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openvpn(8)							    openvpn(8)

NAME
       openvpn - secure IP tunnel daemon.

SYNOPSIS
       openvpn [ options ... ]

INTRODUCTION
       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 Open‐
       VPN, 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: http://openvpn.net/

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

DESCRIPTION
       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  tun‐
       nels.

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

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

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

       --help Show options.

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

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

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

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

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

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

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

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

	      For   examples   of   configuration   files,   see  http://open‐
	      vpn.net/examples.html

	      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

		  # 10.1.0.1 is our local VPN endpoint
		  # 10.1.0.2 is our remote VPN endpoint
		  ifconfig 10.1.0.1 10.1.0.2

		  # Our pre-shared static key
		  secret static.key

   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
	      below.

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

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

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

	      Note  that  since	 UDP  is connectionless, connection failure is
	      defined by the --ping and --ping-restart options.

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

	      If --remote is unspecified, OpenVPN will listen for packets from
	      any IP address, but will not act on those	 packets  unless  they
	      pass all authentication tests.  This requirement for authentica‐
	      tion 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-bal‐
	      ancing and failover capability.

       --remote-random-hostname
	      Prepend a random string (6 bytes, 12 hex characters) to hostname
	      to prevent DNS caching.  For  example,  "foo.bar.gov"  would  be
	      modified to "<random-chars>.foo.bar.gov".

       <connection>
	      Define  a client connection profile.  Client connection profiles
	      are groups of OpenVPN options that describe how to connect to  a
	      given  OpenVPN server.  Client connection profiles are specified
	      within an OpenVPN configuration file, and each profile is brack‐
	      eted 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  connec‐
	      tion list.

	      Here is an example of connection profile usage:

		  client
		  dev tun

		  <connection>
		  remote 198.19.34.56 1194 udp
		  </connection>

		  <connection>
		  remote 198.19.34.56 443 tcp
		  </connection>

		  <connection>
		  remote 198.19.34.56 443 tcp
		  http-proxy 192.168.0.8 8080
		  http-proxy-retry
		  </connection>

		  <connection>
		  remote 198.19.36.99 443 tcp
		  http-proxy 192.168.0.8 8080
		  http-proxy-retry
		  </connection>

		  persist-key
		  persist-tun
		  pkcs12 client.p12
		  ns-cert-type server
		  verb 3

	      First  we	 try to connect to a server at 198.19.34.56:1194 using
	      UDP.  If that fails, we then try to connect to  198.19.34.56:443
	      using  TCP.   If that also fails, then try connecting through an
	      HTTP proxy at 192.168.0.8:8080 to	 198.19.34.56:443  using  TCP.
	      Finally,	try  to	 connect through the same proxy to a server at
	      198.19.36.99:443 using TCP.

	      The following OpenVPN options may be used inside of  a  <connec‐
	      tion> block:

	      bind,    connect-retry,	 connect-retry-max,   connect-timeout,
	      explicit-exit-notify, float, fragment,  http-proxy,  http-proxy-
	      option,  http-proxy-retry,  http-proxy-timeout, link-mtu, local,
	      lport, mssfix, mtu-disc, nobind,	port,  proto,  remote,	rport,
	      socks-proxy, socks-proxy-retry, tun-mtu and tun-mtu-extra.

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

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

       --proto-force p
	      When iterating through connection profiles, only	consider  pro‐
	      files using protocol p ('tcp'|'udp').

       --remote-random
	      When  multiple  --remote address/ports are specified, or if con‐
	      nection 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
	      peers.

	      For  TCP operation, one peer must use --proto tcp-server and the
	      other must use --proto tcp-client.  A  peer  started  with  tcp-
	      server  will  wait  indefinitely	for an incoming connection.  A
	      peer started with tcp-client will attempt	 to  connect,  and  if
	      that  fails, will sleep for 5 seconds (adjustable via the --con‐
	      nect-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 capa‐
	      bility is provided for situations where UDP cannot be used.   In
	      comparison with UDP, TCP will usually be somewhat less efficient
	      and less robust when used over unreliable or congested networks.

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

	      http://sites.inka.de/sites/bigred/devel/tcp-tcp.html

	      There  are certain cases, however, where using TCP may be advan‐
	      tageous from a security and robustness perspective, such as tun‐
	      neling  non-IP  or application-level UDP protocols, or tunneling
	      protocols which don't possess a built-in reliability layer.

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

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

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

       --show-proxy-settings
	      Show  sensed  HTTP or SOCKS proxy settings. Currently, only Win‐
	      dows clients support this option.

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

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

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

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

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

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

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

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

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

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

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

       --socks-proxy-retry
	      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 sec‐
	      onds before failing.

	      Set n to "infinite" to retry indefinitely.

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

       --float
	      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, how‐
	      ever if packets arrive from a new address and pass all authenti‐
	      cation  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 pack‐
	      ets from any address, not only the address which	was  specified
	      in the --remote option.

       --ipchange cmd
	      Run  command cmd when our remote ip-address is initially authen‐
	      ticated or changes.

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

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

	      cmd ip_address port_number

	      Don't use --ipchange in --mode server mode.  Use a --client-con‐
	      nect script instead.

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

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

	      Similarly if our IP address changes due to DHCP, we should  con‐
	      figure  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 assign‐
	      ment 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.

       --nobind
	      Do not bind to local address and port.  The IP stack will	 allo‐
	      cate  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 con‐
	      nections by using the --remote option.

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

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

	      You must use either tun devices on both ends of  the  connection
	      or  tap devices on both ends.  You cannot mix them, as they rep‐
	      resent 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 end‐
	      point of the server's tun interface.  This mode allocates a sin‐
	      gle IP address per connecting client.  Only use when none of the
	      connecting clients are Windows systems.  This mode is  function‐
	      ally 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 con‐
	      necting 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 direc‐
	      tive 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.

