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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".

	      For  forcing  IPv4 or IPv6 connection suffix tcp or udp with 4/6
	      like udp4/udp6/tcp4/tcp6.

	      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,
	      OpenVPN will try them in the order that the system getaddrinfo()
	      presents them, so	priorization and DNS randomization is done  by
	      the  system library.  Unless an IP version is forced by the pro-
	      tocol specification (4/6 suffix),	OpenVPN	will try both IPv4 and
	      IPv6 addresses, in the order getaddrinfo() returns them.

	      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
		  remote-cert-tls 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,  link-mtu,	local,	lport, mssfix, mtu-disc, nobind, port,
	      proto, remote, rport, socks-proxy, 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 [max]
	      Wait  n  seconds	 between  connection attempts (default=5). Re-
	      peated reconnection attempts are slowed down after 5 retries per
	      remote  by  doubling  the	 wait time after each unsuccessful at-
	      tempt. The optional argument max specifies the maximum value  of
	      wait time	in seconds at which it gets capped (default=300).

       --connect-retry-max n
	      n	 specifies  the	 number	of times each --remote or <connection>
	      entry is tried. Specifying n as one would	try each entry exactly
	      once.  A	successful connection resets the counter. (default=un-

	      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. Its content can also  be	speci-
	      fied  in the config file with the	--http-proxy-user-pass option.
	      (See section on inline files)

	      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.

       --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.

	      CUSTOM-HEADER name content -- Adds the custom Header  with  name
	      as name and content as the content of the	custom HTTP header.

       --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.

       --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 [ipv6only]
	      Bind to local address and	port. This is the default  unless  any
	      of --proto tcp-client , --http-proxy or --socks-proxy are	used.

	      If  the  ipv6only	 keyword  is present OpenVPN will bind only to
	      IPv6 (as oposed to IPv6 and IPv4)	when a IPv6 socket is opened.

	      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".

       --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.

       --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.

	      ipv6 -- Redirect IPv6 routing into the tunnel.  This works simi-
	      lar to the def1 flag, that is, more  specific  IPv6  routes  are
	      added  (2000::/4,	 3000::/4),  covering  the  whole IPv6 unicast

	      !ipv4 -- Do not redirect IPv4 traffic - typically	 used  in  the
	      flag pair	ipv6 !ipv4 to redirect IPv6-only.

       --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 interval timeout
	      A	helper directive designed to simplify the expression of	--ping
	      and --ping-restart.

	      This  option  can	be used	on both	client and server side,	but it
	      is in enough to add this on the server side as it	will push  ap-
	      propriate	 --ping	 and --ping-restart options to the client.  If
	      used on both server and client, the values  pushed  from	server
	      will override the	client local values.

	      The  timeout  argument will be twice as long on the server side.
	      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			# Argument: interval
		     ping-restart 120		# Argument: timeout*2
		     push "ping	10"		# Argument: interval
		     push "ping-restart	60"	# Argument: timeout
		     ping 10			# Argument: interval
		     ping-restart 60		# Argument: timeout

	      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.

	      Always  write timestamps and message flags to log	messages, even
	      when they	otherwise would	not be prefixed. In  particular,  this
	      applies to log messages sent to stdout.

       --writepid file
	      Write OpenVPN's main process ID to file.

       --nice n
	      Change  process priority after initialization ( n	greater	than 0
	      is lower priority, n less	than zero is higher priority).

	      (Experimental) Optimize TUN/TAP/UDP I/O  writes  by  avoiding  a
	      call  to	poll/epoll/select  prior  to the write operation.  The
	      purpose of such a	call would normally be to block	until the  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.

       --compress [algorithm]
	      Enable a compression algorithm.

	      The algorithm parameter may be "lzo", "lz4", or empty.  LZO  and
	      LZ4 are different	compression algorithms,	with LZ4 generally of-
	      fering the best performance with least CPU usage.	 For backwards
	      compatibility with OpenVPN versions before 2.4, use "lzo"	(which
	      is identical to the older	option "--comp-lzo yes").

	      If the algorithm parameter is empty, compression will be	turned
	      off,  but	 the  packet framing for compression will still	be en-
	      abled, allowing a	different setting to be	pushed later.

