1OPENVPN(8) System Manager's Manual OPENVPN(8)
2
6 openvpn - Secure IP tunnel daemon
7
9 openvpn [ options ... ]
10 openvpn --help
11
14 OpenVPN is an open source VPN daemon by James Yonan. Because OpenVPN
15 tries to be a universal VPN tool offering a great deal of flexibility,
16 there are a lot of options on this manual page. If you're new to Open‐
17 VPN, you might want to skip ahead to the examples section where you
18 will see how to construct simple VPNs on the command line without even
19 needing a configuration file.
20 Also note that there's more documentation and examples on the OpenVPN
22 web site: https://openvpn.net/
23 And if you would like to see a shorter version of this manual, see the
25 openvpn usage message which can be obtained by running openvpn without
26 any parameters.
27
29 OpenVPN is a robust and highly flexible VPN daemon. OpenVPN supports
30 SSL/TLS security, ethernet bridging, TCP or UDP tunnel transport
31 through proxies or NAT, support for dynamic IP addresses and DHCP,
32 scalability to hundreds or thousands of users, and portability to most
33 major OS platforms.
34 OpenVPN is tightly bound to the OpenSSL library, and derives much of
36 its crypto capabilities from it.
37 OpenVPN supports conventional encryption using a pre-shared secret key
39 (Static Key mode) or public key security (SSL/TLS mode) using client &
40 server certificates. OpenVPN also supports non-encrypted TCP/UDP tun‐
41 nels.
42 OpenVPN is designed to work with the TUN/TAP virtual networking inter‐
44 face that exists on most platforms.
45 Overall, OpenVPN aims to offer many of the key features of IPSec but
47 with a relatively lightweight footprint.
48
50 OpenVPN allows any option to be placed either on the command line or in
51 a configuration file. Though all command line options are preceded by a
52 double-leading-dash ("--"), this prefix can be removed when an option
53 is placed in a configuration file.
54 Generic Options
56 This section covers generic options which are accessible regardless of
57 which mode OpenVPN is configured as.
58 --help Show options.
60 --auth-nocache
62 Don't cache --askpass or --auth-user-pass username/passwords in
63 virtual memory.
64 If specified, this directive will cause OpenVPN to immediately
66 forget username/password inputs after they are used. As a re‐
67 sult, when OpenVPN needs a username/password, it will prompt for
68 input from stdin, which may be multiple times during the dura‐
69 tion of an OpenVPN session.
70 When using --auth-nocache in combination with a user/password
72 file and --chroot or --daemon, make sure to use an absolute
73 path.
74 This directive does not affect the --http-proxy username/pass‐
76 word. It is always cached.
77 --cd dir
79 Change directory to dir prior to reading any files such as con‐
80 figuration files, key files, scripts, etc. dir should be an ab‐
81 solute path, with a leading "/", and without any references to
82 the current directory such as . or ...
83 This option is useful when you are running OpenVPN in --daemon
85 mode, and you want to consolidate all of your OpenVPN control
86 files in one location.
87 --chroot dir
89 Chroot to dir after initialization. --chroot essentially rede‐
90 fines dir as being the top level directory tree (/). OpenVPN
91 will therefore be unable to access any files outside this tree.
92 This can be desirable from a security standpoint.
93 Since the chroot operation is delayed until after initializa‐
95 tion, most OpenVPN options that reference files will operate in
96 a pre-chroot context.
97 In many cases, the dir parameter can point to an empty direc‐
99 tory, however complications can result when scripts or restarts
100 are executed after the chroot operation.
101 Note: The SSL library will probably need /dev/urandom to be
103 available inside the chroot directory dir. This is because SSL
104 libraries occasionally need to collect fresh randomness. Newer
105 linux kernels and some BSDs implement a getrandom() or geten‐
106 tropy() syscall that removes the need for /dev/urandom to be
107 available.
108 --compat-mode version
110 This option provides a convenient way to alter the defaults of
111 OpenVPN to be more compatible with the version version speci‐
112 fied. All of the changes this option applies can also be
113 achieved using individual configuration options.
114 The version specified with this option is the version of OpenVPN
116 peer OpenVPN should try to be compatible with. In general Open‐
117 VPN should be compatible with the last two previous version
118 without this option. E.g. OpenVPN 2.6.0 should be compatible
119 with 2.5.x and 2.4.x without this option. However, there might
120 be some edge cases that still require this option even in these
121 cases.
122 Note: Using this option reverts defaults to no longer recom‐
124 mended values and should be avoided if possible.
125 The following table details what defaults are changed depending
127 on the version specified.
128 • 2.5.x or lower: --allow-compression asym is automatically
130 added to the configuration if no other compression options are
131 present.
132 • 2.4.x or lower: The cipher in --cipher is appended to
134 --data-ciphers.
135 • 2.3.x or lower: --data-cipher-fallback is automatically added
137 with the same cipher as --cipher.
138 • 2.3.6 or lower: --tls-version-min 1.0 is added to the configu‐
140 ration when --tls-version-min is not explicitly set.
141 If not required, this is option should be avoided. Setting this
143 option can lower security or disable features like data-channel
144 offloading.
145 --config file
147 Load additional config options from file where each line corre‐
148 sponds to one command line option, but with the leading -- re‐
149 moved.
150 If --config file is the only option to the openvpn command, the
152 --config can be removed, and the command can be given as openvpn
153 file
154 Note that configuration files can be nested to a reasonable
156 depth.
157 Double quotation or single quotation characters ("", '') can be
159 used to enclose single parameters containing whitespace, and "#"
160 or ";" characters in the first column can be used to denote com‐
161 ments.
162 Note that OpenVPN 2.0 and higher performs backslash-based shell
164 escaping for characters not in single quotations, so the follow‐
165 ing mappings should be observed:
166 \\ Maps to a single backslash character (\).
168 \" Pass a literal doublequote character ("), don't
169 interpret it as enclosing a parameter.
170 \[SPACE] Pass a literal space or tab character, don't
171 interpret it as a parameter delimiter.
172 For example on Windows, use double backslashes to represent
174 pathnames:
175 secret "c:\\OpenVPN\\secret.key"
177 For examples of configuration files, see
179 https://openvpn.net/community-resources/how-to/
180 Here is an example configuration file:
182 #
184 # Sample OpenVPN configuration file for
185 # using a pre-shared static key.
186 #
187 # '#' or ';' may be used to delimit comments.
188 # Use a dynamic tun device.
190 dev tun
191 # Our remote peer
193 remote mypeer.mydomain
194 # 10.1.0.1 is our local VPN endpoint
196 # 10.1.0.2 is our remote VPN endpoint
197 ifconfig 10.1.0.1 10.1.0.2
198 # Our pre-shared static key
200 secret static.key
201 --daemon progname
203 Become a daemon after all initialization functions are com‐
204 pleted.
205 Valid syntaxes:
207 daemon
209 daemon progname
210 This option will cause all message and error output to be sent
212 to the syslog file (such as /var/log/messages), except for the
213 output of scripts and ifconfig commands, which will go to
214 /dev/null unless otherwise redirected. The syslog redirection
215 occurs immediately at the point that --daemon is parsed on the
216 command line even though the daemonization point occurs later.
217 If one of the --log options is present, it will supersede syslog
218 redirection.
219 The optional progname parameter will cause OpenVPN to report its
221 program name to the system logger as progname. This can be use‐
222 ful in linking OpenVPN messages in the syslog file with specific
223 tunnels. When unspecified, progname defaults to openvpn.
224 When OpenVPN is run with the --daemon option, it will try to de‐
226 lay daemonization until the majority of initialization functions
227 which are capable of generating fatal errors are complete. This
228 means that initialization scripts can test the return status of
229 the openvpn command for a fairly reliable indication of whether
230 the command has correctly initialized and entered the packet
231 forwarding event loop.
232 In OpenVPN, the vast majority of errors which occur after ini‐
234 tialization are non-fatal.
235 Note: as soon as OpenVPN has daemonized, it can not ask for
237 usernames, passwords, or key pass phrases anymore. This has cer‐
238 tain consequences, namely that using a password-protected pri‐
239 vate key will fail unless the --askpass option is used to tell
240 OpenVPN to ask for the pass phrase (this requirement is new in
241 v2.3.7, and is a consequence of calling daemon() before initial‐
242 izing the crypto layer).
243 Further, using --daemon together with --auth-user-pass (entered
245 on console) and --auth-nocache will fail as soon as key renego‐
246 tiation (and reauthentication) occurs.
247 --disable-dco
249 Disable "data channel offload" (DCO).
250 On Linux don't use the ovpn-dco device driver, but rather rely
252 on the legacy tun module.
253 You may want to use this option if your server needs to allow
255 clients older than version 2.4 to connect.
256 --disable-occ
258 DEPRECATED Disable "options consistency check" (OCC) in configu‐
259 rations that do not use TLS.
260 Don't output a warning message if option inconsistencies are de‐
262 tected between peers. An example of an option inconsistency
263 would be where one peer uses --dev tun while the other peer uses
264 --dev tap.
265 Use of this option is discouraged, but is provided as a tempo‐
267 rary fix in situations where a recent version of OpenVPN must
268 connect to an old version.
269 --engine engine-name
271 Enable OpenSSL hardware-based crypto engine functionality.
272 Valid syntaxes:
274 engine
276 engine engine-name
277 If engine-name is specified, use a specific crypto engine. Use
279 the --show-engines standalone option to list the crypto engines
280 which are supported by OpenSSL.
281 --fast-io
283 (Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a
284 call to poll/epoll/select prior to the write operation. The pur‐
285 pose of such a call would normally be to block until the device
286 or socket is ready to accept the write. Such blocking is unnec‐
287 essary on some platforms which don't support write blocking on
288 UDP sockets or TUN/TAP devices. In such cases, one can optimize
289 the event loop by avoiding the poll/epoll/select call, improving
290 CPU efficiency by 5% to 10%.
291 This option can only be used on non-Windows systems, when
293 --proto udp is specified, and when --shaper is NOT specified.
294 --group group
296 Similar to the --user option, this option changes the group ID
297 of the OpenVPN process to group after initialization.
298 --ignore-unknown-option args
300 Valid syntax:
301 ignore-unknown-options opt1 opt2 opt3 ... optN
303 When one of options opt1 ... optN is encountered in the configu‐
305 ration file the configuration file parsing does not fail if this
306 OpenVPN version does not support the option. Multiple --ig‐
307 nore-unknown-option options can be given to support a larger
308 number of options to ignore.
309 This option should be used with caution, as there are good secu‐
311 rity reasons for having OpenVPN fail if it detects problems in a
312 config file. Having said that, there are valid reasons for
313 wanting new software features to gracefully degrade when encoun‐
314 tered by older software versions.
315 --ignore-unknown-option is available since OpenVPN 2.3.3.
317 --iproute cmd
319 Set alternate command to execute instead of default iproute2
320 command. May be used in order to execute OpenVPN in unprivi‐
321 leged environment.
322 --keying-material-exporter args
324 Save Exported Keying Material [RFC5705] of len bytes (must be
325 between 16 and 4095 bytes) using label in environment (ex‐
326 ported_keying_material) for use by plugins in OPEN‐
327 VPN_PLUGIN_TLS_FINAL callback.
328 Valid syntax:
330 keying-material-exporter label len
332 Note that exporter labels have the potential to collide with ex‐
334 isting PRF labels. In order to prevent this, labels MUST begin
335 with EXPORTER.
336 --mlock
338 Disable paging by calling the POSIX mlockall function. Requires
339 that OpenVPN be initially run as root (though OpenVPN can subse‐
340 quently downgrade its UID using the --user option).
341 Using this option ensures that key material and tunnel data are
343 never written to disk due to virtual memory paging operations
344 which occur under most modern operating systems. It ensures that
345 even if an attacker was able to crack the box running OpenVPN,
346 he would not be able to scan the system swap file to recover
347 previously used ephemeral keys, which are used for a period of
348 time governed by the --reneg options (see below), then are dis‐
349 carded.
350 The downside of using --mlock is that it will reduce the amount
352 of physical memory available to other applications.
353 The limit on how much memory can be locked and how that limit is
355 enforced are OS-dependent. On Linux the default limit that an
356 unprivileged process may lock (RLIMIT_MEMLOCK) is low, and if
357 privileges are dropped later, future memory allocations will
358 very likely fail. The limit can be increased using ulimit or
359 systemd directives depending on how OpenVPN is started.
360 If the platform has the getrlimit(2) system call, OpenVPN will
362 check for the amount of mlock-able memory before calling mlock‐
363 all(2), and tries to increase the limit to 100 MB if less than
364 this is configured. 100 Mb is somewhat arbitrary - it is enough
365 for a moderately-sized OpenVPN deployment, but the memory usage
366 might go beyond that if the number of concurrent clients is
367 high.
368 --nice n
370 Change process priority after initialization (n greater than 0
371 is lower priority, n less than zero is higher priority).
372 --persist-key
374 Don't re-read key files across SIGUSR1 or --ping-restart.
375 This option can be combined with --user to allow restarts trig‐
377 gered by the SIGUSR1 signal. Normally if you drop root privi‐
378 leges in OpenVPN, the daemon cannot be restarted since it will
379 now be unable to re-read protected key files.
380 This option solves the problem by persisting keys across SIGUSR1
382 resets, so they don't need to be re-read.
383 --providers providers
385 Load the list of (OpenSSL) providers. This is mainly useful for
386 using an external provider for key management like tpm2-openssl
387 or to load the legacy provider with
388 --providers legacy default
390 Behaviour of changing this option between SIGHUP might not be
392 well behaving. If you need to change/add/remove this option,
393 fully restart OpenVPN.
394 --remap-usr1 signal
396 Control whether internally or externally generated SIGUSR1 sig‐
397 nals are remapped to SIGHUP (restart without persisting state)
398 or SIGTERM (exit).
399 signal can be set to SIGHUP or SIGTERM. By default, no remapping
401 occurs.
402 --script-security level
404 This directive offers policy-level control over OpenVPN's usage
405 of external programs and scripts. Lower level values are more
406 restrictive, higher values are more permissive. Settings for
407 level:
408 0 Strictly no calling of external programs.
410 1 (Default) Only call built-in executables such as ifcon‐
412 fig, ip, route, or netsh.
413 2 Allow calling of built-in executables and user-defined
415 scripts.
416 3 Allow passwords to be passed to scripts via environmental
418 variables (potentially unsafe).
419 OpenVPN releases before v2.3 also supported a method flag which
421 indicated how OpenVPN should call external commands and scripts.
422 This could be either execve or system. As of OpenVPN 2.3, this
423 flag is no longer accepted. In most *nix environments the ex‐
424 ecve() approach has been used without any issues.
425 Some directives such as --up allow options to be passed to the
427 external script. In these cases make sure the script name does
428 not contain any spaces or the configuration parser will choke
429 because it can't determine where the script name ends and script
430 options start.
431 To run scripts in Windows in earlier OpenVPN versions you needed
433 to either add a full path to the script interpreter which can
434 parse the script or use the system flag to run these scripts. As
435 of OpenVPN 2.3 it is now a strict requirement to have full path
436 to the script interpreter when running non-executables files.
437 This is not needed for executable files, such as .exe, .com,
438 .bat or .cmd files. For example, if you have a Visual Basic
439 script, you must use this syntax now:
440 --up 'C:\\Windows\\System32\\wscript.exe C:\\Program\ Files\\OpenVPN\\config\\my-up-script.vbs'
442 Please note the single quote marks and the escaping of the back‐
444 slashes (\) and the space character.
445 The reason the support for the system flag was removed is due to
447 the security implications with shell expansions when executing
448 scripts via the system() call.
449 --setcon context
451 Apply SELinux context after initialization. This essentially
452 provides the ability to restrict OpenVPN's rights to only net‐
453 work I/O operations, thanks to SELinux. This goes further than
454 --user and --chroot in that those two, while being great secu‐
455 rity features, unfortunately do not protect against privilege
456 escalation by exploitation of a vulnerable system call. You can
457 of course combine all three, but please note that since setcon
458 requires access to /proc you will have to provide it inside the
459 chroot directory (e.g. with mount --bind).
460 Since the setcon operation is delayed until after initializa‐
462 tion, OpenVPN can be restricted to just network-related system
463 calls, whereas by applying the context before startup (such as
464 the OpenVPN one provided in the SELinux Reference Policies) you
465 will have to allow many things required only during initializa‐
466 tion.
467 Like with chroot, complications can result when scripts or
469 restarts are executed after the setcon operation, which is why
470 you should really consider using the --persist-key and --per‐
471 sist-tun options.
472 --status args
474 Write operational status to file every n seconds. n defaults to
475 60 if not specified.
476 Valid syntaxes:
478 status file
480 status file n
481 Status can also be written to the syslog by sending a SIGUSR2
483 signal.
484 With multi-client capability enabled on a server, the status
486 file includes a list of clients and a routing table. The output
487 format can be controlled by the --status-version option in that
488 case.
489 For clients or instances running in point-to-point mode, it will
491 contain the traffic statistics.
492 --status-version n
494 Set the status file format version number to n.
495 This only affects the status file on servers with multi-client
497 capability enabled. Valid status version values:
498 1 Traditional format (default). The client list contains
500 the following fields comma-separated: Common Name, Real
501 Address, Bytes Received, Bytes Sent, Connected Since.
502 2 A more reliable format for external processing. Compared
504 to version 1, the client list contains some additional
505 fields: Virtual Address, Virtual IPv6 Address, Username,
506 Client ID, Peer ID, Data Channel Cipher. Future versions
507 may extend the number of fields.
508 3 Identical to 2, but fields are tab-separated.
510 --test-crypto
512 Do a self-test of OpenVPN's crypto options by encrypting and de‐
513 crypting test packets using the data channel encryption options
514 specified above. This option does not require a peer to func‐
515 tion, and therefore can be specified without --dev or --remote.
516 The typical usage of --test-crypto would be something like this:
518 openvpn --test-crypto --secret key
520 or
522 openvpn --test-crypto --secret key --verb 9
524 This option is very useful to test OpenVPN after it has been
526 ported to a new platform, or to isolate problems in the com‐
527 piler, OpenSSL crypto library, or OpenVPN's crypto code. Since
528 it is a self-test mode, problems with encryption and authentica‐
529 tion can be debugged independently of network and tunnel issues.
530 --tmp-dir dir
532 Specify a directory dir for temporary files. This directory will
533 be used by openvpn processes and script to communicate temporary
534 data with openvpn main process. Note that the directory must be
535 writable by the OpenVPN process after it has dropped it's root
536 privileges.
537 This directory will be used by in the following cases:
539 • --client-connect scripts and OPENVPN_PLUGIN_CLIENT_CONNECT
541 plug-in hook to dynamically generate client-specific configu‐
542 ration client_connect_config_file and return success/failure
543 via client_connect_deferred_file when using deferred client
544 connect method
545 • OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY plug-in hooks returns
547 success/failure via auth_control_file when using deferred auth
548 method and pending authentication via pending_auth_file.
549 --use-prediction-resistance
551 Enable prediction resistance on mbed TLS's RNG.
552 Enabling prediction resistance causes the RNG to reseed in each
554 call for random. Reseeding this often can quickly deplete the
555 kernel entropy pool.
556 If you need this option, please consider running a daemon that
558 adds entropy to the kernel pool.
559 --user user
561 Change the user ID of the OpenVPN process to user after initial‐
562 ization, dropping privileges in the process. This option is use‐
563 ful to protect the system in the event that some hostile party
564 was able to gain control of an OpenVPN session. Though OpenVPN's
565 security features make this unlikely, it is provided as a second
566 line of defense.
567 By setting user to an unprivileged user dedicated to run open‐
569 vpn, the hostile party would be limited in what damage they
570 could cause. Of course once you take away privileges, you cannot
571 return them to an OpenVPN session. This means, for example, that
572 if you want to reset an OpenVPN daemon with a SIGUSR1 signal
573 (for example in response to a DHCP reset), you should make use
574 of one or more of the --persist options to ensure that OpenVPN
575 doesn't need to execute any privileged operations in order to
576 restart (such as re-reading key files or running ifconfig on the
577 TUN device).
578 NOTE: Previous versions of openvpn used nobody as the example
580 unpriviledged user. It is not recommended to actually use that
581 user since it is usually used by other system services already.
582 Always create a dedicated user for openvpn.
583 --writepid file
585 Write OpenVPN's main process ID to file.
586 Log options
588 --echo parms
589 Echo parms to log output.
590 Designed to be used to send messages to a controlling applica‐
592 tion which is receiving the OpenVPN log output.
593 --errors-to-stderr
595 Output errors to stderr instead of stdout unless log output is
596 redirected by one of the --log options.
597 --log file
599 Output logging messages to file, including output to std‐
600 out/stderr which is generated by called scripts. If file already
601 exists it will be truncated. This option takes effect immedi‐
602 ately when it is parsed in the command line and will supersede
603 syslog output if --daemon is also specified. This option is per‐
604 sistent over the entire course of an OpenVPN instantiation and
605 will not be reset by SIGHUP, SIGUSR1, or --ping-restart.
606 Note that on Windows, when OpenVPN is started as a service, log‐
608 ging occurs by default without the need to specify this option.
609 --log-append file
611 Append logging messages to file. If file does not exist, it
612 will be created. This option behaves exactly like --log except
613 that it appends to rather than truncating the log file.
614 --machine-readable-output
616 Always write timestamps and message flags to log messages, even
617 when they otherwise would not be prefixed. In particular, this
618 applies to log messages sent to stdout.
619 --mute n
621 Log at most n consecutive messages in the same category. This is
622 useful to limit repetitive logging of similar message types.
623 --mute-replay-warnings
625 Silence the output of replay warnings, which are a common false
626 alarm on WiFi networks. This option preserves the security of
627 the replay protection code without the verbosity associated with
628 warnings about duplicate packets.
629 --suppress-timestamps
631 Avoid writing timestamps to log messages, even when they other‐
632 wise would be prepended. In particular, this applies to log mes‐
633 sages sent to stdout.
634 --syslog progname
636 Direct log output to system logger, but do not become a daemon.
637 See --daemon directive above for description of progname parame‐
638 ter.
639 --verb n
641 Set output verbosity to n (default 1). Each level shows all info
642 from the previous levels. Level 3 is recommended if you want a
643 good summary of what's happening without being swamped by out‐
644 put.
645 0 No output except fatal errors.
647 1 to 4 Normal usage range.
649 5 Outputs R and W characters to the console for each packet
651 read and write, uppercase is used for TCP/UDP packets and
652 lowercase is used for TUN/TAP packets.
653 6 to 11
655 Debug info range (see errlevel.h in the source code for
656 additional information on debug levels).
657 Protocol options
659 Options in this section affect features available in the OpenVPN wire
660 protocol. Many of these options also define the encryption options of
661 the data channel in the OpenVPN wire protocol. These options must be
662 configured in a compatible way between both the local and remote side.
663 --allow-compression mode
665 As described in the --compress option, compression is a poten‐
666 tially dangerous option. This option allows controlling the be‐
667 haviour of OpenVPN when compression is used and allowed.
668 Valid syntaxes:
670 allow-compression
672 allow-compression mode
673 The mode argument can be one of the following values:
675 asym OpenVPN will only decompress downlink packets but not
677 compress uplink packets. This also allows migrating to
678 disable compression when changing both server and client
679 configurations to remove compression at the same time is
680 not a feasible option.
681 no (default)
683 OpenVPN will refuse any compression. If data-channel of‐
684 floading is enabled, OpenVPN will additionally also
685 refuse compression framing (stub).
686 yes OpenVPN will send and receive compressed packets.
688 --auth alg
690 Authenticate data channel packets and (if enabled) tls-auth con‐
691 trol channel packets with HMAC using message digest algorithm
692 alg. (The default is SHA1 ). HMAC is a commonly used message au‐
693 thentication algorithm (MAC) that uses a data string, a secure
694 hash algorithm and a key to produce a digital signature.
695 The OpenVPN data channel protocol uses encrypt-then-mac (i.e.
697 first encrypt a packet then HMAC the resulting ciphertext),
698 which prevents padding oracle attacks.
699 If an AEAD cipher mode (e.g. GCM) is chosen then the specified
701 --auth algorithm is ignored for the data channel and the authen‐
702 tication method of the AEAD cipher is used instead. Note that
703 alg still specifies the digest used for tls-auth.
704 In static-key encryption mode, the HMAC key is included in the
706 key file generated by --genkey. In TLS mode, the HMAC key is dy‐
707 namically generated and shared between peers via the TLS control
708 channel. If OpenVPN receives a packet with a bad HMAC it will
709 drop the packet. HMAC usually adds 16 or 20 bytes per packet.
710 Set alg=none to disable authentication.
711 For more information on HMAC see
713 http://www.cs.ucsd.edu/users/mihir/papers/hmac.html
714 --cipher alg
716 This option should not be used any longer in TLS mode and still
717 exists for two reasons:
718 • compatibility with old configurations still carrying it
720 around;
721 • allow users connecting to OpenVPN peers older than 2.6.0 to
723 have --cipher configured the same way as the remote counter‐
724 part. This can avoid MTU/frame size warnings.
725 Before 2.4.0, this option was used to select the cipher to be
727 configured on the data channel, however, later versions usually
728 ignored this directive in favour of a negotiated cipher. Start‐
729 ing with 2.6.0, this option is always ignored in TLS mode when
730 it comes to configuring the cipher and will only control the ci‐
731 pher for --secret pre-shared-key mode (note: this mode is depre‐
732 cated and strictly not recommended).
733 If you wish to specify the cipher to use on the data channel,
735 please see --data-ciphers (for regular negotiation) and
736 --data-ciphers-fallback (for a fallback option when the negotia‐
737 tion cannot take place because the other peer is old or has ne‐
738 gotiation disabled).
739 To see ciphers that are available with OpenVPN, use the
741 --show-ciphers option.
742 Set alg to none to disable encryption.
744 --compress algorithm
746 DEPRECATED Enable a compression algorithm. Compression is gener‐
747 ally not recommended. VPN tunnels which use compression are sus‐
748 ceptible to the VORALCE attack vector. See also the migrate pa‐
749 rameter below.
750 The algorithm parameter may be lzo, lz4, lz4-v2, stub, stub-v2,
752 migrate or empty. LZO and LZ4 are different compression algo‐
753 rithms, with LZ4 generally offering the best performance with
754 least CPU usage.
755 The lz4-v2 and stub-v2 variants implement a better framing that
757 does not add overhead when packets cannot be compressed. All
758 other variants always add one extra framing byte compared to no
759 compression framing.
760 Especially stub-v2 is essentially identical to no compression
762 and no compression framing as its header indicates IP version 5
763 in a tun setup and can (ab)used to complete disable compression
764 to clients. (See the migrate option below)
765 If the algorithm parameter is stub, stub-v2 or empty, compres‐
767 sion will be turned off, but the packet framing for compression
768 will still be enabled, allowing a different setting to be pushed
769 later. Additionally, stub and stub-v2 wil disable announcing
770 lzo and lz4 compression support via IV_ variables to the server.
771 Note: the stub (or empty) option is NOT compatible with the
773 older option --comp-lzo no.
774 Using migrate as compression algorithm enables a special migra‐
776 tion mode. It allows migration away from the --com‐
777 press/--comp-lzo options to no compression. This option sets
778 the server to no compression mode and the server behaves identi‐
779 cal to a server without a compression option for all clients
780 without a compression in their config. However, if a client is
781 detected that indicates that compression is used (via OCC), the
782 server will automatically add --push compress stub-v2 to the
783 client specific configuration if supported by the client and
784 otherwise switch to comp-lzo no and add --push comp-lzo to the
785 client specific configuration.
786 *Security Considerations*
788 Compression and encryption is a tricky combination. If an at‐
790 tacker knows or is able to control (parts of) the plain-text of
791 packets that contain secrets, the attacker might be able to ex‐
792 tract the secret if compression is enabled. See e.g. the CRIME
793 and BREACH attacks on TLS and VORACLE on VPNs which also lever‐
794 age to break encryption. If you are not entirely sure that the
795 above does not apply to your traffic, you are advised to not en‐
796 able compression.
797 --comp-lzo mode
799 DEPRECATED Enable LZO compression algorithm. Compression is
800 generally not recommended. VPN tunnels which uses compression
801 are suspectible to the VORALCE attack vector.
802 Use LZO compression -- may add up to 1 byte per packet for in‐
804 compressible data. mode may be yes, no, or adaptive (default).
805 In a server mode setup, it is possible to selectively turn com‐
807 pression on or off for individual clients.
808 First, make sure the client-side config file enables selective
810 compression by having at least one --comp-lzo directive, such as
811 --comp-lzo no. This will turn off compression by default, but
812 allow a future directive push from the server to dynamically
813 change the on/off/adaptive setting.
814 Next in a --client-config-dir file, specify the compression set‐
816 ting for the client, for example:
817 comp-lzo yes
819 push "comp-lzo yes"
820 The first line sets the comp-lzo setting for the server side of
822 the link, the second sets the client side.
823 --comp-noadapt
825 DEPRECATED When used in conjunction with --comp-lzo, this option
826 will disable OpenVPN's adaptive compression algorithm. Normally,
827 adaptive compression is enabled with --comp-lzo.
