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openvpn(8)		    System Manager's Manual		    openvpn(8)

       openvpn - secure	IP tunnel daemon.

       openvpn [ options ... ]

       OpenVPN	is  an open source VPN daemon by James Yonan.  Because OpenVPN
       tries to	be a universal VPN tool	offering a great deal of  flexibility,
       there are a lot of options on this manual page.	If you're new to 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:

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

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

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

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

       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.

       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 '--' re-

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

	      Note that	configuration files can	 be  nested  to	 a  reasonable

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

	      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

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

	      For  examples of configuration files, see

	      Here is an example configuration file:

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

		  # Use	a dynamic tun device.
		  dev tun

		  # Our	remote peer
		  remote mypeer.mydomain

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

		  # Our	pre-shared static key
		  secret static.key

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

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

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

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

	      proto indicates the protocol to use when connecting with the re-
	      mote, 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 de-
	      fined 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,
	      the first	address	returned by the	system getaddrinfo()  function
	      will  be used (no	DNS randomization inside OpenVPN 2.3.x,	and it
	      will not try multiple addresses).

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

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

		  dev tun

		  remote 1194 udp

		  remote 443 tcp

		  remote 443 tcp
		  http-proxy 8080

		  remote 443 tcp
		  http-proxy 8080

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

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

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

	      bind,  connect-retry,  connect-retry-max,	 connect-timeout,  ex-
	      plicit-exit-notify,  float, fragment, http-proxy,	http-proxy-op-
	      tion,  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

	      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').

	      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

	      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 ei-
	      ther 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

	      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 (de-

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

	      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  au-
	      tomatically  determine  the authentication method, but to	reject
	      weak authentication protocols such as HTTP Basic Authentication.

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

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

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

	      VERSION version -- Set  HTTP  version  number  to	 version  (de-

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

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

	      Retry indefinitely on Socks proxy	errors.	 If a Socks proxy  er-
	      ror 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.

	      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), op-
	      tionally 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  au-
	      thenticated peer on its new IP address.

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

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

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

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

	      Do not bind to local address and port.  The IP stack will	 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

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

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

	      tun devices encapsulate IPv4 or IPv6 (OSI	Layer 3) while tap de-
	      vices 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  di-
	      rective 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 se-
	      mantics when some	or all of the connecting clients might be Win-
	      dows 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.

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

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

	      See below	for further IPv6-related configuration options.

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

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

	      On Windows systems, select the TAP-Win32 adapter which is	 named
	      node in the Network Connections Control Panel or the raw GUID of
	      the adapter enclosed by braces.  The --show-adapters option  un-
	      der  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  lo-
	      cal VPN endpoint.	 For TUN devices in point-to-point mode, rn is
	      the IP address of	the remote VPN endpoint.  For TAP devices,  or
	      TUN  devices  used with --topology subnet, rn is the subnet mask
	      of the virtual network segment which is being  created  or  con-
	      nected to.

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

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

	      This  option,  while  primarily a	proxy for the ifconfig(8) 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.

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

	      Don't  output  an	options	consistency check warning if the --if-
	      config 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	--dis-
	      able-occ	option)	while only disabling the ifconfig component of
	      the check.

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

	      gateway default -- taken from --route-gateway or the second  pa-
	      rameter 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, ei-
	      ther  in the local configuration file, or	pulled from an OpenVPN
	      server.  By default, n=100.

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

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

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

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

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

	      On  Windows, --route-delay tries to be more intelligent by 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-de-

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

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

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

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

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

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

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

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

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

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

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

	      This option performs three steps:

	      (1) Create a static route	for the	--remote  address  which  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  re-
	      versed so	that the original default route	is restored.

	      Option flags:

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

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

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

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

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

	      block-local  -- Block access to local LAN	when the tunnel	is ac-
	      tive, 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 un-
	      less you know what you're	doing.

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

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

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

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

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

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

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

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

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

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

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

	      --fragment adds 4	bytes of overhead per datagram.

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

	      It should	also be	noted that this	option is not meant to replace
	      UDP fragmentation	at the IP stack	level.	It is only meant as  a
	      last  resort  when path MTU discovery is broken.	Using this op-
	      tion 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-

       --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 encapsula-
	      tion overhead has	been added  in,	 but  not  including  the  UDP
	      header itself. Resulting packet would be at most 28 bytes	larger
	      for IPv4 and 48 bytes for	IPv6 (20/40 bytes for IP header	and  8
	      bytes for	UDP header). Default value of 1450 allows IPv4 packets
	      to be transmitted	over a link with MTU 1473 or higher without IP
	      level fragmentation.