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

	      This option is deprecated	in favor of the	newer  --compress  op-

	      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

	      Allows  usage for	external private key file instead of --key op-
	      tion (client-only).

       --management-external-cert certificate-hint
	      Allows usage for external	certificate instead of	--cert	option
	      (client-only).  certificate-hint is an arbitrary string which is
	      passed to	a management interface client as an argument of	 NEED-
	      CERTIFICATE notification.	 Requires --management-external-key.

	      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.

	      The module-pathname argument can be just a filename or  a	 file-
	      name  with a relative or absolute	path.  The format of the file-
	      name and path defines if the plug-in will	be loaded from	a  de-
	      fault plug-in directory or outside this directory.

		  --plugin path	       Effective directory used
		  ====================================================		DEFAULT_DIR/
		   subdir/	DEFAULT_DIR/subdir/
		   ./subdir/	CWD/subdir/
		   /usr/lib/my/	/usr/lib/my/

	      DEFAULT_DIR  is replaced by the default plug-in directory, which
	      is configured at the build time of OpenVPN.  CWD is the  current
	      directory	 where	OpenVPN	 was  started or the directory OpenVPN
	      have swithed into	via the	--cd option before  the	 --plugin  op-

	      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.

       --keying-material-exporter label	len
	      Save  Exported  Keying  Material [RFC5705] of len	bytes (must be
	      between 16 and 4095  bytes)  using  label	 in  environment  (ex-
	      ported_keying_material)	 for   use   by	  plugins   in	 OPEN-
	      VPN_PLUGIN_TLS_FINAL callback.

	      Note that	exporter labels	have the potential to collide with ex-
	      isting  PRF  labels. In order to prevent this, labels MUST begin
	      with "EXPORTER".

	      This option requires OpenSSL 1.0.1 or newer.

   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,	 --auth-token,	--persist-key,	--per-
	      sist-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-remove opt
	      selectively remove all --push options matching  "opt"  from  the
	      option  list  for	 a  client.   "opt"  is	matched	as a substring
	      against the whole	option string to-be-pushed to the  client,  so
	      --push-remove  route  would  remove  all	--push	route ...  and
	      --push route-ipv6	...  statements, while	--push-remove  'route-
	      ipv6 2001:' would	only remove IPv6 routes	for 2001:... networks.

	      --push-remove  can  only	be  used in a client-specific context,
	      like in a	--client-config-dir file, or  --client-connect	script
	      or plugin	-- similar to --push-reset, just more selective.

	      NOTE:  to	 change	 an option, --push-remove can be used to first
	      remove the old value, and	then add a new --push option with  the
	      new value.

	      Push  additional	information  about  the	client to server.  The
	      following	data is	always pushed to the server:

	      IV_VER=<version> -- the client OpenVPN version

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

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

	      IV_LZ4=1 -- if the client	supports LZ4 compressions.

	      IV_PROTO=2 -- if the client supports peer-id floating mechansim

	      IV_NCP=2	-- negotiable ciphers, client supports --cipher	pushed
	      by the server, a value of	2 or greater indicates client supports
	      AES-GCM-128 and AES-GCM-256.

	      IV_UI_VER=<gui_id> <version> -- the UI version of	a UI if	one is
	      running, for example "de.blinkt.openvpn 0.5.47" for the  Android

	      When --push-peer-info is enabled the additional information con-
	      sists of the following data:

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

	      IV_SSL=<version  string>	-- the ssl version used	by the client,
	      e.g. "OpenSSL 1.0.2f 28 Jan 2016".

	      IV_PLAT_VER=x.y -	the version of the operating system, e.g.  6.1
	      for Windows 7.

	      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, --push-remove, --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 either --tls-auth	or --tls-crypt.

       --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.

       --auth-gen-token	[lifetime]
	      After   successful  user/password	 authentication,  the  OpenVPN
	      server will with this option generate a temporary	authentication
	      token and	push that to client.  On the following renegotiations,
	      the OpenVPN client will pass this	token  instead	of  the	 users
	      password.	  On  the server side the server will do the token au-
	      thentication internally and it will NOT do  any  additional  au-
	      thentications  against configured	external user/password authen-
	      tication mechanisms.