828 Adaptive compression tries to optimize the case where you have
830 compression enabled, but you are sending predominantly incom‐
831 pressible (or pre-compressed) packets over the tunnel, such as
832 an FTP or rsync transfer of a large, compressed file. With adap‐
833 tive compression, OpenVPN will periodically sample the compres‐
834 sion process to measure its efficiency. If the data being sent
835 over the tunnel is already compressed, the compression effi‐
836 ciency will be very low, triggering openvpn to disable compres‐
837 sion for a period of time until the next re-sample test.
838 --key-direction
840 Alternative way of specifying the optional direction parameter
841 for the --tls-auth and --secret options. Useful when using in‐
842 line files (See section on inline files).
843 --data-ciphers cipher-list
845 Restrict the allowed ciphers to be negotiated to the ciphers in
846 cipher-list. cipher-list is a colon-separated list of ciphers,
847 and defaults to AES-256-GCM:AES-128-GCM:CHACHA20-POLY1305 when
848 Chacha20-Poly1305 is available and otherwise
849 AES-256-GCM:AES-128-GCM.
850 For servers, the first cipher from cipher-list that is also sup‐
852 ported by the client will be pushed to clients that support ci‐
853 pher negotiation.
854 For more details see the chapter on Data channel cipher negotia‐
856 tion. Especially if you need to support clients with OpenVPN
857 versions older than 2.4!
858 Starting with OpenVPN 2.6 a cipher can be prefixed with a ? to
860 mark it as optional. This allows including ciphers in the list
861 that may not be available on all platforms. E.g.
862 AES-256-GCM:AES-128-GCM:?CHACHA20-POLY1305 would only enable
863 Chacha20-Poly1305 if the underlying SSL library (and its config‐
864 uration) supports it.
865 Cipher negotiation is enabled in client-server mode only. I.e.
867 if --mode is set to server (server-side, implied by setting
868 --server ), or if --pull is specified (client-side, implied by
869 setting --client).
870 If no common cipher is found during cipher negotiation, the con‐
872 nection is terminated. To support old clients/old servers that
873 do not provide any cipher negotiation support see --data-ci‐
874 phers-fallback.
875 If --compat-mode is set to a version older than 2.5.0 the cipher
877 specified by --cipher will be appended to --data-ciphers if not
878 already present.
879 This list is restricted to be 127 chars long after conversion to
881 OpenVPN ciphers.
882 This option was called --ncp-ciphers in OpenVPN 2.4 but has been
884 renamed to --data-ciphers in OpenVPN 2.5 to more accurately re‐
885 flect its meaning.
886 --data-ciphers-fallback alg
888 Configure a cipher that is used to fall back to if we could not
889 determine which cipher the peer is willing to use.
890 This option should only be needed to connect to peers that are
892 running OpenVPN 2.3 or older versions, and have been configured
893 with --enable-small (typically used on routers or other embedded
894 devices).
895 --secret args
897 DEPRECATED Enable Static Key encryption mode (non-TLS). Use
898 pre-shared secret file which was generated with --genkey.
899 Valid syntaxes:
901 secret file
903 secret file direction
904 The optional direction parameter enables the use of 4 distinct
906 keys (HMAC-send, cipher-encrypt, HMAC-receive, cipher-decrypt),
907 so that each data flow direction has a different set of HMAC and
908 cipher keys. This has a number of desirable security properties
909 including eliminating certain kinds of DoS and message replay
910 attacks.
911 When the direction parameter is omitted, 2 keys are used bidi‐
913 rectionally, one for HMAC and the other for encryption/decryp‐
914 tion.
915 The direction parameter should always be complementary on either
917 side of the connection, i.e. one side should use 0 and the other
918 should use 1, or both sides should omit it altogether.
919 The direction parameter requires that file contains a 2048 bit
921 key. While pre-1.5 versions of OpenVPN generate 1024 bit key
922 files, any version of OpenVPN which supports the direction pa‐
923 rameter, will also support 2048 bit key file generation using
924 the --genkey option.
925 Static key encryption mode has certain advantages, the primary
927 being ease of configuration.
928 There are no certificates or certificate authorities or compli‐
930 cated negotiation handshakes and protocols. The only requirement
931 is that you have a pre-existing secure channel with your peer
932 (such as ssh) to initially copy the key. This requirement, along
933 with the fact that your key never changes unless you manually
934 generate a new one, makes it somewhat less secure than TLS mode
935 (see below). If an attacker manages to steal your key, every‐
936 thing that was ever encrypted with it is compromised. Contrast
937 that to the perfect forward secrecy features of TLS mode (using
938 Diffie Hellman key exchange), where even if an attacker was able
939 to steal your private key, he would gain no information to help
940 him decrypt past sessions.
941 Another advantageous aspect of Static Key encryption mode is
943 that it is a handshake-free protocol without any distinguishing
944 signature or feature (such as a header or protocol handshake se‐
945 quence) that would mark the ciphertext packets as being gener‐
946 ated by OpenVPN. Anyone eavesdropping on the wire would see
947 nothing but random-looking data.
948 --tran-window n
950 Transition window -- our old key can live this many seconds af‐
951 ter a new a key renegotiation begins (default 3600 seconds).
952 This feature allows for a graceful transition from old to new
953 key, and removes the key renegotiation sequence from the criti‐
954 cal path of tunnel data forwarding.
955 Client Options
957 The client options are used when connecting to an OpenVPN server con‐
958 figured to use --server, --server-bridge, or --mode server in its con‐
959 figuration.
960 --allow-pull-fqdn
962 Allow client to pull DNS names from server (rather than being
963 limited to IP address) for --ifconfig, --route, and
964 --route-gateway.
965 --allow-recursive-routing
967 When this option is set, OpenVPN will not drop incoming tun
968 packets with same destination as host.
969 --auth-token token
971 This is not an option to be used directly in any configuration
972 files, but rather push this option from a --client-connect
973 script or a --plugin which hooks into the OPEN‐
974 VPN_PLUGIN_CLIENT_CONNECT or OPENVPN_PLUGIN_CLIENT_CONNECT_V2
975 calls. This option provides a possibility to replace the clients
976 password with an authentication token during the lifetime of the
977 OpenVPN client.
978 Whenever the connection is renegotiated and the
980 --auth-user-pass-verify script or --plugin making use of the
981 OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY hook is triggered, it will
982 pass over this token as the password instead of the password the
983 user provided. The authentication token can only be reset by a
984 full reconnect where the server can push new options to the
985 client. The password the user entered is never preserved once an
986 authentication token has been set. If the OpenVPN server side
987 rejects the authentication token then the client will receive an
988 AUTH_FAILED and disconnect.
989 The purpose of this is to enable two factor authentication meth‐
991 ods, such as HOTP or TOTP, to be used without needing to re‐
992 trieve a new OTP code each time the connection is renegotiated.
993 Another use case is to cache authentication data on the client
994 without needing to have the users password cached in memory dur‐
995 ing the life time of the session.
996 To make use of this feature, the --client-connect script or
998 --plugin needs to put
999 push "auth-token UNIQUE_TOKEN_VALUE"
1001 into the file/buffer for dynamic configuration data. This will
1003 then make the OpenVPN server to push this value to the client,
1004 which replaces the local password with the UNIQUE_TOKEN_VALUE.
1005 Newer clients (2.4.7+) will fall back to the original password
1007 method after a failed auth. Older clients will keep using the
1008 token value and react according to --auth-retry
1009 --auth-token-user base64username
1011 Companion option to --auth-token. This options allows one to
1012 override the username used by the client when reauthenticating
1013 with the auth-token. It also allows one to use --auth-token in
1014 setups that normally do not use username and password.
1015 The username has to be base64 encoded.
1017 --auth-user-pass
1019 Authenticate with server using username/password.
1020 Valid syntaxes:
1022 auth-user-pass
1024 auth-user-pass up
1025 If up is present, it must be a file containing username/password
1027 on 2 lines. If the password line is missing, OpenVPN will prompt
1028 for one.
1029 If up is omitted, username/password will be prompted from the
1031 console.
1032 The server configuration must specify an --auth-user-pass-verify
1034 script to verify the username/password provided by the client.
1035 --auth-retry type
1037 Controls how OpenVPN responds to username/password verification
1038 errors such as the client-side response to an AUTH_FAILED mes‐
1039 sage from the server or verification failure of the private key
1040 password.
1041 Normally used to prevent auth errors from being fatal on the
1043 client side, and to permit username/password requeries in case
1044 of error.
1045 An AUTH_FAILED message is generated by the server if the client
1047 fails --auth-user-pass authentication, or if the server-side
1048 --client-connect script returns an error status when the client
1049 tries to connect.
1050 type can be one of:
1052 none Client will exit with a fatal error (this is the de‐
1054 fault).
1055 nointeract
1057 Client will retry the connection without requerying for
1058 an --auth-user-pass username/password. Use this option
1059 for unattended clients.
1060 interact
1062 Client will requery for an --auth-user-pass user‐
1063 name/password and/or private key password before attempt‐
1064 ing a reconnection.
1065 Note that while this option cannot be pushed, it can be con‐
1067 trolled from the management interface.
1068 --client
1070 A helper directive designed to simplify the configuration of
1071 OpenVPN's client mode. This directive is equivalent to:
1072 pull
1074 tls-client
1075 --client-nat args
1077 This pushable client option sets up a stateless one-to-one NAT
1078 rule on packet addresses (not ports), and is useful in cases
1079 where routes or ifconfig settings pushed to the client would
1080 create an IP numbering conflict.
1081 Examples:
1083 client-nat snat 192.168.0.0/255.255.0.0
1085 client-nat dnat 10.64.0.0/255.255.0.0
1086 network/netmask (for example 192.168.0.0/255.255.0.0) defines
1088 the local view of a resource from the client perspective, while
1089 alias/netmask (for example 10.64.0.0/255.255.0.0) defines the
1090 remote view from the server perspective.
1091 Use snat (source NAT) for resources owned by the client and dnat
1093 (destination NAT) for remote resources.
1094 Set --verb 6 for debugging info showing the transformation of
1096 src/dest addresses in packets.
1097 --connect-retry args
1099 Wait n seconds between connection attempts (default 1). Re‐
1100 peated reconnection attempts are slowed down after 5 retries per
1101 remote by doubling the wait time after each unsuccessful at‐
1102 tempt.
1103 Valid syntaxes:
1105 connect retry n
1107 connect retry n max
1108 If the optional argument max is specified, the maximum wait time
1110 in seconds gets capped at that value (default 300).
1111 --connect-retry-max n
1113 n specifies the number of times each --remote or <connection>
1114 entry is tried. Specifying n as 1 would try each entry exactly
1115 once. A successful connection resets the counter. (default un‐
1116 limited).
1117 --connect-timeout n
1119 See --server-poll-timeout.
1120 --dns args
1122 Client DNS configuration to be used with the connection.
1123 Valid syntaxes:
1125 dns search-domains domain [domain ...]
1127 dns server n address addr[:port] [addr[:port] ...]
1128 dns server n resolve-domains domain [domain ...]
1129 dns server n dnssec yes|optional|no
1130 dns server n transport DoH|DoT|plain
1131 dns server n sni server-name
1132 The --dns search-domains directive takes one or more domain
1134 names to be added as DNS domain suffixes. If it is repeated mul‐
1135 tiple times within a configuration the domains are appended,
1136 thus e.g. domain names pushed by a server will amend locally de‐
1137 fined ones.
1138 The --dns server directive is used to configure DNS server n.
1140 The server id n must be a value between -128 and 127. For pushed
1141 DNS server options it must be between 0 and 127. The server id
1142 is used to group options and also for ordering the list of con‐
1143 figured DNS servers; lower numbers come first. DNS servers being
1144 pushed to a client replace already configured DNS servers with
1145 the same server id.
1146 The address option configures the IPv4 and / or IPv6 address(es)
1148 of the DNS server. Up to eight addresses can be specified per
1149 DNS server. Optionally a port can be appended after a colon.
1150 IPv6 addresses need to be enclosed in brackets if a port is ap‐
1151 pended.
1152 The resolve-domains option takes one or more DNS domains used to
1154 define a split-dns or dns-routing setup, where only the given
1155 domains are resolved by the server. Systems which do not support
1156 fine grained DNS domain configuration will ignore this setting.
1157 The dnssec option is used to configure validation of DNSSEC
1159 records. While the exact semantics may differ for resolvers on
1160 different systems, yes likely makes validation mandatory, no
1161 disables it, and optional uses it opportunistically.
1162 The transport option enables DNS-over-HTTPS (DoH) or
1164 DNS-over-TLS (DoT) for a DNS server. The sni option can be used
1165 with them to specify the server-name for TLS server name indica‐
1166 tion.
1167 Each server has to have at least one address configured for a
1169 configuration to be valid. All the other options can be omitted.
1170 Note that not all options may be supported on all platforms. As
1172 soon support for different systems is implemented, information
1173 will be added here how unsupported options are treated.
1174 The --dns option will eventually obsolete the --dhcp-option di‐
1176 rective. Until then it will replace configuration at the places
1177 --dhcp-option puts it, so that --dns overrides --dhcp-option.
1178 Thus, --dns can be used today to migrate from --dhcp-option.
1179 --explicit-exit-notify n
1181 In UDP client mode or point-to-point mode, send server/peer an
1182 exit notification if tunnel is restarted or OpenVPN process is
1183 exited. In client mode, on exit/restart, this option will tell
1184 the server to immediately close its client instance object
1185 rather than waiting for a timeout.
1186 If both server and client support sending this message using the
1188 control channel, the message will be sent as control-channel
1189 message. Otherwise the message is sent as data-channel message,
1190 which will be ignored by data-channel offloaded peers.
1191 The n parameter (default 1 if not present) controls the maximum
1193 number of attempts that the client will try to resend the exit
1194 notification message if messages are sent in data-channel mode.
1195 In UDP server mode, send RESTART control channel command to con‐
1197 nected clients. The n parameter (default 1 if not present) con‐
1198 trols client behavior. With n = 1 client will attempt to recon‐
1199 nect to the same server, with n = 2 client will advance to the
1200 next server.
1201 OpenVPN will not send any exit notifications unless this option
1203 is enabled.
1204 --inactive args
1206 Causes OpenVPN to exit after n seconds of inactivity on the
1207 TUN/TAP device. The time length of inactivity is measured since
1208 the last incoming or outgoing tunnel packet. The default value
1209 is 0 seconds, which disables this feature.
1210 Valid syntaxes:
1212 inactive n
1214 inactive n bytes
1215 If the optional bytes parameter is included, exit if less than
1217 bytes of combined in/out traffic are produced on the tun/tap de‐
1218 vice in n seconds.
1219 In any case, OpenVPN's internal ping packets (which are just
1221 keepalives) and TLS control packets are not considered "activ‐
1222 ity", nor are they counted as traffic, as they are used inter‐
1223 nally by OpenVPN and are not an indication of actual user activ‐
1224 ity.
1225 --proto-force p
1227 When iterating through connection profiles, only consider pro‐
1228 files using protocol p (tcp | udp).
1229 Note that this specifically only filters by the transport layer
1231 protocol, i.e. UDP or TCP. This does not affect whether IPv4 or
1232 IPv6 is used as IP protocol.
1233 For implementation reasons the option accepts the 4 and 6 suf‐
1235 fixes when specifying the protocol (i.e. udp4 / udp6 / tcp4 /
1236 tcp6). However, these behave the same as without the suffix and
1237 should be avoided to prevent confusion.
1238 --pull This option must be used on a client which is connecting to a
1240 multi-client server. It indicates to OpenVPN that it should ac‐
1241 cept options pushed by the server, provided they are part of the
1242 legal set of pushable options (note that the --pull option is
1243 implied by --client ).
1244 In particular, --pull allows the server to push routes to the
1246 client, so you should not use --pull or --client in situations
1247 where you don't trust the server to have control over the
1248 client's routing table.
1249 --pull-filter args
1251 Filter options on the client pushed by the server to the client.
1252 Valid syntaxes:
1254 pull-filter accept text
1256 pull-filter ignore text
1257 pull-filter reject text
1258 Filter options received from the server if the option starts
1260 with text. The action flag accept allows the option, ignore re‐
1261 moves it and reject flags an error and triggers a SIGUSR1
1262 restart. The filters may be specified multiple times, and each
1263 filter is applied in the order it is specified. The filtering of
1264 each option stops as soon as a match is found. Unmatched options
1265 are accepted by default.
1266 Prefix comparison is used to match text against the received op‐
1268 tion so that
1269 pull-filter ignore "route"
1271 would remove all pushed options starting with route which would
1273 include, for example, route-gateway. Enclose text in quotes to
1274 embed spaces.
1275 pull-filter accept "route 192.168.1."
1277 pull-filter ignore "route "
1278 would remove all routes that do not start with 192.168.1.
1280 Note that reject may result in a repeated cycle of failure and
1282 reconnect, unless multiple remotes are specified and connection
1283 to the next remote succeeds. To silently ignore an option pushed
1284 by the server, use ignore.
1285 --push-peer-info
1287 Push additional information about the client to server. The fol‐
1288 lowing data is always pushed to the server:
1289 IV_VER=<version>
1291 The client OpenVPN version
1292 IV_PLAT=[linux|solaris|openbsd|mac|netbsd|freebsd|win]
1294 The client OS platform
1295 IV_LZO_STUB=1
1297 If client was built with LZO stub capability
1298 IV_LZ4=1
1300 If the client supports LZ4 compressions.
1301 IV_PROTO
1303 Details about protocol extensions that the peer supports.
1304 The variable is a bitfield and the bits are defined as
1305 follows (starting a bit 0 for the first (unused) bit:
1306 • bit 1: The peer supports peer-id floating mechanism
1308 • bit 2: The client expects a push-reply and the server
1310 may send this reply without waiting for a push-request
1311 first.
1312 • bit 3: The client is capable of doing key derivation
1314 using RFC5705 key material exporter.
1315 • bit 4: The client is capable of accepting additional
1317 arguments to the AUTH_PENDING message.
1318 IV_NCP=2
1320 Negotiable ciphers, client supports --cipher pushed by
1321 the server, a value of 2 or greater indicates client sup‐
1322 ports AES-GCM-128 and AES-GCM-256.
1323 IV_CIPHERS=<ncp-ciphers>
1325 The client announces the list of supported ciphers con‐
1326 figured with the --data-ciphers option to the server.
1327 IV_MTU=<max_mtu>
1329 The client announces the support of pushable MTU and the
1330 maximum MTU it is willing to accept.
1331 IV_GUI_VER=<gui_id> <version>
1333 The UI version of a UI if one is running, for example
1334 de.blinkt.openvpn 0.5.47 for the Android app.
1335 IV_SSO=[crtext,][openurl,][proxy_url]
1337 Additional authentication methods supported by the
1338 client. This may be set by the client UI/GUI using
1339 --setenv
1340 When --push-peer-info is enabled the additional information con‐
1342 sists of the following data:
1343 IV_HWADDR=<string>
1345 This is intended to be a unique and persistent ID of the
1346 client. The string value can be any readable ASCII
1347 string up to 64 bytes. OpenVPN 2.x and some other imple‐
1348 mentations use the MAC address of the client's interface
1349 used to reach the default gateway. If this string is gen‐
1350 erated by the client, it should be consistent and pre‐
1351 served across independent session and preferably re-in‐
1352 stallations and upgrades.
1353 IV_SSL=<version string>
1355 The ssl version used by the client, e.g. OpenSSL 1.0.2f
1356 28 Jan 2016.
1357 IV_PLAT_VER=x.y
1359 The version of the operating system, e.g. 6.1 for Windows
1360 7.
1361 UV_<name>=<value>
1363 Client environment variables whose names start with UV_
1364 --remote args
1366 Remote host name or IP address, port and protocol.
1367 Valid syntaxes:
1369 remote host
1371 remote host port
1372 remote host port proto
1373 The port and proto arguments are optional. The OpenVPN client
1375 will try to connect to a server at host:port. The proto argu‐
1376 ment indicates the protocol to use when connecting with the re‐
1377 mote, and may be tcp or udp. To enforce IPv4 or IPv6 connec‐
1378 tions add a 4 or 6 suffix; like udp4 / udp6 / tcp4 / tcp6.
1379 On the client, multiple --remote options may be specified for
1381 redundancy, each referring to a different OpenVPN server, in the
1382 order specified by the list of --remote options. Specifying mul‐
1383 tiple --remote options for this purpose is a special case of the
1384 more general connection-profile feature. See the <connection>
1385 documentation below.
1386 The client will move on to the next host in the list, in the
1388 event of connection failure. Note that at any given time, the
1389 OpenVPN client will at most be connected to one server.
1390 Examples:
1392 remote server1.example.net
1394 remote server1.example.net 1194
1395 remote server2.example.net 1194 tcp
1396 Note: Since UDP is connectionless, connection failure is de‐
1398 fined by the --ping and --ping-restart options.
1399 Also, if you use multiple --remote options, AND you are
1401 dropping root privileges on the client with --user and/or
1402 --group AND the client is running a non-Windows OS, if
1403 the client needs to switch to a different server, and
1404 that server pushes back different TUN/TAP or route set‐
1405 tings, the client may lack the necessary privileges to
1406 close and reopen the TUN/TAP interface. This could cause
1407 the client to exit with a fatal error.
1408 If --remote is unspecified, OpenVPN will listen for packets from
1410 any IP address, but will not act on those packets unless they
1411 pass all authentication tests. This requirement for authentica‐
1412 tion is binding on all potential peers, even those from known
1413 and supposedly trusted IP addresses (it is very easy to forge a
1414 source IP address on a UDP packet).
1415 When used in TCP mode, --remote will act as a filter, rejecting
1417 connections from any host which does not match host.
1418 If host is a DNS name which resolves to multiple IP addresses,
1420 OpenVPN will try them in the order that the system getaddrinfo()
1421 presents them, so priorization and DNS randomization is done by
1422 the system library. Unless an IP version is forced by the proto‐
1423 col specification (4/6 suffix), OpenVPN will try both IPv4 and
1424 IPv6 addresses, in the order getaddrinfo() returns them.
1425 --remote-random
1427 When multiple --remote address/ports are specified, or if con‐
1428 nection profiles are being used, initially randomize the order
1429 of the list as a kind of basic load-balancing measure.
1430 --remote-random-hostname
1432 Prepend a random string (6 bytes, 12 hex characters) to hostname
1433 to prevent DNS caching. For example, "foo.bar.gov" would be mod‐
1434 ified to "<random-chars>.foo.bar.gov".
1435 --resolv-retry n
1437 If hostname resolve fails for --remote, retry resolve for n sec‐
1438 onds before failing.
1439 Set n to infinite to retry indefinitely.
1441 By default, --resolv-retry infinite is enabled. You can disable
1443 by setting n=0.
1444 --single-session
1446 After initially connecting to a remote peer, disallow any new
1447 connections. Using this option means that a remote peer cannot
1448 connect, disconnect, and then reconnect.
1449 If the daemon is reset by a signal or --ping-restart, it will
1451 allow one new connection.
1452 --single-session can be used with --ping-exit or --inactive to
1454 create a single dynamic session that will exit when finished.
1455 --server-poll-timeout n
1457 When connecting to a remote server do not wait for more than n
1458 seconds for a response before trying the next server. The de‐
1459 fault value is 120. This timeout includes proxy and TCP connect
1460 timeouts.
1461 --static-challenge args
1463 Enable static challenge/response protocol
1464 Valid syntax:
1466 static-challenge text echo
1468 The text challenge text is presented to the user which describes
1470 what information is requested. The echo flag indicates if the
1471 user's input should be echoed on the screen. Valid echo values
1472 are 0 or 1.
1473 See management-notes.txt in the OpenVPN distribution for a de‐
1475 scription of the OpenVPN challenge/response protocol.
1476 --show-proxy-settings
1478 Show sensed HTTP or SOCKS proxy settings. Currently, only Win‐
1479 dows clients support this option.
1480 --http-proxy args
1482 Connect to remote host through an HTTP proxy. This requires at
1483 least an address server and port argument. If HTTP Proxy-Au‐
1484 thenticate is required, a file name to an authfile file contain‐
1485 ing a username and password on 2 lines can be given, or stdin to
1486 prompt from console. Its content can also be specified in the
1487 config file with the --http-proxy-user-pass option. (See section
1488 on inline files)
1489 The last optional argument is an auth-method which should be one
1491 of none, basic, or ntlm.
1492 HTTP Digest authentication is supported as well, but only via
1494 the auto or auto-nct flags (below). This must replace the auth‐
1495 file argument.
1496 The auto flag causes OpenVPN to automatically determine the
1498 auth-method and query stdin or the management interface for
1499 username/password credentials, if required. This flag exists on
1500 OpenVPN 2.1 or higher.
1501 The auto-nct flag (no clear-text auth) instructs OpenVPN to au‐
1503 tomatically determine the authentication method, but to reject
1504 weak authentication protocols such as HTTP Basic Authentication.
1505 Examples:
1507 http-proxy proxy.example.net 3128
1509 http-proxy proxy.example.net 3128 authfile.txt
1510 http-proxy proxy.example.net 3128 stdin
1511 http-proxy proxy.example.net 3128 auto basic
1512 http-proxy proxy.example.net 3128 auto-nct ntlm
1513 --http-proxy-option args
1515 Set extended HTTP proxy options. Requires an option type as ar‐
1516 gument and an optional parameter to the type. Repeat to set
1517 multiple options.
1518 VERSION version
1520 Set HTTP version number to version (default 1.0).
1521 AGENT user-agent
1523 Set HTTP "User-Agent" string to user-agent.
1524 CUSTOM-HEADER name content
1526 Adds the custom Header with name as name and content as
1527 the content of the custom HTTP header.
1528 Examples:
1530 http-proxy-option VERSION 1.1
1532 http-proxy-option AGENT OpenVPN/2.4
1533 http-proxy-option X-Proxy-Flag some-flags
1534 --socks-proxy args
1536 Connect to remote host through a Socks5 proxy. A required
1537 server argument is needed. Optionally a port (default 1080) and
1538 authfile can be given. The authfile is a file containing a
1539 username and password on 2 lines, or stdin can be used to prompt
1540 from console.
1541 Server Options
1543 Starting with OpenVPN 2.0, a multi-client TCP/UDP server mode is sup‐
1544 ported, and can be enabled with the --mode server option. In server
1545 mode, OpenVPN will listen on a single port for incoming client connec‐
1546 tions. All client connections will be routed through a single tun or
1547 tap interface. This mode is designed for scalability and should be able
1548 to support hundreds or even thousands of clients on sufficiently fast
1549 hardware. SSL/TLS authentication must be used in this mode.
1550 --auth-gen-token args
1552 Returns an authentication token to successfully authenticated
1553 clients.
1554 Valid syntax:
1556 auth-gen-token [lifetime] [renewal-time] [external-auth]
1558 After successful user/password authentication, the OpenVPN
1560 server will with this option generate a temporary authentication
1561 token and push that to the client. On the following renegotia‐
1562 tions, the OpenVPN client will pass this token instead of the
1563 users password. On the server side the server will do the token
1564 authentication internally and it will NOT do any additional au‐
1565 thentications against configured external user/password authen‐
1566 tication mechanisms.
1567 The tokens implemented by this mechanism include an initial
1569 timestamp and a renew timestamp and are secured by HMAC.
1570 The lifetime argument defines how long the generated token is
1572 valid. The lifetime is defined in seconds. If lifetime is not
1573 set or it is set to 0, the token will never expire.
1574 If renewal-time is not set it defaults to reneg-sec.
1576 The token will expire either after the configured lifetime of
1578 the token is reached or after not being renewed for more than 2
1579 * renewal-time seconds. Clients will be sent renewed tokens on
1580 every TLS renegotiation. If renewal-time is lower than reneg-sec
1581 the server will push an updated temporary authentication token
1582 every reneweal-time seconds. This is done to invalidate a token
1583 if a client is disconnected for a sufficiently long time, while
1584 at the same time permitting much longer token lifetimes for ac‐
1585 tive clients.
1586 This feature is useful for environments which are configured to
1588 use One Time Passwords (OTP) as part of the user/password au‐
1589 thentications and that authentication mechanism does not imple‐
1590 ment any auth-token support.
1591 When the external-auth keyword is present the normal authentica‐
1593 tion method will always be called even if auth-token succeeds.
1594 Normally other authentications method are skipped if auth-token
1595 verification succeeds or fails.
1596 This option postpones this decision to the external authentica‐
1598 tion methods and checks the validity of the account and do other
1599 checks.
1600 In this mode the environment will have a session_id variable
1602 that holds the session id from auth-gen-token. Also an environ‐
1603 ment variable session_state is present. This variable indicates
1604 whether the auth-token has succeeded or not. It can have the
1605 following values:
1606 Initial
1608 No token from client.
1609 Authenticated
1611 Token is valid and not expired.
1612 Expired
1614 Token is valid but has expired.
1615 Invalid
1617 Token is invalid (failed HMAC or wrong length)
1618 AuthenticatedEmptyUser / ExpiredEmptyUser
1620 The token is not valid with the username sent from the
1621 client but would be valid (or expired) if we assume an
1622 empty username was used instead. These two cases are a
1623 workaround for behaviour in OpenVPN 3. If this work‐
1624 around is not needed these two cases should be handled in
1625 the same way as Invalid.
