation on the management interface, see the
              management-notes.txt  file  in  the  management  folder  of  the
              OpenVPN source distribution.

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

              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

              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.

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

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

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

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

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

       --plugin module-pathname [init-string]
              Load plug-in module from the file module-pathname, passing init-
              string  as  an  argument  to the module initialization function.
              Multiple plugin modules may be loaded into one OpenVPN  process.

              For  more information and examples on how to build OpenVPN plug-
              in modules, see the README file in  the  plugin  folder  of  the
              OpenVPN source distribution.

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

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

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

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

              For example, --server expands as follows:

                   mode server
                   push "topology [topology]"

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

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

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

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

       --server-bridge [nogw]

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

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

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

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

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

              For  example,  server-bridge
     expands as 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.

              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
              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.

              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 script
              Run script on client  connection.   The  script  is  passed  the
              common  name  and IP address of the just-authenticated client as
              environmental  variables  (see  environmental  variable  section
              below).   The  script  is also passed the pathname of a not-yet-
              created temporary file  as  $1  (i.e.  the  first  command  line
              argument),  to  be  used  by  the  script  to  pass  dynamically
              generated config file directives back to OpenVPN.

              If the script wants to generate a  dynamic  config  file  to  be
              applied  on the server when the client connects, it should write
              it to the file named by $1.

              See the --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

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

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

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

              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 --client-connect scripts to dynamically generate
              client-specific configuration files.

       --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.

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

              cmd will be executed with 3 parameters:

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

              OpenVPN will execute script as a shell command to  validate  the
              username/password provided by the client.

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

              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.

              Allow Common Name, X509 Subject, and username strings to include
              any  printable  character including space, but excluding control
              characters such as tab, newline, and carriage-return.

              By  default,  OpenVPN  will  remap  any  character  other   than
              alphanumeric,  underbar  (’_’), dash (’-’), dot (’.’), and slash
              (’/’) to underbar (’_’).  The X509 Subject string as returned by
              the  tls_id  environmental  variable,  can  additionally contain
              colon (’:’) or equal (’=’).

              While name remapping is performed for security reasons to reduce
              the   possibility   of  introducing  string  expansion  security
              vulnerabilities in  user-defined  authentication  scripts,  this
              option  is  provided  for  those  cases where it is desirable to
              disable the remapping feature.  Don’t use this option unless you
              know what you are doing!

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

              Not implemented on Windows.

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

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


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

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

       --auth-user-pass [up]
              Authenticate with server using username/password.  up is a  file
              containing username/password on 2 lines (Note: OpenVPN will only
              read passwords from a  file  if  it  has  been  built  with  the
              --enable-password-save   configure  option,  or  on  Windows  by
              defining ENABLE_PASSWORD_SAVE in config-win32.h).

              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.

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

       --explicit-exit-notify [n]
              In UDP client mode or point-to-point mode, send  server/peer  an
              exit  notification  if tunnel is restarted or OpenVPN process is
              exited.  In client mode, on exit/restart, this option will  tell
              the  server  to  immediately  close  its  client instance object
              rather than waiting for a timeout.  The n parameter  (default=1)
              controls  the  maximum  number  of  retries that the client will
              attempt to resend the exit notification message.

   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.

       --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 packets with cipher algorithm alg.  The default  is  BF-
              CBC, an abbreviation for Blowfish in Cipher Block Chaining mode.
              Blowfish has the advantages of  being  fast,  very  secure,  and
              allowing  key  sizes of up to 448 bits.  Blowfish is designed to
              be used in situations where keys are changed infrequently.

              For      more      information      on       blowfish,       see

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

              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.

       --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 ).

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

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

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

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

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

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

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

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

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

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

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

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

              cryptoapicert "SUBJ:Peter Runestig"

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

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

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

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

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

              In  method  1 (the default for OpenVPN 1.x), both sides generate
              random encrypt and HMAC-send keys which  are  forwarded  to  the
              other host over the TLS channel.

              In  method 2, (the default for OpenVPN 2.0) the client generates
              a random key.  Both client and server also generate some  random
              seed  material.   All  key source material is exchanged over the
              TLS channel. The actual keys are generated  using  the  TLS  PRF
              function,  taking  source  entropy  from both client and server.
              Method 2 is designed to  closely  parallel  the  key  generation
              process used by TLS 1.0.

              Note that in TLS mode, two separate levels of keying occur:

              (1)  The TLS connection is initially negotiated, with both sides
              of the  connection  producing  certificates  and  verifying  the
              certificate (or other authentication info provided) of the other
              side.  The --key-method parameter has no effect on this 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  (":").
              If  you  require  a  high level of security, you may want to set
              this parameter manually, to prevent a  version  rollback  attack
              where  a  man-in-the-middle attacker tries to force two peers to
              negotiate to the lowest level of  security  they  both  support.
              Use --show-tls to see a list of supported TLS ciphers.

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

       --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)  A freeform passphrase file.  In this case the HMAC key will
              be derived by taking a secure hash of this file, similar to  the
              md5sum(1) or sha1sum(1) commands.

              OpenVPN  will  first  try  format  (1), and if the file fails to
              parse as a static key file, format (2) will be used.

              See the --secret option for more  information  on  the  optional
              direction parameter.

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

              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 (Note: OpenVPN will only read passwords from  a
              file  if  it  has  been  built  with  the --enable-password-save
              configure option, or on Windows by defining ENABLE_PASSWORD_SAVE
              in config-win32.h).

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

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

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

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

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

              cmd certificate_depth X509_NAME_oneline

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

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

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

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

              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.

       --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, --tls-remote, or

       --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 Authentication"

              The  key  usage  is  digitalSignature  and  ( keyEncipherment or
              keyAgreement ).