	      The lifetime argument defines how	long the  generated  token  is
	      valid.   The lifetime is defined in seconds.  If lifetime	is not
	      set or it	is set to 0, the token will never expire.

	      This feature is useful for environments which is	configured  to
	      use  One	Time  Passwords	(OTP) as part of the user/password au-
	      thentications and	that authentication mechanism does not	imple-
	      ment any auth-token support.

	      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, ifconfig, comp-lzo, frag-
	      ment, 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.

       --client-cert-not-required (DEPRECATED)
	      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.

	      Please note: This	option is now deprecated and will  be  removed
	      in  OpenVPN  v2.5.  It is	replaced by --verify-client-cert which
	      allows for more  flexibility.  The  option  --verify-client-cert
	      none is functionally equivalent to --client-cert-not-required

       --verify-client-cert none|optional|require
	      Specify  whether	the  client is required	to supply a valid cer-

	      Possible options are

	      none : a client certificate is not required. the client need  to
	      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.

	      --verify-client-cert  none   is	functionally   equivalent   to

	      optional	: a client may present a certificate but it is not re-
	      quired to	do so.	When using this	directive, you should also use
	      a	 --auth-user-pass-verify script	to ensure that clients are au-
	      thenticated using	a certificate, a  username  and	 password,  or
	      possibly even both.

	      Again,  the entire responsibility	of authentication will rest on
	      your --auth-user-pass-verify script, so keep in mind  that  bugs
	      in your script could potentially compromise the security of your

	      require :	this is	the default option. A client  is  required  to
	      present a	certificate, otherwise VPN access is refused.

	      If you don't use this directive (or use --verify-client-cert re-
	      quire ) 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 in	OpenVPN	v2.5.  So  please  up-
	      date your	scripts/plug-ins 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
	      in OpenVPN 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.

       --pull-filter accept|ignore|reject text
	      Filter  options  received	 from  the server if the option	starts
	      with text.  Runs on client. The action flag  accept  allows  the
	      option, ignore removes it	and reject flags an error and triggers
	      a	SIGUSR1	restart.  The filters may be specified multiple	times,
	      and  each	 filter	 is  applied in	the order it is	specified. The
	      filtering	of each	option stops as	soon as	a match	is found.  Un-
	      matched options are accepted by default.

	      Prefix comparison	is used	to match text against the received op-
	      tion so that

		  --pull-filter	ignore "route"

	      would remove all pushed options starting with route which	 would
	      include,	for example, route-gateway.  Enclose text in quotes to
	      embed spaces.

		  --pull-filter	accept "route 192.168.1."
		  --pull-filter	ignore "route "

	      would remove all routes that do not start	with 192.168.1.

	      This option may be used only on clients.	Note that  reject  may
	      result in	a repeated cycle of failure and	reconnect, unless mul-
	      tiple remotes are	specified and connection to  the  next	remote
	      succeeds.	To silently ignore an option pushed by the server, use

       --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,	--connect-timeout n
	      When  connecting	to a remote server do not wait for more	than n
	      seconds waiting for a response before trying  the	 next  server.
	      The  default  value is 120s. This	timeout	includes proxy and TCP
	      connect timeouts.

       --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.

	      In UDP server mode, send RESTART control channel command to con-
	      nected  clients. The n parameter (default=1) controls client be-
	      havior. With n = 1 client	will attempt to	reconnect to the  same
	      server, with n = 2 client	will advance to	the next server.

	      OpenVPN  will not	send any exit notifications unless this	option
	      is enabled.

	      When this	option is set, OpenVPN	will  not  drop	 incoming  tun
	      packets with same	destination as host.

   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 data	channel	packets	and (if	enabled) tls-auth con-
	      trol channel 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.

	      The  OpenVPN  data  channel protocol uses	encrypt-then-mac (i.e.
	      first encrypt a packet, then  HMAC  the  resulting  ciphertext),
	      which prevents padding oracle attacks.

	      If  an  AEAD  cipher  mode  (e.g.	 GCM) is chosen, the specified
	      --auth algorithm is ignored for the data channel,	 and  the  au-
	      thentication  method  of	the AEAD cipher	is used	instead.  Note
	      that alg still specifies the digest used for tls-auth.

	      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.