1626 Warning: Use this feature only if you want your authentication
1628 method called on every verification. Since the external authen‐
1629 tication is called it needs to also indicate a success or fail‐
1630 ure of the authentication. It is strongly recommended to return
1631 an authentication failure in the case of the Invalid/Expired
1632 auth-token with the external-auth option unless the client could
1633 authenticate in another acceptable way (e.g. client certifi‐
1634 cate), otherwise returning success will lead to authentication
1635 bypass (as does returning success on a wrong password from a
1636 script).
1637 --auth-gen-token-secret file
1639 Specifies a file that holds a secret for the HMAC used in
1640 --auth-gen-token If file is not present OpenVPN will generate a
1641 random secret on startup. This file should be used if auth-token
1642 should validate after restarting a server or if client should be
1643 able to roam between multiple OpenVPN servers with their
1644 auth-token.
1645 --auth-user-pass-optional
1647 Allow connections by clients that do not specify a user‐
1648 name/password. Normally, when --auth-user-pass-verify or --man‐
1649 agement-client-auth are specified (or an authentication plugin
1650 module), the OpenVPN server daemon will require connecting
1651 clients to specify a username and password. This option makes
1652 the submission of a username/password by clients optional, pass‐
1653 ing the responsibility to the user-defined authentication mod‐
1654 ule/script to accept or deny the client based on other factors
1655 (such as the setting of X509 certificate fields). When this op‐
1656 tion is used, and a connecting client does not submit a user‐
1657 name/password, the user-defined authentication module/script
1658 will see the username and password as being set to empty strings
1659 (""). The authentication module/script MUST have logic to detect
1660 this condition and respond accordingly.
1661 --ccd-exclusive
1663 Require, as a condition of authentication, that a connecting
1664 client has a --client-config-dir file.
1665 --client-config-dir dir
1667 Specify a directory dir for custom client config files. After a
1668 connecting client has been authenticated, OpenVPN will look in
1669 this directory for a file having the same name as the client's
1670 X509 common name. If a matching file exists, it will be opened
1671 and parsed for client-specific configuration options. If no
1672 matching file is found, OpenVPN will instead try to open and
1673 parse a default file called "DEFAULT", which may be provided but
1674 is not required. Note that the configuration files must be read‐
1675 able by the OpenVPN process after it has dropped it's root priv‐
1676 ileges.
1677 This file can specify a fixed IP address for a given client us‐
1679 ing --ifconfig-push, as well as fixed subnets owned by the
1680 client using --iroute.
1681 One of the useful properties of this option is that it allows
1683 client configuration files to be conveniently created, edited,
1684 or removed while the server is live, without needing to restart
1685 the server.
1686 The following options are legal in a client-specific context:
1688 --push, --push-reset, --push-remove, --iroute, --ifconfig-push,
1689 --vlan-pvid and --config.
1690 --client-to-client
1692 Because the OpenVPN server mode handles multiple clients through
1693 a single tun or tap interface, it is effectively a router. The
1694 --client-to-client flag tells OpenVPN to internally route
1695 client-to-client traffic rather than pushing all client-origi‐
1696 nating traffic to the TUN/TAP interface.
1697 When this option is used, each client will "see" the other
1699 clients which are currently connected. Otherwise, each client
1700 will only see the server. Don't use this option if you want to
1701 firewall tunnel traffic using custom, per-client rules.
1702 Please note that when using data channel offload this option has
1704 no effect. Packets are always sent to the tunnel interface and
1705 then routed based on the system routing table.
1706 --disable
1708 Disable a particular client (based on the common name) from con‐
1709 necting. Don't use this option to disable a client due to key
1710 or password compromise. Use a CRL (certificate revocation list)
1711 instead (see the --crl-verify option).
1712 This option must be associated with a specific client instance,
1714 which means that it must be specified either in a client in‐
1715 stance config file using --client-config-dir or dynamically gen‐
1716 erated using a --client-connect script.
1717 --connect-freq args
1719 Allow a maximum of n new connections per sec seconds from
1720 clients.
1721 Valid syntax:
1723 connect-freq n sec
1725 This is designed to contain DoS attacks which flood the server
1727 with connection requests using certificates which will ulti‐
1728 mately fail to authenticate.
1729 This limit applies after --connect-freq-initial and only applies
1731 to client that have completed the three-way handshake or client
1732 that use --tls-crypt-v2 without cookie support (allow-noncookie
1733 argument to --tls-crypt-v2).
1734 This is an imperfect solution however, because in a real DoS
1736 scenario, legitimate connections might also be refused.
1737 For the best protection against DoS attacks in server mode, use
1739 --proto udp and either --tls-auth or --tls-crypt.
1740 --connect-freq-initial args
1742 (UDP only) Allow a maximum of n initial connection packet re‐
1743 sponses per sec seconds from the OpenVPN server to clients.
1744 Valid syntax:
1746 connect-freq-initial n sec
1748 OpenVPN starting at 2.6 is very efficient in responding to ini‐
1750 tial connection packets. When not limiting the initial responses
1751 an OpenVPN daemon can be abused in reflection attacks. This op‐
1752 tion is designed to limit the rate OpenVPN will respond to ini‐
1753 tial attacks.
1754 Connection attempts that complete the initial three-way hand‐
1756 shake will not be counted against the limit. The default is to
1757 allow 100 initial connection per 10s.
1758 --duplicate-cn
1760 Allow multiple clients with the same common name to concurrently
1761 connect. In the absence of this option, OpenVPN will disconnect
1762 a client instance upon connection of a new client having the
1763 same common name.
1764 --ifconfig-pool args
1766 Set aside a pool of subnets to be dynamically allocated to con‐
1767 necting clients, similar to a DHCP server.
1768 Valid syntax:
1770 ifconfig-pool start-IP end-IP [netmask]
1772 For tun-style tunnels, each client will be given a /30 subnet
1774 (for interoperability with Windows clients). For tap-style tun‐
1775 nels, individual addresses will be allocated, and the optional
1776 netmask parameter will also be pushed to clients.
1777 --ifconfig-ipv6-pool args
1779 Specify an IPv6 address pool for dynamic assignment to clients.
1780 Valid args:
1782 ifconfig-ipv6-pool ipv6addr/bits
1784 The pool starts at ipv6addr and matches the offset determined
1786 from the start of the IPv4 pool. If the host part of the given
1787 IPv6 address is 0, the pool starts at ipv6addr +1.
1788 --ifconfig-pool-persist args
1790 Persist/unpersist ifconfig-pool data to file, at seconds inter‐
1791 vals (default 600), as well as on program startup and shutdown.
1792 Valid syntax:
1794 ifconfig-pool-persist file [seconds]
1796 The goal of this option is to provide a long-term association
1798 between clients (denoted by their common name) and the virtual
1799 IP address assigned to them from the ifconfig-pool. Maintaining
1800 a long-term association is good for clients because it allows
1801 them to effectively use the --persist-tun option.
1802 file is a comma-delimited ASCII file, formatted as <Com‐
1804 mon-Name>,<IP-address>.
1805 If seconds = 0, file will be treated as read-only. This is use‐
1807 ful if you would like to treat file as a configuration file.
1808 Note that the entries in this file are treated by OpenVPN as
1810 suggestions only, based on past associations between a common
1811 name and IP address. They do not guarantee that the given com‐
1812 mon name will always receive the given IP address. If you want
1813 guaranteed assignment, use --ifconfig-push
1814 --ifconfig-push args
1816 Push virtual IP endpoints for client tunnel, overriding the
1817 --ifconfig-pool dynamic allocation.
1818 Valid syntax:
1820 ifconfig-push local remote-netmask [alias]
1822 The parameters local and remote-netmask are set according to the
1824 --ifconfig directive which you want to execute on the client ma‐
1825 chine to configure the remote end of the tunnel. Note that the
1826 parameters local and remote-netmask are from the perspective of
1827 the client, not the server. They may be DNS names rather than IP
1828 addresses, in which case they will be resolved on the server at
1829 the time of client connection.
1830 The optional alias parameter may be used in cases where NAT
1832 causes the client view of its local endpoint to differ from the
1833 server view. In this case local/remote-netmask will refer to the
1834 server view while alias/remote-netmask will refer to the client
1835 view.
1836 This option must be associated with a specific client instance,
1838 which means that it must be specified either in a client in‐
1839 stance config file using --client-config-dir or dynamically gen‐
1840 erated using a --client-connect script.
1841 Remember also to include a --route directive in the main OpenVPN
1843 config file which encloses local, so that the kernel will know
1844 to route it to the server's TUN/TAP interface.
1845 OpenVPN's internal client IP address selection algorithm works
1847 as follows:
1848 1. Use --client-connect script generated file for static IP
1850 (first choice).
1851 2. Use --client-config-dir file for static IP (next choice).
1853 3. Use --ifconfig-pool allocation for dynamic IP (last choice).
1855 --ifconfig-ipv6-push args
1857 for --client-config-dir per-client static IPv6 interface config‐
1858 uration, see --client-config-dir and --ifconfig-push for more
1859 details.
1860 Valid syntax:
1862 ifconfig-ipv6-push ipv6addr/bits ipv6remote
1864 --multihome
1866 Configure a multi-homed UDP server. This option needs to be used
1867 when a server has more than one IP address (e.g. multiple inter‐
1868 faces, or secondary IP addresses), and is not using --local to
1869 force binding to one specific address only. This option will add
1870 some extra lookups to the packet path to ensure that the UDP re‐
1871 ply packets are always sent from the address that the client is
1872 talking to. This is not supported on all platforms, and it adds
1873 more processing, so it's not enabled by default.
1874 Notes:
1876 • This option is only relevant for UDP servers.
1878 • If you do an IPv6+IPv4 dual-stack bind on a Linux ma‐
1880 chine with multiple IPv4 address, connections to IPv4
1881 addresses will not work right on kernels before 3.15,
1882 due to missing kernel support for the IPv4-mapped case
1883 (some distributions have ported this to earlier kernel
1884 versions, though).
1885 --iroute args
1887 Generate an internal route to a specific client. The netmask pa‐
1888 rameter, if omitted, defaults to 255.255.255.255.
1889 Valid syntax:
1891 iroute network [netmask]
1893 This directive can be used to route a fixed subnet from the
1895 server to a particular client, regardless of where the client is
1896 connecting from. Remember that you must also add the route to
1897 the system routing table as well (such as by using the --route
1898 directive). The reason why two routes are needed is that the
1899 --route directive routes the packet from the kernel to OpenVPN.
1900 Once in OpenVPN, the --iroute directive routes to the specific
1901 client.
1902 However, when using DCO, the --iroute directive is usually
1904 enough for DCO to fully configure the routing table. The extra
1905 --route directive is required only if the expected behaviour is
1906 to route the traffic for a specific network to the VPN interface
1907 also when the responsible client is not connected (traffic will
1908 then be dropped).
1909 This option must be specified either in a client instance config
1911 file using --client-config-dir or dynamically generated using a
1912 --client-connect script.
1913 The --iroute directive also has an important interaction with
1915 --push "route ...". --iroute essentially defines a subnet which
1916 is owned by a particular client (we will call this client A). If
1917 you would like other clients to be able to reach A's subnet, you
1918 can use --push "route ..." together with --client-to-client to
1919 effect this. In order for all clients to see A's subnet, OpenVPN
1920 must push this route to all clients EXCEPT for A, since the sub‐
1921 net is already owned by A. OpenVPN accomplishes this by not not
1922 pushing a route to a client if it matches one of the client's
1923 iroutes.
1924 --iroute-ipv6 args
1926 for --client-config-dir per-client static IPv6 route configura‐
1927 tion, see --iroute for more details how to setup and use this,
1928 and how --iroute and --route interact.
1929 Valid syntax:
1931 iroute-ipv6 ipv6addr/bits
1933 --max-clients n
1935 Limit server to a maximum of n concurrent clients.
1936 --max-routes-per-client n
1938 Allow a maximum of n internal routes per client (default 256).
1939 This is designed to help contain DoS attacks where an authenti‐
1940 cated client floods the server with packets appearing to come
1941 from many unique MAC addresses, forcing the server to deplete
1942 virtual memory as its internal routing table expands. This di‐
1943 rective can be used in a --client-config-dir file or auto-gener‐
1944 ated by a --client-connect script to override the global value
1945 for a particular client.
1946 Note that this directive affects OpenVPN's internal routing ta‐
1948 ble, not the kernel routing table.
1949 --opt-verify
1951 DEPRECATED Clients that connect with options that are incompati‐
1952 ble with those of the server will be disconnected.
1953 Options that will be compared for compatibility include
1955 dev-type, link-mtu, tun-mtu, proto, ifconfig, comp-lzo, frag‐
1956 ment, keydir, cipher, auth, keysize, secret, no-replay,
1957 tls-auth, key-method, tls-server and tls-client.
1958 This option requires that --disable-occ NOT be used.
1960 --port-share args
1962 Share OpenVPN TCP with another service
1963 Valid syntax:
1965 port-share host port [dir]
1967 When run in TCP server mode, share the OpenVPN port with another
1969 application, such as an HTTPS server. If OpenVPN senses a con‐
1970 nection to its port which is using a non-OpenVPN protocol, it
1971 will proxy the connection to the server at host:port. Currently
1972 only designed to work with HTTP/HTTPS, though it would be theo‐
1973 retically possible to extend to other protocols such as ssh.
1974 dir specifies an optional directory where a temporary file with
1976 name N containing content C will be dynamically generated for
1977 each proxy connection, where N is the source IP:port of the
1978 client connection and C is the source IP:port of the connection
1979 to the proxy receiver. This directory can be used as a dictio‐
1980 nary by the proxy receiver to determine the origin of the con‐
1981 nection. Each generated file will be automatically deleted when
1982 the proxied connection is torn down.
1983 Not implemented on Windows.
1985 --push option
1987 Push a config file option back to the client for remote execu‐
1988 tion. Note that option must be enclosed in double quotes ("").
1989 The client must specify --pull in its config file. The set of
1990 options which can be pushed is limited by both feasibility and
1991 security. Some options such as those which would execute scripts
1992 are banned, since they would effectively allow a compromised
1993 server to execute arbitrary code on the client. Other options
1994 such as TLS or MTU parameters cannot be pushed because the
1995 client needs to know them before the connection to the server
1996 can be initiated.
1997 This is a partial list of options which can currently be pushed:
1999 --route, --route-gateway, --route-delay, --redirect-gateway,
2000 --ip-win32, --dhcp-option, --dns, --inactive, --ping,
2001 --ping-exit, --ping-restart, --setenv, --auth-token, --per‐
2002 sist-key, --persist-tun, --echo, --comp-lzo, --socket-flags,
2003 --sndbuf, --rcvbuf, --session-timeout
2004 --push-remove opt
2006 Selectively remove all --push options matching "opt" from the
2007 option list for a client. opt is matched as a substring against
2008 the whole option string to-be-pushed to the client, so
2009 --push-remove route would remove all --push route ... and --push
2010 route-ipv6 ... statements, while --push-remove "route-ipv6
2011 2001:" would only remove IPv6 routes for 2001:... networks.
2012 --push-remove can only be used in a client-specific context,
2014 like in a --client-config-dir file, or --client-connect script
2015 or plugin -- similar to --push-reset, just more selective.
2016 NOTE: to change an option, --push-remove can be used to first
2018 remove the old value, and then add a new --push option with the
2019 new value.
2020 NOTE 2: due to implementation details, 'ifconfig' and 'ifcon‐
2022 fig-ipv6' can only be removed with an exact match on the option
2023 ( push-remove ifconfig), no substring matching and no matching
2024 on the IPv4/IPv6 address argument is possible.
2025 --push-reset
2027 Don't inherit the global push list for a specific client in‐
2028 stance. Specify this option in a client-specific context such
2029 as with a --client-config-dir configuration file. This option
2030 will ignore --push options at the global config file level.
2031 NOTE: --push-reset is very thorough: it will remove almost all
2033 options from the list of to-be-pushed options. In many cases,
2034 some of these options will need to be re-configured afterwards -
2035 specifically, --topology subnet and --route-gateway will get
2036 lost and this will break client configs in many cases. Thus,
2037 for most purposes, --push-remove is better suited to selectively
2038 remove push options for individual clients.
2039 --server args
2041 A helper directive designed to simplify the configuration of
2042 OpenVPN's server mode. This directive will set up an OpenVPN
2043 server which will allocate addresses to clients out of the given
2044 network/netmask. The server itself will take the .1 address of
2045 the given network for use as the server-side endpoint of the lo‐
2046 cal TUN/TAP interface. If the optional nopool flag is given, no
2047 dynamic IP address pool will prepared for VPN clients.
2048 Valid syntax:
2050 server network netmask [nopool]
2052 For example, --server 10.8.0.0 255.255.255.0 expands as follows:
2054 mode server
2056 tls-server
2057 push "topology [topology]"
2058 if dev tun AND (topology == net30 OR topology == p2p):
2060 ifconfig 10.8.0.1 10.8.0.2
2061 if !nopool:
2062 ifconfig-pool 10.8.0.4 10.8.0.251
2063 route 10.8.0.0 255.255.255.0
2064 if client-to-client:
2065 push "route 10.8.0.0 255.255.255.0"
2066 else if topology == net30:
2067 push "route 10.8.0.1"
2068 if dev tap OR (dev tun AND topology == subnet):
2070 ifconfig 10.8.0.1 255.255.255.0
2071 if !nopool:
2072 ifconfig-pool 10.8.0.2 10.8.0.253 255.255.255.0
2073 push "route-gateway 10.8.0.1"
2074 if route-gateway unset:
2075 route-gateway 10.8.0.2
2076 Don't use --server if you are ethernet bridging. Use
2078 --server-bridge instead.
2079 --server-bridge args
2081 A helper directive similar to --server which is designed to sim‐
2082 plify the configuration of OpenVPN's server mode in ethernet
2083 bridging configurations.
2084 Valid syntaxes:
2086 server-bridge gateway netmask pool-start-IP pool-end-IP
2088 server-bridge [nogw]
2089 If --server-bridge is used without any parameters, it will en‐
2091 able a DHCP-proxy mode, where connecting OpenVPN clients will
2092 receive an IP address for their TAP adapter from the DHCP server
2093 running on the OpenVPN server-side LAN. Note that only clients
2094 that support the binding of a DHCP client with the TAP adapter
2095 (such as Windows) can support this mode. The optional nogw flag
2096 (advanced) indicates that gateway information should not be
2097 pushed to the client.
2098 To configure ethernet bridging, you must first use your OS's
2100 bridging capability to bridge the TAP interface with the ether‐
2101 net NIC interface. For example, on Linux this is done with the
2102 brctl tool, and with Windows XP it is done in the Network Con‐
2103 nections Panel by selecting the ethernet and TAP adapters and
2104 right-clicking on "Bridge Connections".
2105 Next you you must manually set the IP/netmask on the bridge in‐
2107 terface. The gateway and netmask parameters to --server-bridge
2108 can be set to either the IP/netmask of the bridge interface, or
2109 the IP/netmask of the default gateway/router on the bridged sub‐
2110 net.
2111 Finally, set aside a IP range in the bridged subnet, denoted by
2113 pool-start-IP and pool-end-IP, for OpenVPN to allocate to con‐
2114 necting clients.
2115 For example, server-bridge 10.8.0.4 255.255.255.0 10.8.0.128
2117 10.8.0.254 expands as follows:
2118 mode server
2120 tls-server
2121 ifconfig-pool 10.8.0.128 10.8.0.254 255.255.255.0
2123 push "route-gateway 10.8.0.4"
2124 In another example, --server-bridge (without parameters) expands
2126 as follows:
2127 mode server
2129 tls-server
2130 push "route-gateway dhcp"
2132 Or --server-bridge nogw expands as follows:
2134 mode server
2136 tls-server
2137 --server-ipv6 args
2139 Convenience-function to enable a number of IPv6 related options
2140 at once, namely --ifconfig-ipv6, --ifconfig-ipv6-pool and --push
2141 tun-ipv6.
2142 Valid syntax:
2144 server-ipv6 ipv6addr/bits
2146 Pushing of the --tun-ipv6 directive is done for older clients
2148 which require an explicit --tun-ipv6 in their configuration.
2149 --stale-routes-check args
2151 Remove routes which haven't had activity for n seconds (i.e. the
2152 ageing time). This check is run every t seconds (i.e. check in‐
2153 terval).
2154 Valid syntax:
2156 stale-routes-check n [t]
2158 If t is not present it defaults to n.
2160 This option helps to keep the dynamic routing table small. See
2162 also --max-routes-per-client
2163 --username-as-common-name
2165 Use the authenticated username as the common-name, rather than
2166 the common-name from the client certificate. Requires that some
2167 form of --auth-user-pass verification is in effect. As the re‐
2168 placement happens after --auth-user-pass verification, the veri‐
2169 fication script or plugin will still receive the common-name
2170 from the certificate.
2171 The common_name environment variable passed to scripts and plug‐
2173 ins invoked after authentication (e.g, client-connect script)
2174 and file names parsed in client-config directory will match the
2175 username.
2176 --verify-client-cert mode
2178 Specify whether the client is required to supply a valid cer‐
2179 tificate.
2180 Possible mode options are:
2182 none A client certificate is not required. the client needs to
2184 authenticate using username/password only. Be aware that
2185 using this directive is less secure than requiring cer‐
2186 tificates from all clients.
2187 If you use this directive, the entire responsibility of
2189 authentication will rest on your --auth-user-pass-verify
2190 script, so keep in mind that bugs in your script could
2191 potentially compromise the security of your VPN.
2192 --verify-client-cert none is functionally equivalent to
2194 --client-cert-not-required.
2195 optional
2197 A client may present a certificate but it is not required
2198 to do so. When using this directive, you should also use
2199 a --auth-user-pass-verify script to ensure that clients
2200 are authenticated using a certificate, a username and
2201 password, or possibly even both.
2202 Again, the entire responsibility of authentication will
2204 rest on your --auth-user-pass-verify script, so keep in
2205 mind that bugs in your script could potentially compro‐
2206 mise the security of your VPN.
2207 require
2209 This is the default option. A client is required to
2210 present a certificate, otherwise VPN access is refused.
2211 If you don't use this directive (or use --verify-client-cert re‐
2213 quire) but you also specify an --auth-user-pass-verify script,
2214 then OpenVPN will perform double authentication. The client cer‐
2215 tificate verification AND the --auth-user-pass-verify script
2216 will need to succeed in order for a client to be authenticated
2217 and accepted onto the VPN.
2218 --vlan-tagging
2220 Server-only option. Turns the OpenVPN server instance into a
2221 switch that understands VLAN-tagging, based on IEEE 802.1Q.
2222 The server TAP device and each of the connecting clients is seen
2224 as a port of the switch. All client ports are in untagged mode
2225 and the server TAP device is VLAN-tagged, untagged or accepts
2226 both, depending on the --vlan-accept setting.
2227 Ethernet frames with a prepended 802.1Q tag are called "tagged".
2229 If the VLAN Identifier (VID) field in such a tag is non-zero,
2230 the frame is called "VLAN-tagged". If the VID is zero, but the
2231 Priority Control Point (PCP) field is non-zero, the frame is
2232 called "prio-tagged". If there is no 802.1Q tag, the frame is
2233 "untagged".
2234 Using the --vlan-pvid v option once per client (see
2236 --client-config-dir), each port can be associated with a certain
2237 VID. Packets can only be forwarded between ports having the
2238 same VID. Therefore, clients with differing VIDs are completely
2239 separated from one-another, even if --client-to-client is acti‐
2240 vated.
2241 The packet filtering takes place in the OpenVPN server. Clients
2243 should not have any VLAN tagging configuration applied.
2244 The --vlan-tagging option is off by default. While turned off,
2246 OpenVPN accepts any Ethernet frame and does not perform any spe‐
2247 cial processing for VLAN-tagged packets.
2248 This option can only be activated in --dev tap mode.
2250 --vlan-accept args
2252 Configure the VLAN tagging policy for the server TAP device.
2253 Valid syntax:
2255 vlan-accept all|tagged|untagged
2257 The following modes are available:
2259 tagged Admit only VLAN-tagged frames. Only VLAN-tagged packets
2261 are accepted, while untagged or priority-tagged packets
2262 are dropped when entering the server TAP device.
2263 untagged
2265 Admit only untagged and prio-tagged frames. VLAN-tagged
2266 packets are not accepted, while untagged or prior‐
2267 ity-tagged packets entering the server TAP device are
2268 tagged with the value configured for the global
2269 --vlan-pvid setting.
2270 all (default)
2272 Admit all frames. All packets are admitted and then
2273 treated like untagged or tagged mode respectively.
2274 Note: Some vendors refer to switch ports running in tagged mode
2276 as "trunk ports" and switch ports running in untagged
2277 mode as "access ports".
2278 Packets forwarded from clients to the server are VLAN-tagged
2280 with the originating client's PVID, unless the VID matches the
2281 global --vlan-pvid, in which case the tag is removed.
2282 If no PVID is configured for a given client (see --vlan-pvid)
2284 packets are tagged with 1 by default.
2285 --vlan-pvid v
2287 Specifies which VLAN identifier a "port" is associated with.
2288 Only valid when --vlan-tagging is specified.
2289 In the client context, the setting specifies which VLAN ID a
2291 client is associated with. In the global context, the VLAN ID of
2292 the server TAP device is set. The latter only makes sense for
2293 --vlan-accept untagged and --vlan-accept all modes.
2294 Valid values for v go from 1 through to 4094. The global value
2296 defaults to 1. If no --vlan-pvid is specified in the client con‐
2297 text, the global value is inherited.
2298 In some switch implementations, the PVID is also referred to as
2300 "Native VLAN".
2301
2303 SSL Library information
2304 --show-ciphers
2305 (Standalone) Show all cipher algorithms to use with the --cipher
2306 option.
2307 --show-digests
2309 (Standalone) Show all message digest algorithms to use with the
2310 --auth option.
2311 --show-tls
2313 (Standalone) Show all TLS ciphers supported by the crypto li‐
2314 brary. OpenVPN uses TLS to secure the control channel, over
2315 which the keys that are used to protect the actual VPN traffic
2316 are exchanged. The TLS ciphers will be sorted from highest pref‐
2317 erence (most secure) to lowest.
2318 Be aware that whether a cipher suite in this list can actually
2320 work depends on the specific setup of both peers (e.g. both
2321 peers must support the cipher, and an ECDSA cipher suite will
2322 not work if you are using an RSA certificate, etc.).
2323 --show-engines
2325 (Standalone) Show currently available hardware-based crypto ac‐
2326 celeration engines supported by the OpenSSL library.
2327 --show-groups
2329 (Standalone) Show all available elliptic curves/groups to use
2330 with the --ecdh-curve and tls-groups options.
2331 Generating key material
2333 --genkey args
2334 (Standalone) Generate a key to be used of the type keytype. if
2335 keyfile is left out or empty the key will be output on stdout.
2336 See the following sections for the different keytypes.
2337 Valid syntax:
2339 --genkey keytype keyfile
2341 Valid keytype arguments are:
2343 secret Standard OpenVPN shared secret keys
2345 tls-crypt Alias for secret
2347 tls-auth Alias for secret
2349 auth-token Key used for --auth-gen-token-key
2351 tls-crypt-v2-server TLS Crypt v2 server key
2353 tls-crypt-v2-client TLS Crypt v2 client key
2355 Examples:
2357 $ openvpn --genkey secret shared.key
2359 $ openvpn --genkey tls-crypt shared.key
2360 $ openvpn --genkey tls-auth shared.key
2361 $ openvpn --genkey tls-crypt-v2-server v2crypt-server.key
2362 $ openvpn --tls-crypt-v2 v2crypt-server.key --genkey tls-crypt-v2-client v2crypt-client-1.key
2363 • Generating Shared Secret Keys Generate a shared secret, for
2365 use with the --secret, --tls-auth or --tls-crypt options.
2366 Syntax:
2368 $ openvpn --genkey secret|tls-crypt|tls-auth keyfile
2370 The key is saved in keyfile. All three variants (--secret,
2372 tls-crypt and tls-auth) generate the same type of key. The
2373 aliases are added for convenience.
2374 If using this for --secret, this file must be shared with the
2376 peer over a pre-existing secure channel such as scp(1).
2377 • Generating TLS Crypt v2 Server key Generate a --tls-crypt-v2
2379 key to be used by an OpenVPN server. The key is stored in
2380 keyfile.
2381 Syntax:
2383 --genkey tls-crypt-v2-server keyfile
2385 • Generating TLS Crypt v2 Client key Generate a --tls-crypt-v2
2387 key to be used by OpenVPN clients. The key is stored in key‐
2388 file.
2389 Syntax
2391 --genkey tls-crypt-v2-client keyfile [metadata]
2393 If supplied, include the supplied metadata in the wrapped
2395 client key. This metadata must be supplied in base64-encoded
2396 form. The metadata must be at most 733 bytes long (980 charac‐
2397 ters in base64, though note that 980 base64 characters can en‐
2398 code more than 733 bytes).
2399 If no metadata is supplied, OpenVPN will use a 64-bit unix
2401 timestamp representing the current time in UTC, encoded in
2402 network order, as metadata for the generated key.
2403 A tls-crypt-v2 client key is wrapped using a server key. To
2405 generate a client key, the user must therefore supply the
2406 server key using the --tls-crypt-v2 option.
