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 random. Newer linux
105 kernels and some BSDs implement a getrandom() or getentropy()
106 syscall that removes the need for /dev/urandom to be available.
107 --config file
109 Load additional config options from file where each line corre‐
110 sponds to one command line option, but with the leading '--' re‐
111 moved.
112 If --config file is the only option to the openvpn command, the
114 --config can be removed, and the command can be given as openvpn
115 file
116 Note that configuration files can be nested to a reasonable
118 depth.
119 Double quotation or single quotation characters ("", '') can be
121 used to enclose single parameters containing whitespace, and "#"
122 or ";" characters in the first column can be used to denote com‐
123 ments.
124 Note that OpenVPN 2.0 and higher performs backslash-based shell
126 escaping for characters not in single quotations, so the follow‐
127 ing mappings should be observed:
128 \\ Maps to a single backslash character (\).
130 \" Pass a literal doublequote character ("), don't
131 interpret it as enclosing a parameter.
132 \[SPACE] Pass a literal space or tab character, don't
133 interpret it as a parameter delimiter.
134 For example on Windows, use double backslashes to represent
136 pathnames:
137 secret "c:\\OpenVPN\\secret.key"
139 For examples of configuration files, see
141 https://openvpn.net/community-resources/how-to/
142 Here is an example configuration file:
144 #
146 # Sample OpenVPN configuration file for
147 # using a pre-shared static key.
148 #
149 # '#' or ';' may be used to delimit comments.
150 # Use a dynamic tun device.
152 dev tun
153 # Our remote peer
155 remote mypeer.mydomain
156 # 10.1.0.1 is our local VPN endpoint
158 # 10.1.0.2 is our remote VPN endpoint
159 ifconfig 10.1.0.1 10.1.0.2
160 # Our pre-shared static key
162 secret static.key
163 --daemon progname
165 Become a daemon after all initialization functions are com‐
166 pleted. This option will cause all message and error output to
167 be sent to the syslog file (such as /var/log/messages), except
168 for the output of scripts and ifconfig commands, which will go
169 to /dev/null unless otherwise redirected. The syslog redirection
170 occurs immediately at the point that --daemon is parsed on the
171 command line even though the daemonization point occurs later.
172 If one of the --log options is present, it will supersede syslog
173 redirection.
174 The optional progname parameter will cause OpenVPN to report its
176 program name to the system logger as progname. This can be use‐
177 ful in linking OpenVPN messages in the syslog file with specific
178 tunnels. When unspecified, progname defaults to "openvpn".
179 When OpenVPN is run with the --daemon option, it will try to de‐
181 lay daemonization until the majority of initialization functions
182 which are capable of generating fatal errors are complete. This
183 means that initialization scripts can test the return status of
184 the openvpn command for a fairly reliable indication of whether
185 the command has correctly initialized and entered the packet
186 forwarding event loop.
187 In OpenVPN, the vast majority of errors which occur after ini‐
189 tialization are non-fatal.
190 Note: as soon as OpenVPN has daemonized, it can not ask for
192 usernames, passwords, or key pass phrases anymore. This has cer‐
193 tain consequences, namely that using a password-protected pri‐
194 vate key will fail unless the --askpass option is used to tell
195 OpenVPN to ask for the pass phrase (this requirement is new in
196 v2.3.7, and is a consequence of calling daemon() before initial‐
197 izing the crypto layer).
198 Further, using --daemon together with --auth-user-pass (entered
200 on console) and --auth-nocache will fail as soon as key renego‐
201 tiation (and reauthentication) occurs.
202 --disable-occ
204 Don't output a warning message if option inconsistencies are de‐
205 tected between peers. An example of an option inconsistency
206 would be where one peer uses --dev tun while the other peer uses
207 --dev tap.
208 Use of this option is discouraged, but is provided as a tempo‐
210 rary fix in situations where a recent version of OpenVPN must
211 connect to an old version.
212 --engine engine-name
214 Enable OpenSSL hardware-based crypto engine functionality.
215 If engine-name is specified, use a specific crypto engine. Use
217 the --show-engines standalone option to list the crypto engines
218 which are supported by OpenSSL.
219 --fast-io
221 (Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a
222 call to poll/epoll/select prior to the write operation. The pur‐
223 pose of such a call would normally be to block until the device
224 or socket is ready to accept the write. Such blocking is unnec‐
225 essary on some platforms which don't support write blocking on
226 UDP sockets or TUN/TAP devices. In such cases, one can optimize
227 the event loop by avoiding the poll/epoll/select call, improving
228 CPU efficiency by 5% to 10%.
229 This option can only be used on non-Windows systems, when
231 --proto udp is specified, and when --shaper is NOT specified.
232 --group group
234 Similar to the --user option, this option changes the group ID
235 of the OpenVPN process to group after initialization.
236 --ignore-unknown-option args
238 Valid syntax:
239 ignore-unknown-options opt1 opt2 opt3 ... optN
241 When one of options opt1 ... optN is encountered in the configu‐
243 ration file the configuration file parsing does not fail if this
244 OpenVPN version does not support the option. Multiple --ig‐
245 nore-unknown-option options can be given to support a larger
246 number of options to ignore.
247 This option should be used with caution, as there are good secu‐
249 rity reasons for having OpenVPN fail if it detects problems in a
250 config file. Having said that, there are valid reasons for
251 wanting new software features to gracefully degrade when encoun‐
252 tered by older software versions.
253 --ignore-unknown-option is available since OpenVPN 2.3.3.
255 --iproute cmd
257 Set alternate command to execute instead of default iproute2
258 command. May be used in order to execute OpenVPN in unprivi‐
259 leged environment.
260 --keying-material-exporter args
262 Save Exported Keying Material [RFC5705] of len bytes (must be
263 between 16 and 4095 bytes) using label in environment (ex‐
264 ported_keying_material) for use by plugins in OPEN‐
265 VPN_PLUGIN_TLS_FINAL callback.
266 Valid syntax:
268 keying-material-exporter label len
270 Note that exporter labels have the potential to collide with ex‐
272 isting PRF labels. In order to prevent this, labels MUST begin
273 with EXPORTER.
274 --mlock
276 Disable paging by calling the POSIX mlockall function. Requires
277 that OpenVPN be initially run as root (though OpenVPN can subse‐
278 quently downgrade its UID using the --user option).
279 Using this option ensures that key material and tunnel data are
281 never written to disk due to virtual memory paging operations
282 which occur under most modern operating systems. It ensures that
283 even if an attacker was able to crack the box running OpenVPN,
284 he would not be able to scan the system swap file to recover
285 previously used ephemeral keys, which are used for a period of
286 time governed by the --reneg options (see below), then are dis‐
287 carded.
288 The downside of using --mlock is that it will reduce the amount
290 of physical memory available to other applications.
291 The limit on how much memory can be locked and how that limit is
293 enforced are OS-dependent. On Linux the default limit that an
294 unprivileged process may lock (RLIMIT_MEMLOCK) is low, and if
295 privileges are dropped later, future memory allocations will
296 very likely fail. The limit can be increased using ulimit or
297 systemd directives depending on how OpenVPN is started.
298 --nice n
300 Change process priority after initialization (n greater than 0
301 is lower priority, n less than zero is higher priority).
302 --persist-key
304 Don't re-read key files across SIGUSR1 or --ping-restart.
305 This option can be combined with --user nobody to allow restarts
307 triggered by the SIGUSR1 signal. Normally if you drop root priv‐
308 ileges in OpenVPN, the daemon cannot be restarted since it will
309 now be unable to re-read protected key files.
310 This option solves the problem by persisting keys across SIGUSR1
312 resets, so they don't need to be re-read.
313 --remap-usr1 signal
315 Control whether internally or externally generated SIGUSR1 sig‐
316 nals are remapped to SIGHUP (restart without persisting state)
317 or SIGTERM (exit).
318 signal can be set to SIGHUP or SIGTERM. By default, no remapping
320 occurs.
321 --script-security level
323 This directive offers policy-level control over OpenVPN's usage
324 of external programs and scripts. Lower level values are more
325 restrictive, higher values are more permissive. Settings for
326 level:
327 0 Strictly no calling of external programs.
329 1 (Default) Only call built-in executables such as ifcon‐
331 fig, ip, route, or netsh.
332 2 Allow calling of built-in executables and user-defined
334 scripts.
335 3 Allow passwords to be passed to scripts via environmental
337 variables (potentially unsafe).
338 OpenVPN releases before v2.3 also supported a method flag which
340 indicated how OpenVPN should call external commands and scripts.
341 This could be either execve or system. As of OpenVPN 2.3, this
342 flag is no longer accepted. In most *nix environments the ex‐
343 ecve() approach has been used without any issues.
344 Some directives such as --up allow options to be passed to the
346 external script. In these cases make sure the script name does
347 not contain any spaces or the configuration parser will choke
348 because it can't determine where the script name ends and script
349 options start.
350 To run scripts in Windows in earlier OpenVPN versions you needed
352 to either add a full path to the script interpreter which can
353 parse the script or use the system flag to run these scripts. As
354 of OpenVPN 2.3 it is now a strict requirement to have full path
355 to the script interpreter when running non-executables files.
356 This is not needed for executable files, such as .exe, .com,
357 .bat or .cmd files. For example, if you have a Visual Basic
358 script, you must use this syntax now:
359 --up 'C:\\Windows\\System32\\wscript.exe C:\\Program\ Files\\OpenVPN\\config\\my-up-script.vbs'
361 Please note the single quote marks and the escaping of the back‐
363 slashes (\) and the space character.
364 The reason the support for the system flag was removed is due to
366 the security implications with shell expansions when executing
367 scripts via the system() call.
368 --setcon context
370 Apply SELinux context after initialization. This essentially
371 provides the ability to restrict OpenVPN's rights to only net‐
372 work I/O operations, thanks to SELinux. This goes further than
373 --user and --chroot in that those two, while being great secu‐
374 rity features, unfortunately do not protect against privilege
375 escalation by exploitation of a vulnerable system call. You can
376 of course combine all three, but please note that since setcon
377 requires access to /proc you will have to provide it inside the
378 chroot directory (e.g. with mount --bind).
379 Since the setcon operation is delayed until after initializa‐
381 tion, OpenVPN can be restricted to just network-related system
382 calls, whereas by applying the context before startup (such as
383 the OpenVPN one provided in the SELinux Reference Policies) you
384 will have to allow many things required only during initializa‐
385 tion.
386 Like with chroot, complications can result when scripts or
388 restarts are executed after the setcon operation, which is why
389 you should really consider using the --persist-key and --per‐
390 sist-tun options.
391 --status args
393 Write operational status to file every n seconds.
394 Valid syntaxes:
396 status file
398 status file n
399 Status can also be written to the syslog by sending a SIGUSR2
401 signal.
402 With multi-client capability enabled on a server, the status
404 file includes a list of clients and a routing table. The output
405 format can be controlled by the --status-version option in that
406 case.
407 For clients or instances running in point-to-point mode, it will
409 contain the traffic statistics.
410 --status-version n
412 Set the status file format version number to n.
413 This only affects the status file on servers with multi-client
415 capability enabled. Valid status version values:
416 1 Traditional format (default). The client list contains
418 the following fields comma-separated: Common Name, Real
419 Address, Bytes Received, Bytes Sent, Connected Since.
420 2 A more reliable format for external processing. Compared
422 to version 1, the client list contains some additional
423 fields: Virtual Address, Virtual IPv6 Address, Username,
424 Client ID, Peer ID, Data Channel Cipher. Future versions
425 may extend the number of fields.
426 3 Identical to 2, but fields are tab-separated.
428 --test-crypto
430 Do a self-test of OpenVPN's crypto options by encrypting and de‐
431 crypting test packets using the data channel encryption options
432 specified above. This option does not require a peer to func‐
433 tion, and therefore can be specified without --dev or --remote.
