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openvpn(8)							    openvpn(8)

NAME
       openvpn - secure IP tunnel daemon.

SYNOPSIS
       openvpn [ options ... ]

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

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

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

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

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

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

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

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

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

       --help Show options.

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

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

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

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

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

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

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

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

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

	      Here is an example configuration file:

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

		  # Use a dynamic tun device.
		  dev tun

		  # Our remote peer
		  remote mypeer.mydomain

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

		  # Our pre-shared static key
		  secret static.key

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

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

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

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

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

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

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

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

	      If --remote is unspecified, OpenVPN will listen for packets from
	      any IP address, but will not act on those	 packets  unless  they
	      pass all authentication tests.  This requirement for authentica‐
	      tion is binding on all potential peers, even  those  from	 known
	      and  supposedly trusted IP addresses (it is very easy to forge a
	      source IP address on a UDP packet).

	      When used in TCP mode, --remote will act as a filter,  rejecting
	      connections from any host which does not match host.

	      If  host	is a DNS name which resolves to multiple IP addresses,
	      one will be randomly chosen, providing a sort of basic load-bal‐
	      ancing and failover capability.

       --remote-random-hostname
	      Add  a  random string (6 characters) to first DNS label of host‐
	      name to prevent DNS caching.  For example,  "foo.bar.gov"	 would
	      be modified to "<random-chars>.foo.bar.gov".

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

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

	      --remote-random can be used to initially "scramble" the  connec‐
	      tion list.

	      Here is an example of connection profile usage:

		  client
		  dev tun

		  <connection>
		  remote 198.19.34.56 1194 udp
		  </connection>

		  <connection>
		  remote 198.19.34.56 443 tcp
		  </connection>

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       --resolv-retry n
	      If hostname resolve fails for --remote, retry resolve for n sec‐
	      onds before failing.

	      Set n to "infinite" to retry indefinitely.

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

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

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

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

	      Execute as:

	      cmd ip_address port_number

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

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

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

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

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

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

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

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

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

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

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

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

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

	      tun  devices  encapsulate	 IPv4  or IPv6 (OSI Layer 3) while tap
	      devices encapsulate Ethernet 802.3 (OSI Layer 2).

       --dev-type device-type
	      Which device type are we using?  device-type should be tun  (OSI
	      Layer  3)	 or  tap  (OSI	Layer 2).  Use this option only if the
	      TUN/TAP device used with --dev does not begin with tun or tap.

       --topology mode
	      Configure virtual addressing topology when running in --dev  tun
	      mode.   This  directive  has no meaning in --dev tap mode, which
	      always uses a subnet topology.

	      If you set this  directive  on  the  server,  the	 --server  and
	      --server-bridge  directives  will automatically push your chosen
	      topology setting to clients as well.  This directive can also be
	      manually	pushed	to  clients.   Like  the --dev directive, this
	      directive must always be compatible between client and server.

	      mode can be one of:

	      net30 -- Use a point-to-point topology, by  allocating  one  /30
	      subnet  per  client.   This  is designed to allow point-to-point
	      semantics when some or all of the connecting  clients  might  be
	      Windows systems.	This is the default on OpenVPN 2.0.

	      p2p  --  Use a point-to-point topology where the remote endpoint
	      of the client's tun interface always points to  the  local  end‐
	      point of the server's tun interface.  This mode allocates a sin‐
	      gle IP address per connecting client.  Only use when none of the
	      connecting  clients are Windows systems.	This mode is function‐
	      ally equivalent to the --ifconfig-pool-linear directive which is
	      available in OpenVPN 2.0 and is now deprecated.

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

	      This option exists in OpenVPN 2.1 or higher.

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

	      See below for further IPv6-related configuration options.

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

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

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

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

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

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

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

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

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

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

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

       --ifconfig-nowarn
	      Don't  output  an	 options  consistency  check  warning  if  the
	      --ifconfig  option  on this side of the connection doesn't match
	      the remote side.	This is useful when you	 want  to  retain  the
	      overall  benefits	 of  the  options  consistency check (also see
	      --disable-occ option) while only disabling the  ifconfig	compo‐
	      nent of the check.

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

	      This  option  will also silence warnings about potential address
	      conflicts which occasionally annoy  more	experienced  users  by
	      triggering "false positive" warnings.

       --route network/IP [netmask] [gateway] [metric]
	      Add  route  to  routing  table  after connection is established.
	      Multiple routes can be specified.	 Routes will be	 automatically
	      torn down in reverse order prior to TUN/TAP device close.

	      This  option is intended as a convenience proxy for the route(8)
	      shell command, while at the same time providing portable	seman‐
	      tics across OpenVPN's platform space.

	      netmask default -- 255.255.255.255

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

	      metric default -- taken from --route-metric otherwise 0.

	      The default can be specified by leaving an option blank or  set‐
	      ting it to "nil".

	      The  network  and	 gateway parameters can also be specified as a
	      DNS or /etc/hosts file resolvable name, or as one of three  spe‐
	      cial keywords:

	      vpn_gateway  --  The remote VPN endpoint address (derived either
	      from --route-gateway or the second parameter to --ifconfig  when
	      --dev tun is specified).

	      net_gateway  --  The  pre-existing IP default gateway, read from
	      the routing table (not supported on all OSes).

	      remote_host -- The --remote address if OpenVPN is being  run  in
	      client mode, and is undefined in server mode.

