OpenVPN Tunnel Options


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 authentication 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-balancing and failover capability.
Add a random string (6 characters) to first DNS label of hostname to prevent DNS caching. For example, "" would be modified to "<random-chars>".
Define a client connection profile. Client connection profiles are groups of OpenVPN options that describe how to connect to a given OpenVPN server. Client connection profiles are specified within an OpenVPN configuration file, and each profile is bracketed 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 connection list.
Here is an example of connection profile usage:
client  dev tun    <connection>  remote 1194 udp  </connection>    <connection>  remote 443 tcp  </connection>    <connection>  remote 443 tcp  http-proxy 8080  http-proxy-retry  </connection>    <connection>  remote 443 tcp  http-proxy 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 using UDP. If that fails, we then try to connect to using TCP. If that also fails, then try connecting through an HTTP proxy at to using TCP. Finally, try to connect through the same proxy to a server at using TCP.
The following OpenVPN options may be used inside of a <connection> block:
bind, connect-retry, connect-retry-max, connect-timeout, explicit-exit-notify, float, fragment, http-proxy, http-proxy-option, http-proxy-retry, http-proxy-timeout, link-mtu, local, lport, mssfix, mtu-disc, nobind, port, proto, remote, rport, socks-proxy, socks-proxy-retry, tun-mtu and tun-mtu-extra.
A defaulting mechanism exists for specifying options to apply to all <connection> profiles. If any of the above options (with the exception of remote ) appear outside of a <connection> block, but in a configuration file which has one or more <connection> blocks, the option setting will be used as a default for <connection> blocks which follow it in the configuration file.
For example, suppose the nobind option were placed in the sample 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 profiles using protocol p ('tcp'|'udp').
When multiple --remote address/ports are specified, or if connection 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 --connect-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 capability 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:
There are certain cases, however, where using TCP may be advantageous from a security and robustness perspective, such as tunneling 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 connection attempt (default=infinite).
Show sensed HTTP or SOCKS proxy settings. Currently, only Windows 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.
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).
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 seconds before failing.
Set n to "infinite" to retry indefinitely.
By default, --resolv-retry infinite is enabled. You can disable by setting n=0.
Allow remote peer to change its IP address and/or port number, such as due to DHCP (this is the default if --remote is not used). --float when specified with --remote allows an OpenVPN session to initially connect to a peer at a known address, however if packets arrive from a new address and pass all authentication 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 packets from any address, not only the address which was specified in the --remote option.
--ipchange cmd
Run command cmd when our remote ip-address is initially authenticated or changes.
cmd consists of a path to script (or executable program), optionally followed by arguments. The path and arguments may be single- or double-quoted and/or escaped using a backslash, and should be separated by one or more spaces.
When cmd is executed two arguments are appended after any arguments specified in cmd , as follows:
cmd ip_address port_number
Don't use --ipchange in --mode server mode. Use a --client-connect script instead.
See the "Environmental Variables" section below for additional parameters passed as environmental variables.
If you are running in a dynamic IP address environment where the IP addresses of either peer could change without notice, you can use this script, for example, to edit the /etc/hosts file with the current address of the peer. The script will be run every time the remote peer changes its IP address.
Similarly if our IP address changes due to DHCP, we should configure 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 assignment 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 to local address and port. This is the default unless any of --proto tcp-client , --http-proxy or --socks-proxy are used.
Do not bind to local address and port. The IP stack will allocate 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 connections 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 represent 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 endpoint of the server's tun interface. This mode allocates a single IP address per connecting client. Only use when none of the connecting clients are Windows systems. This mode is functionally 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 connecting client and works on Windows as well. Only available when server and clients are OpenVPN 2.1 or higher, or OpenVPN 2.0.x which has been manually patched with the --topology directive code. When used on Windows, requires version 8.2 or higher of the TAP-Win32 driver. When used on *nix, requires that the tun driver supports an ifconfig(8) command which sets a subnet instead of a remote endpoint IP address.