       --tun-ipv6
	      Build a tun link capable of forwarding IPv6 traffic.  Should  be
	      used  in	conjunction  with  --dev tun or --dev tunX.  A warning
	      will be displayed if no specific IPv6 TUN support	 for  your  OS
	      has been compiled into OpenVPN.

	      See below for further IPv6-related configuration options.

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

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

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

	      For TUN devices, which facilitate virtual point-to-point IP con‐
	      nections,	 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 simi‐
	      larly configured.	 If you are attempting to connect to a	remote
	      ethernet bridge, the IP address and subnet should be set to val‐
	      ues 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) com‐
	      mand, is designed to simplify TUN/TAP  tunnel  configuration  by
	      providing	 a standard interface to the different ifconfig imple‐
	      mentations on different platforms.

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

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

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

       --ifconfig-nowarn
	      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 compo‐
	      nent 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 seman‐
	      tics across OpenVPN's platform space.

	      netmask default -- 255.255.255.255

	      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 set‐
	      ting it to "default".

	      The network and gateway parameters can also be  specified	 as  a
	      DNS  or /etc/hosts file resolvable name, or as one of three spe‐
	      cial 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 Open‐
	      VPN 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 immedi‐
	      ately upon connection establishment.  If --route-delay is	 omit‐
	      ted,  routes will be added immediately after TUN/TAP device open
	      and --up script execution, before any --user or  --group	privi‐
	      lege 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 wait‐
	      ing w seconds (w=30 by default) for  the	TAP-Win32  adapter  to
	      come up before adding routes.

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

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

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

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

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

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

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

       --route-nopull
	      When  used  with	--client  or  --pull, accept options pushed by
	      server EXCEPT for routes and dhcp options like DNS servers.

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

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

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

	      network/netmask (for  example  192.168.0.0/255.255.0.0)  defines
	      the  local view of a resource from the client perspective, while
	      alias/netmask (for example  10.64.0.0/255.255.0.0)  defines  the
	      remote view from the server perspective.

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

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

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

	      This option performs three steps:

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

	      (2) Delete the default gateway route.

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

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

	      Option flags:

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

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

	      def1  --	Use this flag to override the default gateway by using
	      0.0.0.0/1 and 128.0.0.0/1 rather than 0.0.0.0/0.	This  has  the
	      benefit  of  overriding  but not wiping out the original default
	      gateway.

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

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

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

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

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

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

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

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

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

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

       --mtu-disc type
	      Should we do Path MTU discovery on TCP/UDP channel?   Only  sup‐
	      ported  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)

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

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

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

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

	      --fragment adds 4 bytes of overhead per datagram.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       --socket-flags flags...
	      Apply  the  given	 flags	to the OpenVPN transport socket.  Cur‐
	      rently, 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 con‐
	      nection 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	 shap‐
	      ing: 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-pri‐
	      ority data such as off-site backups over the  reduced  bandwidth
	      tunnel, and other data over the full-speed tunnel.

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

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

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

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

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

       --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	 Open‐
	      VPN  ping	 packets  are  not echoed like IP ping packets).  When
	      used in one of OpenVPN's secure modes  (where  --secret,	--tls-
	      server,  or  --tls-client is specified), the ping packet will be
	      cryptographically secure.

	      This option has two intended uses:

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

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

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

	      For example,

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

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

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

	      This option is useful in cases  where  the  remote  peer	has  a
	      dynamic  IP  address and a low-TTL DNS name is used to track the
	      IP address using	a  service  such  as  http://dyndns.org/  +  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  sec‐
	      onds  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	--per‐
	      sist-tun,	  --persist-key,  --persist-local-ip,  and  --persist-
	      remote-ip options.

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

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

	      The server timeout is set twice the value of  the	 second	 argu‐
	      ment.   This  ensures that a timeout is dectected on client side
	      before the server side drops the connection.

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

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

       --ping-timer-rem
	      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 con‐
	      nects.

       --persist-tun
	      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.

       --persist-key
	      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.

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

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

       --mlock
	      Disable paging by calling the POSIX mlockall function.  Requires
	      that OpenVPN be initially run as root (though OpenVPN can subse‐
	      quently 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 Open‐
	      VPN, he would not be able	 to  scan  the	system	swap  file  to
	      recover  previously  used	 ephemeral  keys, which are used for a
	      period of time governed by the --reneg options (see below), then
	      are discarded.

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

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

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

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

	      For --dev tun execute as:

	      cmd   tun_dev   tun_mtu	link_mtu   ifconfig_local_ip	ifcon‐
	      fig_remote_ip [ init | restart ]

	      For --dev tap execute as:

	      cmd  tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask
	      [ init | restart ]

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

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

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

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

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

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

	      Note  that  OpenVPN also provides the --ifconfig option to auto‐
	      matically 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 10.0.0.0 netmask 255.255.255.0 gw $5

       --up-delay
	      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" proto‐
	      col.

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

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

	      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.

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

       --up-restart
	      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
	      script.

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

	      This option should be used with caution, as there are good secu‐
	      rity 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 encoun‐
	      tered by older software versions.

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

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

	      See also --ignore-unknown-option

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

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

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

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

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

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

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

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

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

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

	      Please note the single quote marks and the escaping of the back‐
	      slashes (\) and the space character.

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

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

	      Use of this option is discouraged, but is provided as  a	tempo‐
	      rary  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 initial‐
	      ization,	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 sig‐
	      nal (for example in response to a DHCP reset), you  should  make
	      use of one or more of the --persist options to ensure that Open‐
	      VPN 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 con‐
	      figuration 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	 rede‐
	      fines  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 initializa‐
	      tion, most OpenVPN options that reference files will operate  in
	      a pre-chroot context.