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

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

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

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

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

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

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

       --sndbuf	size
	      Set  the TCP/UDP socket send buffer size.	 Defaults to operation
	      system default.

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

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

       --socket-flags flags...
	      Apply the	given flags to the  OpenVPN  transport	socket.	  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

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

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

       --shaper	n
	      Limit bandwidth of outgoing tunnel data to n bytes per second on
	      the TCP/UDP port.	 Note that this	will only work if mode is  set
	      to  p2p.	If you want to limit the bandwidth in both directions,
	      use this option on both peers.

	      OpenVPN uses the following algorithm to implement	traffic	 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 be-
	      tween 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 de-
	      vice 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-

       --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

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

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

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

	      In client	mode, the --ping-restart parameter is set to 120  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-re-
	      mote-ip options.

	      Also note	that --ping-exit and --ping-restart are	 mutually  ex-
	      clusive 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 detected	on client side
	      before the server	side drops the connection.

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

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

	      Run the --ping-exit / --ping-restart timer only if we have a re-
	      mote 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-

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

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

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

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

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

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

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

	      Disable paging by	calling	the POSIX mlockall function.  Requires
	      that OpenVPN be initially	run as root (though OpenVPN can	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  re-
	      cover  previously	 used ephemeral	keys, which are	used for a pe-
	      riod 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), op-
	      tionally followed	by arguments. The path and  arguments  may  be
	      single-  or  double-quoted and/or	escaped	using a	backslash, and
	      should be	separated by one or more spaces.

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

	      For --dev	tun execute as:

	      cmd  tun_dev  tun_mtu  link_mtu  ifconfig_local_ip  ifconfig_re-
	      mote_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 op-
	      tion.  If	a restart occurs, and --up-restart has been specified,
	      the up script will be called with	restart	as the last parameter.

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

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

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

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

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

	      route add	-net netmask gw $5

	      Delay TUN/TAP open and possible --up script execution until  af-
	      ter 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  ab-
	      sence of tunnel data, since UDP is a "connectionless" protocol.

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

       --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 us-
	      ing a backslash, and should be separated by one or more spaces.

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

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

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

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

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

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

	      This option should be used with caution, as there	are good 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 --ig-
	      nore-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

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

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

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

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

	      Don't output a warning message if	option inconsistencies are de-
	      tected 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 re-
	      turn them	to an OpenVPN session.	This means, for	example,  that
	      if  you  want  to	 reset an OpenVPN daemon with a	SIGUSR1	signal
	      (for example in response to a DHCP reset), you should  make  use
	      of  one  or more of the --persist	options	to ensure that OpenVPN
	      doesn't need to execute any privileged operations	 in  order  to
	      restart (such as re-reading key files or running ifconfig	on the
	      TUN device).

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

       --cd dir
	      Change  directory	to dir prior to	reading	any files such as con-
	      figuration files,	key files, scripts, etc.  dir should be	an ab-
	      solute  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:  The  SSL  library	will  probably need /dev/urandom to be
	      available	inside the chroot directory dir.  This is because  SSL
	      libraries	 occasionally  need  to	 collect  fresh	random.	 Newer
	      linux kernels and	some BSDs implement a  getrandom()  or	geten-
	      tropy()  syscall	that  removes  the need	for /dev/urandom to be

       --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-

	      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 su-
	      percede 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 de-
	      lay daemonization	until the majority of initialization functions
	      which are	capable	of generating fatal errors are complete.  This
	      means that initialization	scripts	can test the return status  of
	      the  openvpn command for a fairly	reliable indication of whether
	      the command has correctly	initialized  and  entered  the	packet
	      forwarding event loop.

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

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

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

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

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

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

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

	      The  wait/nowait	option must match what is specified in the in-
	      etd/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-

	      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

       --log file
	      Output logging  messages	to  file,  including  output  to  std-
	      out/stderr  which	 is  generated by called scripts.  If file al-
	      ready exists it will be truncated.  This option takes effect im-
	      mediately	 when  it  is  parsed in the command line and will su-
	      percede syslog output if --daemon	or --inetd is also  specified.
	      This  option  is persistent over the entire course of an OpenVPN
	      instantiation and	will not  be  reset  by	 SIGHUP,  SIGUSR1,  or

	      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.

	      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).

	      (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 de-
	      vice 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, im-
	      proving CPU efficiency by	5% to 10%.