	      Using BF-CBC is no longer	recommended, because  of  it's	64-bit
	      block  size.  This small block size allows attacks based on col-
	      lisions,	as  demonstrated  by  SWEET32.	  See	https://commu- for	details.

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

	      Set alg=none to disable encryption.

	      As of OpenVPN 2.4, cipher	negotiation (NCP) can override the ci-
	      pher specified by	--cipher.  See --ncp-ciphers and --ncp-disable
	      for more on NCP.

       --ncp-ciphers cipher_list
	      Restrict the allowed ciphers to be negotiated to the ciphers  in
	      cipher_list.   cipher_list is a colon-separated list of ciphers,
	      and defaults to "AES-256-GCM:AES-128-GCM".

	      For servers, the first cipher from cipher_list will be pushed to
	      clients that support cipher negotiation.

	      Cipher  negotiation is enabled in	client-server mode only.  I.e.
	      if --mode	is set to 'server' (server-side,  implied  by  setting
	      --server	),  or if --pull is specified (client-side, implied by
	      setting --client).

	      If both peers support and	do not disable NCP, the	negotiated ci-
	      pher will	override the cipher specified by --cipher.

	      Additionally, to allow for more smooth transition, if NCP	is en-
	      abled, OpenVPN will inherit the cipher of	the peer if  that  ci-
	      pher  is different from the local	--cipher setting, but the peer
	      cipher is	one of the ciphers specified in	--ncp-ciphers.	E.g. a
	      non-NCP client (<=2.3, or	with --ncp-disabled set) connecting to
	      a	NCP server (2.4+) with "--cipher  BF-CBC"  and	"--ncp-ciphers
	      AES-256-GCM:AES-256-CBC"	set  can  either specify "--cipher BF-
	      CBC" or "--cipher	AES-256-CBC" and both will work.

	      Disable "negotiable crypto parameters".	This  completely  dis-
	      ables cipher negotiation.

       --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 specified,	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.


	      DEPRECATED This option will be removed in	OpenVPN	2.5.

	      (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 project provides a set of scripts for managing RSA certifi-
       cates & keys:

	      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).   Not
	      available	with PolarSSL.

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

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

	      Set  file=none  to  disable Diffie Hellman key exchange (and use
	      ECDH only). Note that this requires peers	to be using an SSL li-
	      brary that supports ECDH TLS cipher suites (e.g. OpenSSL 1.0.1+,
	      or PolarSSL 1.3+).

	      Use openssl dhparam -out dh2048.pem 2048 to generate 2048-bit DH
	      parameters. Diffie Hellman parameters may	be considered public.

       --ecdh-curve name
	      Specify  the  curve  to  use  for	elliptic curve Diffie Hellman.
	      Available	curves can be listed with --show-curves.   The	speci-
	      fied curve will only be used for ECDH TLS-ciphers.

	      This option is not supported in mbed TLS builds of OpenVPN.

       --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']
	      Sets the minimum TLS version we will accept from the  peer  (de-
	      fault  is	"1.0").	 Examples for version include "1.0", "1.1", or
	      "1.2".  If 'or-highest' is specified and version is  not	recog-
	      nized,  we will only accept the highest TLS version supported by
	      the local	SSL implementation.

       --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".

       --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 [algo]
	      Specify SHA1  or	SHA256	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 certifi-
	      cate verification	will fail.  Hash is specified as XX:XX:... For


	      The algo flag can	be either SHA1 or SHA256.  If not provided, it
	      defaults to SHA1.

       --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. Method 1	is deprecated in Open-
	      VPN 2.4 ,	and will be removed in OpenVPN 2.5.

	      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:!kDH:!kECDH:!DSS:!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 with	an exception, see below).  OpenVPN al-
	      lows the lifetime	of a key to be expressed as a number of	 bytes
	      encrypted/decrypted,  a  number  of packets, or a	number of sec-
	      onds.  A key renegotiation will be forced	if any of these	 three
	      criteria are met by either peer.

