1openvpn(8) System Manager's Manual openvpn(8)
2
6 openvpn - secure IP tunnel daemon.
7
9 openvpn [ options ... ]
10
12 OpenVPN is an open source VPN daemon by James Yonan. Because OpenVPN
13 tries to be a universal VPN tool offering a great deal of flexibility,
14 there are a lot of options on this manual page. If you're new to Open‐
15 VPN, you might want to skip ahead to the examples section where you
16 will see how to construct simple VPNs on the command line without even
17 needing a configuration file.
18 Also note that there's more documentation and examples on the OpenVPN
20 web site: http://openvpn.net/
21 And if you would like to see a shorter version of this manual, see the
23 openvpn usage message which can be obtained by running openvpn without
24 any parameters.
25
27 OpenVPN is a robust and highly flexible VPN daemon. OpenVPN supports
28 SSL/TLS security, ethernet bridging, TCP or UDP tunnel transport
29 through proxies or NAT, support for dynamic IP addresses and DHCP,
30 scalability to hundreds or thousands of users, and portability to most
31 major OS platforms.
32 OpenVPN is tightly bound to the OpenSSL library, and derives much of
34 its crypto capabilities from it.
35 OpenVPN supports conventional encryption using a pre-shared secret key
37 (Static Key mode) or public key security (SSL/TLS mode) using client &
38 server certificates. OpenVPN also supports non-encrypted TCP/UDP tun‐
39 nels.
40 OpenVPN is designed to work with the TUN/TAP virtual networking inter‐
42 face that exists on most platforms.
43 Overall, OpenVPN aims to offer many of the key features of IPSec but
45 with a relatively lightweight footprint.
46
48 OpenVPN allows any option to be placed either on the command line or in
49 a configuration file. Though all command line options are preceded by
50 a double-leading-dash ("--"), this prefix can be removed when an option
51 is placed in a configuration file.
52 --help Show options.
54 --config file
56 Load additional config options from file where each line corre‐
57 sponds to one command line option, but with the leading '--'
58 removed.
59 If --config file is the only option to the openvpn command, the
61 --config can be removed, and the command can be given as openvpn
62 file
63 Note that configuration files can be nested to a reasonable
65 depth.
66 Double quotation or single quotation characters ("", '') can be
68 used to enclose single parameters containing whitespace, and "#"
69 or ";" characters in the first column can be used to denote com‐
70 ments.
71 Note that OpenVPN 2.0 and higher performs backslash-based shell
73 escaping for characters not in single quotations, so the follow‐
74 ing mappings should be observed:
75 \\ Maps to a single backslash character (\).
77 \" Pass a literal doublequote character ("), don't
78 interpret it as enclosing a parameter.
79 \[SPACE] Pass a literal space or tab character, don't
80 interpret it as a parameter delimiter.
81 For example on Windows, use double backslashes to represent
83 pathnames:
84 secret "c:\\OpenVPN\\secret.key"
86 For examples of configuration files, see http://open‐
88 vpn.net/examples.html
89 Here is an example configuration file:
91 #
93 # Sample OpenVPN configuration file for
94 # using a pre-shared static key.
95 #
96 # '#' or ';' may be used to delimit comments.
97 # Use a dynamic tun device.
99 dev tun
100 # Our remote peer
102 remote mypeer.mydomain
103 # 10.1.0.1 is our local VPN endpoint
105 # 10.1.0.2 is our remote VPN endpoint
106 ifconfig 10.1.0.1 10.1.0.2
107 # Our pre-shared static key
109 secret static.key
110 Tunnel Options:
112 --mode m
113 Set OpenVPN major mode. By default, OpenVPN runs in
114 point-to-point mode ("p2p"). OpenVPN 2.0 introduces a new mode
115 ("server") which implements a multi-client server capability.
116 --local host
118 Local host name or IP address for bind. If specified, OpenVPN
119 will bind to this address only. If unspecified, OpenVPN will
120 bind to all interfaces.
121 --remote host [port] [proto]
123 Remote host name or IP address. On the client, multiple
124 --remote options may be specified for redundancy, each referring
125 to a different OpenVPN server. Specifying multiple --remote
126 options for this purpose is a special case of the more general
127 connection-profile feature. See the <connection> documentation
128 below.
129 The OpenVPN client will try to connect to a server at host:port
131 in the order specified by the list of --remote options.
132 proto indicates the protocol to use when connecting with the
134 remote, and may be "tcp" or "udp".
135 For forcing IPv4 or IPv6 connection suffix tcp or udp with 4/6
137 like udp4/udp6/tcp4/tcp6.
138 The client will move on to the next host in the list, in the
140 event of connection failure. Note that at any given time, the
141 OpenVPN client will at most be connected to one server.
142 Note that since UDP is connectionless, connection failure is
144 defined by the --ping and --ping-restart options.
145 Note the following corner case: If you use multiple --remote
147 options, AND you are dropping root privileges on the client with
148 --user and/or --group, AND the client is running a non-Windows
149 OS, if the client needs to switch to a different server, and
150 that server pushes back different TUN/TAP or route settings, the
151 client may lack the necessary privileges to close and reopen the
152 TUN/TAP interface. This could cause the client to exit with a
153 fatal error.
154 If --remote is unspecified, OpenVPN will listen for packets from
156 any IP address, but will not act on those packets unless they
157 pass all authentication tests. This requirement for authentica‐
158 tion is binding on all potential peers, even those from known
159 and supposedly trusted IP addresses (it is very easy to forge a
160 source IP address on a UDP packet).
161 When used in TCP mode, --remote will act as a filter, rejecting
163 connections from any host which does not match host.
164 If host is a DNS name which resolves to multiple IP addresses,
166 OpenVPN will try them in the order that the system getaddrinfo()
167 presents them, so priorization and DNS randomization is done by
168 the system library. Unless an IP version is forced by the pro‐
169 tocol specification (4/6 suffix), OpenVPN will try both IPv4 and
170 IPv6 addresses, in the order getaddrinfo() returns them.
171 --remote-random-hostname
173 Prepend a random string (6 bytes, 12 hex characters) to hostname
174 to prevent DNS caching. For example, "foo.bar.gov" would be
175 modified to "<random-chars>.foo.bar.gov".
176 <connection>
178 Define a client connection profile. Client connection profiles
179 are groups of OpenVPN options that describe how to connect to a
180 given OpenVPN server. Client connection profiles are specified
181 within an OpenVPN configuration file, and each profile is brack‐
182 eted by <connection> and </connection>.
183 An OpenVPN client will try each connection profile sequentially
185 until it achieves a successful connection.
186 --remote-random can be used to initially "scramble" the connec‐
188 tion list.
189 Here is an example of connection profile usage:
191 client
193 dev tun
194 <connection>
196 remote 198.19.34.56 1194 udp
197 </connection>
198 <connection>
200 remote 198.19.34.56 443 tcp
201 </connection>
202 <connection>
204 remote 198.19.34.56 443 tcp
205 http-proxy 192.168.0.8 8080
206 </connection>
207 <connection>
209 remote 198.19.36.99 443 tcp
210 http-proxy 192.168.0.8 8080
211 </connection>
212 persist-key
214 persist-tun
215 pkcs12 client.p12
216 remote-cert-tls server
217 verb 3
218 First we try to connect to a server at 198.19.34.56:1194 using
220 UDP. If that fails, we then try to connect to 198.19.34.56:443
221 using TCP. If that also fails, then try connecting through an
222 HTTP proxy at 192.168.0.8:8080 to 198.19.34.56:443 using TCP.
223 Finally, try to connect through the same proxy to a server at
224 198.19.36.99:443 using TCP.
225 The following OpenVPN options may be used inside of a <connec‐
227 tion> block:
228 bind, connect-retry, connect-retry-max, connect-timeout,
230 explicit-exit-notify, float, fragment, http-proxy,
231 http-proxy-option, link-mtu, local, lport, mssfix, mtu-disc,
232 nobind, port, proto, remote, rport, socks-proxy, tun-mtu and
233 tun-mtu-extra.
234 A defaulting mechanism exists for specifying options to apply to
236 all <connection> profiles. If any of the above options (with
237 the exception of remote ) appear outside of a <connection>
238 block, but in a configuration file which has one or more <con‐
239 nection> blocks, the option setting will be used as a default
240 for <connection> blocks which follow it in the configuration
241 file.
242 For example, suppose the nobind option were placed in the sample
244 configuration file above, near the top of the file, before the
245 first <connection> block. The effect would be as if nobind were
246 declared in all <connection> blocks below it.
247 --proto-force p
249 When iterating through connection profiles, only consider pro‐
250 files using protocol p ('tcp'|'udp').
251 --remote-random
253 When multiple --remote address/ports are specified, or if con‐
254 nection profiles are being used, initially randomize the order
255 of the list as a kind of basic load-balancing measure.
256 --proto p
258 Use protocol p for communicating with remote host. p can be
259 udp, tcp-client, or tcp-server.
260 The default protocol is udp when --proto is not specified.
262 For UDP operation, --proto udp should be specified on both
264 peers.
265 For TCP operation, one peer must use --proto tcp-server and the
267 other must use --proto tcp-client. A peer started with
268 tcp-server will wait indefinitely for an incoming connection. A
269 peer started with tcp-client will attempt to connect, and if
270 that fails, will sleep for 5 seconds (adjustable via the --con‐
271 nect-retry option) and try again infinite or up to N retries
272 (adjustable via the --connect-retry-max option). Both TCP
273 client and server will simulate a SIGUSR1 restart signal if
274 either side resets the connection.
275 OpenVPN is designed to operate optimally over UDP, but TCP capa‐
277 bility is provided for situations where UDP cannot be used. In
278 comparison with UDP, TCP will usually be somewhat less efficient
279 and less robust when used over unreliable or congested networks.
280 This article outlines some of problems with tunneling IP over
282 TCP:
283 http://sites.inka.de/sites/bigred/devel/tcp-tcp.html
285 There are certain cases, however, where using TCP may be advan‐
287 tageous from a security and robustness perspective, such as tun‐
288 neling non-IP or application-level UDP protocols, or tunneling
289 protocols which don't possess a built-in reliability layer.
290 --connect-retry n [max]
292 Wait n seconds between connection attempts (default=5).
293 Repeated reconnection attempts are slowed down after 5 retries
294 per remote by doubling the wait time after each unsuccessful
295 attempt. The optional argument max specifies the maximum value
296 of wait time in seconds at which it gets capped (default=300).
297 --connect-retry-max n
299 n specifies the number of times each --remote or <connection>
300 entry is tried. Specifying n as one would try each entry exactly
301 once. A successful connection resets the counter.
302 (default=unlimited).
303 --show-proxy-settings
305 Show sensed HTTP or SOCKS proxy settings. Currently, only Win‐
306 dows clients support this option.
307 --http-proxy server port [authfile|'auto'|'auto-nct'] [auth-method]
309 Connect to remote host through an HTTP proxy at address server
310 and port port. If HTTP Proxy-Authenticate is required, authfile
311 is a file containing a username and password on 2 lines, or
312 "stdin" to prompt from console. Its content can also be speci‐
313 fied in the config file with the --http-proxy-user-pass option.
314 (See section on inline files)
315 auth-method should be one of "none", "basic", or "ntlm".
317 HTTP Digest authentication is supported as well, but only via
319 the auto or auto-nct flags (below).
320 The auto flag causes OpenVPN to automatically determine the
322 auth-method and query stdin or the management interface for
323 username/password credentials, if required. This flag exists on
324 OpenVPN 2.1 or higher.
325 The auto-nct flag (no clear-text auth) instructs OpenVPN to
327 automatically determine the authentication method, but to reject
328 weak authentication protocols such as HTTP Basic Authentication.
329 --http-proxy-option type [parm]
331 Set extended HTTP proxy options. Repeat to set multiple
332 options.
333 VERSION version -- Set HTTP version number to version
335 (default=1.0).
336 AGENT user-agent -- Set HTTP "User-Agent" string to user-agent.
338 CUSTOM-HEADER name content -- Adds the custom Header with name
340 as name and content as the content of the custom HTTP header.
341 --socks-proxy server [port] [authfile]
343 Connect to remote host through a Socks5 proxy at address server
344 and port port (default=1080). authfile (optional) is a file
345 containing a username and password on 2 lines, or "stdin" to
346 prompt from console.
347 --resolv-retry n
349 If hostname resolve fails for --remote, retry resolve for n sec‐
350 onds before failing.
351 Set n to "infinite" to retry indefinitely.
353 By default, --resolv-retry infinite is enabled. You can disable
355 by setting n=0.
356 --float
358 Allow remote peer to change its IP address and/or port number,
359 such as due to DHCP (this is the default if --remote is not
360 used). --float when specified with --remote allows an OpenVPN
361 session to initially connect to a peer at a known address, how‐
362 ever if packets arrive from a new address and pass all authenti‐
363 cation tests, the new address will take control of the session.
364 This is useful when you are connecting to a peer which holds a
365 dynamic address such as a dial-in user or DHCP client.
366 Essentially, --float tells OpenVPN to accept authenticated pack‐
368 ets from any address, not only the address which was specified
369 in the --remote option.
370 --ipchange cmd
372 Run command cmd when our remote ip-address is initially authen‐
373 ticated or changes.
374 cmd consists of a path to script (or executable program),
376 optionally followed by arguments. The path and arguments may be
377 single- or double-quoted and/or escaped using a backslash, and
378 should be separated by one or more spaces.
379 When cmd is executed two arguments are appended after any argu‐
381 ments specified in cmd , as follows:
382 cmd ip_address port_number
384 Don't use --ipchange in --mode server mode. Use a --client-con‐
386 nect script instead.
387 See the "Environmental Variables" section below for additional
389 parameters passed as environmental variables.
390 If you are running in a dynamic IP address environment where the
392 IP addresses of either peer could change without notice, you can
393 use this script, for example, to edit the /etc/hosts file with
394 the current address of the peer. The script will be run every
395 time the remote peer changes its IP address.
396 Similarly if our IP address changes due to DHCP, we should con‐
398 figure our IP address change script (see man page for dhcpcd(8)
399 ) to deliver a SIGHUP or SIGUSR1 signal to OpenVPN. OpenVPN
400 will then reestablish a connection with its most recently
401 authenticated peer on its new IP address.
402 --port port
404 TCP/UDP port number or port name for both local and remote (sets
405 both --lport and --rport options to given port). The current
406 default of 1194 represents the official IANA port number assign‐
407 ment for OpenVPN and has been used since version 2.0-beta17.
408 Previous versions used port 5000 as the default.
409 --lport port
411 Set local TCP/UDP port number or name. Cannot be used together
412 with --nobind option.
413 --rport port
415 Set TCP/UDP port number or name used by the --remote option. The
416 port can also be set directly using the --remote option.
417 --bind [ipv6only]
419 Bind to local address and port. This is the default unless any
420 of --proto tcp-client , --http-proxy or --socks-proxy are used.
421 If the ipv6only keyword is present OpenVPN will bind only to
423 IPv6 (as oposed to IPv6 and IPv4) when a IPv6 socket is opened.
424 --nobind
427 Do not bind to local address and port. The IP stack will allo‐
428 cate a dynamic port for returning packets. Since the value of
429 the dynamic port could not be known in advance by a peer, this
430 option is only suitable for peers which will be initiating con‐
431 nections by using the --remote option.
432 --dev tunX | tapX | null
434 TUN/TAP virtual network device ( X can be omitted for a dynamic
435 device.)
436 See examples section below for an example on setting up a TUN
438 device.
439 You must use either tun devices on both ends of the connection
441 or tap devices on both ends. You cannot mix them, as they rep‐
442 resent different underlying network layers.
443 tun devices encapsulate IPv4 or IPv6 (OSI Layer 3) while tap
445 devices encapsulate Ethernet 802.3 (OSI Layer 2).
446 --dev-type device-type
448 Which device type are we using? device-type should be tun (OSI
449 Layer 3) or tap (OSI Layer 2). Use this option only if the
450 TUN/TAP device used with --dev does not begin with tun or tap.
451 --topology mode
453 Configure virtual addressing topology when running in --dev tun
454 mode. This directive has no meaning in --dev tap mode, which
455 always uses a subnet topology.
456 If you set this directive on the server, the --server and
458 --server-bridge directives will automatically push your chosen
459 topology setting to clients as well. This directive can also be
460 manually pushed to clients. Like the --dev directive, this
461 directive must always be compatible between client and server.
462 mode can be one of:
464 net30 -- Use a point-to-point topology, by allocating one /30
466 subnet per client. This is designed to allow point-to-point
467 semantics when some or all of the connecting clients might be
468 Windows systems. This is the default on OpenVPN 2.0.
469 p2p -- Use a point-to-point topology where the remote endpoint
471 of the client's tun interface always points to the local end‐
472 point of the server's tun interface. This mode allocates a sin‐
473 gle IP address per connecting client. Only use when none of the
474 connecting clients are Windows systems. This mode is function‐
475 ally equivalent to the --ifconfig-pool-linear directive which is
476 available in OpenVPN 2.0, is deprecated and will be removed in
477 OpenVPN 2.5
478 subnet -- Use a subnet rather than a point-to-point topology by
480 configuring the tun interface with a local IP address and subnet
481 mask, similar to the topology used in --dev tap and ethernet
482 bridging mode. This mode allocates a single IP address per con‐
483 necting client and works on Windows as well. Only available
484 when server and clients are OpenVPN 2.1 or higher, or OpenVPN
485 2.0.x which has been manually patched with the --topology direc‐
486 tive code. When used on Windows, requires version 8.2 or higher
487 of the TAP-Win32 driver. When used on *nix, requires that the
488 tun driver supports an ifconfig(8) command which sets a subnet
489 instead of a remote endpoint IP address.
490 This option exists in OpenVPN 2.1 or higher.
492 Note: Using --topology subnet changes the interpretation of the
494 arguments of --ifconfig to mean "address netmask", no longer
495 "local remote".
496 --dev-node node
498 Explicitly set the device node rather than using /dev/net/tun,
499 /dev/tun, /dev/tap, etc. If OpenVPN cannot figure out whether
500 node is a TUN or TAP device based on the name, you should also
501 specify --dev-type tun or --dev-type tap.
502 Under Mac OS X this option can be used to specify the default
504 tun implementation. Using --dev-node utun forces usage of the
505 native Darwin tun kernel support. Use --dev-node utunN to select
506 a specific utun instance. To force using the tun.kext
507 (/dev/tunX) use --dev-node tun. When not specifying a
508 --dev-node option openvpn will first try to open utun, and fall
509 back to tun.kext.
510 On Windows systems, select the TAP-Win32 adapter which is named
512 node in the Network Connections Control Panel or the raw GUID of
513 the adapter enclosed by braces. The --show-adapters option
514 under Windows can also be used to enumerate all available
515 TAP-Win32 adapters and will show both the network connections
516 control panel name and the GUID for each TAP-Win32 adapter.
517 --lladdr address
519 Specify the link layer address, more commonly known as the MAC
520 address. Only applied to TAP devices.
521 --iproute cmd
523 Set alternate command to execute instead of default iproute2
524 command. May be used in order to execute OpenVPN in unprivi‐
525 leged environment.
526 --ifconfig l rn
528 Set TUN/TAP adapter parameters. l is the IP address of the
529 local VPN endpoint. For TUN devices in point-to-point mode, rn
530 is the IP address of the remote VPN endpoint. For TAP devices,
531 or TUN devices used with --topology subnet, rn is the subnet
532 mask of the virtual network segment which is being created or
533 connected to.
534 For TUN devices, which facilitate virtual point-to-point IP con‐
536 nections (when used in --topology net30 or p2p mode), the proper
537 usage of --ifconfig is to use two private IP addresses which are
538 not a member of any existing subnet which is in use. The IP
539 addresses may be consecutive and should have their order
540 reversed on the remote peer. After the VPN is established, by
541 pinging rn, you will be pinging across the VPN.
542 For TAP devices, which provide the ability to create virtual
544 ethernet segments, or TUN devices in --topology subnet mode
545 (which create virtual "multipoint networks"), --ifconfig is used
546 to set an IP address and subnet mask just as a physical ethernet
547 adapter would be similarly configured. If you are attempting to
548 connect to a remote ethernet bridge, the IP address and subnet
549 should be set to values which would be valid on the the bridged
550 ethernet segment (note also that DHCP can be used for the same
551 purpose).
552 This option, while primarily a proxy for the ifconfig(8) com‐
554 mand, is designed to simplify TUN/TAP tunnel configuration by
555 providing a standard interface to the different ifconfig imple‐
556 mentations on different platforms.
557 --ifconfig parameters which are IP addresses can also be speci‐
559 fied as a DNS or /etc/hosts file resolvable name.
560 For TAP devices, --ifconfig should not be used if the TAP inter‐
562 face will be getting an IP address lease from a DHCP server.
563 --ifconfig-noexec
565 Don't actually execute ifconfig/netsh commands, instead pass
566 --ifconfig parameters to scripts using environmental variables.
567 --ifconfig-nowarn
569 Don't output an options consistency check warning if the
570 --ifconfig option on this side of the connection doesn't match
571 the remote side. This is useful when you want to retain the
572 overall benefits of the options consistency check (also see
573 --disable-occ option) while only disabling the ifconfig compo‐
574 nent of the check.
575 For example, if you have a configuration where the local host
577 uses --ifconfig but the remote host does not, use --ifcon‐
578 fig-nowarn on the local host.
579 This option will also silence warnings about potential address
581 conflicts which occasionally annoy more experienced users by
582 triggering "false positive" warnings.
583 --route network/IP [netmask] [gateway] [metric]
585 Add route to routing table after connection is established.
586 Multiple routes can be specified. Routes will be automatically
587 torn down in reverse order prior to TUN/TAP device close.
588 This option is intended as a convenience proxy for the route(8)
590 shell command, while at the same time providing portable seman‐
591 tics across OpenVPN's platform space.
592 netmask default -- 255.255.255.255
594 gateway default -- taken from --route-gateway or the second
596 parameter to --ifconfig when --dev tun is specified.
597 metric default -- taken from --route-metric otherwise 0.
599 The default can be specified by leaving an option blank or set‐
601 ting it to "default".
602 The network and gateway parameters can also be specified as a
604 DNS or /etc/hosts file resolvable name, or as one of three spe‐
605 cial keywords:
606 vpn_gateway -- The remote VPN endpoint address (derived either
608 from --route-gateway or the second parameter to --ifconfig when
609 --dev tun is specified).
610 net_gateway -- The pre-existing IP default gateway, read from
612 the routing table (not supported on all OSes).
613 remote_host -- The --remote address if OpenVPN is being run in
615 client mode, and is undefined in server mode.
616 --route-gateway gw|'dhcp'
618 Specify a default gateway gw for use with --route.
619 If dhcp is specified as the parameter, the gateway address will
621 be extracted from a DHCP negotiation with the OpenVPN
622 server-side LAN.
623 --route-metric m
625 Specify a default metric m for use with --route.
626 --route-delay [n] [w]
628 Delay n seconds (default=0) after connection establishment,
629 before adding routes. If n is 0, routes will be added immedi‐
630 ately upon connection establishment. If --route-delay is omit‐
631 ted, routes will be added immediately after TUN/TAP device open
632 and --up script execution, before any --user or --group privi‐
633 lege downgrade (or --chroot execution.)
634 This option is designed to be useful in scenarios where DHCP is
636 used to set tap adapter addresses. The delay will give the DHCP
637 handshake time to complete before routes are added.
638 On Windows, --route-delay tries to be more intelligent by wait‐
640 ing w seconds (w=30 by default) for the TAP-Win32 adapter to
641 come up before adding routes.
642 --route-up cmd
644 Run command cmd after routes are added, subject to
645 --route-delay.
646 cmd consists of a path to script (or executable program),
648 optionally followed by arguments. The path and arguments may be
649 single- or double-quoted and/or escaped using a backslash, and
650 should be separated by one or more spaces.
651 See the "Environmental Variables" section below for additional
653 parameters passed as environmental variables.
654 --route-pre-down cmd
656 Run command cmd before routes are removed upon disconnection.
657 cmd consists of a path to script (or executable program),
659 optionally followed by arguments. The path and arguments may be
660 single- or double-quoted and/or escaped using a backslash, and
661 should be separated by one or more spaces.
662 See the "Environmental Variables" section below for additional
664 parameters passed as environmental variables.
665 --route-noexec
667 Don't add or remove routes automatically. Instead pass routes
668 to --route-up script using environmental variables.
669 --route-nopull
671 When used with --client or --pull, accept options pushed by
672 server EXCEPT for routes, block-outside-dns and dhcp options
673 like DNS servers.