2407 Servers can use --tls-crypt-v2-verify to specify a metadata
2409 verification command.
2410 • Generate Authentication Token key Generate a new secret that
2412 can be used with --auth-gen-token-secret
2413 Syntax:
2415 --genkey auth-token [keyfile]
2417 Note: This file should be kept secret to the server as anyone
2419 that has access to this file will be able to generate
2420 auth tokens that the OpenVPN server will accept as
2421 valid.
2422 Data Channel Renegotiation
2424 When running OpenVPN in client/server mode, the data channel will use a
2425 separate ephemeral encryption key which is rotated at regular inter‐
2426 vals.
2427 --reneg-bytes n
2429 Renegotiate data channel key after n bytes sent or received
2430 (disabled by default with an exception, see below). OpenVPN al‐
2431 lows the lifetime of a key to be expressed as a number of bytes
2432 encrypted/decrypted, a number of packets, or a number of sec‐
2433 onds. A key renegotiation will be forced if any of these three
2434 criteria are met by either peer.
2435 If using ciphers with cipher block sizes less than 128-bits,
2437 --reneg-bytes is set to 64MB by default, unless it is explicitly
2438 disabled by setting the value to 0, but this is HIGHLY DISCOUR‐
2439 AGED as this is designed to add some protection against the
2440 SWEET32 attack vector. For more information see the --cipher op‐
2441 tion.
2442 --reneg-pkts n
2444 Renegotiate data channel key after n packets sent and received
2445 (disabled by default).
2446 --reneg-sec args
2448 Renegotiate data channel key after at most max seconds (default
2449 3600) and at least min seconds (default is 90% of max for
2450 servers, and equal to max for clients).
2451 reneg-sec max [min]
2453 The effective --reneg-sec value used is per session pseudo-uni‐
2455 form-randomized between min and max.
2456 With the default value of 3600 this results in an effective per
2458 session value in the range of 3240 .. 3600 seconds for servers,
2459 or just 3600 for clients.
2460 When using dual-factor authentication, note that this default
2462 value may cause the end user to be challenged to reauthorize
2463 once per hour.
2464 Also, keep in mind that this option can be used on both the
2466 client and server, and whichever uses the lower value will be
2467 the one to trigger the renegotiation. A common mistake is to set
2468 --reneg-sec to a higher value on either the client or server,
2469 while the other side of the connection is still using the de‐
2470 fault value of 3600 seconds, meaning that the renegotiation will
2471 still occur once per 3600 seconds. The solution is to increase
2472 --reneg-sec on both the client and server, or set it to 0 on one
2473 side of the connection (to disable), and to your chosen value on
2474 the other side.
2475 TLS Mode Options
2477 TLS mode is the most powerful crypto mode of OpenVPN in both security
2478 and flexibility. TLS mode works by establishing control and data chan‐
2479 nels which are multiplexed over a single TCP/UDP port. OpenVPN initi‐
2480 ates a TLS session over the control channel and uses it to exchange ci‐
2481 pher and HMAC keys to protect the data channel. TLS mode uses a robust
2482 reliability layer over the UDP connection for all control channel com‐
2483 munication, while the data channel, over which encrypted tunnel data
2484 passes, is forwarded without any mediation. The result is the best of
2485 both worlds: a fast data channel that forwards over UDP with only the
2486 overhead of encrypt, decrypt, and HMAC functions, and a control channel
2487 that provides all of the security features of TLS, including certifi‐
2488 cate-based authentication and Diffie Hellman forward secrecy.
2489 To use TLS mode, each peer that runs OpenVPN should have its own local
2491 certificate/key pair (--cert and --key), signed by the root certificate
2492 which is specified in --ca.
2493 When two OpenVPN peers connect, each presents its local certificate to
2495 the other. Each peer will then check that its partner peer presented a
2496 certificate which was signed by the master root certificate as speci‐
2497 fied in --ca.
2498 If that check on both peers succeeds, then the TLS negotiation will
2500 succeed, both OpenVPN peers will exchange temporary session keys, and
2501 the tunnel will begin passing data.
2502 The OpenVPN project provides a set of scripts for managing RSA certifi‐
2504 cates and keys: https://github.com/OpenVPN/easy-rsa
2505 --askpass file
2507 Get certificate password from console or file before we daemo‐
2508 nize.
2509 Valid syntaxes:
2511 askpass
2513 askpass file
2514 For the extremely security conscious, it is possible to protect
2516 your private key with a password. Of course this means that ev‐
2517 ery time the OpenVPN daemon is started you must be there to type
2518 the password. The --askpass option allows you to start OpenVPN
2519 from the command line. It will query you for a password before
2520 it daemonizes. To protect a private key with a password you
2521 should omit the -nodes option when you use the openssl command
2522 line tool to manage certificates and private keys.
2523 If file is specified, read the password from the first line of
2525 file. Keep in mind that storing your password in a file to a
2526 certain extent invalidates the extra security provided by using
2527 an encrypted key.
2528 --ca file
2530 Certificate authority (CA) file in .pem format, also referred to
2531 as the root certificate. This file can have multiple certifi‐
2532 cates in .pem format, concatenated together. You can construct
2533 your own certificate authority certificate and private key by
2534 using a command such as:
2535 openssl req -nodes -new -x509 -keyout ca.key -out ca.crt
2537 Then edit your openssl.cnf file and edit the certificate vari‐
2539 able to point to your new root certificate ca.crt.
2540 For testing purposes only, the OpenVPN distribution includes a
2542 sample CA certificate (ca.crt). Of course you should never use
2543 the test certificates and test keys distributed with OpenVPN in
2544 a production environment, since by virtue of the fact that they
2545 are distributed with OpenVPN, they are totally insecure.
2546 --capath dir
2548 Directory containing trusted certificates (CAs and CRLs). Not
2549 available with mbed TLS.
2550 CAs in the capath directory are expected to be named <hash>.<n>.
2552 CRLs are expected to be named <hash>.r<n>. See the -CApath op‐
2553 tion of openssl verify, and the -hash option of openssl x509,
2554 openssl crl and X509_LOOKUP_hash_dir()[22m(3) for more information.
2555 Similar to the --crl-verify option, CRLs are not mandatory -
2557 OpenVPN will log the usual warning in the logs if the relevant
2558 CRL is missing, but the connection will be allowed.
2559 --cert file
2561 Local peer's signed certificate in .pem format -- must be signed
2562 by a certificate authority whose certificate is in --ca file.
2563 Each peer in an OpenVPN link running in TLS mode should have its
2564 own certificate and private key file. In addition, each certifi‐
2565 cate should have been signed by the key of a certificate author‐
2566 ity whose public key resides in the --ca certificate authority
2567 file. You can easily make your own certificate authority (see
2568 above) or pay money to use a commercial service such as
2569 thawte.com (in which case you will be helping to finance the
2570 world's second space tourist :). To generate a certificate, you
2571 can use a command such as:
2572 openssl req -nodes -new -keyout mycert.key -out mycert.csr
2574 If your certificate authority private key lives on another ma‐
2576 chine, copy the certificate signing request (mycert.csr) to this
2577 other machine (this can be done over an insecure channel such as
2578 email). Now sign the certificate with a command such as:
2579 openssl ca -out mycert.crt -in mycert.csr
2581 Now copy the certificate (mycert.crt) back to the peer which
2583 initially generated the .csr file (this can be over a public
2584 medium). Note that the openssl ca command reads the location of
2585 the certificate authority key from its configuration file such
2586 as /usr/share/ssl/openssl.cnf -- note also that for certificate
2587 authority functions, you must set up the files index.txt (may be
2588 empty) and serial (initialize to 01).
2589 --crl-verify args
2591 Check peer certificate against a Certificate Revocation List.
2592 Valid syntax:
2594 crl-verify file/directory flag
2596 Examples:
2598 crl-verify crl-file.pem
2600 crl-verify /etc/openvpn/crls dir
2601 A CRL (certificate revocation list) is used when a particular
2603 key is compromised but when the overall PKI is still intact.
2604 Suppose you had a PKI consisting of a CA, root certificate, and
2606 a number of client certificates. Suppose a laptop computer con‐
2607 taining a client key and certificate was stolen. By adding the
2608 stolen certificate to the CRL file, you could reject any connec‐
2609 tion which attempts to use it, while preserving the overall in‐
2610 tegrity of the PKI.
2611 The only time when it would be necessary to rebuild the entire
2613 PKI from scratch would be if the root certificate key itself was
2614 compromised.
2615 The option is not mandatory - if the relevant CRL is missing,
2617 OpenVPN will log a warning in the logs - e.g.
2618 VERIFY WARNING: depth=0, unable to get certificate CRL
2620 but the connection will be allowed. If the optional dir flag is
2622 specified, enable a different mode where the crl-verify is
2623 pointed at a directory containing files named as revoked serial
2624 numbers (the files may be empty, the contents are never read).
2625 If a client requests a connection, where the client certificate
2626 serial number (decimal string) is the name of a file present in
2627 the directory, it will be rejected.
2628 Note: As the crl file (or directory) is read every time a peer
2630 connects, if you are dropping root privileges with
2631 --user, make sure that this user has sufficient privi‐
2632 leges to read the file.
2633 --dh file
2635 File containing Diffie Hellman parameters in .pem format (re‐
2636 quired for --tls-server only).
2637 Set file to none to disable Diffie Hellman key exchange (and use
2639 ECDH only). Note that this requires peers to be using an SSL li‐
2640 brary that supports ECDH TLS cipher suites (e.g. OpenSSL 1.0.1+,
2641 or mbed TLS 2.0+).
2642 Use openssl dhparam -out dh2048.pem 2048 to generate 2048-bit DH
2644 parameters. Diffie Hellman parameters may be considered public.
2645 --ecdh-curve name
2647 Specify the curve to use for elliptic curve Diffie Hellman.
2648 Available curves can be listed with --show-curves. The specified
2649 curve will only be used for ECDH TLS-ciphers.
2650 This option is not supported in mbed TLS builds of OpenVPN.
2652 --extra-certs file
2654 Specify a file containing one or more PEM certs (concatenated
2655 together) that complete the local certificate chain.
2656 This option is useful for "split" CAs, where the CA for server
2658 certs is different than the CA for client certs. Putting certs
2659 in this file allows them to be used to complete the local cer‐
2660 tificate chain without trusting them to verify the peer-submit‐
2661 ted certificate, as would be the case if the certs were placed
2662 in the ca file.
2663 --hand-window n
2665 Handshake Window -- the TLS-based key exchange must finalize
2666 within n seconds of handshake initiation by any peer (default 60
2667 seconds). If the handshake fails we will attempt to reset our
2668 connection with our peer and try again. Even in the event of
2669 handshake failure we will still use our expiring key for up to
2670 --tran-window seconds to maintain continuity of transmission of
2671 tunnel data.
2672 The --hand-window parameter also controls the amount of time
2674 that the OpenVPN client repeats the pull request until it times
2675 out.
2676 --key file
2678 Local peer's private key in .pem format. Use the private key
2679 which was generated when you built your peer's certificate (see
2680 --cert file above).
2681 --pkcs12 file
2683 Specify a PKCS #12 file containing local private key, local cer‐
2684 tificate, and root CA certificate. This option can be used in‐
2685 stead of --ca, --cert, and --key. Not available with mbed TLS.
2686 --remote-cert-eku oid
2688 Require that peer certificate was signed with an explicit ex‐
2689 tended key usage.
2690 This is a useful security option for clients, to ensure that the
2692 host they connect to is a designated server.
2693 The extended key usage should be encoded in oid notation, or
2695 OpenSSL symbolic representation.
2696 --remote-cert-ku key-usage
2698 Require that peer certificate was signed with an explicit
2699 key-usage.
2700 If present in the certificate, the keyUsage value is validated
2702 by the TLS library during the TLS handshake. Specifying this op‐
2703 tion without arguments requires this extension to be present (so
2704 the TLS library will verify it).
2705 If key-usage is a list of usage bits, the keyUsage field must
2707 have at least the same bits set as the bits in one of the values
2708 supplied in the key-usage list.
2709 The key-usage values in the list must be encoded in hex, e.g.
2711 remote-cert-ku a0
2713 --remote-cert-tls type
2715 Require that peer certificate was signed with an explicit key
2716 usage and extended key usage based on RFC3280 TLS rules.
2717 Valid syntaxes:
2719 remote-cert-tls server
2721 remote-cert-tls client
2722 This is a useful security option for clients, to ensure that the
2724 host they connect to is a designated server. Or the other way
2725 around; for a server to verify that only hosts with a client
2726 certificate can connect.
2727 The --remote-cert-tls client option is equivalent to
2729 remote-cert-ku
2731 remote-cert-eku "TLS Web Client Authentication"
2732 The --remote-cert-tls server option is equivalent to
2734 remote-cert-ku
2736 remote-cert-eku "TLS Web Server Authentication"
2737 This is an important security precaution to protect against a
2739 man-in-the-middle attack where an authorized client attempts to
2740 connect to another client by impersonating the server. The at‐
2741 tack is easily prevented by having clients verify the server
2742 certificate using any one of --remote-cert-tls, --ver‐
2743 ify-x509-name, --peer-fingerprint or --tls-verify.
2744 --tls-auth args
2746 Add an additional layer of HMAC authentication on top of the TLS
2747 control channel to mitigate DoS attacks and attacks on the TLS
2748 stack.
2749 Valid syntaxes:
2751 tls-auth file
2753 tls-auth file 0
2754 tls-auth file 1
2755 In a nutshell, --tls-auth enables a kind of "HMAC firewall" on
2757 OpenVPN's TCP/UDP port, where TLS control channel packets bear‐
2758 ing an incorrect HMAC signature can be dropped immediately with‐
2759 out response.
2760 file (required) is a file in OpenVPN static key format which can
2762 be generated by --genkey.
2763 Older versions (up to OpenVPN 2.3) supported a freeform
2765 passphrase file. This is no longer supported in newer versions
2766 (v2.4+).
2767 See the --secret option for more information on the optional di‐
2769 rection parameter.
2770 --tls-auth is recommended when you are running OpenVPN in a mode
2772 where it is listening for packets from any IP address, such as
2773 when --remote is not specified, or --remote is specified with
2774 --float.
2775 The rationale for this feature is as follows. TLS requires a
2777 multi-packet exchange before it is able to authenticate a peer.
2778 During this time before authentication, OpenVPN is allocating
2779 resources (memory and CPU) to this potential peer. The potential
2780 peer is also exposing many parts of OpenVPN and the OpenSSL li‐
2781 brary to the packets it is sending. Most successful network at‐
2782 tacks today seek to either exploit bugs in programs (such as
2783 buffer overflow attacks) or force a program to consume so many
2784 resources that it becomes unusable. Of course the first line of
2785 defense is always to produce clean, well-audited code. OpenVPN
2786 has been written with buffer overflow attack prevention as a top
2787 priority. But as history has shown, many of the most widely used
2788 network applications have, from time to time, fallen to buffer
2789 overflow attacks.
2790 So as a second line of defense, OpenVPN offers this special
2792 layer of authentication on top of the TLS control channel so
2793 that every packet on the control channel is authenticated by an
2794 HMAC signature and a unique ID for replay protection. This sig‐
2795 nature will also help protect against DoS (Denial of Service)
2796 attacks. An important rule of thumb in reducing vulnerability to
2797 DoS attacks is to minimize the amount of resources a potential,
2798 but as yet unauthenticated, client is able to consume.
2799 --tls-auth does this by signing every TLS control channel packet
2801 with an HMAC signature, including packets which are sent before
2802 the TLS level has had a chance to authenticate the peer. The re‐
2803 sult is that packets without the correct signature can be
2804 dropped immediately upon reception, before they have a chance to
2805 consume additional system resources such as by initiating a TLS
2806 handshake. --tls-auth can be strengthened by adding the --re‐
2807 play-persist option which will keep OpenVPN's replay protection
2808 state in a file so that it is not lost across restarts.
2809 It should be emphasized that this feature is optional and that
2811 the key file used with --tls-auth gives a peer nothing more than
2812 the power to initiate a TLS handshake. It is not used to encrypt
2813 or authenticate any tunnel data.
2814 Use --tls-crypt instead if you want to use the key file to not
2816 only authenticate, but also encrypt the TLS control channel.
2817 --tls-groups list
2819 A list of allowable groups/curves in order of preference.
2820 Set the allowed elliptic curves/groups for the TLS session.
2822 These groups are allowed to be used in signatures and key ex‐
2823 change.
2824 mbedTLS currently allows all known curves per default.
2826 OpenSSL 1.1+ restricts the list per default to
2828 "X25519:secp256r1:X448:secp521r1:secp384r1".
2830 If you use certificates that use non-standard curves, you might
2832 need to add them here. If you do not force the ecdh curve by us‐
2833 ing --ecdh-curve, the groups for ecdh will also be picked from
2834 this list.
2835 OpenVPN maps the curve name secp256r1 to prime256v1 to allow
2837 specifying the same tls-groups option for mbedTLS and OpenSSL.
2838 Warning: this option not only affects elliptic curve certifi‐
2840 cates but also the key exchange in TLS 1.3 and using this option
2841 improperly will disable TLS 1.3.
2842 --tls-cert-profile profile
2844 Set the allowed cryptographic algorithms for certificates ac‐
2845 cording to profile.
2846 The following profiles are supported:
2848 insecure
2850 Identical for mbed TLS to legacy
2851 legacy (default)
2853 SHA1 and newer, RSA 2048-bit+, any elliptic curve.
2854 preferred
2856 SHA2 and newer, RSA 2048-bit+, any elliptic curve.
2857 suiteb SHA256/SHA384, ECDSA with P-256 or P-384.
2859 This option is only fully supported for mbed TLS builds. OpenSSL
2861 builds use the following approximation:
2862 insecure
2864 sets "security level 0"
2865 legacy (default)
2867 sets "security level 1"
2868 preferred
2870 sets "security level 2"
2871 suiteb sets "security level 3" and --tls-cipher "SUITEB128".
2873 OpenVPN will migrate to 'preferred' as default in the future.
2875 Please ensure that your keys already comply.
2876 WARNING: --tls-ciphers, --tls-ciphersuites and tls-groups
2878 These options are expert features, which - if used correctly -
2879 can improve the security of your VPN connection. But it is also
2880 easy to unwittingly use them to carefully align a gun with your
2881 foot, or just break your connection. Use with care!
2882 --tls-cipher l
2884 A list l of allowable TLS ciphers delimited by a colon (":").
2885 These setting can be used to ensure that certain cipher suites
2887 are used (or not used) for the TLS connection. OpenVPN uses TLS
2888 to secure the control channel, over which the keys that are used
2889 to protect the actual VPN traffic are exchanged.
2890 The supplied list of ciphers is (after potential OpenSSL/IANA
2892 name translation) simply supplied to the crypto library. Please
2893 see the OpenSSL and/or mbed TLS documentation for details on the
2894 cipher list interpretation.
2895 For OpenSSL, the --tls-cipher is used for TLS 1.2 and below.
2897 Use --show-tls to see a list of TLS ciphers supported by your
2899 crypto library.
2900 The default for --tls-cipher is to use mbed TLS's default cipher
2902 list when using mbed TLS or DE‐
2903 FAULT:!EXP:!LOW:!MEDIUM:!kDH:!kECDH:!DSS:!PSK:!SRP:!kRSA when
2904 using OpenSSL.
2905 --tls-ciphersuites l
2907 Same as --tls-cipher but for TLS 1.3 and up. mbed TLS has no TLS
2908 1.3 support yet and only the --tls-cipher setting is used.
2909 The default for --tls-ciphersuites is to use the crypto li‐
2911 brary's default.
2912 --tls-client
2914 Enable TLS and assume client role during TLS handshake.
2915 --tls-crypt keyfile
2917 Encrypt and authenticate all control channel packets with the
2918 key from keyfile. (See --tls-auth for more background.)
2919 Encrypting (and authenticating) control channel packets:
2921 • provides more privacy by hiding the certificate used for the
2923 TLS connection,
2924 • makes it harder to identify OpenVPN traffic as such,
2926 • provides "poor-man's" post-quantum security, against attackers
2928 who will never know the pre-shared key (i.e. no forward se‐
2929 crecy).
2930 In contrast to --tls-auth, --tls-crypt does not require the user
2932 to set --key-direction.
2933 Security Considerations
2935 All peers use the same --tls-crypt pre-shared group key to au‐
2937 thenticate and encrypt control channel messages. To ensure that
2938 IV collisions remain unlikely, this key should not be used to
2939 encrypt more than 2^48 client-to-server or 2^48 server-to-client
2940 control channel messages. A typical initial negotiation is about
2941 10 packets in each direction. Assuming both initial negotiation
2942 and renegotiations are at most 2^16 (65536) packets (to be con‐
2943 servative), and (re)negotiations happen each minute for each
2944 user (24/7), this limits the tls-crypt key lifetime to 8171
2945 years divided by the number of users. So a setup with 1000 users
2946 should rotate the key at least once each eight years. (And a
2947 setup with 8000 users each year.)
2948 If IV collisions were to occur, this could result in the secu‐
2950 rity of --tls-crypt degrading to the same security as using
2951 --tls-auth. That is, the control channel still benefits from
2952 the extra protection against active man-in-the-middle-attacks
2953 and DoS attacks, but may no longer offer extra privacy and
2954 post-quantum security on top of what TLS itself offers.
2955 For large setups or setups where clients are not trusted, con‐
2957 sider using --tls-crypt-v2 instead. That uses per-client unique
2958 keys, and thereby improves the bounds to 'rotate a client key at
2959 least once per 8000 years'.
2960 --tls-crypt-v2 keyfile
2962 Valid syntax:
2963 tls-crypt-v2 keyfile
2965 tls-crypt-v2 keyfile force-cookie
2966 tls-crypt-v2 keyfile allow-noncookie
2967 Use client-specific tls-crypt keys.
2969 For clients, keyfile is a client-specific tls-crypt key. Such a
2971 key can be generated using the --genkey tls-crypt-v2-client op‐
2972 tion.
2973 For servers, keyfile is used to unwrap client-specific keys sup‐
2975 plied by the client during connection setup. This key must be
2976 the same as the key used to generate the client-specific key
2977 (see --genkey tls-crypt-v2-client).
2978 On servers, this option can be used together with the --tls-auth
2980 or --tls-crypt option. In that case, the server will detect
2981 whether the client is using client-specific keys, and automati‐
2982 cally select the right mode.
2983 The optional parameters force-cookie allows only tls-crypt-v2
2985 clients that support a cookie based stateless three way hand‐
2986 shake that avoids replay attacks and state exhaustion on the
2987 server side (OpenVPN 2.6 and later). The option allow-noncookie
2988 explicitly allows older tls-crypt-v2 clients. The default is
2989 (currently) allow-noncookie.
2990 --tls-crypt-v2-verify cmd
2992 Run command cmd to verify the metadata of the client-specific
2993 tls-crypt-v2 key of a connecting client. This allows server ad‐
2994 ministrators to reject client connections, before exposing the
2995 TLS stack (including the notoriously dangerous X.509 and ASN.1
2996 stacks) to the connecting client.
2997 OpenVPN supplies the following environment variables to the com‐
2999 mand:
3000 • script_type is set to tls-crypt-v2-verify
3002 • metadata_type is set to 0 if the metadata was user supplied,
3004 or 1 if it's a 64-bit unix timestamp representing the key cre‐
3005 ation time.
3006 • metadata_file contains the filename of a temporary file that
3008 contains the client metadata.
3009 The command can reject the connection by exiting with a non-zero
3011 exit code.
3012 --tls-exit
3014 Exit on TLS negotiation failure.
3015 --tls-export-cert directory
3017 Store the certificates the clients use upon connection to this
3018 directory. This will be done before --tls-verify is called. The
3019 certificates will use a temporary name and will be deleted when
3020 the tls-verify script returns. The file name used for the cer‐
3021 tificate is available via the peer_cert environment variable.
3022 --tls-server
3024 Enable TLS and assume server role during TLS handshake. Note
3025 that OpenVPN is designed as a peer-to-peer application. The des‐
3026 ignation of client or server is only for the purpose of negoti‐
3027 ating the TLS control channel.
3028 --tls-timeout n
3030 Packet retransmit timeout on TLS control channel if no acknowl‐
3031 edgment from remote within n seconds (default 2). When OpenVPN
3032 sends a control packet to its peer, it will expect to receive an
3033 acknowledgement within n seconds or it will retransmit the
3034 packet, subject to a TCP-like exponential backoff algorithm.
3035 This parameter only applies to control channel packets. Data
3036 channel packets (which carry encrypted tunnel data) are never
3037 acknowledged, sequenced, or retransmitted by OpenVPN because the
3038 higher level network protocols running on top of the tunnel such
3039 as TCP expect this role to be left to them.
3040 --tls-version-min args
3042 Sets the minimum TLS version we will accept from the peer (de‐
3043 fault in 2.6.0 and later is "1.2").
3044 Valid syntax:
3046 tls-version-min version ['or-highest']
3048 Examples for version include 1.0, 1.1, or 1.2. If or-highest is
3050 specified and version is not recognized, we will only accept the
3051 highest TLS version supported by the local SSL implementation.
3052 --tls-version-max version
3054 Set the maximum TLS version we will use (default is the highest
3055 version supported). Examples for version include 1.0, 1.1, or
3056 1.2.
3057 --verify-hash args
3059 DEPRECATED Specify SHA1 or SHA256 fingerprint for level-1 cert.
3060 Valid syntax:
3062 verify-hash hash [algo]
3064 The level-1 cert is the CA (or intermediate cert) that signs the
3066 leaf certificate, and is one removed from the leaf certificate
3067 in the direction of the root. When accepting a connection from a
3068 peer, the level-1 cert fingerprint must match hash or certifi‐
3069 cate verification will fail. Hash is specified as XX:XX:... For
3070 example:
3071 AD:B0:95:D8:09:C8:36:45:12:A9:89:C8:90:09:CB:13:72:A6:AD:16
3073 The algo flag can be either SHA1 or SHA256. If not provided, it
3075 defaults to SHA1.
3076 This option can also be inlined
3078 <verify-hash>
3080 00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff:00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff
3081 11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff:00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff:00
3082 </verify-hash>
3083 If the option is inlined, algo is always SHA256.
3085 --peer-fingerprint args
3087 Specify a SHA256 fingerprint or list of SHA256 fingerprints
3088 to verify the peer certificate against. The peer certificate
3089 must match one of the fingerprint or certificate verification
3090 will fail. The option can also be inlined
3091 Valid syntax:
3093 peer-fingerprint AD:B0:95:D8:09:...
3095 or inline:
3097 <peer-fingerprint>
3099 00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff:00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff
3100 11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff:00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff:00
3101 </peer-fingerprint>
3102 When the --peer-fingerprint option is used, specifying a CA with
3104 --ca or --capath is optional. This allows the he --peer-finger‐
3105 print to be used as alternative to a PKI with self-signed cer‐
3106 tificates for small setups. See the examples section for such a
3107 setup.
3108 --verify-x509-name args
3110 Accept connections only if a host's X.509 name is equal to name.
3111 The remote host must also pass all other tests of verification.
3112 Valid syntax:
3114 verify-x509 name type
3116 Which X.509 name is compared to name depends on the setting of
3118 type. type can be subject to match the complete subject DN (de‐
3119 fault), name to match a subject RDN or name-prefix to match a
3120 subject RDN prefix. Which RDN is verified as name depends on the
3121 --x509-username-field option. But it defaults to the common name
3122 (CN), e.g. a certificate with a subject DN
3123 C=KG, ST=NA, L=Bishkek, CN=Server-1
3125 would be matched by:
3127 verify-x509-name 'C=KG, ST=NA, L=Bishkek, CN=Server-1'
3129 verify-x509-name Server-1 name
3130 verify-x509-name Server- name-prefix
3131 The last example is useful if you want a client to only accept
3133 connections to Server-1, Server-2, etc.
3134 --verify-x509-name is a useful replacement for the --tls-verify
3136 option to verify the remote host, because --verify-x509-name
3137 works in a --chroot environment without any dependencies.
3138 Using a name prefix is a useful alternative to managing a CRL
3140 (Certificate Revocation List) on the client, since it allows the
3141 client to refuse all certificates except for those associated
3142 with designated servers.
3143 NOTE: Test against a name prefix only when you are using Open‐
3145 VPN with a custom CA certificate that is under your con‐
3146 trol. Never use this option with type name-prefix when
3147 your client certificates are signed by a third party,
3148 such as a commercial web CA.
3149 --x509-track attribute
3151 Save peer X509 attribute value in environment for use by plugins
3152 and management interface. Prepend a + to attribute to save val‐
3153 ues from full cert chain. Values will be encoded as
3154 X509_<depth>_<attribute>=<value>. Multiple --x509-track options
3155 can be defined to track multiple attributes.
3156 --x509-username-field args
3158 Fields in the X.509 certificate subject to be used as the user‐
3159 name (default CN). If multiple fields are specified their values
3160 will be concatenated into the one username using _ symbol as a
3161 separator.
3162 Valid syntax:
3164 x509-username-field [ext:]fieldname [[ext:]fieldname...]