       --max-routes n
	      Allow  a	maximum	 number	 of n --route options to be specified,
	      either in the local configuration file, or pulled from an	 Open‐
	      VPN server.  By default, n=100.

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

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

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

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

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

	      On Windows, --route-delay tries to be more intelligent by	 wait‐
	      ing  w  seconds  (w=30  by default) for the TAP-Win32 adapter to
	      come up before adding routes.

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

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

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

       --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.

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

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

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

	      This option performs three steps:

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

	      (2) Delete the default gateway route.

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

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

	      Option flags:

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

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

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

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

	      Using the def1 flag is highly recommended.

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

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

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

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

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

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

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

       --mtu-disc type
	      Should  we  do Path MTU discovery on TCP/UDP channel?  Only sup‐
	      ported on OSes such as Linux that supports the necessary	system
	      call to set.

	      'no' -- Never send DF (Don't Fragment) frames
	      'maybe' -- Use per-route hints
	      'yes' -- Always DF (Don't Fragment)

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

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

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

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

	      --fragment adds 4 bytes of overhead per datagram.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	      OpenVPN uses the following algorithm to implement traffic	 shap‐
	      ing: Given a shaper rate of n bytes per second, after a datagram
	      write of b bytes is queued on the TCP/UDP port, wait  a  minimum
	      of (b / n) seconds before queuing the next write.

	      It  should  be  noted  that  OpenVPN  supports  multiple tunnels
	      between the same two peers, allowing you to construct full-speed
	      and reduced bandwidth tunnels at the same time, routing low-pri‐
	      ority data such as off-site backups over the  reduced  bandwidth
	      tunnel, and other data over the full-speed tunnel.

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

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

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

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

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

       --ping n
	      Ping remote over the TCP/UDP control channel if no packets  have
	      been  sent  for at least n seconds (specify --ping on both peers
	      to cause ping packets to be sent in both directions since	 Open‐
	      VPN  ping	 packets  are  not echoed like IP ping packets).  When
	      used in one of OpenVPN's secure modes  (where  --secret,	--tls-
	      server,  or  --tls-client is specified), the ping packet will be
	      cryptographically secure.

	      This option has two intended uses:

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

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

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

	      For example,

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

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

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

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

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

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

	      In client mode, the --ping-restart parameter is set to 120  sec‐
	      onds  by default.	 This default will hold until the client pulls
	      a replacement value from the server, based  on  the  --keepalive
	      setting  in the server configuration.  To disable the 120 second
	      default, set --ping-restart 0 on the client.

	      See the signals section below for more information on SIGUSR1.

	      Note that the behavior of SIGUSR1 can be modified by the	--per‐
	      sist-tun,	  --persist-key,  --persist-local-ip,  and  --persist-
	      remote-ip options.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	      For --dev tun execute as:

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

	      For --dev tap execute as:

	      cmd  tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask
	      [ init | restart ]

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

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

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

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

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

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

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

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

	      route add -net 10.0.0.0 netmask 255.255.255.0 gw $5

       --up-delay
	      Delay TUN/TAP open and  possible	--up  script  execution	 until
	      after TCP/UDP connection establishment with peer.

	      In  --proto  udp	mode, this option normally requires the use of
	      --ping to allow  connection  initiation  to  be  sensed  in  the
	      absence  of  tunnel data, since UDP is a "connectionless" proto‐
	      col.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       --cd dir
	      Change directory to dir prior to reading any files such as  con‐
	      figuration  files,  key  files,  scripts, etc.  dir should be an
	      absolute path, with a leading "/", and without any references to
	      the current directory such as "." or "..".

	      This  option  is useful when you are running OpenVPN in --daemon
	      mode, and you want to consolidate all of	your  OpenVPN  control
	      files in one location.

       --chroot dir
	      Chroot  to dir after initialization.  --chroot essentially rede‐
	      fines dir as being the top level directory  tree	(/).   OpenVPN
	      will  therefore be unable to access any files outside this tree.
	      This can be desirable from a security standpoint.

	      Since the chroot operation is delayed  until  after  initializa‐
	      tion,  most OpenVPN options that reference files will operate in
	      a pre-chroot context.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	      Designed	to  be used to send messages to a controlling applica‐
	      tion which is receiving the OpenVPN log output.

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

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

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

	      0 -- No output except fatal errors.
	      1 to 4 -- Normal usage range.
	      5 -- Output R and W characters to the console  for  each	packet
	      read and write, uppercase is used for TCP/UDP packets and lower‐
	      case is used for TUN/TAP packets.
	      6 to 11 -- Debug	info  range  (see  errlevel.h  for  additional
	      information on debug levels).

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

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

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

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

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

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

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

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

		  comp-lzo yes
		  push "comp-lzo yes"

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

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

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

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

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

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

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

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

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

       --management-client
	      Management interface will connect as a  TCP  client  to  IP:port
	      specified by --management rather than listen as a TCP server.