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

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

	      Note: this option	is only	relevant for UDP servers.

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

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

	      Designed to be used to send messages to a	 controlling  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

	      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 in-
	      formation	on debug levels).

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

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

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

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

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

	      In  a server mode	setup, it is possible to selectively turn 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.

	      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	incom-
	      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  ef-
	      ficiency	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 do-
	      main 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	direc-
	      tives 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 (local-
	      host) to restrict	accessibility of the management	server to  lo-
	      cal clients.

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

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

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

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

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

	      Make OpenVPN forget passwords when  management  session  discon-

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

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

	      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.

	      Report tunnel up/down events to management interface.

	      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

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

	      For example, --server expands as follows:

		   mode	server
		   push	"topology [topology]"

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

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

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

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

       --server-bridge ['nogw']

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

	      If  --server-bridge  is used without any parameters, it will en-
	      able 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 in-
	      terface.	The gateway and	netmask	parameters to  --server-bridge
	      can  be set to either the	IP/netmask of the bridge interface, or
	      the IP/netmask of	the default gateway/router on the bridged sub-

	      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 expands as follows:

		  mode server

		  push "route-gateway"

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

		  mode server

		  push "route-gateway dhcp"

	      Or --server-bridge nogw expands as follows:

		  mode server

       --push option
	      Push  a  config file option back to the client for remote	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 op-
	      tions such as TLS	or MTU parameters cannot be pushed because the
	      client  needs  to	 know them before the connection to the	server
	      can be initiated.

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

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

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

	      IV_VER=<version> -- the client OpenVPN version

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

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

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

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

	      Disable a	particular client (based on the	common name) from 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 in-
	      stance config file using --client-config-dir or dynamically gen-
	      erated 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-

	      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

	      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 ma-
	      chine  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  in-
	      stance config file using --client-config-dir or dynamically gen-
	      erated using a --client-connect script.

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

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

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

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

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

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

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

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

	      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),  op-
	      tionally	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 ar-
	      gument  (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 ap-
	      plied on the server when the client connects, it should write it
	      to the file named	by the last argument.

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

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

       --client-disconnect cmd
	      Like --client-connect but	called on  client  instance  shutdown.
	      Will  not	be called unless the --client-connect script and 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-

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

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

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

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

       --tmp-dir dir
	      Specify a	directory dir for  temporary  files.   This  directory
	      will be used by openvpn processes	and script to communicate 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

	      *	 OPENVPN_PLUGIN_ENABLE_PF  plugin hook to pass filtering rules
	      via pf_file

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

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

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

	      When OpenVPN is tunneling	data from a TUN/TAP device to a	remote
	      client  over  a  TCP connection, it is possible that the TUN/TAP
	      device might produce data	at a faster rate than the TCP  connec-
	      tion  can	support.  When the number of output packets queued be-
	      fore sending to the TCP socket reaches this limit	 for  a	 given
	      client  connection,  OpenVPN will	start to drop outgoing packets
	      directed at this client.

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

	      The macro	expands	as follows:

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

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

       --max-routes-per-client n
	      Allow a maximum of n internal routes per	client	(default=256).
	      This  is designed	to help	contain	DoS attacks where an 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  di-
	      rective can be used in a --client-config-dir file	or auto-gener-
	      ated 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), op-
	      tionally 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-

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

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

	      Normally,	the cmd	script will use	the information	provided above
	      to  set  appropriate  firewall entries on	the VPN	TUN/TAP	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),  op-
	      tionally	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-

	      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 re-
	      turns.  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/ in the OpenVPN source distribution.

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

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

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

	      Allow  connections  by  clients  that  do	 not  specify  a 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 op-
	      tion 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 de-
	      tect this	condition and respond accordingly.

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

	      If you use this directive, the entire responsibility of  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.

	      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/

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

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

	      The  no-remapping	 mode flag can be used with the	--compat-names
	      option to	be compatible with the now deprecated --no-name-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  in-
	      stead  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.

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


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

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

       --auth-user-pass	[up]
	      Authenticate with	server using username/password.	 up is a  file
	      containing username/password on 2	lines. If the password line is
	      missing, OpenVPN will prompt for one.

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

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

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

	      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  de-
	      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

	      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  de-
	      scription	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  re-
	      sponse  before trying the	next server.  As this only makes sense
	      in client-to-server setups, it cannot be used in	point-to-point
	      setups using --secret symmetrical	key mode.