3166 Typically, this option is specified with fieldname arguments as
3168 either of the following:
3169 x509-username-field emailAddress
3171 x509-username-field ext:subjectAltName
3172 x509-username-field CN serialNumber
3173 The first example uses the value of the emailAddress attribute
3175 in the certificate's Subject field as the username. The second
3176 example uses the ext: prefix to signify that the X.509 extension
3177 fieldname subjectAltName be searched for an rfc822Name (email)
3178 field to be used as the username. In cases where there are mul‐
3179 tiple email addresses in ext:fieldname, the last occurrence is
3180 chosen. The last example uses the value of the CN attribute in
3181 the Subject field, combined with the _ separator and the hexa‐
3182 decimal representation of the certificate's serialNumber.
3183 When this option is used, the --verify-x509-name option will
3185 match against the chosen fieldname instead of the Common Name.
3186 Only the subjectAltName and issuerAltName X.509 extensions and
3188 serialNumber X.509 attribute are supported.
3189 Please note: This option has a feature which will convert an
3191 all-lowercase fieldname to uppercase characters, e.g., ou -> OU.
3192 A mixed-case fieldname or one having the ext: prefix will be
3193 left as-is. This automatic upcasing feature is deprecated and
3194 will be removed in a future release.
3195 Non-compliant symbols are being replaced with the _ symbol, same
3197 as the field separator, so concatenating multiple fields with
3198 such or _ symbols can potentially lead to username collisions.
3199 PKCS#11 / SmartCard options
3201 --pkcs11-cert-private args
3202 Set if access to certificate object should be performed after
3203 login. Every provider has its own setting.
3204 Valid syntaxes:
3206 pkcs11-cert-private 0
3208 pkcs11-cert-private 1
3209 --pkcs11-id name
3211 Specify the serialized certificate id to be used. The id can be
3212 gotten by the standalone --show-pkcs11-ids option. See also the
3213 description of --pkcs11-providers option.
3214 --pkcs11-id-management
3216 Acquire PKCS#11 id from management interface. In this case a
3217 NEED-STR 'pkcs11-id-request' real-time message will be trig‐
3218 gered, application may use pkcs11-id-count command to retrieve
3219 available number of certificates, and pkcs11-id-get command to
3220 retrieve certificate id and certificate body. See also the de‐
3221 scription of --pkcs11-providers option.
3222 --pkcs11-pin-cache seconds
3224 Specify how many seconds the PIN can be cached, the default is
3225 until the token is removed.
3226 --pkcs11-private-mode mode
3228 Specify which method to use in order to perform private key op‐
3229 erations. A different mode can be specified for each provider.
3230 Mode is encoded as hex number, and can be a mask one of the fol‐
3231 lowing:
3232 0 (default) Try to determine automatically.
3234 1 Use sign.
3236 2 Use sign recover.
3238 4 Use decrypt.
3240 8 Use unwrap.
3242 --pkcs11-protected-authentication args
3244 Use PKCS#11 protected authentication path, useful for biometric
3245 and external keypad devices. Every provider has its own setting.
3246 Valid syntaxes:
3248 pkcs11-protected-authentication 0
3250 pkcs11-protected-authentication 1
3251 --pkcs11-providers providers
3253 Specify an RSA Security Inc. PKCS #11 Cryptographic Token Inter‐
3254 face (Cryptoki) providers to load. A space-separated list of one
3255 or more provider library names may be specified. This option
3256 along with --pkcs11-id or pkcs11-id-management can be used in‐
3257 stead of --cert and --key or --pkcs12.
3258 If p11-kit is present on the system and was enabled during
3260 build, its p11-kit-proxy.so module will be loaded by default if
3261 either the --pkcs11-id or --pkcs11-id-management options is
3262 present without --pkcs11-providers. If default loading is not
3263 enabled in the build and no providers are specified, the former
3264 options will be ignored.
3265 --show-pkcs11-ids args
3267 (Standalone) Show PKCS#11 token object list.
3268 Valid syntax:
3270 show-pkcs11 [provider] [cert_private]
3272 Specify cert_private as 1 if certificates are stored as private
3274 objects.
3275 If p11-kit is present on the system, the provider argument is
3277 optional; if omitted the default p11-kit-proxy.so module will be
3278 queried.
3279 --verb option can be used BEFORE this option to produce debug‐
3281 ging information.
3282
3284 OpenVPN 2.4 and higher have the capability to negotiate the data cipher
3285 that is used to encrypt data packets. This section describes the mecha‐
3286 nism in more detail and the different backwards compatibility mechanism
3287 with older server and clients.
3288 OpenVPN 2.5 and later behaviour
3290 When both client and server are at least running OpenVPN 2.5, that the
3291 order of the ciphers of the server's --data-ciphers is used to pick the
3292 the data cipher. That means that the first cipher in that list that is
3293 also in the client's --data-ciphers list is chosen. If no common cipher
3294 is found the client is rejected with a AUTH_FAILED message (as seen in
3295 client log):
3296 AUTH: Received control message: AUTH_FAILED,Data channel cipher ne‐
3297 gotiation failed (no shared cipher)
3298 OpenVPN 2.5 and later will only allow the ciphers specified in
3300 --data-ciphers. If --data-ciphers is not set the default is
3301 AES-256-GCM:AES-128-GCM. In 2.6 and later the default is changed to
3302 AES-256-GCM:AES-128-GCM:CHACHA20-POLY1305 when Chacha20-Poly1305 is
3303 available.
3304 For backwards compatibility OpenVPN 2.6 and later with --compat-mode
3306 2.4.x (or lower) and OpenVPN 2.5 will automatically add a cipher speci‐
3307 fied using the --cipher option to this list.
3308 OpenVPN 2.4 clients
3310 The negotiation support in OpenVPN 2.4 was the first iteration of the
3311 implementation and still had some quirks. Its main goal was "upgrade to
3312 AES-256-GCM when possible". An OpenVPN 2.4 client that is built
3313 against a crypto library that supports AES in GCM mode and does not
3314 have --ncp-disable will always announce support for AES-256-GCM and
3315 AES-128-GCM to a server by sending IV_NCP=2.
3316 This only causes a problem if --ncp-ciphers option has been changed
3318 from the default of AES-256-GCM:AES-128-GCM to a value that does not
3319 include these two ciphers. When an OpenVPN server tries to use
3320 AES-256-GCM or AES-128-GCM the connection will then fail. It is there‐
3321 fore recommended to always have the AES-256-GCM and AES-128-GCM ciphers
3322 to the --ncp-ciphers options to avoid this behaviour.
3323 OpenVPN 3 clients
3325 Clients based on the OpenVPN 3.x library (‐
3326 https://github.com/openvpn/openvpn3/) do not have a configurable
3327 --ncp-ciphers or --data-ciphers option. Newer versions by default dis‐
3328 able legacy AES-CBC, BF-CBC, and DES-CBC ciphers. These clients will
3329 always announce support for all their supported AEAD ciphers
3330 (AES-256-GCM, AES-128-GCM and in newer versions also
3331 Chacha20-Poly1305).
3332 To support OpenVPN 3.x based clients at least one of these ciphers
3334 needs to be included in the server's --data-ciphers option.
3335 OpenVPN 2.3 and older clients (and clients with --ncp-disable)
3337 When a client without cipher negotiation support connects to a server
3338 the cipher specified with the --cipher option in the client configura‐
3339 tion must be included in the --data-ciphers option of the server to al‐
3340 low the client to connect. Otherwise the client will be sent the
3341 AUTH_FAILED message that indicates no shared cipher.
3342 If the client is 2.3 or older and has been configured with the --en‐
3344 able-small ./configure argument, using data-ciphers-fallback cipher in
3345 the server config file with the explicit cipher used by the client is
3346 necessary.
3347 OpenVPN 2.4 server
3349 When a client indicates support for AES-128-GCM and AES-256-GCM (with
3350 IV_NCP=2) an OpenVPN 2.4 server will send the first cipher of the
3351 --ncp-ciphers to the OpenVPN client regardless of what the cipher is.
3352 To emulate the behaviour of an OpenVPN 2.4 client as close as possible
3353 and have compatibility to a setup that depends on this quirk, adding
3354 AES-128-GCM and AES-256-GCM to the client's --data-ciphers option is
3355 required. OpenVPN 2.5+ will only announce the IV_NCP=2 flag if those
3356 ciphers are present.
3357 OpenVPN 2.3 and older servers (and servers with --ncp-disable)
3359 The cipher used by the server must be included in --data-ciphers to al‐
3360 low the client connecting to a server without cipher negotiation sup‐
3361 port. (For compatibility OpenVPN 2.5 will also accept the cipher set
3362 with --cipher)
3363 If the server is 2.3 or older and has been configured with the --en‐
3365 able-small ./configure argument, adding --data-ciphers-fallback cipher
3366 to the client config with the explicit cipher used by the server is
3367 necessary.
3368 Blowfish in CBC mode (BF-CBC) deprecation
3370 The --cipher option defaulted to BF-CBC in OpenVPN 2.4 and older ver‐
3371 sion. The default was never changed to ensure backwards compatibility.
3372 In OpenVPN 2.5 this behaviour has now been changed so that if the --ci‐
3373 pher is not explicitly set it does not allow the weak BF-CBC cipher any
3374 more and needs to explicitly added as --cipher BFC-CBC or added to
3375 --data-ciphers.
3376 We strongly recommend to switching away from BF-CBC to a more secure
3378 cipher as soon as possible instead.
3379
3381 OpenVPN consists of two sides of network configuration. One side is
3382 the link between the local and remote side, the other side is the vir‐
3383 tual network adapter (tun/tap device).
3384 Link Options
3386 This link options section covers options related to the connection be‐
3387 tween the local and the remote host.
3388 --bind keywords
3390 Bind to local address and port. This is the default unless any
3391 of --proto tcp-client , --http-proxy or --socks-proxy are used.
3392 If the optional ipv6only keyword is present OpenVPN will bind
3394 only to IPv6 (as opposed to IPv6 and IPv4) when a IPv6 socket is
3395 opened.
3396 --float
3398 Allow remote peer to change its IP address and/or port number,
3399 such as due to DHCP (this is the default if --remote is not
3400 used). --float when specified with --remote allows an OpenVPN
3401 session to initially connect to a peer at a known address, how‐
3402 ever if packets arrive from a new address and pass all authenti‐
3403 cation tests, the new address will take control of the session.
3404 This is useful when you are connecting to a peer which holds a
3405 dynamic address such as a dial-in user or DHCP client.
3406 Essentially, --float tells OpenVPN to accept authenticated pack‐
3408 ets from any address, not only the address which was specified
3409 in the --remote option.
3410 --fragment args
3412 Valid syntax:
3413 fragment max
3415 fragment max mtu
3416 Enable internal datagram fragmentation so that no UDP datagrams
3418 are sent which are larger than max bytes.
3419 If the mtu parameter is present the max parameter is interpreted
3421 to include IP and UDP encapsulation overhead. The mtu parameter
3422 is introduced in OpenVPN version 2.6.0.
3423 If the mtu parameter is absent, the max parameter is interpreted
3425 in the same way as the --link-mtu parameter, i.e. the UDP
3426 packet size after encapsulation overhead has been added in, but
3427 not including the UDP header itself.
3428 The --fragment option only makes sense when you are using the
3430 UDP protocol (--proto udp).
3431 --fragment adds 4 bytes of overhead per datagram.
3433 See the --mssfix option below for an important related option to
3435 --fragment.
3436 It should also be noted that this option is not meant to replace
3438 UDP fragmentation at the IP stack level. It is only meant as a
3439 last resort when path MTU discovery is broken. Using this option
3440 is less efficient than fixing path MTU discovery for your IP
3441 link and using native IP fragmentation instead.
3442 Having said that, there are circumstances where using OpenVPN's
3444 internal fragmentation capability may be your only option, such
3445 as tunneling a UDP multicast stream which requires fragmenta‐
3446 tion.
3447 --keepalive args
3449 A helper directive designed to simplify the expression of --ping
3450 and --ping-restart.
3451 Valid syntax:
3453 keepalive interval timeout
3455 Send ping once every interval seconds, restart if ping is not
3457 received for timeout seconds.
3458 This option can be used on both client and server side, but it
3460 is enough to add this on the server side as it will push appro‐
3461 priate --ping and --ping-restart options to the client. If used
3462 on both server and client, the values pushed from server will
3463 override the client local values.
3464 The timeout argument will be twice as long on the server side.
3466 This ensures that a timeout is detected on client side before
3467 the server side drops the connection.
3468 For example, --keepalive 10 60 expands as follows:
3470 if mode server:
3472 ping 10 # Argument: interval
3473 ping-restart 120 # Argument: timeout*2
3474 push "ping 10" # Argument: interval
3475 push "ping-restart 60" # Argument: timeout
3476 else
3477 ping 10 # Argument: interval
3478 ping-restart 60 # Argument: timeout
3479 --link-mtu n
3481 DEPRECATED Sets an upper bound on the size of UDP packets which
3482 are sent between OpenVPN peers. It's best not to set this param‐
3483 eter unless you know what you're doing.
3484 Due to variable header size of IP header (20 bytes for IPv4 and
3486 40 bytes for IPv6) and dynamically negotiated data channel ci‐
3487 pher, this option is not reliable. It is recommended to set
3488 tun-mtu with enough headroom instead.
3489 --local host
3491 Local host name or IP address for bind. If specified, OpenVPN
3492 will bind to this address only. If unspecified, OpenVPN will
3493 bind to all interfaces.
3494 --lport port
3496 Set local TCP/UDP port number or name. Cannot be used together
3497 with --nobind option.
3498 --mark value
3500 Mark encrypted packets being sent with value. The mark value can
3501 be matched in policy routing and packetfilter rules. This option
3502 is only supported in Linux and does nothing on other operating
3503 systems.
3504 --mode m
3506 Set OpenVPN major mode. By default, OpenVPN runs in
3507 point-to-point mode (p2p). OpenVPN 2.0 introduces a new mode
3508 (server) which implements a multi-client server capability.
3509 --mssfix args
3511 Valid syntax:
3512 mssfix max [mtu]
3514 mssfix max [fixed]
3516 mssfix
3518 Announce to TCP sessions running over the tunnel that they
3520 should limit their send packet sizes such that after OpenVPN has
3521 encapsulated them, the resulting UDP packet size that OpenVPN
3522 sends to its peer will not exceed max bytes. The default value
3523 is 1492 mtu. Use 0 as max to disable mssfix.
3524 If the mtu parameter is specified the max value is interpreted
3526 as the resulting packet size of VPN packets including the IP and
3527 UDP header. Support for the mtu parameter was added with Open‐
3528 VPN version 2.6.0.
3529 If the mtu parameter is not specified, the max parameter is in‐
3531 terpreted in the same way as the --link-mtu parameter, i.e. the
3532 UDP packet size after encapsulation overhead has been added in,
3533 but not including the UDP header itself. Resulting packet would
3534 be at most 28 bytes larger for IPv4 and 48 bytes for IPv6 (20/40
3535 bytes for IP header and 8 bytes for UDP header). Default value
3536 of 1450 allows OpenVPN packets to be transmitted over IPv4 on a
3537 link with MTU 1478 or higher without IP level fragmentation (and
3538 1498 for IPv6).
3539 If the fixed parameter is specified, OpenVPN will make no at‐
3541 tempt to calculate the VPN encapsulation overhead but instead
3542 will set the MSS to limit the size of the payload IP packets to
3543 the specified number. IPv4 packets will have the MSS value low‐
3544 ered to mssfix - 40 and IPv6 packets to mssfix - 60.
3545 if --mssfix is specified is specified without any parameter it
3547 inherits the parameters of --fragment if specified or uses the
3548 default for --mssfix otherwise.
3549 The --mssfix option only makes sense when you are using the UDP
3551 protocol for OpenVPN peer-to-peer communication, i.e. --proto
3552 udp.
3553 --mssfix and --fragment can be ideally used together, where
3555 --mssfix will try to keep TCP from needing packet fragmentation
3556 in the first place, and if big packets come through anyhow (from
3557 protocols other than TCP), --fragment will internally fragment
3558 them.
3559 --max-packet-size, --fragment, and --mssfix are designed to work
3561 around cases where Path MTU discovery is broken on the network
3562 path between OpenVPN peers.
3563 The usual symptom of such a breakdown is an OpenVPN connection
3565 which successfully starts, but then stalls during active usage.
3566 If --fragment and --mssfix are used together, --mssfix will take
3568 its default max parameter from the --fragment max option.
3569 Therefore, one could lower the maximum UDP packet size to 1300
3571 (a good first try for solving MTU-related connection problems)
3572 with the following options:
3573 --tun-mtu 1500 --fragment 1300 --mssfix
3575 If the max-packet-size size option is used in the configuration
3577 it will also act as if mssfix size mtu was specified in the con‐
3578 figuration.
3579 --mtu-disc type
3581 Should we do Path MTU discovery on TCP/UDP channel? Only sup‐
3582 ported on OSes such as Linux that supports the necessary system
3583 call to set.
3584 Valid types:
3586 no Never send DF (Don't Fragment) frames
3588 maybe Use per-route hints
3590 yes Always DF (Don't Fragment)
3592 --mtu-test
3594 To empirically measure MTU on connection startup, add the
3595 --mtu-test option to your configuration. OpenVPN will send ping
3596 packets of various sizes to the remote peer and measure the
3597 largest packets which were successfully received. The --mtu-test
3598 process normally takes about 3 minutes to complete.
3599 --nobind
3601 Do not bind to local address and port. The IP stack will allo‐
3602 cate a dynamic port for returning packets. Since the value of
3603 the dynamic port could not be known in advance by a peer, this
3604 option is only suitable for peers which will be initiating con‐
3605 nections by using the --remote option.
3606 --passtos
3608 Set the TOS field of the tunnel packet to what the payload's TOS
3609 is.
3610 --ping n
3612 Ping remote over the TCP/UDP control channel if no packets have
3613 been sent for at least n seconds (specify --ping on both peers
3614 to cause ping packets to be sent in both directions since Open‐
3615 VPN ping packets are not echoed like IP ping packets). When used
3616 in one of OpenVPN's secure modes (where --secret, --tls-server
3617 or --tls-client is specified), the ping packet will be crypto‐
3618 graphically secure.
3619 This option has two intended uses:
3621 1. Compatibility with stateful firewalls. The periodic ping will
3623 ensure that a stateful firewall rule which allows OpenVPN UDP
3624 packets to pass will not time out.
3625 2. To provide a basis for the remote to test the existence of
3627 its peer using the --ping-exit option.
3628 When using OpenVPN in server mode see also --keepalive.
3630 --ping-exit n
3632 Causes OpenVPN to exit after n seconds pass without reception of
3633 a ping or other packet from remote. This option can be combined
3634 with --inactive, --ping and --ping-exit to create a two-tiered
3635 inactivity disconnect.
3636 For example,
3638 openvpn [options...] --inactive 3600 --ping 10 --ping-exit 60
3640 when used on both peers will cause OpenVPN to exit within 60
3642 seconds if its peer disconnects, but will exit after one hour if
3643 no actual tunnel data is exchanged.
3644 --ping-restart n
3646 Similar to --ping-exit, but trigger a SIGUSR1 restart after n
3647 seconds pass without reception of a ping or other packet from
3648 remote.
3649 This option is useful in cases where the remote peer has a dy‐
3651 namic IP address and a low-TTL DNS name is used to track the IP
3652 address using a service such as https://www.nsupdate.info/ + a
3653 dynamic DNS client such as ddclient.
3654 If the peer cannot be reached, a restart will be triggered,
3656 causing the hostname used with --remote to be re-resolved (if
3657 --resolv-retry is also specified).
3658 In server mode, --ping-restart, --inactive or any other type of
3660 internally generated signal will always be applied to individual
3661 client instance objects, never to whole server itself. Note also
3662 in server mode that any internally generated signal which would
3663 normally cause a restart, will cause the deletion of the client
3664 instance object instead.
3665 In client mode, the --ping-restart parameter is set to 120 sec‐
3667 onds by default. This default will hold until the client pulls a
3668 replacement value from the server, based on the --keepalive set‐
3669 ting in the server configuration. To disable the 120 second de‐
3670 fault, set --ping-restart 0 on the client.
3671 See the signals section below for more information on SIGUSR1.
3673 Note that the behavior of SIGUSR1 can be modified by the --per‐
3675 sist-tun, --persist-key, --persist-local-ip and --persist-re‐
3676 mote-ip options.
3677 Also note that --ping-exit and --ping-restart are mutually ex‐
3679 clusive and cannot be used together.
3680 --ping-timer-rem
3682 Run the --ping-exit / --ping-restart timer only if we have a re‐
3683 mote address. Use this option if you are starting the daemon in
3684 listen mode (i.e. without an explicit --remote peer), and you
3685 don't want to start clocking timeouts until a remote peer con‐
3686 nects.
3687 --proto p
3689 Use protocol p for communicating with remote host. p can be udp,
3690 tcp-client, or tcp-server. You can also limit OpenVPN to use
3691 only IPv4 or only IPv6 by specifying p as udp4, tcp4-client,
3692 tcp4-server or udp6, tcp6-client, tcp6-server, respectively.
3693 The default protocol is udp when --proto is not specified.
3695 For UDP operation, --proto udp should be specified on both
3697 peers.
3698 For TCP operation, one peer must use --proto tcp-server and the
3700 other must use --proto tcp-client. A peer started with
3701 tcp-server will wait indefinitely for an incoming connection. A
3702 peer started with tcp-client will attempt to connect, and if
3703 that fails, will sleep for 5 seconds (adjustable via the --con‐
3704 nect-retry option) and try again infinite or up to N retries
3705 (adjustable via the --connect-retry-max option). Both TCP client
3706 and server will simulate a SIGUSR1 restart signal if either side
3707 resets the connection.
3708 OpenVPN is designed to operate optimally over UDP, but TCP capa‐
3710 bility is provided for situations where UDP cannot be used. In
3711 comparison with UDP, TCP will usually be somewhat less efficient
3712 and less robust when used over unreliable or congested networks.
3713 This article outlines some of problems with tunneling IP over
3715 TCP: http://sites.inka.de/sites/bigred/devel/tcp-tcp.html
3716 There are certain cases, however, where using TCP may be advan‐
3718 tageous from a security and robustness perspective, such as tun‐
3719 neling non-IP or application-level UDP protocols, or tunneling
3720 protocols which don't possess a built-in reliability layer.
3721 --port port
3723 TCP/UDP port number or port name for both local and remote (sets
3724 both --lport and --rport options to given port). The current de‐
3725 fault of 1194 represents the official IANA port number assign‐
3726 ment for OpenVPN and has been used since version 2.0-beta17.
3727 Previous versions used port 5000 as the default.
3728 --rport port
3730 Set TCP/UDP port number or name used by the --remote option. The
3731 port can also be set directly using the --remote option.
3732 --replay-window args
3734 Modify the replay protection sliding-window size and time win‐
3735 dow.
3736 Valid syntaxes:
3738 replay-window n
3740 replay-window n t
3741 Use a replay protection sliding-window of size n and a time win‐
3743 dow of t seconds.
3744 By default n is 64 (the IPSec default) and t is 15 seconds.
3746 This option is only relevant in UDP mode, i.e. when either
3748 --proto udp is specified, or no --proto option is specified.
3749 When OpenVPN tunnels IP packets over UDP, there is the possibil‐
3751 ity that packets might be dropped or delivered out of order. Be‐
3752 cause OpenVPN, like IPSec, is emulating the physical network
3753 layer, it will accept an out-of-order packet sequence, and will
3754 deliver such packets in the same order they were received to the
3755 TCP/IP protocol stack, provided they satisfy several con‐
3756 straints.
3757 a. The packet cannot be a replay (unless --no-replay is speci‐
3759 fied, which disables replay protection altogether).
3760 b. If a packet arrives out of order, it will only be accepted if
3762 the difference between its sequence number and the highest
3763 sequence number received so far is less than n.
3764 c. If a packet arrives out of order, it will only be accepted if
3766 it arrives no later than t seconds after any packet contain‐
3767 ing a higher sequence number.
3768 If you are using a network link with a large pipeline (meaning
3770 that the product of bandwidth and latency is high), you may want
3771 to use a larger value for n. Satellite links in particular often
3772 require this.
3773 If you run OpenVPN at --verb 4, you will see the message
3775 "PID_ERR replay-window backtrack occurred [x]" every time the
3776 maximum sequence number backtrack seen thus far increases. This
3777 can be used to calibrate n.
3778 There is some controversy on the appropriate method of handling
3780 packet reordering at the security layer.
3781 Namely, to what extent should the security layer protect the en‐
3783 capsulated protocol from attacks which masquerade as the kinds
3784 of normal packet loss and reordering that occur over IP net‐
3785 works?
3786 The IPSec and OpenVPN approach is to allow packet reordering
3788 within a certain fixed sequence number window.
3789 OpenVPN adds to the IPSec model by limiting the window size in
3791 time as well as sequence space.
3792 OpenVPN also adds TCP transport as an option (not offered by
3794 IPSec) in which case OpenVPN can adopt a very strict attitude
3795 towards message deletion and reordering: Don't allow it. Since
3796 TCP guarantees reliability, any packet loss or reordering event
3797 can be assumed to be an attack.
3798 In this sense, it could be argued that TCP tunnel transport is
3800 preferred when tunneling non-IP or UDP application protocols
3801 which might be vulnerable to a message deletion or reordering
3802 attack which falls within the normal operational parameters of
3803 IP networks.
3804 So I would make the statement that one should never tunnel a
3806 non-IP protocol or UDP application protocol over UDP, if the
3807 protocol might be vulnerable to a message deletion or reordering
3808 attack that falls within the normal operating parameters of what
3809 is to be expected from the physical IP layer. The problem is
3810 easily fixed by simply using TCP as the VPN transport layer.
3811 --replay-persist file
3813 Persist replay-protection state across sessions using file to
3814 save and reload the state.
3815 This option will keep a disk copy of the current replay protec‐
3817 tion state (i.e. the most recent packet timestamp and sequence
3818 number received from the remote peer), so that if an OpenVPN
3819 session is stopped and restarted, it will reject any replays of
3820 packets which were already received by the prior session.
3821 This option only makes sense when replay protection is enabled
3823 (the default) and you are using either --secret (shared-secret
3824 key mode) or TLS mode with --tls-auth.
3825 --session-timeout n
3827 Raises SIGTERM for the client instance after n seconds since the
3828 beginning of the session, forcing OpenVPN to disconnect. In
3829 client mode, OpenVPN will disconnect and exit, while in server
3830 mode all client sessions are terminated.
3831 This option can also be specified in a client instance config
3833 file using --client-config-dir or dynamically generated using a
3834 --client-connect script. In these cases, only the related client
3835 session is terminated.
3836 --socket-flags flags
3838 Apply the given flags to the OpenVPN transport socket. Cur‐
3839 rently, only TCP_NODELAY is supported.
3840 The TCP_NODELAY socket flag is useful in TCP mode, and causes
3842 the kernel to send tunnel packets immediately over the TCP con‐
3843 nection without trying to group several smaller packets into a
3844 larger packet. This can result in a considerably improvement in
3845 latency.
3846 This option is pushable from server to client, and should be
3848 used on both client and server for maximum effect.
3849 --tcp-nodelay
3851 This macro sets the TCP_NODELAY socket flag on the server as
3852 well as pushes it to connecting clients. The TCP_NODELAY flag
3853 disables the Nagle algorithm on TCP sockets causing packets to
3854 be transmitted immediately with low latency, rather than waiting
3855 a short period of time in order to aggregate several packets
3856 into a larger containing packet. In VPN applications over TCP,
3857 TCP_NODELAY is generally a good latency optimization.
3858 The macro expands as follows:
3860 if mode server:
3862 socket-flags TCP_NODELAY
3863 push "socket-flags TCP_NODELAY"
3864 --max-packet-size size
3866 This option will instruct OpenVPN to try to limit the maximum
3867 on-write packet size by restricting the control channel packet
3868 size and setting --mssfix.
3869 OpenVPN will try to keep its control channel messages below this
3871 size but due to some constraints in the protocol this is not al‐
3872 ways possible. If the option is not set, the control packet max‐
3873 imum size defaults to 1250. The control channel packet size
3874 will be restricted to values between 154 and 2048. The maximum
3875 packet size includes encapsulation overhead like UDP and IP.
3876 In terms of --mssfix it will expand to:
3878 mssfix size mtu
3880 If you need to set --mssfix for data channel and control channel
3882 maximum packet size independently, use --max-packet-size first,
3883 followed by a --mssfix in the configuration.
3884 In general the default size of 1250 should work almost univer‐
3886 sally apart from specific corner cases, especially since IPv6
3887 requires a MTU of 1280 or larger.
3888 Virtual Network Adapter (VPN interface)
3890 Options in this section relates to configuration of the virtual tun/tap
3891 network interface, including setting the VPN IP address and network
3892 routing.
3893 --bind-dev device
3895 (Linux only) Set device to bind the server socket to a Virtual
3896 Routing and Forwarding device
3897 --block-ipv6
3899 On the client, instead of sending IPv6 packets over the VPN tun‐
3900 nel, all IPv6 packets are answered with an ICMPv6 no route host
3901 message. On the server, all IPv6 packets from clients are an‐
3902 swered with an ICMPv6 no route to host message. This options is
3903 intended for cases when IPv6 should be blocked and other options
3904 are not available. --block-ipv6 will use the remote IPv6 as
3905 source address of the ICMPv6 packets if set, otherwise will use
3906 fe80::7 as source address.