434 The typical usage of --test-crypto would be something like this:
436 openvpn --test-crypto --secret key
438 or
440 openvpn --test-crypto --secret key --verb 9
442 This option is very useful to test OpenVPN after it has been
444 ported to a new platform, or to isolate problems in the com‐
445 piler, OpenSSL crypto library, or OpenVPN's crypto code. Since
446 it is a self-test mode, problems with encryption and authentica‐
447 tion can be debugged independently of network and tunnel issues.
448 --tmp-dir dir
450 Specify a directory dir for temporary files. This directory will
451 be used by openvpn processes and script to communicate temporary
452 data with openvpn main process. Note that the directory must be
453 writable by the OpenVPN process after it has dropped it's root
454 privileges.
455 This directory will be used by in the following cases:
457 • --client-connect scripts and OPENVPN_PLUGIN_CLIENT_CONNECT
459 plug-in hook to dynamically generate client-specific configu‐
460 ration client_connect_config_file and return success/failure
461 via client_connect_deferred_file when using deferred client
462 connect method
463 • OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY plug-in hooks returns
465 success/failure via auth_control_file when using deferred auth
466 method
467 • OPENVPN_PLUGIN_ENABLE_PF plugin hook to pass filtering rules
469 via pf_file
470 --use-prediction-resistance
472 Enable prediction resistance on mbed TLS's RNG.
473 Enabling prediction resistance causes the RNG to reseed in each
475 call for random. Reseeding this often can quickly deplete the
476 kernel entropy pool.
477 If you need this option, please consider running a daemon that
479 adds entropy to the kernel pool.
480 --user user
482 Change the user ID of the OpenVPN process to user after initial‐
483 ization, dropping privileges in the process. This option is use‐
484 ful to protect the system in the event that some hostile party
485 was able to gain control of an OpenVPN session. Though OpenVPN's
486 security features make this unlikely, it is provided as a second
487 line of defense.
488 By setting user to nobody or somebody similarly unprivileged,
490 the hostile party would be limited in what damage they could
491 cause. Of course once you take away privileges, you cannot re‐
492 turn them to an OpenVPN session. This means, for example, that
493 if you want to reset an OpenVPN daemon with a SIGUSR1 signal
494 (for example in response to a DHCP reset), you should make use
495 of one or more of the --persist options to ensure that OpenVPN
496 doesn't need to execute any privileged operations in order to
497 restart (such as re-reading key files or running ifconfig on the
498 TUN device).
499 --writepid file
501 Write OpenVPN's main process ID to file.
502 Log options
504 --echo parms
505 Echo parms to log output.
506 Designed to be used to send messages to a controlling applica‐
508 tion which is receiving the OpenVPN log output.
509 --errors-to-stderr
511 Output errors to stderr instead of stdout unless log output is
512 redirected by one of the --log options.
513 --log file
515 Output logging messages to file, including output to std‐
516 out/stderr which is generated by called scripts. If file already
517 exists it will be truncated. This option takes effect immedi‐
518 ately when it is parsed in the command line and will supersede
519 syslog output if --daemon or --inetd is also specified. This op‐
520 tion is persistent over the entire course of an OpenVPN instan‐
521 tiation and will not be reset by SIGHUP, SIGUSR1, or
522 --ping-restart.
523 Note that on Windows, when OpenVPN is started as a service, log‐
525 ging occurs by default without the need to specify this option.
526 --log-append file
528 Append logging messages to file. If file does not exist, it
529 will be created. This option behaves exactly like --log except
530 that it appends to rather than truncating the log file.
531 --machine-readable-output
533 Always write timestamps and message flags to log messages, even
534 when they otherwise would not be prefixed. In particular, this
535 applies to log messages sent to stdout.
536 --mute n
538 Log at most n consecutive messages in the same category. This is
539 useful to limit repetitive logging of similar message types.
540 --mute-replay-warnings
542 Silence the output of replay warnings, which are a common false
543 alarm on WiFi networks. This option preserves the security of
544 the replay protection code without the verbosity associated with
545 warnings about duplicate packets.
546 --suppress-timestamps
548 Avoid writing timestamps to log messages, even when they other‐
549 wise would be prepended. In particular, this applies to log mes‐
550 sages sent to stdout.
551 --syslog progname
553 Direct log output to system logger, but do not become a daemon.
554 See --daemon directive above for description of progname parame‐
555 ter.
556 --verb n
558 Set output verbosity to n (default 1). Each level shows all info
559 from the previous levels. Level 3 is recommended if you want a
560 good summary of what's happening without being swamped by out‐
561 put.
562 0 No output except fatal errors.
564 1 to 4 Normal usage range.
566 5 Outputs R and W characters to the console for each packet
568 read and write, uppercase is used for TCP/UDP packets and
569 lowercase is used for TUN/TAP packets.
570 6 to 11
572 Debug info range (see errlevel.h in the source code for
573 additional information on debug levels).
574 Protocol options
576 Options in this section affect features available in the OpenVPN wire
577 protocol. Many of these options also define the encryption options of
578 the data channel in the OpenVPN wire protocol. These options must be
579 configured in a compatible way between both the local and remote side.
580 --allow-compression mode
582 As described in the --compress option, compression is a poten‐
583 tially dangerous option. This option allows controlling the be‐
584 haviour of OpenVPN when compression is used and allowed.
585 Valid syntaxes:
587 allow-compression
589 allow-compression mode
590 The mode argument can be one of the following values:
592 asym (default)
594 OpenVPN will only decompress downlink packets but not
595 compress uplink packets. This also allows migrating to
596 disable compression when changing both server and client
597 configurations to remove compression at the same time is
598 not a feasible option.
599 no OpenVPN will refuse any non-stub compression.
601 yes OpenVPN will send and receive compressed packets.
603 --auth alg
605 Authenticate data channel packets and (if enabled) tls-auth con‐
606 trol channel packets with HMAC using message digest algorithm
607 alg. (The default is SHA1 ). HMAC is a commonly used message au‐
608 thentication algorithm (MAC) that uses a data string, a secure
609 hash algorithm and a key to produce a digital signature.
610 The OpenVPN data channel protocol uses encrypt-then-mac (i.e.
612 first encrypt a packet then HMAC the resulting ciphertext),
613 which prevents padding oracle attacks.
614 If an AEAD cipher mode (e.g. GCM) is chosen then the specified
616 --auth algorithm is ignored for the data channel and the authen‐
617 tication method of the AEAD cipher is used instead. Note that
618 alg still specifies the digest used for tls-auth.
619 In static-key encryption mode, the HMAC key is included in the
621 key file generated by --genkey. In TLS mode, the HMAC key is dy‐
622 namically generated and shared between peers via the TLS control
623 channel. If OpenVPN receives a packet with a bad HMAC it will
624 drop the packet. HMAC usually adds 16 or 20 bytes per packet.
625 Set alg=none to disable authentication.
626 For more information on HMAC see
628 http://www.cs.ucsd.edu/users/mihir/papers/hmac.html
629 --cipher alg
631 This option is deprecated for server-client mode. --data-ciphers
632 or possibly --data-ciphers-fallback` should be used instead.
633 Encrypt data channel packets with cipher algorithm alg.
635 The default is BF-CBC, an abbreviation for Blowfish in Cipher
637 Block Chaining mode. When cipher negotiation (NCP) is allowed,
638 OpenVPN 2.4 and newer on both client and server side will auto‐
639 matically upgrade to AES-256-GCM. See --data-ciphers and
640 --ncp-disable for more details on NCP.
641 Using BF-CBC is no longer recommended, because of its 64-bit
643 block size. This small block size allows attacks based on colli‐
644 sions, as demonstrated by SWEET32. See
645 https://community.openvpn.net/openvpn/wiki/SWEET32 for details.
646 Due to this, support for BF-CBC, DES, CAST5, IDEA and RC2 ci‐
647 phers will be removed in OpenVPN 2.6.
648 To see other ciphers that are available with OpenVPN, use the
650 --show-ciphers option.
651 Set alg to none to disable encryption.
653 --compress algorithm
655 DEPRECATED Enable a compression algorithm. Compression is gen‐
656 erally not recommended. VPN tunnels which use compression are
657 susceptible to the VORALCE attack vector.
658 The algorithm parameter may be lzo, lz4, lz4-v2, stub, stub-v2
660 or empty. LZO and LZ4 are different compression algorithms,
661 with LZ4 generally offering the best performance with least CPU
662 usage.
663 The lz4-v2 and stub-v2 variants implement a better framing that
665 does not add overhead when packets cannot be compressed. All
666 other variants always add one extra framing byte compared to no
667 compression framing.
668 If the algorithm parameter is stub, stub-v2 or empty, compres‐
670 sion will be turned off, but the packet framing for compression
671 will still be enabled, allowing a different setting to be pushed
672 later. Additionally, stub and stub-v2 wil disable announcing
673 lzo and lz4 compression support via IV_ variables to the server.
674 Note: the stub (or empty) option is NOT compatible with the
676 older option --comp-lzo no.
677 *Security Considerations*
679 Compression and encryption is a tricky combination. If an at‐
681 tacker knows or is able to control (parts of) the plain-text of
682 packets that contain secrets, the attacker might be able to ex‐
683 tract the secret if compression is enabled. See e.g. the CRIME
684 and BREACH attacks on TLS and VORACLE on VPNs which also lever‐
685 age to break encryption. If you are not entirely sure that the
686 above does not apply to your traffic, you are advised to not en‐
687 able compression.
688 --comp-lzo mode
690 DEPRECATED Enable LZO compression algorithm. Compression is
691 generally not recommended. VPN tunnels which uses compression
692 are suspectible to the VORALCE attack vector.
693 Use LZO compression -- may add up to 1 byte per packet for in‐
695 compressible data. mode may be yes, no, or adaptive (default).
696 In a server mode setup, it is possible to selectively turn com‐
698 pression on or off for individual clients.
699 First, make sure the client-side config file enables selective
701 compression by having at least one --comp-lzo directive, such as
702 --comp-lzo no. This will turn off compression by default, but
703 allow a future directive push from the server to dynamically
704 change the on/off/adaptive setting.
705 Next in a --client-config-dir file, specify the compression set‐
707 ting for the client, for example:
708 comp-lzo yes
710 push "comp-lzo yes"
711 The first line sets the comp-lzo setting for the server side of
713 the link, the second sets the client side.
714 --comp-noadapt
716 DEPRECATED When used in conjunction with --comp-lzo, this option
717 will disable OpenVPN's adaptive compression algorithm. Normally,
718 adaptive compression is enabled with --comp-lzo.
719 Adaptive compression tries to optimize the case where you have
721 compression enabled, but you are sending predominantly incom‐
722 pressible (or pre-compressed) packets over the tunnel, such as
723 an FTP or rsync transfer of a large, compressed file. With adap‐
724 tive compression, OpenVPN will periodically sample the compres‐
725 sion process to measure its efficiency. If the data being sent
726 over the tunnel is already compressed, the compression effi‐
727 ciency will be very low, triggering openvpn to disable compres‐
728 sion for a period of time until the next re-sample test.
729 --key-direction
731 Alternative way of specifying the optional direction parameter
732 for the --tls-auth and --secret options. Useful when using in‐
733 line files (See section on inline files).
734 --keysize n
736 DEPRECATED This option will be removed in OpenVPN 2.6.
737 Size of cipher key in bits (optional). If unspecified, defaults
739 to cipher-specific default. The --show-ciphers option (see be‐
740 low) shows all available OpenSSL ciphers, their default key
741 sizes, and whether the key size can be changed. Use care in
742 changing a cipher's default key size. Many ciphers have not been
743 extensively cryptanalyzed with non-standard key lengths, and a
744 larger key may offer no real guarantee of greater security, or
745 may even reduce security.