This option exists in OpenVPN 2.1 or higher.
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 control 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 unprivileged 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 connected to.
For TUN devices, which facilitate virtual point-to-point IP connections, 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 similarly configured. If you are attempting to connect to a remote ethernet bridge, the IP address and subnet should be set to values which would be valid on the the bridged ethernet segment (note also that DHCP can be used for the same purpose).
This option, while primarily a proxy for the ifconfig(8) command, is designed to simplify TUN/TAP tunnel configuration by providing a standard interface to the different ifconfig implementations on different platforms.
--ifconfig parameters which are IP addresses can also be specified as a DNS or /etc/hosts file resolvable name.
For TAP devices, --ifconfig should not be used if the TAP interface will be getting an IP address lease from a DHCP server.
Don't actually execute ifconfig/netsh commands, instead pass --ifconfig parameters to scripts using environmental variables.
Don't output an options consistency check warning if the --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 component 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 semantics across OpenVPN's platform space.
netmask default --
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 setting it to "default".
The network and gateway parameters can also be specified as a DNS or /etc/hosts file resolvable name, or as one of three special 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 OpenVPN server. By default, n=100.
--route-gateway gw|'dhcp'
Specify a default gateway gw for use with --route.
If dhcp is specified as the parameter, the gateway address will be extracted from a DHCP negotiation with the OpenVPN server-side LAN.
--route-metric m
Specify a default metric m for use with --route.
--route-delay [n] [w]
Delay n seconds (default=0) after connection establishment, before adding routes. If n is 0, routes will be added immediately upon connection establishment. If --route-delay is omitted, routes will be added immediately after TUN/TAP device open and --up script execution, before any --user or --group privilege downgrade (or --chroot execution.)
This option is designed to be useful in scenarios where DHCP is used to set tap adapter addresses. The delay will give the DHCP handshake time to complete before routes are added.
On Windows, --route-delay tries to be more intelligent by waiting w seconds (w=30 by default) for the TAP-Win32 adapter to come up before adding routes.
--route-up cmd
Run command cmd after routes are added, subject to --route-delay.
cmd consists of a path to script (or executable program), optionally followed by arguments. The path and arguments may be single- or double-quoted and/or escaped using a backslash, and should be separated by one or more spaces.
See the "Environmental Variables" section below for additional parameters passed as environmental variables.
--route-pre-down cmd
Run command cmd before routes are removed upon disconnection.
cmd consists of a path to script (or executable program), optionally followed by arguments. The path and arguments may be single- or double-quoted and/or escaped using a backslash, and should be separated by one or more spaces.
See the "Environmental Variables" section below for additional parameters passed as environmental variables.
Don't add or remove routes automatically. Instead pass routes to --route-up script using environmental variables.
When used with --client or --pull, accept options pushed by server EXCEPT for routes and dhcp options like DNS servers.
When used on the client, this option effectively bars the server from adding routes to the client's routing table, however note that this option still allows the server to set the TCP/IP properties of the client's TUN/TAP interface.
Allow client to pull DNS names from server (rather than being limited to IP address) for --ifconfig, --route, and --route-gateway.
--client-nat snat|dnat network netmask alias
This pushable client option sets up a stateless one-to-one NAT rule on packet addresses (not ports), and is useful in cases where routes or ifconfig settings pushed to the client would create an IP numbering conflict.
network/netmask (for example defines the local view of a resource from the client perspective, while alias/netmask (for example defines the remote view from the server perspective.
Use snat (source NAT) for resources owned by the client and dnat (destination NAT) for remote resources.
Set --verb 6 for debugging info showing the transformation of src/dest addresses in packets.
--redirect-gateway flags...
Automatically execute routing commands to cause all outgoing IP traffic to be redirected over the VPN. This is a client-side option.
This option performs three steps:
(1) Create a static route for the --remote address which forwards to the pre-existing default gateway. This is done so that (3) will not create a routing loop.
