Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
OPENVPN(8)		    System Manager's Manual		    OPENVPN(8)

NAME
       openvpn - Secure	IP tunnel daemon

SYNOPSIS
       openvpn [ options ... ]
       openvpn	--help

INTRODUCTION
       OpenVPN	is  an	open source VPN	daemon by James	Yonan. Because OpenVPN
       tries to	be a universal VPN tool	offering a great deal of  flexibility,
       there  are a lot	of options on this manual page.	If you're new to Open-
       VPN, you	might want to skip ahead to the	 examples  section  where  you
       will  see how to	construct simple VPNs on the command line without even
       needing a configuration file.

       Also note that there's more documentation and examples on  the  OpenVPN
       web site: https://openvpn.net/

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

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

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

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

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

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

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

   Generic Options
       This section covers generic options which are accessible	regardless  of
       which mode OpenVPN is configured	as.

       --help Show options.

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

	      If specified, this directive will	cause OpenVPN  to  immediately
	      forget  username/password	 inputs	 after they are	used. As a 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
	      path.

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

       --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  getentropy()
	      syscall that removes the need for	/dev/urandom to	be available.

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

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

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

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

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

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

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

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

	      For     examples	    of	    configuration      files,	   see
	      https://openvpn.net/community-resources/how-to/

	      Here is an example configuration file:

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

		 # Use a dynamic tun device.
		 dev tun

		 # Our remote peer
		 remote	mypeer.mydomain

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

		 # Our pre-shared static key
		 secret	static.key

       --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 redirection
	      occurs immediately at the	point that --daemon is parsed  on  the
	      command  line  even though the daemonization point occurs	later.
	      If one of	the --log options is present, it will supersede	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 cer-
	      tain  consequences,  namely that using a password-protected pri-
	      vate key will fail unless	the --askpass option is	used  to  tell
	      OpenVPN  to  ask for the pass phrase (this requirement is	new in
	      v2.3.7, and is a consequence of calling daemon() before initial-
	      izing 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.

       --disable-occ
	      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.

       --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.

       --fast-io
	      (Experimental) Optimize TUN/TAP/UDP I/O  writes  by  avoiding  a
	      call to poll/epoll/select	prior to the write operation. The pur-
	      pose of such a call would	normally be to block until the	device
	      or  socket is ready to accept the	write. Such blocking is	unnec-
	      essary on	some platforms which don't support write  blocking  on
	      UDP  sockets or TUN/TAP devices. In such cases, one can optimize
	      the event	loop by	avoiding the poll/epoll/select call, improving
	      CPU efficiency by	5% to 10%.

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

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

       --ignore-unknown-option args
	      Valid syntax:

		 ignore-unknown-options	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
	      wanting new software features to gracefully degrade when encoun-
	      tered by older software versions.

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

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

       --keying-material-exporter args
	      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.

	      Valid syntax:

		 keying-material-exporter label	len

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

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

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

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

	      The limit	on how much memory can be locked and how that limit is
	      enforced	are  OS-dependent.  On Linux the default limit that an
	      unprivileged process may lock (RLIMIT_MEMLOCK) is	 low,  and  if
	      privileges  are  dropped	later,	future memory allocations will
	      very likely fail.	The limit can be  increased  using  ulimit  or
	      systemd directives depending on how OpenVPN is started.

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

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

	      This option can be combined with --user nobody to	allow restarts
	      triggered	by the SIGUSR1 signal. Normally	if you drop root priv-
	      ileges 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.

       --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.

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

	      0	     Strictly no calling of external programs.

	      1	     (Default) Only call built-in executables such  as	ifcon-
		     fig, ip, route, or	netsh.

	      2	     Allow  calling  of	 built-in executables and user-defined
		     scripts.

	      3	     Allow passwords to	be passed to scripts via environmental
		     variables (potentially unsafe).

	      OpenVPN  releases	before v2.3 also supported a method flag which
	      indicated	how OpenVPN should call	external commands and scripts.
	      This  could  be either execve or system. As of OpenVPN 2.3, 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 2.3 it	is now a strict	requirement to have full  path
	      to  the  script  interpreter when	running	non-executables	files.
	      This is not needed for executable	files,	such  as  .exe,	 .com,
	      .bat  or	.cmd  files.  For  example, if you have	a Visual Basic
	      script, you must use this	syntax now:

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

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

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

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

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

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

       --status	args
	      Write operational	status to file every n seconds.

	      Valid syntaxes:

		 status	file
		 status	file n

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

	      With multi-client	capability enabled on  a  server,  the	status
	      file  includes a list of clients and a routing table. The	output
	      format can be controlled by the --status-version option in  that
	      case.

	      For clients or instances running in point-to-point mode, it will
	      contain the traffic statistics.

       --status-version	n
	      Set the status file format version number	to n.

	      This only	affects	the status file	on servers  with  multi-client
	      capability enabled.  Valid status	version	values:

	      1	     Traditional  format  (default).  The client list contains
		     the following fields comma-separated: Common  Name,  Real
		     Address, Bytes Received, Bytes Sent, Connected Since.

	      2	     A	more reliable format for external processing. Compared
		     to	version	1, the client list  contains  some  additional
		     fields:  Virtual Address, Virtual IPv6 Address, Username,
		     Client ID,	Peer ID, Data Channel Cipher. Future  versions
		     may extend	the number of fields.

	      3	     Identical to 2, but fields	are tab-separated.

       --test-crypto
	      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

	      or

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

	      This option is very useful to test OpenVPN  after	 it  has  been
	      ported  to  a  new  platform, or to isolate problems in the com-
	      piler, OpenSSL crypto library, or	OpenVPN's crypto  code.	 Since
	      it is a self-test	mode, problems with encryption and authentica-
	      tion can be debugged independently of network and	tunnel issues.

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

	      This directory will be used by in	the following cases:

	      o	--client-connect  scripts  and	 OPENVPN_PLUGIN_CLIENT_CONNECT
		plug-in	 hook to dynamically generate client-specific configu-
		ration client_connect_config_file and  return  success/failure
		via  client_connect_deferred_file  when	 using deferred	client
		connect	method

	      o	OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY  plug-in  hooks   returns
		success/failure	via auth_control_file when using deferred auth
		method

	      o	OPENVPN_PLUGIN_ENABLE_PF plugin	hook to	pass  filtering	 rules
		via pf_file

       --use-prediction-resistance
	      Enable prediction	resistance on mbed TLS'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.

       --user user
	      Change the user ID of the	OpenVPN	process	to user	after initial-
	      ization, dropping	privileges in the process. This	option is use-
	      ful 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).

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

   Log options
       --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.

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

       --log file
	      Output logging  messages	to  file,  including  output  to  std-
	      out/stderr which is generated by called scripts. If file already
	      exists it	will be	truncated. This	option	takes  effect  immedi-
	      ately  when  it is parsed	in the command line and	will supersede
	      syslog output if --daemon	or --inetd is also specified. This op-
	      tion  is persistent over the entire course of an OpenVPN instan-
	      tiation  and  will  not  be  reset  by   SIGHUP,	 SIGUSR1,   or
	      --ping-restart.

	      Note that	on Windows, when OpenVPN is started as a service, log-
	      ging occurs by default without the need to specify this option.

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

       --machine-readable-output
	      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.

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

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

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

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

       --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  out-
	      put.

	      0	     No	output except fatal errors.

	      1	to 4 Normal usage range.

	      5	     Outputs R and W characters	to the console for each	packet
		     read and write, uppercase is used for TCP/UDP packets and
		     lowercase is used for TUN/TAP packets.

	      6	to 11
		     Debug  info  range	(see errlevel.h	in the source code for
		     additional	information on debug levels).

   Protocol options
       Options in this section affect features available in the	 OpenVPN  wire
       protocol.   Many	of these options also define the encryption options of
       the data	channel	in the OpenVPN wire protocol.  These options  must  be
       configured in a compatible way between both the local and remote	side.

       --allow-compression mode
	      As  described  in	the --compress option, compression is a	poten-
	      tially dangerous option.	This option allows controlling the be-
	      haviour of OpenVPN when compression is used and allowed.

	      Valid syntaxes:

		 allow-compression
		 allow-compression mode

	      The mode argument	can be one of the following values:

	      asym (default)
		     OpenVPN  will  only  decompress  downlink packets but not
		     compress uplink packets.  This also allows	 migrating  to
		     disable  compression when changing	both server and	client
		     configurations to remove compression at the same time  is
		     not a feasible option.

	      no     OpenVPN will refuse any non-stub compression.

	      yes    OpenVPN will send and receive compressed packets.

       --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 au-
	      thentication 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 then the specified
	      --auth algorithm is ignored for the data channel and the authen-
	      tication	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 dy-
	      namically	generated and shared between peers via the TLS control
	      channel.	If  OpenVPN  receives a	packet with a bad HMAC it will
	      drop the packet. HMAC usually adds 16 or 20  bytes  per  packet.
	      Set alg=none to disable authentication.

	      For	 more	     information       on	HMAC	   see
	      http://www.cs.ucsd.edu/users/mihir/papers/hmac.html

       --cipher	alg
	      This option is deprecated	for server-client mode.	--data-ciphers
	      or possibly --data-ciphers-fallback` should be used instead.

	      Encrypt data channel packets with	cipher algorithm alg.

	      The  default  is	BF-CBC,	an abbreviation	for Blowfish in	Cipher
	      Block Chaining mode. When	cipher negotiation (NCP)  is  allowed,
	      OpenVPN  2.4 and newer on	both client and	server side will auto-
	      matically	 upgrade  to  AES-256-GCM.   See  --data-ciphers   and
	      --ncp-disable for	more details on	NCP.

	      Using  BF-CBC  is	 no  longer recommended, because of its	64-bit
	      block size. This small block size	allows attacks based on	colli-
	      sions,	   as	   demonstrated	     by	     SWEET32.	   See
	      https://community.openvpn.net/openvpn/wiki/SWEET32 for  details.
	      Due  to  this,  support for BF-CBC, DES, CAST5, IDEA and RC2 ci-
	      phers will be removed in OpenVPN 2.6.

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

	      Set alg to none to disable encryption.

       --compress algorithm
	      DEPRECATED  Enable a compression algorithm.  Compression is gen-
	      erally not recommended.  VPN tunnels which use  compression  are
	      susceptible to the VORALCE attack	vector.

	      The  algorithm  parameter	may be lzo, lz4, lz4-v2, stub, stub-v2
	      or empty.	 LZO and LZ4  are  different  compression  algorithms,
	      with  LZ4	generally offering the best performance	with least CPU
	      usage.

	      The lz4-v2 and stub-v2 variants implement	a better framing  that
	      does  not	 add  overhead	when packets cannot be compressed. All
	      other variants always add	one extra framing byte compared	to  no
	      compression framing.

	      If  the  algorithm parameter is stub, stub-v2 or empty, compres-
	      sion will	be turned off, but the packet framing for  compression
	      will still be enabled, allowing a	different setting to be	pushed
	      later.  Additionally, stub and stub-v2  wil  disable  announcing
	      lzo and lz4 compression support via IV_ variables	to the server.

	      Note:  the  stub	(or  empty)  option is NOT compatible with the
	      older option --comp-lzo no.

	      *Security	Considerations*

	      Compression and encryption is a tricky combination.  If  an  at-
	      tacker  knows or is able to control (parts of) the plain-text of
	      packets that contain secrets, the	attacker might be able to  ex-
	      tract  the  secret if compression	is enabled. See	e.g. the CRIME
	      and BREACH attacks on TLS	and VORACLE on VPNs which also	lever-
	      age  to  break encryption. If you	are not	entirely sure that the
	      above does not apply to your traffic, you	are advised to not en-
	      able compression.

       --comp-lzo mode
	      DEPRECATED  Enable  LZO  compression  algorithm.	Compression is
	      generally	not recommended.  VPN tunnels which  uses  compression
	      are suspectible to the VORALCE attack vector.

	      Use  LZO	compression -- may add up to 1 byte per	packet for in-
	      compressible data. mode may be yes, no, or adaptive (default).

	      In a server mode setup, it is possible to	selectively turn  com-
	      pression on or off for individual	clients.

	      First,  make  sure the client-side config	file enables selective
	      compression by having at least one --comp-lzo directive, such as
	      --comp-lzo  no.  This  will turn off compression by default, but
	      allow a future directive push from  the  server  to  dynamically
	      change the on/off/adaptive setting.

	      Next in a	--client-config-dir file, specify the compression set-
	      ting for the client, for example:

		 comp-lzo yes
		 push "comp-lzo	yes"

	      The first	line sets the comp-lzo setting for the server side  of
	      the link,	the second sets	the client side.