746 --data-ciphers cipher-list
748 Restrict the allowed ciphers to be negotiated to the ciphers in
749 cipher-list. cipher-list is a colon-separated list of ciphers,
750 and defaults to AES-256-GCM:AES-128-GCM.
751 For servers, the first cipher from cipher-list that is also sup‐
753 ported by the client will be pushed to clients that support ci‐
754 pher negotiation.
755 Cipher negotiation is enabled in client-server mode only. I.e.
757 if --mode is set to 'server' (server-side, implied by setting
758 --server ), or if --pull is specified (client-side, implied by
759 setting --client).
760 If no common cipher is found during cipher negotiation, the con‐
762 nection is terminated. To support old clients/old servers that
763 do not provide any cipher negotiation support see --data-ci‐
764 phers-fallback.
765 Additionally, to allow for more smooth transition, if NCP is en‐
767 abled, OpenVPN will inherit the cipher of the peer if that ci‐
768 pher is different from the local --cipher setting, but the peer
769 cipher is one of the ciphers specified in --data-ciphers. E.g. a
770 non-NCP client (<=v2.3, or with --ncp-disabled set) connecting
771 to a NCP server (v2.4+) with --cipher BF-CBC and --data-ciphers
772 AES-256-GCM:AES-256-CBC set can either specify --cipher BF-CBC
773 or --cipher AES-256-CBC and both will work.
774 Note for using NCP with an OpenVPN 2.4 peer: This list must in‐
776 clude the AES-256-GCM and AES-128-GCM ciphers.
777 This list is restricted to be 127 chars long after conversion to
779 OpenVPN ciphers.
780 This option was called --ncp-ciphers in OpenVPN 2.4 but has been
782 renamed to --data-ciphers in OpenVPN 2.5 to more accurately re‐
783 flect its meaning.
784 --data-ciphers-fallback alg
786 Configure a cipher that is used to fall back to if we could not
787 determine which cipher the peer is willing to use.
788 This option should only be needed to connect to peers that are
790 running OpenVPN 2.3 and older version, and have been configured
791 with --enable-small (typically used on routers or other embedded
792 devices).
793 --ncp-disable
795 DEPRECATED Disable "Negotiable Crypto Parameters". This com‐
796 pletely disables cipher negotiation.
797 --secret args
799 Enable Static Key encryption mode (non-TLS). Use pre-shared se‐
800 cret file which was generated with --genkey.
801 Valid syntaxes:
803 secret file
805 secret file direction
806 The optional direction parameter enables the use of 4 distinct
808 keys (HMAC-send, cipher-encrypt, HMAC-receive, cipher-decrypt),
809 so that each data flow direction has a different set of HMAC and
810 cipher keys. This has a number of desirable security properties
811 including eliminating certain kinds of DoS and message replay
812 attacks.
813 When the direction parameter is omitted, 2 keys are used bidi‐
815 rectionally, one for HMAC and the other for encryption/decryp‐
816 tion.
817 The direction parameter should always be complementary on either
819 side of the connection, i.e. one side should use 0 and the other
820 should use 1, or both sides should omit it altogether.
821 The direction parameter requires that file contains a 2048 bit
823 key. While pre-1.5 versions of OpenVPN generate 1024 bit key
824 files, any version of OpenVPN which supports the direction pa‐
825 rameter, will also support 2048 bit key file generation using
826 the --genkey option.
827 Static key encryption mode has certain advantages, the primary
829 being ease of configuration.
830 There are no certificates or certificate authorities or compli‐
832 cated negotiation handshakes and protocols. The only requirement
833 is that you have a pre-existing secure channel with your peer
834 (such as ssh) to initially copy the key. This requirement, along
835 with the fact that your key never changes unless you manually
836 generate a new one, makes it somewhat less secure than TLS mode
837 (see below). If an attacker manages to steal your key, every‐
838 thing that was ever encrypted with it is compromised. Contrast
839 that to the perfect forward secrecy features of TLS mode (using
840 Diffie Hellman key exchange), where even if an attacker was able
841 to steal your private key, he would gain no information to help
842 him decrypt past sessions.
843 Another advantageous aspect of Static Key encryption mode is
845 that it is a handshake-free protocol without any distinguishing
846 signature or feature (such as a header or protocol handshake se‐
847 quence) that would mark the ciphertext packets as being gener‐
848 ated by OpenVPN. Anyone eavesdropping on the wire would see
849 nothing but random-looking data.
850 --tran-window n
852 Transition window -- our old key can live this many seconds af‐
853 ter a new a key renegotiation begins (default 3600 seconds).
854 This feature allows for a graceful transition from old to new
855 key, and removes the key renegotiation sequence from the criti‐
856 cal path of tunnel data forwarding.
857 Client Options
859 The client options are used when connecting to an OpenVPN server con‐
860 figured to use --server, --server-bridge, or --mode server in its con‐
861 figuration.
862 --allow-pull-fqdn
864 Allow client to pull DNS names from server (rather than being
865 limited to IP address) for --ifconfig, --route, and
866 --route-gateway.
867 --allow-recursive-routing
869 When this option is set, OpenVPN will not drop incoming tun
870 packets with same destination as host.
871 --auth-token token
873 This is not an option to be used directly in any configuration
874 files, but rather push this option from a --client-connect
875 script or a --plugin which hooks into the OPEN‐
876 VPN_PLUGIN_CLIENT_CONNECT or OPENVPN_PLUGIN_CLIENT_CONNECT_V2
877 calls. This option provides a possibility to replace the clients
878 password with an authentication token during the lifetime of the
879 OpenVPN client.
880 Whenever the connection is renegotiated and the
882 --auth-user-pass-verify script or --plugin making use of the
883 OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY hook is triggered, it will
884 pass over this token as the password instead of the password the
885 user provided. The authentication token can only be reset by a
886 full reconnect where the server can push new options to the
887 client. The password the user entered is never preserved once an
888 authentication token has been set. If the OpenVPN server side
889 rejects the authentication token then the client will receive an
890 AUTH_FAILED and disconnect.
891 The purpose of this is to enable two factor authentication meth‐
893 ods, such as HOTP or TOTP, to be used without needing to re‐
894 trieve a new OTP code each time the connection is renegotiated.
895 Another use case is to cache authentication data on the client
896 without needing to have the users password cached in memory dur‐
897 ing the life time of the session.
898 To make use of this feature, the --client-connect script or
900 --plugin needs to put
901 push "auth-token UNIQUE_TOKEN_VALUE"
903 into the file/buffer for dynamic configuration data. This will
905 then make the OpenVPN server to push this value to the client,
906 which replaces the local password with the UNIQUE_TOKEN_VALUE.
907 Newer clients (2.4.7+) will fall back to the original password
909 method after a failed auth. Older clients will keep using the
910 token value and react according to --auth-retry
911 --auth-user-pass
913 Authenticate with server using username/password.
914 Valid syntaxes:
916 auth-user-pass
918 auth-user-pass up
919 If up is present, it must be a file containing username/password
921 on 2 lines. If the password line is missing, OpenVPN will prompt
922 for one.
923 If up is omitted, username/password will be prompted from the
925 console.
926 The server configuration must specify an --auth-user-pass-verify
928 script to verify the username/password provided by the client.
929 --auth-retry type
931 Controls how OpenVPN responds to username/password verification
932 errors such as the client-side response to an AUTH_FAILED mes‐
933 sage from the server or verification failure of the private key
934 password.
935 Normally used to prevent auth errors from being fatal on the
937 client side, and to permit username/password requeries in case
938 of error.
939 An AUTH_FAILED message is generated by the server if the client
941 fails --auth-user-pass authentication, or if the server-side
942 --client-connect script returns an error status when the client
943 tries to connect.
944 type can be one of:
946 none Client will exit with a fatal error (this is the de‐
948 fault).
949 nointeract
951 Client will retry the connection without requerying for
952 an --auth-user-pass username/password. Use this option
953 for unattended clients.
954 interact
956 Client will requery for an --auth-user-pass user‐
957 name/password and/or private key password before attempt‐
958 ing a reconnection.
959 Note that while this option cannot be pushed, it can be con‐
961 trolled from the management interface.
962 --client
964 A helper directive designed to simplify the configuration of
965 OpenVPN's client mode. This directive is equivalent to:
966 pull
968 tls-client
969 --client-nat args
971 This pushable client option sets up a stateless one-to-one NAT
972 rule on packet addresses (not ports), and is useful in cases
973 where routes or ifconfig settings pushed to the client would
974 create an IP numbering conflict.
975 Examples:
977 client-nat snat 192.168.0.0/255.255.0.0
979 client-nat dnat 10.64.0.0/255.255.0.0
980 network/netmask (for example 192.168.0.0/255.255.0.0) defines
982 the local view of a resource from the client perspective, while
983 alias/netmask (for example 10.64.0.0/255.255.0.0) defines the
984 remote view from the server perspective.
985 Use snat (source NAT) for resources owned by the client and dnat
987 (destination NAT) for remote resources.
988 Set --verb 6 for debugging info showing the transformation of
990 src/dest addresses in packets.
991 --connect-retry n
993 Wait n seconds between connection attempts (default 5). Re‐
994 peated reconnection attempts are slowed down after 5 retries per
995 remote by doubling the wait time after each unsuccessful at‐
996 tempt. An optional argument max specifies the maximum value of
997 wait time in seconds at which it gets capped (default 300).
998 --connect-retry-max n
1000 n specifies the number of times each --remote or <connection>
1001 entry is tried. Specifying n as 1 would try each entry exactly
1002 once. A successful connection resets the counter. (default un‐
1003 limited).
1004 --connect-timeout n
1006 See --server-poll-timeout.
1007 --explicit-exit-notify n
1009 In UDP client mode or point-to-point mode, send server/peer an
1010 exit notification if tunnel is restarted or OpenVPN process is
1011 exited. In client mode, on exit/restart, this option will tell
1012 the server to immediately close its client instance object
1013 rather than waiting for a timeout.
1014 The n parameter (default 1 if not present) controls the maximum
1016 number of attempts that the client will try to resend the exit
1017 notification message.
1018 In UDP server mode, send RESTART control channel command to con‐
1020 nected clients. The n parameter (default 1 if not present) con‐
1021 trols client behavior. With n = 1 client will attempt to recon‐
1022 nect to the same server, with n = 2 client will advance to the
1023 next server.
1024 OpenVPN will not send any exit notifications unless this option
1026 is enabled.
1027 --inactive args
1029 Causes OpenVPN to exit after n seconds of inactivity on the
1030 TUN/TAP device. The time length of inactivity is measured since
1031 the last incoming or outgoing tunnel packet. The default value
1032 is 0 seconds, which disables this feature.
1033 Valid syntaxes:
1035 inactive n
1037 inactive n bytes
1038 If the optional bytes parameter is included, exit if less than
1040 bytes of combined in/out traffic are produced on the tun/tap de‐
1041 vice in n seconds.
1042 In any case, OpenVPN's internal ping packets (which are just
1044 keepalives) and TLS control packets are not considered "activ‐
1045 ity", nor are they counted as traffic, as they are used inter‐
1046 nally by OpenVPN and are not an indication of actual user activ‐
1047 ity.
1048 --proto-force p
1050 When iterating through connection profiles, only consider pro‐
1051 files using protocol p (tcp | udp).
1052 --pull This option must be used on a client which is connecting to a
1054 multi-client server. It indicates to OpenVPN that it should ac‐
1055 cept options pushed by the server, provided they are part of the
1056 legal set of pushable options (note that the --pull option is
1057 implied by --client ).
1058 In particular, --pull allows the server to push routes to the
1060 client, so you should not use --pull or --client in situations
1061 where you don't trust the server to have control over the
1062 client's routing table.