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

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

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

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

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

	      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 pa-
	      rameter, 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 se-
	      quence) that would mark the ciphertext packets as	 being	gener-
	      ated  by	OpenVPN.   Anyone  eavesdropping on the	wire would see
	      nothing but random-looking data.

	      Alternative way of specifying the	optional  direction  parameter
	      for  the	--tls-auth and --secret	options. Useful	when using in-
	      line 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

       --cipher	alg
	      Encrypt data channel packets with	cipher algorithm alg.  The de-
	      fault  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	infre-

	      For   more  information  on  blowfish,  see  http://www.counter-

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

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

	      Set alg=none to disable encryption.

       --keysize n
	      Size of cipher key in bits (optional).  If unspecified, defaults
	      to cipher-specific default.  The --show-ciphers option (see  be-
	      low)  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

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

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

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

	      OpenVPN provides datagram	replay protection by default.

	      Replay protection	is accomplished	by tagging each	outgoing 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 al-
	      ready 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-

	      (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  of-
	      ten require this.

	      If  you  run  OpenVPN at --verb 4, you will see the message "Re-
	      play-window backtrack occurred [x]" every	time the  maximum  se-
	      quence  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 en-
	      capsulated protocol from attacks which masquerade	as  the	 kinds
	      of  normal  packet  loss	and reordering that occur over IP net-

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

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

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

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

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

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

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

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

	      This option will keep a disk copy	of the current replay  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.

	      (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.

	      Enable prediction	resistance on PolarSSL's RNG.

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

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

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

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

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

	      openvpn --test-crypto --secret key


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

	      This  option  is	very  useful to	test OpenVPN after it has been
	      ported to	a new platform,	or to isolate  problems	 in  the  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 ci-
       pher and	HMAC keys to protect the data channel.	TLS mode uses a	robust
       reliability layer over the UDP connection for all control channel  com-
       munication,  while  the	data channel, over which encrypted tunnel data
       passes, is forwarded without any	mediation.  The	result is the best  of
       both  worlds:  a	fast data channel that forwards	over UDP with only the
       overhead	of encrypt, decrypt, and HMAC functions, and a control channel
       that  provides  all of the security features of TLS, including certifi-
       cate-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-

	      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.

	      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

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

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

	      openssl dhparam -out dh1024.pem 1024

	      to  generate  your  own, or use the existing dh1024.pem file in-
	      cluded with the OpenVPN distribution.  Diffie Hellman parameters
	      may be considered	public.

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

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

	      If  your	certificate authority private key lives	on another ma-
	      chine, 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']
	      Enable TLS version negotiation, and set the minimum TLS  version
	      we  will	accept from the	peer (default is "1.0").  Examples for
	      version include "1.0", "1.1",  or	 "1.2".	  If  'or-highest'  is
	      specified	and version is not recognized, we will only accept the
	      highest TLS version supported by the local SSL implementation.

	      Also see --tls-version-max below,	for information	on compatibil-

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

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

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

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

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

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

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

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

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

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

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

       --cryptoapicert select-string
	      Load the certificate and private key from	the  Windows  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 (":").

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

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

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

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

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

       --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  af-
	      ter  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.

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

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

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

	      Exit on TLS negotiation failure.

       --tls-auth file [direction]
	      Add an additional	layer of HMAC authentication on	top of the TLS
	      control channel to protect against DoS attacks.

	      In  a  nutshell, --tls-auth enables a kind of "HMAC firewall" on
	      OpenVPN's	TCP/UDP	port, where TLS	control	channel	packets	 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-

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

	      (2) DEPRECATED A freeform	passphrase file.   In  this  case  the
	      HMAC  key	 will be derived by taking a secure hash of this file,
	      similar to the md5sum(1) or sha1sum(1) commands. This option  is
	      deprecated  and  will  stop working in OpenVPN 2.4 and newer re-

	      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 di-
	      rection parameter.

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

	      The  rationale  for  this	feature	is as follows.	TLS requires a
	      multi-packet exchange before it is able to authenticate a	 peer.
	      During  this  time  before authentication, OpenVPN is allocating
	      resources	(memory	and CPU) to this potential peer.   The	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 --re-
	      play-persist option which	will keep OpenVPN's replay  protection
	      state in a file so that it is not	lost across restarts.