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

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

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

       --management-signal
	      Send SIGUSR1 signal to OpenVPN  if  management  session  discon‐
	      nects.   This  is	 useful when you wish to disconnect an OpenVPN
	      session on user logoff.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       --server-bridge ['nogw']

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

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

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

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

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

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

		  mode server
		  tls-server

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

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

		  mode server
		  tls-server

		  push "route-gateway dhcp"

	      Or --server-bridge nogw expands as follows:

		  mode server
		  tls-server

       --push option
	      Push a config file option back to the client for	remote	execu‐
	      tion.   Note that option must be enclosed in double quotes ("").
	      The client must specify --pull in its config file.  The  set  of
	      options  which  can be pushed is limited by both feasibility and
	      security.	 Some  options	such  as  those	 which	would  execute
	      scripts are banned, since they would effectively allow a compro‐
	      mised server to execute arbitrary code  on  the  client.	 Other
	      options  such  as TLS or MTU parameters cannot be pushed because
	      the client needs to know	them  before  the  connection  to  the
	      server can be initiated.

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

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

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

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

       --ifconfig-pool start-IP end-IP [netmask]
	      Set aside a pool of subnets to be dynamically allocated to  con‐
	      necting  clients,	 similar to a DHCP server.  For tun-style tun‐
	      nels, each client will be given a /30 subnet (for interoperabil‐
	      ity  with	 Windows  clients).  For tap-style tunnels, individual
	      addresses will be allocated, and the optional netmask  parameter
	      will also be pushed to clients.

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

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

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

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

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

       --ifconfig-pool-linear
	      Modifies the --ifconfig-pool directive  to  allocate  individual
	      TUN  interface  addresses	 for  clients rather than /30 subnets.
	      NOTE:  This option is incompatible with Windows clients.

	      This option is deprecated, and should be replaced with  --topol‐
	      ogy p2p which is functionally equivalent.

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

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

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

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

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

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

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

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

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

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

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

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

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

       --client-connect script
	      Run  script on client connection.	 The script is passed the com‐
	      mon name and IP address  of  the	just-authenticated  client  as
	      environmental  variables	(see  environmental  variable  section
	      below).  The script is also passed the  pathname	of  a  freshly
	      created  temporary file as $1 (i.e. the first command line argu‐
	      ment), to be used by the script to  pass	dynamically  generated
	      config file directives back to OpenVPN.

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

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

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

       --client-disconnect
	      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 script
	      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.

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

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

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

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

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

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

	      This directory will be used by in the following cases:

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

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

	      *	 OPENVPN_PLUGIN_ENABLE_PF  plugin hook to pass filtering rules
	      via pf_file

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

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

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

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

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

	      The macro expands as follows:

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

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

       --max-routes-per-client n
	      Allow a maximum of n internal routes per	client	(default=256).
	      This  is designed to help contain DoS attacks where an authenti‐
	      cated client floods the server with packets  appearing  to  come
	      from  many  unique  MAC addresses, forcing the server to deplete
	      virtual memory as its  internal  routing	table  expands.	  This
	      directive can be used in a --client-config-dir file or auto-gen‐
	      erated by a --client-connect script to override the global value
	      for a particular client.

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

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

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

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

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

	      cmd will be executed with 3 parameters:

	      [1] operation -- "add", "update", or "delete" based  on  whether
	      or  not the address is being added to, modified, or deleted from
	      OpenVPN's internal routing table.
	      [2] address -- The address being learned or unlearned.  This can
	      be  an IPv4 address such as "198.162.10.14", an IPv4 subnet such
	      as "198.162.10.0/24", or an ethernet MAC address (when --dev tap
	      is being used) such as "00:FF:01:02:03:04".
	      [3] common name -- The common name on the certificate associated
	      with the client linked to this address.  Only present for	 "add"
	      or "update" operations, not "delete".

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

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

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

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

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

	      If method is set to "via-file", OpenVPN will write the  username
	      and  password  to	 the first two lines of a temporary file.  The
	      filename will be passed as an argument to script, and  the  file
	      will  be	automatically  deleted	by  OpenVPN  after  the script
	      returns.	The location of the temporary file  is	controlled  by
	      the  --tmp-dir option, and will default to the current directory
	      if unspecified.  For security, consider setting --tmp-dir	 to  a
	      volatile	storage medium such as /dev/shm (if available) to pre‐
	      vent the username/password file from touching the hard drive.

	      The script should examine the username and password, returning a
	      success  exit code (0) if the client's authentication request is
	      to be accepted, or a failure code (1) to reject the client.

	      This directive is designed to enable  a  plugin-style  interface
	      for extending OpenVPN's authentication capabilities.

	      To  protect  against a client passing a maliciously formed user‐
	      name or password string, the username string must	 consist  only
	      of  these	 characters: alphanumeric, underbar ('_'), dash ('-'),
	      dot ('.'), or at ('@').  The password string can consist of  any
	      printable	 characters  except for CR or LF.  Any illegal charac‐
	      ters in either the username or password string will be converted
	      to underbar ('_').