	      If  using	 ciphers  with	cipher block sizes less	than 128-bits,
	      --reneg-bytes is set to 64MB by default, unless it is explicitly
	      disabled	by setting the value to	0, but this is HIGHLY DISCOUR-
	      AGED as this is designed to  add	some  protection  against  the
	      SWEET32  attack  vector.	 For more information see the --cipher

       --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 mitigate DoS	attacks	and attacks on the TLS

	      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 file	in OpenVPN static key format which can
	      be generated by --genkey

	      Older versions (up to 2.3) supported a freeform passphrase file.
	      This is no longer	supported in newer versions (2.4+).

	      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 key file used	with --tls-auth	gives a	peer nothing more than
	      the  power  to  initiate a TLS handshake.	 It is not used	to en-
	      crypt or authenticate any	tunnel data.

	      Use --tls-crypt instead if you want to use the key file  to  not
	      only authenticate, but also encrypt the TLS control channel.

       --tls-crypt keyfile

	      Encrypt  and  authenticate  all control channel packets with the
	      key from keyfile.	 (See --tls-auth for more background.)

	      Encrypting (and authenticating) control channel packets:

	      o	provides more privacy by hiding	the certificate	used  for  the
		TLS connection,

	      o	makes it harder	to identify OpenVPN traffic as such,

	      o	provides "poor-man's" post-quantum security, against attackers
		who will never know the	pre-shared key (i.e.  no  forward  se-

	      In  contrast  to	--tls-auth, --tls-crypt	does *not* require the
	      user to set --key-direction.

	      Security Considerations

	      All peers	use the	same --tls-crypt pre-shared group key  to  au-
	      thenticate and encrypt control channel messages.	To ensure that
	      IV collisions remain unlikely, this key should not  be  used  to
	      encrypt more than	2^48 client-to-server or 2^48 server-to-client
	      control channel messages.	  A  typical  initial  negotiation  is
	      about 10 packets in each direction.  Assuming both initial nego-
	      tiation and renegotiations are at	most 2^16 (65536) packets  (to
	      be  conservative),  and  (re)negotiations	happen each minute for
	      each user	(24/7),	this limits the	tls-crypt key lifetime to 8171
	      years  divided  by  the  number  of users.  So a setup with 1000
	      users should rotate the key at  least  once  each	 eight	years.
	      (And a setup with	8000 users each	year.)

	      If  IV  collisions were to occur,	this could result in the secu-
	      rity of --tls-crypt degrading to	the  same  security  as	 using
	      --tls-auth.   That  is,  the control channel still benefits from
	      the extra	protection  against  active  man-in-the-middle-attacks
	      and DoS attacks, but may no longer offer extra privacy and post-
	      quantum security on top of what TLS itself offers.

       --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.

       --auth-token token
	      This  is	not an option to be used directly in any configuration
	      files, but rather	 push  this  option  from  a  --client-connect
	      script	or   a	 --plugin   which   hooks   into   the	 OPEN-
	      calls.   This  option  provides  a  possibility  to  replace the
	      clients password with an authentication token during  the	 life-
	      time of the OpenVPN client.

	      Whenever	  the	 connection    is    renegotiated    and   the
	      --auth-user-pass-verify script or	--plugin  making  use  of  the
	      OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY  hook is triggered, it will
	      pass over	this token as the password instead of the password the
	      user  provided.  The authentication token	can only be reset by a
	      full reconnect where the server can  push	 new  options  to  the
	      client.	The  password the user entered is never	preserved once
	      an authentication	token have been	set.  If  the  OpenVPN	server
	      side  rejects  the authentication	token, the client will receive
	      an AUTH_FAIL and disconnect.

	      The purpose of this is to	enable two factor authentication meth-
	      ods,  such  as  HOTP  or TOTP, to	be used	without	needing	to re-
	      trieve a new OTP code each time the connection is	 renegotiated.
	      Another  use  case is to cache authentication data on the	client
	      without needing to have the users	password cached	in memory dur-
	      ing the life time	of the session.

	      To  make	use  of	 this  feature,	the --client-connect script or
	      --plugin needs to	put

		  push "auth-token UNIQUE_TOKEN_VALUE"

	      into the file/buffer for dynamic configuration data.  This  will
	      then  make  the OpenVPN server to	push this value	to the client,
	      which replaces the local password	with the UNIQUE_TOKEN_VALUE.

       --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.

	      Only  the	 subjectAltName	and issuerAltName X.509	extensions are

	      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.

       --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.