3907 For this option to make sense you actually have to route traffic
3909 to the tun interface. The following example config block would
3910 send all IPv6 traffic to OpenVPN and answer all requests with no
3911 route to host, effectively blocking IPv6 (to avoid IPv6 connec‐
3912 tions from dual-stacked clients leaking around IPv4-only VPN
3913 services).
3914 Client config
3916 --ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1
3918 --redirect-gateway ipv6
3919 --block-ipv6
3920 Server config
3922 Push a "valid" ipv6 config to the client and block on the
3923 server
3924 --push "ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1"
3926 --push "redirect-gateway ipv6"
3927 --block-ipv6
3928 Note: this option does not influence traffic sent from the
3930 server towards the client (neither on the server nor on the
3931 client side). This is not seen as necessary, as such traffic
3932 can be most easily avoided by not configuring IPv6 on the server
3933 tun, or setting up a server-side firewall rule.
3934 --dev device
3936 TUN/TAP virtual network device which can be tunX, tapX, null or
3937 an arbitrary name string (X can be omitted for a dynamic de‐
3938 vice.)
3939 See examples section below for an example on setting up a TUN
3941 device.
3942 You must use either tun devices on both ends of the connection
3944 or tap devices on both ends. You cannot mix them, as they repre‐
3945 sent different underlying network layers:
3946 tun devices encapsulate IPv4 or IPv6 (OSI Layer 3)
3948 tap devices encapsulate Ethernet 802.3 (OSI Layer 2).
3950 Valid syntaxes:
3952 dev tun2
3954 dev tap4
3955 dev ovpn
3956 What happens if the device name is not tun or tap is platform
3958 dependent.
3959 On most platforms, tunN (e.g. tun2, tun30) and tapN (e.g. tap3)
3961 will create a numbered tun/tap interface with the number speci‐
3962 fied - this is useful if multiple OpenVPN instances are active,
3963 and the instance-to-device mapping needs to be known. Some
3964 platforms do not support "numbered tap", so trying --dev tap3
3965 will fail.
3966 Arbitrary device names (e.g. --dev tun-home) will only work on
3968 FreeBSD (with the DCO kernel driver for tun devices) and Linux
3969 (for both tun and tap devices, DCO and tun/tap driver).
3970 If such a device name starts with tun or tap (e.g. tun-home),
3972 OpenVPN will choose the right device type automatically. Other‐
3973 wise the desired device type needs to be specified with
3974 --dev-type tun or --dev-type tap.
3975 On Windows, only the names tun and tap are supported. Selection
3977 among multiple installed drivers or driver instances is done
3978 with --dev-node and --windows-driver.
3979 --dev-node node
3981 This is a highly system dependent option to influence tun/tap
3982 driver selection.
3983 On Linux, tun/tap devices are created by accessing /dev/net/tun,
3985 and this device name can be changed using --dev-node ....
3986 Under Mac OS X this option can be used to specify the default
3988 tun implementation. Using --dev-node utun forces usage of the
3989 native Darwin tun kernel support. Use --dev-node utunN to select
3990 a specific utun instance. To force using the tun.kext
3991 (/dev/tunX) use --dev-node tun. When not specifying a --dev-node
3992 option openvpn will first try to open utun, and fall back to
3993 tun.kext.
3994 On Windows systems, select the TAP-Win32 adapter which is named
3996 node in the Network Connections Control Panel or the raw GUID of
3997 the adapter enclosed by braces. The --show-adapters option under
3998 Windows can also be used to enumerate all available TAP-Win32
3999 adapters and will show both the network connections control
4000 panel name and the GUID for each TAP-Win32 adapter.
4001 On other platforms, --dev-node node will influence the naming of
4003 the created tun/tap device, if supported on that platform. If
4004 OpenVPN cannot figure out whether node is a TUN or TAP device
4005 based on the name, you should also specify --dev-type tun or
4006 --dev-type tap.
4007 --dev-type device-type
4009 Which device type are we using? device-type should be tun (OSI
4010 Layer 3) or tap (OSI Layer 2). Use this option only if the
4011 TUN/TAP device used with --dev does not begin with tun or tap.
4012 --dhcp-option args
4014 Set additional network parameters on supported platforms. May be
4015 specified on the client or pushed from the server. On Windows
4016 these options are handled by the tap-windows6 driver by default
4017 or directly by OpenVPN if dhcp is disabled or the wintun driver
4018 is in use. The OpenVPN for Android client also handles them in‐
4019 ternally.
4020 On all other platforms these options are only saved in the
4022 client's environment under the name foreign_option_{n} before
4023 the --up script is called. A plugin or an --up script must be
4024 used to pick up and interpret these as required. Many Linux dis‐
4025 tributions include such scripts and some third-party user inter‐
4026 faces such as tunnelblick also come with scripts that process
4027 these options.
4028 Valid syntax:
4030 dhcp-option type [parm]
4032 DOMAIN name
4034 Set Connection-specific DNS Suffix to name.
4035 ADAPTER_DOMAIN_SUFFIX name
4037 Alias to DOMAIN. This is a compatibility option, it
4038 should not be used in new deployments.
4039 DOMAIN-SEARCH name
4041 Add name to the domain search list. Repeat this option
4042 to add more entries. Up to 10 domains are supported.
4043 DNS address
4045 Set primary domain name server IPv4 or IPv6 address. Re‐
4046 peat this option to set secondary DNS server addresses.
4047 Note: DNS IPv6 servers are currently set using netsh (the
4049 existing DHCP code can only do IPv4 DHCP, and that proto‐
4050 col only permits IPv4 addresses anywhere). The option
4051 will be put into the environment, so an --up script could
4052 act upon it if needed.
4053 WINS address
4055 Set primary WINS server address (NetBIOS over TCP/IP Name
4056 Server). Repeat this option to set secondary WINS server
4057 addresses.
4058 NBDD address
4060 Set primary NBDD server address (NetBIOS over TCP/IP
4061 Datagram Distribution Server). Repeat this option to set
4062 secondary NBDD server addresses.
4063 NTP address
4065 Set primary NTP server address (Network Time Protocol).
4066 Repeat this option to set secondary NTP server addresses.
4067 NBT type
4069 Set NetBIOS over TCP/IP Node type. Possible options:
4070 1 b-node (broadcasts)
4072 2 p-node (point-to-point name queries to a WINS
4074 server)
4075 4 m-node (broadcast then query name server)
4077 8 h-node (query name server, then broadcast).
4079 NBS scope-id
4081 Set NetBIOS over TCP/IP Scope. A NetBIOS Scope ID pro‐
4082 vides an extended naming service for the NetBIOS over
4083 TCP/IP (Known as NBT) module. The primary purpose of a
4084 NetBIOS scope ID is to isolate NetBIOS traffic on a sin‐
4085 gle network to only those nodes with the same NetBIOS
4086 scope ID. The NetBIOS scope ID is a character string that
4087 is appended to the NetBIOS name. The NetBIOS scope ID on
4088 two hosts must match, or the two hosts will not be able
4089 to communicate. The NetBIOS Scope ID also allows comput‐
4090 ers to use the same computer name, as they have different
4091 scope IDs. The Scope ID becomes a part of the NetBIOS
4092 name, making the name unique. (This description of Net‐
4093 BIOS scopes courtesy of NeonSurge@abyss.com)
4094 DISABLE-NBT
4096 Disable Netbios-over-TCP/IP.
4097 code PROXY_HTTP host port Sets a HTTP proxy that should be
4099 used when connected to the VPN.
4100 This option currently only works on OpenVPN for Android
4102 and requires Android 10 or later.
4103 --ifconfig args
4105 Set TUN/TAP adapter parameters. It requires the IP address of
4106 the local VPN endpoint. For TUN devices in point-to-point mode,
4107 the next argument must be the VPN IP address of the remote VPN
4108 endpoint. For TAP devices, or TUN devices used with --topology
4109 subnet, the second argument is the subnet mask of the virtual
4110 network segment which is being created or connected to.
4111 For TUN devices, which facilitate virtual point-to-point IP con‐
4113 nections (when used in --topology net30 or p2p mode), the proper
4114 usage of --ifconfig is to use two private IP addresses which are
4115 not a member of any existing subnet which is in use. The IP ad‐
4116 dresses may be consecutive and should have their order reversed
4117 on the remote peer. After the VPN is established, by pinging
4118 rn, you will be pinging across the VPN.
4119 For TAP devices, which provide the ability to create virtual
4121 ethernet segments, or TUN devices in --topology subnet mode
4122 (which create virtual "multipoint networks"), --ifconfig is used
4123 to set an IP address and subnet mask just as a physical ethernet
4124 adapter would be similarly configured. If you are attempting to
4125 connect to a remote ethernet bridge, the IP address and subnet
4126 should be set to values which would be valid on the the bridged
4127 ethernet segment (note also that DHCP can be used for the same
4128 purpose).
4129 This option, while primarily a proxy for the ifconfig(8) com‐
4131 mand, is designed to simplify TUN/TAP tunnel configuration by
4132 providing a standard interface to the different ifconfig imple‐
4133 mentations on different platforms.
4134 --ifconfig parameters which are IP addresses can also be speci‐
4136 fied as a DNS or /etc/hosts file resolvable name.
4137 For TAP devices, --ifconfig should not be used if the TAP inter‐
4139 face will be getting an IP address lease from a DHCP server.
4140 Examples:
4142 # tun device in net30/p2p mode
4144 ifconfig 10.8.0.2 10.8.0.1
4145 # tun/tap device in subnet mode
4147 ifconfig 10.8.0.2 255.255.255.0
4148 --ifconfig-ipv6 args
4150 Configure an IPv6 address on the tun device.
4151 Valid syntax:
4153 ifconfig-ipv6 ipv6addr/bits [ipv6remote]
4155 The ipv6addr/bits argument is the IPv6 address to use. The sec‐
4157 ond parameter is used as route target for --route-ipv6 if no
4158 gateway is specified.
4159 The --topology option has no influence with --ifconfig-ipv6
4161 --ifconfig-noexec
4163 Don't actually execute ifconfig/netsh commands, instead pass
4164 --ifconfig parameters to scripts using environmental variables.
4165 --ifconfig-nowarn
4167 Don't output an options consistency check warning if the --if‐
4168 config option on this side of the connection doesn't match the
4169 remote side. This is useful when you want to retain the overall
4170 benefits of the options consistency check (also see --dis‐
4171 able-occ option) while only disabling the ifconfig component of
4172 the check.
4173 For example, if you have a configuration where the local host
4175 uses --ifconfig but the remote host does not, use --ifcon‐
4176 fig-nowarn on the local host.
4177 This option will also silence warnings about potential address
4179 conflicts which occasionally annoy more experienced users by
4180 triggering "false positive" warnings.
4181 --lladdr address
4183 Specify the link layer address, more commonly known as the MAC
4184 address. Only applied to TAP devices.
4185 --persist-tun
4187 Don't close and reopen TUN/TAP device or run up/down scripts
4188 across SIGUSR1 or --ping-restart restarts.
4189 SIGUSR1 is a restart signal similar to SIGHUP, but which offers
4191 finer-grained control over reset options.
4192 --redirect-gateway flags
4194 Automatically execute routing commands to cause all outgoing IP
4195 traffic to be redirected over the VPN. This is a client-side op‐
4196 tion.
4197 This option performs three steps:
4199 1. Create a static route for the --remote address which forwards
4201 to the pre-existing default gateway. This is done so that [1m(3)
4202 will not create a routing loop.
4203 2. Delete the default gateway route.
4205 3. Set the new default gateway to be the VPN endpoint address
4207 (derived either from --route-gateway or the second parameter
4208 to --ifconfig when --dev tun is specified).
4209 When the tunnel is torn down, all of the above steps are re‐
4211 versed so that the original default route is restored.
4212 Option flags:
4214 local Add the local flag if both OpenVPN peers are directly
4216 connected via a common subnet, such as with wireless. The
4217 local flag will cause step [1m(1) above to be omitted.
4218 autolocal
4220 Try to automatically determine whether to enable local
4221 flag above.
4222 def1 Use this flag to override the default gateway by using
4224 0.0.0.0/1 and 128.0.0.0/1 rather than 0.0.0.0/0. This has
4225 the benefit of overriding but not wiping out the original
4226 default gateway.
4227 bypass-dhcp
4229 Add a direct route to the DHCP server (if it is non-lo‐
4230 cal) which bypasses the tunnel (Available on Windows
4231 clients, may not be available on non-Windows clients).
4232 bypass-dns
4234 Add a direct route to the DNS server(s) (if they are
4235 non-local) which bypasses the tunnel (Available on Win‐
4236 dows clients, may not be available on non-Windows
4237 clients).
4238 block-local
4240 Block access to local LAN when the tunnel is active, ex‐
4241 cept for the LAN gateway itself. This is accomplished by
4242 routing the local LAN (except for the LAN gateway ad‐
4243 dress) into the tunnel.
4244 ipv6 Redirect IPv6 routing into the tunnel. This works similar
4246 to the def1 flag, that is, more specific IPv6 routes are
4247 added (2000::/4, 3000::/4), covering the whole IPv6 uni‐
4248 cast space.
4249 !ipv4 Do not redirect IPv4 traffic - typically used in the flag
4251 pair ipv6 !ipv4 to redirect IPv6-only.
4252 --redirect-private flags
4254 Like --redirect-gateway, but omit actually changing the default
4255 gateway. Useful when pushing private subnets.
4256 --route args
4258 Add route to routing table after connection is established. Mul‐
4259 tiple routes can be specified. Routes will be automatically torn
4260 down in reverse order prior to TUN/TAP device close.
4261 Valid syntaxes:
4263 route network/IP
4265 route network/IP netmask
4266 route network/IP netmask gateway
4267 route network/IP netmask gateway metric
4268 This option is intended as a convenience proxy for the route(8)
4270 shell command, while at the same time providing portable seman‐
4271 tics across OpenVPN's platform space.
4272 netmask
4274 defaults to 255.255.255.255 when not given
4275 gateway
4277 default taken from --route-gateway or the second parame‐
4278 ter to --ifconfig when --dev tun is specified.
4279 metric default taken from --route-metric if set, otherwise 0.
4281 The default can be specified by leaving an option blank or set‐
4283 ting it to default.
4284 The network and gateway parameters can also be specified as a
4286 DNS or /etc/hosts file resolvable name, or as one of three spe‐
4287 cial keywords:
4288 vpn_gateway
4290 The remote VPN endpoint address (derived either from
4291 --route-gateway or the second parameter to --ifconfig
4292 when --dev tun is specified).
4293 net_gateway
4295 The pre-existing IP default gateway, read from the rout‐
4296 ing table (not supported on all OSes).
4297 remote_host
4299 The --remote address if OpenVPN is being run in client
4300 mode, and is undefined in server mode.
4301 --route-delay args
4303 Valid syntaxes:
4304 route-delay
4306 route-delay n
4307 route-delay n w
4308 Delay n seconds (default 0) after connection establishment, be‐
4310 fore adding routes. If n is 0, routes will be added immediately
4311 upon connection establishment. If --route-delay is omitted,
4312 routes will be added immediately after TUN/TAP device open and
4313 --up script execution, before any --user or --group privilege
4314 downgrade (or --chroot execution.)
4315 This option is designed to be useful in scenarios where DHCP is
4317 used to set tap adapter addresses. The delay will give the DHCP
4318 handshake time to complete before routes are added.
4319 On Windows, --route-delay tries to be more intelligent by wait‐
4321 ing w seconds (default 30) for the TAP-Win32 adapter to come up
4322 before adding routes.
4323 --route-ipv6 args
4325 Setup IPv6 routing in the system to send the specified IPv6 net‐
4326 work into OpenVPN's tun.
4327 Valid syntax:
4329 route-ipv6 ipv6addr/bits [gateway] [metric]
4331 The gateway parameter is only used for IPv6 routes across tap
4333 devices, and if missing, the ipv6remote field from --ifcon‐
4334 fig-ipv6 or --route-ipv6-gateway is used.
4335 --route-gateway arg
4337 Specify a default gateway for use with --route.
4338 If dhcp is specified as the parameter, the gateway address will
4340 be extracted from a DHCP negotiation with the OpenVPN
4341 server-side LAN.
4342 Valid syntaxes:
4344 route-gateway gateway
4346 route-gateway dhcp
4347 --route-ipv6-gateway gw
4349 Specify a default gateway gw for use with --route-ipv6.
4350 --route-metric m
4352 Specify a default metric m for use with --route.
4353 --route-noexec
4355 Don't add or remove routes automatically. Instead pass routes to
4356 --route-up script using environmental variables.
4357 --route-nopull
4359 When used with --client or --pull, accept options pushed by
4360 server EXCEPT for routes, block-outside-dns and dhcp options
4361 like DNS servers.
4362 When used on the client, this option effectively bars the server
4364 from adding routes to the client's routing table, however note
4365 that this option still allows the server to set the TCP/IP prop‐
4366 erties of the client's TUN/TAP interface.
4367 --topology mode
4369 Configure virtual addressing topology when running in --dev tun
4370 mode. This directive has no meaning in --dev tap mode, which al‐
4371 ways uses a subnet topology.
4372 If you set this directive on the server, the --server and
4374 --server-bridge directives will automatically push your chosen
4375 topology setting to clients as well. This directive can also be
4376 manually pushed to clients. Like the --dev directive, this di‐
4377 rective must always be compatible between client and server.
4378 mode can be one of:
4380 net30 Use a point-to-point topology, by allocating one /30 sub‐
4382 net per client. This is designed to allow point-to-point
4383 semantics when some or all of the connecting clients
4384 might be Windows systems. This is the default.
4385 p2p Use a point-to-point topology where the remote endpoint
4387 of the client's tun interface always points to the local
4388 endpoint of the server's tun interface. This mode allo‐
4389 cates a single IP address per connecting client. Only use
4390 when none of the connecting clients are Windows systems.
4391 subnet Use a subnet rather than a point-to-point topology by
4393 configuring the tun interface with a local IP address and
4394 subnet mask, similar to the topology used in --dev tap
4395 and ethernet bridging mode. This mode allocates a single
4396 IP address per connecting client and works on Windows as
4397 well.
4398 Note: Using --topology subnet changes the interpretation of the
4400 arguments of --ifconfig to mean "address netmask", no longer
4401 "local remote".
4402 --tun-mtu args
4404 Valid syntaxes:
4405 tun-mtu tun-mtu
4407 tun-mtu tun-mtu occ-mtu
4408 Take the TUN device MTU to be tun-mtu and derive the link MTU
4410 from it. In most cases, you will probably want to leave this
4411 parameter set to its default value.
4412 The default for tun-mtu is 1500.
4414 The OCC MTU can be used to avoid warnings about mismatched MTU
4416 from clients. If occ-mtu is not specified, it will to default to
4417 the tun-mtu.
4418 The MTU (Maximum Transmission Units) is the maximum datagram
4420 size in bytes that can be sent unfragmented over a particular
4421 network path. OpenVPN requires that packets on the control and
4422 data channels be sent unfragmented.
4423 MTU problems often manifest themselves as connections which hang
4425 during periods of active usage.
4426 It's best to use the --fragment and/or --mssfix options to deal
4428 with MTU sizing issues.
4429 Note: Depending on the platform, the operating system allows one
4431 to receive packets larger than tun-mtu (e.g. Linux and FreeBSD)
4432 but other platforms (like macOS) limit received packets to the
4433 same size as the MTU.
4434 --tun-max-mtu maxmtu
4436 This configures the maximum MTU size that a server can push to
4437 maxmtu, by configuring the internal buffers to allow at least
4438 this packet size. The default for maxmtu is 1600. Currently,
4439 only increasing beyond 1600 is possible, and attempting to re‐
4440 duce max-mtu below 1600 will be ignored.
4441 --tun-mtu-extra n
4443 Assume that the TUN/TAP device might return as many as n bytes
4444 more than the --tun-mtu size on read. This parameter defaults to
4445 0, which is sufficient for most TUN devices. TAP devices may in‐
4446 troduce additional overhead in excess of the MTU size, and a
4447 setting of 32 is the default when TAP devices are used. This pa‐
4448 rameter only controls internal OpenVPN buffer sizing, so there
4449 is no transmission overhead associated with using a larger
4450 value.
4451 TUN/TAP standalone operations
4453 These two standalone operations will require --dev and optionally
4454 --user and/or --group.
4455 --mktun
4457 (Standalone) Create a persistent tunnel on platforms which sup‐
4458 port them such as Linux. Normally TUN/TAP tunnels exist only for
4459 the period of time that an application has them open. This op‐
4460 tion takes advantage of the TUN/TAP driver's ability to build
4461 persistent tunnels that live through multiple instantiations of
4462 OpenVPN and die only when they are deleted or the machine is re‐
4463 booted.
4464 One of the advantages of persistent tunnels is that they elimi‐
4466 nate the need for separate --up and --down scripts to run the
4467 appropriate ifconfig(8) and route(8) commands. These commands
4468 can be placed in the the same shell script which starts or ter‐
4469 minates an OpenVPN session.
4470 Another advantage is that open connections through the
4472 TUN/TAP-based tunnel will not be reset if the OpenVPN peer
4473 restarts. This can be useful to provide uninterrupted connectiv‐
4474 ity through the tunnel in the event of a DHCP reset of the
4475 peer's public IP address (see the --ipchange option above).
4476 One disadvantage of persistent tunnels is that it is harder to
4478 automatically configure their MTU value (see --link-mtu and
4479 --tun-mtu above).
4480 On some platforms such as Windows, TAP-Win32 tunnels are persis‐
4482 tent by default.
4483 --rmtun
4485 (Standalone) Remove a persistent tunnel.
4486 Virtual Routing and Forwarding
4488 Options in this section relates to configuration of virtual routing and
4489 forwarding in combination with the underlying operating system.
4490 As of today this is only supported on Linux, a kernel >= 4.9 is recom‐
4492 mended.
4493 This could come in handy when for example the external network should
4495 be only used as a means to connect to some VPN endpoints and all regu‐
4496 lar traffic should only be routed through any tunnel(s). This could be
4497 achieved by setting up a VRF and configuring the interface connected to
4498 the external network to be part of the VRF. The examples below will
4499 cover this setup.
4500 Another option would be to put the tun/tap interface into a VRF. This
4502 could be done by an up-script which uses the ip link set command shown
4503 below.
4504 VRF setup with iproute2
4506 Create VRF vrf_external and map it to routing table 1023
4507 ip link add vrf_external type vrf table 1023
4509 Move eth0 into vrf_external
4511 ip link set master vrf_external dev eth0
4513 Any prefixes configured on eth0 will be moved from the :code`main`
4515 routing table into routing table 1023
4516 VRF setup with ifupdown
4518 For Debian based Distributions ifupdown2 provides an almost drop-in re‐
4519 placement for ifupdown including VRFs and other features. A configura‐
4520 tion for an interface eth0 being part of VRF code:vrf_external could
4521 look like this:
4522 auto eth0
4524 iface eth0
4525 address 192.0.2.42/24
4526 address 2001:db8:08:15::42/64
4527 gateway 192.0.2.1
4528 gateway 2001:db8:08:15::1
4529 vrf vrf_external
4530 auto vrf_external
4532 iface vrf_external
4533 vrf-table 1023
4534 OpenVPN configuration
4536 The OpenVPN configuration needs to contain this line:
4537 bind-dev vrf_external
4539 Further reading
4541 Wikipedia has nice page one VRFs:
4542 https://en.wikipedia.org/wiki/Virtual_routing_and_forwarding
4543 This talk from the Network Track of FrOSCon 2018 provides an overview
4545 about advanced layer 2 and layer 3 features of Linux
4546 • Slides:
4548 https://www.slideshare.net/BarbarossaTM/l2l3-fr-fortgeschrittene-helle-und-dunkle-magie-im-linuxnetzwerkstack
4549 • Video (german):
4551 https://media.ccc.de/v/froscon2018-2247-l2_l3_fur_fortgeschrittene_-_helle_und_dunkle_magie_im_linux-netzwerkstack
4552
4554 OpenVPN can execute external scripts in various phases of the lifetime
4555 of the OpenVPN process.
4556 Script Order of Execution
4558 1. --up
4559 Executed after TCP/UDP socket bind and TUN/TAP open.
4561 2. --tls-verify
4563 Executed when we have a still untrusted remote peer.
4565 3. --ipchange
4567 Executed after connection authentication, or remote IP address
4569 change.
4570 4. --client-connect
4572 Executed in --mode server mode immediately after client authentica‐
4574 tion.
4575 5. --route-up
4577 Executed after connection authentication, either immediately after,
4579 or some number of seconds after as defined by the --route-delay op‐
4580 tion.
4581 6. --route-pre-down
4583 Executed right before the routes are removed.
4585 7. --client-disconnect
4587 Executed in --mode server mode on client instance shutdown.
4589 8. --down
4591 Executed after TCP/UDP and TUN/TAP close.
4593 9. --learn-address
4595 Executed in --mode server mode whenever an IPv4 address/route or
4597 MAC address is added to OpenVPN's internal routing table.
4598 10. --auth-user-pass-verify
4600 Executed in --mode server mode on new client connections, when the
4602 client is still untrusted.
4603 11. --client-crresponse
4605 Execute in --mode server whenever a client sends a CR_RESPONSE
4606 message
4607 SCRIPT HOOKS
4609 --auth-user-pass-verify args
4610 Require the client to provide a username/password (possibly in
4611 addition to a client certificate) for authentication.
4612 Valid syntax:
4614 auth-user-pass-verify cmd method
4616 OpenVPN will run command cmd to validate the username/password
4618 provided by the client.
4619 cmd consists of a path to a script (or executable program), op‐
4621 tionally followed by arguments. The path and arguments may be
4622 single- or double-quoted and/or escaped using a backslash, and
4623 should be separated by one or more spaces.
4624 If method is set to via-env, OpenVPN will call cmd with the en‐
4626 vironmental variables username and password set to the user‐
4627 name/password strings provided by the client. Beware that this
4628 method is insecure on some platforms which make the environment
4629 of a process publicly visible to other unprivileged processes.
4630 If method is set to via-file, OpenVPN will write the username
4632 and password to the first two lines of a temporary file. The
4633 filename will be passed as an argument to cmd, and the file will
4634 be automatically deleted by OpenVPN after the script returns.
4635 The location of the temporary file is controlled by the
4636 --tmp-dir option, and will default to the current directory if
4637 unspecified. For security, consider setting --tmp-dir to a
4638 volatile storage medium such as /dev/shm (if available) to pre‐
4639 vent the username/password file from touching the hard drive.
4640 The script should examine the username and password, returning a
4642 success exit code (0) if the client's authentication request is
4643 to be accepted, a failure code (1) to reject the client, or a
4644 that the authentication is deferred (2). If the authentication
4645 is deferred, the script must fork/start a background or another
4646 non-blocking operation to continue the authentication in the
4647 background. When finshing the authentication, a 1 or 0 must be
4648 written to the file specified by the auth_control_file.
4649 If the file specified by auth_failed_reason_file exists and has
4651 non-empty content, the content of this file will be used as
4652 AUTH_FAILED message. To avoid race conditions, this file should
4653 be written before auth_control_file.
4654 This auth fail reason can be something simple like "User has
4656 been permanently disabled" but there are also some special auth
4657 failed messages.
4658 The TEMP message indicates that the authentication temporarily
4660 failed and that the client should continue to retry to connect.
4661 The server can optionally give a user readable message and hint
4662 the client a behavior how to proceed. The keywords of the
4663 AUTH_FAILED,TEMP message are comma separated keys/values and
4664 provide a hint to the client how to proceed. Currently defined
4665 keywords are:
4666 backoff s
4668 instructs the client to wait at least s seconds before
4669 the next connection attempt. If the client already uses a
4670 higher delay for reconnection attempt, the delay will not
4671 be shortened.
4672 advance addr
4674 Instructs the client to reconnect to the next (IP) ad‐
4675 dress of the current server.
4676 advance remote
4678 Instructs the client to skip the remaining IP addresses
4679 of the current server and instead connect to the next
4680 server specified in the configuration file.
4681 advance no
4683 Instructs the client to retry connecting to the same
4684 server again.
4685 For example, the message TEMP[backoff 42,advance no]: No free IP
4687 addresses indicates that the VPN connection can currently not
4688 succeed and instructs the client to retry in 42 seconds again.
4689 When deferred authentication is in use, the script can also re‐
4691 quest pending authentication by writing to the file specified by
4692 the auth_pending_file. The first line must be the timeout in
4693 seconds, the required method on the second line (e.g. crtext)
4694 and third line must be the EXTRA as documented in the
4695 client-pending-auth section of doc/management.txt.
4696 This directive is designed to enable a plugin-style interface
4698 for extending OpenVPN's authentication capabilities.
4699 To protect against a client passing a maliciously formed user‐
4701 name or password string, the username string must consist only
4702 of these characters: alphanumeric, underbar ('_'), dash ('-'),
4703 dot ('.'), or at ('@'). The password string can consist of any
4704 printable characters except for CR or LF. Any illegal characters
4705 in either the username or password string will be converted to
4706 underbar ('_').