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

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

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

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

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

       --auth-user-pass-optional
	      Allow  connections  by  clients  that  do	 not  specify  a user‐
	      name/password.  Normally, when --auth-user-pass-verify or --man‐
	      agement-client-auth  is  specified  (or an authentication plugin
	      module), the  OpenVPN  server  daemon  will  require  connecting
	      clients  to  specify a username and password.  This option makes
	      the submission of a username/password by clients optional, pass‐
	      ing  the	responsibility to the user-defined authentication mod‐
	      ule/script to accept or deny the client based on	other  factors
	      (such  as	 the  setting  of X509 certificate fields).  When this
	      option is used, and a connecting client does not submit a	 user‐
	      name/password,  the  user-defined	 authentication	 module/script
	      will see the username and password as being set to empty strings
	      ("").   The  authentication  module/script  MUST	have  logic to
	      detect this condition and respond accordingly.

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

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

	      If you don't use this directive, but you also specify an --auth-
	      user-pass-verify	script,	 then  OpenVPN	will  perform	double
	      authentication.	The  client  certificate  verification AND the
	      --auth-user-pass-verify script will need to succeed in order for
	      a client to be authenticated and accepted onto the VPN.

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

       --no-name-remapping
	      Allow Common Name, X509 Subject, and username strings to include
	      any printable character including space, but  excluding  control
	      characters such as tab, newline, and carriage-return.

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

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

       --port-share host port
	      When run in TCP server mode, share the OpenVPN port with another
	      application,  such as an HTTPS server.  If OpenVPN senses a 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.

	      Not implemented on Windows.

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

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

		   pull
		   tls-client

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

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

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

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

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

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

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

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

	      type can be one of:

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

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

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

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

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

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

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

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

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

	      The direction parameter requires that file contains a  2048  bit
	      key.   While  pre-1.5  versions of OpenVPN generate 1024 bit key
	      files, any version  of  OpenVPN  which  supports	the  direction
	      parameter,  will also support 2048 bit key file generation using
	      the --genkey option.

	      Static key encryption mode has certain advantages,  the  primary
	      being ease of configuration.

	      There  are no certificates or certificate authorities or compli‐
	      cated negotiation handshakes and protocols.  The	only  require‐
	      ment  is	that  you have a pre-existing secure channel with your
	      peer (such as ssh ) to initially copy the	 key.	This  require‐
	      ment, along with the fact that your key never changes unless you
	      manually generate a new one, makes it somewhat less secure  than
	      TLS mode (see below).  If an attacker manages to steal your key,
	      everything that was ever encrypted with it is compromised.  Con‐
	      trast  that  to the perfect forward secrecy features of TLS mode
	      (using Diffie Hellman key exchange), where even if  an  attacker
	      was able to steal your private key, he would gain no information
	      to help him decrypt past sessions.

	      Another advantageous aspect of Static  Key  encryption  mode  is
	      that  it is a handshake-free protocol without any distinguishing
	      signature or feature (such as a  header  or  protocol  handshake
	      sequence) that would mark the ciphertext packets as being gener‐
	      ated by OpenVPN.	Anyone eavesdropping on	 the  wire  would  see
	      nothing but random-looking data.

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

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

	      In  static-key  encryption mode, the HMAC key is included in the
	      key file generated by --genkey.  In TLS mode, the	 HMAC  key  is
	      dynamically  generated and shared between peers via the TLS con‐
	      trol channel.  If OpenVPN receives a packet with a bad  HMAC  it
	      will  drop  the  packet.	 HMAC  usually adds 16 or 20 bytes per
	      packet.  Set alg=none to disable authentication.

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

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

	      For   more  information  on  blowfish,  see  http://www.counter‐
	      pane.com/blowfish.html

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

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

	      Set alg=none to disable encryption.

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

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

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

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

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

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

	      OpenVPN provides datagram replay protection by default.

	      Replay protection is accomplished by tagging each outgoing data‐
	      gram  with an identifier that is guaranteed to be unique for the
	      key being used.  The peer that receives the datagram will	 check
	      for  the	uniqueness  of	the identifier.	 If the identifier was
	      already received in a previous datagram, OpenVPN will  drop  the
	      packet.	Replay	protection is important to defeat attacks such
	      as a SYN flood attack, where the attacker listens in  the	 wire,
	      intercepts  a  TCP  SYN packet (identifying it by the context in
	      which it occurs in relation to other packets), then  floods  the
	      receiving peer with copies of this packet.

	      OpenVPN's replay protection is implemented in slightly different
	      ways, depending on the key management mode you have selected.

	      In Static Key mode or when using an  CFB	or  OFB	 mode  cipher,
	      OpenVPN  uses  a	64  bit unique identifier that combines a time
	      stamp with an incrementing sequence number.

	      When using TLS mode for key exchange  and	 a  CBC	 cipher	 mode,
	      OpenVPN uses only a 32 bit sequence number without a time stamp,
	      since OpenVPN can guarantee the uniqueness  of  this  value  for
	      each key.	 As in IPSec, if the sequence number is close to wrap‐
	      ping back to zero, OpenVPN will trigger a new key exchange.

	      To check for replays, OpenVPN uses the sliding window  algorithm
	      used by IPSec.