       --comp-noadapt
	      DEPRECATED When used in conjunction with --comp-lzo, this	option
	      will disable OpenVPN's adaptive compression algorithm. Normally,
	      adaptive compression is enabled with --comp-lzo.

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

       --key-direction
	      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).

       --keysize n
	      DEPRECATED This option will be removed in	OpenVPN	2.6.

	      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 security, or
	      may even reduce security.

       --data-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 that is also sup-
	      ported  by the client will be pushed to clients that support ci-
	      pher 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 no common cipher is found during cipher negotiation, the con-
	      nection is terminated. To	support	old clients/old	 servers  that
	      do  not  provide	any  cipher negotiation	support	see --data-ci-
	      phers-fallback.

	      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	--data-ciphers.	E.g. a
	      non-NCP client (<=v2.3, or with --ncp-disabled  set)  connecting
	      to  a NCP	server (v2.4+) with --cipher BF-CBC and	--data-ciphers
	      AES-256-GCM:AES-256-CBC set can either specify  --cipher	BF-CBC
	      or --cipher AES-256-CBC and both will work.

	      Note  for	using NCP with an OpenVPN 2.4 peer: This list must in-
	      clude the	AES-256-GCM and	AES-128-GCM ciphers.

	      This list	is restricted to be 127	chars long after conversion to
	      OpenVPN ciphers.

	      This option was called --ncp-ciphers in OpenVPN 2.4 but has been
	      renamed to --data-ciphers	in OpenVPN 2.5 to more accurately  re-
	      flect its	meaning.

       --data-ciphers-fallback alg
	      Configure	 a cipher that is used to fall back to if we could not
	      determine	which cipher the peer is willing to use.

	      This option should only be needed	to connect to peers  that  are
	      running  OpenVPN 2.3 and older version, and have been configured
	      with --enable-small (typically used on routers or	other embedded
	      devices).

       --ncp-disable
	      DEPRECATED  Disable  "Negotiable	Crypto	Parameters". This com-
	      pletely disables cipher negotiation.

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

	      Valid syntaxes:

		 secret	file
		 secret	file direction

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

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

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

	      The direction parameter requires that file contains a  2048  bit
	      key.  While  pre-1.5  versions  of OpenVPN generate 1024 bit key
	      files, any version of OpenVPN which supports the	direction  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 requirement
	      is  that	you  have a pre-existing secure	channel	with your peer
	      (such as ssh) to initially copy the key. This requirement, along
	      with  the	 fact  that your key never changes unless you manually
	      generate a new one, makes	it somewhat less secure	than TLS  mode
	      (see  below).  If	 an attacker manages to	steal your key,	every-
	      thing that was ever encrypted with it is	compromised.  Contrast
	      that  to the perfect forward secrecy features of TLS mode	(using
	      Diffie Hellman key exchange), where even if an attacker was able
	      to  steal	your private key, he would gain	no information to help
	      him decrypt past sessions.

	      Another advantageous aspect of Static  Key  encryption  mode  is
	      that  it is a handshake-free protocol without any	distinguishing
	      signature	or feature (such as a header or	protocol handshake 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.

       --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.

   Client Options
       The  client  options are	used when connecting to	an OpenVPN server con-
       figured to use --server,	--server-bridge, or --mode server in its  con-
       figuration.

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

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

       --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-
	      VPN_PLUGIN_CLIENT_CONNECT	  or  OPENVPN_PLUGIN_CLIENT_CONNECT_V2
	      calls. This option provides a possibility	to replace the clients
	      password with an authentication token during the lifetime	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  has  been set. If the OpenVPN server side
	      rejects the authentication token then the	client will receive an
	      AUTH_FAILED 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.

	      Newer  clients  (2.4.7+) will fall back to the original password
	      method after a failed auth. Older	clients	will  keep  using  the
	      token value and react according to --auth-retry

       --auth-user-pass
	      Authenticate with	server using username/password.

	      Valid syntaxes:

		 auth-user-pass
		 auth-user-pass	up

	      If up is present,	it must	be 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
	      console.

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

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

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

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

	      type can be one of:

	      none   Client  will  exit	 with  a  fatal	error (this is the de-
		     fault).

	      nointeract
		     Client will retry the connection without  requerying  for
		     an	 --auth-user-pass  username/password.  Use this	option
		     for unattended clients.

	      interact
		     Client  will  requery  for	 an   --auth-user-pass	 user-
		     name/password and/or private key password before attempt-
		     ing a reconnection.

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

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

		 pull
		 tls-client

       --client-nat args
	      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.

	      Examples:

		 client-nat snat 192.168.0.0/255.255.0.0
		 client-nat dnat 10.64.0.0/255.255.0.0

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

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

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

       --connect-retry n
	      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.  An  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	1 would	try each entry exactly
	      once. A successful connection resets the counter.	 (default  un-
	      limited).

       --connect-timeout n
	      See --server-poll-timeout.

       --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 if not present) 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 if not	present)  con-
	      trols  client behavior. With n = 1 client	will attempt to	recon-
	      nect 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.

       --inactive args
	      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.

	      Valid syntaxes:

		 inactive n
		 inactive n bytes

	      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-
	      ity.

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

       --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 args
	      Filter options on	the client pushed by the server	to the client.

	      Valid syntaxes:

		 pull-filter accept text
		 pull-filter ignore text
		 pull-filter reject text

	      Filter  options  received	 from  the server if the option	starts
	      with text.  The action flag accept allows	the option, ignore re-
	      moves  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. Unmatched 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.

	      Note that	reject may result in a repeated	cycle of  failure  and
	      reconnect,  unless multiple remotes are specified	and connection
	      to the next remote succeeds. To silently ignore an option	pushed
	      by the server, use ignore.

       --remote	args
	      Remote host name or IP address, port and protocol.

	      Valid syntaxes:

		 remote	host
		 remote	host port
		 remote	host port proto

	      The  port	 and  proto arguments are optional. The	OpenVPN	client
	      will try to connect to a server at host:port.  The  proto	 argu-
	      ment  indicates the protocol to use when connecting with the re-
	      mote, and	may be tcp or udp.  To enforce IPv4  or	 IPv6  connec-
	      tions add	a 4 or 6 suffix; like udp4 / udp6 / tcp4 / tcp6.

	      On  the  client,	multiple --remote options may be specified for
	      redundancy, each referring to a different	OpenVPN	server,	in the
	      order specified by the list of --remote options. Specifying mul-
	      tiple --remote options for this purpose is a special case	of the
	      more  general  connection-profile	 feature. See the <connection>
	      documentation below.

	      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.

	      Examples:

		 remote	server1.example.net
		 remote	server1.example.net 1194
		 remote	server2.example.net 1194 tcp

	      Note:  Since UDP is connectionless, connection  failure  is  de-
		     fined by the --ping and --ping-restart options.

		     Also,  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 set-
		     tings, 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	proto-
	      col specification	(4/6 suffix), OpenVPN will try both  IPv4  and
	      IPv6 addresses, in the order getaddrinfo() returns them.

       --remote-random
	      When  multiple  --remote address/ports are specified, or if con-
	      nection profiles are being used, initially randomize  the	 order
	      of the list as a kind of basic load-balancing measure.

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

       --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.

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

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

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

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

       --static-challenge args
	      Enable static challenge/response protocol

	      Valid syntax:

		 static-challenge text echo

	      The text challenge text is presented to the user which describes
	      what  information	 is requested.	The echo flag indicates	if the
	      user's input should be echoed on the screen.  Valid echo	values
	      are 0 or 1.

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

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

       --http-proxy args
	      Connect  to remote host through an HTTP proxy.  This requires at
	      least an address server and port argument.   If  HTTP  Proxy-Au-
	      thenticate is required, a	file name to an	authfile file contain-
	      ing a username and password on 2 lines can be given, or stdin to
	      prompt  from  console.  Its content can also be specified	in the
	      config file with the --http-proxy-user-pass option. (See section
	      on inline	files)

	      The last optional	argument is an auth-method which 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).  This	must replace the auth-
	      file argument.

	      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.

	      Examples:

		 http-proxy proxy.example.net 3128
		 http-proxy proxy.example.net 3128 authfile.txt
		 http-proxy proxy.example.net 3128 stdin
		 http-proxy proxy.example.net 3128 auto	basic
		 http-proxy proxy.example.net 3128 auto-nct ntlm

       --http-proxy-option args
	      Set  extended HTTP proxy options.	Requires an option type	as ar-
	      gument and an optional parameter to the  type.   Repeat  to  set
	      multiple options.

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

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

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

	      Examples:

		 http-proxy-option VERSION 1.1
		 http-proxy-option AGENT OpenVPN/2.4
		 http-proxy-option X-Proxy-Flag	some-flags

       --socks-proxy args
	      Connect to remote	host  through  a  Socks5  proxy.   A  required
	      server argument is needed.  Optionally a port (default 1080) and
	      authfile can be given.  The authfile  is	a  file	 containing  a
	      username and password on 2 lines,	or stdin can be	used to	prompt
	      from console.

   Server Options
       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.

       --auth-gen-token	args
	      Returns an authentication	token  to  successfully	 authenticated
	      clients.

	      Valid syntax:

		 auth-gen-token	[lifetime] [external-auth]

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

	      The tokens implemented by	 this  mechanism  include  an  initial
	      timestamp	and a renew timestamp and are secured by HMAC.

	      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.

	      The  token  will	expire either after the	configured lifetime of
	      the token	is reached or after not	being renewed for more than  2
	      *	 reneg-sec seconds. Clients will be sent renewed tokens	on ev-
	      ery TLS renogiation to keep the client's token updated. This  is
	      done  to	invalidate  a  token if	a client is disconnected for a
	      sufficently long time, while at the same	time  permitting  much
	      longer token lifetimes for active	clients.

	      This  feature is useful for environments which are 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.

	      When the external-auth keyword is	present	the normal authentica-
	      tion  method  will always	be called even if auth-token succeeds.
	      Normally other authentications method are	skipped	if  auth-token
	      verification suceeds or fails.

	      This  option postpones this decision to the external authentica-
	      tion methods and checks the validity of the account and do other
	      checks.

	      In  this	mode  the  environment will have a session_id variable
	      that holds the session id	from auth-gen-token. Also an  environ-
	      ment  variable session_state is present. This variable indicates
	      whether the auth-token has succeeded or not.  It	can  have  the
	      following	values:

	      Initial
		     No	token from client.

	      Authenticated
		     Token is valid and	not expired.

	      Expired
		     Token is valid but	has expired.

	      Invalid
		     Token is invalid (failed HMAC or wrong length)

	      AuthenticatedEmptyUser / ExpiredEmptyUser
		     The  token	 is  not valid with the	username sent from the
		     client but	would be valid (or expired) if	we  assume  an
		     empty  username  was used instead.	 These two cases are a
		     workaround	for behaviour in OpenVPN  3.   If  this	 work-
		     around is not needed these	two cases should be handled in
		     the same way as Invalid.

	      Warning: Use this	feature	only if	you want  your	authentication
	      method  called on	every verification. Since the external authen-
	      tication is called it needs to also indicate a success or	 fail-
	      ure  of the authentication. It is	strongly recommended to	return
	      an authentication	failure	in the	case  of  the  Invalid/Expired
	      auth-token with the external-auth	option unless the client could
	      authenticate in another acceptable  way  (e.g.  client  certifi-
	      cate),  otherwise	 returning success will	lead to	authentication
	      bypass (as does returning	success	on a  wrong  password  from  a
	      script).

       --auth-gen-token-secret file
	      Specifies	 a  file  that	holds  a  secret  for the HMAC used in
	      --auth-gen-token If file is not present OpenVPN will generate  a
	      random secret on startup.	This file should be used if auth-token
	      should validate after restarting a server	or if client should be
	      able  to	roam  between  multiple	 OpenVPN  servers  with	 their
	      auth-token.

       --auth-user-pass-optional
	      Allow connections	 by  clients  that  do	not  specify  a	 user-
	      name/password.  Normally,	when --auth-user-pass-verify or	--man-
	      agement-client-auth are 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	detect
	      this condition and respond accordingly.

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

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

	      This  file can specify a fixed IP	address	for a given client 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,
	      --vlan-pvid and --config.

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

	      When this	option is used,	 each  client  will  "see"  the	 other
	      clients  which  are  currently connected.	Otherwise, each	client
	      will only	see the	server.	Don't use this option if you  want  to
	      firewall tunnel traffic using custom, per-client rules.

       --disable
	      Disable a	particular client (based on the	common name) from con-
	      necting.	Don't use this option to disable a client due  to  key
	      or  password compromise. Use a CRL (certificate revocation list)
	      instead (see the --crl-verify option).

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

       --connect-freq args
	      Allow  a	maximum	 of  n	new  connections  per sec seconds from
	      clients.