1063 --pull-filter args
1065 Filter options on the client pushed by the server to the client.
1066 Valid syntaxes:
1068 pull-filter accept text
1070 pull-filter ignore text
1071 pull-filter reject text
1072 Filter options received from the server if the option starts
1074 with text. The action flag accept allows the option, ignore re‐
1075 moves it and reject flags an error and triggers a SIGUSR1
1076 restart. The filters may be specified multiple times, and each
1077 filter is applied in the order it is specified. The filtering of
1078 each option stops as soon as a match is found. Unmatched options
1079 are accepted by default.
1080 Prefix comparison is used to match text against the received op‐
1082 tion so that
1083 pull-filter ignore "route"
1085 would remove all pushed options starting with route which would
1087 include, for example, route-gateway. Enclose text in quotes to
1088 embed spaces.
1089 pull-filter accept "route 192.168.1."
1091 pull-filter ignore "route "
1092 would remove all routes that do not start with 192.168.1.
1094 Note that reject may result in a repeated cycle of failure and
1096 reconnect, unless multiple remotes are specified and connection
1097 to the next remote succeeds. To silently ignore an option pushed
1098 by the server, use ignore.
1099 --remote args
1101 Remote host name or IP address, port and protocol.
1102 Valid syntaxes:
1104 remote host
1106 remote host port
1107 remote host port proto
1108 The port and proto arguments are optional. The OpenVPN client
1110 will try to connect to a server at host:port. The proto argu‐
1111 ment indicates the protocol to use when connecting with the re‐
1112 mote, and may be tcp or udp. To enforce IPv4 or IPv6 connec‐
1113 tions add a 4 or 6 suffix; like udp4 / udp6 / tcp4 / tcp6.
1114 On the client, multiple --remote options may be specified for
1116 redundancy, each referring to a different OpenVPN server, in the
1117 order specified by the list of --remote options. Specifying mul‐
1118 tiple --remote options for this purpose is a special case of the
1119 more general connection-profile feature. See the <connection>
1120 documentation below.
1121 The client will move on to the next host in the list, in the
1123 event of connection failure. Note that at any given time, the
1124 OpenVPN client will at most be connected to one server.
1125 Examples:
1127 remote server1.example.net
1129 remote server1.example.net 1194
1130 remote server2.example.net 1194 tcp
1131 Note: Since UDP is connectionless, connection failure is de‐
1133 fined by the --ping and --ping-restart options.
1134 Also, if you use multiple --remote options, AND you are
1136 dropping root privileges on the client with --user and/or
1137 --group AND the client is running a non-Windows OS, if
1138 the client needs to switch to a different server, and
1139 that server pushes back different TUN/TAP or route set‐
1140 tings, the client may lack the necessary privileges to
1141 close and reopen the TUN/TAP interface. This could cause
1142 the client to exit with a fatal error.
1143 If --remote is unspecified, OpenVPN will listen for packets from
1145 any IP address, but will not act on those packets unless they
1146 pass all authentication tests. This requirement for authentica‐
1147 tion is binding on all potential peers, even those from known
1148 and supposedly trusted IP addresses (it is very easy to forge a
1149 source IP address on a UDP packet).
1150 When used in TCP mode, --remote will act as a filter, rejecting
1152 connections from any host which does not match host.
1153 If host is a DNS name which resolves to multiple IP addresses,
1155 OpenVPN will try them in the order that the system getaddrinfo()
1156 presents them, so priorization and DNS randomization is done by
1157 the system library. Unless an IP version is forced by the proto‐
1158 col specification (4/6 suffix), OpenVPN will try both IPv4 and
1159 IPv6 addresses, in the order getaddrinfo() returns them.
1160 --remote-random
1162 When multiple --remote address/ports are specified, or if con‐
1163 nection profiles are being used, initially randomize the order
1164 of the list as a kind of basic load-balancing measure.
1165 --remote-random-hostname
1167 Prepend a random string (6 bytes, 12 hex characters) to hostname
1168 to prevent DNS caching. For example, "foo.bar.gov" would be mod‐
1169 ified to "<random-chars>.foo.bar.gov".
1170 --resolv-retry n
1172 If hostname resolve fails for --remote, retry resolve for n sec‐
1173 onds before failing.
1174 Set n to "infinite" to retry indefinitely.
1176 By default, --resolv-retry infinite is enabled. You can disable
1178 by setting n=0.
1179 --single-session
1181 After initially connecting to a remote peer, disallow any new
1182 connections. Using this option means that a remote peer cannot
1183 connect, disconnect, and then reconnect.
1184 If the daemon is reset by a signal or --ping-restart, it will
1186 allow one new connection.
1187 --single-session can be used with --ping-exit or --inactive to
1189 create a single dynamic session that will exit when finished.
1190 --server-poll-timeout n
1192 When connecting to a remote server do not wait for more than n
1193 seconds for a response before trying the next server. The de‐
1194 fault value is 120s. This timeout includes proxy and TCP connect
1195 timeouts.
1196 --static-challenge args
1198 Enable static challenge/response protocol
1199 Valid syntax:
1201 static-challenge text echo
1203 The text challenge text is presented to the user which describes
1205 what information is requested. The echo flag indicates if the
1206 user's input should be echoed on the screen. Valid echo values
1207 are 0 or 1.
1208 See management-notes.txt in the OpenVPN distribution for a de‐
1210 scription of the OpenVPN challenge/response protocol.
1211 --show-proxy-settings
1213 Show sensed HTTP or SOCKS proxy settings. Currently, only Win‐
1214 dows clients support this option.
1215 --http-proxy args
1217 Connect to remote host through an HTTP proxy. This requires at
1218 least an address server and port argument. If HTTP Proxy-Au‐
1219 thenticate is required, a file name to an authfile file contain‐
1220 ing a username and password on 2 lines can be given, or stdin to
1221 prompt from console. Its content can also be specified in the
1222 config file with the --http-proxy-user-pass option. (See section
1223 on inline files)
1224 The last optional argument is an auth-method which should be one
1226 of none, basic, or ntlm.
1227 HTTP Digest authentication is supported as well, but only via
1229 the auto or auto-nct flags (below). This must replace the auth‐
1230 file argument.
1231 The auto flag causes OpenVPN to automatically determine the
1233 auth-method and query stdin or the management interface for
1234 username/password credentials, if required. This flag exists on
1235 OpenVPN 2.1 or higher.
1236 The auto-nct flag (no clear-text auth) instructs OpenVPN to au‐
1238 tomatically determine the authentication method, but to reject
1239 weak authentication protocols such as HTTP Basic Authentication.
1240 Examples:
1242 http-proxy proxy.example.net 3128
1244 http-proxy proxy.example.net 3128 authfile.txt
1245 http-proxy proxy.example.net 3128 stdin
1246 http-proxy proxy.example.net 3128 auto basic
1247 http-proxy proxy.example.net 3128 auto-nct ntlm
1248 --http-proxy-option args
1250 Set extended HTTP proxy options. Requires an option type as ar‐
1251 gument and an optional parameter to the type. Repeat to set
1252 multiple options.
1253 VERSION version
1255 Set HTTP version number to version (default 1.0).
1256 AGENT user-agent
1258 Set HTTP "User-Agent" string to user-agent.
1259 CUSTOM-HEADER name content
1261 Adds the custom Header with name as name and content as
1262 the content of the custom HTTP header.
1263 Examples:
1265 http-proxy-option VERSION 1.1
1267 http-proxy-option AGENT OpenVPN/2.4
1268 http-proxy-option X-Proxy-Flag some-flags
1269 --socks-proxy args
1271 Connect to remote host through a Socks5 proxy. A required
1272 server argument is needed. Optionally a port (default 1080) and
1273 authfile can be given. The authfile is a file containing a
1274 username and password on 2 lines, or stdin can be used to prompt
1275 from console.
1276 Server Options
1278 Starting with OpenVPN 2.0, a multi-client TCP/UDP server mode is sup‐
1279 ported, and can be enabled with the --mode server option. In server
1280 mode, OpenVPN will listen on a single port for incoming client connec‐
1281 tions. All client connections will be routed through a single tun or
1282 tap interface. This mode is designed for scalability and should be able
1283 to support hundreds or even thousands of clients on sufficiently fast
1284 hardware. SSL/TLS authentication must be used in this mode.
1285 --auth-gen-token args
1287 Returns an authentication token to successfully authenticated
1288 clients.
1289 Valid syntax:
1291 auth-gen-token [lifetime] [external-auth]
1293 After successful user/password authentication, the OpenVPN
1295 server will with this option generate a temporary authentication
1296 token and push that to the client. On the following renegotia‐
1297 tions, the OpenVPN client will pass this token instead of the
1298 users password. On the server side the server will do the token
1299 authentication internally and it will NOT do any additional au‐
1300 thentications against configured external user/password authen‐
1301 tication mechanisms.
1302 The tokens implemented by this mechanism include an initial
1304 timestamp and a renew timestamp and are secured by HMAC.
1305 The lifetime argument defines how long the generated token is
1307 valid. The lifetime is defined in seconds. If lifetime is not
1308 set or it is set to 0, the token will never expire.
1309 The token will expire either after the configured lifetime of
1311 the token is reached or after not being renewed for more than 2
1312 * reneg-sec seconds. Clients will be sent renewed tokens on ev‐
1313 ery TLS renogiation to keep the client's token updated. This is
1314 done to invalidate a token if a client is disconnected for a
1315 sufficently long time, while at the same time permitting much
1316 longer token lifetimes for active clients.
1317 This feature is useful for environments which are configured to
1319 use One Time Passwords (OTP) as part of the user/password au‐
1320 thentications and that authentication mechanism does not imple‐
1321 ment any auth-token support.
1322 When the external-auth keyword is present the normal authentica‐
1324 tion method will always be called even if auth-token succeeds.
1325 Normally other authentications method are skipped if auth-token
1326 verification suceeds or fails.
1327 This option postpones this decision to the external authentica‐
1329 tion methods and checks the validity of the account and do other
1330 checks.
1331 In this mode the environment will have a session_id variable
1333 that holds the session id from auth-gen-token. Also an environ‐
1334 ment variable session_state is present. This variable indicates
1335 whether the auth-token has succeeded or not. It can have the
1336 following values:
1337 Initial
1339 No token from client.
1340 Authenticated
1342 Token is valid and not expired.
1343 Expired
1345 Token is valid but has expired.
1346 Invalid
1348 Token is invalid (failed HMAC or wrong length)
1349 AuthenticatedEmptyUser / ExpiredEmptyUser
1351 The token is not valid with the username sent from the
1352 client but would be valid (or expired) if we assume an
1353 empty username was used instead. These two cases are a
1354 workaround for behaviour in OpenVPN 3. If this work‐
1355 around is not needed these two cases should be handled in
1356 the same way as Invalid.
1357 Warning: Use this feature only if you want your authentication
1359 method called on every verification. Since the external authen‐
1360 tication is called it needs to also indicate a success or fail‐
1361 ure of the authentication. It is strongly recommended to return
1362 an authentication failure in the case of the Invalid/Expired
1363 auth-token with the external-auth option unless the client could
1364 authenticate in another acceptable way (e.g. client certifi‐
1365 cate), otherwise returning success will lead to authentication
1366 bypass (as does returning success on a wrong password from a
1367 script).
1368 --auth-gen-token-secret file
1370 Specifies a file that holds a secret for the HMAC used in
1371 --auth-gen-token If file is not present OpenVPN will generate a
1372 random secret on startup. This file should be used if auth-token
1373 should validate after restarting a server or if client should be
1374 able to roam between multiple OpenVPN servers with their
1375 auth-token.