       --replay-window n [t]
	      Use a replay protection sliding-window of size n and a time win‐
	      dow of t seconds.

	      By default n is 64 (the IPSec default) and t is 15 seconds.

	      This option is only relevant in  UDP  mode,  i.e.	  when	either
	      --proto udp is specified, or no --proto option is specified.

	      When OpenVPN tunnels IP packets over UDP, there is the possibil‐
	      ity that packets might be dropped or  delivered  out  of	order.
	      Because  OpenVPN,	 like IPSec, is emulating the physical network
	      layer, it will accept an out-of-order packet sequence, and  will
	      deliver such packets in the same order they were received to the
	      TCP/IP  protocol	stack,	provided  they	satisfy	 several  con‐
	      straints.

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

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

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

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

	      If  you  run  OpenVPN  at	 --verb	 4,  you  will see the message
	      "Replay-window backtrack occurred [x]" every  time  the  maximum
	      sequence	number backtrack seen thus far increases.  This can be
	      used to calibrate n.

	      There is some controversy on the appropriate method of  handling
	      packet reordering at the security layer.

	      Namely,  to  what	 extent	 should the security layer protect the
	      encapsulated protocol from attacks which masquerade as the kinds
	      of  normal  packet  loss	and reordering that occur over IP net‐
	      works?

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

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

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

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

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

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

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

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

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

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

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

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

	      IV is implemented differently depending on the cipher mode used.

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

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

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

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

	      openvpn --test-crypto --secret key

	      or

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

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

   TLS Mode Options:
       TLS mode is the most powerful crypto mode of OpenVPN in	both  security
       and flexibility.	 TLS mode works by establishing control and data chan‐
       nels which are multiplexed over a single TCP/UDP port.  OpenVPN	initi‐
       ates  a	TLS  session  over the control channel and uses it to exchange
       cipher and HMAC keys to protect the data	 channel.   TLS	 mode  uses  a
       robust  reliability layer over the UDP connection for all control chan‐
       nel communication, while the data channel, over which encrypted	tunnel
       data  passes,  is  forwarded  without any mediation.  The result is the
       best of both worlds: a fast data channel that forwards  over  UDP  with
       only  the  overhead of encrypt, decrypt, and HMAC functions, and a con‐
       trol channel that provides all of the security features of TLS, includ‐
       ing   certificate-based	 authentication	 and  Diffie  Hellman  forward
       secrecy.

       To use TLS mode, each peer that runs OpenVPN should have its own	 local
       certificate/key	pair ( --cert and --key ), signed by the root certifi‐
       cate which is specified in --ca.

       When two OpenVPN peers connect, each presents its local certificate  to
       the other.  Each peer will then check that its partner peer presented a
       certificate which was signed by the master root certificate  as	speci‐
       fied in --ca.

       If  that	 check	on  both peers succeeds, then the TLS negotiation will
       succeed, both OpenVPN peers will exchange temporary session  keys,  and
       the tunnel will begin passing data.

       The  OpenVPN  distribution  contains  a set of scripts for managing RSA
       certificates & keys, located in the easy-rsa subdirectory.

       The easy-rsa package is also rendered in web  form  here:  http://open‐
       vpn.net/easyrsa.html

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

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

       --ca file
	      Certificate authority (CA) file in .pem format, also referred to
	      as  the  root certificate.  This file can have multiple certifi‐
	      cates in .pem format, concatenated together.  You can  construct
	      your  own	 certificate  authority certificate and private key by
	      using a command such as:

	      openssl req -nodes -new -x509 -keyout ca.key -out ca.crt

	      Then edit your openssl.cnf file and edit the  certificate	 vari‐
	      able to point to your new root certificate ca.crt.

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

       --capath dir
	      Directory	  containing  trusted  certificates  (CAs  and	CRLs).
	      Available with OpenSSL version >= 0.9.7 dev.

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

	      openssl dhparam -out dh1024.pem 1024

	      to  generate  your  own,	or  use	 the  existing dh1024.pem file
	      included with the OpenVPN distribution.  Diffie Hellman  parame‐
	      ters may be considered public.

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

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

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

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

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

       --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
	      instead of --ca, --cert, and --key.

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

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

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

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

       --pkcs11-protected-authentication [0|1]...
	      Use PKCS#11 protected authentication path, useful for  biometric
	      and  external  keypad  devices.  Every provider has its own set‐
	      ting.

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

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

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

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

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

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

	      To select a certificate, based on a substring search in the cer‐
	      tificate's subject:

	      cryptoapicert "SUBJ:Peter Runestig"

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

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

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

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

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

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

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

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

	      (1) The TLS connection is initially negotiated, with both	 sides
	      of  the connection producing certificates and verifying the cer‐
	      tificate (or other authentication info provided)	of  the	 other
	      side.  The --key-method parameter has no effect on this process.

	      (2)  After the TLS connection is established, the tunnel session
	      keys are separately negotiated  over  the	 existing  secure  TLS
	      channel.	 Here,	--key-method  determines the derivation of the
	      tunnel session keys.