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

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

       --setcon context
	      Apply SELinux context  after  initialization.  This  essentially
	      provides	the  ability to restrict OpenVPN's rights to only net‐
	      work I/O operations, thanks to SELinux. This goes	 further  than
	      --user  and  --chroot in that those two, while being great secu‐
	      rity 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  initializa‐
	      tion,  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  initializa‐
	      tion.

	      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 --per‐
	      sist-tun options.

       --daemon [progname]
	      Become a daemon after  all  initialization  functions  are  com‐
	      pleted.	This option will cause all message and error output to
	      be sent to the syslog file (such as  /var/log/messages),	except
	      for  the	output of scripts and ifconfig commands, which will go
	      to /dev/null unless otherwise redirected.	 The syslog  redirect‐
	      ion  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 use‐
	      ful in linking OpenVPN messages in the syslog file with specific
	      tunnels.	When unspecified, progname defaults to "openvpn".

	      When  OpenVPN  is	 run  with the --daemon option, it will try to
	      delay daemonization until the majority of	 initialization	 func‐
	      tions which are capable of generating fatal errors are complete.
	      This means that initialization scripts can test the return  sta‐
	      tus  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 ini‐
	      tialization 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 parame‐
	      ter.

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

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

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

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

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

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

       --log file
	      Output logging  messages	to  file,  including  output  to  std‐
	      out/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	speci‐
	      fied.   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, log‐
	      ging occurs by default without the need to specify this option.

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

       --suppress-timestamps
	      Avoid writing timestamps to log messages, even when they	other‐
	      wise would be prepended. In particular, this applies to log mes‐
	      sages 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).

       --fast-io
	      (Experimental)  Optimize	TUN/TAP/UDP  I/O  writes by avoiding a
	      call to poll/epoll/select prior to  the  write  operation.   The
	      purpose  of  such	 a  call  would normally be to block until the
	      device or socket is ready to accept the write.  Such blocking is
	      unnecessary on some platforms which don't support write blocking
	      on UDP sockets or TUN/TAP devices.  In such cases, one can opti‐
	      mize  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.

       --multihome
	      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  applica‐
	      tion which is receiving the OpenVPN log output.

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

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

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

	      0 -- No output except fatal errors.
	      1 to 4 -- Normal usage range.
	      5	 --  Output  R and W characters to the console for each packet
	      read and write, uppercase is used for TCP/UDP packets and lower‐
	      case 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
	      signal.

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

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

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

	      In  a server mode setup, it is possible to selectively turn com‐
	      pression 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 set‐
	      ting 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.

       --comp-noadapt
	      When used in conjunction with --comp-lzo, this option will  dis‐
	      able  OpenVPN's adaptive compression algorithm.  Normally, adap‐
	      tive compression is enabled with --comp-lzo.

	      Adaptive compression tries to optimize the case where  you  have
	      compression  enabled,  but  you are sending predominantly uncom‐
	      pressible (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  com‐
	      pression	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 com‐
	      pression 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 func‐
	      tions.   pw-file,	 if specified, is a password file (password on
	      first line) or "stdin" to prompt from standard input.  The pass‐
	      word  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  man‐
	      agement  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	 Open‐
	      VPN source distribution.

	      It  is  strongly recommended that IP be set to 127.0.0.1 (local‐
	      host) to restrict accessibility  of  the	management  server  to
	      local clients.

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

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

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

       --management-query-proxy
	      Query management channel for proxy server information for a spe‐
	      cific --remote (client-only).

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

       --management-forget-disconnect
	      Make OpenVPN forget passwords when  management  session  discon‐
	      nects.

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

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

       --management-signal
	      Send SIGUSR1 signal to OpenVPN  if  management  session  discon‐
	      nects.   This  is	 useful when you wish to disconnect an OpenVPN
	      session on user logoff. For --management-client this  option  is
	      not needed since a disconnect will always generate a SIGTERM.

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

       --management-up-down
	      Report tunnel up/down events to management interface.

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

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

       --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/open‐
	      vpn/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 mod‐
	      ule/script controls an authentication function (such as tls-ver‐
	      ify,  auth-user-pass-verify, or client-connect), then every mod‐
	      ule and script must return success (0) in order for the  connec‐
	      tion to be authenticated.

   Server Mode
       Starting	 with  OpenVPN 2.0, a multi-client TCP/UDP server mode is sup‐
       ported, and can be enabled with the --mode server  option.   In	server
       mode,  OpenVPN will listen on a single port for incoming client connec‐
       tions.  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 10.8.0.0 255.255.255.0 expands as follows:

		   mode server
		   tls-server
		   push "topology [topology]"

		   if dev tun AND (topology == net30 OR topology == p2p):
		     ifconfig 10.8.0.1 10.8.0.2
		     if !nopool:
		       ifconfig-pool 10.8.0.4 10.8.0.251
		     route 10.8.0.0 255.255.255.0
		     if client-to-client:
		       push "route 10.8.0.0 255.255.255.0"
		     else if topology == net30:
		       push "route 10.8.0.1"

		   if dev tap OR (dev tun AND topology == subnet):
		     ifconfig 10.8.0.1 255.255.255.0
		     if !nopool:
		       ifconfig-pool 10.8.0.2 10.8.0.254 255.255.255.0
		     push "route-gateway 10.8.0.1"

	      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 sim‐
	      plify 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 ether‐
	      net NIC interface.  For example, on Linux this is done with  the
	      brctl  tool,  and with Windows XP it is done in the Network Con‐
	      nections 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 inter‐
	      face, 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  con‐
	      necting clients.