1376 --auth-user-pass-optional
1378 Allow connections by clients that do not specify a user‐
1379 name/password. Normally, when --auth-user-pass-verify or --man‐
1380 agement-client-auth are specified (or an authentication plugin
1381 module), the OpenVPN server daemon will require connecting
1382 clients to specify a username and password. This option makes
1383 the submission of a username/password by clients optional, pass‐
1384 ing the responsibility to the user-defined authentication mod‐
1385 ule/script to accept or deny the client based on other factors
1386 (such as the setting of X509 certificate fields). When this op‐
1387 tion is used, and a connecting client does not submit a user‐
1388 name/password, the user-defined authentication module/script
1389 will see the username and password as being set to empty strings
1390 (""). The authentication module/script MUST have logic to detect
1391 this condition and respond accordingly.
1392 --ccd-exclusive
1394 Require, as a condition of authentication, that a connecting
1395 client has a --client-config-dir file.
1396 --client-config-dir dir
1398 Specify a directory dir for custom client config files. After a
1399 connecting client has been authenticated, OpenVPN will look in
1400 this directory for a file having the same name as the client's
1401 X509 common name. If a matching file exists, it will be opened
1402 and parsed for client-specific configuration options. If no
1403 matching file is found, OpenVPN will instead try to open and
1404 parse a default file called "DEFAULT", which may be provided but
1405 is not required. Note that the configuration files must be read‐
1406 able by the OpenVPN process after it has dropped it's root priv‐
1407 ileges.
1408 This file can specify a fixed IP address for a given client us‐
1410 ing --ifconfig-push, as well as fixed subnets owned by the
1411 client using --iroute.
1412 One of the useful properties of this option is that it allows
1414 client configuration files to be conveniently created, edited,
1415 or removed while the server is live, without needing to restart
1416 the server.
1417 The following options are legal in a client-specific context:
1419 --push, --push-reset, --push-remove, --iroute, --ifconfig-push,
1420 --vlan-pvid and --config.
1421 --client-to-client
1423 Because the OpenVPN server mode handles multiple clients through
1424 a single tun or tap interface, it is effectively a router. The
1425 --client-to-client flag tells OpenVPN to internally route
1426 client-to-client traffic rather than pushing all client-origi‐
1427 nating traffic to the TUN/TAP interface.
1428 When this option is used, each client will "see" the other
1430 clients which are currently connected. Otherwise, each client
1431 will only see the server. Don't use this option if you want to
1432 firewall tunnel traffic using custom, per-client rules.
1433 --disable
1435 Disable a particular client (based on the common name) from con‐
1436 necting. Don't use this option to disable a client due to key
1437 or password compromise. Use a CRL (certificate revocation list)
1438 instead (see the --crl-verify option).
1439 This option must be associated with a specific client instance,
1441 which means that it must be specified either in a client in‐
1442 stance config file using --client-config-dir or dynamically gen‐
1443 erated using a --client-connect script.
1444 --connect-freq args
1446 Allow a maximum of n new connections per sec seconds from
1447 clients.
1448 Valid syntax:
1450 connect-freq n sec
1452 This is designed to contain DoS attacks which flood the server
1454 with connection requests using certificates which will ulti‐
1455 mately fail to authenticate.
1456 This is an imperfect solution however, because in a real DoS
1458 scenario, legitimate connections might also be refused.
1459 For the best protection against DoS attacks in server mode, use
1461 --proto udp and either --tls-auth or --tls-crypt.
1462 --duplicate-cn
1464 Allow multiple clients with the same common name to concurrently
1465 connect. In the absence of this option, OpenVPN will disconnect
1466 a client instance upon connection of a new client having the
1467 same common name.
1468 --ifconfig-pool args
1470 Set aside a pool of subnets to be dynamically allocated to con‐
1471 necting clients, similar to a DHCP server.
1472 Valid syntax:
1474 ifconfig-pool start-IP end-IP [netmask]
1476 For tun-style tunnels, each client will be given a /30 subnet
1478 (for interoperability with Windows clients). For tap-style tun‐
1479 nels, individual addresses will be allocated, and the optional
1480 netmask parameter will also be pushed to clients.
1481 --ifconfig-ipv6-pool args
1483 Specify an IPv6 address pool for dynamic assignment to clients.
1484 Valid args:
1486 ifconfig-ipv6-pool ipv6addr/bits
1488 The pool starts at ipv6addr and matches the offset determined
1490 from the start of the IPv4 pool. If the host part of the given
1491 IPv6 address is 0, the pool starts at ipv6addr +1.
1492 --ifconfig-pool-persist args
1494 Persist/unpersist ifconfig-pool data to file, at seconds inter‐
1495 vals (default 600), as well as on program startup and shutdown.
1496 Valid syntax:
1498 ifconfig-pool-persist file [seconds]
1500 The goal of this option is to provide a long-term association
1502 between clients (denoted by their common name) and the virtual
1503 IP address assigned to them from the ifconfig-pool. Maintaining
1504 a long-term association is good for clients because it allows
1505 them to effectively use the --persist-tun option.
1506 file is a comma-delimited ASCII file, formatted as <Com‐
1508 mon-Name>,<IP-address>.
1509 If seconds = 0, file will be treated as read-only. This is use‐
1511 ful if you would like to treat file as a configuration file.
1512 Note that the entries in this file are treated by OpenVPN as
1514 suggestions only, based on past associations between a common
1515 name and IP address. They do not guarantee that the given com‐
1516 mon name will always receive the given IP address. If you want
1517 guaranteed assignment, use --ifconfig-push
1518 --ifconfig-push args
1520 Push virtual IP endpoints for client tunnel, overriding the
1521 --ifconfig-pool dynamic allocation.
1522 Valid syntax:
1524 ifconfig-push local remote-netmask [alias]
1526 The parameters local and remote-netmask are set according to the
1528 --ifconfig directive which you want to execute on the client ma‐
1529 chine to configure the remote end of the tunnel. Note that the
1530 parameters local and remote-netmask are from the perspective of
1531 the client, not the server. They may be DNS names rather than IP
1532 addresses, in which case they will be resolved on the server at
1533 the time of client connection.
1534 The optional alias parameter may be used in cases where NAT
1536 causes the client view of its local endpoint to differ from the
1537 server view. In this case local/remote-netmask will refer to the
1538 server view while alias/remote-netmask will refer to the client
1539 view.
1540 This option must be associated with a specific client instance,
1542 which means that it must be specified either in a client in‐
1543 stance config file using --client-config-dir or dynamically gen‐
1544 erated using a --client-connect script.
1545 Remember also to include a --route directive in the main OpenVPN
1547 config file which encloses local, so that the kernel will know
1548 to route it to the server's TUN/TAP interface.
1549 OpenVPN's internal client IP address selection algorithm works
1551 as follows:
1552 1. Use --client-connect script generated file for static IP
1554 (first choice).
1555 2. Use --client-config-dir file for static IP (next choice).
1557 3. Use --ifconfig-pool allocation for dynamic IP (last choice).
1559 --ifconfig-ipv6-push args
1561 for --client-config-dir per-client static IPv6 interface config‐
1562 uration, see --client-config-dir and --ifconfig-push for more
1563 details.
1564 Valid syntax:
1566 ifconfig-ipv6-push ipv6addr/bits ipv6remote
1568 --inetd args
1570 Valid syntaxes:
1571 inetd
1573 inetd wait
1574 inetd nowait
1575 inetd wait progname
1576 Use this option when OpenVPN is being run from the inetd or
1578 xinetd(8) server.
1579 The wait and nowait option must match what is specified in the
1581 inetd/xinetd config file. The nowait mode can only be used with
1582 --proto tcp-server The default is wait. The nowait mode can be
1583 used to instantiate the OpenVPN daemon as a classic TCP server,
1584 where client connection requests are serviced on a single port
1585 number. For additional information on this kind of configura‐
1586 tion, see the OpenVPN FAQ:
1587 https://community.openvpn.net/openvpn/wiki/325-openvpn-as-a--forking-tcp-server-which-can-service-multiple-clients-over-a-single-tcp-port
1588 This option precludes the use of --daemon, --local or --remote.
1590 Note that this option causes message and error output to be han‐
1591 dled in the same way as the --daemon option. The optional prog‐
1592 name parameter is also handled exactly as in --daemon.
1593 Also note that in wait mode, each OpenVPN tunnel requires a sep‐
1595 arate TCP/UDP port and a separate inetd or xinetd entry. See the
1596 OpenVPN 1.x HOWTO for an example on using OpenVPN with xinetd:
1597 https://openvpn.net/community-resources/1xhowto/
1598 --multihome
1600 Configure a multi-homed UDP server. This option needs to be used
1601 when a server has more than one IP address (e.g. multiple inter‐
1602 faces, or secondary IP addresses), and is not using --local to
1603 force binding to one specific address only. This option will add
1604 some extra lookups to the packet path to ensure that the UDP re‐
1605 ply packets are always sent from the address that the client is
1606 talking to. This is not supported on all platforms, and it adds
1607 more processing, so it's not enabled by default.
1608 Notes:
1610 • This option is only relevant for UDP servers.
1612 • If you do an IPv6+IPv4 dual-stack bind on a Linux ma‐
1614 chine with multiple IPv4 address, connections to IPv4
1615 addresses will not work right on kernels before 3.15,
1616 due to missing kernel support for the IPv4-mapped case
1617 (some distributions have ported this to earlier kernel
1618 versions, though).
1619 --iroute args
1621 Generate an internal route to a specific client. The netmask pa‐
1622 rameter, if omitted, defaults to 255.255.255.255.
1623 Valid syntax:
1625 iroute network [netmask]
1627 This directive can be used to route a fixed subnet from the
1629 server to a particular client, regardless of where the client is
1630 connecting from. Remember that you must also add the route to
1631 the system routing table as well (such as by using the --route
1632 directive). The reason why two routes are needed is that the
1633 --route directive routes the packet from the kernel to OpenVPN.
1634 Once in OpenVPN, the --iroute directive routes to the specific
1635 client.
1636 This option must be specified either in a client instance config
1638 file using --client-config-dir or dynamically generated using a
1639 --client-connect script.
1640 The --iroute directive also has an important interaction with
1642 --push "route ...". --iroute essentially defines a subnet which
1643 is owned by a particular client (we will call this client A). If
1644 you would like other clients to be able to reach A's subnet, you
1645 can use --push "route ..." together with --client-to-client to
1646 effect this. In order for all clients to see A's subnet, OpenVPN
1647 must push this route to all clients EXCEPT for A, since the sub‐
1648 net is already owned by A. OpenVPN accomplishes this by not not
1649 pushing a route to a client if it matches one of the client's
1650 iroutes.
1651 --iroute-ipv6 args
1653 for --client-config-dir per-client static IPv6 route configura‐
1654 tion, see --iroute for more details how to setup and use this,
1655 and how --iroute and --route interact.
1656 Valid syntax:
1658 iroute-ipv6 ipv6addr/bits
1660 --max-clients n
1662 Limit server to a maximum of n concurrent clients.
1663 --max-routes-per-client n
1665 Allow a maximum of n internal routes per client (default 256).
1666 This is designed to help contain DoS attacks where an authenti‐
1667 cated client floods the server with packets appearing to come
1668 from many unique MAC addresses, forcing the server to deplete
1669 virtual memory as its internal routing table expands. This di‐
1670 rective can be used in a --client-config-dir file or auto-gener‐
1671 ated by a --client-connect script to override the global value
1672 for a particular client.
1673 Note that this directive affects OpenVPN's internal routing ta‐
1675 ble, not the kernel routing table.
1676 --opt-verify
1678 Clients that connect with options that are incompatible with
1679 those of the server will be disconnected.
1680 Options that will be compared for compatibility include
1682 dev-type, link-mtu, tun-mtu, proto, ifconfig, comp-lzo, frag‐
1683 ment, keydir, cipher, auth, keysize, secret, no-replay,
1684 tls-auth, key-method, tls-server and tls-client.