674 When used on the client, this option effectively bars the server
676 from adding routes to the client's routing table, however note
677 that this option still allows the server to set the TCP/IP prop‐
678 erties of the client's TUN/TAP interface.
679 --allow-pull-fqdn
681 Allow client to pull DNS names from server (rather than being
682 limited to IP address) for --ifconfig, --route, and
683 --route-gateway.
684 --client-nat snat|dnat network netmask alias
686 This pushable client option sets up a stateless one-to-one NAT
687 rule on packet addresses (not ports), and is useful in cases
688 where routes or ifconfig settings pushed to the client would
689 create an IP numbering conflict.
690 network/netmask (for example 192.168.0.0/255.255.0.0) defines
692 the local view of a resource from the client perspective, while
693 alias/netmask (for example 10.64.0.0/255.255.0.0) defines the
694 remote view from the server perspective.
695 Use snat (source NAT) for resources owned by the client and dnat
697 (destination NAT) for remote resources.
698 Set --verb 6 for debugging info showing the transformation of
700 src/dest addresses in packets.
701 --redirect-gateway flags...
703 Automatically execute routing commands to cause all outgoing IP
704 traffic to be redirected over the VPN. This is a client-side
705 option.
706 This option performs three steps:
708 [1m(1) Create a static route for the --remote address which for‐
710 wards to the pre-existing default gateway. This is done so that
711 [1m(3) will not create a routing loop.
712 [1m(2) Delete the default gateway route.
714 [1m(3) Set the new default gateway to be the VPN endpoint address
716 (derived either from --route-gateway or the second parameter to
717 --ifconfig when --dev tun is specified).
718 When the tunnel is torn down, all of the above steps are
720 reversed so that the original default route is restored.
721 Option flags:
723 local -- Add the local flag if both OpenVPN peers are directly
725 connected via a common subnet, such as with wireless. The local
726 flag will cause step 1 above to be omitted.
727 autolocal -- Try to automatically determine whether to enable
729 local flag above.
730 def1 -- Use this flag to override the default gateway by using
732 0.0.0.0/1 and 128.0.0.0/1 rather than 0.0.0.0/0. This has the
733 benefit of overriding but not wiping out the original default
734 gateway.
735 bypass-dhcp -- Add a direct route to the DHCP server (if it is
737 non-local) which bypasses the tunnel (Available on Windows
738 clients, may not be available on non-Windows clients).
739 bypass-dns -- Add a direct route to the DNS server(s) (if they
741 are non-local) which bypasses the tunnel (Available on Windows
742 clients, may not be available on non-Windows clients).
743 block-local -- Block access to local LAN when the tunnel is
745 active, except for the LAN gateway itself. This is accomplished
746 by routing the local LAN (except for the LAN gateway address)
747 into the tunnel.
748 ipv6 -- Redirect IPv6 routing into the tunnel. This works simi‐
750 lar to the def1 flag, that is, more specific IPv6 routes are
751 added (2000::/4, 3000::/4), covering the whole IPv6 unicast
752 space.
753 !ipv4 -- Do not redirect IPv4 traffic - typically used in the
755 flag pair ipv6 !ipv4 to redirect IPv6-only.
756 --link-mtu n
758 Sets an upper bound on the size of UDP packets which are sent
759 between OpenVPN peers. It's best not to set this parameter
760 unless you know what you're doing.
761 --redirect-private [flags]
763 Like --redirect-gateway, but omit actually changing the default
764 gateway. Useful when pushing private subnets.
765 --tun-mtu n
767 Take the TUN device MTU to be n and derive the link MTU from it
768 (default=1500). In most cases, you will probably want to leave
769 this parameter set to its default value.
770 The MTU (Maximum Transmission Units) is the maximum datagram
772 size in bytes that can be sent unfragmented over a particular
773 network path. OpenVPN requires that packets on the control or
774 data channels be sent unfragmented.
775 MTU problems often manifest themselves as connections which hang
777 during periods of active usage.
778 It's best to use the --fragment and/or --mssfix options to deal
780 with MTU sizing issues.
781 --tun-mtu-extra n
783 Assume that the TUN/TAP device might return as many as n bytes
784 more than the --tun-mtu size on read. This parameter defaults
785 to 0, which is sufficient for most TUN devices. TAP devices may
786 introduce additional overhead in excess of the MTU size, and a
787 setting of 32 is the default when TAP devices are used. This
788 parameter only controls internal OpenVPN buffer sizing, so there
789 is no transmission overhead associated with using a larger
790 value.
791 --mtu-disc type
793 Should we do Path MTU discovery on TCP/UDP channel? Only sup‐
794 ported on OSes such as Linux that supports the necessary system
795 call to set.
796 'no' -- Never send DF (Don't Fragment) frames
798 'maybe' -- Use per-route hints
799 'yes' -- Always DF (Don't Fragment)
800 --mtu-test
802 To empirically measure MTU on connection startup, add the
803 --mtu-test option to your configuration. OpenVPN will send ping
804 packets of various sizes to the remote peer and measure the
805 largest packets which were successfully received. The
806 --mtu-test process normally takes about 3 minutes to complete.
807 --fragment max
809 Enable internal datagram fragmentation so that no UDP datagrams
810 are sent which are larger than max bytes.
811 The max parameter is interpreted in the same way as the
813 --link-mtu parameter, i.e. the UDP packet size after encapsula‐
814 tion overhead has been added in, but not including the UDP
815 header itself.
816 The --fragment option only makes sense when you are using the
818 UDP protocol ( --proto udp ).
819 --fragment adds 4 bytes of overhead per datagram.
821 See the --mssfix option below for an important related option to
823 --fragment.
824 It should also be noted that this option is not meant to replace
826 UDP fragmentation at the IP stack level. It is only meant as a
827 last resort when path MTU discovery is broken. Using this
828 option is less efficient than fixing path MTU discovery for your
829 IP link and using native IP fragmentation instead.
830 Having said that, there are circumstances where using OpenVPN's
832 internal fragmentation capability may be your only option, such
833 as tunneling a UDP multicast stream which requires fragmenta‐
834 tion.
835 --mssfix max
837 Announce to TCP sessions running over the tunnel that they
838 should limit their send packet sizes such that after OpenVPN has
839 encapsulated them, the resulting UDP packet size that OpenVPN
840 sends to its peer will not exceed max bytes. The default value
841 is 1450.
842 The max parameter is interpreted in the same way as the
844 --link-mtu parameter, i.e. the UDP packet size after encapsula‐
845 tion overhead has been added in, but not including the UDP
846 header itself. Resulting packet would be at most 28 bytes larger
847 for IPv4 and 48 bytes for IPv6 (20/40 bytes for IP header and 8
848 bytes for UDP header). Default value of 1450 allows IPv4 packets
849 to be transmitted over a link with MTU 1473 or higher without IP
850 level fragmentation.
851 The --mssfix option only makes sense when you are using the UDP
853 protocol for OpenVPN peer-to-peer communication, i.e. --proto
854 udp.
855 --mssfix and --fragment can be ideally used together, where
857 --mssfix will try to keep TCP from needing packet fragmentation
858 in the first place, and if big packets come through anyhow (from
859 protocols other than TCP), --fragment will internally fragment
860 them.
861 Both --fragment and --mssfix are designed to work around cases
863 where Path MTU discovery is broken on the network path between
864 OpenVPN peers.
865 The usual symptom of such a breakdown is an OpenVPN connection
867 which successfully starts, but then stalls during active usage.
868 If --fragment and --mssfix are used together, --mssfix will take
870 its default max parameter from the --fragment max option.
871 Therefore, one could lower the maximum UDP packet size to 1300
873 (a good first try for solving MTU-related connection problems)
874 with the following options:
875 --tun-mtu 1500 --fragment 1300 --mssfix
877 --sndbuf size
879 Set the TCP/UDP socket send buffer size. Defaults to operation
880 system default.
881 --rcvbuf size
883 Set the TCP/UDP socket receive buffer size. Defaults to opera‐
884 tion system default.
885 --mark value
887 Mark encrypted packets being sent with value. The mark value can
888 be matched in policy routing and packetfilter rules. This option
889 is only supported in Linux and does nothing on other operating
890 systems.
891 --socket-flags flags...
893 Apply the given flags to the OpenVPN transport socket. Cur‐
894 rently, only TCP_NODELAY is supported.
895 The TCP_NODELAY socket flag is useful in TCP mode, and causes
897 the kernel to send tunnel packets immediately over the TCP con‐
898 nection without trying to group several smaller packets into a
899 larger packet. This can result in a considerably improvement in
900 latency.
901 This option is pushable from server to client, and should be
903 used on both client and server for maximum effect.
904 --txqueuelen n
906 (Linux only) Set the TX queue length on the TUN/TAP interface.
907 Currently defaults to 100.
908 --shaper n
910 Limit bandwidth of outgoing tunnel data to n bytes per second on
911 the TCP/UDP port. Note that this will only work if mode is set
912 to p2p. If you want to limit the bandwidth in both directions,
913 use this option on both peers.
914 OpenVPN uses the following algorithm to implement traffic shap‐
916 ing: Given a shaper rate of n bytes per second, after a datagram
917 write of b bytes is queued on the TCP/UDP port, wait a minimum
918 of (b / n) seconds before queuing the next write.
919 It should be noted that OpenVPN supports multiple tunnels
921 between the same two peers, allowing you to construct full-speed
922 and reduced bandwidth tunnels at the same time, routing low-pri‐
923 ority data such as off-site backups over the reduced bandwidth
924 tunnel, and other data over the full-speed tunnel.
925 Also note that for low bandwidth tunnels (under 1000 bytes per
927 second), you should probably use lower MTU values as well (see
928 above), otherwise the packet latency will grow so large as to
929 trigger timeouts in the TLS layer and TCP connections running
930 over the tunnel.
931 OpenVPN allows n to be between 100 bytes/sec and 100 Mbytes/sec.
933 --inactive n [bytes]
935 Causes OpenVPN to exit after n seconds of inactivity on the
936 TUN/TAP device. The time length of inactivity is measured since
937 the last incoming or outgoing tunnel packet. The default value
938 is 0 seconds, which disables this feature.
939 If the optional bytes parameter is included, exit if less than
941 bytes of combined in/out traffic are produced on the tun/tap
942 device in n seconds.
943 In any case, OpenVPN's internal ping packets (which are just
945 keepalives) and TLS control packets are not considered "activ‐
946 ity", nor are they counted as traffic, as they are used inter‐
947 nally by OpenVPN and are not an indication of actual user activ‐
948 ity.
949 --ping n
951 Ping remote over the TCP/UDP control channel if no packets have
952 been sent for at least n seconds (specify --ping on both peers
953 to cause ping packets to be sent in both directions since Open‐
954 VPN ping packets are not echoed like IP ping packets). When
955 used in one of OpenVPN's secure modes (where --secret,
956 --tls-server, or --tls-client is specified), the ping packet
957 will be cryptographically secure.
958 This option has two intended uses:
960 (1) Compatibility with stateful firewalls. The periodic ping
962 will ensure that a stateful firewall rule which allows OpenVPN
963 UDP packets to pass will not time out.
964 (2) To provide a basis for the remote to test the existence of
966 its peer using the --ping-exit option.
967 --ping-exit n
969 Causes OpenVPN to exit after n seconds pass without reception of
970 a ping or other packet from remote. This option can be combined
971 with --inactive, --ping, and --ping-exit to create a two-tiered
972 inactivity disconnect.
973 For example,
975 openvpn [options...] --inactive 3600 --ping 10 --ping-exit 60
977 when used on both peers will cause OpenVPN to exit within 60
979 seconds if its peer disconnects, but will exit after one hour if
980 no actual tunnel data is exchanged.
981 --ping-restart n
983 Similar to --ping-exit, but trigger a SIGUSR1 restart after n
984 seconds pass without reception of a ping or other packet from
985 remote.
986 This option is useful in cases where the remote peer has a
988 dynamic IP address and a low-TTL DNS name is used to track the
989 IP address using a service such as http://dyndns.org/ + a
990 dynamic DNS client such as ddclient.
991 If the peer cannot be reached, a restart will be triggered,
993 causing the hostname used with --remote to be re-resolved (if
994 --resolv-retry is also specified).
995 In server mode, --ping-restart, --inactive, or any other type of
997 internally generated signal will always be applied to individual
998 client instance objects, never to whole server itself. Note
999 also in server mode that any internally generated signal which
1000 would normally cause a restart, will cause the deletion of the
1001 client instance object instead.
1002 In client mode, the --ping-restart parameter is set to 120 sec‐
1004 onds by default. This default will hold until the client pulls
1005 a replacement value from the server, based on the --keepalive
1006 setting in the server configuration. To disable the 120 second
1007 default, set --ping-restart 0 on the client.
1008 See the signals section below for more information on SIGUSR1.
1010 Note that the behavior of SIGUSR1 can be modified by the --per‐
1012 sist-tun, --persist-key, --persist-local-ip, and --per‐
1013 sist-remote-ip options.
1014 Also note that --ping-exit and --ping-restart are mutually
1016 exclusive and cannot be used together.
1017 --keepalive interval timeout
1019 A helper directive designed to simplify the expression of --ping
1020 and --ping-restart.
1021 This option can be used on both client and server side, but it
1023 is enough to add this on the server side as it will push appro‐
1024 priate --ping and --ping-restart options to the client. If used
1025 on both server and client, the values pushed from server will
1026 override the client local values.
1027 The timeout argument will be twice as long on the server side.
1029 This ensures that a timeout is detected on client side before
1030 the server side drops the connection.
1031 For example, --keepalive 10 60 expands as follows:
1033 if mode server:
1035 ping 10 # Argument: interval
1036 ping-restart 120 # Argument: timeout*2
1037 push "ping 10" # Argument: interval
1038 push "ping-restart 60" # Argument: timeout
1039 else
1040 ping 10 # Argument: interval
1041 ping-restart 60 # Argument: timeout
1042 --ping-timer-rem
1044 Run the --ping-exit / --ping-restart timer only if we have a
1045 remote address. Use this option if you are starting the daemon
1046 in listen mode (i.e. without an explicit --remote peer), and you
1047 don't want to start clocking timeouts until a remote peer con‐
1048 nects.
1049 --persist-tun
1051 Don't close and reopen TUN/TAP device or run up/down scripts
1052 across SIGUSR1 or --ping-restart restarts.
1053 SIGUSR1 is a restart signal similar to SIGHUP, but which offers
1055 finer-grained control over reset options.
1056 --persist-key
1058 Don't re-read key files across SIGUSR1 or --ping-restart.
1059 This option can be combined with --user nobody to allow restarts
1061 triggered by the SIGUSR1 signal. Normally if you drop root
1062 privileges in OpenVPN, the daemon cannot be restarted since it
1063 will now be unable to re-read protected key files.
1064 This option solves the problem by persisting keys across SIGUSR1
1066 resets, so they don't need to be re-read.
1067 --persist-local-ip
1069 Preserve initially resolved local IP address and port number
1070 across SIGUSR1 or --ping-restart restarts.
1071 --persist-remote-ip
1073 Preserve most recently authenticated remote IP address and port
1074 number across SIGUSR1 or --ping-restart restarts.
1075 --mlock
1077 Disable paging by calling the POSIX mlockall function. Requires
1078 that OpenVPN be initially run as root (though OpenVPN can subse‐
1079 quently downgrade its UID using the --user option).
1080 Using this option ensures that key material and tunnel data are
1082 never written to disk due to virtual memory paging operations
1083 which occur under most modern operating systems. It ensures
1084 that even if an attacker was able to crack the box running Open‐
1085 VPN, he would not be able to scan the system swap file to
1086 recover previously used ephemeral keys, which are used for a
1087 period of time governed by the --reneg options (see below), then
1088 are discarded.
1089 The downside of using --mlock is that it will reduce the amount
1091 of physical memory available to other applications.
1092 --up cmd
1094 Run command cmd after successful TUN/TAP device open (pre --user
1095 UID change).
1096 cmd consists of a path to script (or executable program),
1098 optionally followed by arguments. The path and arguments may be
1099 single- or double-quoted and/or escaped using a backslash, and
1100 should be separated by one or more spaces.
1101 The up command is useful for specifying route commands which
1103 route IP traffic destined for private subnets which exist at the
1104 other end of the VPN connection into the tunnel.
1105 For --dev tun execute as:
1107 cmd tun_dev tun_mtu link_mtu ifconfig_local_ip ifcon‐
1109 fig_remote_ip [ init | restart ]
1110 For --dev tap execute as:
1112 cmd tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask
1114 [ init | restart ]
1115 See the "Environmental Variables" section below for additional
1117 parameters passed as environmental variables.
1118 Note that if cmd includes arguments, all OpenVPN-generated argu‐
1120 ments will be appended to them to build an argument list with
1121 which the executable will be called.
1122 Typically, cmd will run a script to add routes to the tunnel.
1124 Normally the up script is called after the TUN/TAP device is
1126 opened. In this context, the last command line parameter passed
1127 to the script will be init. If the --up-restart option is also
1128 used, the up script will be called for restarts as well. A
1129 restart is considered to be a partial reinitialization of Open‐
1130 VPN where the TUN/TAP instance is preserved (the --persist-tun
1131 option will enable such preservation). A restart can be gener‐
1132 ated by a SIGUSR1 signal, a --ping-restart timeout, or a connec‐
1133 tion reset when the TCP protocol is enabled with the --proto
1134 option. If a restart occurs, and --up-restart has been speci‐
1135 fied, the up script will be called with restart as the last
1136 parameter.
1137 NOTE: on restart, OpenVPN will not pass the full set of environ‐
1139 ment variables to the script. Namely, everything related to
1140 routing and gateways will not be passed, as nothing needs to be
1141 done anyway - all the routing setup is already in place. Addi‐
1142 tionally, the up-restart script will run with the downgraded
1143 UID/GID settings (if configured).
1144 The following standalone example shows how the --up script can
1146 be called in both an initialization and restart context. (NOTE:
1147 for security reasons, don't run the following example unless UDP
1148 port 9999 is blocked by your firewall. Also, the example will
1149 run indefinitely, so you should abort with control-c).
1150 openvpn --dev tun --port 9999 --verb 4 --ping-restart 10 --up
1152 'echo up' --down 'echo down' --persist-tun --up-restart
1153 Note that OpenVPN also provides the --ifconfig option to auto‐
1155 matically ifconfig the TUN device, eliminating the need to
1156 define an --up script, unless you also want to configure routes
1157 in the --up script.
1158 If --ifconfig is also specified, OpenVPN will pass the ifconfig
1160 local and remote endpoints on the command line to the --up
1161 script so that they can be used to configure routes such as:
1162 route add -net 10.0.0.0 netmask 255.255.255.0 gw $5
1164 --up-delay
1166 Delay TUN/TAP open and possible --up script execution until
1167 after TCP/UDP connection establishment with peer.
1168 In --proto udp mode, this option normally requires the use of
1170 --ping to allow connection initiation to be sensed in the
1171 absence of tunnel data, since UDP is a "connectionless" proto‐
1172 col.
1173 On Windows, this option will delay the TAP-Win32 media state
1175 transitioning to "connected" until connection establishment,
1176 i.e. the receipt of the first authenticated packet from the
1177 peer.
1178 --down cmd
1180 Run command cmd after TUN/TAP device close (post --user UID
1181 change and/or --chroot ). cmd consists of a path to script (or
1182 executable program), optionally followed by arguments. The path
1183 and arguments may be single- or double-quoted and/or escaped
1184 using a backslash, and should be separated by one or more spa‐
1185 ces.
1186 Called with the same parameters and environmental variables as
1188 the --up option above.
1189 Note that if you reduce privileges by using --user and/or
1191 --group, your --down script will also run at reduced privilege.
1192 --down-pre
1194 Call --down cmd/script before, rather than after, TUN/TAP close.
1195 --up-restart
1197 Enable the --up and --down scripts to be called for restarts as
1198 well as initial program start. This option is described more
1199 fully above in the --up option documentation.
1200 --setenv name value
1202 Set a custom environmental variable name=value to pass to
1203 script.
1204 --setenv FORWARD_COMPATIBLE 1
1206 Relax config file syntax checking so that unknown directives
1207 will trigger a warning but not a fatal error, on the assumption
1208 that a given unknown directive might be valid in future OpenVPN
1209 versions.
1210 This option should be used with caution, as there are good secu‐
1212 rity reasons for having OpenVPN fail if it detects problems in a
1213 config file. Having said that, there are valid reasons for
1214 wanting new software features to gracefully degrade when encoun‐
1215 tered by older software versions.
1216 It is also possible to tag a single directive so as not to trig‐
1218 ger a fatal error if the directive isn't recognized. To do
1219 this, prepend the following before the directive: setenv opt
1220 Versions prior to OpenVPN 2.3.3 will always ignore options set
1222 with the setenv opt directive.
1223 See also --ignore-unknown-option
1225 --setenv-safe name value
1227 Set a custom environmental variable OPENVPN_name=value to pass
1228 to script.
1229 This directive is designed to be pushed by the server to
1231 clients, and the prepending of "OPENVPN_" to the environmental
1232 variable is a safety precaution to prevent a LD_PRELOAD style
1233 attack from a malicious or compromised server.
1234 --ignore-unknown-option opt1 opt2 opt3 ... optN
1236 When one of options opt1 ... optN is encountered in the configu‐
1237 ration file the configuration file parsing does not fail if this
1238 OpenVPN version does not support the option. Multiple
1239 --ignore-unknown-option options can be given to support a larger
1240 number of options to ignore.
1241 This option should be used with caution, as there are good secu‐
1243 rity reasons for having OpenVPN fail if it detects problems in a
1244 config file. Having said that, there are valid reasons for want‐
1245 ing new software features to gracefully degrade when encountered
1246 by older software versions.
1247 --ignore-unknown-option is available since OpenVPN 2.3.3.
1249 --script-security level
1251 This directive offers policy-level control over OpenVPN's usage
1252 of external programs and scripts. Lower level values are more
1253 restrictive, higher values are more permissive. Settings for
1254 level:
1255 0 -- Strictly no calling of external programs.
1257 1 -- (Default) Only call built-in executables such as ifconfig,
1258 ip, route, or netsh.
1259 2 -- Allow calling of built-in executables and user-defined
1260 scripts.
1261 3 -- Allow passwords to be passed to scripts via environmental
1262 variables (potentially unsafe).
1263 OpenVPN releases before v2.3 also supported a method flag which
1265 indicated how OpenVPN should call external commands and scripts.
1266 This could be either execve or system. As of OpenVPN 2.3, this
1267 flag is no longer accepted. In most *nix environments the
1268 execve() approach has been used without any issues.
1269 Some directives such as --up allow options to be passed to the
1271 external script. In these cases make sure the script name does
1272 not contain any spaces or the configuration parser will choke
1273 because it can't determine where the script name ends and script
1274 options start.
1275 To run scripts in Windows in earlier OpenVPN versions you needed
1277 to either add a full path to the script interpreter which can
1278 parse the script or use the system flag to run these scripts.
1279 As of OpenVPN 2.3 it is now a strict requirement to have full
1280 path to the script interpreter when running non-executables
1281 files. This is not needed for executable files, such as .exe,
1282 .com, .bat or .cmd files. For example, if you have a Visual
1283 Basic script, you must use this syntax now:
1284 --up 'C:\\Windows\\System32\\wscript.exe C:\\Program\ Files\\OpenVPN\\config\\my-up-script.vbs'
1286 Please note the single quote marks and the escaping of the back‐
1288 slashes (\) and the space character.
1289 The reason the support for the system flag was removed is due to
1291 the security implications with shell expansions when executing
1292 scripts via the system() call.
1293 --disable-occ
1295 Don't output a warning message if option inconsistencies are
1296 detected between peers. An example of an option inconsistency
1297 would be where one peer uses --dev tun while the other peer uses
1298 --dev tap.
1299 Use of this option is discouraged, but is provided as a tempo‐
1301 rary fix in situations where a recent version of OpenVPN must
1302 connect to an old version.
1303 --user user
1305 Change the user ID of the OpenVPN process to user after initial‐
1306 ization, dropping privileges in the process. This option is
1307 useful to protect the system in the event that some hostile
1308 party was able to gain control of an OpenVPN session. Though
1309 OpenVPN's security features make this unlikely, it is provided
1310 as a second line of defense.