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

       --crl-verify crl
              Check peer certificate against the file crl in PEM format.

              A  CRL  (certificate  revocation list) is used when a particular
              key is compromised but when the overall PKI is still intact.

              Suppose you had a PKI consisting of a CA, root certificate,  and
              a  number  of  client  certificates.   Suppose a laptop computer
              containing a client key and certificate was stolen.   By  adding
              the  stolen  certificate  to  the CRL file, you could reject any
              connection which  attempts  to  use  it,  while  preserving  the
              overall integrity of the 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

   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 (TLS used only as a control
              channel).   The  TLS  ciphers  will  be  sorted   from   highest
              preference (most secure) to lowest.

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

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

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

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

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

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

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

              dynamic  [offset]  [lease-time]  --  Automatically  set  the  IP
              address and netmask by replying to DHCP query messages generated
              by the kernel.  This mode is probably  the  "cleanest"  solution
              for  setting  the TCP/IP properties since it uses the well-known
              DHCP protocol.  There are, however, two prerequisites for  using
              this  mode:  (1) The TCP/IP properties for the TAP-Win32 adapter
              must be set to "Obtain an IP  address  automatically,"  and  (2)
              OpenVPN  needs  to  claim an IP address in the subnet for use as
              the virtual DHCP server address.  By default in --dev tap  mode,
              OpenVPN  will  take  the  normally  unused  first address in the
              subnet.  For example, if  your  subnet  is  netmask
    , then OpenVPN will take the IP address
              to use as the virtual DHCP server address.  In --dev  tun  mode,
              OpenVPN  will  cause the DHCP server to masquerade as if it were
              coming from the remote endpoint.  The optional offset  parameter
              is an integer which is > -256 and < 256 and which defaults to 0.
              If offset is positive, the DHCP server will masquerade as the IP
              address at network address + offset.  If offset is negative, the
              DHCP server will masquerade  as  the  IP  address  at  broadcast
              address + offset.  The Windows ipconfig /all command can be used
              to show what Windows thinks the DHCP server address is.  OpenVPN
              will  "claim"  this address, so make sure to use a free address.
              Having said that, different  OpenVPN  instantiations,  including
              different  ends  of  the  same  connection,  can  share the same
              virtual DHCP server address.  The lease-time parameter  controls
              the  lease  time  of  the DHCP assignment given to the TAP-Win32
              adapter, and is denoted in seconds.  Normally a very long  lease
              time  is preferred because it prevents routes involving the TAP-
              Win32 adapter from being lost when the  system  goes  to  sleep.
              The default lease time is one year.

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

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

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

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

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

       --dhcp-option type [parm]
              Set extended TAP-Win32 TCP/IP  properties,  must  be  used  with
              --ip-win32  dynamic  or --ip-win32 adaptive.  This option can be
              used to  set  additional  TCP/IP  properties  on  the  TAP-Win32
              adapter,  and  is particularly useful for configuring an OpenVPN
              client to access a Samba server across the VPN.

              DOMAIN name -- Set Connection-specific DNS Suffix.

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

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

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

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

              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.

              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.

              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.

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


       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 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.

              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 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.

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

              One of 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

              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.

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

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

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

              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.

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

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

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



       SIGHUP Cause OpenVPN to close  all  TUN/TAP  and  network  connections,
              restart,  re-read  the  configuration  file (if any), and reopen
              TUN/TAP and network connections.

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

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

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

       If you have Linux 2.2 or earlier, you should obtain version 1.1 of  the
       TUN/TAP  driver  from  and follow the
       installation instructions.


       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.

       If  you  have  Linux  2.2, you should obtain version 1.1 of the TUN/TAP
       driver   from   and    follow    the
       installation instructions.

       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 may:

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

       On june:

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

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

       On may:


       On june:


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

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

              openvpn --genkey --secret key

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

       On may:

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

       On june:

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

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

       On may:


       On june:


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

       First, build a separate certificate/key pair for both may and june (see
       above where --cert is discussed for more info).  Then construct  Diffie
       Hellman  parameters  (see above where --dh is discussed for more info).
       You can also  use  the  included  test  files  client.crt,  client.key,
       server.crt,    server.key    and    ca.crt.    The   .crt   files   are
       certificates/public-keys, the .key files are private keys,  and  ca.crt
       is  a  certification  authority  who  has  signed  both  client.crt and
       server.crt.  For Diffie Hellman parameters you  can  use  the  included
       file  dh1024.pem.   Note  that  all  client,  server,  and  certificate
       authority certificates and keys included in  the  OpenVPN  distribution
       are totally insecure and should be used for testing only.

       On may:

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

       On june:

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

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

       On may:


       On june:


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

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

       Assuming  you  can  ping across the tunnel, the next step is to route a
       real subnet over the secure tunnel.  Suppose that may and june have two
       network  interfaces  each, one connected to the internet, and the other
       to a private network.  Our goal is to  securely  connect  both  private
       networks.   We will assume that may’s private subnet is and
       june’s is

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

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

       and enable TUN packet forwarding through the firewall:

              iptables -A FORWARD -i tun+ -j ACCEPT

       On may:

              route add -net netmask gw

       On june:

              route add -net netmask gw

       Now any machine on the subnet can access any machine on the subnet over the secure tunnel (or vice versa).

       In a production environment, you could put the route  command(s)  in  a
       shell script and execute with the --up option.


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

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

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

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

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

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

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

       You  should also add firewall rules to allow incoming IP traffic on TUN
       or TAP devices such 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) 2002-2009 OpenVPN Technologies, Inc. This program is free
       software; you can redistribute it and/or modify it under the  terms  of
       the  GNU  General  Public  License  version  2 as published by the Free
       Software Foundation.


       James Yonan <>

                               17 November 2008                     openvpn(8)