	      For  example,  server-bridge  10.8.0.4  255.255.255.0 10.8.0.128
	      10.8.0.254 expands as follows:

		  mode server
		  tls-server

		  ifconfig-pool 10.8.0.128 10.8.0.254 255.255.255.0
		  push "route-gateway 10.8.0.4"

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

		  mode server
		  tls-server

		  push "route-gateway dhcp"

	      Or --server-bridge nogw expands as follows:

		  mode server
		  tls-server

       --push option
	      Push  a  config file option back to the client for remote execu‐
	      tion.  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 compro‐
	      mised  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

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

       --push-peer-info
	      Push  additional	information  about  the client to server.  The
	      additional information consists of the following data:

	      IV_VER=<version> -- the client OpenVPN version

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

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

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

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

       --disable
	      Disable a particular client (based on the common name) from con‐
	      necting.	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 con‐
	      necting clients, similar to a DHCP server.  For  tun-style  tun‐
	      nels, each client will be given a /30 subnet (for interoperabil‐
	      ity 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	inter‐
	      vals (default=600), as well as on program startup and shutdown.

	      The  goal	 of  this option is to provide a long-term association
	      between clients (denoted by their common name) and  the  virtual
	      IP address assigned to them from the ifconfig-pool.  Maintaining
	      a long-term association is good for clients  because  it	allows
	      them to effectively use the --persist-tun option.

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

	      If seconds = 0, file will be treated as read-only.  This is use‐
	      ful 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 com‐
	      mon name will always receive the given IP address.  If you  want
	      guaranteed assignment, use --ifconfig-push

       --ifconfig-pool-linear
	      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 --topol‐
	      ogy p2p which is functionally equivalent.

       --ifconfig-push local remote-netmask [alias]
	      Push virtual IP endpoints	 for  client  tunnel,  overriding  the
	      --ifconfig-pool dynamic allocation.

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

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

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

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

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

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

       --iroute network [netmask]
	      Generate	an  internal  route  to a specific client. The netmask
	      parameter, if omitted, defaults to 255.255.255.255.

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

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

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

       --client-to-client
	      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-origi‐
	      nating 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.

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

       --client-connect cmd
	      Run command cmd on client connection.

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

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

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

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

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

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

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

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

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

	      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.

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

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

	      This directory will be used by in the following cases:

	      * --client-connect scripts to dynamically	 generate  client-spe‐
	      cific configuration files.

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

	      *	 OPENVPN_PLUGIN_ENABLE_PF  plugin hook to pass filtering rules
	      via pf_file

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

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

       --tcp-queue-limit n
	      Maximum number of output packets queued before TCP (default=64).

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

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

	      The macro expands as follows:

		   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 authenti‐
	      cated 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-gen‐
	      erated by a --client-connect script to override the global value
	      for a particular client.

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

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

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

	      If t is not present it defaults to n

	      This  option helps to keep the dynamic routing table small.  See
	      also --max-routes-per-client

       --connect-freq n sec
	      Allow a maximum of  n  new  connections  per  sec	 seconds  from
	      clients.	 This  is  designed to contain DoS attacks which flood
	      the server with connection  requests  using  certificates	 which
	      will ultimately fail to authenticate.

	      This  is	an  imperfect  solution however, because in a real DoS
	      scenario, legitimate connections might also be refused.

	      For the best protection against DoS attacks in server mode,  use
	      --proto udp and --tls-auth.

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

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

	      Three arguments will be appended to any arguments in cmd as fol‐
	      lows:

	      [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 "198.162.10.14", an IPv4 subnet  such
	      as "198.162.10.0/24", 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 inter‐
	      face.  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	 poli‐
	      cies  with regard to the client's high-level common name, rather
	      than the low level client virtual addresses.

       --auth-user-pass-verify cmd method
	      Require the client to provide a username/password	 (possibly  in
	      addition to a client certificate) for authentication.

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

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

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

	      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 pre‐
	      vent 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 user‐
	      name 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 charac‐
	      ters 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  han‐
	      dled.   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  sam‐
	      ple-scripts/auth-pam.pl in the OpenVPN source distribution.

       --opt-verify
	      Clients  that  connect  with  options that are incompatible with
	      those of the server will be disconnected.

	      Options that will be compared  for  compatibility	 include  dev-
	      type,  link-mtu,	tun-mtu,  proto, tun-ipv6, ifconfig, comp-lzo,
	      fragment, keydir, cipher, auth, keysize, secret, no-replay,  no-
	      iv, tls-auth, key-method, tls-server, and tls-client.

	      This option requires that --disable-occ NOT be used.

       --auth-user-pass-optional
	      Allow  connections  by  clients  that  do	 not  specify  a user‐
	      name/password.  Normally, when --auth-user-pass-verify or --man‐
	      agement-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, pass‐
	      ing  the	responsibility to the user-defined authentication mod‐
	      ule/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	 user‐
	      name/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.

       --client-cert-not-required
	      Don't require client certificate, client will authenticate using
	      username/password	 only.	 Be aware that using this directive is
	      less secure than requiring certificates from all clients.

	      If you use this directive, the entire responsibility of  authen‐
	      tication	will  rest  on your --auth-user-pass-verify script, so
	      keep in mind that bugs in your script could potentially  compro‐
	      mise 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.

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

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

	      /C=US/L=Somewhere/CN=John Doe/emailAddress=john@example.com

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

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

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

	      C=US, L=Somewhere, CN=John Doe, emailAddress=john@example.com

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

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

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

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

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

       --port-share host port [dir]
	      When run in TCP server mode, share the OpenVPN port with another
	      application, such as an HTTPS server.  If OpenVPN senses a  con‐
	      nection  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 theo‐
	      retically possible to extend to other protocols such as ssh.

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

	      Not implemented on Windows.

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

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

		   pull
		   tls-client

       --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 defin‐
	      ing ENABLE_PASSWORD_SAVE in win/settings.in).