1311 By setting user to nobody or somebody similarly unprivileged,
1313 the hostile party would be limited in what damage they could
1314 cause. Of course once you take away privileges, you cannot
1315 return them to an OpenVPN session. This means, for example,
1316 that if you want to reset an OpenVPN daemon with a SIGUSR1 sig‐
1317 nal (for example in response to a DHCP reset), you should make
1318 use of one or more of the --persist options to ensure that Open‐
1319 VPN doesn't need to execute any privileged operations in order
1320 to restart (such as re-reading key files or running ifconfig on
1321 the TUN device).
1322 --group group
1324 Similar to the --user option, this option changes the group ID
1325 of the OpenVPN process to group after initialization.
1326 --cd dir
1328 Change directory to dir prior to reading any files such as con‐
1329 figuration files, key files, scripts, etc. dir should be an
1330 absolute path, with a leading "/", and without any references to
1331 the current directory such as "." or "..".
1332 This option is useful when you are running OpenVPN in --daemon
1334 mode, and you want to consolidate all of your OpenVPN control
1335 files in one location.
1336 --chroot dir
1338 Chroot to dir after initialization. --chroot essentially rede‐
1339 fines dir as being the top level directory tree (/). OpenVPN
1340 will therefore be unable to access any files outside this tree.
1341 This can be desirable from a security standpoint.
1342 Since the chroot operation is delayed until after initializa‐
1344 tion, most OpenVPN options that reference files will operate in
1345 a pre-chroot context.
1346 In many cases, the dir parameter can point to an empty direc‐
1348 tory, however complications can result when scripts or restarts
1349 are executed after the chroot operation.
1350 Note: The SSL library will probably need /dev/urandom to be
1352 available inside the chroot directory dir. This is because SSL
1353 libraries occasionally need to collect fresh random. Newer
1354 linux kernels and some BSDs implement a getrandom() or geten‐
1355 tropy() syscall that removes the need for /dev/urandom to be
1356 available.
1357 --setcon context
1359 Apply SELinux context after initialization. This essentially
1360 provides the ability to restrict OpenVPN's rights to only net‐
1361 work I/O operations, thanks to SELinux. This goes further than
1362 --user and --chroot in that those two, while being great secu‐
1363 rity features, unfortunately do not protect against privilege
1364 escalation by exploitation of a vulnerable system call. You can
1365 of course combine all three, but please note that since setcon
1366 requires access to /proc you will have to provide it inside the
1367 chroot directory (e.g. with mount --bind).
1368 Since the setcon operation is delayed until after initializa‐
1370 tion, OpenVPN can be restricted to just network-related system
1371 calls, whereas by applying the context before startup (such as
1372 the OpenVPN one provided in the SELinux Reference Policies) you
1373 will have to allow many things required only during initializa‐
1374 tion.
1375 Like with chroot, complications can result when scripts or
1377 restarts are executed after the setcon operation, which is why
1378 you should really consider using the --persist-key and --per‐
1379 sist-tun options.
1380 --daemon [progname]
1382 Become a daemon after all initialization functions are com‐
1383 pleted. This option will cause all message and error output to
1384 be sent to the syslog file (such as /var/log/messages), except
1385 for the output of scripts and ifconfig commands, which will go
1386 to /dev/null unless otherwise redirected. The syslog redirect‐
1387 ion occurs immediately at the point that --daemon is parsed on
1388 the command line even though the daemonization point occurs
1389 later. If one of the --log options is present, it will
1390 supercede syslog redirection.
1391 The optional progname parameter will cause OpenVPN to report its
1393 program name to the system logger as progname. This can be use‐
1394 ful in linking OpenVPN messages in the syslog file with specific
1395 tunnels. When unspecified, progname defaults to "openvpn".
1396 When OpenVPN is run with the --daemon option, it will try to
1398 delay daemonization until the majority of initialization func‐
1399 tions which are capable of generating fatal errors are complete.
1400 This means that initialization scripts can test the return sta‐
1401 tus of the openvpn command for a fairly reliable indication of
1402 whether the command has correctly initialized and entered the
1403 packet forwarding event loop.
1404 In OpenVPN, the vast majority of errors which occur after ini‐
1406 tialization are non-fatal.
1407 Note: as soon as OpenVPN has daemonized, it can not ask for
1409 usernames, passwords, or key pass phrases anymore. This has
1410 certain consequences, namely that using a password-protected
1411 private key will fail unless the --askpass option is used to
1412 tell OpenVPN to ask for the pass phrase (this requirement is new
1413 in v2.3.7, and is a consequence of calling daemon() before ini‐
1414 tializing the crypto layer).
1415 Further, using --daemon together with --auth-user-pass (entered
1417 on console) and --auth-nocache will fail as soon as key renego‐
1418 tiation (and reauthentication) occurs.
1419 --syslog [progname]
1421 Direct log output to system logger, but do not become a daemon.
1422 See --daemon directive above for description of progname parame‐
1423 ter.
1424 --errors-to-stderr
1426 Output errors to stderr instead of stdout unless log output is
1427 redirected by one of the --log options.
1428 --passtos
1430 Set the TOS field of the tunnel packet to what the payload's TOS
1431 is.
1432 --inetd [wait|nowait] [progname]
1434 Use this option when OpenVPN is being run from the inetd or
1435 xinetd(8) server.
1436 The wait/nowait option must match what is specified in the
1438 inetd/xinetd config file. The nowait mode can only be used with
1439 --proto tcp-server. The default is wait. The nowait mode can
1440 be used to instantiate the OpenVPN daemon as a classic TCP
1441 server, where client connection requests are serviced on a sin‐
1442 gle port number. For additional information on this kind of
1443 configuration, see the OpenVPN FAQ: http://open‐
1444 vpn.net/faq.html#oneport
1445 This option precludes the use of --daemon, --local, or --remote.
1447 Note that this option causes message and error output to be han‐
1448 dled in the same way as the --daemon option. The optional prog‐
1449 name parameter is also handled exactly as in --daemon.
1450 Also note that in wait mode, each OpenVPN tunnel requires a sep‐
1452 arate TCP/UDP port and a separate inetd or xinetd entry. See
1453 the OpenVPN 1.x HOWTO for an example on using OpenVPN with
1454 xinetd: http://openvpn.net/1xhowto.html
1455 --log file
1457 Output logging messages to file, including output to std‐
1458 out/stderr which is generated by called scripts. If file
1459 already exists it will be truncated. This option takes effect
1460 immediately when it is parsed in the command line and will
1461 supercede syslog output if --daemon or --inetd is also speci‐
1462 fied. This option is persistent over the entire course of an
1463 OpenVPN instantiation and will not be reset by SIGHUP, SIGUSR1,
1464 or --ping-restart.
1465 Note that on Windows, when OpenVPN is started as a service, log‐
1467 ging occurs by default without the need to specify this option.
1468 --log-append file
1470 Append logging messages to file. If file does not exist, it
1471 will be created. This option behaves exactly like --log except
1472 that it appends to rather than truncating the log file.
1473 --suppress-timestamps
1475 Avoid writing timestamps to log messages, even when they other‐
1476 wise would be prepended. In particular, this applies to log mes‐
1477 sages sent to stdout.
1478 --machine-readable-output
1480 Always write timestamps and message flags to log messages, even
1481 when they otherwise would not be prefixed. In particular, this
1482 applies to log messages sent to stdout.
1483 --writepid file
1485 Write OpenVPN's main process ID to file.
1486 --nice n
1488 Change process priority after initialization ( n greater than 0
1489 is lower priority, n less than zero is higher priority).
1490 --fast-io
1492 (Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a
1493 call to poll/epoll/select prior to the write operation. The
1494 purpose of such a call would normally be to block until the
1495 device or socket is ready to accept the write. Such blocking is
1496 unnecessary on some platforms which don't support write blocking
1497 on UDP sockets or TUN/TAP devices. In such cases, one can opti‐
1498 mize the event loop by avoiding the poll/epoll/select call,
1499 improving CPU efficiency by 5% to 10%.
1500 This option can only be used on non-Windows systems, when
1502 --proto udp is specified, and when --shaper is NOT specified.
1503 --multihome
1505 Configure a multi-homed UDP server. This option needs to be
1506 used when a server has more than one IP address (e.g. multiple
1507 interfaces, or secondary IP addresses), and is not using --local
1508 to force binding to one specific address only. This option will
1509 add some extra lookups to the packet path to ensure that the UDP
1510 reply packets are always sent from the address that the client
1511 is talking to. This is not supported on all platforms, and it
1512 adds more processing, so it's not enabled by default.
1513 Note: this option is only relevant for UDP servers.
1515 Note 2: if you do an IPv6+IPv4 dual-stack bind on a Linux
1517 machine with multiple IPv4 address, connections to IPv4
1518 addresses will not work right on kernels before 3.15, due to
1519 missing kernel support for the IPv4-mapped case (some distribu‐
1520 tions have ported this to earlier kernel versions, though).
1521 --echo [parms...]
1523 Echo parms to log output.
1524 Designed to be used to send messages to a controlling applica‐
1526 tion which is receiving the OpenVPN log output.
1527 --remap-usr1 signal
1529 Control whether internally or externally generated SIGUSR1 sig‐
1530 nals are remapped to SIGHUP (restart without persisting state)
1531 or SIGTERM (exit).
1532 signal can be set to "SIGHUP" or "SIGTERM". By default, no
1534 remapping occurs.
1535 --verb n
1537 Set output verbosity to n (default=1). Each level shows all
1538 info from the previous levels. Level 3 is recommended if you
1539 want a good summary of what's happening without being swamped by
1540 output.
1541 0 -- No output except fatal errors.
1543 1 to 4 -- Normal usage range.
1544 5 -- Output R and W characters to the console for each packet
1545 read and write, uppercase is used for TCP/UDP packets and lower‐
1546 case is used for TUN/TAP packets.
1547 6 to 11 -- Debug info range (see errlevel.h for additional
1548 information on debug levels).
1549 --status file [n]
1551 Write operational status to file every n seconds.
1552 Status can also be written to the syslog by sending a SIGUSR2
1554 signal.
1555 With multi-client capability enabled on a server, the status
1557 file includes a list of clients and a routing table. The output
1558 format can be controlled by the --status-version option in that
1559 case.
1560 For clients or instances running in point-to-point mode, it will
1562 contain the traffic statistics.
1563 --status-version [n]
1565 Set the status file format version number to n.
1566 This only affects the status file on servers with multi-client
1568 capability enabled.
1569 1 -- traditional format (default). The client list contains the
1571 following fields comma-separated: Common Name, Real Address,
1572 Bytes Received, Bytes Sent, Connected Since.
1573 2 -- a more reliable format for external processing. Compared to
1574 version 1, the client list contains some additional fields: Vir‐
1575 tual Address, Virtual IPv6 Address, Username, Client ID, Peer
1576 ID. Future versions may extend the number of fields.
1577 3 -- identical to 2, but fields are tab-separated.
1578 --mute n
1581 Log at most n consecutive messages in the same category. This
1582 is useful to limit repetitive logging of similar message types.
1583 --compress [algorithm]
1585 Enable a compression algorithm.
1586 The algorithm parameter may be "lzo", "lz4", or empty. LZO and
1588 LZ4 are different compression algorithms, with LZ4 generally
1589 offering the best performance with least CPU usage. For back‐
1590 wards compatibility with OpenVPN versions before v2.4, use "lzo"
1591 (which is identical to the older option "--comp-lzo yes").
1592 If the algorithm parameter is empty, compression will be turned
1594 off, but the packet framing for compression will still be
1595 enabled, allowing a different setting to be pushed later.
1596 Security Considerations
1598 Compression and encryption is a tricky combination. If an
1600 attacker knows or is able to control (parts of) the plaintext of
1601 packets that contain secrets, the attacker might be able to
1602 extract the secret if compression is enabled. See e.g. the
1603 CRIME and BREACH attacks on TLS which also leverage compression
1604 to break encryption. If you are not entirely sure that the
1605 above does not apply to your traffic, you are advised to *not*
1606 enable compression.
1607 --comp-lzo [mode]
1610 DEPRECATED This option will be removed in a future OpenVPN
1611 release. Use the newer --compress instead.
1612 Use LZO compression -- may add up to 1 byte per packet for
1614 incompressible data. mode may be "yes", "no", or "adaptive"
1615 (default).
1616 In a server mode setup, it is possible to selectively turn com‐
1618 pression on or off for individual clients.
1619 First, make sure the client-side config file enables selective
1621 compression by having at least one --comp-lzo directive, such as
1622 --comp-lzo no. This will turn off compression by default, but
1623 allow a future directive push from the server to dynamically
1624 change the on/off/adaptive setting.
1625 Next in a --client-config-dir file, specify the compression set‐
1627 ting for the client, for example:
1628 comp-lzo yes
1630 push "comp-lzo yes"
1631 The first line sets the comp-lzo setting for the server side of
1633 the link, the second sets the client side.
1634 --comp-noadapt
1636 When used in conjunction with --comp-lzo, this option will dis‐
1637 able OpenVPN's adaptive compression algorithm. Normally, adap‐
1638 tive compression is enabled with --comp-lzo.
1639 Adaptive compression tries to optimize the case where you have
1641 compression enabled, but you are sending predominantly incom‐
1642 pressible (or pre-compressed) packets over the tunnel, such as
1643 an FTP or rsync transfer of a large, compressed file. With
1644 adaptive compression, OpenVPN will periodically sample the com‐
1645 pression process to measure its efficiency. If the data being
1646 sent over the tunnel is already compressed, the compression
1647 efficiency will be very low, triggering openvpn to disable com‐
1648 pression for a period of time until the next re-sample test.
1649 --management socket-name unix [pw-file] (recommended)
1651 --management IP port [pw-file]
1652 Enable a management server on a socket-name Unix socket on those
1653 platforms supporting it, or on a designated TCP port.
1654 pw-file , if specified, is a password file where the password
1656 must be on first line. Instead of a filename it can use the
1657 keyword stdin which will prompt the user for a password to use
1658 when OpenVPN is starting.
1659 For unix sockets, the default behaviour is to create a unix
1661 domain socket that may be connected to by any process. Use the
1662 --management-client-user and --management-client-group direc‐
1663 tives to restrict access.
1664 The management interface provides a special mode where the TCP
1666 management link can operate over the tunnel itself. To enable
1667 this mode, set IP to tunnel. Tunnel mode will cause the man‐
1668 agement interface to listen for a TCP connection on the local
1669 VPN address of the TUN/TAP interface.
1670 BEWARE of enabling the management interface over TCP. In these
1672 cases you should ALWAYS make use of pw-file to password protect
1673 the management interface. Any user who can connect to this TCP
1674 IP:port will be able to manage and control (and interfere with)
1675 the OpenVPN process. It is also strongly recommended to set IP
1676 to 127.0.0.1 (localhost) to restrict accessibility of the man‐
1677 agement server to local clients.
1678 While the management port is designed for programmatic control
1680 of OpenVPN by other applications, it is possible to telnet to
1681 the port, using a telnet client in "raw" mode. Once connected,
1682 type "help" for a list of commands.
1683 For detailed documentation on the management interface, see the
1685 management-notes.txt file in the management folder of the Open‐
1686 VPN source distribution.
1687 --management-client
1690 Management interface will connect as a TCP/unix domain client to
1691 IP:port specified by --management rather than listen as a TCP
1692 server or on a unix domain socket.
1693 If the client connection fails to connect or is disconnected, a
1695 SIGTERM signal will be generated causing OpenVPN to quit.
1696 --management-query-passwords
1698 Query management channel for private key password and
1699 --auth-user-pass username/password. Only query the management
1700 channel for inputs which ordinarily would have been queried from
1701 the console.
1702 --management-query-proxy
1704 Query management channel for proxy server information for a spe‐
1705 cific --remote (client-only).
1706 --management-query-remote
1708 Allow management interface to override --remote directives
1709 (client-only).
1710 --management-external-key
1712 Allows usage for external private key file instead of --key
1713 option (client-only).
1714 --management-external-cert certificate-hint
1716 Allows usage for external certificate instead of --cert option
1717 (client-only). certificate-hint is an arbitrary string which is
1718 passed to a management interface client as an argument of
1719 NEED-CERTIFICATE notification. Requires --management-exter‐
1720 nal-key.
1721 --management-forget-disconnect
1723 Make OpenVPN forget passwords when management session discon‐
1724 nects.
1725 This directive does not affect the --http-proxy username/pass‐
1727 word. It is always cached.
1728 --management-hold
1730 Start OpenVPN in a hibernating state, until a client of the man‐
1731 agement interface explicitly starts it with the hold release
1732 command.
1733 --management-signal
1735 Send SIGUSR1 signal to OpenVPN if management session discon‐
1736 nects. This is useful when you wish to disconnect an OpenVPN
1737 session on user logoff. For --management-client this option is
1738 not needed since a disconnect will always generate a SIGTERM.
1739 --management-log-cache n
1741 Cache the most recent n lines of log file history for usage by
1742 the management channel.
1743 --management-up-down
1745 Report tunnel up/down events to management interface.
1746 --management-client-auth
1748 Gives management interface client the responsibility to authen‐
1749 ticate clients after their client certificate has been verified.
1750 See management-notes.txt in OpenVPN distribution for detailed
1751 notes.
1752 --management-client-pf
1754 Management interface clients must specify a packet filter file
1755 for each connecting client. See management-notes.txt in OpenVPN
1756 distribution for detailed notes.
1757 --management-client-user u
1759 When the management interface is listening on a unix domain
1760 socket, only allow connections from user u.
1761 --management-client-group g
1763 When the management interface is listening on a unix domain
1764 socket, only allow connections from group g.
1765 --plugin module-pathname [init-string]
1767 Load plug-in module from the file module-pathname, passing
1768 init-string as an argument to the module initialization func‐
1769 tion. Multiple plugin modules may be loaded into one OpenVPN
1770 process.
1771 The module-pathname argument can be just a filename or a file‐
1773 name with a relative or absolute path. The format of the file‐
1774 name and path defines if the plug-in will be loaded from a
1775 default plug-in directory or outside this directory.
1776 --plugin path Effective directory used
1778 ====================================================
1779 myplug.so DEFAULT_DIR/myplug.so
1780 subdir/myplug.so DEFAULT_DIR/subdir/myplug.so
1781 ./subdir/myplug.so CWD/subdir/myplug.so
1782 /usr/lib/my/plug.so /usr/lib/my/plug.so
1783 DEFAULT_DIR is replaced by the default plug-in directory, which
1785 is configured at the build time of OpenVPN. CWD is the current
1786 directory where OpenVPN was started or the directory OpenVPN
1787 have swithed into via the --cd option before the --plugin
1788 option.
1789 For more information and examples on how to build OpenVPN
1791 plug-in modules, see the README file in the plugin folder of the
1792 OpenVPN source distribution.
1793 If you are using an RPM install of OpenVPN, see /usr/lib64/open‐
1795 vpn/plugin. The documentation is in doc and the actual plugin
1796 modules are in lib.
1797 Multiple plugin modules can be cascaded, and modules can be used
1799 in tandem with scripts. The modules will be called by OpenVPN
1800 in the order that they are declared in the config file. If both
1801 a plugin and script are configured for the same callback, the
1802 script will be called last. If the return code of the mod‐
1803 ule/script controls an authentication function (such as tls-ver‐
1804 ify, auth-user-pass-verify, or client-connect), then every mod‐
1805 ule and script must return success (0) in order for the connec‐
1806 tion to be authenticated.
1807 --keying-material-exporter label len
1809 Save Exported Keying Material [RFC5705] of len bytes (must be
1810 between 16 and 4095 bytes) using label in environment
1811 (exported_keying_material) for use by plugins in OPENVPN_PLUG‐
1812 IN_TLS_FINAL callback.
1813 Note that exporter labels have the potential to collide with
1815 existing PRF labels. In order to prevent this, labels MUST begin
1816 with "EXPORTER".
1817 This option requires OpenSSL 1.0.1 or newer.
1819 Server Mode
1821 Starting with OpenVPN 2.0, a multi-client TCP/UDP server mode is sup‐
1822 ported, and can be enabled with the --mode server option. In server
1823 mode, OpenVPN will listen on a single port for incoming client connec‐
1824 tions. All client connections will be routed through a single tun or
1825 tap interface. This mode is designed for scalability and should be
1826 able to support hundreds or even thousands of clients on sufficiently
1827 fast hardware. SSL/TLS authentication must be used in this mode.
1828 --server network netmask ['nopool']
1830 A helper directive designed to simplify the configuration of
1831 OpenVPN's server mode. This directive will set up an OpenVPN
1832 server which will allocate addresses to clients out of the given
1833 network/netmask. The server itself will take the ".1" address
1834 of the given network for use as the server-side endpoint of the
1835 local TUN/TAP interface.
1836 For example, --server 10.8.0.0 255.255.255.0 expands as follows:
1838 mode server
1840 tls-server
1841 push "topology [topology]"
1842 if dev tun AND (topology == net30 OR topology == p2p):
1844 ifconfig 10.8.0.1 10.8.0.2
1845 if !nopool:
1846 ifconfig-pool 10.8.0.4 10.8.0.251
1847 route 10.8.0.0 255.255.255.0
1848 if client-to-client:
1849 push "route 10.8.0.0 255.255.255.0"
1850 else if topology == net30:
1851 push "route 10.8.0.1"
1852 if dev tap OR (dev tun AND topology == subnet):
1854 ifconfig 10.8.0.1 255.255.255.0
1855 if !nopool:
1856 ifconfig-pool 10.8.0.2 10.8.0.253 255.255.255.0
1857 push "route-gateway 10.8.0.1"
1858 if route-gateway unset:
1859 route-gateway 10.8.0.2
1860 Don't use --server if you are ethernet bridging. Use
1863 --server-bridge instead.
1864 --server-bridge gateway netmask pool-start-IP pool-end-IP
1866 --server-bridge ['nogw']
1868 A helper directive similar to --server which is designed to sim‐
1870 plify the configuration of OpenVPN's server mode in ethernet
1871 bridging configurations.
1872 If --server-bridge is used without any parameters, it will
1874 enable a DHCP-proxy mode, where connecting OpenVPN clients will
1875 receive an IP address for their TAP adapter from the DHCP server
1876 running on the OpenVPN server-side LAN. Note that only clients
1877 that support the binding of a DHCP client with the TAP adapter
1878 (such as Windows) can support this mode. The optional nogw flag
1879 (advanced) indicates that gateway information should not be
1880 pushed to the client.
1881 To configure ethernet bridging, you must first use your OS's
1883 bridging capability to bridge the TAP interface with the ether‐
1884 net NIC interface. For example, on Linux this is done with the
1885 brctl tool, and with Windows XP it is done in the Network Con‐
1886 nections Panel by selecting the ethernet and TAP adapters and
1887 right-clicking on "Bridge Connections".
1888 Next you you must manually set the IP/netmask on the bridge
1890 interface. The gateway and netmask parameters to
1891 --server-bridge can be set to either the IP/netmask of the
1892 bridge interface, or the IP/netmask of the default gate‐
1893 way/router on the bridged subnet.
1894 Finally, set aside a IP range in the bridged subnet, denoted by
1896 pool-start-IP and pool-end-IP, for OpenVPN to allocate to con‐
1897 necting clients.
1898 For example, server-bridge 10.8.0.4 255.255.255.0 10.8.0.128
1900 10.8.0.254 expands as follows:
1901 mode server
1903 tls-server
1904 ifconfig-pool 10.8.0.128 10.8.0.254 255.255.255.0
1906 push "route-gateway 10.8.0.4"
1907 In another example, --server-bridge (without parameters) expands
1909 as follows:
1910 mode server
1912 tls-server
1913 push "route-gateway dhcp"
1915 Or --server-bridge nogw expands as follows:
1917 mode server
1919 tls-server
1920 --push option
1922 Push a config file option back to the client for remote execu‐
1923 tion. Note that option must be enclosed in double quotes ("").
1924 The client must specify --pull in its config file. The set of
1925 options which can be pushed is limited by both feasibility and
1926 security. Some options such as those which would execute
1927 scripts are banned, since they would effectively allow a compro‐
1928 mised server to execute arbitrary code on the client. Other
1929 options such as TLS or MTU parameters cannot be pushed because
1930 the client needs to know them before the connection to the
1931 server can be initiated.
1932 This is a partial list of options which can currently be pushed:
1934 --route, --route-gateway, --route-delay, --redirect-gateway,
1935 --ip-win32, --dhcp-option, --inactive, --ping, --ping-exit,
1936 --ping-restart, --setenv, --auth-token, --persist-key, --per‐
1937 sist-tun, --echo, --comp-lzo, --socket-flags, --sndbuf, --rcvbuf
1938 --push-reset
1940 Don't inherit the global push list for a specific client
1941 instance. Specify this option in a client-specific context such
1942 as with a --client-config-dir configuration file. This option
1943 will ignore --push options at the global config file level.