1685 This option requires that --disable-occ NOT be used.
1687 --port-share args
1689 Share OpenVPN TCP with another service
1690 Valid syntax:
1692 port-share host port [dir]
1694 When run in TCP server mode, share the OpenVPN port with another
1696 application, such as an HTTPS server. If OpenVPN senses a con‐
1697 nection to its port which is using a non-OpenVPN protocol, it
1698 will proxy the connection to the server at host:port. Currently
1699 only designed to work with HTTP/HTTPS, though it would be theo‐
1700 retically possible to extend to other protocols such as ssh.
1701 dir specifies an optional directory where a temporary file with
1703 name N containing content C will be dynamically generated for
1704 each proxy connection, where N is the source IP:port of the
1705 client connection and C is the source IP:port of the connection
1706 to the proxy receiver. This directory can be used as a dictio‐
1707 nary by the proxy receiver to determine the origin of the con‐
1708 nection. Each generated file will be automatically deleted when
1709 the proxied connection is torn down.
1710 Not implemented on Windows.
1712 --push option
1714 Push a config file option back to the client for remote execu‐
1715 tion. Note that option must be enclosed in double quotes ("").
1716 The client must specify --pull in its config file. The set of
1717 options which can be pushed is limited by both feasibility and
1718 security. Some options such as those which would execute scripts
1719 are banned, since they would effectively allow a compromised
1720 server to execute arbitrary code on the client. Other options
1721 such as TLS or MTU parameters cannot be pushed because the
1722 client needs to know them before the connection to the server
1723 can be initiated.
1724 This is a partial list of options which can currently be pushed:
1726 --route, --route-gateway, --route-delay, --redirect-gateway,
1727 --ip-win32, --dhcp-option, --inactive, --ping, --ping-exit,
1728 --ping-restart, --setenv, --auth-token, --persist-key, --per‐
1729 sist-tun, --echo, --comp-lzo, --socket-flags, --sndbuf, --rcvbuf
1730 --push-peer-info
1732 Push additional information about the client to server. The fol‐
1733 lowing data is always pushed to the server:
1734 IV_VER=<version>
1736 The client OpenVPN version
1737 IV_PLAT=[linux|solaris|openbsd|mac|netbsd|freebsd|win]
1739 The client OS platform
1740 IV_LZO_STUB=1
1742 If client was built with LZO stub capability
1743 IV_LZ4=1
1745 If the client supports LZ4 compressions.
1746 IV_PROTO
1748 Details about protocol extensions that the peer supports.
1749 The variable is a bitfield and the bits are defined as
1750 follows (starting a bit 0 for the first (unused) bit:
1751 • bit 1: The peer supports peer-id floating mechanism
1753 • bit 2: The client expects a push-reply and the server
1755 may send this reply without waiting for a push-request
1756 first.
1757 IV_NCP=2
1759 Negotiable ciphers, client supports --cipher pushed by
1760 the server, a value of 2 or greater indicates client sup‐
1761 ports AES-GCM-128 and AES-GCM-256.
1762 IV_CIPHERS=<ncp-ciphers>
1764 The client announces the list of supported ciphers con‐
1765 figured with the --data-ciphers option to the server.
1766 IV_GUI_VER=<gui_id> <version>
1768 The UI version of a UI if one is running, for example
1769 de.blinkt.openvpn 0.5.47 for the Android app.
1770 When --push-peer-info is enabled the additional information con‐
1772 sists of the following data:
1773 IV_HWADDR=<mac address>
1775 The MAC address of clients default gateway
1776 IV_SSL=<version string>
1778 The ssl version used by the client, e.g. OpenSSL 1.0.2f
1779 28 Jan 2016.
1780 IV_PLAT_VER=x.y
1782 The version of the operating system, e.g. 6.1 for Windows
1783 7.
1784 UV_<name>=<value>
1786 Client environment variables whose names start with UV_
1787 --push-remove opt
1789 Selectively remove all --push options matching "opt" from the
1790 option list for a client. opt is matched as a substring against
1791 the whole option string to-be-pushed to the client, so
1792 --push-remove route would remove all --push route ... and --push
1793 route-ipv6 ... statements, while --push-remove "route-ipv6
1794 2001:" would only remove IPv6 routes for 2001:... networks.
1795 --push-remove can only be used in a client-specific context,
1797 like in a --client-config-dir file, or --client-connect script
1798 or plugin -- similar to --push-reset, just more selective.
1799 NOTE: to change an option, --push-remove can be used to first
1801 remove the old value, and then add a new --push option with the
1802 new value.
1803 NOTE 2: due to implementation details, 'ifconfig' and 'ifcon‐
1805 fig-ipv6' can only be removed with an exact match on the option
1806 ( push-remove ifconfig), no substring matching and no matching
1807 on the IPv4/IPv6 address argument is possible.
1808 --push-reset
1810 Don't inherit the global push list for a specific client in‐
1811 stance. Specify this option in a client-specific context such
1812 as with a --client-config-dir configuration file. This option
1813 will ignore --push options at the global config file level.
1814 NOTE: --push-reset is very thorough: it will remove almost all
1816 options from the list of to-be-pushed options. In many cases,
1817 some of these options will need to be re-configured afterwards -
1818 specifically, --topology subnet and --route-gateway will get
1819 lost and this will break client configs in many cases. Thus,
1820 for most purposes, --push-remove is better suited to selectively
1821 remove push options for individual clients.
1822 --server args
1824 A helper directive designed to simplify the configuration of
1825 OpenVPN's server mode. This directive will set up an OpenVPN
1826 server which will allocate addresses to clients out of the given
1827 network/netmask. The server itself will take the .1 address of
1828 the given network for use as the server-side endpoint of the lo‐
1829 cal TUN/TAP interface. If the optional nopool flag is given, no
1830 dynamic IP address pool will prepared for VPN clients.
1831 Valid syntax:
1833 server network netmask [nopool]
1835 For example, --server 10.8.0.0 255.255.255.0 expands as follows:
1837 mode server
1839 tls-server
1840 push "topology [topology]"
1841 if dev tun AND (topology == net30 OR topology == p2p):
1843 ifconfig 10.8.0.1 10.8.0.2
1844 if !nopool:
1845 ifconfig-pool 10.8.0.4 10.8.0.251
1846 route 10.8.0.0 255.255.255.0
1847 if client-to-client:
1848 push "route 10.8.0.0 255.255.255.0"
1849 else if topology == net30:
1850 push "route 10.8.0.1"
1851 if dev tap OR (dev tun AND topology == subnet):
1853 ifconfig 10.8.0.1 255.255.255.0
1854 if !nopool:
1855 ifconfig-pool 10.8.0.2 10.8.0.253 255.255.255.0
1856 push "route-gateway 10.8.0.1"
1857 if route-gateway unset:
1858 route-gateway 10.8.0.2
1859 Don't use --server if you are ethernet bridging. Use
1861 --server-bridge instead.
1862 --server-bridge args
1864 A helper directive similar to --server which is designed to sim‐
1865 plify the configuration of OpenVPN's server mode in ethernet
1866 bridging configurations.
1867 Valid syntaxes:
1869 server-bridge gateway netmask pool-start-IP pool-end-IP
1871 server-bridge [nogw]
1872 If --server-bridge is used without any parameters, it will en‐
1874 able a DHCP-proxy mode, where connecting OpenVPN clients will
1875 receive an IP address for their TAP adapter from the DHCP server
1876 running on the OpenVPN server-side LAN. Note that only clients
1877 that support the binding of a DHCP client with the TAP adapter
1878 (such as Windows) can support this mode. The optional nogw flag
1879 (advanced) indicates that gateway information should not be
1880 pushed to the client.
1881 To configure ethernet bridging, you must first use your OS's
1883 bridging capability to bridge the TAP interface with the ether‐
1884 net NIC interface. For example, on Linux this is done with the
1885 brctl tool, and with Windows XP it is done in the Network Con‐
1886 nections Panel by selecting the ethernet and TAP adapters and
1887 right-clicking on "Bridge Connections".
1888 Next you you must manually set the IP/netmask on the bridge in‐
1890 terface. The gateway and netmask parameters to --server-bridge
1891 can be set to either the IP/netmask of the bridge interface, or
1892 the IP/netmask of the default gateway/router on the bridged sub‐
1893 net.
1894 Finally, set aside a IP range in the bridged subnet, denoted by
1896 pool-start-IP and pool-end-IP, for OpenVPN to allocate to con‐
1897 necting clients.
1898 For example, server-bridge 10.8.0.4 255.255.255.0 10.8.0.128
1900 10.8.0.254 expands as follows:
1901 mode server
1903 tls-server
1904 ifconfig-pool 10.8.0.128 10.8.0.254 255.255.255.0
1906 push "route-gateway 10.8.0.4"
1907 In another example, --server-bridge (without parameters) expands
1909 as follows:
1910 mode server
1912 tls-server
1913 push "route-gateway dhcp"
1915 Or --server-bridge nogw expands as follows:
1917 mode server
1919 tls-server
1920 --server-ipv6 args
1922 Convenience-function to enable a number of IPv6 related options
1923 at once, namely --ifconfig-ipv6, --ifconfig-ipv6-pool and --push
1924 tun-ipv6.
1925 Valid syntax:
1927 server-ipv6 ipv6addr/bits
1929 Pushing of the --tun-ipv6 directive is done for older clients
1931 which require an explicit --tun-ipv6 in their configuration.
1932 --stale-routes-check args
1934 Remove routes which haven't had activity for n seconds (i.e. the
1935 ageing time). This check is run every t seconds (i.e. check in‐
1936 terval).
1937 Valid syntax:
1939 stale-routes-check n [t]
1941 If t is not present it defaults to n.
1943 This option helps to keep the dynamic routing table small. See
1945 also --max-routes-per-client
1946 --username-as-common-name
1948 Use the authenticated username as the common-name, rather than
1949 the common-name from the client certificate. Requires that some
1950 form of --auth-user-pass verification is in effect. As the re‐
1951 placement happens after --auth-user-pass verification, the veri‐
1952 fication script or plugin will still receive the common-name
1953 from the certificate.
1954 The common_name environment variable passed to scripts and plug‐
1956 ins invoked after authentication (e.g, client-connect script)
1957 and file names parsed in client-config directory will match the
1958 username.
1959 --verify-client-cert mode
1961 Specify whether the client is required to supply a valid cer‐
1962 tificate.
1963 Possible mode options are:
1965 none A client certificate is not required. the client needs to
1967 authenticate using username/password only. Be aware that
1968 using this directive is less secure than requiring cer‐
1969 tificates from all clients.
1970 If you use this directive, the entire responsibility of
1972 authentication will rest on your --auth-user-pass-verify
1973 script, so keep in mind that bugs in your script could
1974 potentially compromise the security of your VPN.
1975 --verify-client-cert none is functionally equivalent to
1977 --client-cert-not-required.
1978 optional
1980 A client may present a certificate but it is not required
1981 to do so. When using this directive, you should also use
1982 a --auth-user-pass-verify script to ensure that clients
1983 are authenticated using a certificate, a username and
1984 password, or possibly even both.
1985 Again, the entire responsibility of authentication will
1987 rest on your --auth-user-pass-verify script, so keep in
1988 mind that bugs in your script could potentially compro‐
1989 mise the security of your VPN.
1990 require
1992 This is the default option. A client is required to
1993 present a certificate, otherwise VPN access is refused.
1994 If you don't use this directive (or use --verify-client-cert re‐
1996 quire) but you also specify an --auth-user-pass-verify script,
1997 then OpenVPN will perform double authentication. The client cer‐
1998 tificate verification AND the --auth-user-pass-verify script
1999 will need to succeed in order for a client to be authenticated
2000 and accepted onto the VPN.