(2) Delete the default gateway route.
(3) Set the new default gateway to be the VPN endpoint address (derived either from --route-gateway or the second parameter to --ifconfig when --dev tun is specified).
When the tunnel is torn down, all of the above steps are reversed so that the original default route is restored.
Option flags:
local -- Add the local flag if both OpenVPN servers are directly connected via a common subnet, such as with wireless. The local flag will cause step 1 above to be omitted.
autolocal -- Try to automatically determine whether to enable local flag above.
def1 -- Use this flag to override the default gateway by using and rather than This has the benefit of overriding but not wiping out the original default gateway.
bypass-dhcp -- Add a direct route to the DHCP server (if it is non-local) which bypasses the tunnel (Available on Windows clients, may not be available on non-Windows clients).
bypass-dns -- Add a direct route to the DNS server(s) (if they are non-local) which bypasses the tunnel (Available on Windows clients, may not be available on non-Windows clients).
block-local -- Block access to local LAN when the tunnel is active, except for the LAN gateway itself. This is accomplished by routing the local LAN (except for the LAN gateway address) into the tunnel.
--link-mtu n
Sets an upper bound on the size of UDP packets which are sent between OpenVPN peers. It's best not to set this parameter unless you know what you're doing.
--redirect-private [flags]
Like --redirect-gateway, but omit actually changing the default gateway. Useful when pushing private subnets.
--tun-mtu n
Take the TUN device MTU to be n and derive the link MTU from it (default=1500). In most cases, you will probably want to leave this parameter set to its default value.
The MTU (Maximum Transmission Units) is the maximum datagram size in bytes that can be sent unfragmented over a particular network path. OpenVPN requires that packets on the control or data channels be sent unfragmented.
MTU problems often manifest themselves as connections which hang during periods of active usage.
It's best to use the --fragment and/or --mssfix options to deal with MTU sizing issues.
--tun-mtu-extra n
Assume that the TUN/TAP device might return as many as n bytes more than the --tun-mtu size on read. This parameter defaults to 0, which is sufficient for most TUN devices. TAP devices may introduce additional overhead in excess of the MTU size, and a setting of 32 is the default when TAP devices are used. This parameter only controls internal OpenVPN buffer sizing, so there is no transmission overhead associated with using a larger value.
--mtu-disc type
Should we do Path MTU discovery on TCP/UDP channel? Only supported on OSes such as Linux that supports the necessary system call to set.
'no' -- Never send DF (Don't Fragment) frames
'maybe' -- Use per-route hints
'yes' -- Always DF (Don't Fragment)
To empirically measure MTU on connection startup, add the --mtu-test option to your configuration. OpenVPN will send ping packets of various sizes to the remote peer and measure the largest packets which were successfully received. The --mtu-test process normally takes about 3 minutes to complete.
--fragment max
Enable internal datagram fragmentation so that no UDP datagrams are sent which are larger than max bytes.
The max parameter is interpreted in the same way as the --link-mtu parameter, i.e. the UDP packet size after 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 fragmentation.
--mssfix max
Announce to TCP sessions running over the tunnel that they should limit their send packet sizes such that after OpenVPN has encapsulated them, the resulting UDP packet size that OpenVPN sends to its peer will not exceed max bytes. The default value is 1450.
The max parameter is interpreted in the same way as the --link-mtu parameter, i.e. the UDP packet size after encapsulation overhead has been added in, but not including the UDP header itself.
The --mssfix option only makes sense when you are using the UDP protocol for OpenVPN peer-to-peer communication, i.e. --proto udp.
--mssfix and --fragment can be ideally used together, where --mssfix will try to keep TCP from needing packet fragmentation in the first place, and if big packets come through anyhow (from protocols other than TCP), --fragment will internally fragment them.
Both --fragment and --mssfix are designed to work around cases where Path MTU discovery is broken on the network path between OpenVPN peers.
The usual symptom of such a breakdown is an OpenVPN connection which successfully starts, but then stalls during active usage.