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

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

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

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

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

	      type can be one of:

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

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

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

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

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

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

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

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

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

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

	      When  the	 direction parameter is omitted, 2 keys are used bidi‐
	      rectionally, one for HMAC and the other  for  encryption/decryp‐
	      tion.

	      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  compli‐
	      cated  negotiation  handshakes and protocols.  The only require‐
	      ment is that you have a pre-existing secure  channel  with  your
	      peer  (such  as  ssh ) to initially copy the key.	 This require‐
	      ment, 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.  Con‐
	      trast 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 gener‐
	      ated  by	OpenVPN.   Anyone  eavesdropping on the wire would see
	      nothing but random-looking data.

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

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

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

	      In static-key encryption mode, the HMAC key is included  in  the
	      key  file	 generated  by --genkey.  In TLS mode, the HMAC key is
	      dynamically generated and shared between peers via the TLS  con‐
	      trol  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
	      http://www.cs.ucsd.edu/users/mihir/papers/hmac.html

       --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   http://www.counter‐
	      pane.com/blowfish.html

	      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
	      modes.

	      Set alg=none to disable encryption.

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

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

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

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

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

       --no-replay
	      (Advanced)  Disable OpenVPN's protection against replay attacks.
	      Don't use this option unless you are prepared to make a tradeoff
	      of greater efficiency in exchange for less security.

	      OpenVPN provides datagram replay protection by default.

	      Replay protection is accomplished by tagging each outgoing data‐
	      gram 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 wrap‐
	      ping 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 win‐
	      dow 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 possibil‐
	      ity  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  con‐
	      straints.

	      (a) The packet cannot be a replay (unless --no-replay is	speci‐
	      fied, 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  contain‐
	      ing 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  net‐
	      works?

	      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.

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

       --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 protec‐
	      tion state (i.e. the most recent packet timestamp	 and  sequence
	      number  received	from  the  remote peer), so that if an OpenVPN
	      session is stopped and restarted, it will reject any replays  of
	      packets which were already received by the prior session.

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

       --no-iv
	      (Advanced)  Disable  OpenVPN's  use of IV (cipher initialization
	      vector).	Don't use this option unless you are prepared to  make
	      a tradeoff of greater efficiency in exchange for less security.

	      OpenVPN  uses  an IV by default, and requires it for CFB and OFB
	      cipher modes (which are totally insecure without it).  Using  an
	      IV  is  important	 for security when multiple messages are being
	      encrypted/decrypted with the same key.

	      IV is implemented differently depending on the cipher mode used.

	      In CBC mode, OpenVPN uses a pseudo-random IV for each packet.

	      In CFB/OFB mode, OpenVPN uses a unique sequence number and  time
	      stamp as the IV.	In fact, in CFB/OFB mode, OpenVPN uses a data‐
	      gram space-saving optimization that uses the  unique  identifier
	      for datagram replay protection as the IV.

       --use-prediction-resistance
	      Enable prediction resistance on PolarSSL's RNG.

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

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

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

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

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

	      openvpn --test-crypto --secret key

	      or

	      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  com‐
	      piler,  OpenSSL crypto library, or OpenVPN's crypto code.	 Since
	      it is a self-test mode, problems with encryption and authentica‐
	      tion 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 chan‐
       nels  which are multiplexed over a single TCP/UDP port.	OpenVPN initi‐
       ates 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	 chan‐
       nel  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  con‐
       trol channel that provides all of the security features of TLS, includ‐
       ing  certificate-based  authentication  and  Diffie   Hellman   forward
       secrecy.

       To  use TLS mode, each peer that runs OpenVPN should have its own local
       certificate/key pair ( --cert and --key ), signed by the root  certifi‐
       cate 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 speci‐
       fied 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: http://open‐
       vpn.net/easyrsa.html

       --tls-server
	      Enable TLS and assume server role during	TLS  handshake.	  Note
	      that  OpenVPN  is	 designed  as a peer-to-peer application.  The
	      designation of client or server is only for the purpose of nego‐
	      tiating the TLS control channel.

       --tls-client
	      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  certifi‐
	      cates  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 vari‐
	      able to point to your new root certificate ca.crt.

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

       --capath dir
	      Directory	 containing  trusted  certificates  (CAs  and	CRLs).
	      Available with OpenSSL version >= 0.9.7 dev.  Not available with
	      PolarSSL.

       --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  parame‐
	      ters 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  cer‐
	      tificate	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 thawte.com (in which case you will be helping to finance
	      the world's second space tourist :).  To generate a certificate,
	      you can use a command such as:

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

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

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

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

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

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

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

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

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

       --verify-hash hash
	      Specify SHA1 fingerprint for level-1 cert.  The level-1 cert  is
	      the  CA  (or intermediate cert) that signs the leaf certificate,
	      and is one removed from the leaf certificate in the direction of
	      the  root.  When accepting a connection from a peer, the level-1
	      cert fingerprint must match  hash	 or  certificate  verification
	      will  fail.   Hash  is  specified	 as  XX:XX:...	 For  example:
	      AD:B0:95:D8:09:C8:36:45:12:A9:89:C8:90:09:CB:13:72:A6:AD:16

       --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.

       --pkcs11-id-management
	      Acquire PKCS#11 id from management interface.  In	 this  case  a
	      NEED-STR	'pkcs11-id-request'  real-time	message	 will be trig‐
	      gered, 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  set‐
	      ting.

       --pkcs11-providers provider...
	      Specify  a RSA Security Inc. PKCS #11 Cryptographic Token Inter‐
	      face (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  Certifi‐
	      cate System Store (Windows/OpenSSL Only).