4707 Care must be taken by any user-defined scripts to avoid creating
4709 a security vulnerability in the way that these strings are han‐
4710 dled. Never use these strings in such a way that they might be
4711 escaped or evaluated by a shell interpreter.
4712 For a sample script that performs PAM authentication, see sam‐
4714 ple-scripts/auth-pam.pl in the OpenVPN source distribution.
4715 --client-crresponse
4717 Executed when the client sends a text based challenge re‐
4718 sponse.
4719 Valid syntax:
4721 client-crresponse cmd
4723 OpenVPN will write the response of the client into a temporary
4725 file. The filename will be passed as an argument to cmd, and
4726 the file will be automatically deleted by OpenVPN after the
4727 script returns.
4728 The response is passed as is from the client. The script needs
4730 to check itself if the input is valid, e.g. if the input is
4731 valid base64 encoding.
4732 The script can either directly write the result of the verifica‐
4734 tion to auth_control_file or further defer it. See
4735 `--auth-user-pass-verify`` for details.
4736 For a sample script that implement TOTP (RFC 6238) based
4738 two-factor authentication, see sample-scripts/totpauth.py.
4739 --client-connect cmd
4741 Run command cmd on client connection.
4742 cmd consists of a path to a script (or executable program), op‐
4744 tionally followed by arguments. The path and arguments may be
4745 single- or double-quoted and/or escaped using a backslash, and
4746 should be separated by one or more spaces.
4747 The command is passed the common name and IP address of the
4749 just-authenticated client as environmental variables (see envi‐
4750 ronmental variable section below). The command is also passed
4751 the pathname of a freshly created temporary file as the last ar‐
4752 gument (after any arguments specified in cmd ), to be used by
4753 the command to pass dynamically generated config file directives
4754 back to OpenVPN.
4755 If the script wants to generate a dynamic config file to be ap‐
4757 plied on the server when the client connects, it should write it
4758 to the file named by the last argument.
4759 See the --client-config-dir option below for options which can
4761 be legally used in a dynamically generated config file.
4762 Note that the return value of script is significant. If script
4764 returns a non-zero error status, it will cause the client to be
4765 disconnected.
4766 If a --client-connect wants to defer the generating of the con‐
4768 figuration then the script needs to use the client_connect_de‐
4769 ferred_file and client_connect_config_file environment vari‐
4770 ables, and write status accordingly into these files. See the
4771 Environmental Variables section for more details.
4772 --client-disconnect cmd
4774 Like --client-connect but called on client instance shutdown.
4775 Will not be called unless the --client-connect script and plug‐
4776 ins (if defined) were previously called on this instance with
4777 successful (0) status returns.
4778 The exception to this rule is if the --client-disconnect command
4780 or plugins are cascaded, and at least one client-connect func‐
4781 tion succeeded, then ALL of the client-disconnect functions for
4782 scripts and plugins will be called on client instance object
4783 deletion, even in cases where some of the related client-connect
4784 functions returned an error status.
4785 The --client-disconnect command is not passed any extra argu‐
4787 ments (only those arguments specified in cmd, if any).
4788 --down cmd
4790 Run command cmd after TUN/TAP device close (post --user UID
4791 change and/or --chroot ). cmd consists of a path to script (or
4792 executable program), optionally followed by arguments. The path
4793 and arguments may be single- or double-quoted and/or escaped us‐
4794 ing a backslash, and should be separated by one or more spaces.
4795 Called with the same parameters and environmental variables as
4797 the --up option above.
4798 Note that if you reduce privileges by using --user and/or
4800 --group, your --down script will also run at reduced privilege.
4801 --down-pre
4803 Call --down cmd/script before, rather than after, TUN/TAP close.
4804 --ipchange cmd
4806 Run command cmd when our remote ip-address is initially authen‐
4807 ticated or changes.
4808 cmd consists of a path to a script (or executable program), op‐
4810 tionally followed by arguments. The path and arguments may be
4811 single- or double-quoted and/or escaped using a backslash, and
4812 should be separated by one or more spaces.
4813 When cmd is executed two arguments are appended after any argu‐
4815 ments specified in cmd , as follows:
4816 cmd ip address port number
4818 Don't use --ipchange in --mode server mode. Use a --client-con‐
4820 nect script instead.
4821 See the Environmental Variables section below for additional pa‐
4823 rameters passed as environmental variables.
4824 If you are running in a dynamic IP address environment where the
4826 IP addresses of either peer could change without notice, you can
4827 use this script, for example, to edit the /etc/hosts file with
4828 the current address of the peer. The script will be run every
4829 time the remote peer changes its IP address.
4830 Similarly if our IP address changes due to DHCP, we should con‐
4832 figure our IP address change script (see man page for dhcpcd(8))
4833 to deliver a SIGHUP or SIGUSR1 signal to OpenVPN. OpenVPN will
4834 then re-establish a connection with its most recently authenti‐
4835 cated peer on its new IP address.
4836 --learn-address cmd
4838 Run command cmd to validate client virtual addresses or routes.
4839 cmd consists of a path to a script (or executable program), op‐
4841 tionally followed by arguments. The path and arguments may be
4842 single- or double-quoted and/or escaped using a backslash, and
4843 should be separated by one or more spaces.
4844 Three arguments will be appended to any arguments in cmd as fol‐
4846 lows:
4847 $1 - [operation]
4849 "add", "update", or "delete" based on whether or not the
4850 address is being added to, modified, or deleted from
4851 OpenVPN's internal routing table.
4852 $2 - [address]
4854 The address being learned or unlearned. This can be an
4855 IPv4 address such as "198.162.10.14", an IPv4 subnet such
4856 as "198.162.10.0/24", or an ethernet MAC address (when
4857 --dev tap is being used) such as "00:FF:01:02:03:04".
4858 $3 - [common name]
4860 The common name on the certificate associated with the
4861 client linked to this address. Only present for "add" or
4862 "update" operations, not "delete".
4863 On "add" or "update" methods, if the script returns a failure
4865 code (non-zero), OpenVPN will reject the address and will not
4866 modify its internal routing table.
4867 Normally, the cmd script will use the information provided above
4869 to set appropriate firewall entries on the VPN TUN/TAP inter‐
4870 face. Since OpenVPN provides the association between virtual IP
4871 or MAC address and the client's authenticated common name, it
4872 allows a user-defined script to configure firewall access poli‐
4873 cies with regard to the client's high-level common name, rather
4874 than the low level client virtual addresses.
4875 --route-up cmd
4877 Run command cmd after routes are added, subject to --route-de‐
4878 lay.
4879 cmd consists of a path to a script (or executable program), op‐
4881 tionally followed by arguments. The path and arguments may be
4882 single- or double-quoted and/or escaped using a backslash, and
4883 should be separated by one or more spaces.
4884 See the Environmental Variables section below for additional pa‐
4886 rameters passed as environmental variables.
4887 --route-pre-down cmd
4889 Run command cmd before routes are removed upon disconnection.
4890 cmd consists of a path to a script (or executable program), op‐
4892 tionally followed by arguments. The path and arguments may be
4893 single- or double-quoted and/or escaped using a backslash, and
4894 should be separated by one or more spaces.
4895 See the Environmental Variables section below for additional pa‐
4897 rameters passed as environmental variables.
4898 --setenv args
4900 Set a custom environmental variable name=value to pass to
4901 script.
4902 Valid syntaxes:
4904 setenv name value
4906 setenv FORWARD_COMPATIBLE 1
4907 setenv opt config_option
4908 By setting FORWARD_COMPATIBLE to 1, the config file syntax
4910 checking is relaxed so that unknown directives will trigger a
4911 warning but not a fatal error, on the assumption that a given
4912 unknown directive might be valid in future OpenVPN versions.
4913 This option should be used with caution, as there are good secu‐
4915 rity reasons for having OpenVPN fail if it detects problems in a
4916 config file. Having said that, there are valid reasons for
4917 wanting new software features to gracefully degrade when encoun‐
4918 tered by older software versions.
4919 It is also possible to tag a single directive so as not to trig‐
4921 ger a fatal error if the directive isn't recognized. To do this,
4922 prepend the following before the directive: setenv opt
4923 Versions prior to OpenVPN 2.3.3 will always ignore options set
4925 with the setenv opt directive.
4926 See also --ignore-unknown-option
4928 --setenv-safe args
4930 Set a custom environmental variable OPENVPN_name to value to
4931 pass to scripts.
4932 Valid syntaxes:
4934 setenv-safe name value
4936 This directive is designed to be pushed by the server to
4938 clients, and the prepending of OPENVPN_ to the environmental
4939 variable is a safety precaution to prevent a LD_PRELOAD style
4940 attack from a malicious or compromised server.
4941 --tls-verify cmd
4943 Run command cmd to verify the X509 name of a pending TLS connec‐
4944 tion that has otherwise passed all other tests of certification
4945 (except for revocation via --crl-verify directive; the revoca‐
4946 tion test occurs after the --tls-verify test).
4947 cmd should return 0 to allow the TLS handshake to proceed, or 1
4949 to fail.
4950 cmd consists of a path to a script (or executable program), op‐
4952 tionally followed by arguments. The path and arguments may be
4953 single- or double-quoted and/or escaped using a backslash, and
4954 should be separated by one or more spaces.
4955 When cmd is executed two arguments are appended after any argu‐
4957 ments specified in cmd, as follows:
4958 cmd certificate_depth subject
4960 These arguments are, respectively, the current certificate depth
4962 and the X509 subject distinguished name (dn) of the peer.
4963 This feature is useful if the peer you want to trust has a cer‐
4965 tificate which was signed by a certificate authority who also
4966 signed many other certificates, where you don't necessarily want
4967 to trust all of them, but rather be selective about which peer
4968 certificate you will accept. This feature allows you to write a
4969 script which will test the X509 name on a certificate and decide
4970 whether or not it should be accepted. For a simple perl script
4971 which will test the common name field on the certificate, see
4972 the file verify-cn in the OpenVPN distribution.
4973 See the Environmental Variables section below for additional pa‐
4975 rameters passed as environmental variables.
4976 --up cmd
4978 Run command cmd after successful TUN/TAP device open (pre --user
4979 UID change).
4980 cmd consists of a path to a script (or executable program), op‐
4982 tionally followed by arguments. The path and arguments may be
4983 single- or double-quoted and/or escaped using a backslash, and
4984 should be separated by one or more spaces.
4985 The up command is useful for specifying route commands which
4987 route IP traffic destined for private subnets which exist at the
4988 other end of the VPN connection into the tunnel.
4989 For --dev tun execute as:
4991 cmd tun_dev tun_mtu 0 ifconfig_local_ip ifconfig_remote_ip [init | restart]
4993 For --dev tap execute as:
4995 cmd tap_dev tap_mtu 0 ifconfig_local_ip ifconfig_netmask [init | restart]
4997 See the Environmental Variables section below for additional pa‐
4999 rameters passed as environmental variables. The 0 argument used
5000 to be link_mtu which is no longer passed to scripts - to keep
5001 the argument order, it was replaced with 0.
5002 Note that if cmd includes arguments, all OpenVPN-generated argu‐
5004 ments will be appended to them to build an argument list with
5005 which the executable will be called.
5006 Typically, cmd will run a script to add routes to the tunnel.
5008 Normally the up script is called after the TUN/TAP device is
5010 opened. In this context, the last command line parameter passed
5011 to the script will be init. If the --up-restart option is also
5012 used, the up script will be called for restarts as well. A
5013 restart is considered to be a partial reinitialization of Open‐
5014 VPN where the TUN/TAP instance is preserved (the --persist-tun
5015 option will enable such preservation). A restart can be gener‐
5016 ated by a SIGUSR1 signal, a --ping-restart timeout, or a connec‐
5017 tion reset when the TCP protocol is enabled with the --proto op‐
5018 tion. If a restart occurs, and --up-restart has been specified,
5019 the up script will be called with restart as the last parameter.
5020 NOTE: On restart, OpenVPN will not pass the full set of envi‐
5022 ronment variables to the script. Namely, everything re‐
5023 lated to routing and gateways will not be passed, as
5024 nothing needs to be done anyway - all the routing setup
5025 is already in place. Additionally, the up-restart script
5026 will run with the downgraded UID/GID settings (if config‐
5027 ured).
5028 The following standalone example shows how the --up script can
5030 be called in both an initialization and restart context. (NOTE:
5031 for security reasons, don't run the following example unless UDP
5032 port 9999 is blocked by your firewall. Also, the example will
5033 run indefinitely, so you should abort with control-c).
5034 openvpn --dev tun --port 9999 --verb 4 --ping-restart 10 \
5036 --up 'echo up' --down 'echo down' --persist-tun \
5037 --up-restart
5038 Note that OpenVPN also provides the --ifconfig option to auto‐
5040 matically ifconfig the TUN device, eliminating the need to de‐
5041 fine an --up script, unless you also want to configure routes in
5042 the --up script.
5043 If --ifconfig is also specified, OpenVPN will pass the ifconfig
5045 local and remote endpoints on the command line to the --up
5046 script so that they can be used to configure routes such as:
5047 route add -net 10.0.0.0 netmask 255.255.255.0 gw $5
5049 --up-delay
5051 Delay TUN/TAP open and possible --up script execution until af‐
5052 ter TCP/UDP connection establishment with peer.
5053 In --proto udp mode, this option normally requires the use of
5055 --ping to allow connection initiation to be sensed in the ab‐
5056 sence of tunnel data, since UDP is a "connectionless" protocol.
5057 On Windows, this option will delay the TAP-Win32 media state
5059 transitioning to "connected" until connection establishment,
5060 i.e. the receipt of the first authenticated packet from the
5061 peer.
5062 --up-restart
5064 Enable the --up and --down scripts to be called for restarts as
5065 well as initial program start. This option is described more
5066 fully above in the --up option documentation.
5067 String Types and Remapping
5069 In certain cases, OpenVPN will perform remapping of characters in
5070 strings. Essentially, any characters outside the set of permitted char‐
5071 acters for each string type will be converted to underbar ('_').
5072 Q: Why is string remapping necessary?
5074 It's an important security feature to prevent the malicious cod‐
5075 ing of strings from untrusted sources to be passed as parameters
5076 to scripts, saved in the environment, used as a common name,
5077 translated to a filename, etc.
5078 Q: Can string remapping be disabled?
5080 Yes, by using the --no-name-remapping option, however this
5081 should be considered an advanced option.
5082 Here is a brief rundown of OpenVPN's current string types and the per‐
5084 mitted character class for each string:
5085 X509 Names
5087 Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), at ('@'),
5088 colon (':'), slash ('/'), and equal ('='). Alphanumeric is de‐
5089 fined as a character which will cause the C library isalnum()
5090 function to return true.
5091 Common Names
5093 Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), and at
5094 ('@').
5095 --auth-user-pass username
5097 Same as Common Name, with one exception: starting with OpenVPN
5098 2.0.1, the username is passed to the OPEN‐
5099 VPN_PLUGIN_AUTH_USER_PASS_VERIFY plugin in its raw form, without
5100 string remapping.
5101 --auth-user-pass password
5103 Any "printable" character except CR or LF. Printable is defined
5104 to be a character which will cause the C library isprint() func‐
5105 tion to return true.
5106 --client-config-dir filename as derived from common name or`username
5108 Alphanumeric, underbar ('_'), dash ('-'), and dot ('.') except
5109 for "." or ".." as standalone strings. As of v2.0.1-rc6, the at
5110 ('@') character has been added as well for compatibility with
5111 the common name character class.
5112 Environmental variable names
5114 Alphanumeric or underbar ('_').
5115 Environmental variable values
5117 Any printable character.
5118 For all cases, characters in a string which are not members of the le‐
5120 gal character class for that string type will be remapped to underbar
5121 ('_').
5122 Environmental Variables
5124 Once set, a variable is persisted indefinitely until it is reset by a
5125 new value or a restart,
5126 As of OpenVPN 2.0-beta12, in server mode, environmental variables set
5128 by OpenVPN are scoped according to the client objects they are associ‐
5129 ated with, so there should not be any issues with scripts having access
5130 to stale, previously set variables which refer to different client in‐
5131 stances.
5132 bytes_received
5134 Total number of bytes received from client during VPN session.
5135 Set prior to execution of the --client-disconnect script.
5136 bytes_sent
5138 Total number of bytes sent to client during VPN session. Set
5139 prior to execution of the --client-disconnect script.
5140 client_connect_config_file
5142 The path to the configuration file that should be written to by
5143 the --client-connect script (optional, if per-session configura‐
5144 tion is desired). This is the same file name as passed via com‐
5145 mand line argument on the call to the --client-connect script.
5146 client_connect_deferred_file
5148 This file can be optionally written to in order to to communi‐
5149 cate a status code of the --client-connect script or plgin.
5150 Only the first character in the file is relevant. It must be
5151 either 1 to indicate normal script execution, 0 indicates an er‐
5152 ror (in the same way that a non zero exit status does) or 2 to
5153 indicate that the script deferred returning the config file.
5154 For deferred (background) handling, the script or plugin MUST
5156 write 2 to the file to indicate the deferral and then return
5157 with exit code 0 to signal deferred handler started OK.
5158 A background process or similar must then take care of writing
5160 the configuration to the file indicated by the client_con‐
5161 nect_config_file environment variable and when finished, write
5162 the a 1 to this file (or 0 in case of an error).
5163 The absence of any character in the file when the script fin‐
5165 ishes executing is interpreted the same as 1. This allows
5166 scripts that are not written to support the defer mechanism to
5167 be used unmodified.
5168 common_name
5170 The X509 common name of an authenticated client. Set prior to
5171 execution of --client-connect, --client-disconnect and
5172 --auth-user-pass-verify scripts.
5173 config Name of first --config file. Set on program initiation and reset
5175 on SIGHUP.
5176 daemon Set to "1" if the --daemon directive is specified, or "0" other‐
5178 wise. Set on program initiation and reset on SIGHUP.
5179 daemon_log_redirect
5181 Set to "1" if the --log or --log-append directives are speci‐
5182 fied, or "0" otherwise. Set on program initiation and reset on
5183 SIGHUP.
5184 dev The actual name of the TUN/TAP device, including a unit number
5186 if it exists. Set prior to --up or --down script execution.
5187 dev_idx
5189 On Windows, the device index of the TUN/TAP adapter (to be used
5190 in netsh.exe calls which sometimes just do not work right with
5191 interface names). Set prior to --up or --down script execution.
5192 dns_* The --dns configuration options will be made available to script
5194 execution through this set of environment variables. Variables
5195 appear only if the corresponding option has a value assigned.
5196 For the semantics of each individual variable, please refer to
5197 the documentation for --dns.
5198 dns_search_domain_{n}
5200 dns_server_{n}_address_{m}
5201 dns_server_{n}_port_{m}
5202 dns_server_{n}_resolve_domain_{m}
5203 dns_server_{n}_dnssec
5204 dns_server_{n}_transport
5205 dns_server_{n}_sni
5206 foreign_option_{n}
5208 An option pushed via --push to a client which does not natively
5209 support it, such as --dhcp-option on a non-Windows system, will
5210 be recorded to this environmental variable sequence prior to
5211 --up script execution.
5212 ifconfig_broadcast
5214 The broadcast address for the virtual ethernet segment which is
5215 derived from the --ifconfig option when --dev tap is used. Set
5216 prior to OpenVPN calling the ifconfig or netsh (windows version
5217 of ifconfig) commands which normally occurs prior to --up script
5218 execution.
5219 ifconfig_ipv6_local
5221 The local VPN endpoint IPv6 address specified in the --ifcon‐
5222 fig-ipv6 option (first parameter). Set prior to OpenVPN calling
5223 the ifconfig or code:netsh (windows version of ifconfig) com‐
5224 mands which normally occurs prior to --up script execution.
5225 ifconfig_ipv6_netbits
5227 The prefix length of the IPv6 network on the VPN interface. De‐
5228 rived from the /nnn parameter of the IPv6 address in the --if‐
5229 config-ipv6 option (first parameter). Set prior to OpenVPN call‐
5230 ing the ifconfig or netsh (windows version of ifconfig) commands
5231 which normally occurs prior to --up script execution.
5232 ifconfig_ipv6_remote
5234 The remote VPN endpoint IPv6 address specified in the --ifcon‐
5235 fig-ipv6 option (second parameter). Set prior to OpenVPN calling
5236 the ifconfig or netsh (windows version of ifconfig) commands
5237 which normally occurs prior to --up script execution.
5238 ifconfig_local
5240 The local VPN endpoint IP address specified in the --ifconfig
5241 option (first parameter). Set prior to OpenVPN calling the if‐
5242 config or netsh (windows version of ifconfig) commands which
5243 normally occurs prior to --up script execution.
5244 ifconfig_remote
5246 The remote VPN endpoint IP address specified in the --ifconfig
5247 option (second parameter) when --dev tun is used. Set prior to
5248 OpenVPN calling the ifconfig or netsh (windows version of ifcon‐
5249 fig) commands which normally occurs prior to --up script execu‐
5250 tion.
5251 ifconfig_netmask
5253 The subnet mask of the virtual ethernet segment that is speci‐
5254 fied as the second parameter to --ifconfig when --dev tap is be‐
5255 ing used. Set prior to OpenVPN calling the ifconfig or netsh
5256 (windows version of ifconfig) commands which normally occurs
5257 prior to --up script execution.
5258 ifconfig_pool_local_ip
5260 The local virtual IP address for the TUN/TAP tunnel taken from
5261 an --ifconfig-push directive if specified, or otherwise from the
5262 ifconfig pool (controlled by the --ifconfig-pool config file di‐
5263 rective). Only set for --dev tun tunnels. This option is set on
5264 the server prior to execution of the --client-connect and
5265 --client-disconnect scripts.
5266 ifconfig_pool_netmask
5268 The virtual IP netmask for the TUN/TAP tunnel taken from an
5269 --ifconfig-push directive if specified, or otherwise from the
5270 ifconfig pool (controlled by the --ifconfig-pool config file di‐
5271 rective). Only set for --dev tap tunnels. This option is set on
5272 the server prior to execution of the --client-connect and
5273 --client-disconnect scripts.
5274 ifconfig_pool_remote_ip
5276 The remote virtual IP address for the TUN/TAP tunnel taken from
5277 an --ifconfig-push directive if specified, or otherwise from the
5278 ifconfig pool (controlled by the --ifconfig-pool config file di‐
5279 rective). This option is set on the server prior to execution of
5280 the --client-connect and --client-disconnect scripts.
5281 link_mtu
5283 No longer passed to scripts since OpenVPN 2.6.0. Used to be the
5284 maximum packet size (not including the IP header) of tunnel data
5285 in UDP tunnel transport mode.
5286 local The --local parameter. Set on program initiation and reset on
5288 SIGHUP.
5289 local_port
5291 The local port number or name, specified by --port or --lport.
5292 Set on program initiation and reset on SIGHUP.
5293 password
5295 The password provided by a connecting client. Set prior to
5296 --auth-user-pass-verify script execution only when the via-env
5297 modifier is specified, and deleted from the environment after
5298 the script returns.
5299 proto The --proto parameter. Set on program initiation and reset on
5301 SIGHUP.
5302 remote_{n}
5304 The --remote parameter. Set on program initiation and reset on
5305 SIGHUP.
5306 remote_port_{n}
5308 The remote port number, specified by --port or --rport. Set on
5309 program initiation and reset on SIGHUP.
5310 route_net_gateway
5312 The pre-existing default IP gateway in the system routing table.
5313 Set prior to --up script execution.
5314 route_vpn_gateway
5316 The default gateway used by --route options, as specified in ei‐
5317 ther the --route-gateway option or the second parameter to --if‐
5318 config when --dev tun is specified. Set prior to --up script ex‐
5319 ecution.
5320 route_{parm}_{n}
5322 A set of variables which define each route to be added, and are
5323 set prior to --up script execution.
5324 parm will be one of network, netmask", gateway, or metric.
5326 n is the OpenVPN route number, starting from 1.
5328 If the network or gateway are resolvable DNS names, their IP ad‐
5330 dress translations will be recorded rather than their names as
5331 denoted on the command line or configuration file.
5332 route_ipv6_{parm}_{n}
5334 A set of variables which define each IPv6 route to be added, and
5335 are set prior to --up script execution.
5336 parm will be one of network, gateway or metric. route_ipv6_net‐
5338 work_{n} contains netmask as /nnn, unlike IPv4 where it is
5339 passed in a separate environment variable.
5340 n is the OpenVPN route number, starting from 1.
5342 If the network or gateway are resolvable DNS names, their IP ad‐
5344 dress translations will be recorded rather than their names as
5345 denoted on the command line or configuration file.
5346 peer_cert
5348 Temporary file name containing the client certificate upon con‐
5349 nection. Useful in conjunction with --tls-verify.
5350 script_context
5352 Set to "init" or "restart" prior to up/down script execution.
5353 For more information, see documentation for --up.
5354 script_type
5356 Prior to execution of any script, this variable is set to the
5357 type of script being run. It can be one of the following: up,
5358 down, ipchange, route-up, tls-verify, auth-user-pass-verify,
5359 client-connect, client-disconnect or learn-address. Set prior to
5360 execution of any script.
5361 signal The reason for exit or restart. Can be one of sigusr1, sighup,
5363 sigterm, sigint, inactive (controlled by --inactive option),
5364 ping-exit (controlled by --ping-exit option), ping-restart (con‐
5365 trolled by --ping-restart option), connection-reset (triggered
5366 on TCP connection reset), error or unknown (unknown signal).
5367 This variable is set just prior to down script execution.
5368 time_ascii
5370 Client connection timestamp, formatted as a human-readable time
5371 string. Set prior to execution of the --client-connect script.
5372 time_duration
5374 The duration (in seconds) of the client session which is now
5375 disconnecting. Set prior to execution of the --client-disconnect
5376 script.
5377 time_unix
5379 Client connection timestamp, formatted as a unix integer
5380 date/time value. Set prior to execution of the --client-connect
5381 script.
5382 tls_digest_{n} / tls_digest_sha256_{n}
5384 Contains the certificate SHA1 / SHA256 fingerprint, where n is
5385 the verification level. Only set for TLS connections. Set prior
5386 to execution of --tls-verify script.
5387 tls_id_{n}
5389 A series of certificate fields from the remote peer, where n is
5390 the verification level. Only set for TLS connections. Set prior
5391 to execution of --tls-verify script.
5392 tls_serial_{n}
5394 The serial number of the certificate from the remote peer, where
5395 n is the verification level. Only set for TLS connections. Set
5396 prior to execution of --tls-verify script. This is in the form
5397 of a decimal string like "933971680", which is suitable for do‐
5398 ing serial-based OCSP queries (with OpenSSL, do not prepend "0x"
5399 to the string) If something goes wrong while reading the value
5400 from the certificate it will be an empty string, so your code
5401 should check that. See the contrib/OCSP_check/OCSP_check.sh
5402 script for an example.
5403 tls_serial_hex_{n}
5405 Like tls_serial_{n}, but in hex form (e.g. 12:34:56:78:9A).
5406 tun_mtu
5408 The MTU of the TUN/TAP device. Set prior to --up or --down
5409 script execution.
5410 trusted_ip / trusted_ip6)
5412 Actual IP address of connecting client or peer which has been
5413 authenticated. Set prior to execution of --ipchange,
5414 --client-connect and --client-disconnect scripts. If using ipv6
5415 endpoints (udp6, tcp6), trusted_ip6 will be set instead.
5416 trusted_port
5418 Actual port number of connecting client or peer which has been
5419 authenticated. Set prior to execution of --ipchange,
5420 --client-connect and --client-disconnect scripts.
5421 untrusted_ip / untrusted_ip6
5423 Actual IP address of connecting client or peer which has not
5424 been authenticated yet. Sometimes used to nmap the connecting
5425 host in a --tls-verify script to ensure it is firewalled prop‐
5426 erly. Set prior to execution of --tls-verify and
5427 --auth-user-pass-verify scripts. If using ipv6 endpoints (udp6,
5428 tcp6), untrusted_ip6 will be set instead.
5429 untrusted_port
5431 Actual port number of connecting client or peer which has not
5432 been authenticated yet. Set prior to execution of --tls-verify
5433 and --auth-user-pass-verify scripts.
5434 username
5436 The username provided by a connecting client. Set prior to
5437 --auth-user-pass-verify script execution only when the via-env
5438 modifier is specified.
5439 X509_{n}_{subject_field}
5441 An X509 subject field from the remote peer certificate, where n
5442 is the verification level. Only set for TLS connections. Set
5443 prior to execution of --tls-verify script. This variable is sim‐
5444 ilar to tls_id_{n} except the component X509 subject fields are
5445 broken out, and no string remapping occurs on these field values
5446 (except for remapping of control characters to "_"). For exam‐
5447 ple, the following variables would be set on the OpenVPN server
5448 using the sample client certificate in sample-keys (client.crt).
5449 Note that the verification level is 0 for the client certificate
5450 and 1 for the CA certificate.
5451 X509_0_emailAddress=me@myhost.mydomain
5453 X509_0_CN=Test-Client
5454 X509_0_O=OpenVPN-TEST
5455 X509_0_ST=NA
5456 X509_0_C=KG
5457 X509_1_emailAddress=me@myhost.mydomain
5458 X509_1_O=OpenVPN-TEST
5459 X509_1_L=BISHKEK
5460 X509_1_ST=NA
5461 X509_1_C=KG
5462 Management Interface Options
5464 OpenVPN provides a feature rich socket based management interface for
5465 both server and client mode operations.