       --ns-cert-type client|server (DEPRECATED)
	      This option is deprecated.  Use the more modern equivalent --re-
	      mote-cert-tls instead.  This option will be removed  in  OpenVPN

	      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

	      If present in the	certificate, the keyUsage value	 is  validated
	      by  the  TLS  library during the TLS handshake.  Specifying this
	      option without arguments requires	this extension to  be  present
	      (so the TLS library will verify it).

	      If the list v...	is also	supplied, the keyUsage field must have
	      at least the same	bits set as the	bits in	one of the values sup-
	      plied in the list	v...

	      The  key	usage  values in the list must be encoded in hex, e.g.
	      "--remote-cert-ku	a0"

       --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.  Or the other way
	      around; for a server to verify that only	hosts  with  a	client
	      certificate can connect.

	      The  --remote-cert-tls  client  option  is  equivalent  to --re-
	      mote-cert-ku --remote-cert-eku "TLS Web Client Authentication"

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

	      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.

	      (Standalone)  Show all available elliptic	curves to use with the
	      --ecdh-curve option.

   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
	      -1.  If offset is	positive, the DHCP server will	masquerade  as
	      the  IP address at network address + offset.  If offset is nega-
	      tive, the	DHCP server will  masquerade  as  the  IP  address  at
	      broadcast	 address  + offset.  The Windows ipconfig /all command
	      can be used to show what Windows thinks the DHCP server  address
	      is.   OpenVPN  will  "claim" this	address, so make sure to use a
	      free address.  Having said that,	different  OpenVPN  instantia-
	      tions,  including	 different  ends  of  the same connection, can
	      share the	same virtual DHCP server address.  The lease-time  pa-
	      rameter  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 in-
	      volving 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 IPv4 address.	Repeat
	      this option to set secondary DNS server addresses.

	      DNS6  addr  -- Set primary domain	name server IPv6 address.  Re-
	      peat this	option to set secondary	DNS server IPv6	addresses.

	      Note: currently this is handled using netsh (the	existing  DHCP
	      code  can	only do	IPv4 DHCP, and that protocol only permits IPv4
	      addresses	anywhere).  The	option will be put into	 the  environ-
	      ment, so an --up script could act	upon it	if needed.

	      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  no effect now, as it	is enabled by default starting
	      with version 2.4.1.

	      Run 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.

   Standalone Debug Options:
       --show-gateway [v6target]
	      (Standalone)  Show current IPv4 and IPv6 default gateway and in-
	      terface towards the gateway (if the protocol in question is  en-
	      abled).	If  an	IPv6  address  is passed as argument, the IPv6
	      route for	this host is reported.

   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''.  The	gateway	parameter is only used
	      for  IPv6	 routes	 across	 ``tap''  devices, and if missing, the
	      ``ipv6remote'' field from	--ifconfig-ipv6	is used.

       --server-ipv6 ipv6addr/bits
	      convenience-function to enable a number of IPv6 related  options
	      at once, namely --ifconfig-ipv6, --ifconfig-ipv6-pool and	--push
	      tun-ipv6 Is only accepted	if ``--mode server''  or  ``--server''
	      is  set.	Pushing	 of the	--tun-ipv6 directive is	done for older
	      clients which require an explicit	``--tun-ipv6'' in  their  con-

       --ifconfig-ipv6-pool ipv6addr/bits
	      Specify  an IPv6 address pool for	dynamic	assignment to clients.
	      The pool starts at ipv6addr and matches  the  offset  determined
	      from the start of	the IPv4 pool.

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

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

       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 or name, 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

       tls_digest_{n} /	tls_digest_sha256_{n}
	      Contains the certificate SHA1 / SHA256 fingerprint, where	 n  is
	      the  verification	 level.	  Only	set  for TLS connections.  Set
	      prior to execution of --tls-verify script.

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

	      The serial number	of the certificate from	the remote peer, where
	      n	is the verification level.  Only set for TLS connections.  Set
	      prior to execution of --tls-verify script. This is in  the  form
	      of  a decimal string like	"933971680", which is suitable for 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, --crl-verify,
       --http-proxy-user-pass, --tls-auth and --tls-crypt options.

       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 <>

				25 August 2016			    openvpn(8)


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