	      Valid syntax:

		 connect-freq n	sec

	      This is designed to contain DoS attacks which flood  the	server
	      with  connection	requests  using	 certificates which will ulti-
	      mately 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.

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

       --ifconfig-pool args
	      Set  aside a pool	of subnets to be dynamically allocated to con-
	      necting clients, similar to a DHCP server.

	      Valid syntax:

		 ifconfig-pool start-IP	end-IP [netmask]

	      For tun-style tunnels, each client will be given	a  /30	subnet
	      (for interoperability with Windows clients).  For	tap-style tun-
	      nels, individual addresses will be allocated, and	 the  optional
	      netmask parameter	will also be pushed to clients.

       --ifconfig-ipv6-pool args
	      Specify an IPv6 address pool for dynamic assignment to clients.

	      Valid args:

		 ifconfig-ipv6-pool ipv6addr/bits

	      The  pool	 starts	 at ipv6addr and matches the offset determined
	      from the start of	the IPv4 pool.	If the host part of the	 given
	      IPv6 address is 0, the pool starts at ipv6addr +1.

       --ifconfig-pool-persist args
	      Persist/unpersist	 ifconfig-pool data to file, at	seconds	inter-
	      vals (default 600), as well as on	program	startup	and shutdown.

	      Valid syntax:

		 ifconfig-pool-persist file [seconds]

	      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	 <Com-
	      mon-Name>,<IP-address>.

	      If  seconds = 0, file will be treated as read-only. This is use-
	      ful if you would like to treat file as a configuration file.

	      Note that	the entries in this file are  treated  by  OpenVPN  as
	      suggestions  only,  based	 on past associations between a	common
	      name and IP address.  They do not	guarantee that the given  com-
	      mon  name	 will always receive the given IP address. If you want
	      guaranteed assignment, use --ifconfig-push

       --ifconfig-push args
	      Push virtual IP endpoints	 for  client  tunnel,  overriding  the
	      --ifconfig-pool dynamic allocation.

	      Valid syntax:

		 ifconfig-push local remote-netmask [alias]

	      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 choice).

       --ifconfig-ipv6-push args
	      for --client-config-dir per-client static	IPv6 interface config-
	      uration,	see  --client-config-dir  and --ifconfig-push for more
	      details.

	      Valid syntax:

		 ifconfig-ipv6-push ipv6addr/bits ipv6remote

       --inetd args
	      Valid syntaxes:

		 inetd
		 inetd wait
		 inetd nowait
		 inetd wait progname

	      Use this option when OpenVPN is being  run  from	the  inetd  or
	      xinetd(8)	server.

	      The  wait	 and nowait option must	match what is specified	in the
	      inetd/xinetd config file.	The nowait mode	can only be used  with
	      --proto  tcp-server The default is wait.	The nowait mode	can be
	      used to instantiate the OpenVPN daemon as	a classic TCP  server,
	      where  client  connection	requests are serviced on a single port
	      number. For additional information on this  kind	of  configura-
	      tion,	      see	    the		 OpenVPN	  FAQ:
	      https://community.openvpn.net/openvpn/wiki/325-openvpn-as-a--forking-tcp-server-which-can-service-multiple-clients-over-a-single-tcp-port

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

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

       --multihome
	      Configure	a multi-homed UDP server. This option needs to be used
	      when a server has	more than one IP address (e.g. multiple	inter-
	      faces,  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 re-
	      ply 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.

	      Notes:

		     o This option is only relevant for	UDP servers.

		     o 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 kernel support for the IPv4-mapped case
		       (some distributions have	ported this to earlier	kernel
		       versions, though).

       --iroute	args
	      Generate an internal route to a specific client. The netmask pa-
	      rameter, if omitted, defaults to 255.255.255.255.

	      Valid syntax:

		 iroute	network	[netmask]

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

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

	      The  --iroute  directive	also has an important interaction with
	      --push "route ...". --iroute essentially defines a subnet	 which
	      is owned by a particular client (we will call this client	A). If
	      you would	like other clients to be able to reach A's subnet, you
	      can  use	--push "route ..." together with --client-to-client to
	      effect this. In order for	all clients to see A's subnet, OpenVPN
	      must push	this route to all clients EXCEPT for A,	since the sub-
	      net 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.

       --iroute-ipv6 args
	      for --client-config-dir per-client static	IPv6 route  configura-
	      tion,  see  --iroute for more details how	to setup and use this,
	      and how --iroute and --route interact.

	      Valid syntax:

		 iroute-ipv6 ipv6addr/bits

       --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.

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

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

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

       --port-share args
	      Share OpenVPN TCP	with another service

	      Valid syntax:

		 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.

       --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 compromised
	      server to	execute	arbitrary code on the  client.	Other  options
	      such  as	TLS  or	 MTU  parameters  cannot be pushed because the
	      client needs to know them	before the connection  to  the	server
	      can be initiated.

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

       --push-peer-info
	      Push additional information about	the client to server. The fol-
	      lowing 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
		     Details about protocol extensions that the	peer supports.
		     The  variable  is	a bitfield and the bits	are defined as
		     follows (starting a bit 0 for the first (unused) bit:

		     o bit 1: The peer supports	peer-id	floating mechanism

		     o bit 2: The client expects a push-reply and  the	server
		       may  send this reply without waiting for	a push-request
		       first.

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

	      IV_CIPHERS=<ncp-ciphers>
		     The client	announces the list of supported	 ciphers  con-
		     figured with the --data-ciphers option to the server.

	      IV_GUI_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 app.

	      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	gateway

	      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_

       --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.

	      NOTE 2: due to implementation details,  'ifconfig'  and  'ifcon-
	      fig-ipv6'	 can only be removed with an exact match on the	option
	      (	push-remove ifconfig), no substring matching and  no  matching
	      on the IPv4/IPv6 address argument	is possible.

       --push-reset
	      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.

	      NOTE: --push-reset is very thorough: it will remove  almost  all
	      options  from  the list of to-be-pushed options.	In many	cases,
	      some of these options will need to be re-configured afterwards -
	      specifically,  --topology	 subnet	 and  --route-gateway will get
	      lost and this will break client configs in  many	cases.	 Thus,
	      for most purposes, --push-remove is better suited	to selectively
	      remove push options for individual clients.

       --server	args
	      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 lo-
	      cal  TUN/TAP interface. If the optional nopool flag is given, no
	      dynamic IP address pool will prepared for	VPN clients.

	      Valid syntax:

		 server	network	netmask	[nopool]

	      For example, --server 10.8.0.0 255.255.255.0 expands as follows:

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

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

		 if dev	tap OR (dev tun	AND topology ==	subnet):
		   ifconfig 10.8.0.1 255.255.255.0
		   if !nopool:
		     ifconfig-pool 10.8.0.2 10.8.0.253 255.255.255.0
		   push	"route-gateway 10.8.0.1"
		   if route-gateway unset:
		     route-gateway 10.8.0.2

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

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

	      Valid syntaxes:

		 server-bridge gateway netmask pool-start-IP pool-end-IP
		 server-bridge [nogw]

	      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-
	      net.

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

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

		 mode server
		 tls-server

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

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

		 mode server
		 tls-server

		 push "route-gateway dhcp"

	      Or --server-bridge nogw expands as follows:

		 mode server
		 tls-server

       --server-ipv6 args
	      Convenience-function  to enable a	number of IPv6 related options
	      at once, namely --ifconfig-ipv6, --ifconfig-ipv6-pool and	--push
	      tun-ipv6.

	      Valid syntax:

		 server-ipv6 ipv6addr/bits

	      Pushing  of  the	--tun-ipv6 directive is	done for older clients
	      which require an explicit	--tun-ipv6 in their configuration.

       --stale-routes-check args
	      Remove routes which haven't had activity for n seconds (i.e. the
	      ageing time).  This check	is run every t seconds (i.e. check in-
	      terval).

	      Valid syntax:

		 stale-routes-check n [t]

	      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

       --username-as-common-name
	      Use  the	authenticated username as the common-name, rather than
	      the common-name from the client certificate. Requires that  some
	      form  of	--auth-user-pass verification is in effect. As the re-
	      placement	happens	after --auth-user-pass verification, the veri-
	      fication	script	or  plugin  will still receive the common-name
	      from the certificate.

	      The common_name environment variable passed to scripts and plug-
	      ins  invoked  after  authentication (e.g,	client-connect script)
	      and file names parsed in client-config directory will match  the
	      username.

       --verify-client-cert mode
	      Specify  whether	the  client is required	to supply a valid cer-
	      tificate.

	      Possible mode options are:

	      none   A client certificate is not required. the client needs to
		     authenticate  using username/password only. Be aware that
		     using this	directive is less secure than  requiring  cer-
		     tificates from all	clients.

		     If	 you  use this directive, the entire responsibility of
		     authentication will rest on your  --auth-user-pass-verify
		     script,  so  keep	in mind	that bugs in your script could
		     potentially compromise the	security of your VPN.

		     --verify-client-cert none is functionally	equivalent  to
		     --client-cert-not-required.

	      optional
		     A client may present a certificate	but it is not required
		     to	do so.	When using this	directive, you should also use
		     a	--auth-user-pass-verify	 script	to ensure that clients
		     are authenticated 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 compro-
		     mise the security of your VPN.

	      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 cer-
	      tificate 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.

       --vlan-tagging
	      Server-only option. Turns	the OpenVPN  server  instance  into  a
	      switch that understands VLAN-tagging, based on IEEE 802.1Q.

	      The server TAP device and	each of	the connecting clients is seen
	      as a port	of the switch. All client ports	are in	untagged  mode
	      and  the	server	TAP device is VLAN-tagged, untagged or accepts
	      both, depending on the --vlan-accept setting.

	      Ethernet frames with a prepended 802.1Q tag are called "tagged".
	      If  the  VLAN  Identifier	(VID) field in such a tag is non-zero,
	      the frame	is called "VLAN-tagged". If the	VID is zero,  but  the
	      Priority	Control	 Point	(PCP)  field is	non-zero, the frame is
	      called "prio-tagged". If there is	no 802.1Q tag,	the  frame  is
	      "untagged".

	      Using   the   --vlan-pvid	  v   option   once  per  client  (see
	      --client-config-dir), each port can be associated	with a certain
	      VID.   Packets  can  only	 be forwarded between ports having the
	      same VID.	 Therefore, clients with differing VIDs	are completely
	      separated	 from one-another, even	if --client-to-client is acti-
	      vated.

	      The packet filtering takes place in the OpenVPN server.  Clients
	      should not have any VLAN tagging configuration applied.

	      The  --vlan-tagging  option is off by default. While turned off,
	      OpenVPN accepts any Ethernet frame and does not perform any spe-
	      cial processing for VLAN-tagged packets.

	      This option can only be activated	in --dev tap mode.

       --vlan-accept args
	      Configure	the VLAN tagging policy	for the	server TAP device.

	      Valid syntax:

		 vlan-accept  all|tagged|untagged

	      The following modes are available:

	      tagged Admit  only  VLAN-tagged frames. Only VLAN-tagged packets
		     are accepted, while untagged or  priority-tagged  packets
		     are dropped when entering the server TAP device.

	      untagged
		     Admit  only untagged and prio-tagged frames.  VLAN-tagged
		     packets  are  not	accepted,  while  untagged  or	prior-
		     ity-tagged	 packets  entering  the	 server	TAP device are
		     tagged  with  the	value  configured   for	  the	global
		     --vlan-pvid setting.

	      all (default)
		     Admit  all	 frames.   All	packets	 are admitted and then
		     treated like untagged or tagged mode respectively.

	      Note:  Some vendors refer	to switch ports	running	in tagged mode
		     as	 "trunk	 ports"	 and  switch ports running in untagged
		     mode as "access ports".

	      Packets forwarded	from clients to	 the  server  are  VLAN-tagged
	      with  the	 originating client's PVID, unless the VID matches the
	      global --vlan-pvid, in which case	the tag	is removed.

	      If no PVID is configured for a given  client  (see  --vlan-pvid)
	      packets are tagged with 1	by default.

       --vlan-pvid v
	      Specifies	 which	VLAN  identifier  a "port" is associated with.
	      Only valid when --vlan-tagging is	speficied.

	      In the client context, the setting specifies  which  VLAN	 ID  a
	      client is	associated with. In the	global context,	the VLAN ID of
	      the server TAP device is set. The	latter only  makes  sense  for
	      --vlan-accept untagged and --vlan-accept all modes.

	      Valid  values  for v go from 1 through to	4094. The global value
	      defaults to 1. If	no --vlan-pvid is specified in the client con-
	      text, the	global value is	inherited.

	      In  some switch implementations, the PVID	is also	referred to as
	      "Native VLAN".