	      It  should  be emphasized	that this feature is optional and that
	      the passphrase/key file used with	--tls-auth gives a peer	 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-

	      For  the extremely security conscious, it	is possible to protect
	      your private key with a password.	 Of course this	means that ev-
	      ery time the OpenVPN daemon is started you must be there to type
	      the password.  The --askpass option allows you to	start  OpenVPN
	      from  the	command	line.  It will query you for a password	before
	      it daemonizes.  To protect a private key	with  a	 password  you
	      should  omit  the	-nodes option when you use the openssl command
	      line tool	to manage certificates and private keys.

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

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

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

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

	      This directive does not affect the  --http-proxy	username/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), op-
	      tionally 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 [ext:]fieldname
	      Field  in	 the X.509 certificate subject to be used as the user-
	      name (default=CN).  Typically, this  option  is  specified  with
	      fieldname	as either of the following:

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

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

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

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

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

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

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

	      Using a common name prefix is a useful alternative to managing a
	      CRL (Certificate Revocation List)	on the client, since it	allows
	      the client to refuse all certificates except for	those  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 --ch-
	      root environment too.

	      Please also note:	This option is now deprecated.	It will	be re-
	      moved 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 de-
	      pends 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	--ver-
	      ify-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

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

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

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

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

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

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

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

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

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

       --remote-cert-eku oid
	      Require that peer	certificate was	signed with  an	 explicit  ex-
	      tended 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 --re-
	      mote-cert-ku 80 08 88 --remote-cert-eku "TLS Web Client  Authen-

	      The key usage is digitalSignature	and/or keyAgreement.

	      The  --remote-cert-tls  server  option  is  equivalent  to --re-
	      mote-cert-ku a0 88 --remote-cert-eku "TLS	Web Server Authentica-

	      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  at-
	      tack  is	easily	prevented  by having clients verify the	server
	      certificate  using  any	one   of   --remote-cert-tls,	--ver-
	      ify-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  in-
	      tegrity of the PKI.

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

	      If  the  optional	dir flag is specified, enable a	different mode
	      where crl	is a directory containing files	named as  revoked  se-
	      rial  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.

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

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

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

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

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

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

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

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

       --secret	file
	      Write key	to file.

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

	      (Standalone) Create a persistent tunnel on platforms which  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 re-

	      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.

	      (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  de-
	      fault,  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 ig-
	      nored. A warning is logged when this is found in the  configura-
	      tion 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  ad-
	      dress  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  netmask, then OpenVPN will take the	IP address
	      to use as	the virtual DHCP server	address.  In --dev  tun	 mode,
	      OpenVPN  will  cause the DHCP server to masquerade as if it were
	      coming from the remote endpoint.	The optional offset  parameter
	      is an integer which is > -256 and	< 256 and which	defaults to 0.
	      If offset	is positive, the DHCP server will masquerade as	the IP
	      address at network address + offset.  If offset is negative, the
	      DHCP server will masquerade as the IP address at	broadcast  ad-
	      dress  +	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 oc-
	      cur  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  op-
	      tions:  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 broadcast).

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

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

	      Note that	if --dhcp-option is pushed via --push to a non-windows
	      client, the option will be saved in the client's environment be-
	      fore the up  script  is  called,	under  the  name  "foreign_op-

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

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

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

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

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

	      Ask Windows to renew the TAP adapter lease on startup.  This op-
	      tion  is normally	unnecessary, as	Windows	automatically triggers
	      a	DHCP renegotiation on the TAP adapter when it comes  up,  how-
	      ever  if	you set	the TAP-Win32 adapter Media Status property to
	      "Always Connected", you may need this flag.

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

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

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

	      (Standalone) Show	available TAP-Win32 adapters which can be  se-
	      lected 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

	      (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

	      (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.

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

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

   IPv6	Related	Options
       The following options exist to support IPv6 tunneling  in  peer-to-peer
       and client-server mode.	All options are	modeled	after their IPv4 coun-
       terparts, so more detailed explanations given there apply here as  well
       (except for --topology ,	which has no effect on IPv6).

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

       --route-ipv6 ipv6addr/bits [gateway] [metric]
	      setup IPv6 routing in the	system to send the specified IPv6 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.	 Due to	implementation details,	the pool size must  be
	      between /64 and /112.

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

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

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

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

	      Executed when we have a still untrusted remote peer.

	      Executed	after  connection authentication, or remote IP address

	      Executed in --mode server	mode immediately after client  authen-

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

	      Executed right before the	routes are removed.

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

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

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

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

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

       Q: Why is string	remapping necessary?

       A:  It's	 an important security feature to prevent the malicious	coding
       of strings from	untrusted  sources  to	be  passed  as	parameters  to
       scripts,	saved in the environment, used as a common name, translated to
       a filename, etc.