2001 --vlan-tagging
2003 Server-only option. Turns the OpenVPN server instance into a
2004 switch that understands VLAN-tagging, based on IEEE 802.1Q.
2005 The server TAP device and each of the connecting clients is seen
2007 as a port of the switch. All client ports are in untagged mode
2008 and the server TAP device is VLAN-tagged, untagged or accepts
2009 both, depending on the --vlan-accept setting.
2010 Ethernet frames with a prepended 802.1Q tag are called "tagged".
2012 If the VLAN Identifier (VID) field in such a tag is non-zero,
2013 the frame is called "VLAN-tagged". If the VID is zero, but the
2014 Priority Control Point (PCP) field is non-zero, the frame is
2015 called "prio-tagged". If there is no 802.1Q tag, the frame is
2016 "untagged".
2017 Using the --vlan-pvid v option once per client (see
2019 --client-config-dir), each port can be associated with a certain
2020 VID. Packets can only be forwarded between ports having the
2021 same VID. Therefore, clients with differing VIDs are completely
2022 separated from one-another, even if --client-to-client is acti‐
2023 vated.
2024 The packet filtering takes place in the OpenVPN server. Clients
2026 should not have any VLAN tagging configuration applied.
2027 The --vlan-tagging option is off by default. While turned off,
2029 OpenVPN accepts any Ethernet frame and does not perform any spe‐
2030 cial processing for VLAN-tagged packets.
2031 This option can only be activated in --dev tap mode.
2033 --vlan-accept args
2035 Configure the VLAN tagging policy for the server TAP device.
2036 Valid syntax:
2038 vlan-accept all|tagged|untagged
2040 The following modes are available:
2042 tagged Admit only VLAN-tagged frames. Only VLAN-tagged packets
2044 are accepted, while untagged or priority-tagged packets
2045 are dropped when entering the server TAP device.
2046 untagged
2048 Admit only untagged and prio-tagged frames. VLAN-tagged
2049 packets are not accepted, while untagged or prior‐
2050 ity-tagged packets entering the server TAP device are
2051 tagged with the value configured for the global
2052 --vlan-pvid setting.
2053 all (default)
2055 Admit all frames. All packets are admitted and then
2056 treated like untagged or tagged mode respectively.
2057 Note: Some vendors refer to switch ports running in tagged mode
2059 as "trunk ports" and switch ports running in untagged
2060 mode as "access ports".
2061 Packets forwarded from clients to the server are VLAN-tagged
2063 with the originating client's PVID, unless the VID matches the
2064 global --vlan-pvid, in which case the tag is removed.
2065 If no PVID is configured for a given client (see --vlan-pvid)
2067 packets are tagged with 1 by default.
2068 --vlan-pvid v
2070 Specifies which VLAN identifier a "port" is associated with.
2071 Only valid when --vlan-tagging is speficied.
2072 In the client context, the setting specifies which VLAN ID a
2074 client is associated with. In the global context, the VLAN ID of
2075 the server TAP device is set. The latter only makes sense for
2076 --vlan-accept untagged and --vlan-accept all modes.
2077 Valid values for v go from 1 through to 4094. The global value
2079 defaults to 1. If no --vlan-pvid is specified in the client con‐
2080 text, the global value is inherited.
2081 In some switch implementations, the PVID is also referred to as
2083 "Native VLAN".
2084
2086 SSL Library information
2087 --show-ciphers
2088 (Standalone) Show all cipher algorithms to use with the --cipher
2089 option.
2090 --show-digests
2092 (Standalone) Show all message digest algorithms to use with the
2093 --auth option.
2094 --show-tls
2096 (Standalone) Show all TLS ciphers supported by the crypto li‐
2097 brary. OpenVPN uses TLS to secure the control channel, over
2098 which the keys that are used to protect the actual VPN traffic
2099 are exchanged. The TLS ciphers will be sorted from highest pref‐
2100 erence (most secure) to lowest.
2101 Be aware that whether a cipher suite in this list can actually
2103 work depends on the specific setup of both peers (e.g. both
2104 peers must support the cipher, and an ECDSA cipher suite will
2105 not work if you are using an RSA certificate, etc.).
2106 --show-engines
2108 (Standalone) Show currently available hardware-based crypto ac‐
2109 celeration engines supported by the OpenSSL library.
2110 --show-groups
2112 (Standalone) Show all available elliptic curves/groups to use
2113 with the --ecdh-curve and tls-groups options.
2114 Generating key material
2116 --genkey args
2117 (Standalone) Generate a key to be used of the type keytype. if
2118 keyfile is left out or empty the key will be output on stdout.
2119 See the following sections for the different keytypes.
2120 Valid syntax:
2122 --genkey keytype keyfile
2124 Valid keytype arguments are:
2126 secret Standard OpenVPN shared secret keys
2128 tls-crypt Alias for secret
2130 tls-auth Alias for secret
2132 auth-token Key used for --auth-gen-token-key
2134 tls-crypt-v2-server TLS Crypt v2 server key
2136 tls-crypt-v2-client TLS Crypt v2 client key
2138 Examples:
2140 $ openvpn --genkey secret shared.key
2142 $ openvpn --genkey tls-crypt shared.key
2143 $ openvpn --genkey tls-auth shared.key
2144 $ openvpn --genkey tls-crypt-v2-server v2crypt-server.key
2145 $ openvpn --tls-crypt-v2 v2crypt-server.key --genkey tls-crypt-v2-client v2crypt-client-1.key
2146 • Generating Shared Secret Keys Generate a shared secret, for
2148 use with the --secret, --tls-auth or --tls-crypt options.
2149 Syntax:
2151 $ openvpn --genkey secret|tls-crypt|tls-auth keyfile
2153 The key is saved in keyfile. All three variants (--secret,
2155 tls-crypt and tls-auth) generate the same type of key. The
2156 aliases are added for convenience.
2157 If using this for --secret, this file must be shared with the
2159 peer over a pre-existing secure channel such as scp(1).
2160 • Generating TLS Crypt v2 Server key Generate a --tls-crypt-v2
2162 key to be used by an OpenVPN server. The key is stored in
2163 keyfile.
2164 Syntax:
2166 --genkey tls-crypt-v2-server keyfile
2168 • Generating TLS Crypt v2 Client key Generate a --tls-crypt-v2
2170 key to be used by OpenVPN clients. The key is stored in key‐
2171 file.
2172 Syntax
2174 --genkey tls-crypt-v2-client keyfile [metadata]
2176 If supplied, include the supplied metadata in the wrapped
2178 client key. This metadata must be supplied in base64-encoded
2179 form. The metadata must be at most 735 bytes long (980 bytes
2180 in base64).
2181 If no metadata is supplied, OpenVPN will use a 64-bit unix
2183 timestamp representing the current time in UTC, encoded in
2184 network order, as metadata for the generated key.
2185 A tls-crypt-v2 client key is wrapped using a server key. To
2187 generate a client key, the user must therefore supply the
2188 server key using the --tls-crypt-v2 option.
2189 Servers can use --tls-crypt-v2-verify to specify a metadata
2191 verification command.
2192 • Generate Authentication Token key Generate a new secret that
2194 can be used with --auth-gen-token-secret
2195 Syntax:
2197 --genkey auth-token [keyfile]
2199 Note: This file should be kept secret to the server as anyone
2201 that has access to this file will be able to generate
2202 auth tokens that the OpenVPN server will accept as
2203 valid.
2204 Data Channel Renegotiation
2206 When running OpenVPN in client/server mode, the data channel will use a
2207 separate ephemeral encryption key which is rotated at regular inter‐
2208 vals.
2209 --reneg-bytes n
2211 Renegotiate data channel key after n bytes sent or received
2212 (disabled by default with an exception, see below). OpenVPN al‐
2213 lows the lifetime of a key to be expressed as a number of bytes
2214 encrypted/decrypted, a number of packets, or a number of sec‐
2215 onds. A key renegotiation will be forced if any of these three
2216 criteria are met by either peer.
2217 If using ciphers with cipher block sizes less than 128-bits,
2219 --reneg-bytes is set to 64MB by default, unless it is explicitly
2220 disabled by setting the value to 0, but this is HIGHLY DISCOUR‐
2221 AGED as this is designed to add some protection against the
2222 SWEET32 attack vector. For more information see the --cipher op‐
2223 tion.
2224 --reneg-pkts n
2226 Renegotiate data channel key after n packets sent and received
2227 (disabled by default).
2228 --reneg-sec args
2230 Renegotiate data channel key after at most max seconds (default
2231 3600) and at least min seconds (default is 90% of max for
2232 servers, and equal to max for clients).
2233 reneg-sec max [min]
2235 The effective --reneg-sec value used is per session pseudo-uni‐
2237 form-randomized between min and max.
2238 With the default value of 3600 this results in an effective per
2240 session value in the range of 3240 .. 3600 seconds for servers,
2241 or just 3600 for clients.
2242 When using dual-factor authentication, note that this default
2244 value may cause the end user to be challenged to reauthorize
2245 once per hour.
2246 Also, keep in mind that this option can be used on both the
2248 client and server, and whichever uses the lower value will be
2249 the one to trigger the renegotiation. A common mistake is to set
2250 --reneg-sec to a higher value on either the client or server,
2251 while the other side of the connection is still using the de‐
2252 fault value of 3600 seconds, meaning that the renegotiation will
2253 still occur once per 3600 seconds. The solution is to increase
2254 --reneg-sec on both the client and server, or set it to 0 on one
2255 side of the connection (to disable), and to your chosen value on
2256 the other side.
2257 TLS Mode Options
2259 TLS mode is the most powerful crypto mode of OpenVPN in both security
2260 and flexibility. TLS mode works by establishing control and data chan‐
2261 nels which are multiplexed over a single TCP/UDP port. OpenVPN initi‐
2262 ates a TLS session over the control channel and uses it to exchange ci‐
2263 pher and HMAC keys to protect the data channel. TLS mode uses a robust
2264 reliability layer over the UDP connection for all control channel com‐
2265 munication, while the data channel, over which encrypted tunnel data
2266 passes, is forwarded without any mediation. The result is the best of
2267 both worlds: a fast data channel that forwards over UDP with only the
2268 overhead of encrypt, decrypt, and HMAC functions, and a control channel
2269 that provides all of the security features of TLS, including certifi‐
2270 cate-based authentication and Diffie Hellman forward secrecy.
2271 To use TLS mode, each peer that runs OpenVPN should have its own local
2273 certificate/key pair (--cert and --key), signed by the root certificate
2274 which is specified in --ca.
2275 When two OpenVPN peers connect, each presents its local certificate to
2277 the other. Each peer will then check that its partner peer presented a
2278 certificate which was signed by the master root certificate as speci‐
2279 fied in --ca.
2280 If that check on both peers succeeds, then the TLS negotiation will
2282 succeed, both OpenVPN peers will exchange temporary session keys, and
2283 the tunnel will begin passing data.
2284 The OpenVPN project provides a set of scripts for managing RSA certifi‐
2286 cates and keys: https://github.com/OpenVPN/easy-rsa
2287 --askpass file
2289 Get certificate password from console or file before we daemo‐
2290 nize.
2291 Valid syntaxes:
2293 askpass
2295 askpass file
2296 For the extremely security conscious, it is possible to protect
2298 your private key with a password. Of course this means that ev‐
2299 ery time the OpenVPN daemon is started you must be there to type
2300 the password. The --askpass option allows you to start OpenVPN
2301 from the command line. It will query you for a password before
2302 it daemonizes. To protect a private key with a password you
2303 should omit the -nodes option when you use the openssl command
2304 line tool to manage certificates and private keys.