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

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

       --show-tls
	      (Standalone) Show	all TLS	ciphers	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 pref-
	      erence (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.).

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

       --show-groups
	      (Standalone) Show	all available elliptic	curves/groups  to  use
	      with the --ecdh-curve and	tls-groups options.

   Generating key material
       --genkey	args
	      (Standalone)  Generate  a	key to be used of the type keytype. if
	      keyfile is left out or empty the key will	be output  on  stdout.
	      See the following	sections for the different keytypes.

	      Valid syntax:

		 --genkey keytype keyfile

	      Valid keytype arguments are:

	      secret		    Standard OpenVPN shared secret keys

	      tls-crypt		    Alias for secret

	      tls-auth		    Alias for secret

	      auth-token	    Key	used for --auth-gen-token-key

	      tls-crypt-v2-server   TLS	Crypt v2 server	key

	      tls-crypt-v2-client   TLS	Crypt v2 client	key

	      Examples:

		 $ openvpn --genkey secret shared.key
		 $ openvpn --genkey tls-crypt shared.key
		 $ openvpn --genkey tls-auth shared.key
		 $ openvpn --genkey tls-crypt-v2-server	v2crypt-server.key
		 $ openvpn --tls-crypt-v2 v2crypt-server.key --genkey tls-crypt-v2-client v2crypt-client-1.key

	      o	Generating  Shared  Secret  Keys Generate a shared secret, for
		use with the --secret, --tls-auth or --tls-crypt options.

		Syntax:

		   $ openvpn --genkey secret|tls-crypt|tls-auth	keyfile

		The key	is saved in keyfile.  All  three  variants  (--secret,
		tls-crypt  and	tls-auth)  generate  the same type of key. The
		aliases	are added for convenience.

		If using this for --secret, this file must be shared with  the
		peer over a pre-existing secure	channel	such as	scp(1).

	      o	Generating  TLS	 Crypt v2 Server key Generate a	--tls-crypt-v2
		key to be used by an OpenVPN server.  The  key	is  stored  in
		keyfile.

		Syntax:

		   --genkey tls-crypt-v2-server	keyfile

	      o	Generating  TLS	 Crypt v2 Client key Generate a	--tls-crypt-v2
		key to be used by OpenVPN clients.  The	key is stored in  key-
		file.

		Syntax

		   --genkey tls-crypt-v2-client	keyfile	[metadata]

		If  supplied,  include	the  supplied  metadata	in the wrapped
		client key. This metadata must be supplied  in	base64-encoded
		form.  The  metadata must be at	most 735 bytes long (980 bytes
		in base64).

		If no metadata is supplied, OpenVPN will  use  a  64-bit  unix
		timestamp  representing	 the  current  time in UTC, encoded in
		network	order, as metadata for the generated key.

		A tls-crypt-v2 client key is wrapped using a  server  key.  To
		generate  a  client  key,  the	user must therefore supply the
		server key using the --tls-crypt-v2 option.

		Servers	can use	--tls-crypt-v2-verify to  specify  a  metadata
		verification command.

	      o	Generate  Authentication  Token	key Generate a new secret that
		can be used with --auth-gen-token-secret

		Syntax:

		   --genkey auth-token [keyfile]

		Note:  This file should	be kept	secret to the server as	anyone
		       that  has  access to this file will be able to generate
		       auth tokens that	the  OpenVPN  server  will  accept  as
		       valid.

   Data	Channel	Renegotiation
       When running OpenVPN in client/server mode, the data channel will use a
       separate	ephemeral encryption key which is rotated  at  regular	inter-
       vals.

       --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 op-
	      tion.

       --reneg-pkts n
	      Renegotiate  data	 channel key after n packets sent and received
	      (disabled	by default).

       --reneg-sec args
	      Renegotiate data channel key after at most max seconds  (default
	      3600)  and  at  least  min  seconds  (default  is	90% of max for
	      servers, and equal to max	for clients).

		 reneg-sec max [min]

	      The effective --reneg-sec	value used is per session  pseudo-uni-
	      form-randomized between min and max.

	      With  the	default	value of 3600 this results in an effective per
	      session value in the range of 3240 .. 3600 seconds for  servers,
	      or just 3600 for clients.

	      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 de-
	      fault value of 3600 seconds, meaning that	the renegotiation will
	      still  occur  once per 3600 seconds. The solution	is to increase
	      --reneg-sec on both the client and server, or set	it to 0	on one
	      side of the connection (to disable), and to your chosen value on
	      the other	side.

   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 certificate
       which is	specified in --ca.

       When  two OpenVPN peers connect,	each presents its local	certificate to
       the other. Each peer will then check that its partner peer presented  a
       certificate  which  was signed by the master root certificate as	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 and keys: https://github.com/OpenVPN/easy-rsa

       --askpass file
	      Get  certificate	password from console or file before we	daemo-
	      nize.

	      Valid syntaxes:

		 askpass
		 askpass file

	      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.

       --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 mbed TLS.

	      CAs in the capath	directory are expected to be named <hash>.<n>.
	      CRLs  are	 expected to be	named <hash>.r<n>. See the -CApath op-
	      tion of openssl verify, and the -hash option  of	openssl	 x509,
	      openssl crl and X509_LOOKUP_hash_dir()(3)	for more information.

	      Similar  to  the	--crl-verify  option, CRLs are not mandatory -
	      OpenVPN will log the usual warning in the	logs if	 the  relevant
	      CRL is missing, but the connection will be allowed.

       --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 certifi-
	      cate should have been signed by the key of a certificate author-
	      ity whose	public key resides in the --ca	certificate  authority
	      file.  You  can  easily make your	own certificate	authority (see
	      above) or	 pay  money  to	 use  a	 commercial  service  such  as
	      thawte.com  (in  which  case  you	will be	helping	to finance the
	      world's second space tourist :). To generate a certificate,  you
	      can use a	command	such as:

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

	      If  your	certificate authority private key lives	on another 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).

       --crl-verify args
	      Check peer certificate against a Certificate Revocation List.

	      Valid syntax:

		 crl-verify file/directory flag

	      Examples:

		 crl-verify crl-file.pem
		 crl-verify /etc/openvpn/crls dir

	      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
	      compromised.

	      The option is not	mandatory - if the relevant  CRL  is  missing,
	      OpenVPN will log a warning in the	logs - e.g.

		 VERIFY	WARNING: depth=0, unable to get	certificate CRL

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

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

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

	      Set file to 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 mbed TLS 2.0+).

	      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 specified
	      curve will only be used for ECDH TLS-ciphers.

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

       --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.

       --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.

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

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

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

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

	      If key-usage is a	list of	usage bits, the	 keyUsage  field  must
	      have at least the	same bits set as the bits in one of the	values
	      supplied in the key-usage	list.

	      The key-usage values in the list must be encoded in hex, e.g.

		 remote-cert-ku	a0

       --remote-cert-tls type
	      Require that peer	certificate was	signed with  an	 explicit  key
	      usage and	extended key usage based on RFC3280 TLS	rules.

	      Valid syntaxes:

		 remote-cert-tls server
		 remote-cert-tls client

	      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

		 remote-cert-ku
		 remote-cert-eku "TLS Web Client Authentication"

	      The --remote-cert-tls server option is equivalent	to

		 remote-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.

       --tls-auth args
	      Add an additional	layer of HMAC authentication on	top of the TLS
	      control channel to mitigate DoS attacks and attacks on  the  TLS
	      stack.

	      Valid syntaxes:

		 tls-auth file
		 tls-auth file 0
		 tls-auth file 1

	      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	 OpenVPN  2.3)	supported  a  freeform
	      passphrase file.	This is	no longer supported in newer  versions
	      (v2.4+).

	      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
	      --float.

	      The  rationale  for  this	 feature is as follows.	TLS requires a
	      multi-packet exchange before it is able to authenticate a	 peer.
	      During  this  time  before authentication, OpenVPN is allocating
	      resources	(memory	and CPU) to this potential peer. The potential
	      peer  is also exposing many parts	of OpenVPN and the OpenSSL li-
	      brary to the packets it is sending. Most successful network  at-
	      tacks  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  potential,
	      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 re-
	      sult 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 encrypt
	      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-groups list
	      A	list of	allowable groups/curves	in order of preference.

	      Set  the	allowed	 elliptic  curves/groups  for the TLS session.
	      These groups are allowed to be used in signatures	 and  key  ex-
	      change.

	      mbedTLS currently	allows all known curves	per default.

	      OpenSSL 1.1+ restricts the list per default to

		 "X25519:secp256r1:X448:secp521r1:secp384r1".

	      If  you use certificates that use	non-standard curves, you might
	      need to add them here. If	you do not force the ecdh curve	by us-
	      ing  --ecdh-curve,  the groups for ecdh will also	be picked from
	      this list.

	      OpenVPN maps the curve name secp256r1  to	 prime256v1  to	 allow
	      specifying the same tls-groups option for	mbedTLS	and OpenSSL.

	      Warning:	this  option  not only affects elliptic	curve certifi-
	      cates but	also the key exchange in TLS 1.3 and using this	option
	      improperly will disable TLS 1.3.

       --tls-cert-profile profile
	      Set  the	allowed	 cryptographic algorithms for certificates ac-
	      cording to profile.

	      The following profiles are supported:

	      legacy (default)
		     SHA1 and newer, RSA 2048-bit+, any	elliptic curve.

	      preferred
		     SHA2 and newer, RSA 2048-bit+, any	elliptic curve.

	      suiteb SHA256/SHA384, ECDSA with P-256 or	P-384.

	      This option is only fully	supported for mbed TLS builds. OpenSSL
	      builds use the following approximation:

	      legacy (default)
		     sets "security level 1"

	      preferred
		     sets "security level 2"

	      suiteb sets "security level 3" and --tls-cipher "SUITEB128".

	      OpenVPN  will  migrate  to 'preferred' as	default	in the future.
	      Please ensure that your keys already comply.

       WARNING:	--tls-ciphers, --tls-ciphersuites and tls-groups
	      These options are	expert features, which - if used  correctly  -
	      can  improve the security	of your	VPN connection.	But it is also
	      easy to unwittingly use them to carefully	align a	gun with  your
	      foot, or just break your connection. Use with care!

       --tls-cipher l
	      A	list l of allowable TLS	ciphers	delimited by a colon (":").

	      These  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 mbed TLS documentation for	details	on the
	      cipher list interpretation.

	      For OpenSSL, the --tls-cipher is used for	TLS 1.2	and below.

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

	      The default for --tls-cipher is to use mbed TLS's	default	cipher
	      list	 when	    using	mbed	  TLS	   or	   DE-
	      FAULT:!EXP:!LOW:!MEDIUM:!kDH:!kECDH:!DSS:!PSK:!SRP:!kRSA	  when
	      using OpenSSL.

       --tls-ciphersuites l
	      Same as --tls-cipher but for TLS 1.3 and up. mbed	TLS has	no TLS
	      1.3 support yet and only the --tls-cipher	setting	is used.

	      The default for --tls-ciphersuites is  to	 use  the  crypto  li-
	      brary's default.

       --tls-client
	      Enable TLS and assume client role	during TLS handshake.

       --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-
		crecy).

	      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 negotiation
	      and renegotiations are at	most 2^16 (65536) packets (to be  con-
	      servative),  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.

	      For large	setups or setups where clients are not	trusted,  con-
	      sider  using --tls-crypt-v2 instead. That	uses per-client	unique
	      keys, and	thereby	improves the bounds to 'rotate a client	key at
	      least once per 8000 years'.

       --tls-crypt-v2 keyfile
	      Use client-specific tls-crypt keys.

	      For  clients, keyfile is a client-specific tls-crypt key.	Such a
	      key can be generated using the --genkey tls-crypt-v2-client  op-
	      tion.

	      For servers, keyfile is used to unwrap client-specific keys sup-
	      plied by the client during connection setup. This	 key  must  be
	      the  same	 as  the  key used to generate the client-specific key
	      (see --genkey tls-crypt-v2-client).

	      On servers, this option can be used together with	the --tls-auth
	      or  --tls-crypt  option.	In  that  case,	the server will	detect
	      whether the client is using client-specific keys,	and  automati-
	      cally select the right mode.

       --tls-crypt-v2-verify cmd
	      Run  command  cmd	 to verify the metadata	of the client-specific
	      tls-crypt-v2 key of a connecting client. This allows server  ad-
	      ministrators  to	reject client connections, before exposing the
	      TLS stack	(including the notoriously dangerous X.509  and	 ASN.1
	      stacks) to the connecting	client.