       --tls-cipher l
	      A list l of allowable TLS ciphers delimited by  a	 colon	(":").
	      If  you  require	a  high level of security, you may want to set
	      this parameter manually, to prevent a  version  rollback	attack
	      where  a	man-in-the-middle attacker tries to force two peers to
	      negotiate to the lowest level of	security  they	both  support.
	      Use --show-tls to see a list of supported TLS ciphers.

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

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

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

       --reneg-sec n
	      Renegotiate data channel key after n seconds (default=3600).

	      When  using  dual-factor	authentication, note that this default
	      value may cause the end user to  be  challenged  to  reauthorize
	      once per hour.

	      Also,  keep  in  mind  that  this option can be used on both the
	      client and server, and whichever uses the lower  value  will  be
	      the  one	to  trigger the renegotiation.	A common mistake is to
	      set --reneg-sec to a  higher  value  on  either  the  client  or
	      server,  while  the  other side of the connection is still using
	      the default value of 3600 seconds, meaning that  the  renegotia‐
	      tion will still occur once per 3600 seconds.  The solution is to
	      increase --reneg-sec on both the client and server, or set it to
	      0 on one side of the connection (to disable), and to your chosen
	      value on the other side.

       --hand-window n
	      Handshake Window -- the TLS-based	 key  exchange	must  finalize
	      within  n seconds of handshake initiation by any peer (default =
	      60 seconds).  If the handshake fails we will  attempt  to	 reset
	      our  connection  with our peer and try again.  Even in the event
	      of handshake failure we will still use our expiring key  for  up
	      to  --tran-window seconds to maintain continuity of transmission
	      of tunnel data.

       --tran-window n
	      Transition window -- our old key	can  live  this	 many  seconds
	      after a new a key renegotiation begins (default = 3600 seconds).
	      This feature allows for a graceful transition from  old  to  new
	      key,  and removes the key renegotiation sequence from the criti‐
	      cal path of tunnel data forwarding.

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

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

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

       --tls-exit
	      Exit on TLS negotiation failure.

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

	      In  a  nutshell, --tls-auth enables a kind of "HMAC firewall" on
	      OpenVPN's TCP/UDP port, where TLS control channel packets	 bear‐
	      ing an incorrect HMAC signature can be dropped immediately with‐
	      out response.

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

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

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

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

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

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

	      The  rationale  for  this feature is as follows.	TLS requires a
	      multi-packet exchange before it is able to authenticate a	 peer.
	      During  this  time  before authentication, OpenVPN is allocating
	      resources (memory and CPU) to this potential peer.   The	poten‐
	      tial peer is also exposing many parts of OpenVPN and the OpenSSL
	      library to the packets it is sending.  Most  successful  network
	      attacks  today  seek to either exploit bugs in programs (such as
	      buffer overflow attacks) or force a program to consume  so  many
	      resources that it becomes unusable.  Of course the first line of
	      defense is always to produce clean, well-audited code.   OpenVPN
	      has been written with buffer overflow attack prevention as a top
	      priority.	 But as history has shown, many	 of  the  most	widely
	      used  network  applications  have,  from time to time, fallen to
	      buffer overflow attacks.

	      So as a second line of  defense,	OpenVPN	 offers	 this  special
	      layer  of	 authentication	 on  top of the TLS control channel so
	      that every packet on the control channel is authenticated by  an
	      HMAC signature and a unique ID for replay protection.  This sig‐
	      nature will also help protect against DoS	 (Denial  of  Service)
	      attacks.	 An  important rule of thumb in reducing vulnerability
	      to DoS attacks is to minimize the amount of resources  a	poten‐
	      tial, but as yet unauthenticated, client is able to consume.

	      --tls-auth does this by signing every TLS control channel packet
	      with an HMAC signature, including packets which are sent	before
	      the  TLS	level  has had a chance to authenticate the peer.  The
	      result is that packets without  the  correct  signature  can  be
	      dropped immediately upon reception, before they have a chance to
	      consume additional system resources such as by initiating a  TLS
	      handshake.    --tls-auth	can  be	 strengthened  by  adding  the
	      --replay-persist option which will keep OpenVPN's replay protec‐
	      tion state in a file so that it is not lost across restarts.

	      It  should  be emphasized that this feature is optional and that
	      the passphrase/key file used with --tls-auth gives a peer	 noth‐
	      ing  more than the power to initiate a TLS handshake.  It is not
	      used to encrypt or authenticate any tunnel data.

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

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

	      If file is specified, read the password from the first  line  of
	      file.   Keep  in	mind that storing your password in a file to a
	      certain extent invalidates the extra security provided by	 using
	      an  encrypted key (Note: OpenVPN will only read passwords from a
	      file if it has been built with the  --enable-password-save  con‐
	      figure option, or on Windows by defining ENABLE_PASSWORD_SAVE in
	      win/settings.in).

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

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

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

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

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

	      Note that cmd is a command line and as such may (if enclosed  in
	      quotes)  contain whitespace separated arguments.	The first word
	      of cmd is the shell command to execute and the  remaining	 words
	      are  its	arguments.   When  cmd	is  executed two arguments are
	      appended, as follows:

	      cmd certificate_depth X509_NAME_oneline

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	      The  extended  key  usage	 should be encoded in oid notation, or
	      OpenSSL symbolic representation.