If --fragment and --mssfix are used together, --mssfix will take its default max parameter from the --fragment max option.
Therefore, one could lower the maximum UDP packet size to 1300 (a good first try for solving MTU-related connection problems) with the following options:
--tun-mtu 1500 --fragment 1300 --mssfix
--sndbuf size
Set the TCP/UDP socket send buffer size. Currently defaults to 65536 bytes.
--rcvbuf size
Set the TCP/UDP socket receive buffer size. Currently defaults to 65536 bytes.
--mark value
Mark encrypted packets being sent with value. The mark value can be matched in policy routing and packetfilter rules. This option is only supported in Linux and does nothing on other operating systems.
--socket-flags flags...
Apply the given flags to the OpenVPN transport socket. Currently, 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 connection 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 shaping: 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-priority 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 "activity", nor are they counted as traffic, as they are used internally by OpenVPN and are not an indication of actual user activity.
--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 OpenVPN 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 + 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 seconds 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 behaviour of SIGUSR1 can be modified by the --persist-tun, --persist-key, --persist-local-ip, and --persist-remote-ip options.
Also note that --ping-exit and --ping-restart are mutually exclusive and cannot be used together.
--keepalive n m
A helper directive designed to simplify the expression of --ping and --ping-restart in server mode configurations.
The server timeout is set twice the value of the second argument. This ensures that a timeout is dectected on client side before the server side drops the connection.
For example, --keepalive 10 60 expands as follows:
 if mode server:     ping 10     ping-restart 120     push "ping 10"     push "ping-restart 60"   else     ping 10     ping-restart 60  
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 connects.
Don't close and reopen TUN/TAP device or run up/down scripts across SIGUSR1 or --ping-restart restarts.
SIGUSR1 is a restart signal similar to SIGHUP, but which offers finer-grained control over reset options.
Don't re-read key files across SIGUSR1 or --ping-restart.
This option can be combined with --user nobody to allow restarts triggered by the SIGUSR1 signal. Normally if you drop root privileges in OpenVPN, the daemon cannot be restarted since it will now be unable to re-read protected key files.
This option solves the problem by persisting keys across SIGUSR1 resets, so they don't need to be re-read.
Preserve initially resolved local IP address and port number across SIGUSR1 or --ping-restart restarts.
Preserve most recently authenticated remote IP address and port number across SIGUSR1 or --ping-restart restarts.
Disable paging by calling the POSIX mlockall function. Requires that OpenVPN be initially run as root (though OpenVPN can subsequently downgrade its UID using the --user option).
Using this option ensures that key material and tunnel data are never written to disk due to virtual memory paging operations which occur under most modern operating systems. It ensures that even if an attacker was able to crack the box running OpenVPN, he would not be able to scan the system swap file to recover previously used ephemeral keys, which are used for a period of time governed by the --reneg options (see below), then are discarded.
The downside of using --mlock is that it will reduce the amount of physical memory available to other applications.
--up cmd
Run command cmd after successful TUN/TAP device open (pre --user UID change).
cmd consists of a path to script (or executable program), optionally followed by arguments. The path and arguments may be single- or double-quoted and/or escaped using a backslash, and should be separated by one or more spaces.
The up command is useful for specifying route commands which route IP traffic destined for private subnets which exist at the other end of the VPN connection into the tunnel.
For --dev tun execute as:
cmd tun_dev tun_mtu link_mtu ifconfig_local_ip ifconfig_remote_ip [ init | restart ]
For --dev tap execute as:
cmd tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask [ init | restart ]
See the "Environmental Variables" section below for additional parameters passed as environmental variables.
Note that if cmd includes arguments, all OpenVPN-generated arguments will be appended to them to build an argument list with which the executable will be called.
Typically, cmd will run a script to add routes to the tunnel.