	      OpenVPN supplies the following environment variables to the com-
	      mand:

	      o	script_type is set to tls-crypt-v2-verify

	      o	metadata_type is set to	0 if the metadata was  user  supplied,
		or 1 if	it's a 64-bit unix timestamp representing the key cre-
		ation time.

	      o	metadata_file contains the filename of a temporary  file  that
		contains the client metadata.

	      The command can reject the connection by exiting with a non-zero
	      exit code.

       --tls-exit
	      Exit on TLS negotiation failure.

       --tls-export-cert directory
	      Store the	certificates the clients use 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.

       --tls-server
	      Enable TLS and assume server role	 during	 TLS  handshake.  Note
	      that OpenVPN is designed as a peer-to-peer application. The des-
	      ignation of client or server is only for the purpose of  negoti-
	      ating the	TLS control channel.

       --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.

       --tls-version-min args
	      Sets the minimum TLS version we will accept from the  peer  (de-
	      fault is "1.0").

	      Valid syntax:

		 tls-version-min version ['or-highest']

	      Examples	for version include 1.0, 1.1, or 1.2. If or-highest is
	      specified	and version is not recognized, we will only accept the
	      highest TLS version supported by the local SSL implementation.

       --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.

       --verify-hash args
	      Specify SHA1 or SHA256 fingerprint for level-1 cert.

	      Valid syntax:

		 verify-hash hash [algo]

	      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
	      example:

		 AD:B0:95:D8:09:C8:36:45:12:A9:89:C8:90:09:CB:13:72:A6:AD:16

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

       --verify-x509-name args
	      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.

	      Valid syntax:

		 verify-x509 name type

	      Which X.509 name is compared to name depends on the  setting  of
	      type.  type can be subject to match the complete subject DN (de-
	      fault), name to match a subject RDN or name-prefix  to  match  a
	      subject RDN prefix. Which	RDN is verified	as name	depends	on the
	      --x509-username-field option. But	it defaults to the common name
	      (CN), e.g. a certificate with a subject DN

		 C=KG, ST=NA, L=Bishkek, CN=Server-1

	      would be matched by:

		 verify-x509-name 'C=KG, ST=NA,	L=Bishkek, CN=Server-1'
		 verify-x509-name Server-1 name
		 verify-x509-name Server- name-prefix

	      The  last	 example is useful 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 Open-
		     VPN with a	custom CA certificate that is under your  con-
		     trol.  Never  use	this option with type name-prefix when
		     your client certificates are signed  by  a	 third	party,
		     such as a commercial web CA.

       --x509-track attribute
	      Save peer	X509 attribute value in	environment for	use by plugins
	      and management interface.	Prepend	a + to attribute to save  val-
	      ues   from   full	  cert	 chain.	 Values	 will  be  encoded  as
	      X509_<depth>_<attribute>=<value>.	Multiple --x509-track  options
	      can be defined to	track multiple attributes.

       --x509-username-field args
	      Field  in	 the X.509 certificate subject to be used as the user-
	      name (default CN).

	      Valid syntax:

		 x509-username-field [ext:]fieldname

	      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
	      chosen.

	      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
	      supported.

	      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.

   PKCS#11 / SmartCard options
       --pkcs11-cert-private args
	      Set  if  access  to certificate object should be performed after
	      login.  Every provider has its own setting.

	      Valid syntaxes:

		 pkcs11-cert-private 0
		 pkcs11-cert-private 1

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

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

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

       --pkcs11-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-
	      lowing:

	      0	(default)   Try	to determine automatically.

	      1		    Use	sign.

	      2		    Use	sign recover.

	      4		    Use	decrypt.

	      8		    Use	unwrap.

       --pkcs11-protected-authentication args
	      Use  PKCS#11 protected authentication path, useful for biometric
	      and external keypad devices. Every provider has its own setting.

	      Valid syntaxes:

		 pkcs11-protected-authentication 0
		 pkcs11-protected-authentication 1

       --pkcs11-providers provider
	      Specify an 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 p11-kit-proxy.so	module
	      will   be	 loaded	 by  default  if  either  the  --pkcs11-id  or
	      --pkcs11-id-management	options	   are	  specified    without
	      --pkcs11-provider	being given.

       --show-pkcs11-ids args
	      (Standalone) Show	PKCS#11	token object list.

	      Valid syntax:

		 show-pkcs11 [provider]	[cert_private]

	      Specify  cert_private as 1 if certificates are stored as private
	      objects.

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

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

DATA CHANNEL CIPHER NEGOTIATION
       OpenVPN 2.4 and higher have the capability to negotiate the data	cipher
       that is used to encrypt data packets. This section describes the	mecha-
       nism in more detail and the different backwards compatibility mechanism
       with older server and clients.

   OpenVPN 2.5 and higher behaviour
       When both client	and server are at least	running	OpenVPN	2.5, that  the
       order of	the ciphers of the server's --data-ciphers is used to pick the
       the data	cipher.	 That means that the first cipher in that list that is
       also in the client's --data-ciphers list	is chosen. If no common	cipher
       is found	the client is rejected with a AUTH_FAILED message (as seen  in
       client log):
	  AUTH:	 Received control message: AUTH_FAILED,Data channel cipher ne-
	  gotiation failed (no shared cipher)

       OpenVPN 2.5 will	only allow the ciphers specified in --data-ciphers. To
       ensure  backwards compatibility also if a cipher	is specified using the
       --cipher	option it is automatically added to this list. If both options
       are unset the default is	AES-256-GCM:AES-128-GCM.

   OpenVPN 2.4 clients
       The  negotiation	 support in OpenVPN 2.4	was the	first iteration	of the
       implementation and still	had some quirks. Its main goal was "upgrade to
       AES-256-GCM  when  possible".   An  OpenVPN  2.4	 client	 that is built
       against a crypto	library	that supports AES in GCM  mode	and  does  not
       have  --ncp-disable  will  always  announce support for AES-256-GCM and
       AES-128-GCM to a	server by sending IV_NCP=2.

       This only causes	a problem if --ncp-ciphers  option  has	 been  changed
       from  the  default  of AES-256-GCM:AES-128-GCM to a value that does not
       include	these  two  ciphers.  When  a  OpenVPN	servers	 try  to   use
       AES-256-GCM  or AES-128-GCM the connection will then fail. It is	there-
       fore recommended	to always have the AES-256-GCM and AES-128-GCM ciphers
       to the --ncp-ciphers options to avoid this behaviour.

   OpenVPN 3 clients
       Clients	   based     on	    the	    OpenVPN	3.x	library	    (-
       https://github.com/openvpn/openvpn3/)  do  not  have   a	  configurable
       --ncp-ciphers  or --data-ciphers	option.	Instead	these clients will an-
       nounce support for  all	their  supported  AEAD	ciphers	 (AES-256-GCM,
       AES-128-GCM and in newer	versions also Chacha20-Poly1305).

       To  support  OpenVPN  3.x  based	 clients at least one of these ciphers
       needs to	be included in the server's --data-ciphers option.

   OpenVPN 2.3 and older clients (and clients with --ncp-disable)
       When a client without cipher negotiation	support	connects to  a	server
       the  cipher specified with the --cipher option in the client configura-
       tion must be included in	the --data-ciphers option of the server	to al-
       low  the	 client	 to  connect.  Otherwise  the  client will be sent the
       AUTH_FAILED message that	indicates no shared cipher.

       If the client is	2.3 or older and has been configured  with  the	 --en-
       able-small  ./configure argument, using data-ciphers-fallback cipher in
       the server config file with the explicit	cipher used by the  client  is
       necessary.

   OpenVPN 2.4 server
       When  a	client indicates support for AES-128-GCM and AES-256-GCM (with
       IV_NCP=2) an OpenVPN 2.4	server will  send  the	first  cipher  of  the
       --ncp-ciphers  to  the OpenVPN client regardless	of what	the cipher is.
       To emulate the behaviour	of an OpenVPN 2.4 client as close as  possible
       and  have  compatibility	 to a setup that depends on this quirk,	adding
       AES-128-GCM and AES-256-GCM to the client's  --data-ciphers  option  is
       required.  OpenVPN  2.5+	 will only announce the	IV_NCP=2 flag if those
       ciphers are present.

   OpenVPN 2.3 and older servers (and servers with --ncp-disable)
       The cipher used by the server must be included in --data-ciphers	to al-
       low  the	 client	connecting to a	server without cipher negotiation sup-
       port.  (For compatibility OpenVPN 2.5 will also accept the  cipher  set
       with --cipher)

       If  the	server is 2.3 or older and  has	been configured	with the --en-
       able-small ./configure argument,	adding data-ciphers-fallback cipher to
       the client config with the explicit cipher used by the server is	neces-
       sary.

   Blowfish in CBC mode	(BF-CBC) deprecation
       The --cipher option defaulted to	BF-CBC in OpenVPN 2.4 and  older  ver-
       sion.  The default was never changed to ensure backwards	compatibility.
       In OpenVPN 2.5 this behaviour has now been changed so that if the --ci-
       pher is not explicitly set it does not allow the	weak BF-CBC cipher any
       more and	needs to explicitly added as  --cipher	BFC-CBC	 or  added  to
       --data-ciphers.

       We  strongly  recommend	to switching away from BF-CBC to a more	secure
       cipher as soon as possible instead.

NETWORK	CONFIGURATION
       OpenVPN consists	of two sides of	network	configuration.	 One  side  is
       the  link between the local and remote side, the	other side is the vir-
       tual network adapter (tun/tap device).

   Link	Options
       This link options section covers	options	related	to the connection  be-
       tween the local and the remote host.

       --bind keywords
	      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 optional ipv6only keyword is present  OpenVPN  will  bind
	      only to IPv6 (as opposed to IPv6 and IPv4) when a	IPv6 socket is
	      opened.

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

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

       --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
	      --fragment.

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

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

       --keepalive args
	      A	helper directive designed to simplify the expression of	--ping
	      and --ping-restart.

	      Valid syntax:

		 keepalive interval timeout

	      This  option  can	be used	on both	client and server side,	but it
	      is enough	to add this on the server side as it will push	appro-
	      priate  --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
		 else
		     ping 10			# Argument: interval
		     ping-restart 60		# Argument: timeout

       --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.

       --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.

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

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

       --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.

       --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
	      udp.

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

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

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

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

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

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

       --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.

	      Valid types:

	      no      Never send DF (Don't Fragment) frames

	      maybe   Use per-route hints

	      yes     Always DF	(Don't Fragment)

       --mtu-test
	      To empirically  measure  MTU  on	connection  startup,  add  the
	      --mtu-test  option to your configuration.	OpenVPN	will send ping
	      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.

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

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

       --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  crypto-
	      graphically secure.

	      This option has two intended uses:

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

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

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

	      For example,

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

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

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

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

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

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

	      In  client mode, the --ping-restart parameter is set to 120 sec-
	      onds by default. This default will hold until the	client pulls a
	      replacement value	from the server, based on the --keepalive set-
	      ting in the server configuration.	To disable the 120 second  de-
	      fault, 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.

       --ping-timer-rem
	      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-
	      nects.

       --proto p
	      Use protocol p for communicating with remote host. p can be udp,
	      tcp-client, or tcp-server.

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

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

	      For TCP operation, one peer must use --proto tcp-server and  the
	      other   must   use  --proto  tcp-client.	A  peer	 started  with
	      tcp-server will wait indefinitely	for an incoming	connection.  A
	      peer  started  with  tcp-client  will attempt to connect,	and if
	      that fails, will sleep for 5 seconds (adjustable via the	--con-
	      nect-retry  option)  and	try  again infinite or up to N retries
	      (adjustable via the --connect-retry-max option). Both TCP	client
	      and server will simulate a SIGUSR1 restart signal	if either side
	      resets the connection.

	      OpenVPN is designed to operate optimally over UDP, but TCP capa-
	      bility  is  provided for situations where	UDP cannot be used. In
	      comparison with UDP, TCP will usually be somewhat	less efficient
	      and less robust when used	over unreliable	or congested networks.

	      This  article  outlines  some of problems	with tunneling IP over
	      TCP: http://sites.inka.de/sites/bigred/devel/tcp-tcp.html

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

       --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 de-
	      fault  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.

       --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.

       --replay-window args
	      Modify the replay	protection sliding-window size and  time  win-
	      dow.

	      Valid syntax:

		 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. Be-
	      cause  OpenVPN,  like  IPSec,  is	emulating the physical network
	      layer, it	will accept an out-of-order packet sequence, and  will
	      deliver such packets in the same order they were received	to the
	      TCP/IP  protocol	stack,	provided  they	satisfy	 several  con-
	      straints.

	      a. The  packet  cannot be	a replay (unless --no-replay is	speci-
		 fied, which disables replay protection	altogether).

	      b. If a packet arrives out of order, it will only	be accepted if
		 the  difference  between  its sequence	number and the highest
		 sequence number received so far is less than n.

	      c. If a packet arrives out of order, it will only	be accepted if
		 it  arrives no	later than t seconds after any packet contain-
		 ing a higher sequence number.