       Q: Can string remapping be disabled?

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

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

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

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

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

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

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

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

       Environmental variable values: Any printable character.

       For  all	cases, characters in a string which are	not members of the le-
       gal 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 in-

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

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

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

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

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

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

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

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

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

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

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

	      The prefix length	of the IPv6 network on the VPN interface.  De-
	      rived from the /nnn parameter of the IPv6	address	in  the	 --if-
	      config-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.

	      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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	      The default gateway used by --route options, as specified	in ei-
	      ther the --route-gateway option or the second parameter to --if-
	      config when --dev	tun is specified.  Set prior  to  --up	script

	      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-

	      n	is the OpenVPN route number, starting from 1.

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

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

	      parm will	be one of "network" or "gateway"  ("netmask"  is  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 ad-
	      dress  translations  will	be recorded rather than	their names as
	      denoted on the command line or configuration file.

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

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

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

       signal The reason for exit or restart.  Can be one of sigusr1,  sighup,
	      sigterm,	sigint,	 inactive  (controlled	by --inactive option),
	      ping-exit	(controlled by --ping-exit option), ping-restart (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.

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

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

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

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

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

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

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

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

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

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

       untrusted_ip (or	untrusted_ip6)
	      Actual IP	address	of connecting client or	 peer  which  has  not
	      been  authenticated  yet.	 Sometimes used	to nmap	the connecting
	      host in a	--tls-verify script to ensure it is  firewalled	 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.

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

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

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


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

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

       Here is an example of an	inline file usage

	   -----END CERTIFICATE-----

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

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

	      Like SIGHUP, except don't	re-read	configuration file, and	possi-
	      bly don't	close and reopen TUN/TAP device,  re-read  key	files,
	      preserve	local  IP  address/port, or preserve most recently au-
	      thenticated  remote  IP  address/port  based  on	--persist-tun,
	      --persist-key,  --persist-local-ip,  and --persist-remote-ip op-
	      tions 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.

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

	      Causes OpenVPN to	exit gracefully.

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

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

       Load driver: modprobe tun

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

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

	      mknod /dev/net/tun c 10 200

	      modprobe tun

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

       Only Linux 2.4 and newer	are supported.

       For other platforms, consult the	INSTALL	file at
       stall.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  bob.exam-	and	If you are constructing	a VPN over the
       internet, then replace and  with  the
       internet	 hostname  or IP address that each machine will	use to contact
       the other over the internet.

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

       Once the	VPN is established, you	have essentially created a secure  al-
       ternate path between the	two hosts which	is addressed by	using the tun-
       nel 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 bob.exam- and you wish to connect to  via  ssh  without
       using  the  VPN (since ssh has its own built-in security) you would use
       the command ssh  However in the same	scenario,  you
       could  also  use	the command telnet to create a	telnet session
       with over the VPN, that would use the VPN  to	secure
       the session rather than ssh.

       You can use any address you wish	for the	tunnel endpoints but make sure
       that they are private addresses (such as	those that begin  with	10  or
       192.168)	 and that they are not part of any existing subnet on the 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 bob:

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

       On alice:

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

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

       On bob:


       On alice:


       The --verb 9 option will	produce	verbose	output,	similar	 to  the  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 se-
       First build a static key	on bob.

	      openvpn --genkey --secret	key

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

       On bob:

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

       On alice:

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

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

       On bob:


       On alice:


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

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

       On bob:

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

       On alice:

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

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

       On bob:


       On alice:


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

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

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

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

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

       and enable TUN packet forwarding	through	the firewall:

	      iptables -A FORWARD -i tun+ -j ACCEPT

       On bob:

	      route add	-net netmask gw

       On alice:

	      route add	-net netmask gw

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

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

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

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

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

       If you are using	HMAC-based packet authentication (the default  in  any
       of  OpenVPN's  secure  modes), having the firewall filter on source ad-
       dress 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 in-
       definitely 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  in-
       coming  packets	will arrive on a TUN or	TAP virtual device unless they
       first pass an HMAC authentication test.


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

       For  a  description  of OpenVPN's underlying protocol, see http://open-

       OpenVPN's web site is at

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

       Report all bugs to the OpenVPN team <>.

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

       This product includes software  developed  by  the  OpenSSL  Project  ( )

       For     more	information	on     the     TLS    protocol,	   see

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

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

       James Yonan <>

			       17 November 2008			    openvpn(8)


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