Normally the up script is called after the TUN/TAP device is opened. In this context, the last command line parameter passed to the script will be init. If the --up-restart option is also used, the up script will be called for restarts as well. A restart is considered to be a partial reinitialization of OpenVPN where the TUN/TAP instance is preserved (the --persist-tun option will enable such preservation). A restart can be generated by a SIGUSR1 signal, a --ping-restart timeout, or a connection reset when the TCP protocol is enabled with the --proto option. If a restart occurs, and --up-restart has been specified, 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 automatically 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 netmask gw $5
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" protocol.
On Windows, this option will delay the TAP-Win32 media state transitioning to "connected" until connection establishment, i.e. the receipt of the first authenticated packet from the peer.
--down cmd
Run command cmd after TUN/TAP device close (post --user UID change and/or --chroot ). cmd consists of a path to script (or executable program), optionally followed by arguments. The path and arguments may be single- or double-quoted and/or escaped using a backslash, and should be separated by one or more spaces.
Called with the same parameters and environmental variables as the --up option above.
Note that if you reduce privileges by using --user and/or --group, your --down script will also run at reduced privilege.
Call --down cmd/script before, rather than after, TUN/TAP close.
Enable the --up and --down scripts to be called for restarts as well as initial program start. This option is described more fully above in the --up option documentation.
--setenv name value
Set a custom environmental variable name=value to pass to script.
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 security 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 encountered 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
This directive offers policy-level control over OpenVPN's usage of external programs and scripts. Lower level values are more restrictive, higher values are more permissive. Settings for level:
0 -- Strictly no calling of external programs.
1 -- (Default) Only call built-in executables such as ifconfig, ip, route, or netsh.
2 -- Allow calling of built-in executables and user-defined scripts.
3 -- Allow passwords to be passed to scripts via environmental variables (potentially unsafe).
OpenVPN releases before v2.3 also supported a method flag which indicated how OpenVPN should call external commands and scripts. This could be either execve or system. As of OpenVPN v2.3, this flag is no longer accepted. In most *nix environments the execve() approach has been used without any issues.
To run scripts in Windows in earlier OpenVPN versions you needed to either add a full path to the script interpreter which can parse the script or use the system flag to run these scripts. As of OpenVPN v2.3 it is now a strict requirement to have full path to the script interpreter when running non-executables files. This is not needed for executable files, such as .exe, .com, .bat or .cmd files. For example, if you have a Visual Basic script, you must use this syntax now:
--up 'C:\\Windows\\System32\\wscript.exe C:\\Program\ Files\\OpenVPN\\config\\my-up-script.vbs'  
Please note the single quote marks and the escaping of the backslashes (\) and the space character.
The reason the support for the system flag was removed is due to the security implications with shell expansions when executing scripts via the system() call.
Don't output a warning message if option inconsistencies are 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 temporary 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 initialization, 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 signal (for example in response to a DHCP reset), you should make use of one or more of the --persist options to ensure that OpenVPN doesn't need to execute any privileged operations in order to restart (such as re-reading key files or running ifconfig on the TUN device).
--group group
Similar to the --user option, this option changes the group ID of the OpenVPN process to group after initialization.
--cd dir
Change directory to dir prior to reading any files such as configuration 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 redefines 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 initialization, most OpenVPN options that reference files will operate in a pre-chroot context.
In many cases, the dir parameter can point to an empty directory, 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 network I/O operations, thanks to SELinux. This goes further than --user and --chroot in that those two, while being great security 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 initialization, 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 initialization.
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 --persist-tun options.
--daemon [progname]
Become a daemon after all initialization functions are completed. This option will cause all message and error output to be sent to the syslog file (such as /var/log/messages), except for the output of scripts and ifconfig commands, which will go to /dev/null unless otherwise redirected. The syslog redirection occurs immediately at the point that --daemon is parsed on the command line even though the daemonization point occurs later. If one of the --log options is present, it will supercede syslog redirection.
The optional progname parameter will cause OpenVPN to report its program name to the system logger as progname. This can be useful 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 functions which are capable of generating fatal errors are complete. This means that initialization scripts can test the return status of the openvpn command for a fairly reliable indication of whether the command has correctly initialized and entered the packet forwarding event loop.