	      If you are using a network link with a large  pipeline  (meaning
	      that the product of bandwidth and	latency	is high), you may want
	      to use a larger value for	n. Satellite links in particular often
	      require this.

	      If  you  run  OpenVPN at --verb 4, you will see the message "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-
	      works?

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

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

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

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

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

       --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.

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

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

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

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

	      The macro	expands	as follows:

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

   Virtual Network Adapter (VPN	interface)
       Options in this section relates to configuration	of the virtual tun/tap
       network interface, including setting the	VPN  IP	 address  and  network
       routing.

       --bind-dev device
	      (Linux  only)  Set device	to bind	the server socket to a Virtual
	      Routing and Forwarding device

       --block-ipv6
	      On the client, instead of	sending	IPv6 packets over the VPN tun-
	      nel,  all	IPv6 packets are answered with an ICMPv6 no route host
	      message. On the server, all IPv6 packets from  clients  are  an-
	      swered  with an ICMPv6 no	route to host message. This options is
	      intended for cases when IPv6 should be blocked and other options
	      are  not	available.  --block-ipv6  will	use the	remote IPv6 as
	      source address of	the ICMPv6 packets if set, otherwise will  use
	      fe80::7 as source	address.

	      For this option to make sense you	actually have to route traffic
	      to the tun interface. The	following example config  block	 would
	      send all IPv6 traffic to OpenVPN and answer all requests with no
	      route to host, effectively blocking IPv6 (to avoid IPv6  connec-
	      tions  from  dual-stacked	 clients  leaking around IPv4-only VPN
	      services).

	      Client config

			--ifconfig-ipv6	fd15:53b6:dead::2/64 fd15:53b6:dead::1
			--redirect-gateway ipv6
			--block-ipv6

	      Server config
		     Push a "valid" ipv6 config	to the client and block	on the
		     server

			--push "ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1"
			--push "redirect-gateway ipv6"
			--block-ipv6

	      Note:  this  option  does	 not  influence	 traffic sent from the
	      server towards the client	(neither on  the  server  nor  on  the
	      client  side).   This  is	not seen as necessary, as such traffic
	      can be most easily avoided by not	configuring IPv6 on the	server
	      tun, or setting up a server-side firewall	rule.

       --dev device
	      TUN/TAP  virtual network device which can	be tunX, tapX, null or
	      an arbitrary name	string (X can be omitted  for  a  dynamic  de-
	      vice.)

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

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

	      tun    devices encapsulate IPv4 or IPv6 (OSI Layer 3)

	      tap    devices encapsulate Ethernet 802.3	(OSI Layer 2).

	      Valid syntaxes:

		 dev tun2
		 dev tap4
		 dev ovpn

	      When the device name starts with tun or tap, the device type  is
	      extracted	 automatically.	 Otherwise the --dev-type option needs
	      to be added as well.

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

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

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

       --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.

       --dhcp-option args
	      Set additional network parameters	on supported platforms.	May be
	      specified	 on  the  client or pushed from	the server. On Windows
	      these options are	handled	by the tap-windows6 driver by  default
	      or  directly by OpenVPN if dhcp is disabled or the wintun	driver
	      is in use. The OpenVPN for Android client	also handles them  in-
	      ternally.

	      On  all  other  platforms	 these	options	 are only saved	in the
	      client's environment under the name  foreign_options_{n}	before
	      the  --up	 script	 is called. A plugin or	an --up	script must be
	      used to pick up and interpret these as required. Many Linux dis-
	      tributions include such scripts and some third-party user	inter-
	      faces such as tunnelblick	also come with	scripts	 that  process
	      these options.

	      Valid syntax:

		 dhcp-options type [parm]

	      DOMAIN name
		     Set Connection-specific DNS Suffix	to name.

	      ADAPTER_DOMAIN_SUFFIX name
		     Alias  to	DOMAIN.	 This  is  a  compatibility option, it
		     should not	be used	in new deployments.

	      DOMAIN-SEARCH name
		     Add name to the domain search list.  Repeat  this	option
		     to	add more entries. Up to	10 domains are supported.

	      DNS address
		     Set primary domain	name server IPv4 or IPv6 address.  Re-
		     peat this option to set secondary DNS server addresses.

		     Note: DNS IPv6 servers are	currently set using netsh (the
		     existing DHCP code	can only do IPv4 DHCP, and that	proto-
		     col only permits IPv4  addresses  anywhere).  The	option
		     will be put into the environment, so an --up script could
		     act upon it if needed.

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

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

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

	      NBT type
		     Set NetBIOS over TCP/IP Node type.	Possible options:

		     1	    b-node (broadcasts)

		     2	    p-node  (point-to-point  name  queries  to	a WINS
			    server)

		     4	    m-node (broadcast then query name server)

		     8	    h-node (query name server, then broadcast).

	      NBS scope-id
		     Set NetBIOS over TCP/IP Scope. A NetBIOS  Scope  ID  pro-
		     vides  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 sin-
		     gle 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 comput-
		     ers 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 Net-
		     BIOS scopes courtesy of NeonSurge@abyss.com)

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

       --ifconfig args
	      Set TUN/TAP adapter parameters. It requires the  IP  address  of
	      the  local VPN endpoint. For TUN devices in point-to-point mode,
	      the next argument	must be	the VPN	IP address of the  remote  VPN
	      endpoint.	 For  TAP devices, or TUN devices used with --topology
	      subnet, the second argument is the subnet	mask  of  the  virtual
	      network segment which is being created or	connected to.

	      For TUN devices, which facilitate	virtual	point-to-point IP 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
	      purpose).

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

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

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

	      Examples:

		 # tun device in net30/p2p mode
		 ifconfig 10.8.0.2 10.8.0.1

		 # tun/tap device in subnet mode
		 ifconfig 10.8.0.2 255.255.255.0

       --ifconfig-ipv6 args
	      Configure	an IPv6	address	on the tun device.

	      Valid syntax:

		 ifconfig-ipv6 ipv6addr/bits [ipv6remote]

	      The ipv6addr/bits	argument is the	IPv6 address to	use. The  sec-
	      ond  parameter  is  used	as route target	for --route-ipv6 if no
	      gateway is specified.

	      The --topology option has	no influence with --ifconfig-ipv6

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

       --ifconfig-nowarn
	      Don't  output  an	options	consistency check warning if the --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.

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

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

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

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

	      This option performs three steps:

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

	      2. Delete	the default gateway route.

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

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

	      Option flags:

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

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

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

	      bypass-dhcp
		     Add a direct route	to the DHCP server (if it  is  non-lo-
		     cal)  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 Win-
		     dows  clients,  may  not  be  available  on   non-Windows
		     clients).

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

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

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

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

       --route args
	      Add route	to routing table after connection is established. Mul-
	      tiple routes can be specified. Routes will be automatically torn
	      down in reverse order prior to TUN/TAP device close.

	      Valid syntaxes:

		 route network/IP
		 route network/IP netmask
		 route network/IP netmask gateway
		 route network/IP netmask gateway metric

	      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
		     defaults to 255.255.255.255 when not given

	      gateway
		     default  taken from --route-gateway or the	second parame-
		     ter to --ifconfig when --dev tun is specified.

	      metric default taken from	--route-metric if set, 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 rout-
		     ing 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-delay args
	      Valid syntaxes:

		 route-delay
		 route-delay n
		 route-delay n m

	      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 (default 30 by default) for the TAP-Win32 adapter
	      to come up before	adding routes.

       --route-ipv6 args
	      Setup IPv6 routing in the	system to send the specified IPv6 net-
	      work into	OpenVPN's tun.

	      Valid syntax:

		 route-ipv6 ipv6addr/bits [gateway] [metric]

	      The  gateway  parameter  is only used for	IPv6 routes across tap
	      devices, and if missing,	the  ipv6remote	 field	from  --ifcon-
	      fig-ipv6 or --route-ipv6-gateway is used.

       --route-gateway arg
	      Specify a	default	gateway	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.

	      Valid syntaxes:

		 route-gateway gateway
		 route-gateway dhcp

       --route-ipv6-gateway gw
	      Specify a	default	gateway	gw for use with	--route-ipv6.

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

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

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

       --topology mode
	      Configure	 virtual addressing topology when running in --dev tun
	      mode. This directive has no meaning in --dev tap mode, which al-
	      ways 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 sub-
		     net per client. This is designed to allow	point-to-point
		     semantics	when  some  or	all  of	the connecting clients
		     might be Windows systems. This is the default on  OpenVPN
		     2.0.

	      p2p    Use  a  point-to-point topology where the remote endpoint
		     of	the client's tun interface always points to the	 local
		     endpoint  of  the server's	tun interface. This mode allo-
		     cates a single IP address per connecting client. Only use
		     when none of the connecting clients are Windows systems.

	      subnet Use  a  subnet  rather  than a point-to-point topology by
		     configuring the tun interface with	a local	IP address and
		     subnet  mask,  similar  to	the topology used in --dev tap
		     and ethernet bridging mode. This mode allocates a	single
		     IP	 address per connecting	client and works on Windows as
		     well. Only	available when server and clients are  OpenVPN
		     2.1  or  higher, or OpenVPN 2.0.x which has been manually
		     patched with the --topology directive code. When used  on
		     Windows,  requires	version	8.2 or higher of the TAP-Win32
		     driver. When used on *nix,	requires that the  tun	driver
		     supports  an  ifconfig(8) command which sets a subnet in-
		     stead of a	remote endpoint	IP address.

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

       --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  and
	      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 in-
	      troduce additional overhead in excess of the  MTU	 size,	and  a
	      setting of 32 is the default when	TAP devices are	used. This pa-
	      rameter only controls internal OpenVPN buffer sizing,  so	 there
	      is  no  transmission  overhead  associated  with	using a	larger
	      value.

   TUN/TAP standalone operations
       These two standalone  operations	 will  require	--dev  and  optionally
       --user and/or --group.

       --mktun
	      (Standalone)  Create a persistent	tunnel on platforms which sup-
	      port them	such as	Linux. Normally	TUN/TAP	tunnels	exist only for
	      the  period  of time that	an application has them	open. This op-
	      tion 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-
	      booted.

	      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 connectiv-
	      ity through the tunnel in	the event  of  a  DHCP	reset  of  the
	      peer's public IP address (see the	--ipchange option above).

	      One  disadvantage	 of persistent tunnels is that it is harder to
	      automatically configure their  MTU  value	 (see  --link-mtu  and
	      --tun-mtu	above).

	      On some platforms	such as	Windows, TAP-Win32 tunnels are persis-
	      tent by default.

       --rmtun
	      (Standalone) Remove a persistent tunnel.

   Virtual Routing and Forwarding
       Options in this section relates to configuration	of virtual routing and
       forwarding in combination with the underlying operating system.

       As  of today this is only supported on Linux, a kernel >= 4.9 is	recom-
       mended.

       This could come in handy	when for example the external  network	should
       be  only	used as	a means	to connect to some VPN endpoints and all regu-
       lar traffic should only be routed through any tunnel(s).	 This could be
       achieved	by setting up a	VRF and	configuring the	interface connected to
       the external network to be part of the VRF.  The	 examples  below  will
       cover this setup.

       Another	option	would be to put	the tun/tap interface into a VRF. This
       could be	done by	an up-script which uses	the ip link set	command	 shown
       below.

   VRF setup with iproute2
       Create VRF vrf_external and map it to routing table 1023

	  ip link add vrf_external type	vrf table 1023

       Move eth0 into vrf_external

	  ip link set master vrf_external dev eth0

       Any  prefixes  configured  on  eth0  will be moved from the :code`main`
       routing table into routing table	1023

   VRF setup with ifupdown
       For Debian based	Distributions ifupdown2	provides an almost drop-in re-
       placement for ifupdown including	VRFs and other features.  A configura-
       tion for	an interface eth0 being	part of	 VRF  code:vrf_external	 could
       look like this:

	  auto eth0
	  iface	eth0
	      address 192.0.2.42/24
	      address 2001:db8:08:15::42/64
	      gateway 192.0.2.1
	      gateway 2001:db8:08:15::1
	      vrf vrf_external

	  auto vrf_external
	  iface	vrf_external
	      vrf-table	1023

   OpenVPN configuration
       The OpenVPN configuration needs to contain this line:

	  bind-dev vrf_external

   Further reading
       Wikipedia	 has	     nice	  page	      one	 VRFs:
       https://en.wikipedia.org/wiki/Virtual_routing_and_forwarding

       This talk from the Network Track	of FrOSCon 2018	provides  an  overview
       about advanced layer 2 and layer	3 features of Linux

	  o Slides:
	    https://www.slideshare.net/BarbarossaTM/l2l3-fr-fortgeschrittene-helle-und-dunkle-magie-im-linuxnetzwerkstack

	  o Video						     (german):
	    https://media.ccc.de/v/froscon2018-2247-l2_l3_fur_fortgeschrittene_-_helle_und_dunkle_magie_im_linux-netzwerkstack

SCRIPTING INTEGRATION
       OpenVPN	can execute external scripts in	various	phases of the lifetime
       of the OpenVPN process.