1944 NOTE: --push-reset is very thorough: it will remove almost all
1946 options from the list of to-be-pushed options. In many cases,
1947 some of these options will need to be re-configured afterwards -
1948 specifically, --topology subnet and --route-gateway will get
1949 lost and this will break client configs in many cases. Thus,
1950 for most purposes, --push-remove is better suited to selectively
1951 remove push options for individual clients.
1952 --push-remove opt
1954 selectively remove all --push options matching "opt" from the
1955 option list for a client. "opt" is matched as a substring
1956 against the whole option string to-be-pushed to the client, so
1957 --push-remove route would remove all --push route ... and
1958 --push route-ipv6 ... statements, while --push-remove
1959 'route-ipv6 2001:' would only remove IPv6 routes for 2001:...
1960 networks.
1961 --push-remove can only be used in a client-specific context,
1963 like in a --client-config-dir file, or --client-connect script
1964 or plugin -- similar to --push-reset, just more selective.
1965 NOTE: to change an option, --push-remove can be used to first
1967 remove the old value, and then add a new --push option with the
1968 new value.
1969 --push-peer-info
1971 Push additional information about the client to server. The
1972 following data is always pushed to the server:
1973 IV_VER=<version> -- the client OpenVPN version
1975 IV_PLAT=[linux|solaris|openbsd|mac|netbsd|freebsd|win] -- the
1977 client OS platform
1978 IV_LZO_STUB=1 -- if client was built with LZO stub capability
1980 IV_LZ4=1 -- if the client supports LZ4 compressions.
1982 IV_PROTO=2 -- if the client supports peer-id floating mechansim
1984 IV_NCP=2 -- negotiable ciphers, client supports --cipher pushed
1986 by the server, a value of 2 or greater indicates client supports
1987 AES-GCM-128 and AES-GCM-256.
1988 IV_GUI_VER=<gui_id> <version> -- the UI version of a UI if one
1990 is running, for example "de.blinkt.openvpn 0.5.47" for the
1991 Android app.
1992 When --push-peer-info is enabled the additional information con‐
1994 sists of the following data:
1995 IV_HWADDR=<mac address> -- the MAC address of clients default
1997 gateway
1998 IV_SSL=<version string> -- the ssl version used by the client,
2000 e.g. "OpenSSL 1.0.2f 28 Jan 2016".
2001 IV_PLAT_VER=x.y - the version of the operating system, e.g. 6.1
2003 for Windows 7.
2004 UV_<name>=<value> -- client environment variables whose names
2006 start with "UV_"
2007 --disable
2009 Disable a particular client (based on the common name) from con‐
2010 necting. Don't use this option to disable a client due to key
2011 or password compromise. Use a CRL (certificate revocation list)
2012 instead (see the --crl-verify option).
2013 This option must be associated with a specific client instance,
2015 which means that it must be specified either in a client
2016 instance config file using --client-config-dir or dynamically
2017 generated using a --client-connect script.
2018 --ifconfig-pool start-IP end-IP [netmask]
2020 Set aside a pool of subnets to be dynamically allocated to con‐
2021 necting clients, similar to a DHCP server. For tun-style tun‐
2022 nels, each client will be given a /30 subnet (for interoperabil‐
2023 ity with Windows clients). For tap-style tunnels, individual
2024 addresses will be allocated, and the optional netmask parameter
2025 will also be pushed to clients.
2026 --ifconfig-pool-persist file [seconds]
2029 Persist/unpersist ifconfig-pool data to file, at seconds inter‐
2030 vals (default=600), as well as on program startup and shutdown.
2031 The goal of this option is to provide a long-term association
2033 between clients (denoted by their common name) and the virtual
2034 IP address assigned to them from the ifconfig-pool. Maintaining
2035 a long-term association is good for clients because it allows
2036 them to effectively use the --persist-tun option.
2037 file is a comma-delimited ASCII file, formatted as <Com‐
2039 mon-Name>,<IP-address>.
2040 If seconds = 0, file will be treated as read-only. This is use‐
2042 ful if you would like to treat file as a configuration file.
2043 Note that the entries in this file are treated by OpenVPN as
2045 suggestions only, based on past associations between a common
2046 name and IP address. They do not guarantee that the given com‐
2047 mon name will always receive the given IP address. If you want
2048 guaranteed assignment, use --ifconfig-push
2049 --ifconfig-pool-linear
2052 DEPRECATED This option will be removed in OpenVPN 2.5
2053 Modifies the --ifconfig-pool directive to allocate individual
2055 TUN interface addresses for clients rather than /30 subnets.
2056 NOTE: This option is incompatible with Windows clients.
2057 This option is deprecated, and should be replaced with --topol‐
2059 ogy p2p which is functionally equivalent.
2060 --ifconfig-push local remote-netmask [alias]
2062 Push virtual IP endpoints for client tunnel, overriding the
2063 --ifconfig-pool dynamic allocation.
2064 The parameters local and remote-netmask are set according to the
2066 --ifconfig directive which you want to execute on the client
2067 machine to configure the remote end of the tunnel. Note that
2068 the parameters local and remote-netmask are from the perspective
2069 of the client, not the server. They may be DNS names rather
2070 than IP addresses, in which case they will be resolved on the
2071 server at the time of client connection.
2072 The optional alias parameter may be used in cases where NAT
2074 causes the client view of its local endpoint to differ from the
2075 server view. In this case local/remote-netmask will refer to
2076 the server view while alias/remote-netmask will refer to the
2077 client view.
2078 This option must be associated with a specific client instance,
2080 which means that it must be specified either in a client
2081 instance config file using --client-config-dir or dynamically
2082 generated using a --client-connect script.
2083 Remember also to include a --route directive in the main OpenVPN
2085 config file which encloses local, so that the kernel will know
2086 to route it to the server's TUN/TAP interface.
2087 OpenVPN's internal client IP address selection algorithm works
2089 as follows:
2090 1 -- Use --client-connect script generated file for static IP
2092 (first choice).
2093 2 -- Use --client-config-dir file for static IP (next choice).
2094 3 -- Use --ifconfig-pool allocation for dynamic IP (last
2095 choice).
2096 --iroute network [netmask]
2098 Generate an internal route to a specific client. The netmask
2099 parameter, if omitted, defaults to 255.255.255.255.
2100 This directive can be used to route a fixed subnet from the
2102 server to a particular client, regardless of where the client is
2103 connecting from. Remember that you must also add the route to
2104 the system routing table as well (such as by using the --route
2105 directive). The reason why two routes are needed is that the
2106 --route directive routes the packet from the kernel to OpenVPN.
2107 Once in OpenVPN, the --iroute directive routes to the specific
2108 client.
2109 This option must be specified either in a client instance config
2111 file using --client-config-dir or dynamically generated using a
2112 --client-connect script.
2113 The --iroute directive also has an important interaction with
2115 --push "route ...". --iroute essentially defines a subnet which
2116 is owned by a particular client (we will call this client A).
2117 If you would like other clients to be able to reach A's subnet,
2118 you can use --push "route ..." together with --client-to-client
2119 to effect this. In order for all clients to see A's subnet,
2120 OpenVPN must push this route to all clients EXCEPT for A, since
2121 the subnet is already owned by A. OpenVPN accomplishes this by
2122 not not pushing a route to a client if it matches one of the
2123 client's iroutes.
2124 --client-to-client
2126 Because the OpenVPN server mode handles multiple clients through
2127 a single tun or tap interface, it is effectively a router. The
2128 --client-to-client flag tells OpenVPN to internally route
2129 client-to-client traffic rather than pushing all client-origi‐
2130 nating traffic to the TUN/TAP interface.
2131 When this option is used, each client will "see" the other
2133 clients which are currently connected. Otherwise, each client
2134 will only see the server. Don't use this option if you want to
2135 firewall tunnel traffic using custom, per-client rules.
2136 --duplicate-cn
2138 Allow multiple clients with the same common name to concurrently
2139 connect. In the absence of this option, OpenVPN will disconnect
2140 a client instance upon connection of a new client having the
2141 same common name.
2142 --client-connect cmd
2144 Run command cmd on client connection.
2145 cmd consists of a path to script (or executable program),
2147 optionally followed by arguments. The path and arguments may be
2148 single- or double-quoted and/or escaped using a backslash, and
2149 should be separated by one or more spaces.
2150 The command is passed the common name and IP address of the
2152 just-authenticated client as environmental variables (see envi‐
2153 ronmental variable section below). The command is also passed
2154 the pathname of a freshly created temporary file as the last
2155 argument (after any arguments specified in cmd ), to be used by
2156 the command to pass dynamically generated config file directives
2157 back to OpenVPN.
2158 If the script wants to generate a dynamic config file to be
2160 applied on the server when the client connects, it should write
2161 it to the file named by the last argument.
2162 See the --client-config-dir option below for options which can
2164 be legally used in a dynamically generated config file.
2165 Note that the return value of script is significant. If script
2167 returns a non-zero error status, it will cause the client to be
2168 disconnected.
2169 --client-disconnect cmd
2171 Like --client-connect but called on client instance shutdown.
2172 Will not be called unless the --client-connect script and plug‐
2173 ins (if defined) were previously called on this instance with
2174 successful (0) status returns.
2175 The exception to this rule is if the --client-disconnect command
2177 or plugins are cascaded, and at least one client-connect func‐
2178 tion succeeded, then ALL of the client-disconnect functions for
2179 scripts and plugins will be called on client instance object
2180 deletion, even in cases where some of the related client-connect
2181 functions returned an error status.
2182 The --client-disconnect command is not passed any extra argu‐
2184 ments (only those arguments specified in cmd if any).
2185 --client-config-dir dir
2187 Specify a directory dir for custom client config files. After a
2188 connecting client has been authenticated, OpenVPN will look in
2189 this directory for a file having the same name as the client's
2190 X509 common name. If a matching file exists, it will be opened
2191 and parsed for client-specific configuration options. If no
2192 matching file is found, OpenVPN will instead try to open and
2193 parse a default file called "DEFAULT", which may be provided but
2194 is not required. Note that the configuration files must be read‐
2195 able by the OpenVPN process after it has dropped it's root priv‐
2196 ileges.
2197 This file can specify a fixed IP address for a given client
2199 using --ifconfig-push, as well as fixed subnets owned by the
2200 client using --iroute.
2201 One of the useful properties of this option is that it allows
2203 client configuration files to be conveniently created, edited,
2204 or removed while the server is live, without needing to restart
2205 the server.
2206 The following options are legal in a client-specific context:
2208 --push, --push-reset, --push-remove, --iroute, --ifconfig-push,
2209 and --config.
2210 --ccd-exclusive
2212 Require, as a condition of authentication, that a connecting
2213 client has a --client-config-dir file.
2214 --tmp-dir dir
2216 Specify a directory dir for temporary files. This directory
2217 will be used by openvpn processes and script to communicate tem‐
2218 porary data with openvpn main process. Note that the directory
2219 must be writable by the OpenVPN process after it has dropped
2220 it's root privileges.
2221 This directory will be used by in the following cases:
2223 * --client-connect scripts to dynamically generate client-spe‐
2225 cific configuration files.
2226 * OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY plugin hook to return
2228 success/failure via auth_control_file when using deferred auth
2229 method
2230 * OPENVPN_PLUGIN_ENABLE_PF plugin hook to pass filtering rules
2232 via pf_file
2233 --hash-size r v
2235 Set the size of the real address hash table to r and the virtual
2236 address table to v. By default, both tables are sized at 256
2237 buckets.
2238 --bcast-buffers n
2240 Allocate n buffers for broadcast datagrams (default=256).
2241 --tcp-queue-limit n
2243 Maximum number of output packets queued before TCP (default=64).
2244 When OpenVPN is tunneling data from a TUN/TAP device to a remote
2246 client over a TCP connection, it is possible that the TUN/TAP
2247 device might produce data at a faster rate than the TCP connec‐
2248 tion can support. When the number of output packets queued
2249 before sending to the TCP socket reaches this limit for a given
2250 client connection, OpenVPN will start to drop outgoing packets
2251 directed at this client.
2252 --tcp-nodelay
2254 This macro sets the TCP_NODELAY socket flag on the server as
2255 well as pushes it to connecting clients. The TCP_NODELAY flag
2256 disables the Nagle algorithm on TCP sockets causing packets to
2257 be transmitted immediately with low latency, rather than waiting
2258 a short period of time in order to aggregate several packets
2259 into a larger containing packet. In VPN applications over TCP,
2260 TCP_NODELAY is generally a good latency optimization.
2261 The macro expands as follows:
2263 if mode server:
2265 socket-flags TCP_NODELAY
2266 push "socket-flags TCP_NODELAY"
2267 --max-clients n
2269 Limit server to a maximum of n concurrent clients.
2270 --max-routes-per-client n
2272 Allow a maximum of n internal routes per client (default=256).
2273 This is designed to help contain DoS attacks where an authenti‐
2274 cated client floods the server with packets appearing to come
2275 from many unique MAC addresses, forcing the server to deplete
2276 virtual memory as its internal routing table expands. This
2277 directive can be used in a --client-config-dir file or auto-gen‐
2278 erated by a --client-connect script to override the global value
2279 for a particular client.
2280 Note that this directive affects OpenVPN's internal routing ta‐
2282 ble, not the kernel routing table.
2283 --stale-routes-check n [t]
2285 Remove routes haven't had activity for n seconds (i.e. the age‐
2286 ing time).
2287 This check is ran every t seconds (i.e. check interval).
2289 If t is not present it defaults to n
2291 This option helps to keep the dynamic routing table small. See
2293 also --max-routes-per-client
2294 --connect-freq n sec
2296 Allow a maximum of n new connections per sec seconds from
2297 clients. This is designed to contain DoS attacks which flood
2298 the server with connection requests using certificates which
2299 will ultimately fail to authenticate.
2300 This is an imperfect solution however, because in a real DoS
2302 scenario, legitimate connections might also be refused.
2303 For the best protection against DoS attacks in server mode, use
2305 --proto udp and either --tls-auth or --tls-crypt.
2306 --learn-address cmd
2308 Run command cmd to validate client virtual addresses or routes.
2309 cmd consists of a path to script (or executable program),
2311 optionally followed by arguments. The path and arguments may be
2312 single- or double-quoted and/or escaped using a backslash, and
2313 should be separated by one or more spaces.
2314 Three arguments will be appended to any arguments in cmd as fol‐
2316 lows:
2317 [1] operation -- "add", "update", or "delete" based on whether
2319 or not the address is being added to, modified, or deleted from
2320 OpenVPN's internal routing table.
2321 [2] address -- The address being learned or unlearned. This can
2322 be an IPv4 address such as "198.162.10.14", an IPv4 subnet such
2323 as "198.162.10.0/24", or an ethernet MAC address (when --dev tap
2324 is being used) such as "00:FF:01:02:03:04".
2325 [3] common name -- The common name on the certificate associated
2326 with the client linked to this address. Only present for "add"
2327 or "update" operations, not "delete".
2328 On "add" or "update" methods, if the script returns a failure
2330 code (non-zero), OpenVPN will reject the address and will not
2331 modify its internal routing table.
2332 Normally, the cmd script will use the information provided above
2334 to set appropriate firewall entries on the VPN TUN/TAP inter‐
2335 face. Since OpenVPN provides the association between virtual IP
2336 or MAC address and the client's authenticated common name, it
2337 allows a user-defined script to configure firewall access poli‐
2338 cies with regard to the client's high-level common name, rather
2339 than the low level client virtual addresses.
2340 --auth-user-pass-verify cmd method
2342 Require the client to provide a username/password (possibly in
2343 addition to a client certificate) for authentication.
2344 OpenVPN will run command cmd to validate the username/password
2346 provided by the client.
2347 cmd consists of a path to script (or executable program),
2349 optionally followed by arguments. The path and arguments may be
2350 single- or double-quoted and/or escaped using a backslash, and
2351 should be separated by one or more spaces.
2352 If method is set to "via-env", OpenVPN will call script with the
2354 environmental variables username and password set to the user‐
2355 name/password strings provided by the client. Be aware that
2356 this method is insecure on some platforms which make the envi‐
2357 ronment of a process publicly visible to other unprivileged pro‐
2358 cesses.
2359 If method is set to "via-file", OpenVPN will write the username
2361 and password to the first two lines of a temporary file. The
2362 filename will be passed as an argument to script, and the file
2363 will be automatically deleted by OpenVPN after the script
2364 returns. The location of the temporary file is controlled by
2365 the --tmp-dir option, and will default to the current directory
2366 if unspecified. For security, consider setting --tmp-dir to a
2367 volatile storage medium such as /dev/shm (if available) to pre‐
2368 vent the username/password file from touching the hard drive.
2369 The script should examine the username and password, returning a
2371 success exit code (0) if the client's authentication request is
2372 to be accepted, or a failure code (1) to reject the client.
2373 This directive is designed to enable a plugin-style interface
2375 for extending OpenVPN's authentication capabilities.
2376 To protect against a client passing a maliciously formed user‐
2378 name or password string, the username string must consist only
2379 of these characters: alphanumeric, underbar ('_'), dash ('-'),
2380 dot ('.'), or at ('@'). The password string can consist of any
2381 printable characters except for CR or LF. Any illegal charac‐
2382 ters in either the username or password string will be converted
2383 to underbar ('_').
2384 Care must be taken by any user-defined scripts to avoid creating
2386 a security vulnerability in the way that these strings are han‐
2387 dled. Never use these strings in such a way that they might be
2388 escaped or evaluated by a shell interpreter.
2389 For a sample script that performs PAM authentication, see sam‐
2391 ple-scripts/auth-pam.pl in the OpenVPN source distribution.
2392 --auth-gen-token [lifetime]
2394 After successful user/password authentication, the OpenVPN
2395 server will with this option generate a temporary authentication
2396 token and push that to client. On the following renegotiations,
2397 the OpenVPN client will pass this token instead of the users
2398 password. On the server side the server will do the token
2399 authentication internally and it will NOT do any additional
2400 authentications against configured external user/password
2401 authentication mechanisms.
2402 The lifetime argument defines how long the generated token is
2404 valid. The lifetime is defined in seconds. If lifetime is not
2405 set or it is set to 0, the token will never expire.
2406 This feature is useful for environments which is configured to
2408 use One Time Passwords (OTP) as part of the user/password
2409 authentications and that authentication mechanism does not
2410 implement any auth-token support.
2411 --opt-verify
2413 Clients that connect with options that are incompatible with
2414 those of the server will be disconnected.
2415 Options that will be compared for compatibility include
2417 dev-type, link-mtu, tun-mtu, proto, ifconfig, comp-lzo, frag‐
2418 ment, keydir, cipher, auth, keysize, secret, no-replay, no-iv,
2419 tls-auth, key-method, tls-server, and tls-client.
2420 This option requires that --disable-occ NOT be used.
2422 --auth-user-pass-optional
2424 Allow connections by clients that do not specify a user‐
2425 name/password. Normally, when --auth-user-pass-verify or --man‐
2426 agement-client-auth is specified (or an authentication plugin
2427 module), the OpenVPN server daemon will require connecting
2428 clients to specify a username and password. This option makes
2429 the submission of a username/password by clients optional, pass‐
2430 ing the responsibility to the user-defined authentication mod‐
2431 ule/script to accept or deny the client based on other factors
2432 (such as the setting of X509 certificate fields). When this
2433 option is used, and a connecting client does not submit a user‐
2434 name/password, the user-defined authentication module/script
2435 will see the username and password as being set to empty strings
2436 (""). The authentication module/script MUST have logic to
2437 detect this condition and respond accordingly.
2438 --client-cert-not-required
2440 DEPRECATED This option will be removed in OpenVPN 2.5
2441 Don't require client certificate, client will authenticate using
2443 username/password only. Be aware that using this directive is
2444 less secure than requiring certificates from all clients.
2445 Please note: This is replaced by --verify-client-cert which
2447 allows for more flexibility. The option --verify-client-cert
2448 none is functionally equivalent to --client-cert-not-required
2449 --verify-client-cert none|optional|require
2452 Specify whether the client is required to supply a valid cer‐
2453 tificate.
2454 Possible options are
2456 none : a client certificate is not required. the client need to
2458 authenticate using username/password only. Be aware that using
2459 this directive is less secure than requiring certificates from
2460 all clients.
2461 If you use this directive, the entire responsibility of authen‐
2463 tication will rest on your --auth-user-pass-verify script, so
2464 keep in mind that bugs in your script could potentially compro‐
2465 mise the security of your VPN.
2466 --verify-client-cert none is functionally equivalent to
2468 --client-cert-not-required.
2469 optional : a client may present a certificate but it is not
2471 required to do so. When using this directive, you should also
2472 use a --auth-user-pass-verify script to ensure that clients are
2473 authenticated using a certificate, a username and password, or
2474 possibly even both.
2475 Again, the entire responsibility of authentication will rest on
2477 your --auth-user-pass-verify script, so keep in mind that bugs
2478 in your script could potentially compromise the security of your
2479 VPN.
2480 require : this is the default option. A client is required to
2482 present a certificate, otherwise VPN access is refused.
2483 If you don't use this directive (or use --verify-client-cert
2485 require ) but you also specify an --auth-user-pass-verify
2486 script, then OpenVPN will perform double authentication. The
2487 client certificate verification AND the --auth-user-pass-verify
2488 script will need to succeed in order for a client to be authen‐
2489 ticated and accepted onto the VPN.
2490 --username-as-common-name
2492 For --auth-user-pass-verify authentication, use the authenti‐
2493 cated username as the common name, rather than the common name
2494 from the client cert.
2495 --compat-names [no-remapping]
2497 DEPRECATED This option will be removed in OpenVPN 2.5
2498 Until OpenVPN v2.3 the format of the X.509 Subject fields was
2500 formatted like this:
2501 /C=US/L=Somewhere/CN=John Doe/emailAddress=john@example.com
2503 In addition the old behaviour was to remap any character other
2505 than alphanumeric, underscore ('_'), dash ('-'), dot ('.'), and
2506 slash ('/') to underscore ('_'). The X.509 Subject string as
2507 returned by the tls_id environmental variable, could addition‐
2508 ally contain colon (':') or equal ('=').
2509 When using the --compat-names option, this old formatting and
2511 remapping will be re-enabled again. This is purely implemented
2512 for compatibility reasons when using older plug-ins or scripts
2513 which does not handle the new formatting or UTF-8 characters.
2514 In OpenVPN 2.3 the formatting of these fields changed into a
2516 more standardised format. It now looks like:
2517 C=US, L=Somewhere, CN=John Doe, emailAddress=john@example.com
2519 The new default format in OpenVPN 2.3 also does not do the char‐
2521 acter remapping which happened earlier. This new format enables
2522 proper support for UTF-8 characters in the usernames, X.509 Sub‐
2523 ject fields and Common Name variables and it complies to the RFC
2524 2253, UTF-8 String Representation of Distinguished Names.
2525 The no-remapping mode flag can be used with the --compat-names
2527 option to be compatible with the now deprecated --no-name-remap‐
2528 ping option. It is only available at the server. When this mode
2529 flag is used, the Common Name, Subject, and username strings are
2530 allowed to include any printable character including space, but
2531 excluding control characters such as tab, newline, and car‐
2532 riage-return. no-remapping is only available on the server side.
2533 Please note: This option is immediately deprecated. It is only
2535 implemented to make the transition to the new formatting less
2536 intrusive. It will be removed in OpenVPN 2.5. So please update
2537 your scripts/plug-ins where necessary.
2538 --no-name-remapping
2540 DEPRECATED This option will be removed in OpenVPN 2.5
2541 The --no-name-remapping option is an alias for --com‐
2543 pat-names no-remapping. It ensures compatibility with server
2544 configurations using the --no-name-remapping option.
2545 Please note: This option is now deprecated. It will be removed
2547 in OpenVPN 2.5. So please make sure you support the new X.509
2548 name formatting described with the --compat-names option as soon
2549 as possible.
2550 --port-share host port [dir]
2552 When run in TCP server mode, share the OpenVPN port with another
2553 application, such as an HTTPS server. If OpenVPN senses a con‐
2554 nection to its port which is using a non-OpenVPN protocol, it
2555 will proxy the connection to the server at host:port. Currently
2556 only designed to work with HTTP/HTTPS, though it would be theo‐
2557 retically possible to extend to other protocols such as ssh.