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

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

	      The --remote-cert-tls client option is equivalent	 to  --remote-
	      cert-ku  80  08 88 --remote-cert-eku "TLS Web Client Authentica‐
	      tion"

	      The key usage is digitalSignature and/or keyAgreement.

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

	      The key usage is digitalSignature and ( keyEncipherment or keyA‐
	      greement ).

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

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

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

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

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

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

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

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

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

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

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

       --secret file
	      Write key to file.

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

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

	      One of the advantages of persistent tunnels is that they	elimi‐
	      nate  the	 need  for separate --up and --down scripts to run the
	      appropriate ifconfig(8) and route(8) commands.   These  commands
	      can  be placed in the the same shell script which starts or ter‐
	      minates an OpenVPN session.

	      Another advantage is that open connections through the  TUN/TAP-
	      based  tunnel  will  not	be reset if the OpenVPN peer restarts.
	      This can be useful to provide uninterrupted connectivity through
	      the  tunnel in the event of a DHCP reset of the peer's public IP
	      address (see the --ipchange option above).

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

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

       --rmtun
	      (Standalone) Remove a persistent tunnel.

       --dev tunX | tapX
	      TUN/TAP device

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

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

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

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

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

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

	      dynamic  [offset]	 [lease-time]  --  Automatically  set  the  IP
	      address and netmask by replying to DHCP query messages generated
	      by the kernel.  This mode is probably  the  "cleanest"  solution
	      for  setting  the TCP/IP properties since it uses the well-known
	      DHCP protocol.  There are, however, two prerequisites for	 using
	      this  mode:  (1) The TCP/IP properties for the TAP-Win32 adapter
	      must be set to "Obtain an IP  address  automatically,"  and  (2)
	      OpenVPN  needs  to  claim an IP address in the subnet for use as
	      the virtual DHCP server address.	By default in --dev tap	 mode,
	      OpenVPN  will take the normally unused first address in the sub‐
	      net.   For  example,  if	your  subnet  is  192.168.4.0  netmask
	      255.255.255.0, then OpenVPN will take the IP address 192.168.4.0
	      to use as the virtual DHCP server address.  In --dev  tun	 mode,
	      OpenVPN  will  cause the DHCP server to masquerade as if it were
	      coming from the remote endpoint.	The optional offset  parameter
	      is an integer which is > -256 and < 256 and which defaults to 0.
	      If offset is positive, the DHCP server will masquerade as the IP
	      address at network address + offset.  If offset is negative, the
	      DHCP server will masquerade  as  the  IP	address	 at  broadcast
	      address + offset.	 The Windows ipconfig /all command can be used
	      to show what Windows thinks the DHCP server address is.  OpenVPN
	      will  "claim"  this address, so make sure to use a free address.
	      Having said that, different  OpenVPN  instantiations,  including
	      different	 ends  of the same connection, can share the same vir‐
	      tual DHCP server address.	 The lease-time parameter controls the
	      lease  time  of  the  DHCP  assignment  given  to	 the TAP-Win32
	      adapter, and is denoted in seconds.  Normally a very long	 lease
	      time  is preferred because it prevents routes involving the TAP-
	      Win32 adapter from being lost when the  system  goes  to	sleep.
	      The default lease time is one year.

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

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

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

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

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

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

	      DOMAIN name -- Set Connection-specific DNS Suffix.

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

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

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

	      NTP  addr -- Set primary NTP server address (Network Time Proto‐
	      col).  Repeat this option to set secondary NTP server addresses.

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

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

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

	      Note that if --dhcp-option is pushed via --push to a non-windows
	      client, the option will be saved	in  the	 client's  environment
	      before   the   up	  script  is  called,  under  the  name	 "for‐
	      eign_option_{n}".

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

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

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

       --dhcp-renew
	      Ask Windows to renew the TAP adapter  lease  on  startup.	  This
	      option  is  normally unnecessary, as Windows automatically trig‐
	      gers a DHCP renegotiation on the TAP adapter when it  comes  up,
	      however  if  you set the TAP-Win32 adapter Media Status property
	      to "Always Connected", you may need this flag.

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

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

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

       --service exit-event [0|1]
	      Should be used when OpenVPN is being automatically  executed  by
	      another  program	in such a context that no interaction with the
	      user via display or keyboard is possible.	 In general, end-users
	      should  never need to explicitly use this option, as it is auto‐
	      matically added by the OpenVPN  service  wrapper	when  a	 given
	      OpenVPN configuration is being run as a service.

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

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

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

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

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

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

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

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

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

   PKCS#11 Standalone Options:
       --show-pkcs11-ids provider [cert_private]
	      (Standalone) Show PKCS#11 token object list.  Specify  cert_pri‐
	      vate as 1 if certificates are stored as private objects.

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

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

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

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

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

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

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

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

SCRIPTING AND ENVIRONMENTAL VARIABLES
       OpenVPN	exports	 a  series of environmental variables for use by user-
       defined scripts.

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

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

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

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

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

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

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

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

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

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

       Q: Why is string remapping necessary?

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

       Q: Can string remapping be disabled?