   Script Order	of Execution
       1.  --up

	   Executed after TCP/UDP socket bind and TUN/TAP open.

       2.  --tls-verify

	   Executed when we have a still untrusted remote peer.

       3.  --ipchange

	   Executed after connection  authentication,  or  remote  IP  address
	   change.

       4.  --client-connect

	   Executed in --mode server mode immediately after client authentica-
	   tion.

       5.  --route-up

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

       6.  --route-pre-down

	   Executed right before the routes are	removed.

       7.  --client-disconnect

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

       8.  --down

	   Executed after TCP/UDP and TUN/TAP close.

       9.  --learn-address

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

       10. --auth-user-pass-verify

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

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

	      Valid syntax:

		 auth-user-pass-verify cmd method

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

	      cmd consists of a	path to	a 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. Beware that this
	      method is	insecure on some platforms which make the  environment
	      of a process publicly visible to other unprivileged processes.

	      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 characters
	      in  either  the username or password string will be converted to
	      underbar ('_').

	      Care must	be taken by any	user-defined scripts to	avoid creating
	      a	 security vulnerability	in the way that	these strings are han-
	      dled. Never use these strings in such a way that they  might  be
	      escaped or evaluated by a	shell interpreter.

	      For  a  sample script that performs PAM authentication, see sam-
	      ple-scripts/auth-pam.pl in the OpenVPN source distribution.

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

	      cmd consists of a	path to	a 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
	      disconnected.

	      If a --client-connect wants to defer the generating of the  con-
	      figuration  then	the script needs to use	the client_connect_de-
	      ferred_file  and	client_connect_config_file  environment	 vari-
	      ables,  and  write status	accordingly into these files.  See the
	      Environmental Variables section for more details.

       --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 not passed  any  extra	 argu-
	      ments (only those	arguments specified in cmd, if any).

       --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.

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

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

	      cmd consists of a	path to	a 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 pa-
	      rameters 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  re-establish a connection with its most recently authenti-
	      cated peer on its	new IP address.

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

	      cmd consists of a	path to	a 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-
	      lows:

	      $1 - [operation]
		     "add", "update", or "delete" based	on whether or not  the
		     address  is  being	 added	to,  modified, or deleted from
		     OpenVPN's internal	routing	table.

	      $2 - [address]
		     The address being learned or unlearned. This  can	be  an
		     IPv4 address such as "198.162.10.14", an IPv4 subnet such
		     as	"198.162.10.0/24", or an ethernet  MAC	address	 (when
		     --dev tap is being	used) such as "00:FF:01:02:03:04".

	      $3 - [common name]
		     The  common  name	on the certificate associated with the
		     client linked to this address. Only present for "add"  or
		     "update" operations, not "delete".

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

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

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

	      cmd consists of a	path to	a 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 pa-
	      rameters passed as environmental variables.

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

	      cmd consists of a	path to	a 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 pa-
	      rameters passed as environmental variables.

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

	      Valid syntaxes:

		 setenv	name value
		 setenv	FORWARD_COMPATIBLE 1
		 setenv	opt config_option

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

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

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

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

	      See also --ignore-unknown-option

       --setenv-safe args
	      Set  a  custom  environmental  variable OPENVPN_name to value to
	      pass to scripts.

	      Valid syntaxes:

		 setenv-safe name value

	      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.

       --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 a 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 subject distinguished name (dn) 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 pa-
	      rameters passed as environmental variables.

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

	      cmd consists of a	path to	a 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_remote_ip [init | restart]

	      For --dev	tap execute as:

		 cmd tap_dev tap_mtu link_mtu ifconfig_local_ip	ifconfig_netmask [init | restart]

	      See the Environmental Variables section below for	additional pa-
	      rameters 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	 envi-
		     ronment  variables	 to the	script.	Namely,	everything re-
		     lated to routing and gateways  will  not  be  passed,  as
		     nothing  needs  to	be done	anyway - all the routing setup
		     is	already	in place. Additionally,	the up-restart	script
		     will run with the downgraded UID/GID settings (if config-
		     ured).

	      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	10.0.0.0 netmask 255.255.255.0 gw $5

       --up-delay
	      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
	      peer.

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

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

       Q: Why is string	remapping necessary?
	      It's an important	security feature to prevent the	malicious cod-
	      ing 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?
	      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 remapping.

       --auth-user-pass	password
	      Any  "printable" character except	CR or LF. Printable is defined
	      to be a character	which will cause the C library isprint() func-
	      tion 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 v2.0.1-rc6,	the at
	      ('@')  character	has  been added	as well	for compatibility with
	      the common name character	class.

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

       Environmental variable values
	      Any printable character.

       For all cases, characters in a string which are not members of the  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-
       stances.

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

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

       client_connect_config_file
	      The  path	to the configuration file that should be written to by
	      the --client-connect script (optional, if	per-session configura-
	      tion is desired).	 This is the same file name as passed via com-
	      mand line	argument on the	call to	the --client-connect script.

       client_connect_deferred_file
	      This file	can be optionally written to in	order to  to  communi-
	      cate  a  status  code  of	 the --client-connect script or	plgin.
	      Only the first character in the file is relevant.	  It  must  be
	      either 1 to indicate normal script execution, 0 indicates	an er-
	      ror (in the same way that	a non zero exit	status does) or	 2  to
	      indicate that the	script deferred	returning the config file.

	      For  deferred  (background)  handling, the script	or plugin MUST
	      write 2 to the file to indicate the  deferral  and  then	return
	      with exit	code 0 to signal deferred handler started OK.

	      A	 background  process or	similar	must then take care of writing
	      the configuration	to  the	 file  indicated  by  the  client_con-
	      nect_config_file	environment  variable and when finished, write
	      the a 1 to this file (or 0 in case of an error).

	      The absence of any character in the file when  the  script  fin-
	      ishes  executing	is  interpreted	 the  same  as	1. This	allows
	      scripts that are not written to support the defer	 mechanism  to
	      be used unmodified.

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

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

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

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

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

       dev_idx
	      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.

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

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

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

       ifconfig_ipv6_netbits
	      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 call-
	      ing the ifconfig or netsh	(windows version of ifconfig) commands
	      which normally occurs prior to --up script execution.

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

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

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

       ifconfig_netmask
	      The subnet mask of the virtual ethernet segment that  is	speci-
	      fied as the second parameter to --ifconfig when --dev tap	is 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.

       ifconfig_pool_local_ip
	      The local	virtual	IP address for the TUN/TAP tunnel  taken  from
	      an --ifconfig-push directive if specified, or otherwise from the
	      ifconfig pool (controlled	by the --ifconfig-pool config file 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.

       ifconfig_pool_netmask
	      The  virtual  IP	netmask	 for  the TUN/TAP tunnel taken from an
	      --ifconfig-push directive	if specified, or  otherwise  from  the
	      ifconfig pool (controlled	by the --ifconfig-pool config file 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.

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

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

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

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

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

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

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

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

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

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

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

	      parm will	be one of network, netmask", gateway, or metric.

	      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.

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

	      parm will	be one of network, gateway or metric.  route_ipv6_net-
	      work_{n}	contains  netmask  as  /nnn,  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.

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

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

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

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

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

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

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

       tls_digest_{n} /	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.

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

       tls_serial_{n}
	      The serial number	of the certificate from	the remote peer, where
	      n	 is  the verification level. Only set for TLS connections. Set
	      prior to execution of --tls-verify script. This is in  the  form
	      of  a 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/OCSP_check.sh
	      script for an example.

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

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

       trusted_ip / 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.

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

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

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

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

       X509_{n}_{subject_field}
	      An  X509 subject field from the remote peer certificate, where n
	      is the verification level. Only set  for	TLS  connections.  Set
	      prior to execution of --tls-verify script. This variable is sim-
	      ilar 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	 exam-
	      ple,  the	following variables would be set on the	OpenVPN	server
	      using the	sample client certificate in sample-keys (client.crt).
	      Note that	the verification level is 0 for	the client certificate
	      and 1 for	the CA certificate.

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

   Management Interface	Options
       OpenVPN provides	a feature rich socket based management	interface  for
       both server and client mode operations.

       --management args
	      Enable a management server on a socket-name Unix socket on those
	      platforms	supporting it, or on a designated TCP port.

	      Valid syntaxes:

		 management socket-name	unix	      #
		 management socket-name	unix pw-file  #	(recommended)
		 management IP port		      #	(INSECURE)
		 management IP port pw-file	      #

	      pw-file, if specified, is	a password  file  where	 the  password
	      must be on first line. Instead of	a filename it can use the key-
	      word stdin which will prompt the user for	a password to use when
	      OpenVPN is starting.

	      For  unix	sockets, the default behaviour is to create a unix do-
	      main socket that may be connected	to by  any  process.  Use  the
	      --management-client-user	and  --management-client-group	direc-
	      tives 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	to tunnel. Tunnel mode will cause the  manage-
	      ment  interface  to listen for a TCP connection on the local VPN
	      address of the TUN/TAP interface.

	      *BEWARE* of enabling the management interface over TCP. In these
	      cases  you should	ALWAYS make use	of pw-file to password protect
	      the management interface.	Any user who can connect to  this  TCP
	      IP:port  will be able to manage and control (and interfere with)
	      the OpenVPN process. It is also strongly recommended to  set  IP
	      to  127.0.0.1  (localhost) to restrict accessibility of the man-
	      agement server to	local clients.

	      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.

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

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

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

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

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

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

       --management-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-exter-
	      nal-key.

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

	      Valid syntaxes:

		 management-external-key
		 management-external-key nopadding
		 management-external-key pkcs1
		 management-external-key nopadding pkcs1

	      The optional parameters nopadding	and pkcs1 signal  support  for
	      different	 padding algorithms. See doc/mangement-notes.txt for a
	      complete description of this feature.

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

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

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

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

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

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

       --management-query-remote
	      Allow  management	 interface  to	override  --remote  directives
	      (client-only).

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

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

   Plug-in Interface Options
       OpenVPN can be extended by loading external plug-in modules at runtime.
       These plug-ins must be prebuilt and adhere to the OpenVPN Plug-In API.

       --plugin	args
	      Loads an OpenVPN plug-in module.

	      Valid syntax:

		 plugin	module-name
		 plugin	module-name "arguments"

	      The module-name needs to be the first argument,  indicating  the
	      plug-in to load.	The second argument is an optional init	string
	      which will be passed directly to the plug-in.  If	the init  con-
	      sists of multiple	arguments it must be enclosed in double-quotes
	      (").  Multiple plugin modules may	be  loaded  into  one  OpenVPN
	      process.

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

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

	      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  switched  into via the --cd	option before the --plugin op-
	      tion.

	      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.

   Windows-Specific Options
       --allow-nonadmin	TAP-adapter
	      (Standalone) Set TAP-adapter to allow access  from  non-adminis-
	      trative accounts.	If TAP-adapter is omitted, all TAP adapters on
	      the system will be configured to	allow  non-admin  access.  The
	      non-admin	 access	 setting  will	only persist for the length of
	      time that	the TAP-Win32 device object and	driver remain  loaded,
	      and  will	need to	be re-enabled after a reboot, or if the	driver
	      is unloaded and reloaded.	This directive can only	be used	by  an
	      administrator.

       --block-outside-dns
	      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 un-
	      known options from server	does not trigger fatal errors.

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

	      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.

       --dhcp-release
	      Ask Windows to release the TAP adapter lease on  shutdown.  This
	      option  has  no effect now, as it	is enabled by default starting
	      with OpenVPN 2.4.1.

       --dhcp-renew
	      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.

       --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.  In-
		     stead output a message to the console telling the user to
		     configure the adapter manually and	indicating the IP/net-
		     mask which	OpenVPN	expects	the adapter to be set to.

	      dynamic [offset] [lease-time]
		     Automatically  set	the IP address and netmask by replying
		     to	DHCP query messages generated  by  the	kernel.	  This
		     mode  is probably the "cleanest" solution for setting the
		     TCP/IP properties since it	uses the well-known DHCP  pro-
		     tocol.  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  nor-
		     mally unused first	address	in the subnet. For example, if
		     your subnet is 192.168.4.0	 netmask  255.255.255.0,  then
		     OpenVPN  will  take  the IP address 192.168.4.0 to	use as
		     the virtual DHCP server  address.	 In  --dev  tun	 mode,
		     OpenVPN will cause	the DHCP server	to masquerade as if it
		     were coming from the remote endpoint.