2558 dir specifies an optional directory where a temporary file with
2560 name N containing content C will be dynamically generated for
2561 each proxy connection, where N is the source IP:port of the
2562 client connection and C is the source IP:port of the connection
2563 to the proxy receiver. This directory can be used as a dictio‐
2564 nary by the proxy receiver to determine the origin of the con‐
2565 nection. Each generated file will be automatically deleted when
2566 the proxied connection is torn down.
2567 Not implemented on Windows.
2569 Client Mode
2571 Use client mode when connecting to an OpenVPN server which has
2572 --server, --server-bridge, or --mode server in it's configuration.
2573 --client
2575 A helper directive designed to simplify the configuration of
2576 OpenVPN's client mode. This directive is equivalent to:
2577 pull
2579 tls-client
2580 --pull This option must be used on a client which is connecting to a
2582 multi-client server. It indicates to OpenVPN that it should
2583 accept options pushed by the server, provided they are part of
2584 the legal set of pushable options (note that the --pull option
2585 is implied by --client ).
2586 In particular, --pull allows the server to push routes to the
2588 client, so you should not use --pull or --client in situations
2589 where you don't trust the server to have control over the
2590 client's routing table.
2591 --pull-filter accept|ignore|reject text
2593 Filter options received from the server if the option starts
2594 with text. Runs on client. The action flag accept allows the
2595 option, ignore removes it and reject flags an error and triggers
2596 a SIGUSR1 restart. The filters may be specified multiple times,
2597 and each filter is applied in the order it is specified. The
2598 filtering of each option stops as soon as a match is found.
2599 Unmatched options are accepted by default.
2600 Prefix comparison is used to match text against the received
2602 option so that
2603 --pull-filter ignore "route"
2605 would remove all pushed options starting with route which would
2607 include, for example, route-gateway. Enclose text in quotes to
2608 embed spaces.
2609 --pull-filter accept "route 192.168.1."
2611 --pull-filter ignore "route "
2612 would remove all routes that do not start with 192.168.1.
2614 This option may be used only on clients. Note that reject may
2616 result in a repeated cycle of failure and reconnect, unless mul‐
2617 tiple remotes are specified and connection to the next remote
2618 succeeds. To silently ignore an option pushed by the server, use
2619 ignore.
2620 --auth-user-pass [up]
2622 Authenticate with server using username/password. up is a file
2623 containing username/password on 2 lines. If the password line is
2624 missing, OpenVPN will prompt for one.
2625 If up is omitted, username/password will be prompted from the
2627 console.
2628 The server configuration must specify an --auth-user-pass-verify
2630 script to verify the username/password provided by the client.
2631 --auth-retry type
2633 Controls how OpenVPN responds to username/password verification
2634 errors such as the client-side response to an AUTH_FAILED mes‐
2635 sage from the server or verification failure of the private key
2636 password.
2637 Normally used to prevent auth errors from being fatal on the
2639 client side, and to permit username/password requeries in case
2640 of error.
2641 An AUTH_FAILED message is generated by the server if the client
2643 fails --auth-user-pass authentication, or if the server-side
2644 --client-connect script returns an error status when the client
2645 tries to connect.
2646 type can be one of:
2648 none -- Client will exit with a fatal error (this is the
2650 default).
2651 nointeract -- Client will retry the connection without requery‐
2652 ing for an --auth-user-pass username/password. Use this option
2653 for unattended clients.
2654 interact -- Client will requery for an --auth-user-pass user‐
2655 name/password and/or private key password before attempting a
2656 reconnection.
2657 Note that while this option cannot be pushed, it can be con‐
2659 trolled from the management interface.
2660 --static-challenge t e
2662 Enable static challenge/response protocol using challenge text
2663 t, with echo flag given by e (0|1).
2664 The echo flag indicates whether or not the user's response to
2666 the challenge should be echoed.
2667 See management-notes.txt in the OpenVPN distribution for a
2669 description of the OpenVPN challenge/response protocol.
2670 --server-poll-timeout n, --connect-timeout n
2672 When connecting to a remote server do not wait for more than n
2673 seconds waiting for a response before trying the next server.
2674 The default value is 120s. This timeout includes proxy and TCP
2675 connect timeouts.
2676 --explicit-exit-notify [n]
2678 In UDP client mode or point-to-point mode, send server/peer an
2679 exit notification if tunnel is restarted or OpenVPN process is
2680 exited. In client mode, on exit/restart, this option will tell
2681 the server to immediately close its client instance object
2682 rather than waiting for a timeout. The n parameter (default=1)
2683 controls the maximum number of attempts that the client will try
2684 to resend the exit notification message.
2685 In UDP server mode, send RESTART control channel command to con‐
2687 nected clients. The n parameter (default=1) controls client
2688 behavior. With n = 1 client will attempt to reconnect to the
2689 same server, with n = 2 client will advance to the next server.
2690 OpenVPN will not send any exit notifications unless this option
2692 is enabled.
2693 --allow-recursive-routing
2695 When this option is set, OpenVPN will not drop incoming tun
2696 packets with same destination as host.
2697 Data Channel Encryption Options:
2699 These options are meaningful for both Static & TLS-negotiated key modes
2700 (must be compatible between peers).
2701 --secret file [direction]
2703 Enable Static Key encryption mode (non-TLS). Use pre-shared
2704 secret file which was generated with --genkey.
2705 The optional direction parameter enables the use of 4 distinct
2707 keys (HMAC-send, cipher-encrypt, HMAC-receive, cipher-decrypt),
2708 so that each data flow direction has a different set of HMAC and
2709 cipher keys. This has a number of desirable security properties
2710 including eliminating certain kinds of DoS and message replay
2711 attacks.
2712 When the direction parameter is omitted, 2 keys are used bidi‐
2714 rectionally, one for HMAC and the other for encryption/decryp‐
2715 tion.
2716 The direction parameter should always be complementary on either
2718 side of the connection, i.e. one side should use "0" and the
2719 other should use "1", or both sides should omit it altogether.
2720 The direction parameter requires that file contains a 2048 bit
2722 key. While pre-1.5 versions of OpenVPN generate 1024 bit key
2723 files, any version of OpenVPN which supports the direction
2724 parameter, will also support 2048 bit key file generation using
2725 the --genkey option.
2726 Static key encryption mode has certain advantages, the primary
2728 being ease of configuration.
2729 There are no certificates or certificate authorities or compli‐
2731 cated negotiation handshakes and protocols. The only require‐
2732 ment is that you have a pre-existing secure channel with your
2733 peer (such as ssh ) to initially copy the key. This require‐
2734 ment, along with the fact that your key never changes unless you
2735 manually generate a new one, makes it somewhat less secure than
2736 TLS mode (see below). If an attacker manages to steal your key,
2737 everything that was ever encrypted with it is compromised. Con‐
2738 trast that to the perfect forward secrecy features of TLS mode
2739 (using Diffie Hellman key exchange), where even if an attacker
2740 was able to steal your private key, he would gain no information
2741 to help him decrypt past sessions.
2742 Another advantageous aspect of Static Key encryption mode is
2744 that it is a handshake-free protocol without any distinguishing
2745 signature or feature (such as a header or protocol handshake
2746 sequence) that would mark the ciphertext packets as being gener‐
2747 ated by OpenVPN. Anyone eavesdropping on the wire would see
2748 nothing but random-looking data.
2749 --key-direction
2751 Alternative way of specifying the optional direction parameter
2752 for the --tls-auth and --secret options. Useful when using
2753 inline files (See section on inline files).
2754 --auth alg
2756 Authenticate data channel packets and (if enabled) tls-auth con‐
2757 trol channel packets with HMAC using message digest algorithm
2758 alg. (The default is SHA1 ). HMAC is a commonly used message
2759 authentication algorithm (MAC) that uses a data string, a secure
2760 hash algorithm, and a key, to produce a digital signature.
2761 The OpenVPN data channel protocol uses encrypt-then-mac (i.e.
2763 first encrypt a packet, then HMAC the resulting ciphertext),
2764 which prevents padding oracle attacks.
2765 If an AEAD cipher mode (e.g. GCM) is chosen, the specified
2767 --auth algorithm is ignored for the data channel, and the
2768 authentication method of the AEAD cipher is used instead. Note
2769 that alg still specifies the digest used for tls-auth.
2770 In static-key encryption mode, the HMAC key is included in the
2772 key file generated by --genkey. In TLS mode, the HMAC key is
2773 dynamically generated and shared between peers via the TLS con‐
2774 trol channel. If OpenVPN receives a packet with a bad HMAC it
2775 will drop the packet. HMAC usually adds 16 or 20 bytes per
2776 packet. Set alg=none to disable authentication.
2777 For more information on HMAC see
2779 http://www.cs.ucsd.edu/users/mihir/papers/hmac.html
2780 --cipher alg
2782 Encrypt data channel packets with cipher algorithm alg.
2783 The default is BF-CBC, an abbreviation for Blowfish in Cipher
2785 Block Chaining mode. When cipher negotiation (NCP) is allowed,
2786 OpenVPN 2.4 and newer on both client and server side will auto‐
2787 matically upgrade to AES-256-GCM. See --ncp-ciphers and
2788 --ncp-disable for more details on NCP.
2789 Using BF-CBC is no longer recommended, because of its 64-bit
2791 block size. This small block size allows attacks based on col‐
2792 lisions, as demonstrated by SWEET32. See https://commu‐
2793 nity.openvpn.net/openvpn/wiki/SWEET32 for details. Due to this,
2794 support for BF-CBC, DES, CAST5, IDEA and RC2 ciphers will be
2795 removed in OpenVPN 2.6.
2796 To see other ciphers that are available with OpenVPN, use the
2798 --show-ciphers option.
2799 Set alg=none to disable encryption.
2801 --ncp-ciphers cipher_list
2804 Restrict the allowed ciphers to be negotiated to the ciphers in
2805 cipher_list. cipher_list is a colon-separated list of ciphers,
2806 and defaults to "AES-256-GCM:AES-128-GCM".
2807 For servers, the first cipher from cipher_list will be pushed to
2809 clients that support cipher negotiation.
2810 Cipher negotiation is enabled in client-server mode only. I.e.
2812 if --mode is set to 'server' (server-side, implied by setting
2813 --server ), or if --pull is specified (client-side, implied by
2814 setting --client).
2815 If both peers support and do not disable NCP, the negotiated
2817 cipher will override the cipher specified by --cipher.
2818 Additionally, to allow for more smooth transition, if NCP is
2820 enabled, OpenVPN will inherit the cipher of the peer if that
2821 cipher is different from the local --cipher setting, but the
2822 peer cipher is one of the ciphers specified in --ncp-ciphers.
2823 E.g. a non-NCP client (<=v2.3, or with --ncp-disabled set) con‐
2824 necting to a NCP server (v2.4+) with "--cipher BF-CBC" and
2825 "--ncp-ciphers AES-256-GCM:AES-256-CBC" set can either specify
2826 "--cipher BF-CBC" or "--cipher AES-256-CBC" and both will work.
2827 This list is restricted to be 127 chars long after conversion to
2829 OpenVPN ciphers.
2830 --ncp-disable
2832 Disable "negotiable crypto parameters". This completely dis‐
2833 ables cipher negotiation.
2834 --keysize n
2836 DEPRECATED This option will be removed in OpenVPN 2.6.
2837 Size of cipher key in bits (optional). If unspecified, defaults
2839 to cipher-specific default. The --show-ciphers option (see
2840 below) shows all available OpenSSL ciphers, their default key
2841 sizes, and whether the key size can be changed. Use care in
2842 changing a cipher's default key size. Many ciphers have not
2843 been extensively cryptanalyzed with non-standard key lengths,
2844 and a larger key may offer no real guarantee of greater secu‐
2845 rity, or may even reduce security.
2846 --prng alg [nsl]
2848 (Advanced) For PRNG (Pseudo-random number generator), use digest
2849 algorithm alg (default=sha1), and set nsl (default=16) to the
2850 size in bytes of the nonce secret length (between 16 and 64).
2851 Set alg=none to disable the PRNG and use the OpenSSL RAND_bytes
2853 function instead for all of OpenVPN's pseudo-random number
2854 needs.
2855 --engine [engine-name]
2857 Enable OpenSSL hardware-based crypto engine functionality.
2858 If engine-name is specified, use a specific crypto engine. Use
2860 the --show-engines standalone option to list the crypto engines
2861 which are supported by OpenSSL.
2862 --no-replay
2864 DEPRECATED This option will be removed in OpenVPN 2.5.
2865 (Advanced) Disable OpenVPN's protection against replay attacks.
2867 Don't use this option unless you are prepared to make a tradeoff
2868 of greater efficiency in exchange for less security.
2869 OpenVPN provides datagram replay protection by default.
2871 Replay protection is accomplished by tagging each outgoing data‐
2873 gram with an identifier that is guaranteed to be unique for the
2874 key being used. The peer that receives the datagram will check
2875 for the uniqueness of the identifier. If the identifier was
2876 already received in a previous datagram, OpenVPN will drop the
2877 packet. Replay protection is important to defeat attacks such
2878 as a SYN flood attack, where the attacker listens in the wire,
2879 intercepts a TCP SYN packet (identifying it by the context in
2880 which it occurs in relation to other packets), then floods the
2881 receiving peer with copies of this packet.
2882 OpenVPN's replay protection is implemented in slightly different
2884 ways, depending on the key management mode you have selected.
2885 In Static Key mode or when using an CFB or OFB mode cipher,
2887 OpenVPN uses a 64 bit unique identifier that combines a time
2888 stamp with an incrementing sequence number.
2889 When using TLS mode for key exchange and a CBC cipher mode,
2891 OpenVPN uses only a 32 bit sequence number without a time stamp,
2892 since OpenVPN can guarantee the uniqueness of this value for
2893 each key. As in IPSec, if the sequence number is close to wrap‐
2894 ping back to zero, OpenVPN will trigger a new key exchange.
2895 To check for replays, OpenVPN uses the sliding window algorithm
2897 used by IPSec.
2898 --replay-window n [t]
2900 Use a replay protection sliding-window of size n and a time win‐
2901 dow of t seconds.
2902 By default n is 64 (the IPSec default) and t is 15 seconds.
2904 This option is only relevant in UDP mode, i.e. when either
2906 --proto udp is specified, or no --proto option is specified.
2907 When OpenVPN tunnels IP packets over UDP, there is the possibil‐
2909 ity that packets might be dropped or delivered out of order.
2910 Because OpenVPN, like IPSec, is emulating the physical network
2911 layer, it will accept an out-of-order packet sequence, and will
2912 deliver such packets in the same order they were received to the
2913 TCP/IP protocol stack, provided they satisfy several con‐
2914 straints.
2915 (a) The packet cannot be a replay (unless --no-replay is speci‐
2917 fied, which disables replay protection altogether).
2918 (b) If a packet arrives out of order, it will only be accepted
2920 if the difference between its sequence number and the highest
2921 sequence number received so far is less than n.
2922 (c) If a packet arrives out of order, it will only be accepted
2924 if it arrives no later than t seconds after any packet contain‐
2925 ing a higher sequence number.
2926 If you are using a network link with a large pipeline (meaning
2928 that the product of bandwidth and latency is high), you may want
2929 to use a larger value for n. Satellite links in particular
2930 often require this.
2931 If you run OpenVPN at --verb 4, you will see the message
2933 "Replay-window backtrack occurred [x]" every time the maximum
2934 sequence number backtrack seen thus far increases. This can be
2935 used to calibrate n.
2936 There is some controversy on the appropriate method of handling
2938 packet reordering at the security layer.
2939 Namely, to what extent should the security layer protect the
2941 encapsulated protocol from attacks which masquerade as the kinds
2942 of normal packet loss and reordering that occur over IP net‐
2943 works?
2944 The IPSec and OpenVPN approach is to allow packet reordering
2946 within a certain fixed sequence number window.
2947 OpenVPN adds to the IPSec model by limiting the window size in
2949 time as well as sequence space.
2950 OpenVPN also adds TCP transport as an option (not offered by
2952 IPSec) in which case OpenVPN can adopt a very strict attitude
2953 towards message deletion and reordering: Don't allow it. Since
2954 TCP guarantees reliability, any packet loss or reordering event
2955 can be assumed to be an attack.
2956 In this sense, it could be argued that TCP tunnel transport is
2958 preferred when tunneling non-IP or UDP application protocols
2959 which might be vulnerable to a message deletion or reordering
2960 attack which falls within the normal operational parameters of
2961 IP networks.
2962 So I would make the statement that one should never tunnel a
2964 non-IP protocol or UDP application protocol over UDP, if the
2965 protocol might be vulnerable to a message deletion or reordering
2966 attack that falls within the normal operating parameters of what
2967 is to be expected from the physical IP layer. The problem is
2968 easily fixed by simply using TCP as the VPN transport layer.
2969 --mute-replay-warnings
2971 Silence the output of replay warnings, which are a common false
2972 alarm on WiFi networks. This option preserves the security of
2973 the replay protection code without the verbosity associated with
2974 warnings about duplicate packets.
2975 --replay-persist file
2977 Persist replay-protection state across sessions using file to
2978 save and reload the state.
2979 This option will strengthen protection against replay attacks,
2981 especially when you are using OpenVPN in a dynamic context (such
2982 as with --inetd) when OpenVPN sessions are frequently started
2983 and stopped.
2984 This option will keep a disk copy of the current replay protec‐
2986 tion state (i.e. the most recent packet timestamp and sequence
2987 number received from the remote peer), so that if an OpenVPN
2988 session is stopped and restarted, it will reject any replays of
2989 packets which were already received by the prior session.
2990 This option only makes sense when replay protection is enabled
2992 (the default) and you are using either --secret (shared-secret
2993 key mode) or TLS mode with --tls-auth.
2994 --no-iv
2996 DEPRECATED This option will be removed in OpenVPN 2.5.
2997 (Advanced) Disable OpenVPN's use of IV (cipher initialization
2999 vector). Don't use this option unless you are prepared to make
3000 a tradeoff of greater efficiency in exchange for less security.
3001 OpenVPN uses an IV by default, and requires it for CFB and OFB
3003 cipher modes (which are totally insecure without it). Using an
3004 IV is important for security when multiple messages are being
3005 encrypted/decrypted with the same key.
3006 IV is implemented differently depending on the cipher mode used.
3008 In CBC mode, OpenVPN uses a pseudo-random IV for each packet.
3010 In CFB/OFB mode, OpenVPN uses a unique sequence number and time
3012 stamp as the IV. In fact, in CFB/OFB mode, OpenVPN uses a data‐
3013 gram space-saving optimization that uses the unique identifier
3014 for datagram replay protection as the IV.
3015 --use-prediction-resistance
3017 Enable prediction resistance on mbed TLS's RNG.
3018 Enabling prediction resistance causes the RNG to reseed in each
3020 call for random. Reseeding this often can quickly deplete the
3021 kernel entropy pool.
3022 If you need this option, please consider running a daemon that
3024 adds entropy to the kernel pool.
3025 --test-crypto
3028 Do a self-test of OpenVPN's crypto options by encrypting and
3029 decrypting test packets using the data channel encryption
3030 options specified above. This option does not require a peer to
3031 function, and therefore can be specified without --dev or
3032 --remote.
3033 The typical usage of --test-crypto would be something like this:
3035 openvpn --test-crypto --secret key
3037 or
3039 openvpn --test-crypto --secret key --verb 9
3041 This option is very useful to test OpenVPN after it has been
3043 ported to a new platform, or to isolate problems in the com‐
3044 piler, OpenSSL crypto library, or OpenVPN's crypto code. Since
3045 it is a self-test mode, problems with encryption and authentica‐
3046 tion can be debugged independently of network and tunnel issues.
3047 TLS Mode Options:
3049 TLS mode is the most powerful crypto mode of OpenVPN in both security
3050 and flexibility. TLS mode works by establishing control and data chan‐
3051 nels which are multiplexed over a single TCP/UDP port. OpenVPN initi‐
3052 ates a TLS session over the control channel and uses it to exchange
3053 cipher and HMAC keys to protect the data channel. TLS mode uses a
3054 robust reliability layer over the UDP connection for all control chan‐
3055 nel communication, while the data channel, over which encrypted tunnel
3056 data passes, is forwarded without any mediation. The result is the
3057 best of both worlds: a fast data channel that forwards over UDP with
3058 only the overhead of encrypt, decrypt, and HMAC functions, and a con‐
3059 trol channel that provides all of the security features of TLS, includ‐
3060 ing certificate-based authentication and Diffie Hellman forward
3061 secrecy.
3062 To use TLS mode, each peer that runs OpenVPN should have its own local
3064 certificate/key pair ( --cert and --key ), signed by the root certifi‐
3065 cate which is specified in --ca.
3066 When two OpenVPN peers connect, each presents its local certificate to
3068 the other. Each peer will then check that its partner peer presented a
3069 certificate which was signed by the master root certificate as speci‐
3070 fied in --ca.
3071 If that check on both peers succeeds, then the TLS negotiation will
3073 succeed, both OpenVPN peers will exchange temporary session keys, and
3074 the tunnel will begin passing data.
3075 The OpenVPN project provides a set of scripts for managing RSA certifi‐
3077 cates & keys: https://github.com/OpenVPN/easy-rsa
3078 --tls-server
3080 Enable TLS and assume server role during TLS handshake. Note
3081 that OpenVPN is designed as a peer-to-peer application. The
3082 designation of client or server is only for the purpose of nego‐
3083 tiating the TLS control channel.
3084 --tls-client
3086 Enable TLS and assume client role during TLS handshake.
3087 --ca file
3089 Certificate authority (CA) file in .pem format, also referred to
3090 as the root certificate. This file can have multiple certifi‐
3091 cates in .pem format, concatenated together. You can construct
3092 your own certificate authority certificate and private key by
3093 using a command such as:
3094 openssl req -nodes -new -x509 -keyout ca.key -out ca.crt
3096 Then edit your openssl.cnf file and edit the certificate vari‐
3098 able to point to your new root certificate ca.crt.
3099 For testing purposes only, the OpenVPN distribution includes a
3101 sample CA certificate (ca.crt). Of course you should never use
3102 the test certificates and test keys distributed with OpenVPN in
3103 a production environment, since by virtue of the fact that they
3104 are distributed with OpenVPN, they are totally insecure.
3105 --capath dir
3107 Directory containing trusted certificates (CAs and CRLs). Not
3108 available with mbed TLS.
3109 CAs in the capath directory are expected to be named <hash>.<n>.
3111 CRLs are expected to be named <hash>.r<n>. See the -CApath
3112 option of openssl verify , and the -hash option of openssl x509
3113 , openssl crl and X509_LOOKUP_hash_dir(3) for more information.
3114 Similarly to the --crl-verify option CRLs are not mandatory -
3116 OpenVPN will log the usual warning in the logs if the relevant
3117 CRL is missing, but the connection will be allowed.
3118 --dh file
3120 File containing Diffie Hellman parameters in .pem format
3121 (required for --tls-server only).
3122 Set file=none to disable Diffie Hellman key exchange (and use
3124 ECDH only). Note that this requires peers to be using an SSL
3125 library that supports ECDH TLS cipher suites (e.g. OpenSSL
3126 1.0.1+, or mbed TLS 2.0+).
3127 Use openssl dhparam -out dh2048.pem 2048 to generate 2048-bit DH
3129 parameters. Diffie Hellman parameters may be considered public.
3130 --ecdh-curve name
3132 Specify the curve to use for elliptic curve Diffie Hellman.
3133 Available curves can be listed with --show-curves. The speci‐
3134 fied curve will only be used for ECDH TLS-ciphers.
3135 This option is not supported in mbed TLS builds of OpenVPN.
3137 --cert file
3139 Local peer's signed certificate in .pem format -- must be signed
3140 by a certificate authority whose certificate is in --ca file.
3141 Each peer in an OpenVPN link running in TLS mode should have its
3142 own certificate and private key file. In addition, each cer‐
3143 tificate should have been signed by the key of a certificate
3144 authority whose public key resides in the --ca certificate
3145 authority file. You can easily make your own certificate
3146 authority (see above) or pay money to use a commercial service
3147 such as thawte.com (in which case you will be helping to finance
3148 the world's second space tourist :). To generate a certificate,
3149 you can use a command such as:
3150 openssl req -nodes -new -keyout mycert.key -out mycert.csr
3152 If your certificate authority private key lives on another
3154 machine, copy the certificate signing request (mycert.csr) to
3155 this other machine (this can be done over an insecure channel
3156 such as email). Now sign the certificate with a command such
3157 as:
3158 openssl ca -out mycert.crt -in mycert.csr
3160 Now copy the certificate (mycert.crt) back to the peer which
3162 initially generated the .csr file (this can be over a public
3163 medium). Note that the openssl ca command reads the location of
3164 the certificate authority key from its configuration file such
3165 as /usr/share/ssl/openssl.cnf -- note also that for certificate
3166 authority functions, you must set up the files index.txt (may be
3167 empty) and serial (initialize to 01 ).