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

	      This  makes it possible to use any smart card, supported by Win‐
	      dows, 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 cer‐
	      tificate'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  cer‐
	      tificate	(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  acknowl‐
	      edgment  from remote within n seconds (default=2).  When OpenVPN
	      sends a control packet to its peer, it will expect to receive an
	      acknowledgement  within  n  seconds  or  it  will retransmit the
	      packet, subject to a  TCP-like  exponential  backoff  algorithm.
	      This  parameter  only  applies to control channel packets.  Data
	      channel packets (which carry encrypted tunnel  data)  are	 never
	      acknowledged, sequenced, or retransmitted by OpenVPN because the
	      higher level network protocols running on top of the tunnel such
	      as TCP expect this role to be left to them.

       --reneg-bytes n
	      Renegotiate  data	 channel  key  after  n bytes sent or received
	      (disabled by default).  OpenVPN allows the lifetime of a key  to
	      be  expressed as a number of bytes encrypted/decrypted, a number
	      of packets, or a number of seconds.  A key renegotiation will be
	      forced if any of these three criteria are met by either peer.

       --reneg-pkts n
	      Renegotiate  data	 channel key after n packets sent and received
	      (disabled by 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 renegotia‐
	      tion 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	criti‐
	      cal path of tunnel data forwarding.

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

	      If  the  daemon  is reset by a signal or --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.

       --tls-exit
	      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 bear‐
	      ing an incorrect HMAC signature can be dropped immediately with‐
	      out response.

	      file  (required)	is  a key file which can be in one of two for‐
	      mats:

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

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

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

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

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

	      The rationale for this feature is as follows.   TLS  requires  a
	      multi-packet  exchange before it is able to authenticate a peer.
	      During this time before authentication,  OpenVPN	is  allocating
	      resources	 (memory  and CPU) to this potential peer.  The poten‐
	      tial 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 sig‐
	      nature  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 poten‐
	      tial, but as yet unauthenticated, client is able to consume.

	      --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 protec‐
	      tion state in a file so that it is not lost across restarts.

	      It should be emphasized that this feature is optional  and  that
	      the  passphrase/key file used with --tls-auth gives a peer noth‐
	      ing 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 daemo‐
	      nize.

	      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  com‐
	      mand 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 con‐
	      figure option, or on Windows by defining ENABLE_PASSWORD_SAVE in
	      win/settings.in).

       --auth-nocache
	      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/pass‐
	      word.  It is always cached.

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

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

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

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

	      cmd certificate_depth subject

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

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

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

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

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

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

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

	      Name can also be a common name prefix, for example if you want a
	      client  to  only	accept	connections to "Server-1", "Server-2",
	      etc., you can simply use --tls-remote Server

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

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

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

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

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

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

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

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

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

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

       --ns-cert-type client|server
	      Require  that  peer  certificate	was  signed  with  an explicit
	      nsCertType designation of "client" or "server".

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

	      See  the	easy-rsa/build-key-server script for an example of how
	      to generate a certificate	 with  the  nsCertType	field  set  to
	      "server".

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

	      This is an important security precaution to  protect  against  a
	      man-in-the-middle	 attack where an authorized client attempts to
	      connect to another client	 by  impersonating  the	 server.   The
	      attack  is  easily prevented by having clients verify the server
	      certificate using any one of --ns-cert-type, --verify-x509-name,
	      or --tls-verify.

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

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

	      The  key usage should be encoded in hex, more than one key usage
	      can be specified.

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

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

	      The extended key usage should be encoded	in  oid	 notation,  or
	      OpenSSL symbolic 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  Authentica‐
	      tion"

	      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 keyA‐
	      greement ).

	      This  is	an  important security precaution to protect against a
	      man-in-the-middle attack where an authorized client attempts  to
	      connect  to  another  client  by	impersonating the server.  The
	      attack is easily prevented by having clients verify  the	server
	      certificate   using  any	one  of	 --remote-cert-tls,  --verify-
	      x509-name, or --tls-verify.

       --crl-verify crl ['dir']
	      Check peer certificate against the file crl in PEM format.

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

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

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

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

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

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

       --show-tls
	      (Standalone)  Show  all  TLS ciphers (TLS used only as a control
	      channel).	 The TLS ciphers will be sorted from  highest  prefer‐
	      ence (most secure) to lowest.

       --show-engines
	      (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.

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

       --secret file
	      Write key to file.

   TUN/TAP persistent tunnel config mode:
       Available  with linux 2.4.7+.  These options comprise a standalone mode
       of OpenVPN which can be used to create and delete persistent tunnels.

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

	      One of the advantages of persistent tunnels is that they	elimi‐
	      nate  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 ter‐
	      minates 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 persis‐
	      tent by default.

       --rmtun
	      (Standalone) Remove a persistent tunnel.

       --dev tunX | tapX
	      TUN/TAP device

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

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

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

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

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

	      manual  --  Don't	 set  the IP address or netmask automatically.
	      Instead output a message to the console telling the user to con‐
	      figure  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 sub‐
	      net.   For  example,  if	your  subnet  is  192.168.4.0  netmask
	      255.255.255.0, then OpenVPN will take the IP address 192.168.4.0
	      to use as the virtual DHCP server address.  In --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 vir‐
	      tual 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 seman‐
	      tics,  though  testing has indicated that it works okay in prac‐
	      tice.  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 Proto‐
	      col).  Repeat this option to set secondary NTP server addresses.