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

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

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

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

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

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

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

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

       Environmental variable values: Any printable character.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       route_vpn_gateway
	      The  default  gateway  used  by --route options, as specified in
	      either the --route-gateway option or  the	 second	 parameter  to
	      --ifconfig  when	--dev  tun  is	specified.   Set prior to --up
	      script execution.

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

	      parm  will  be  one of "network", "netmask", "gateway", or "met‐
	      ric".

	      n is the OpenVPN route number, starting from 1.

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

       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.

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

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

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

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

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

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

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

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

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

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

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

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

       X509_{n}_{subject_field}
	      An X509 subject field from the remote peer certificate, where  n
	      is  the  verification level.  Only set for TLS connections.  Set
	      prior to execution of --tls-verify  script.   This  variable  is
	      similar  to  tls_id_{n} except the component X509 subject fields
	      are broken out, and no string remapping occurs  on  these	 field
	      values (except for remapping of control characters to "_").  For
	      example, the following variables would be	 set  on  the  OpenVPN
	      server  using  the  sample  client  certificate  in  sample-keys
	      (client.crt).  Note that the verification level  is  0  for  the
	      client certificate and 1 for the CA certificate.

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

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

       SIGUSR1
	      Like SIGHUP, except don't re-read configuration file, and possi‐
	      bly don't close and reopen TUN/TAP device,  re-read  key	files,
	      preserve	local  IP  address/port,  or  preserve	most  recently
	      authenticated remote IP  address/port  based  on	--persist-tun,
	      --persist-key,   --persist-local-ip,   and   --persist-remote-ip
	      options respectively (see above).

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

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

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

       SIGINT, SIGTERM
	      Causes OpenVPN to exit gracefully.

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

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

       Load driver: modprobe tun

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

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

	      mknod /dev/net/tun c 10 200

	      modprobe tun

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

       Only Linux 2.4 and newer are supported.

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

   Firewall Setup:
       If firewalls exist between the two machines, they should be set to for‐
       ward UDP port 1194 in both directions.  If you do not have control over
       the  firewalls  between	the two machines, you may still be able to use
       OpenVPN by adding --ping 15 to each of the openvpn commands used	 below
       in  the	examples  (this will cause each peer to send out a UDP ping to
       its remote peer once every 15 seconds which will	 cause	many  stateful
       firewalls  to  forward  packets	in both directions without an explicit
       firewall rule).

       If you are using a Linux iptables-based firewall, you may need to enter
       the following command to allow incoming packets on the TUN device:

	      iptables -A INPUT -i tun+ -j ACCEPT

       See  the	 firewalls  section  below for more information on configuring
       firewalls for use with OpenVPN.

   VPN Address Setup:
       For purposes of our example, our two machines will be called may.kg and
       june.kg.	 If you are constructing a VPN over the internet, then replace
       may.kg and june.kg with the internet hostname or IP address  that  each
       machine will use to contact the other over the internet.

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

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

       You can use any address you wish for the tunnel endpoints but make sure
       that they are private addresses (such as those that begin  with	10  or
       192.168)	 and that they are not part of any existing subnet on the net‐
       works of either peer, unless you are bridging.  If you use  an  address
       that  is	 part of your local subnet for either of the tunnel endpoints,
       you will get a weird feedback loop.

   Example 1: A simple tunnel without security
       On may:

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

       On june:

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

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

       On may:

	      ping 10.4.0.2

       On june:

	      ping 10.4.0.1

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

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

	      openvpn --genkey --secret key

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

       On may:

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

       On june:

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

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

       On may:

	      ping 10.4.0.2

       On june:

	      ping 10.4.0.1

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

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

       On may:

	      openvpn --remote june.kg --dev tun1 --ifconfig 10.4.0.1 10.4.0.2
	      --tls-client --ca	 ca.crt	 --cert	 client.crt  --key  client.key
	      --reneg-sec 60 --verb 5

       On june:

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

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

       On may:

	      ping 10.4.0.2

       On june:

	      ping 10.4.0.1

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

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

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

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

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

       and enable TUN packet forwarding through the firewall:

	      iptables -A FORWARD -i tun+ -j ACCEPT

       On may:

	      route add -net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2

       On june:

	      route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1

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

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

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

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

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

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

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

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

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

       You  should also add firewall rules to allow incoming IP traffic on TUN
       or TAP devices such as:

	      iptables -A INPUT -i tun+ -j ACCEPT

       to allow input packets from tun devices,

	      iptables -A FORWARD -i tun+ -j ACCEPT

       to allow input packets from tun devices to be forwarded to other	 hosts
       on the local network,

	      iptables -A INPUT -i tap+ -j ACCEPT

       to allow input packets from tap devices, and

	      iptables -A FORWARD -i tap+ -j ACCEPT

       to  allow input packets from tap devices to be forwarded to other hosts
       on the local network.

       These rules are secure if  you  use  packet  authentication,  since  no
       incoming packets will arrive on a TUN or TAP virtual device unless they
       first pass an HMAC authentication test.

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

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

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

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

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

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

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

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

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

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

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

AUTHORS
       James Yonan <jim@yonan.net>

			       17 November 2008			    openvpn(8)
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