3168 --extra-certs file
3170 Specify a file containing one or more PEM certs (concatenated
3171 together) that complete the local certificate chain.
3172 This option is useful for "split" CAs, where the CA for server
3174 certs is different than the CA for client certs. Putting certs
3175 in this file allows them to be used to complete the local cer‐
3176 tificate chain without trusting them to verify the peer-submit‐
3177 ted certificate, as would be the case if the certs were placed
3178 in the ca file.
3179 --key file
3181 Local peer's private key in .pem format. Use the private key
3182 which was generated when you built your peer's certificate (see
3183 --cert file above).
3184 --tls-version-min version ['or-highest']
3186 Sets the minimum TLS version we will accept from the peer
3187 (default is "1.0"). Examples for version include "1.0", "1.1",
3188 or "1.2". If 'or-highest' is specified and version is not rec‐
3189 ognized, we will only accept the highest TLS version supported
3190 by the local SSL implementation.
3191 --tls-version-max version
3193 Set the maximum TLS version we will use (default is the highest
3194 version supported). Examples for version include "1.0", "1.1",
3195 or "1.2".
3196 --pkcs12 file
3198 Specify a PKCS #12 file containing local private key, local cer‐
3199 tificate, and root CA certificate. This option can be used
3200 instead of --ca, --cert, and --key. Not available with mbed
3201 TLS.
3202 --verify-hash hash [algo]
3204 Specify SHA1 or SHA256 fingerprint for level-1 cert. The
3205 level-1 cert is the CA (or intermediate cert) that signs the
3206 leaf certificate, and is one removed from the leaf certificate
3207 in the direction of the root. When accepting a connection from
3208 a peer, the level-1 cert fingerprint must match hash or certifi‐
3209 cate verification will fail. Hash is specified as XX:XX:... For
3210 example:
3211 AD:B0:95:D8:09:C8:36:45:12:A9:89:C8:90:09:CB:13:72:A6:AD:16
3213 The algo flag can be either SHA1 or SHA256. If not provided, it
3215 defaults to SHA1.
3216 --pkcs11-cert-private [0|1]...
3218 Set if access to certificate object should be performed after
3219 login. Every provider has its own setting.
3220 --pkcs11-id name
3222 Specify the serialized certificate id to be used. The id can be
3223 gotten by the standalone --show-pkcs11-ids option.
3224 --pkcs11-id-management
3226 Acquire PKCS#11 id from management interface. In this case a
3227 NEED-STR 'pkcs11-id-request' real-time message will be trig‐
3228 gered, application may use pkcs11-id-count command to retrieve
3229 available number of certificates, and pkcs11-id-get command to
3230 retrieve certificate id and certificate body.
3231 --pkcs11-pin-cache seconds
3233 Specify how many seconds the PIN can be cached, the default is
3234 until the token is removed.
3235 --pkcs11-protected-authentication [0|1]...
3237 Use PKCS#11 protected authentication path, useful for biometric
3238 and external keypad devices. Every provider has its own set‐
3239 ting.
3240 --pkcs11-providers provider...
3242 Specify a RSA Security Inc. PKCS #11 Cryptographic Token Inter‐
3243 face (Cryptoki) providers to load. This option can be used
3244 instead of --cert, --key, and --pkcs12.
3245 If p11-kit is present on the system, its p11-kit-proxy.so module
3247 will be loaded by default if either the --pkcs11-id or
3248 --pkcs11-id-management options are specified without
3249 --pkcs11-provider being given.
3250 --pkcs11-private-mode mode...
3252 Specify which method to use in order to perform private key
3253 operations. A different mode can be specified for each
3254 provider. Mode is encoded as hex number, and can be a mask one
3255 of the following:
3256 0 (default) -- Try to determine automatically.
3258 1 -- Use sign.
3259 2 -- Use sign recover.
3260 4 -- Use decrypt.
3261 8 -- Use unwrap.
3262 --cryptoapicert select-string
3264 Load the certificate and private key from the Windows Certifi‐
3265 cate System Store (Windows/OpenSSL Only).
3266 Use this option instead of --cert and --key.
3268 This makes it possible to use any smart card, supported by Win‐
3270 dows, but also any kind of certificate, residing in the Cert
3271 Store, where you have access to the private key. This option
3272 has been tested with a couple of different smart cards (GemSAFE,
3273 Cryptoflex, and Swedish Post Office eID) on the client side, and
3274 also an imported PKCS12 software certificate on the server side.
3275 To select a certificate, based on a substring search in the cer‐
3277 tificate's subject:
3278 cryptoapicert "SUBJ:Peter Runestig"
3280 To select a certificate, based on certificate's thumbprint:
3282 cryptoapicert "THUMB:f6 49 24 41 01 b4 ..."
3284 The thumbprint hex string can easily be copy-and-pasted from the
3286 Windows Certificate Store GUI.
3287 --key-method m
3290 DEPRECATED This option will be removed in OpenVPN 2.5
3291 Use data channel key negotiation method m. The key method must
3293 match on both sides of the connection.
3294 After OpenVPN negotiates a TLS session, a new set of keys for
3296 protecting the tunnel data channel is generated and exchanged
3297 over the TLS session.
3298 In method 1 (the default for OpenVPN 1.x), both sides generate
3300 random encrypt and HMAC-send keys which are forwarded to the
3301 other host over the TLS channel. Method 1 is deprecated in Open‐
3302 VPN 2.4 , and will be removed in OpenVPN 2.5.
3303 In method 2, (the default for OpenVPN 2.0) the client generates
3305 a random key. Both client and server also generate some random
3306 seed material. All key source material is exchanged over the
3307 TLS channel. The actual keys are generated using the TLS PRF
3308 function, taking source entropy from both client and server.
3309 Method 2 is designed to closely parallel the key generation
3310 process used by TLS 1.0.
3311 Note that in TLS mode, two separate levels of keying occur:
3313 (1) The TLS connection is initially negotiated, with both sides
3315 of the connection producing certificates and verifying the cer‐
3316 tificate (or other authentication info provided) of the other
3317 side. The --key-method parameter has no effect on this process.
3318 (2) After the TLS connection is established, the tunnel session
3320 keys are separately negotiated over the existing secure TLS
3321 channel. Here, --key-method determines the derivation of the
3322 tunnel session keys.
3323 --tls-cipher l
3325 --tls-ciphersuites l
3326 A list l of allowable TLS ciphers delimited by a colon (":").
3327 These setting can be used to ensure that certain cipher suites
3329 are used (or not used) for the TLS connection. OpenVPN uses TLS
3330 to secure the control channel, over which the keys that are used
3331 to protect the actual VPN traffic are exchanged.
3332 The supplied list of ciphers is (after potential OpenSSL/IANA
3334 name translation) simply supplied to the crypto library. Please
3335 see the OpenSSL and/or mbed TLS documentation for details on the
3336 cipher list interpretation.
3337 For OpenSSL, the --tls-cipher is used for TLS 1.2 and below. For
3339 TLS 1.3 and up, the --tls-ciphersuites setting is used. mbed TLS
3340 has no TLS 1.3 support yet and only the --tls-cipher setting is
3341 used.
3342 Use --show-tls to see a list of TLS ciphers supported by your
3344 crypto library.
3345 Warning! --tls-cipher and --tls-ciphersuites are expert fea‐
3347 tures, which - if used correcly - can improve the security of
3348 your VPN connection. But it is also easy to unwittingly use
3349 them to carefully align a gun with your foot, or just break your
3350 connection. Use with care!
3351 The default for --tls-cipher is to use mbed TLS's default cipher
3353 list when using mbed TLS or
3354 "DEFAULT:!EXP:!LOW:!MEDIUM:!kDH:!kECDH:!DSS:!PSK:!SRP:!kRSA"
3355 when using OpenSSL.
3356 The default for --tls-ciphersuites is to use the crypto
3358 library's default.
3359 --tls-cert-profile profile
3361 Set the allowed cryptographic algorithms for certificates
3362 according to profile.
3363 The following profiles are supported:
3365 legacy (default): SHA1 and newer, RSA 2048-bit+, any elliptic
3367 curve.
3368 preferred : SHA2 and newer, RSA 2048-bit+, any elliptic curve.
3370 suiteb : SHA256/SHA384, ECDSA with P-256 or P-384.
3372 This option is only fully supported for mbed TLS builds.
3374 OpenSSL builds use the following approximation:
3375 legacy (default): sets "security level 1"
3377 preferred : sets "security level 2"
3379 suiteb : sets "security level 3" and --tls-cipher "SUITEB128".
3381 OpenVPN will migrate to 'preferred' as default in the future.
3383 Please ensure that your keys already comply.
3384 --tls-timeout n
3386 Packet retransmit timeout on TLS control channel if no acknowl‐
3387 edgment from remote within n seconds (default=2). When OpenVPN
3388 sends a control packet to its peer, it will expect to receive an
3389 acknowledgement within n seconds or it will retransmit the
3390 packet, subject to a TCP-like exponential backoff algorithm.
3391 This parameter only applies to control channel packets. Data
3392 channel packets (which carry encrypted tunnel data) are never
3393 acknowledged, sequenced, or retransmitted by OpenVPN because the
3394 higher level network protocols running on top of the tunnel such
3395 as TCP expect this role to be left to them.
3396 --reneg-bytes n
3398 Renegotiate data channel key after n bytes sent or received
3399 (disabled by default with an exception, see below). OpenVPN
3400 allows the lifetime of a key to be expressed as a number of
3401 bytes encrypted/decrypted, a number of packets, or a number of
3402 seconds. A key renegotiation will be forced if any of these
3403 three criteria are met by either peer.
3404 If using ciphers with cipher block sizes less than 128-bits,
3406 --reneg-bytes is set to 64MB by default, unless it is explicitly
3407 disabled by setting the value to 0, but this is HIGHLY DISCOUR‐
3408 AGED as this is designed to add some protection against the
3409 SWEET32 attack vector. For more information see the --cipher
3410 option.
3411 --reneg-pkts n
3413 Renegotiate data channel key after n packets sent and received
3414 (disabled by default).
3415 --reneg-sec n
3417 Renegotiate data channel key after n seconds (default=3600).
3418 When using dual-factor authentication, note that this default
3420 value may cause the end user to be challenged to reauthorize
3421 once per hour.
3422 Also, keep in mind that this option can be used on both the
3424 client and server, and whichever uses the lower value will be
3425 the one to trigger the renegotiation. A common mistake is to
3426 set --reneg-sec to a higher value on either the client or
3427 server, while the other side of the connection is still using
3428 the default value of 3600 seconds, meaning that the renegotia‐
3429 tion will still occur once per 3600 seconds. The solution is to
3430 increase --reneg-sec on both the client and server, or set it to
3431 0 on one side of the connection (to disable), and to your chosen
3432 value on the other side.
3433 --hand-window n
3435 Handshake Window -- the TLS-based key exchange must finalize
3436 within n seconds of handshake initiation by any peer (default =
3437 60 seconds). If the handshake fails we will attempt to reset
3438 our connection with our peer and try again. Even in the event
3439 of handshake failure we will still use our expiring key for up
3440 to --tran-window seconds to maintain continuity of transmission
3441 of tunnel data.
3442 --tran-window n
3444 Transition window -- our old key can live this many seconds
3445 after a new a key renegotiation begins (default = 3600 seconds).
3446 This feature allows for a graceful transition from old to new
3447 key, and removes the key renegotiation sequence from the criti‐
3448 cal path of tunnel data forwarding.
3449 --single-session
3451 After initially connecting to a remote peer, disallow any new
3452 connections. Using this option means that a remote peer cannot
3453 connect, disconnect, and then reconnect.
3454 If the daemon is reset by a signal or --ping-restart, it will
3456 allow one new connection.
3457 --single-session can be used with --ping-exit or --inactive to
3459 create a single dynamic session that will exit when finished.
3460 --tls-exit
3462 Exit on TLS negotiation failure.
3463 --tls-auth file [direction]
3465 Add an additional layer of HMAC authentication on top of the TLS
3466 control channel to mitigate DoS attacks and attacks on the TLS
3467 stack.
3468 In a nutshell, --tls-auth enables a kind of "HMAC firewall" on
3470 OpenVPN's TCP/UDP port, where TLS control channel packets bear‐
3471 ing an incorrect HMAC signature can be dropped immediately with‐
3472 out response.
3473 file (required) is a file in OpenVPN static key format which can
3475 be generated by --genkey
3476 Older versions (up to OpenVPN 2.3) supported a freeform
3478 passphrase file. This is no longer supported in newer versions
3479 (v2.4+).
3480 See the --secret option for more information on the optional
3482 direction parameter.
3483 --tls-auth is recommended when you are running OpenVPN in a mode
3485 where it is listening for packets from any IP address, such as
3486 when --remote is not specified, or --remote is specified with
3487 --float.
3488 The rationale for this feature is as follows. TLS requires a
3490 multi-packet exchange before it is able to authenticate a peer.
3491 During this time before authentication, OpenVPN is allocating
3492 resources (memory and CPU) to this potential peer. The poten‐
3493 tial peer is also exposing many parts of OpenVPN and the OpenSSL
3494 library to the packets it is sending. Most successful network
3495 attacks today seek to either exploit bugs in programs (such as
3496 buffer overflow attacks) or force a program to consume so many
3497 resources that it becomes unusable. Of course the first line of
3498 defense is always to produce clean, well-audited code. OpenVPN
3499 has been written with buffer overflow attack prevention as a top
3500 priority. But as history has shown, many of the most widely
3501 used network applications have, from time to time, fallen to
3502 buffer overflow attacks.
3503 So as a second line of defense, OpenVPN offers this special
3505 layer of authentication on top of the TLS control channel so
3506 that every packet on the control channel is authenticated by an
3507 HMAC signature and a unique ID for replay protection. This sig‐
3508 nature will also help protect against DoS (Denial of Service)
3509 attacks. An important rule of thumb in reducing vulnerability
3510 to DoS attacks is to minimize the amount of resources a poten‐
3511 tial, but as yet unauthenticated, client is able to consume.
3512 --tls-auth does this by signing every TLS control channel packet
3514 with an HMAC signature, including packets which are sent before
3515 the TLS level has had a chance to authenticate the peer. The
3516 result is that packets without the correct signature can be
3517 dropped immediately upon reception, before they have a chance to
3518 consume additional system resources such as by initiating a TLS
3519 handshake. --tls-auth can be strengthened by adding the
3520 --replay-persist option which will keep OpenVPN's replay protec‐
3521 tion state in a file so that it is not lost across restarts.
3522 It should be emphasized that this feature is optional and that
3524 the key file used with --tls-auth gives a peer nothing more than
3525 the power to initiate a TLS handshake. It is not used to
3526 encrypt or authenticate any tunnel data.
3527 Use --tls-crypt instead if you want to use the key file to not
3529 only authenticate, but also encrypt the TLS control channel.
3530 --tls-crypt keyfile
3532 Encrypt and authenticate all control channel packets with the
3534 key from keyfile. (See --tls-auth for more background.)
3535 Encrypting (and authenticating) control channel packets:
3537 · provides more privacy by hiding the certificate used for the
3539 TLS connection,
3540 · makes it harder to identify OpenVPN traffic as such,
3542 · provides "poor-man's" post-quantum security, against attackers
3544 who will never know the pre-shared key (i.e. no forward
3545 secrecy).
3546 In contrast to --tls-auth, --tls-crypt does *not* require the
3549 user to set --key-direction.
3550 Security Considerations
3552 All peers use the same --tls-crypt pre-shared group key to
3554 authenticate and encrypt control channel messages. To ensure
3555 that IV collisions remain unlikely, this key should not be used
3556 to encrypt more than 2^48 client-to-server or 2^48
3557 server-to-client control channel messages. A typical initial
3558 negotiation is about 10 packets in each direction. Assuming
3559 both initial negotiation and renegotiations are at most 2^16
3560 (65536) packets (to be conservative), and (re)negotiations hap‐
3561 pen each minute for each user (24/7), this limits the tls-crypt
3562 key lifetime to 8171 years divided by the number of users. So a
3563 setup with 1000 users should rotate the key at least once each
3564 eight years. (And a setup with 8000 users each year.)
3565 If IV collisions were to occur, this could result in the secu‐
3567 rity of --tls-crypt degrading to the same security as using
3568 --tls-auth. That is, the control channel still benefits from
3569 the extra protection against active man-in-the-middle-attacks
3570 and DoS attacks, but may no longer offer extra privacy and
3571 post-quantum security on top of what TLS itself offers.
3572 --askpass [file]
3574 Get certificate password from console or file before we daemo‐
3575 nize.
3576 For the extremely security conscious, it is possible to protect
3578 your private key with a password. Of course this means that
3579 every time the OpenVPN daemon is started you must be there to
3580 type the password. The --askpass option allows you to start
3581 OpenVPN from the command line. It will query you for a password
3582 before it daemonizes. To protect a private key with a password
3583 you should omit the -nodes option when you use the openssl com‐
3584 mand line tool to manage certificates and private keys.
3585 If file is specified, read the password from the first line of
3587 file. Keep in mind that storing your password in a file to a
3588 certain extent invalidates the extra security provided by using
3589 an encrypted key.
3590 --auth-nocache
3592 Don't cache --askpass or --auth-user-pass username/passwords in
3593 virtual memory.
3594 If specified, this directive will cause OpenVPN to immediately
3596 forget username/password inputs after they are used. As a
3597 result, when OpenVPN needs a username/password, it will prompt
3598 for input from stdin, which may be multiple times during the
3599 duration of an OpenVPN session.
3600 When using --auth-nocache in combination with a user/password
3602 file and --chroot or --daemon, make sure to use an absolute
3603 path.
3604 This directive does not affect the --http-proxy username/pass‐
3606 word. It is always cached.
3607 --auth-token token
3609 This is not an option to be used directly in any configuration
3610 files, but rather push this option from a --client-connect
3611 script or a --plugin which hooks into the OPENVPN_PLUG‐
3612 IN_CLIENT_CONNECT or OPENVPN_PLUGIN_CLIENT_CONNECT_V2 calls.
3613 This option provides a possibility to replace the clients pass‐
3614 word with an authentication token during the lifetime of the
3615 OpenVPN client.
3616 Whenever the connection is renegotiated and the
3618 --auth-user-pass-verify script or --plugin making use of the
3619 OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY hook is triggered, it will
3620 pass over this token as the password instead of the password the
3621 user provided. The authentication token can only be reset by a
3622 full reconnect where the server can push new options to the
3623 client. The password the user entered is never preserved once
3624 an authentication token have been set. If the OpenVPN server
3625 side rejects the authentication token, the client will receive
3626 an AUTH_FAIL and disconnect.
3627 The purpose of this is to enable two factor authentication meth‐
3629 ods, such as HOTP or TOTP, to be used without needing to
3630 retrieve a new OTP code each time the connection is renegoti‐
3631 ated. Another use case is to cache authentication data on the
3632 client without needing to have the users password cached in mem‐
3633 ory during the life time of the session.
3634 To make use of this feature, the --client-connect script or
3636 --plugin needs to put
3637 push "auth-token UNIQUE_TOKEN_VALUE"
3639 into the file/buffer for dynamic configuration data. This will
3641 then make the OpenVPN server to push this value to the client,
3642 which replaces the local password with the UNIQUE_TOKEN_VALUE.
3643 Newer clients (2.4.7+) will fall back to the original password
3645 method after a failed auth. Older clients will keep using the
3646 token value and react acording to --auth-retry
3647 --tls-verify cmd
3649 Run command cmd to verify the X509 name of a pending TLS connec‐
3650 tion that has otherwise passed all other tests of certification
3651 (except for revocation via --crl-verify directive; the revoca‐
3652 tion test occurs after the --tls-verify test).
3653 cmd should return 0 to allow the TLS handshake to proceed, or 1
3655 to fail.
3656 cmd consists of a path to script (or executable program),
3658 optionally followed by arguments. The path and arguments may be
3659 single- or double-quoted and/or escaped using a backslash, and
3660 should be separated by one or more spaces.
3661 When cmd is executed two arguments are appended after any argu‐
3663 ments specified in cmd , as follows:
3664 cmd certificate_depth subject
3666 These arguments are, respectively, the current certificate depth
3668 and the X509 subject distinguished name (dn) of the peer.
3669 This feature is useful if the peer you want to trust has a cer‐
3671 tificate which was signed by a certificate authority who also
3672 signed many other certificates, where you don't necessarily want
3673 to trust all of them, but rather be selective about which peer
3674 certificate you will accept. This feature allows you to write a
3675 script which will test the X509 name on a certificate and decide
3676 whether or not it should be accepted. For a simple perl script
3677 which will test the common name field on the certificate, see
3678 the file verify-cn in the OpenVPN distribution.
3679 See the "Environmental Variables" section below for additional
3681 parameters passed as environmental variables.
3682 --tls-export-cert directory
3684 Store the certificates the clients uses upon connection to this
3685 directory. This will be done before --tls-verify is called. The
3686 certificates will use a temporary name and will be deleted when
3687 the tls-verify script returns. The file name used for the cer‐
3688 tificate is available via the peer_cert environment variable.
3689 --x509-username-field [ext:]fieldname
3691 Field in the X.509 certificate subject to be used as the user‐
3692 name (default=CN). Typically, this option is specified with
3693 fieldname as either of the following:
3694 --x509-username-field emailAddress
3696 --x509-username-field ext:subjectAltName
3697 The first example uses the value of the "emailAddress" attribute
3699 in the certificate's Subject field as the username. The second
3700 example uses the ext: prefix to signify that the X.509 extension
3701 fieldname "subjectAltName" be searched for an rfc822Name (email)
3702 field to be used as the username. In cases where there are mul‐
3703 tiple email addresses in ext:fieldname, the last occurrence is
3704 chosen.
3705 When this option is used, the --verify-x509-name option will
3707 match against the chosen fieldname instead of the Common Name.
3708 Only the subjectAltName and issuerAltName X.509 extensions are
3710 supported.
3711 Please note: This option has a feature which will convert an
3713 all-lowercase fieldname to uppercase characters, e.g., ou -> OU.
3714 A mixed-case fieldname or one having the ext: prefix will be
3715 left as-is. This automatic upcasing feature is deprecated and
3716 will be removed in a future release.
3717 --verify-x509-name name type
3719 Accept connections only if a host's X.509 name is equal to name.
3720 The remote host must also pass all other tests of verification.
3721 Which X.509 name is compared to name depends on the setting of
3723 type. type can be "subject" to match the complete subject DN
3724 (default), "name" to match a subject RDN or "name-prefix" to
3725 match a subject RDN prefix. Which RDN is verified as name
3726 depends on the --x509-username-field option. But it defaults to
3727 the common name (CN), e.g. a certificate with a subject DN
3728 "C=KG, ST=NA, L=Bishkek, CN=Server-1" would be matched by:
3729 --verify-x509-name 'C=KG, ST=NA, L=Bishkek, CN=Server-1' and
3731 --verify-x509-name Server-1 name or you could use --ver‐
3732 ify-x509-name Server- name-prefix if you want a client to only
3733 accept connections to "Server-1", "Server-2", etc.
3734 --verify-x509-name is a useful replacement for the --tls-verify
3736 option to verify the remote host, because --verify-x509-name
3737 works in a --chroot environment without any dependencies.
3738 Using a name prefix is a useful alternative to managing a CRL
3740 (Certificate Revocation List) on the client, since it allows the
3741 client to refuse all certificates except for those associated
3742 with designated servers.
3743 NOTE: Test against a name prefix only when you are using OpenVPN
3745 with a custom CA certificate that is under your control. Never
3746 use this option with type "name-prefix" when your client cer‐
3747 tificates are signed by a third party, such as a commercial web
3748 CA.
3749 --x509-track attribute
3751 Save peer X509 attribute value in environment for use by plugins
3752 and management interface. Prepend a '+' to attribute to save
3753 values from full cert chain. Values will be encoded as
3754 X509_<depth>_<attribute>=<value>. Multiple --x509-track options
3755 can be defined to track multiple attributes.
3756 --ns-cert-type client|server
3758 DEPRECATED This option will be removed in OpenVPN 2.5. Use the
3759 more modern equivalent --remote-cert-tls instead. This option
3760 will be removed in OpenVPN 2.5.
3761 Require that peer certificate was signed with an explicit
3763 nsCertType designation of "client" or "server".