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

	      NBS scope-id -- Set NetBIOS over TCP/IP Scope. A	NetBIOS	 Scope
	      ID  provides  an	extended  naming  service for the NetBIOS over
	      TCP/IP (Known as NBT) module. The primary purpose of  a  NetBIOS
	      scope  ID	 is  to isolate NetBIOS traffic on a single network to
	      only those nodes with the same NetBIOS scope  ID.	  The  NetBIOS
	      scope  ID	 is a character string that is appended to the NetBIOS
	      name. The NetBIOS scope ID on two hosts must match, or  the  two
	      hosts will not be able to communicate. The NetBIOS Scope ID also
	      allows computers to use the same computer	 name,	as  they  have
	      different	 scope IDs. The Scope ID becomes a part of the NetBIOS
	      name, making the name  unique.   (This  description  of  NetBIOS
	      scopes courtesy of NeonSurge@abyss.com)

	      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	 "for‐
	      eign_option_{n}".

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

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

       --show-net-up
	      Output OpenVPN's view of the system routing  table  and  network
	      adapter list to the syslog or log file after the TUN/TAP adapter
	      has been brought up and any routes have been added.

       --dhcp-renew
	      Ask Windows to renew the TAP adapter  lease  on  startup.	  This
	      option  is  normally unnecessary, as Windows automatically trig‐
	      gers 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.

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

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

       --pause-exit
	      Put  up  a  "press  any  key to continue" message on the console
	      prior to OpenVPN program exit.   This  option  is	 automatically
	      used by the Windows explorer when OpenVPN is run on a configura‐
	      tion 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 auto‐
	      matically 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  pro‐
	      cesses to exit.

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

       --show-adapters
	      (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-adminis‐
	      trative  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.

       --show-valid-subnets
	      (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 neces‐
	      sary for the TAP-Win32 driver to impose certain  constraints  on
	      TUN endpoint address selection.

	      Namely,  the  point-to-point endpoints used in TUN device emula‐
	      tion must be the middle two addresses of a /30  subnet  (netmask
	      255.255.255.252).

       --show-net
	      (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_pri‐
	      vate as 1 if certificates are stored as private objects.

	      --verb  option  can be used BEFORE this option to produce debug‐
	      ging information.

   IPv6 Related Options
       The following options exist to support IPv6 tunneling  in  peer-to-peer
       and  client-server mode.	 As of now, this is just very basic documenta‐
       tion of the IPv6-related options. More documentation can	 be  found  on
       http://www.greenie.net/ipv6/openvpn.html.

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

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

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

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

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

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

SCRIPTING AND ENVIRONMENTAL VARIABLES
       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.

       --tls-verify
	      Executed when we have a still untrusted remote peer.

       --ipchange
	      Executed after connection authentication, or remote  IP  address
	      change.

       --client-connect
	      Executed	in --mode server mode immediately after client authen‐
	      tication.

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

       --route-pre-down
	      Executed right before the routes are removed.

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

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

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

       --auth-user-pass-verify
	      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  per‐
       mitted 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() func‐
       tion 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	 OPEN‐
       VPN_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
       class.

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

       Environmental variable values: Any printable character.

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

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

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

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

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

       common_name
	      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" other‐
	      wise.  Set on program initiation and reset on SIGHUP.

       daemon_log_redirect
	      Set  to  "1"  if the --log or --log-append directives are speci‐
	      fied, 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.

       foreign_option_{n}
	      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.

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

       ifconfig_ipv6_local
	      The local VPN endpoint IPv6 address specified in the --ifconfig-
	      ipv6 option (first parameter).  Set prior to OpenVPN calling the
	      ifconfig	or  netsh (windows version of ifconfig) commands which
	      normally occurs prior to --up script execution.

       ifconfig_ipv6_netbits
	      The prefix length of the IPv6  network  on  the  VPN  interface.
	      Derived  from  the  /nnn	parameter  of  the IPv6 address in the
	      --ifconfig-ipv6 option (first parameter).	 Set prior to  OpenVPN
	      calling the ifconfig or netsh (windows version of ifconfig) com‐
	      mands which normally occurs prior to --up script execution.

       ifconfig_ipv6_remote
	      The remote VPN endpoint IPv6 address specified in	 the  --ifcon‐
	      fig-ipv6	option (second parameter).  Set prior to OpenVPN call‐
	      ing the ifconfig or netsh (windows version of ifconfig) commands
	      which normally occurs prior to --up script execution.

       ifconfig_local
	      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.

       ifconfig_remote
	      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 ifcon‐
	      fig)  commands which normally occurs prior to --up script execu‐
	      tion.

       ifconfig_netmask
	      The subnet mask of the virtual ethernet segment that  is	speci‐
	      fied  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.

       ifconfig_pool_local_ip
	      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.

       ifconfig_pool_netmask
	      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.

       ifconfig_pool_remote_ip
	      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.

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

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

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

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

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

       remote_{n}
	      The --remote parameter.  Set on program initiation and reset  on
	      SIGHUP.

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

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

       route_vpn_gateway
	      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.

       route_{parm}_{n}
	      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 "met‐
	      ric".

	      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.

       route_ipv6_{parm}_{n}
	      A set of variables which define each IPv6 route to be added, and
	      are set prior to --up script execution.

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

	      n is the OpenVPN route number, starting from 1.

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

       peer_cert
	      Temporary	 file name containing the client certificate upon con‐
	      nection.	Useful in conjunction with --tls-verify

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

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

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

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

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

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

       tls_digest_{n}
	      Contains	the  certificate  SHA1	fingerprint/digest hash value,
	      where n is the verification level.  Only	set  for  TLS  connec‐
	      tions.  Set prior to execution of --tls-verify script.

       tls_id_{n}
	      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.

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

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

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

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

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

       untrusted_port
	      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.

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

       X509_{n}_{subject_field}
	      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.

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

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

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

       Here is an example of an inline file usage

	   <cert>
	   -----BEGIN CERTIFICATE-----
	   [...]
	   -----END CERTIFICATE-----
	   </cert>

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

SIGNALS
       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.