		     The optional offset parameter is an integer  which	 is  >
		     -256  and	<  256	and which defaults to -1. If offset is
		     positive, the DHCP	server will masquerade as the  IP  ad-
		     dress at network address +	offset.	If offset is negative,
		     the DHCP server will masquerade  as  the  IP  address  at
		     broadcast address + offset.

		     The  Windows  ipconfig  /all  command can be used to show
		     what Windows thinks the DHCP server address  is.  OpenVPN
		     will "claim" this address,	so make	sure to	use a free ad-
		     dress. 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 parameter controls the lease time  of  the
		     DHCP  assignment  given  to the TAP-Win32 adapter,	and is
		     denoted in	seconds. Normally a very long  lease  time  is
		     preferred	 because  it  prevents	routes	involving  the
		     TAP-Win32 adapter from being lost when the	system goes to
		     sleep. The	default	lease time is one year.

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

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

	      adaptive (Default)
		     Try  dynamic  method  initially and fail over to netsh if
		     the DHCP negotiation with the TAP-Win32 adapter does  not
		     succeed  in  20 seconds. Such failures have been known to
		     occur when	 certain  third-party  firewall	 packages  in-
		     stalled  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 config-
		     uration.

       --pause-exit
	      Put  up  a  "press  any  key to continue"	message	on the console
	      prior to OpenVPN program exit. This option is automatically used
	      by  the  Windows explorer	when OpenVPN is	run on a configuration
	      file using the right-click explorer menu.

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

       --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.

       --service args
	      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.

	      Valid syntax:

		 service exit-event [0|1]

	      In  general,  end-users should never need	to explicitly use this
	      option, as it is automatically  added  by	 the  OpenVPN  service
	      wrapper  when  a	given  OpenVPN configuration is	being run as a
	      service.

	      exit-event is the	name of	a Windows  global  event  object,  and
	      OpenVPN will continuously	monitor	the state of this event	object
	      and exit when it becomes signaled.

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

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

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

       --show-adapters
	      (Standalone)  Show available TAP-Win32 adapters which can	be se-
	      lected using the --dev-node option. On non-Windows systems,  the
	      ifconfig(8) command provides similar functionality.

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

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

       --show-valid-subnets
	      (Standalone) Show	valid subnets for --dev	tun  emulation.	 Since
	      the  TAP-Win32  driver exports an	ethernet interface to Windows,
	      and since	TUN devices are	point-to-point in nature, it is	neces-
	      sary  for	 the TAP-Win32 driver to impose	certain	constraints on
	      TUN endpoint address selection.

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

       --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.

       --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 has changed behaviour	since 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.

       --windows-driver	drv
	      Specifies	which tun driver to use. Values	are tap-windows6  (de-
	      fault)  and wintun.  This	is a Windows-only option.  wintun" re-
	      quires --dev tun and the OpenVPN process to run elevated,	or  be
	      invoked using the	Interactive Service.

   Standalone Debug Options
       --show-gateway args
	      (Standalone)  Show current IPv4 and IPv6 default gateway and in-
	      terface towards the gateway (if the protocol in question is  en-
	      abled).

	      Valid syntax:

		 --show-gateway
		 --show-gateway	IPv6-target

	      For IPv6 this queries the	route towards ::/128, or the specified
	      IPv6 target address if passed as argument.  For IPv4  on	Linux,
	      Windows, MacOS and BSD it	looks for a 0.0.0.0/0 route.  If there
	      are more specific	routes,	the result will	not always be matching
	      the route	of the IPv4 packets to the VPN gateway.

   Advanced Expert Options
       These  are options only required	when special tweaking is needed, often
       used when debugging or testing out special usage	scenarios.

       --hash-size args
	      Set the size of the real address hash table to r and the virtual
	      address table to v.

	      Valid syntax:

		 hash-size r v

	      By default, both tables are sized	at 256 buckets.

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

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

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

       --prng args
	      (Advanced)  Change the PRNG (Pseudo-random number	generator) pa-
	      rameters

	      Valid syntaxes:

		 prng alg
		 prng alg nsl

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

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

       --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.

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

       --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.

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

UNSUPPORTED OPTIONS
       Options	listed	in this	section	have been removed from OpenVPN and are
       no longer supported

       --client-cert-not-required
	      Removed in OpenVPN 2.5.  This should  be	replaxed  with	--ver-
	      ify-client-cert none.

       --ifconfig-pool-linear
	      Removed in OpenVPN 2.5.  This should be replaced with --topology
	      p2p.

       --key-method
	      Removed in OpenVPN 2.5.  This option should not be used, as  us-
	      ing the old key-method weakens the VPN tunnel security.  The old
	      key-method was also only needed when the remote side  was	 older
	      than OpenVPN 2.0.

       --no-iv
	      Removed  in  OpenVPN  2.5.  This option should not be used as it
	      weakens the VPN tunnel security.	This has been  a  NOOP	option
	      since OpenVPN 2.4.

       --no-replay
	      Removed  in  OpenVPN  2.5.  This option should not be used as it
	      weakens the VPN tunnel security.

       --ns-cert-type
	      Removed in OpenVPN 2.5.  The nsCertType field is no longer  sup-
	      ported  in  recent SSL/TLS libraries.  If	your certificates does
	      not include key usage and	extended key usage fields,  they  must
	      be  upgraded and the --remote-cert-tls option should be used in-
	      stead.

CONNECTION PROFILES
       Client configuration files may contain multiple remote servers which it
       will  attempt to	connect	against.  But there are	some configuration op-
       tions which are related to specific --remote options.   For  these  use
       cases, connection profiles are the solution.

       By enacpulating the --remote option and related options within <connec-
       tion> and </connection>,	these options are handled as a group.

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

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

       Here is an example of connection	profile	usage:

	  client
	  dev tun

	  <connection>
	  remote 198.19.34.56 1194 udp
	  </connection>

	  <connection>
	  remote 198.19.34.56 443 tcp
	  </connection>

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

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

	  persist-key
	  persist-tun
	  pkcs12 client.p12
	  remote-cert-tls server
	  verb 3

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

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

       bind,	connect-retry,	  connect-retry-max,	connect-timeout,   ex-
       plicit-exit-notify,  float,  fragment,  http-proxy,  http-proxy-option,
       key-direction,  link-mtu, local,	lport, mssfix, mtu-disc, nobind, port,
       proto, remote, rport, socks-proxy, tls-auth,  tls-crypt,	 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 configura-
       tion file which has one or more <connection> blocks, the	option setting
       will  be	 used  as a default for	<connection> blocks which follow it in
       the configuration file.

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

INLINE FILE SUPPORT
       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,      --auth-gen-token-secret,
       --tls-crypt and --tls-crypt-v2 options.

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

       Here is an example of an	inline file usage

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

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

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

       SIGUSR1
	      Like  SIGHUP`, except don't re-read configuration	file, and pos-
	      sibly 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 for more information.

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

       SIGINT, SIGTERM
	      Causes OpenVPN to	exit gracefully.

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

   Firewall Setup:
       If firewalls exist between the two machines, they should	be set to for-
       ward  the  port	OpenVPN	is configured to use, in both directions.  The
       default for OpenVPN is 1194/udp.	 If you	do not have control  over  the
       firewalls  between the two machines, you	may still be able to use Open-
       VPN 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	 fire-
       walls  to  forward packets in both directions without an	explicit fire-
       wall rule).

       Please see your operating system	guides for how to configure the	 fire-
       wall on your systems.

   VPN Address Setup:
       For  purposes of	our example, our two machines will be called bob.exam-
       ple.com and alice.example.com. If you are constructing a	VPN  over  the
       internet,  then	replace	bob.example.com	and alice.example.com 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 ma-
       chine  will  use	 the tunnel endpoint of	the other machine to access it
       over the	VPN. In	our example, the tunnel	endpoint  for  bob.example.com
       will be 10.4.0.1	and for	alice.example.com, 10.4.0.2.

       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-
       ple.com	and  you  wish to connect to alice.example.com via ssh without
       using the VPN (since ssh	has its	own built-in security) you  would  use
       the  command  ssh  alice.example.com. However in	the same scenario, you
       could also use the command telnet 10.4.0.2 to create a  telnet  session
       with  alice.example.com	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 alice.example.com --dev tun1	\
		   --ifconfig 10.4.0.1 10.4.0.2	--verb 9

       On alice:

	  openvpn --remote bob.example.com --dev tun1 \
		   --ifconfig 10.4.0.2 10.4.0.1	--verb 9

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

       On bob:

	  ping 10.4.0.2

       On alice:

	  ping 10.4.0.1

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

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

	  openvpn --genkey --secret key

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

       On bob:

	  openvpn --remote alice.example.com --dev tun1	 \
		   --ifconfig 10.4.0.1 10.4.0.2	--verb 5 \
		   --secret key

       On alice:

	  openvpn --remote bob.example.com --dev tun1	\
		  --ifconfig 10.4.0.2 10.4.0.1 --verb 5	\
		  --secret key

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

       On bob:

	  ping 10.4.0.2

       On alice:

	  ping 10.4.0.1

   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:  The client or server designation only has	meaning	 for  the  TLS
	      subsystem.   It	has  no	 bearing  on  OpenVPN's	 peer-to-peer,
	      UDP-based	communication model.*

       First, build a separate certificate/key pair for	 both  bob  and	 alice
       (see  above  where  --cert  is discussed	for more info).	Then construct
       Diffie Hellman parameters (see above where --dh is discussed  for  more
       info). You can also use the included test files client.crt, client.key,
       server.crt, server.key and ca.crt. The .crt files are certificates/pub-
       lic-keys,  the  .key files are private keys, and	ca.crt is a certifica-
       tion authority who has signed  both  client.crt	and  server.crt.   For
       Diffie Hellman parameters you can use the included file dh2048.pem.

       WARNING:
	      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 alice.example.com --dev tun1	   \
		  --ifconfig 10.4.0.1 10.4.0.2		   \
		  --tls-client --ca ca.crt		   \
		  --cert client.crt --key client.key	   \
		  --reneg-sec 60 --verb	5

       On alice:

	  openvpn --remote bob.example.com --dev tun1	   \
		  --ifconfig 10.4.0.2 10.4.0.1		   \
		  --tls-server --dh dh1024.pem --ca ca.crt \
		  --cert server.crt --key server.key	   \
		  --reneg-sec 60 --verb	5

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

       On bob:

	  ping 10.4.0.2

       On alice:

	  ping 10.4.0.1

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

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

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

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

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

       This setting is not persistent.	Please see your	operating systems doc-
       umentation how to properly configure IP forwarding, which is also  per-
       sistent through system boots.

       If  your	system is configured with a firewall.  Please see your operat-
       ing systems guide on how	to configure the firewall.  You	typically want
       to  allow  traffic coming from and going	to the tun/tap adapter OpenVPN
       is configured to	use.

       On bob:

	  route	add -net 10.0.1.0 netmask 255.255.255.0	gw 10.4.0.2

       On alice:

	  route	add -net 10.0.0.0 netmask 255.255.255.0	gw 10.4.0.1

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

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

FAQ
       https://community.openvpn.net/openvpn/wiki/FAQ

HOWTO
       For a more comprehensive	guide to setting up OpenVPN  in	 a  production
       setting,		see	    the		OpenVPN	       HOWTO	    at
       https://openvpn.net/community-resources/how-to/

PROTOCOL
       For   a	 description   of   OpenVPN's	underlying    protocol,	   see
       https://openvpn.net/community-resources/openvpn-protocol/

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

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

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

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

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

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

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

COPYRIGHT
       Copyright (C) 2002-2020 OpenVPN Inc This	program	is free	software;  you
       can redistribute	it and/or modify it under the terms of the GNU General
       Public License version 2	as published by	the Free Software Foundation.

AUTHORS
       James Yonan james@openvpn.net

								    OPENVPN(8)

NAME | SYNOPSIS | INTRODUCTION | DESCRIPTION | OPTIONS | ENCRYPTION OPTIONS | DATA CHANNEL CIPHER NEGOTIATION | NETWORK CONFIGURATION | SCRIPTING INTEGRATION | UNSUPPORTED OPTIONS | CONNECTION PROFILES | INLINE FILE SUPPORT | SIGNALS | EXAMPLES | FAQ | HOWTO | PROTOCOL | WEB | BUGS | SEE ALSO | NOTES | COPYRIGHT | AUTHORS

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=openvpn&sektion=8&manpath=FreeBSD+13.0-RELEASE+and+Ports>

home | help