3764 This is a useful security option for clients, to ensure that the
3766 host they connect with is a designated server.
3767 See the easy-rsa/build-key-server script for an example of how
3769 to generate a certificate with the nsCertType field set to
3770 "server".
3771 If the server certificate's nsCertType field is set to "server",
3773 then the clients can verify this with --ns-cert-type server.
3774 This is an important security precaution to protect against a
3776 man-in-the-middle attack where an authorized client attempts to
3777 connect to another client by impersonating the server. The
3778 attack is easily prevented by having clients verify the server
3779 certificate using any one of --ns-cert-type, --verify-x509-name,
3780 or --tls-verify.
3781 --remote-cert-ku [v...]
3783 Require that peer certificate was signed with an explicit key
3784 usage.
3785 If present in the certificate, the keyUsage value is validated
3787 by the TLS library during the TLS handshake. Specifying this
3788 option without arguments requires this extension to be present
3789 (so the TLS library will verify it).
3790 If the list v... is also supplied, the keyUsage field must have
3792 at least the same bits set as the bits in one of the values sup‐
3793 plied in the list v...
3794 The key usage values in the list must be encoded in hex, e.g.
3796 "--remote-cert-ku a0"
3797 --remote-cert-eku oid
3799 Require that peer certificate was signed with an explicit
3800 extended key usage.
3801 This is a useful security option for clients, to ensure that the
3803 host they connect to is a designated server.
3804 The extended key usage should be encoded in oid notation, or
3806 OpenSSL symbolic representation.
3807 --remote-cert-tls client|server
3809 Require that peer certificate was signed with an explicit key
3810 usage and extended key usage based on RFC3280 TLS rules.
3811 This is a useful security option for clients, to ensure that the
3813 host they connect to is a designated server. Or the other way
3814 around; for a server to verify that only hosts with a client
3815 certificate can connect.
3816 The --remote-cert-tls client option is equivalent to
3818 --remote-cert-ku --remote-cert-eku "TLS Web Client Authentica‐
3819 tion"
3820 The --remote-cert-tls server option is equivalent to
3822 --remote-cert-ku --remote-cert-eku "TLS Web Server Authentica‐
3823 tion"
3824 This is an important security precaution to protect against a
3826 man-in-the-middle attack where an authorized client attempts to
3827 connect to another client by impersonating the server. The
3828 attack is easily prevented by having clients verify the server
3829 certificate using any one of --remote-cert-tls, --ver‐
3830 ify-x509-name, or --tls-verify.
3831 --crl-verify crl ['dir']
3833 Check peer certificate against the file crl in PEM format.
3834 A CRL (certificate revocation list) is used when a particular
3836 key is compromised but when the overall PKI is still intact.
3837 Suppose you had a PKI consisting of a CA, root certificate, and
3839 a number of client certificates. Suppose a laptop computer con‐
3840 taining a client key and certificate was stolen. By adding the
3841 stolen certificate to the CRL file, you could reject any connec‐
3842 tion which attempts to use it, while preserving the overall
3843 integrity of the PKI.
3844 The only time when it would be necessary to rebuild the entire
3846 PKI from scratch would be if the root certificate key itself was
3847 compromised.
3848 The option is not mandatory - if the relevant CRL is missing,
3850 OpenVPN will log a warning in the logs - e.g. "VERIFY WARNING:
3851 depth=0, unable to get certificate CRL" - but the connection
3852 will be allowed.
3853 If the optional dir flag is specified, enable a different mode
3855 where crl is a directory containing files named as revoked
3856 serial numbers (the files may be empty, the contents are never
3857 read). If a client requests a connection, where the client cer‐
3858 tificate serial number (decimal string) is the name of a file
3859 present in the directory, it will be rejected.
3860 Note: As the crl file (or directory) is read every time a peer
3862 connects, if you are dropping root privileges with --user, make
3863 sure that this user has sufficient privileges to read the file.
3864 SSL Library information:
3866 --show-ciphers
3867 (Standalone) Show all cipher algorithms to use with the --cipher
3868 option.
3869 --show-digests
3871 (Standalone) Show all message digest algorithms to use with the
3872 --auth option.
3873 --show-tls
3875 (Standalone) Show all TLS ciphers supported by the crypto
3876 library. OpenVPN uses TLS to secure the control channel, over
3877 which the keys that are used to protect the actual VPN traffic
3878 are exchanged. The TLS ciphers will be sorted from highest
3879 preference (most secure) to lowest.
3880 Be aware that whether a cipher suite in this list can actually
3882 work depends on the specific setup of both peers (e.g. both
3883 peers must support the cipher, and an ECDSA cipher suite will
3884 not work if you are using an RSA certificate, etc.).
3885 --show-engines
3887 (Standalone) Show currently available hardware-based crypto
3888 acceleration engines supported by the OpenSSL library.
3889 --show-curves
3891 (Standalone) Show all available elliptic curves to use with the
3892 --ecdh-curve option.
3893 Generate a random key:
3895 Used only for non-TLS static key encryption mode.
3896 --genkey
3898 (Standalone) Generate a random key to be used as a shared
3899 secret, for use with the --secret option. This file must be
3900 shared with the peer over a pre-existing secure channel such as
3901 scp(1)
3902 --secret file
3904 Write key to file.
3905 TUN/TAP persistent tunnel config mode:
3907 Available with Linux 2.4.7+. These options comprise a standalone mode
3908 of OpenVPN which can be used to create and delete persistent tunnels.
3909 --mktun
3911 (Standalone) Create a persistent tunnel on platforms which sup‐
3912 port them such as Linux. Normally TUN/TAP tunnels exist only
3913 for the period of time that an application has them open. This
3914 option takes advantage of the TUN/TAP driver's ability to build
3915 persistent tunnels that live through multiple instantiations of
3916 OpenVPN and die only when they are deleted or the machine is
3917 rebooted.
3918 One of the advantages of persistent tunnels is that they elimi‐
3920 nate the need for separate --up and --down scripts to run the
3921 appropriate ifconfig(8) and route(8) commands. These commands
3922 can be placed in the the same shell script which starts or ter‐
3923 minates an OpenVPN session.
3924 Another advantage is that open connections through the
3926 TUN/TAP-based tunnel will not be reset if the OpenVPN peer
3927 restarts. This can be useful to provide uninterrupted connec‐
3928 tivity through the tunnel in the event of a DHCP reset of the
3929 peer's public IP address (see the --ipchange option above).
3930 One disadvantage of persistent tunnels is that it is harder to
3932 automatically configure their MTU value (see --link-mtu and
3933 --tun-mtu above).
3934 On some platforms such as Windows, TAP-Win32 tunnels are persis‐
3936 tent by default.
3937 --rmtun
3939 (Standalone) Remove a persistent tunnel.
3940 --dev tunX | tapX
3942 TUN/TAP device
3943 --user user
3945 Optional user to be owner of this tunnel.
3946 --group group
3948 Optional group to be owner of this tunnel.
3949 Windows-Specific Options:
3951 --win-sys path
3952 Set the Windows system directory pathname to use when looking
3953 for system executables such as route.exe and netsh.exe. By
3954 default, if this directive is not specified, OpenVPN will use
3955 the SystemRoot environment variable.
3956 This option have changed behaviour in OpenVPN 2.3. Earlier you
3958 had to define --win-sys env to use the SystemRoot environment
3959 variable, otherwise it defaulted to C:\WINDOWS. It is not
3960 needed to use the env keyword any more, and it will just be
3961 ignored. A warning is logged when this is found in the configu‐
3962 ration file.
3963 --ip-win32 method
3965 When using --ifconfig on Windows, set the TAP-Win32 adapter IP
3966 address and netmask using method. Don't use this option unless
3967 you are also using --ifconfig.
3968 manual -- Don't set the IP address or netmask automatically.
3970 Instead output a message to the console telling the user to con‐
3971 figure the adapter manually and indicating the IP/netmask which
3972 OpenVPN expects the adapter to be set to.
3973 dynamic [offset] [lease-time] -- Automatically set the IP
3975 address and netmask by replying to DHCP query messages generated
3976 by the kernel. This mode is probably the "cleanest" solution
3977 for setting the TCP/IP properties since it uses the well-known
3978 DHCP protocol. There are, however, two prerequisites for using
3979 this mode: (1) The TCP/IP properties for the TAP-Win32 adapter
3980 must be set to "Obtain an IP address automatically," and (2)
3981 OpenVPN needs to claim an IP address in the subnet for use as
3982 the virtual DHCP server address. By default in --dev tap mode,
3983 OpenVPN will take the normally unused first address in the sub‐
3984 net. For example, if your subnet is 192.168.4.0 netmask
3985 255.255.255.0, then OpenVPN will take the IP address 192.168.4.0
3986 to use as the virtual DHCP server address. In --dev tun mode,
3987 OpenVPN will cause the DHCP server to masquerade as if it were
3988 coming from the remote endpoint. The optional offset parameter
3989 is an integer which is > -256 and < 256 and which defaults to
3990 -1. If offset is positive, the DHCP server will masquerade as
3991 the IP address at network address + offset. If offset is nega‐
3992 tive, the DHCP server will masquerade as the IP address at
3993 broadcast address + offset. The Windows ipconfig /all command
3994 can be used to show what Windows thinks the DHCP server address
3995 is. OpenVPN will "claim" this address, so make sure to use a
3996 free address. Having said that, different OpenVPN instantia‐
3997 tions, including different ends of the same connection, can
3998 share the same virtual DHCP server address. The lease-time
3999 parameter controls the lease time of the DHCP assignment given
4000 to the TAP-Win32 adapter, and is denoted in seconds. Normally a
4001 very long lease time is preferred because it prevents routes
4002 involving the TAP-Win32 adapter from being lost when the system
4003 goes to sleep. The default lease time is one year.
4004 netsh -- Automatically set the IP address and netmask using the
4006 Windows command-line "netsh" command. This method appears to
4007 work correctly on Windows XP but not Windows 2000.
4008 ipapi -- Automatically set the IP address and netmask using the
4010 Windows IP Helper API. This approach does not have ideal seman‐
4011 tics, though testing has indicated that it works okay in prac‐
4012 tice. If you use this option, it is best to leave the TCP/IP
4013 properties for the TAP-Win32 adapter in their default state,
4014 i.e. "Obtain an IP address automatically."
4015 adaptive -- (Default) Try dynamic method initially and fail over
4017 to netsh if the DHCP negotiation with the TAP-Win32 adapter does
4018 not succeed in 20 seconds. Such failures have been known to
4019 occur when certain third-party firewall packages installed on
4020 the client machine block the DHCP negotiation used by the
4021 TAP-Win32 adapter. Note that if the netsh failover occurs, the
4022 TAP-Win32 adapter TCP/IP properties will be reset from DHCP to
4023 static, and this will cause future OpenVPN startups using the
4024 adaptive mode to use netsh immediately, rather than trying
4025 dynamic first. To "unstick" the adaptive mode from using netsh,
4026 run OpenVPN at least once using the dynamic mode to restore the
4027 TAP-Win32 adapter TCP/IP properties to a DHCP configuration.
4028 --route-method m
4030 Which method m to use for adding routes on Windows?
4031 adaptive (default) -- Try IP helper API first. If that fails,
4033 fall back to the route.exe shell command.
4034 ipapi -- Use IP helper API.
4035 exe -- Call the route.exe shell command.
4036 --dhcp-option type [parm]
4038 Set extended TAP-Win32 TCP/IP properties, must be used with
4039 --ip-win32 dynamic or --ip-win32 adaptive. This option can be
4040 used to set additional TCP/IP properties on the TAP-Win32
4041 adapter, and is particularly useful for configuring an OpenVPN
4042 client to access a Samba server across the VPN.
4043 DOMAIN name -- Set Connection-specific DNS Suffix.
4045 DNS addr -- Set primary domain name server IPv4 or IPv6 address.
4047 Repeat this option to set secondary DNS server addresses.
4048 Note: DNS IPv6 servers are currently set using netsh (the exist‐
4050 ing DHCP code can only do IPv4 DHCP, and that protocol only per‐
4051 mits IPv4 addresses anywhere). The option will be put into the
4052 environment, so an --up script could act upon it if needed.
4053 WINS addr -- Set primary WINS server address (NetBIOS over
4055 TCP/IP Name Server). Repeat this option to set secondary WINS
4056 server addresses.
4057 NBDD addr -- Set primary NBDD server address (NetBIOS over
4059 TCP/IP Datagram Distribution Server) Repeat this option to set
4060 secondary NBDD server addresses.
4061 NTP addr -- Set primary NTP server address (Network Time Proto‐
4063 col). Repeat this option to set secondary NTP server addresses.
4064 NBT type -- Set NetBIOS over TCP/IP Node type. Possible
4066 options: 1 = b-node (broadcasts), 2 = p-node (point-to-point
4067 name queries to a WINS server), 4 = m-node (broadcast then query
4068 name server), and 8 = h-node (query name server, then broad‐
4069 cast).
4070 NBS scope-id -- Set NetBIOS over TCP/IP Scope. A NetBIOS Scope
4072 ID provides an extended naming service for the NetBIOS over
4073 TCP/IP (Known as NBT) module. The primary purpose of a NetBIOS
4074 scope ID is to isolate NetBIOS traffic on a single network to
4075 only those nodes with the same NetBIOS scope ID. The NetBIOS
4076 scope ID is a character string that is appended to the NetBIOS
4077 name. The NetBIOS scope ID on two hosts must match, or the two
4078 hosts will not be able to communicate. The NetBIOS Scope ID also
4079 allows computers to use the same computer name, as they have
4080 different scope IDs. The Scope ID becomes a part of the NetBIOS
4081 name, making the name unique. (This description of NetBIOS
4082 scopes courtesy of NeonSurge@abyss.com)
4083 DISABLE-NBT -- Disable Netbios-over-TCP/IP.
4085 Note that if --dhcp-option is pushed via --push to a non-windows
4087 client, the option will be saved in the client's environment
4088 before the up script is called, under the name "for‐
4089 eign_option_{n}".
4090 --tap-sleep n
4092 Cause OpenVPN to sleep for n seconds immediately after the
4093 TAP-Win32 adapter state is set to "connected".
4094 This option is intended to be used to troubleshoot problems with
4096 the --ifconfig and --ip-win32 options, and is used to give the
4097 TAP-Win32 adapter time to come up before Windows IP Helper API
4098 operations are applied to it.
4099 --show-net-up
4101 Output OpenVPN's view of the system routing table and network
4102 adapter list to the syslog or log file after the TUN/TAP adapter
4103 has been brought up and any routes have been added.
4104 --block-outside-dns
4106 Block DNS servers on other network adapters to prevent DNS
4107 leaks. This option prevents any application from accessing TCP
4108 or UDP port 53 except one inside the tunnel. It uses Windows
4109 Filtering Platform (WFP) and works on Windows Vista or later.
4110 This option is considered unknown on non-Windows platforms and
4112 unsupported on Windows XP, resulting in fatal error. You may
4113 want to use --setenv opt or --ignore-unknown-option (not suit‐
4114 able for Windows XP) to ignore said error. Note that pushing
4115 unknown options from server does not trigger fatal errors.
4116 --dhcp-renew
4118 Ask Windows to renew the TAP adapter lease on startup. This
4119 option is normally unnecessary, as Windows automatically trig‐
4120 gers a DHCP renegotiation on the TAP adapter when it comes up,
4121 however if you set the TAP-Win32 adapter Media Status property
4122 to "Always Connected", you may need this flag.
4123 --dhcp-release
4125 Ask Windows to release the TAP adapter lease on shutdown. This
4126 option has no effect now, as it is enabled by default starting
4127 with OpenVPN 2.4.1.
4128 --register-dns
4130 Run ipconfig /flushdns and ipconfig /registerdns on connection
4131 initiation. This is known to kick Windows into recognizing
4132 pushed DNS servers.
4133 --pause-exit
4135 Put up a "press any key to continue" message on the console
4136 prior to OpenVPN program exit. This option is automatically
4137 used by the Windows explorer when OpenVPN is run on a configura‐
4138 tion file using the right-click explorer menu.
4139 --service exit-event [0|1]
4141 Should be used when OpenVPN is being automatically executed by
4142 another program in such a context that no interaction with the
4143 user via display or keyboard is possible. In general, end-users
4144 should never need to explicitly use this option, as it is auto‐
4145 matically added by the OpenVPN service wrapper when a given
4146 OpenVPN configuration is being run as a service.
4147 exit-event is the name of a Windows global event object, and
4149 OpenVPN will continuously monitor the state of this event object
4150 and exit when it becomes signaled.
4151 The second parameter indicates the initial state of exit-event
4153 and normally defaults to 0.
4154 Multiple OpenVPN processes can be simultaneously executed with
4156 the same exit-event parameter. In any case, the controlling
4157 process can signal exit-event, causing all such OpenVPN pro‐
4158 cesses to exit.
4159 When executing an OpenVPN process using the --service directive,
4161 OpenVPN will probably not have a console window to output sta‐
4162 tus/error messages, therefore it is useful to use --log or
4163 --log-append to write these messages to a file.
4164 --show-adapters
4166 (Standalone) Show available TAP-Win32 adapters which can be
4167 selected using the --dev-node option. On non-Windows systems,
4168 the ifconfig(8) command provides similar functionality.
4169 --allow-nonadmin [TAP-adapter]
4171 (Standalone) Set TAP-adapter to allow access from non-adminis‐
4172 trative accounts. If TAP-adapter is omitted, all TAP adapters
4173 on the system will be configured to allow non-admin access. The
4174 non-admin access setting will only persist for the length of
4175 time that the TAP-Win32 device object and driver remain loaded,
4176 and will need to be re-enabled after a reboot, or if the driver
4177 is unloaded and reloaded. This directive can only be used by an
4178 administrator.
4179 --show-valid-subnets
4181 (Standalone) Show valid subnets for --dev tun emulation. Since
4182 the TAP-Win32 driver exports an ethernet interface to Windows,
4183 and since TUN devices are point-to-point in nature, it is neces‐
4184 sary for the TAP-Win32 driver to impose certain constraints on
4185 TUN endpoint address selection.
4186 Namely, the point-to-point endpoints used in TUN device emula‐
4188 tion must be the middle two addresses of a /30 subnet (netmask
4189 255.255.255.252).
4190 --show-net
4192 (Standalone) Show OpenVPN's view of the system routing table and
4193 network adapter list.
4194 PKCS#11 Standalone Options:
4196 --show-pkcs11-ids [provider] [cert_private]
4197 (Standalone) Show PKCS#11 token object list. Specify cert_pri‐
4198 vate as 1 if certificates are stored as private objects.
4199 If p11-kit is present on the system, the provider argument is
4201 optional; if omitted the default p11-kit-proxy.so module will be
4202 queried.
4203 --verb option can be used BEFORE this option to produce debug‐
4205 ging information.
4206 Standalone Debug Options:
4208 --show-gateway [v6target]
4209 (Standalone) Show current IPv4 and IPv6 default gateway and
4210 interface towards the gateway (if the protocol in question is
4211 enabled). If an IPv6 address is passed as argument, the IPv6
4212 route for this host is reported.
4213 IPv6 Related Options
4215 The following options exist to support IPv6 tunneling in peer-to-peer
4216 and client-server mode. All options are modeled after their IPv4 coun‐
4217 terparts, so more detailed explanations given there apply here as well
4218 (except for --topology , which has no effect on IPv6).
4219 --ifconfig-ipv6 ipv6addr/bits ipv6remote
4221 configure IPv6 address ipv6addr/bits on the ``tun'' device. The
4222 second parameter is used as route target for --route-ipv6 if no
4223 gateway is specified.
4224 --route-ipv6 ipv6addr/bits [gateway] [metric]
4226 setup IPv6 routing in the system to send the specified IPv6 net‐
4227 work into OpenVPN's ``tun''. The gateway parameter is only used
4228 for IPv6 routes across ``tap'' devices, and if missing, the
4229 ``ipv6remote'' field from --ifconfig-ipv6 is used.
4230 --server-ipv6 ipv6addr/bits
4232 convenience-function to enable a number of IPv6 related options
4233 at once, namely --ifconfig-ipv6, --ifconfig-ipv6-pool and --push
4234 tun-ipv6 Is only accepted if ``--mode server'' or ``--server''
4235 is set. Pushing of the --tun-ipv6 directive is done for older
4236 clients which require an explicit ``--tun-ipv6'' in their con‐
4237 figuration.
4238 --ifconfig-ipv6-pool ipv6addr/bits
4240 Specify an IPv6 address pool for dynamic assignment to clients.
4241 The pool starts at ipv6addr and matches the offset determined
4242 from the start of the IPv4 pool.
4243 --ifconfig-ipv6-push ipv6addr/bits ipv6remote
4245 for ccd/ per-client static IPv6 interface configuration, see
4246 --client-config-dir and --ifconfig-push for more details.
4247 --iroute-ipv6 ipv6addr/bits
4249 for ccd/ per-client static IPv6 route configuration, see
4250 --iroute for more details how to setup and use this, and how
4251 --iroute and --route interact.
4252
4255 OpenVPN exports a series of environmental variables for use by
4256 user-defined scripts.
4257 Script Order of Execution
4259 --up Executed after TCP/UDP socket bind and TUN/TAP open.
4260 --tls-verify
4262 Executed when we have a still untrusted remote peer.
4263 --ipchange
4265 Executed after connection authentication, or remote IP address
4266 change.
4267 --client-connect
4269 Executed in --mode server mode immediately after client authen‐
4270 tication.
4271 --route-up
4273 Executed after connection authentication, either immediately
4274 after, or some number of seconds after as defined by the
4275 --route-delay option.
4276 --route-pre-down
4278 Executed right before the routes are removed.
4279 --client-disconnect
4281 Executed in --mode server mode on client instance shutdown.
4282 --down Executed after TCP/UDP and TUN/TAP close.
4284 --learn-address
4286 Executed in --mode server mode whenever an IPv4 address/route or
4287 MAC address is added to OpenVPN's internal routing table.
4288 --auth-user-pass-verify
4290 Executed in --mode server mode on new client connections, when
4291 the client is still untrusted.
4292 String Types and Remapping
4294 In certain cases, OpenVPN will perform remapping of characters in
4295 strings. Essentially, any characters outside the set of permitted
4296 characters for each string type will be converted to underbar ('_').
4297 Q: Why is string remapping necessary?
4299 A: It's an important security feature to prevent the malicious coding
4301 of strings from untrusted sources to be passed as parameters to
4302 scripts, saved in the environment, used as a common name, translated to
4303 a filename, etc.
4304 Q: Can string remapping be disabled?
4306 A: Yes, by using the --no-name-remapping option, however this should be
4308 considered an advanced option.
4309 Here is a brief rundown of OpenVPN's current string types and the per‐
4311 mitted character class for each string:
4312 X509 Names: Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), at
4314 ('@'), colon (':'), slash ('/'), and equal ('='). Alphanumeric is
4315 defined as a character which will cause the C library isalnum() func‐
4316 tion to return true.
4317 Common Names: Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), and
4319 at ('@').
4320 --auth-user-pass username: Same as Common Name, with one exception:
4322 starting with OpenVPN 2.0.1, the username is passed to the OPEN‐
4323 VPN_PLUGIN_AUTH_USER_PASS_VERIFY plugin in its raw form, without string
4324 remapping.
4325 --auth-user-pass password: Any "printable" character except CR or LF.
4327 Printable is defined to be a character which will cause the C library
4328 isprint() function to return true.
4329 --client-config-dir filename as derived from common name or username:
4331 Alphanumeric, underbar ('_'), dash ('-'), and dot ('.') except for "."
4332 or ".." as standalone strings. As of v2.0.1-rc6, the at ('@') charac‐
4333 ter has been added as well for compatibility with the common name char‐
4334 acter class.
4335 Environmental variable names: Alphanumeric or underbar ('_').
4337 Environmental variable values: Any printable character.
4339 For all cases, characters in a string which are not members of the
4341 legal character class for that string type will be remapped to underbar
4342 ('_').
4343 Environmental Variables
4345 Once set, a variable is persisted indefinitely until it is reset by a
4346 new value or a restart,
4347 As of OpenVPN 2.0-beta12, in server mode, environmental variables set
4349 by OpenVPN are scoped according to the client objects they are associ‐
4350 ated with, so there should not be any issues with scripts having access
4351 to stale, previously set variables which refer to different client
4352 instances.
4353 bytes_received
4355 Total number of bytes received from client during VPN session.
4356 Set prior to execution of the --client-disconnect script.
4357 bytes_sent
4359 Total number of bytes sent to client during VPN session. Set
4360 prior to execution of the --client-disconnect script.