In OpenVPN, the vast majority of errors which occur after initialization 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 parameter.
Output errors to stderr instead of stdout unless log output is redirected by one of the --log options.
Set the TOS field of the tunnel packet to what the payload's TOS 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 single port number. For additional information on this kind of configuration, see the OpenVPN FAQ:
This option precludes the use of --daemon, --local, or --remote. Note that this option causes message and error output to be handled in the same way as the --daemon option. The optional progname parameter is also handled exactly as in --daemon.
Also note that in wait mode, each OpenVPN tunnel requires a separate TCP/UDP port and a separate inetd or xinetd entry. See the OpenVPN 1.x HOWTO for an example on using OpenVPN with xinetd:
--log file
Output logging messages to file, including output to stdout/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 specified. 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, logging occurs by default without the need to specify this option.
--log-append file
Append logging messages to file. If file does not exist, it will be created. This option behaves exactly like --log except that it appends to rather than truncating the log file.
Avoid writing timestamps to log messages, even when they otherwise would be prepended. In particular, this applies to log messages sent to stdout.
--writepid file
Write OpenVPN's main process ID to file.
--nice n
Change process priority after initialization ( n greater than 0 is lower priority, n less than zero is higher priority).
(Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a call to poll/epoll/select prior to the write operation. The purpose of such a call would normally be to block until the 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 optimize the event loop by avoiding the poll/epoll/select call, improving CPU efficiency by 5% to 10%.
This option can only be used on non-Windows systems, when --proto udp is specified, and when --shaper is NOT specified.
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 application which is receiving the OpenVPN log output.
--remap-usr1 signal
Control whether internally or externally generated SIGUSR1 signals 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 lowercase 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 compression 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 setting for the client, for example:
comp-lzo yes  push "comp-lzo yes"  
The first line sets the comp-lzo setting for the server side of the link, the second sets the client side.
When used in conjunction with --comp-lzo, this option will disable OpenVPN's adaptive compression algorithm. Normally, adaptive compression is enabled with --comp-lzo.
Adaptive compression tries to optimize the case where you have compression enabled, but you are sending predominantly uncompressible (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 compression 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 compression 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 functions. pw-file, if specified, is a password file (password on first line) or "stdin" to prompt from standard input. The password 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 behaviour 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 management 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 OpenVPN source distribution.
It is strongly recommended that IP be set to (localhost) to restrict accessibility of the management server to local clients.
Management interface will connect as a TCP/unix domain client to IP:port specified by --management rather than listen as a TCP server or on a unix domain socket.
If the client connection fails to connect or is disconnected, a SIGTERM signal will be generated causing OpenVPN to quit.
Query management channel for private key password and --auth-user-pass username/password. Only query the management channel for inputs which ordinarily would have been queried from the console.
Query management channel for proxy server information for a specific --remote (client-only).
Allow management interface to override --remote directives (client-only). --management-external-key Allows usage for external private key file instead of --key option (client-only).
Make OpenVPN forget passwords when management session disconnects.
This directive does not affect the --http-proxy username/password. It is always cached.
Start OpenVPN in a hibernating state, until a client of the management interface explicitly starts it with the hold release command.
Send SIGUSR1 signal to OpenVPN if management session disconnects. This is useful when you wish to disconnect an OpenVPN session on user logoff. For --management-client this option is not needed since a disconnect will always generate a SIGTERM.
--management-log-cache n
Cache the most recent n lines of log file history for usage by the management channel.
Report tunnel up/down events to management interface.
Gives management interface client the responsibility to authenticate clients after their client certificate has been verified. See management-notes.txt in OpenVPN distribution for detailed notes.
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/openvpn/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 module/script controls an authentication function (such as tls-verify, auth-user-pass-verify, or client-connect), then every module and script must return success (0) in order for the connection to be authenticated.

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