5466 --management args
5468 Enable a management server on a socket-name Unix socket on those
5469 platforms supporting it, or on a designated TCP port.
5470 Valid syntaxes:
5472 management socket-name unix #
5474 management socket-name unix pw-file # (recommended)
5475 management IP port # (INSECURE)
5476 management IP port pw-file #
5477 pw-file, if specified, is a password file where the password
5479 must be on first line. Instead of a filename it can use the key‐
5480 word stdin which will prompt the user for a password to use when
5481 OpenVPN is starting.
5482 For unix sockets, the default behaviour is to create a unix do‐
5484 main socket that may be connected to by any process. Use the
5485 --management-client-user and --management-client-group direc‐
5486 tives to restrict access.
5487 The management interface provides a special mode where the TCP
5489 management link can operate over the tunnel itself. To enable
5490 this mode, set IP to tunnel. Tunnel mode will cause the manage‐
5491 ment interface to listen for a TCP connection on the local VPN
5492 address of the TUN/TAP interface.
5493 *BEWARE* of enabling the management interface over TCP. In these
5495 cases you should ALWAYS make use of pw-file to password protect
5496 the management interface. Any user who can connect to this TCP
5497 IP:port will be able to manage and control (and interfere with)
5498 the OpenVPN process. It is also strongly recommended to set IP
5499 to 127.0.0.1 (localhost) to restrict accessibility of the man‐
5500 agement server to local clients.
5501 While the management port is designed for programmatic control
5503 of OpenVPN by other applications, it is possible to telnet to
5504 the port, using a telnet client in "raw" mode. Once connected,
5505 type help for a list of commands.
5506 For detailed documentation on the management interface, see the
5508 management-notes.txt file in the management folder of the Open‐
5509 VPN source distribution.
5510 --management-client
5512 Management interface will connect as a TCP/unix domain client to
5513 IP:port specified by --management rather than listen as a TCP
5514 server or on a unix domain socket.
5515 If the client connection fails to connect or is disconnected, a
5517 SIGTERM signal will be generated causing OpenVPN to quit.
5518 --management-client-auth
5520 Gives management interface client the responsibility to authen‐
5521 ticate clients after their client certificate has been verified.
5522 See management-notes.txt in OpenVPN distribution for detailed
5523 notes.
5524 --management-client-group g
5526 When the management interface is listening on a unix domain
5527 socket, only allow connections from group g.
5528 --management-client-user u
5530 When the management interface is listening on a unix domain
5531 socket, only allow connections from user u.
5532 --management-external-cert certificate-hint
5534 Allows usage for external certificate instead of --cert option
5535 (client-only). certificate-hint is an arbitrary string which is
5536 passed to a management interface client as an argument of
5537 NEED-CERTIFICATE notification. Requires --management-exter‐
5538 nal-key.
5539 --management-external-key args
5541 Allows usage for external private key file instead of --key op‐
5542 tion (client-only).
5543 Valid syntaxes:
5545 management-external-key
5547 management-external-key nopadding
5548 management-external-key pkcs1
5549 management-external-key pss
5550 or any combination like:
5552 management-external-key nopadding pkcs1
5554 management-external-key pkcs1 pss
5555 The optional parameters nopadding pkcs1 and pss signal support
5557 for different padding algorithms. See doc/mangement-notes.txt
5558 for a complete description of this feature.
5559 --management-forget-disconnect
5561 Make OpenVPN forget passwords when management session discon‐
5562 nects.
5563 This directive does not affect the --http-proxy username/pass‐
5565 word. It is always cached.
5566 --management-hold
5568 Start OpenVPN in a hibernating state, until a client of the man‐
5569 agement interface explicitly starts it with the hold release
5570 command.
5571 --management-log-cache n
5573 Cache the most recent n lines of log file history for usage by
5574 the management channel.
5575 --management-query-passwords
5577 Query management channel for private key password and
5578 --auth-user-pass username/password. Only query the management
5579 channel for inputs which ordinarily would have been queried from
5580 the console.
5581 --management-query-proxy
5583 Query management channel for proxy server information for a spe‐
5584 cific --remote (client-only).
5585 --management-query-remote
5587 Allow management interface to override --remote directives
5588 (client-only).
5589 --management-signal
5591 Send SIGUSR1 signal to OpenVPN if management session discon‐
5592 nects. This is useful when you wish to disconnect an OpenVPN
5593 session on user logoff. For --management-client this option is
5594 not needed since a disconnect will always generate a SIGTERM.
5595 --management-up-down
5597 Report tunnel up/down events to management interface.
5598 Plug-in Interface Options
5600 OpenVPN can be extended by loading external plug-in modules at runtime.
5601 These plug-ins must be prebuilt and adhere to the OpenVPN Plug-In API.
5602 --plugin args
5604 Loads an OpenVPN plug-in module.
5605 Valid syntax:
5607 plugin module-name
5609 plugin module-name "arguments"
5610 The module-name needs to be the first argument, indicating the
5612 plug-in to load. The second argument is an optional init string
5613 which will be passed directly to the plug-in. If the init con‐
5614 sists of multiple arguments it must be enclosed in double-quotes
5615 ("). Multiple plugin modules may be loaded into one OpenVPN
5616 process.
5617 The module-name argument can be just a filename or a filename
5619 with a relative or absolute path. The format of the filename and
5620 path defines if the plug-in will be loaded from a default
5621 plug-in directory or outside this directory.
5622 --plugin path Effective directory used
5624 ===================== =============================
5625 myplug.so DEFAULT_DIR/myplug.so
5626 subdir/myplug.so DEFAULT_DIR/subdir/myplug.so
5627 ./subdir/myplug.so CWD/subdir/myplug.so
5628 /usr/lib/my/plug.so /usr/lib/my/plug.so
5629 DEFAULT_DIR is replaced by the default plug-in directory, which
5631 is configured at the build time of OpenVPN. CWD is the current
5632 directory where OpenVPN was started or the directory OpenVPN
5633 have switched into via the --cd option before the --plugin op‐
5634 tion.
5635 For more information and examples on how to build OpenVPN
5637 plug-in modules, see the README file in the plugin folder of the
5638 OpenVPN source distribution.
5639 If you are using an RPM install of OpenVPN, see /usr/share/open‐
5641 vpn/plugin. The documentation is in doc and the actual plugin
5642 modules are in lib.
5643 Multiple plugin modules can be cascaded, and modules can be used
5645 in tandem with scripts. The modules will be called by OpenVPN in
5646 the order that they are declared in the config file. If both a
5647 plugin and script are configured for the same callback, the
5648 script will be called last. If the return code of the mod‐
5649 ule/script controls an authentication function (such as tls-ver‐
5650 ify, auth-user-pass-verify, or client-connect), then every mod‐
5651 ule and script must return success (0) in order for the connec‐
5652 tion to be authenticated.
5653 WARNING:
5655 Plug-ins may do deferred execution, meaning the plug-in
5656 will return the control back to the main OpenVPN process
5657 and provide the plug-in result later on via a different
5658 thread or process. OpenVPN does NOT support multiple au‐
5659 thentication plug-ins where more than one plugin tries to
5660 do deferred authentication. If this behaviour is de‐
5661 tected, OpenVPN will shut down upon first authentication.
5662 Windows-Specific Options
5664 --allow-nonadmin TAP-adapter
5665 (Standalone) Set TAP-adapter to allow access from non-adminis‐
5666 trative accounts. If TAP-adapter is omitted, all TAP adapters on
5667 the system will be configured to allow non-admin access. The
5668 non-admin access setting will only persist for the length of
5669 time that the TAP-Win32 device object and driver remain loaded,
5670 and will need to be re-enabled after a reboot, or if the driver
5671 is unloaded and reloaded. This directive can only be used by an
5672 administrator.
5673 --block-outside-dns
5675 Block DNS servers on other network adapters to prevent DNS
5676 leaks. This option prevents any application from accessing TCP
5677 or UDP port 53 except one inside the tunnel. It uses Windows
5678 Filtering Platform (WFP) and works on Windows Vista or later.
5679 This option is considered unknown on non-Windows platforms and
5681 unsupported on Windows XP, resulting in fatal error. You may
5682 want to use --setenv opt or --ignore-unknown-option (not suit‐
5683 able for Windows XP) to ignore said error. Note that pushing un‐
5684 known options from server does not trigger fatal errors.
5685 --cryptoapicert select-string
5687 (Windows/OpenSSL Only) Load the certificate and private key from
5688 the Windows Certificate System Store.
5689 Use this option instead of --cert and --key.
5691 This makes it possible to use any smart card, supported by Win‐
5693 dows, but also any kind of certificate, residing in the Cert
5694 Store, where you have access to the private key. This option has
5695 been tested with a couple of different smart cards (GemSAFE,
5696 Cryptoflex, and Swedish Post Office eID) on the client side, and
5697 also an imported PKCS12 software certificate on the server side.
5698 To select a certificate, based on a substring search in the cer‐
5700 tificate's subject:
5701 cryptoapicert "SUBJ:Peter Runestig"
5703 To select a certificate, based on certificate's thumbprint (SHA1
5705 hash):
5706 cryptoapicert "THUMB:f6 49 24 41 01 b4 ..."
5708 The thumbprint hex string can easily be copy-and-pasted from the
5710 Windows Certificate Store GUI. The embedded spaces in the hex
5711 string are optional.
5712 To select a certificate based on a substring in certificate's
5714 issuer name:
5715 cryptoapicert "ISSUER:Sample CA"
5717 The first non-expired certificate found in the user's store or
5719 the machine store that matches the select-string is used.
5720 --dhcp-release
5722 Ask Windows to release the TAP adapter lease on shutdown. This
5723 option has no effect now, as it is enabled by default starting
5724 with OpenVPN 2.4.1.
5725 --dhcp-renew
5727 Ask Windows to renew the TAP adapter lease on startup. This op‐
5728 tion is normally unnecessary, as Windows automatically triggers
5729 a DHCP renegotiation on the TAP adapter when it comes up, how‐
5730 ever if you set the TAP-Win32 adapter Media Status property to
5731 "Always Connected", you may need this flag.
5732 --ip-win32 method
5734 When using --ifconfig on Windows, set the TAP-Win32 adapter IP
5735 address and netmask using method. Don't use this option unless
5736 you are also using --ifconfig.
5737 manual Don't set the IP address or netmask automatically. In‐
5739 stead output a message to the console telling the user to
5740 configure the adapter manually and indicating the IP/net‐
5741 mask which OpenVPN expects the adapter to be set to.
5742 dynamic [offset] [lease-time]
5744 Automatically set the IP address and netmask by replying
5745 to DHCP query messages generated by the kernel. This
5746 mode is probably the "cleanest" solution for setting the
5747 TCP/IP properties since it uses the well-known DHCP pro‐
5748 tocol. There are, however, two prerequisites for using
5749 this mode:
5750 1. The TCP/IP properties for the TAP-Win32 adapter must
5752 be set to "Obtain an IP address automatically", and
5753 2. OpenVPN needs to claim an IP address in the subnet for
5755 use as the virtual DHCP server address.
5756 By default in --dev tap mode, OpenVPN will take the nor‐
5758 mally unused first address in the subnet. For example, if
5759 your subnet is 192.168.4.0 netmask 255.255.255.0, then
5760 OpenVPN will take the IP address 192.168.4.0 to use as
5761 the virtual DHCP server address. In --dev tun mode,
5762 OpenVPN will cause the DHCP server to masquerade as if it
5763 were coming from the remote endpoint.
5764 The optional offset parameter is an integer which is >
5766 -256 and < 256 and which defaults to 0. If offset is pos‐
5767 itive, the DHCP server will masquerade as the IP address
5768 at network address + offset. If offset is negative, the
5769 DHCP server will masquerade as the IP address at broad‐
5770 cast address + offset.
5771 The Windows ipconfig /all command can be used to show
5773 what Windows thinks the DHCP server address is. OpenVPN
5774 will "claim" this address, so make sure to use a free ad‐
5775 dress. Having said that, different OpenVPN instantia‐
5776 tions, including different ends of the same connection,
5777 can share the same virtual DHCP server address.
5778 The lease-time parameter controls the lease time of the
5780 DHCP assignment given to the TAP-Win32 adapter, and is
5781 denoted in seconds. Normally a very long lease time is
5782 preferred because it prevents routes involving the
5783 TAP-Win32 adapter from being lost when the system goes to
5784 sleep. The default lease time is one year.
5785 netsh Automatically set the IP address and netmask using the
5787 Windows command-line "netsh" command. This method appears
5788 to work correctly on Windows XP but not Windows 2000.
5789 ipapi Automatically set the IP address and netmask using the
5791 Windows IP Helper API. This approach does not have ideal
5792 semantics, though testing has indicated that it works
5793 okay in practice. If you use this option, it is best to
5794 leave the TCP/IP properties for the TAP-Win32 adapter in
5795 their default state, i.e. "Obtain an IP address automati‐
5796 cally."
5797 adaptive (Default)
5799 Try dynamic method initially and fail over to netsh if
5800 the DHCP negotiation with the TAP-Win32 adapter does not
5801 succeed in 20 seconds. Such failures have been known to
5802 occur when certain third-party firewall packages in‐
5803 stalled on the client machine block the DHCP negotiation
5804 used by the TAP-Win32 adapter. Note that if the netsh
5805 failover occurs, the TAP-Win32 adapter TCP/IP properties
5806 will be reset from DHCP to static, and this will cause
5807 future OpenVPN startups using the adaptive mode to use
5808 netsh immediately, rather than trying dynamic first.
5809 To "unstick" the adaptive mode from using netsh, run
5811 OpenVPN at least once using the dynamic mode to restore
5812 the TAP-Win32 adapter TCP/IP properties to a DHCP config‐
5813 uration.
5814 --pause-exit
5816 Put up a "press any key to continue" message on the console
5817 prior to OpenVPN program exit. This option is automatically used
5818 by the Windows explorer when OpenVPN is run on a configuration
5819 file using the right-click explorer menu.
5820 --register-dns
5822 Run ipconfig /flushdns and ipconfig /registerdns on connection
5823 initiation. This is known to kick Windows into recognizing
5824 pushed DNS servers.
5825 --route-method m
5827 Which method m to use for adding routes on Windows?
5828 adaptive (default)
5830 Try IP helper API first. If that fails, fall back to the
5831 route.exe shell command.
5832 ipapi Use IP helper API.
5834 exe Call the route.exe shell command.
5836 --service args
5838 Should be used when OpenVPN is being automatically executed by
5839 another program in such a context that no interaction with the
5840 user via display or keyboard is possible.
5841 Valid syntax:
5843 service exit-event [0|1]
5845 In general, end-users should never need to explicitly use this
5847 option, as it is automatically added by the OpenVPN service
5848 wrapper when a given OpenVPN configuration is being run as a
5849 service.
5850 exit-event is the name of a Windows global event object, and
5852 OpenVPN will continuously monitor the state of this event object
5853 and exit when it becomes signaled.
5854 The second parameter indicates the initial state of exit-event
5856 and normally defaults to 0.
5857 Multiple OpenVPN processes can be simultaneously executed with
5859 the same exit-event parameter. In any case, the controlling
5860 process can signal exit-event, causing all such OpenVPN pro‐
5861 cesses to exit.
5862 When executing an OpenVPN process using the --service directive,
5864 OpenVPN will probably not have a console window to output sta‐
5865 tus/error messages, therefore it is useful to use --log or
5866 --log-append to write these messages to a file.
5867 --show-adapters
5869 (Standalone) Show available TAP-Win32 adapters which can be se‐
5870 lected using the --dev-node option. On non-Windows systems, the
5871 ifconfig(8) command provides similar functionality.
5872 --show-net
5874 (Standalone) Show OpenVPN's view of the system routing table and
5875 network adapter list.
5876 --show-net-up
5878 Output OpenVPN's view of the system routing table and network
5879 adapter list to the syslog or log file after the TUN/TAP adapter
5880 has been brought up and any routes have been added.
5881 --show-valid-subnets
5883 (Standalone) Show valid subnets for --dev tun emulation. Since
5884 the TAP-Win32 driver exports an ethernet interface to Windows,
5885 and since TUN devices are point-to-point in nature, it is neces‐
5886 sary for the TAP-Win32 driver to impose certain constraints on
5887 TUN endpoint address selection.
5888 Namely, the point-to-point endpoints used in TUN device emula‐
5890 tion must be the middle two addresses of a /30 subnet (netmask
5891 255.255.255.252).
5892 --tap-sleep n
5894 Cause OpenVPN to sleep for n seconds immediately after the
5895 TAP-Win32 adapter state is set to "connected".
5896 This option is intended to be used to troubleshoot problems with
5898 the --ifconfig and --ip-win32 options, and is used to give the
5899 TAP-Win32 adapter time to come up before Windows IP Helper API
5900 operations are applied to it.
5901 --win-sys path
5903 Set the Windows system directory pathname to use when looking
5904 for system executables such as route.exe and netsh.exe. By de‐
5905 fault, if this directive is not specified, OpenVPN will use the
5906 SystemRoot environment variable.
5907 This option has changed behaviour since OpenVPN 2.3. Earlier you
5909 had to define --win-sys env to use the SystemRoot environment
5910 variable, otherwise it defaulted to C:\\WINDOWS. It is not
5911 needed to use the env keyword any more, and it will just be ig‐
5912 nored. A warning is logged when this is found in the configura‐
5913 tion file.
5914 --windows-driver drv
5916 Specifies which tun driver to use. Values are ovpn-dco (de‐
5917 fault), tap-windows6 and wintun. ovpn-dco and wintun require
5918 --dev tun. wintun also requires OpenVPN process to run elevated,
5919 or be invoked using the Interactive Service.
5920 Standalone Debug Options
5922 --show-gateway args
5923 (Standalone) Show current IPv4 and IPv6 default gateway and in‐
5924 terface towards the gateway (if the protocol in question is en‐
5925 abled).
5926 Valid syntax:
5928 --show-gateway
5930 --show-gateway IPv6-target
5931 For IPv6 this queries the route towards ::/128, or the specified
5933 IPv6 target address if passed as argument. For IPv4 on Linux,
5934 Windows, MacOS and BSD it looks for a 0.0.0.0/0 route. If there
5935 are more specific routes, the result will not always be matching
5936 the route of the IPv4 packets to the VPN gateway.
5937 Advanced Expert Options
5939 These are options only required when special tweaking is needed, often
5940 used when debugging or testing out special usage scenarios.
5941 --hash-size args
5943 Set the size of the real address hash table to r and the virtual
5944 address table to v.
5945 Valid syntax:
5947 hash-size r v
5949 By default, both tables are sized at 256 buckets.
5951 --bcast-buffers n
5953 Allocate n buffers for broadcast datagrams (default 256).
5954 --persist-local-ip
5956 Preserve initially resolved local IP address and port number
5957 across SIGUSR1 or --ping-restart restarts.
5958 --persist-remote-ip
5960 Preserve most recently authenticated remote IP address and port
5961 number across SIGUSR1 or --ping-restart restarts.
5962 --rcvbuf size
5964 Set the TCP/UDP socket receive buffer size. Defaults to operat‐
5965 ing system default.
5966 --shaper n
5968 Limit bandwidth of outgoing tunnel data to n bytes per second on
5969 the TCP/UDP port. Note that this will only work if mode is set
5970 to p2p. If you want to limit the bandwidth in both directions,
5971 use this option on both peers.
5972 OpenVPN uses the following algorithm to implement traffic shap‐
5974 ing: Given a shaper rate of n bytes per second, after a datagram
5975 write of b bytes is queued on the TCP/UDP port, wait a minimum
5976 of (b / n) seconds before queuing the next write.
5977 It should be noted that OpenVPN supports multiple tunnels be‐
5979 tween the same two peers, allowing you to construct full-speed
5980 and reduced bandwidth tunnels at the same time, routing low-pri‐
5981 ority data such as off-site backups over the reduced bandwidth
5982 tunnel, and other data over the full-speed tunnel.
5983 Also note that for low bandwidth tunnels (under 1000 bytes per
5985 second), you should probably use lower MTU values as well (see
5986 above), otherwise the packet latency will grow so large as to
5987 trigger timeouts in the TLS layer and TCP connections running
5988 over the tunnel.
5989 OpenVPN allows n to be between 100 bytes/sec and 100 Mbytes/sec.
5991 --sndbuf size
5993 Set the TCP/UDP socket send buffer size. Defaults to operating
5994 system default.
5995 --tcp-queue-limit n
5997 Maximum number of output packets queued before TCP (default 64).
5998 When OpenVPN is tunneling data from a TUN/TAP device to a remote
6000 client over a TCP connection, it is possible that the TUN/TAP
6001 device might produce data at a faster rate than the TCP connec‐
6002 tion can support. When the number of output packets queued be‐
6003 fore sending to the TCP socket reaches this limit for a given
6004 client connection, OpenVPN will start to drop outgoing packets
6005 directed at this client.
6006 --txqueuelen n
6008 (Linux only) Set the TX queue length on the TUN/TAP interface.
6009 Currently defaults to operating system default.
6010 --disable-dco
6012 Disables the opportunistic use of data channel offloading if
6013 available. Without this option, OpenVPN will opportunistically
6014 use DCO mode if the config options and the running kernel sup‐
6015 ports using DCO.
6016 Data channel offload currently requires data-ciphers to only
6018 contain AEAD ciphers (AES-GCM and Chacha20-Poly1305) and Linux
6019 with the ovpn-dco module.
6020 Note that some options have no effect or cannot be used when DCO
6022 mode is enabled.
6023 On platforms that do not support DCO disable-dco has no effect.
6025
6027 Options listed in this section have been removed from OpenVPN and are
6028 no longer supported
6029 --client-cert-not-required
6031 Removed in OpenVPN 2.5. This should be replaxed with --ver‐
6032 ify-client-cert none.
6033 --ifconfig-pool-linear
6035 Removed in OpenVPN 2.5. This should be replaced with --topology
6036 p2p.
6037 --key-method
6039 Removed in OpenVPN 2.5. This option should not be used, as us‐
6040 ing the old key-method weakens the VPN tunnel security. The old
6041 key-method was also only needed when the remote side was older
6042 than OpenVPN 2.0.
6043 --management-client-pf
6045 Removed in OpenVPN 2.6. The built-in packet filtering (pf)
6046 functionality has been removed.
6047 --ncp-disable
6049 Removed in OpenVPN 2.6. This option mainly served a role as de‐
6050 bug option when NCP was first introduced. It should no longer
6051 be necessary.
6052 --no-iv
6054 Removed in OpenVPN 2.5. This option should not be used as it
6055 weakens the VPN tunnel security. This has been a NOOP option
6056 since OpenVPN 2.4.
6057 --no-replay
6059 Removed in OpenVPN 2.5. This option should not be used as it
6060 weakens the VPN tunnel security.
6061 --ns-cert-type
6063 Removed in OpenVPN 2.5. The nsCertType field is no longer sup‐
6064 ported in recent SSL/TLS libraries. If your certificates does
6065 not include key usage and extended key usage fields, they must
6066 be upgraded and the --remote-cert-tls option should be used in‐
6067 stead.
6068 --prng Removed in OpenVPN 2.6. We now always use the PRNG of the SSL
6070 library.
6071
6073 Client configuration files may contain multiple remote servers which it
6074 will attempt to connect against. But there are some configuration op‐
6075 tions which are related to specific --remote options. For these use
6076 cases, connection profiles are the solution.
6077 By enacpulating the --remote option and related options within <connec‐
6079 tion> and </connection>, these options are handled as a group.
6080 An OpenVPN client will try each connection profile sequentially until
6082 it achieves a successful connection.
6083 --remote-random can be used to initially "scramble" the connection
6085 list.
6086 Here is an example of connection profile usage:
6088 client
6090 dev tun
6091 <connection>
6093 remote 198.19.34.56 1194 udp
6094 </connection>
6095 <connection>
6097 remote 198.19.34.56 443 tcp
6098 </connection>
6099 <connection>
6101 remote 198.19.34.56 443 tcp
6102 http-proxy 192.168.0.8 8080
6103 </connection>
6104 <connection>
6106 remote 198.19.36.99 443 tcp
6107 http-proxy 192.168.0.8 8080
6108 </connection>
6109 persist-key
6111 persist-tun
6112 pkcs12 client.p12
6113 remote-cert-tls server
6114 verb 3
6115 First we try to connect to a server at 198.19.34.56:1194 using UDP. If
6117 that fails, we then try to connect to 198.19.34.56:443 using TCP. If
6118 that also fails, then try connecting through an HTTP proxy at
6119 192.168.0.8:8080 to 198.19.34.56:443 using TCP. Finally, try to connect
6120 through the same proxy to a server at 198.19.36.99:443 using TCP.
6121 The following OpenVPN options may be used inside of a <connection>
6123 block:
6124 bind, connect-retry, connect-retry-max, connect-timeout, ex‐
6126 plicit-exit-notify, float, fragment, http-proxy, http-proxy-option,
6127 key-direction, link-mtu, local, lport, mssfix, mtu-disc, nobind, port,
6128 proto, remote, rport, socks-proxy, tls-auth, tls-crypt, tun-mtu and,
6129 tun-mtu-extra.
6130 A defaulting mechanism exists for specifying options to apply to all
6132 <connection> profiles. If any of the above options (with the exception
6133 of remote ) appear outside of a <connection> block, but in a configura‐
6134 tion file which has one or more <connection> blocks, the option setting
6135 will be used as a default for <connection> blocks which follow it in
6136 the configuration file.
6137 For example, suppose the nobind option were placed in the sample con‐
6139 figuration file above, near the top of the file, before the first <con‐
6140 nection> block. The effect would be as if nobind were declared in all
6141 <connection> blocks below it.
6142
6144 OpenVPN allows including files in the main configuration for the --ca,
6145 --cert, --dh, --extra-certs, --key, --pkcs12, --secret, --crl-verify,
6146 --http-proxy-user-pass, --tls-auth, --auth-gen-token-secret,
6147 --peer-fingerprint, --tls-crypt, --tls-crypt-v2 and --verify-hash op‐
6148 tions.
6149 Each inline file started by the line <option> and ended by the line
6151 </option>
6152 Here is an example of an inline file usage
6154 <cert>
6156 -----BEGIN CERTIFICATE-----
6157 [...]
6158 -----END CERTIFICATE-----
6159 </cert>
6160 When using the inline file feature with --pkcs12 the inline file has to
6162 be base64 encoded. Encoding of a .p12 file into base64 can be done for
6163 example with OpenSSL by running openssl base64 -in input.p12
6164
6166 SIGHUP Cause OpenVPN to close all TUN/TAP and network connections,
6167 restart, re-read the configuration file (if any), and reopen
6168 TUN/TAP and network connections.
6169 SIGUSR1
6171 Like SIGHUP`, except don't re-read configuration file, and pos‐
6172 sibly don't close and reopen TUN/TAP device, re-read key files,
6173 preserve local IP address/port, or preserve most recently au‐
6174 thenticated remote IP address/port based on --persist-tun,
6175 --persist-key, --persist-local-ip and --persist-remote-ip op‐
6176 tions respectively (see above).
6177 This signal may also be internally generated by a timeout condi‐
6179 tion, governed by the --ping-restart option.
6180 This signal, when combined with --persist-remote-ip, may be sent
6182 when the underlying parameters of the host's network interface
6183 change such as when the host is a DHCP client and is assigned a
6184 new IP address. See --ipchange for more information.
6185 SIGUSR2
6187 Causes OpenVPN to display its current statistics (to the syslog
6188 file if --daemon is used, or stdout otherwise).
6189 SIGINT, SIGTERM
6191 Causes OpenVPN to exit gracefully.
6192
6194 https://community.openvpn.net/openvpn/wiki/FAQ
6195
6197 The manual openvpn-examples(5) gives some examples, especially for
6198 small setups.
6199 For a more comprehensive guide to setting up OpenVPN in a production
6201 setting, see the OpenVPN HOWTO at
6202 https://openvpn.net/community-resources/how-to/
6203
6205 An ongoing effort to document the OpenVPN protocol can be found under
6206 https://github.com/openvpn/openvpn-rfc
6207
6209 OpenVPN's web site is at https://community.openvpn.net/
6210 Go here to download the latest version of OpenVPN, subscribe to the
6212 mailing lists, read the mailing list archives, or browse the Git repos‐
6213 itory.
6214
6216 Report all bugs to the OpenVPN team info@openvpn.net
6217
6219 openvpn-examples(5), dhcpcd(8), ifconfig(8), openssl(1), route(8),
6220 scp(1) ssh(1)
6221
6223 This product includes software developed by the OpenSSL Project (‐
6224 https://www.openssl.org/)
6225 For more information on the TLS protocol, see
6227 http://www.ietf.org/rfc/rfc2246.txt
6228 For more information on the LZO real-time compression library see
6230 https://www.oberhumer.com/opensource/lzo/
6231
6233 Copyright (C) 2002-2020 OpenVPN Inc This program is free software; you
6234 can redistribute it and/or modify it under the terms of the GNU General
6235 Public License version 2 as published by the Free Software Foundation.
6236
6238 James Yonan james@openvpn.net
6239 OPENVPN(8)