4361 common_name
4363 The X509 common name of an authenticated client. Set prior to
4364 execution of --client-connect, --client-disconnect, and
4365 --auth-user-pass-verify scripts.
4366 config Name of first --config file. Set on program initiation and
4368 reset on SIGHUP.
4369 daemon Set to "1" if the --daemon directive is specified, or "0" other‐
4371 wise. Set on program initiation and reset on SIGHUP.
4372 daemon_log_redirect
4374 Set to "1" if the --log or --log-append directives are speci‐
4375 fied, or "0" otherwise. Set on program initiation and reset on
4376 SIGHUP.
4377 dev The actual name of the TUN/TAP device, including a unit number
4379 if it exists. Set prior to --up or --down script execution.
4380 dev_idx
4382 On Windows, the device index of the TUN/TAP adapter (to be used
4383 in netsh.exe calls which sometimes just do not work right with
4384 interface names). Set prior to --up or --down script execution.
4385 foreign_option_{n}
4387 An option pushed via --push to a client which does not natively
4388 support it, such as --dhcp-option on a non-Windows system, will
4389 be recorded to this environmental variable sequence prior to
4390 --up script execution.
4391 ifconfig_broadcast
4393 The broadcast address for the virtual ethernet segment which is
4394 derived from the --ifconfig option when --dev tap is used. Set
4395 prior to OpenVPN calling the ifconfig or netsh (windows version
4396 of ifconfig) commands which normally occurs prior to --up script
4397 execution.
4398 ifconfig_ipv6_local
4400 The local VPN endpoint IPv6 address specified in the --ifcon‐
4401 fig-ipv6 option (first parameter). Set prior to OpenVPN calling
4402 the ifconfig or netsh (windows version of ifconfig) commands
4403 which normally occurs prior to --up script execution.
4404 ifconfig_ipv6_netbits
4406 The prefix length of the IPv6 network on the VPN interface.
4407 Derived from the /nnn parameter of the IPv6 address in the
4408 --ifconfig-ipv6 option (first parameter). Set prior to OpenVPN
4409 calling the ifconfig or netsh (windows version of ifconfig) com‐
4410 mands which normally occurs prior to --up script execution.
4411 ifconfig_ipv6_remote
4413 The remote VPN endpoint IPv6 address specified in the --ifcon‐
4414 fig-ipv6 option (second parameter). Set prior to OpenVPN call‐
4415 ing the ifconfig or netsh (windows version of ifconfig) commands
4416 which normally occurs prior to --up script execution.
4417 ifconfig_local
4419 The local VPN endpoint IP address specified in the --ifconfig
4420 option (first parameter). Set prior to OpenVPN calling the
4421 ifconfig or netsh (windows version of ifconfig) commands which
4422 normally occurs prior to --up script execution.
4423 ifconfig_remote
4425 The remote VPN endpoint IP address specified in the --ifconfig
4426 option (second parameter) when --dev tun is used. Set prior to
4427 OpenVPN calling the ifconfig or netsh (windows version of ifcon‐
4428 fig) commands which normally occurs prior to --up script execu‐
4429 tion.
4430 ifconfig_netmask
4432 The subnet mask of the virtual ethernet segment that is speci‐
4433 fied as the second parameter to --ifconfig when --dev tap is
4434 being used. Set prior to OpenVPN calling the ifconfig or netsh
4435 (windows version of ifconfig) commands which normally occurs
4436 prior to --up script execution.
4437 ifconfig_pool_local_ip
4439 The local virtual IP address for the TUN/TAP tunnel taken from
4440 an --ifconfig-push directive if specified, or otherwise from the
4441 ifconfig pool (controlled by the --ifconfig-pool config file
4442 directive). Only set for --dev tun tunnels. This option is set
4443 on the server prior to execution of the --client-connect and
4444 --client-disconnect scripts.
4445 ifconfig_pool_netmask
4447 The virtual IP netmask for the TUN/TAP tunnel taken from an
4448 --ifconfig-push directive if specified, or otherwise from the
4449 ifconfig pool (controlled by the --ifconfig-pool config file
4450 directive). Only set for --dev tap tunnels. This option is set
4451 on the server prior to execution of the --client-connect and
4452 --client-disconnect scripts.
4453 ifconfig_pool_remote_ip
4455 The remote virtual IP address for the TUN/TAP tunnel taken from
4456 an --ifconfig-push directive if specified, or otherwise from the
4457 ifconfig pool (controlled by the --ifconfig-pool config file
4458 directive). This option is set on the server prior to execution
4459 of the --client-connect and --client-disconnect scripts.
4460 link_mtu
4462 The maximum packet size (not including the IP header) of tunnel
4463 data in UDP tunnel transport mode. Set prior to --up or --down
4464 script execution.
4465 local The --local parameter. Set on program initiation and reset on
4467 SIGHUP.
4468 local_port
4470 The local port number or name, specified by --port or --lport.
4471 Set on program initiation and reset on SIGHUP.
4472 password
4474 The password provided by a connecting client. Set prior to
4475 --auth-user-pass-verify script execution only when the via-env
4476 modifier is specified, and deleted from the environment after
4477 the script returns.
4478 proto The --proto parameter. Set on program initiation and reset on
4480 SIGHUP.
4481 remote_{n}
4483 The --remote parameter. Set on program initiation and reset on
4484 SIGHUP.
4485 remote_port_{n}
4487 The remote port number, specified by --port or --rport. Set on
4488 program initiation and reset on SIGHUP.
4489 route_net_gateway
4491 The pre-existing default IP gateway in the system routing table.
4492 Set prior to --up script execution.
4493 route_vpn_gateway
4495 The default gateway used by --route options, as specified in
4496 either the --route-gateway option or the second parameter to
4497 --ifconfig when --dev tun is specified. Set prior to --up
4498 script execution.
4499 route_{parm}_{n}
4501 A set of variables which define each route to be added, and are
4502 set prior to --up script execution.
4503 parm will be one of "network", "netmask", "gateway", or "met‐
4505 ric".
4506 n is the OpenVPN route number, starting from 1.
4508 If the network or gateway are resolvable DNS names, their IP
4510 address translations will be recorded rather than their names as
4511 denoted on the command line or configuration file.
4512 route_ipv6_{parm}_{n}
4514 A set of variables which define each IPv6 route to be added, and
4515 are set prior to --up script execution.
4516 parm will be one of "network" or "gateway" ("netmask" is con‐
4518 tained as "/nnn" in the route_ipv6_network_{n}, unlike IPv4
4519 where it is passed in a separate environment variable).
4520 n is the OpenVPN route number, starting from 1.
4522 If the network or gateway are resolvable DNS names, their IP
4524 address translations will be recorded rather than their names as
4525 denoted on the command line or configuration file.
4526 peer_cert
4528 Temporary file name containing the client certificate upon con‐
4529 nection. Useful in conjunction with --tls-verify
4530 script_context
4532 Set to "init" or "restart" prior to up/down script execution.
4533 For more information, see documentation for --up.
4534 script_type
4536 Prior to execution of any script, this variable is set to the
4537 type of script being run. It can be one of the following: up,
4538 down, ipchange, route-up, tls-verify, auth-user-pass-verify,
4539 client-connect, client-disconnect, or learn-address. Set prior
4540 to execution of any script.
4541 signal The reason for exit or restart. Can be one of sigusr1, sighup,
4543 sigterm, sigint, inactive (controlled by --inactive option),
4544 ping-exit (controlled by --ping-exit option), ping-restart (con‐
4545 trolled by --ping-restart option), connection-reset (triggered
4546 on TCP connection reset), error, or unknown (unknown signal).
4547 This variable is set just prior to down script execution.
4548 time_ascii
4550 Client connection timestamp, formatted as a human-readable time
4551 string. Set prior to execution of the --client-connect script.
4552 time_duration
4554 The duration (in seconds) of the client session which is now
4555 disconnecting. Set prior to execution of the --client-discon‐
4556 nect script.
4557 time_unix
4559 Client connection timestamp, formatted as a unix integer
4560 date/time value. Set prior to execution of the --client-connect
4561 script.
4562 tls_digest_{n} / tls_digest_sha256_{n}
4564 Contains the certificate SHA1 / SHA256 fingerprint, where n is
4565 the verification level. Only set for TLS connections. Set
4566 prior to execution of --tls-verify script.
4567 tls_id_{n}
4569 A series of certificate fields from the remote peer, where n is
4570 the verification level. Only set for TLS connections. Set
4571 prior to execution of --tls-verify script.
4572 tls_serial_{n}
4574 The serial number of the certificate from the remote peer, where
4575 n is the verification level. Only set for TLS connections. Set
4576 prior to execution of --tls-verify script. This is in the form
4577 of a decimal string like "933971680", which is suitable for
4578 doing serial-based OCSP queries (with OpenSSL, do not prepend
4579 "0x" to the string) If something goes wrong while reading the
4580 value from the certificate it will be an empty string, so your
4581 code should check that. See the con‐
4582 trib/OCSP_check/OCSP_check.sh script for an example.
4583 tls_serial_hex_{n}
4585 Like tls_serial_{n}, but in hex form (e.g. "12:34:56:78:9A").
4586 tun_mtu
4588 The MTU of the TUN/TAP device. Set prior to --up or --down
4589 script execution.
4590 trusted_ip (or trusted_ip6)
4592 Actual IP address of connecting client or peer which has been
4593 authenticated. Set prior to execution of --ipchange,
4594 --client-connect, and --client-disconnect scripts. If using
4595 ipv6 endpoints (udp6, tcp6), trusted_ip6 will be set instead.
4596 trusted_port
4598 Actual port number of connecting client or peer which has been
4599 authenticated. Set prior to execution of --ipchange,
4600 --client-connect, and --client-disconnect scripts.
4601 untrusted_ip (or untrusted_ip6)
4603 Actual IP address of connecting client or peer which has not
4604 been authenticated yet. Sometimes used to nmap the connecting
4605 host in a --tls-verify script to ensure it is firewalled prop‐
4606 erly. Set prior to execution of --tls-verify and
4607 --auth-user-pass-verify scripts. If using ipv6 endpoints (udp6,
4608 tcp6), untrusted_ip6 will be set instead.
4609 untrusted_port
4611 Actual port number of connecting client or peer which has not
4612 been authenticated yet. Set prior to execution of --tls-verify
4613 and --auth-user-pass-verify scripts.
4614 username
4616 The username provided by a connecting client. Set prior to
4617 --auth-user-pass-verify script execution only when the via-env
4618 modifier is specified.
4619 X509_{n}_{subject_field}
4621 An X509 subject field from the remote peer certificate, where n
4622 is the verification level. Only set for TLS connections. Set
4623 prior to execution of --tls-verify script. This variable is
4624 similar to tls_id_{n} except the component X509 subject fields
4625 are broken out, and no string remapping occurs on these field
4626 values (except for remapping of control characters to "_"). For
4627 example, the following variables would be set on the OpenVPN
4628 server using the sample client certificate in sample-keys
4629 (client.crt). Note that the verification level is 0 for the
4630 client certificate and 1 for the CA certificate.
4631 X509_0_emailAddress=me@myhost.mydomain
4633 X509_0_CN=Test-Client
4634 X509_0_O=OpenVPN-TEST
4635 X509_0_ST=NA
4636 X509_0_C=KG
4637 X509_1_emailAddress=me@myhost.mydomain
4638 X509_1_O=OpenVPN-TEST
4639 X509_1_L=BISHKEK
4640 X509_1_ST=NA
4641 X509_1_C=KG
4642
4644 OpenVPN allows including files in the main configuration for the --ca,
4645 --cert, --dh, --extra-certs, --key, --pkcs12, --secret, --crl-verify,
4646 --http-proxy-user-pass, --tls-auth and --tls-crypt options.
4647 Each inline file started by the line <option> and ended by the line
4649 </option>
4650 Here is an example of an inline file usage
4652 <cert>
4654 -----BEGIN CERTIFICATE-----
4655 [...]
4656 -----END CERTIFICATE-----
4657 </cert>
4658 When using the inline file feature with --pkcs12 the inline file has to
4660 be base64 encoded. Encoding of a .p12 file into base64 can be done for
4661 example with OpenSSL by running openssl base64 -in input.p12
4662
4665 SIGHUP Cause OpenVPN to close all TUN/TAP and network connections,
4666 restart, re-read the configuration file (if any), and reopen
4667 TUN/TAP and network connections.
4668 SIGUSR1
4670 Like SIGHUP, except don't re-read configuration file, and possi‐
4671 bly don't close and reopen TUN/TAP device, re-read key files,
4672 preserve local IP address/port, or preserve most recently
4673 authenticated remote IP address/port based on --persist-tun,
4674 --persist-key, --persist-local-ip, and --persist-remote-ip
4675 options respectively (see above).
4676 This signal may also be internally generated by a timeout condi‐
4678 tion, governed by the --ping-restart option.
4679 This signal, when combined with --persist-remote-ip, may be sent
4681 when the underlying parameters of the host's network interface
4682 change such as when the host is a DHCP client and is assigned a
4683 new IP address. See --ipchange above for more information.
4684 SIGUSR2
4686 Causes OpenVPN to display its current statistics (to the syslog
4687 file if --daemon is used, or stdout otherwise).
4688 SIGINT, SIGTERM
4690 Causes OpenVPN to exit gracefully.
4691
4693 If you are running Linux 2.4.7 or higher, you probably have the TUN/TAP
4694 driver already installed. If so, there are still a few things you need
4695 to do:
4696 Make device: mknod /dev/net/tun c 10 200
4698 Load driver: modprobe tun
4700
4702 Prior to running these examples, you should have OpenVPN installed on
4703 two machines with network connectivity between them. If you have not
4704 yet installed OpenVPN, consult the INSTALL file included in the OpenVPN
4705 distribution.
4706 TUN/TAP Setup:
4708 If you are using Linux 2.4 or higher, make the tun device node and load
4709 the tun module:
4710 mknod /dev/net/tun c 10 200
4712 modprobe tun
4714 If you installed from RPM, the mknod step may be omitted, because the
4716 RPM install does that for you.
4717 Only Linux 2.4 and newer are supported.
4719 For other platforms, consult the INSTALL file at http://open‐
4721 vpn.net/install.html for more information.
4722 Firewall Setup:
4724 If firewalls exist between the two machines, they should be set to for‐
4725 ward UDP port 1194 in both directions. If you do not have control over
4726 the firewalls between the two machines, you may still be able to use
4727 OpenVPN by adding --ping 15 to each of the openvpn commands used below
4728 in the examples (this will cause each peer to send out a UDP ping to
4729 its remote peer once every 15 seconds which will cause many stateful
4730 firewalls to forward packets in both directions without an explicit
4731 firewall rule).
4732 If you are using a Linux iptables-based firewall, you may need to enter
4734 the following command to allow incoming packets on the TUN device:
4735 iptables -A INPUT -i tun+ -j ACCEPT
4737 See the firewalls section below for more information on configuring
4739 firewalls for use with OpenVPN.
4740 VPN Address Setup:
4742 For purposes of our example, our two machines will be called bob.exam‐
4743 ple.com and alice.example.com. If you are constructing a VPN over the
4744 internet, then replace bob.example.com and alice.example.com with the
4745 internet hostname or IP address that each machine will use to contact
4746 the other over the internet.
4747 Now we will choose the tunnel endpoints. Tunnel endpoints are private
4749 IP addresses that only have meaning in the context of the VPN. Each
4750 machine will use the tunnel endpoint of the other machine to access it
4751 over the VPN. In our example, the tunnel endpoint for bob.example.com
4752 will be 10.4.0.1 and for alice.example.com, 10.4.0.2.
4753 Once the VPN is established, you have essentially created a secure
4755 alternate path between the two hosts which is addressed by using the
4756 tunnel endpoints. You can control which network traffic passes between
4757 the hosts (a) over the VPN or (b) independently of the VPN, by choosing
4758 whether to use (a) the VPN endpoint address or (b) the public internet
4759 address, to access the remote host. For example if you are on bob.exam‐
4760 ple.com and you wish to connect to alice.example.com via ssh without
4761 using the VPN (since ssh has its own built-in security) you would use
4762 the command ssh alice.example.com. However in the same scenario, you
4763 could also use the command telnet 10.4.0.2 to create a telnet session
4764 with alice.example.com over the VPN, that would use the VPN to secure
4765 the session rather than ssh.
4766 You can use any address you wish for the tunnel endpoints but make sure
4768 that they are private addresses (such as those that begin with 10 or
4769 192.168) and that they are not part of any existing subnet on the net‐
4770 works of either peer, unless you are bridging. If you use an address
4771 that is part of your local subnet for either of the tunnel endpoints,
4772 you will get a weird feedback loop.
4773 Example 1: A simple tunnel without security
4775 On bob:
4776 openvpn --remote alice.example.com --dev tun1 --ifconfig
4778 10.4.0.1 10.4.0.2 --verb 9
4779 On alice:
4781 openvpn --remote bob.example.com --dev tun1 --ifconfig 10.4.0.2
4783 10.4.0.1 --verb 9
4784 Now verify the tunnel is working by pinging across the tunnel.
4786 On bob:
4788 ping 10.4.0.2
4790 On alice:
4792 ping 10.4.0.1
4794 The --verb 9 option will produce verbose output, similar to the tcp‐
4796 dump(8) program. Omit the --verb 9 option to have OpenVPN run quietly.
4797 Example 2: A tunnel with static-key security (i.e. using a pre-shared
4799 secret)
4800 First build a static key on bob.
4801 openvpn --genkey --secret key
4803 This command will build a random key file called key (in ascii format).
4805 Now copy key to alice over a secure medium such as by using the scp(1)
4806 program.
4807 On bob:
4809 openvpn --remote alice.example.com --dev tun1 --ifconfig
4811 10.4.0.1 10.4.0.2 --verb 5 --secret key
4812 On alice:
4814 openvpn --remote bob.example.com --dev tun1 --ifconfig 10.4.0.2
4816 10.4.0.1 --verb 5 --secret key
4817 Now verify the tunnel is working by pinging across the tunnel.
4819 On bob:
4821 ping 10.4.0.2
4823 On alice:
4825 ping 10.4.0.1
4827 Example 3: A tunnel with full TLS-based security
4829 For this test, we will designate bob as the TLS client and alice as the
4830 TLS server. Note that client or server designation only has meaning
4831 for the TLS subsystem. It has no bearing on OpenVPN's peer-to-peer,
4832 UDP-based communication model.
4833 First, build a separate certificate/key pair for both bob and alice
4835 (see above where --cert is discussed for more info). Then construct
4836 Diffie Hellman parameters (see above where --dh is discussed for more
4837 info). You can also use the included test files client.crt,
4838 client.key, server.crt, server.key and ca.crt. The .crt files are cer‐
4839 tificates/public-keys, the .key files are private keys, and ca.crt is a
4840 certification authority who has signed both client.crt and server.crt.
4841 For Diffie Hellman parameters you can use the included file dh1024.pem.
4842 Note that all client, server, and certificate authority certificates
4843 and keys included in the OpenVPN distribution are totally insecure and
4844 should be used for testing only.
4845 On bob:
4847 openvpn --remote alice.example.com --dev tun1 --ifconfig
4849 10.4.0.1 10.4.0.2 --tls-client --ca ca.crt --cert client.crt
4850 --key client.key --reneg-sec 60 --verb 5
4851 On alice:
4853 openvpn --remote bob.example.com --dev tun1 --ifconfig 10.4.0.2
4855 10.4.0.1 --tls-server --dh dh1024.pem --ca ca.crt --cert
4856 server.crt --key server.key --reneg-sec 60 --verb 5
4857 Now verify the tunnel is working by pinging across the tunnel.
4859 On bob:
4861 ping 10.4.0.2
4863 On alice:
4865 ping 10.4.0.1
4867 Notice the --reneg-sec 60 option we used above. That tells OpenVPN to
4869 renegotiate the data channel keys every minute. Since we used --verb 5
4870 above, you will see status information on each new key negotiation.
4871 For production operations, a key renegotiation interval of 60 seconds
4873 is probably too frequent. Omit the --reneg-sec 60 option to use Open‐
4874 VPN's default key renegotiation interval of one hour.
4875 Routing:
4877 Assuming you can ping across the tunnel, the next step is to route a
4878 real subnet over the secure tunnel. Suppose that bob and alice have
4879 two network interfaces each, one connected to the internet, and the
4880 other to a private network. Our goal is to securely connect both pri‐
4881 vate networks. We will assume that bob's private subnet is 10.0.0.0/24
4882 and alice's is 10.0.1.0/24.
4883 First, ensure that IP forwarding is enabled on both peers. On Linux,
4885 enable routing:
4886 echo 1 > /proc/sys/net/ipv4/ip_forward
4888 and enable TUN packet forwarding through the firewall:
4890 iptables -A FORWARD -i tun+ -j ACCEPT
4892 On bob:
4894 route add -net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2
4896 On alice:
4898 route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1
4900 Now any machine on the 10.0.0.0/24 subnet can access any machine on the
4902 10.0.1.0/24 subnet over the secure tunnel (or vice versa).
4903 In a production environment, you could put the route command(s) in a
4905 script and execute with the --up option.
4906
4908 OpenVPN's usage of a single UDP port makes it fairly firewall-friendly.
4909 You should add an entry to your firewall rules to allow incoming Open‐
4910 VPN packets. On Linux 2.4+:
4911 iptables -A INPUT -p udp -s 1.2.3.4 --dport 1194 -j ACCEPT
4913 This will allow incoming packets on UDP port 1194 (OpenVPN's default
4915 UDP port) from an OpenVPN peer at 1.2.3.4.
4916 If you are using HMAC-based packet authentication (the default in any
4918 of OpenVPN's secure modes), having the firewall filter on source
4919 address can be considered optional, since HMAC packet authentication is
4920 a much more secure method of verifying the authenticity of a packet
4921 source. In that case:
4922 iptables -A INPUT -p udp --dport 1194 -j ACCEPT
4924 would be adequate and would not render the host inflexible with respect
4926 to its peer having a dynamic IP address.
4927 OpenVPN also works well on stateful firewalls. In some cases, you may
4929 not need to add any static rules to the firewall list if you are using
4930 a stateful firewall that knows how to track UDP connections. If you
4931 specify --ping n, OpenVPN will be guaranteed to send a packet to its
4932 peer at least once every n seconds. If n is less than the stateful
4933 firewall connection timeout, you can maintain an OpenVPN connection
4934 indefinitely without explicit firewall rules.
4935 You should also add firewall rules to allow incoming IP traffic on TUN
4937 or TAP devices such as:
4938 iptables -A INPUT -i tun+ -j ACCEPT
4940 to allow input packets from tun devices,
4942 iptables -A FORWARD -i tun+ -j ACCEPT
4944 to allow input packets from tun devices to be forwarded to other hosts
4946 on the local network,
4947 iptables -A INPUT -i tap+ -j ACCEPT
4949 to allow input packets from tap devices, and
4951 iptables -A FORWARD -i tap+ -j ACCEPT
4953 to allow input packets from tap devices to be forwarded to other hosts
4955 on the local network.
4956 These rules are secure if you use packet authentication, since no
4958 incoming packets will arrive on a TUN or TAP virtual device unless they
4959 first pass an HMAC authentication test.
4960
4962 http://openvpn.net/faq.html
4963
4965 For a more comprehensive guide to setting up OpenVPN in a production
4966 setting, see the OpenVPN HOWTO at http://openvpn.net/howto.html
4967
4969 For a description of OpenVPN's underlying protocol, see http://open‐
4970 vpn.net/security.html
4971
4973 OpenVPN's web site is at http://openvpn.net/
4974 Go here to download the latest version of OpenVPN, subscribe to the
4976 mailing lists, read the mailing list archives, or browse the SVN repos‐
4977 itory.
4978
4980 Report all bugs to the OpenVPN team <info@openvpn.net>.
4981
4983 dhcpcd(8), ifconfig(8), openssl(1), route(8), scp(1) ssh(1)
4984
4986 This product includes software developed by the OpenSSL Project (
4987 http://www.openssl.org/ )
4988 For more information on the TLS protocol, see
4990 http://www.ietf.org/rfc/rfc2246.txt
4991 For more information on the LZO real-time compression library see
4993 http://www.oberhumer.com/opensource/lzo/
4994
4996 Copyright (C) 2002-2018 OpenVPN Inc This program is free software; you
4997 can redistribute it and/or modify it under the terms of the GNU General
4998 Public License version 2 as published by the Free Software Foundation.
4999
5001 James Yonan <jim@yonan.net>
5002 28 February 2018 openvpn(8)