       SIGUSR1
	      Like SIGHUP, except don't re-read configuration file, and possi‐
	      bly  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 condi‐
	      tion, 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.

       SIGUSR2
	      Causes  OpenVPN to display its current statistics (to the syslog
	      file if --daemon is used, or stdout otherwise).

       SIGINT, SIGTERM
	      Causes OpenVPN to exit gracefully.

TUN/TAP DRIVER SETUP
       If you are running Linux 2.4.7 or higher, you probably have the TUN/TAP
       driver already installed.  If so, there are still a few things you need
       to do:

       Make device: mknod /dev/net/tun c 10 200

       Load driver: modprobe tun

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

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

	      mknod /dev/net/tun c 10 200

	      modprobe tun

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

       Only Linux 2.4 and newer are supported.

       For   other   platforms,	 consult  the  INSTALL	file  at  http://open‐
       vpn.net/install.html for more information.

   Firewall Setup:
       If firewalls exist between the two machines, they should be set to for‐
       ward 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 may.kg and
       june.kg.	 If you are constructing a VPN over the internet, then replace
       may.kg  and  june.kg with the internet hostname or IP address that each
       machine will use to contact the other over the internet.

       Now we will choose the tunnel endpoints.	 Tunnel endpoints are  private
       IP  addresses  that  only have meaning in the context of the VPN.  Each
       machine will use the tunnel endpoint of the other machine to access  it
       over  the  VPN.	In our example, the tunnel endpoint for may.kg will be
       10.4.0.1 and for june.kg, 10.4.0.2.

       Once the VPN is established, you	 have  essentially  created  a	secure
       alternate  path	between	 the two hosts which is addressed by using the
       tunnel endpoints.  You can control which network traffic passes between
       the hosts (a) over the VPN or (b) independently of the VPN, by choosing
       whether to use (a) the VPN endpoint address or (b) the public  internet
       address,	 to  access  the remote host. For example if you are on may.kg
       and you wish to connect to june.kg via ssh without using the VPN (since
       ssh  has	 its  own  built-in  security)	you  would use the command ssh
       june.kg.	 However in the same scenario, you could also use the  command
       telnet  10.4.0.2	 to create a telnet session with june.kg over the VPN,
       that would use the VPN to secure the session rather than 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  net‐
       works  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 june.kg --dev tun1 --ifconfig 10.4.0.1 10.4.0.2
	      --verb 9

       On june:

	      openvpn --remote may.kg --dev tun1 --ifconfig 10.4.0.2  10.4.0.1
	      --verb 9

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

       On may:

	      ping 10.4.0.2

       On june:

	      ping 10.4.0.1

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

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

	      openvpn --genkey --secret key

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

       On may:

	      openvpn --remote june.kg --dev tun1 --ifconfig 10.4.0.1 10.4.0.2
	      --verb 5 --secret key

       On june:

	      openvpn --remote may.kg --dev tun1 --ifconfig 10.4.0.2  10.4.0.1
	      --verb 5 --secret key

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

       On may:

	      ping 10.4.0.2

       On june:

	      ping 10.4.0.1

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

       First, build a separate certificate/key pair for both may and june (see
       above  where --cert is discussed for more info).	 Then construct Diffie
       Hellman parameters (see above where --dh is discussed for  more	info).
       You  can	 also  use  the	 included  test	 files client.crt, client.key,
       server.crt,  server.key	and  ca.crt.   The  .crt  files	 are  certifi‐
       cates/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 june.kg --dev tun1 --ifconfig 10.4.0.1 10.4.0.2
	      --tls-client  --ca  ca.crt  --cert  client.crt  --key client.key
	      --reneg-sec 60 --verb 5

       On june:

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

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

       On may:

	      ping 10.4.0.2

       On june:

	      ping 10.4.0.1

       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 Open‐
       VPN's default key renegotiation interval of one hour.

   Routing:
       Assuming you can ping across the tunnel, the next step is  to  route  a
       real subnet over the secure tunnel.  Suppose that may and june have two
       network interfaces each, one connected to the internet, and  the	 other
       to  a  private  network.	  Our goal is to securely connect both private
       networks.  We will assume that may's private subnet is 10.0.0.0/24  and
       june's is 10.0.1.0/24.

       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 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2

       On june:

	      route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1

       Now any machine on the 10.0.0.0/24 subnet can access any machine on the
       10.0.1.0/24 subnet over the secure tunnel (or vice versa).

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

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

	      iptables -A INPUT -p udp -s 1.2.3.4 --dport 1194 -j ACCEPT

       This will allow incoming packets on UDP port  1194  (OpenVPN's  default
       UDP port) from an OpenVPN peer at 1.2.3.4.

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

	      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.

FAQ
       http://openvpn.net/faq.html

HOWTO
       For  a  more  comprehensive guide to setting up OpenVPN in a production
       setting, see the OpenVPN HOWTO at http://openvpn.net/howto.html

PROTOCOL
       For a description of OpenVPN's underlying  protocol,  see  http://open‐
       vpn.net/security.html

WEB
       OpenVPN's web site is at http://openvpn.net/

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

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

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

NOTES
       This  product  includes	software  developed  by	 the OpenSSL Project (
       http://www.openssl.org/ )

       For    more    information     on     the     TLS     protocol,	   see
       http://www.ietf.org/rfc/rfc2246.txt

       For  more  information  on  the	LZO  real-time compression library see
       http://www.oberhumer.com/opensource/lzo/

COPYRIGHT
       Copyright (C) 2002-2010 OpenVPN Technologies, Inc. This program is free
       software;  you  can redistribute it and/or modify it under the terms of
       the GNU General Public License version 2 as published by the Free Soft‐
       ware Foundation.

AUTHORS
       James Yonan <jim@yonan.net>

			       17 November 2008			    openvpn(8)
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