2305 If file is specified, read the password from the first line of
2307 file. Keep in mind that storing your password in a file to a
2308 certain extent invalidates the extra security provided by using
2309 an encrypted key.
2310 --ca file
2312 Certificate authority (CA) file in .pem format, also referred to
2313 as the root certificate. This file can have multiple certifi‐
2314 cates in .pem format, concatenated together. You can construct
2315 your own certificate authority certificate and private key by
2316 using a command such as:
2317 openssl req -nodes -new -x509 -keyout ca.key -out ca.crt
2319 Then edit your openssl.cnf file and edit the certificate vari‐
2321 able to point to your new root certificate ca.crt.
2322 For testing purposes only, the OpenVPN distribution includes a
2324 sample CA certificate (ca.crt). Of course you should never use
2325 the test certificates and test keys distributed with OpenVPN in
2326 a production environment, since by virtue of the fact that they
2327 are distributed with OpenVPN, they are totally insecure.
2328 --capath dir
2330 Directory containing trusted certificates (CAs and CRLs). Not
2331 available with mbed TLS.
2332 CAs in the capath directory are expected to be named <hash>.<n>.
2334 CRLs are expected to be named <hash>.r<n>. See the -CApath op‐
2335 tion of openssl verify, and the -hash option of openssl x509,
2336 openssl crl and X509_LOOKUP_hash_dir()[22m(3) for more information.
2337 Similar to the --crl-verify option, CRLs are not mandatory -
2339 OpenVPN will log the usual warning in the logs if the relevant
2340 CRL is missing, but the connection will be allowed.
2341 --cert file
2343 Local peer's signed certificate in .pem format -- must be signed
2344 by a certificate authority whose certificate is in --ca file.
2345 Each peer in an OpenVPN link running in TLS mode should have its
2346 own certificate and private key file. In addition, each certifi‐
2347 cate should have been signed by the key of a certificate author‐
2348 ity whose public key resides in the --ca certificate authority
2349 file. You can easily make your own certificate authority (see
2350 above) or pay money to use a commercial service such as
2351 thawte.com (in which case you will be helping to finance the
2352 world's second space tourist :). To generate a certificate, you
2353 can use a command such as:
2354 openssl req -nodes -new -keyout mycert.key -out mycert.csr
2356 If your certificate authority private key lives on another ma‐
2358 chine, copy the certificate signing request (mycert.csr) to this
2359 other machine (this can be done over an insecure channel such as
2360 email). Now sign the certificate with a command such as:
2361 openssl ca -out mycert.crt -in mycert.csr
2363 Now copy the certificate (mycert.crt) back to the peer which
2365 initially generated the .csr file (this can be over a public
2366 medium). Note that the openssl ca command reads the location of
2367 the certificate authority key from its configuration file such
2368 as /usr/share/ssl/openssl.cnf -- note also that for certificate
2369 authority functions, you must set up the files index.txt (may be
2370 empty) and serial (initialize to 01).
2371 --crl-verify args
2373 Check peer certificate against a Certificate Revocation List.
2374 Valid syntax:
2376 crl-verify file/directory flag
2378 Examples:
2380 crl-verify crl-file.pem
2382 crl-verify /etc/openvpn/crls dir
2383 A CRL (certificate revocation list) is used when a particular
2385 key is compromised but when the overall PKI is still intact.
2386 Suppose you had a PKI consisting of a CA, root certificate, and
2388 a number of client certificates. Suppose a laptop computer con‐
2389 taining a client key and certificate was stolen. By adding the
2390 stolen certificate to the CRL file, you could reject any connec‐
2391 tion which attempts to use it, while preserving the overall in‐
2392 tegrity of the PKI.
2393 The only time when it would be necessary to rebuild the entire
2395 PKI from scratch would be if the root certificate key itself was
2396 compromised.
2397 The option is not mandatory - if the relevant CRL is missing,
2399 OpenVPN will log a warning in the logs - e.g.
2400 VERIFY WARNING: depth=0, unable to get certificate CRL
2402 but the connection will be allowed. If the optional dir flag is
2404 specified, enable a different mode where the crl-verify is
2405 pointed at a directory containing files named as revoked serial
2406 numbers (the files may be empty, the contents are never read).
2407 If a client requests a connection, where the client certificate
2408 serial number (decimal string) is the name of a file present in
2409 the directory, it will be rejected.
2410 Note: As the crl file (or directory) is read every time a peer
2412 connects, if you are dropping root privileges with
2413 --user, make sure that this user has sufficient privi‐
2414 leges to read the file.
2415 --dh file
2417 File containing Diffie Hellman parameters in .pem format (re‐
2418 quired for --tls-server only).
2419 Set file to none to disable Diffie Hellman key exchange (and use
2421 ECDH only). Note that this requires peers to be using an SSL li‐
2422 brary that supports ECDH TLS cipher suites (e.g. OpenSSL 1.0.1+,
2423 or mbed TLS 2.0+).
2424 Use openssl dhparam -out dh2048.pem 2048 to generate 2048-bit DH
2426 parameters. Diffie Hellman parameters may be considered public.
2427 --ecdh-curve name
2429 Specify the curve to use for elliptic curve Diffie Hellman.
2430 Available curves can be listed with --show-curves. The specified
2431 curve will only be used for ECDH TLS-ciphers.
2432 This option is not supported in mbed TLS builds of OpenVPN.
2434 --extra-certs file
2436 Specify a file containing one or more PEM certs (concatenated
2437 together) that complete the local certificate chain.
2438 This option is useful for "split" CAs, where the CA for server
2440 certs is different than the CA for client certs. Putting certs
2441 in this file allows them to be used to complete the local cer‐
2442 tificate chain without trusting them to verify the peer-submit‐
2443 ted certificate, as would be the case if the certs were placed
2444 in the ca file.
2445 --hand-window n
2447 Handshake Window -- the TLS-based key exchange must finalize
2448 within n seconds of handshake initiation by any peer (default 60
2449 seconds). If the handshake fails we will attempt to reset our
2450 connection with our peer and try again. Even in the event of
2451 handshake failure we will still use our expiring key for up to
2452 --tran-window seconds to maintain continuity of transmission of
2453 tunnel data.
2454 --key file
2456 Local peer's private key in .pem format. Use the private key
2457 which was generated when you built your peer's certificate (see
2458 --cert file above).
2459 --pkcs12 file
2461 Specify a PKCS #12 file containing local private key, local cer‐
2462 tificate, and root CA certificate. This option can be used in‐
2463 stead of --ca, --cert, and --key. Not available with mbed TLS.
2464 --remote-cert-eku oid
2466 Require that peer certificate was signed with an explicit ex‐
2467 tended key usage.
2468 This is a useful security option for clients, to ensure that the
2470 host they connect to is a designated server.
2471 The extended key usage should be encoded in oid notation, or
2473 OpenSSL symbolic representation.
2474 --remote-cert-ku key-usage
2476 Require that peer certificate was signed with an explicit
2477 key-usage.
2478 If present in the certificate, the keyUsage value is validated
2480 by the TLS library during the TLS handshake. Specifying this op‐
2481 tion without arguments requires this extension to be present (so
2482 the TLS library will verify it).
2483 If key-usage is a list of usage bits, the keyUsage field must
2485 have at least the same bits set as the bits in one of the values
2486 supplied in the key-usage list.
2487 The key-usage values in the list must be encoded in hex, e.g.
2489 remote-cert-ku a0
2491 --remote-cert-tls type
2493 Require that peer certificate was signed with an explicit key
2494 usage and extended key usage based on RFC3280 TLS rules.
2495 Valid syntaxes:
2497 remote-cert-tls server
2499 remote-cert-tls client
2500 This is a useful security option for clients, to ensure that the
2502 host they connect to is a designated server. Or the other way
2503 around; for a server to verify that only hosts with a client
2504 certificate can connect.
2505 The --remote-cert-tls client option is equivalent to
2507 remote-cert-ku
2509 remote-cert-eku "TLS Web Client Authentication"
2510 The --remote-cert-tls server option is equivalent to
2512 remote-cert-ku
2514 remote-cert-eku "TLS Web Server Authentication"
2515 This is an important security precaution to protect against a
2517 man-in-the-middle attack where an authorized client attempts to
2518 connect to another client by impersonating the server. The at‐
2519 tack is easily prevented by having clients verify the server
2520 certificate using any one of --remote-cert-tls, --ver‐
2521 ify-x509-name, or --tls-verify.
2522 --tls-auth args
2524 Add an additional layer of HMAC authentication on top of the TLS
2525 control channel to mitigate DoS attacks and attacks on the TLS
2526 stack.
2527 Valid syntaxes:
2529 tls-auth file
2531 tls-auth file 0
2532 tls-auth file 1
2533 In a nutshell, --tls-auth enables a kind of "HMAC firewall" on
2535 OpenVPN's TCP/UDP port, where TLS control channel packets bear‐
2536 ing an incorrect HMAC signature can be dropped immediately with‐
2537 out response.
2538 file (required) is a file in OpenVPN static key format which can
2540 be generated by --genkey.
2541 Older versions (up to OpenVPN 2.3) supported a freeform
2543 passphrase file. This is no longer supported in newer versions
2544 (v2.4+).
2545 See the --secret option for more information on the optional di‐
2547 rection parameter.
2548 --tls-auth is recommended when you are running OpenVPN in a mode
2550 where it is listening for packets from any IP address, such as
2551 when --remote is not specified, or --remote is specified with
2552 --float.
2553 The rationale for this feature is as follows. TLS requires a
2555 multi-packet exchange before it is able to authenticate a peer.
2556 During this time before authentication, OpenVPN is allocating
2557 resources (memory and CPU) to this potential peer. The potential
2558 peer is also exposing many parts of OpenVPN and the OpenSSL li‐
2559 brary to the packets it is sending. Most successful network at‐
2560 tacks today seek to either exploit bugs in programs (such as
2561 buffer overflow attacks) or force a program to consume so many
2562 resources that it becomes unusable. Of course the first line of
2563 defense is always to produce clean, well-audited code. OpenVPN
2564 has been written with buffer overflow attack prevention as a top
2565 priority. But as history has shown, many of the most widely used
2566 network applications have, from time to time, fallen to buffer
2567 overflow attacks.
2568 So as a second line of defense, OpenVPN offers this special
2570 layer of authentication on top of the TLS control channel so
2571 that every packet on the control channel is authenticated by an
2572 HMAC signature and a unique ID for replay protection. This sig‐
2573 nature will also help protect against DoS (Denial of Service)
2574 attacks. An important rule of thumb in reducing vulnerability to
2575 DoS attacks is to minimize the amount of resources a potential,
2576 but as yet unauthenticated, client is able to consume.
2577 --tls-auth does this by signing every TLS control channel packet
2579 with an HMAC signature, including packets which are sent before
2580 the TLS level has had a chance to authenticate the peer. The re‐
2581 sult is that packets without the correct signature can be
2582 dropped immediately upon reception, before they have a chance to
2583 consume additional system resources such as by initiating a TLS
2584 handshake. --tls-auth can be strengthened by adding the --re‐
2585 play-persist option which will keep OpenVPN's replay protection
2586 state in a file so that it is not lost across restarts.
2587 It should be emphasized that this feature is optional and that
2589 the key file used with --tls-auth gives a peer nothing more than
2590 the power to initiate a TLS handshake. It is not used to encrypt
2591 or authenticate any tunnel data.
2592 Use --tls-crypt instead if you want to use the key file to not
2594 only authenticate, but also encrypt the TLS control channel.
2595 --tls-groups list
2597 A list of allowable groups/curves in order of preference.
2598 Set the allowed elliptic curves/groups for the TLS session.
2600 These groups are allowed to be used in signatures and key ex‐
2601 change.
2602 mbedTLS currently allows all known curves per default.
2604 OpenSSL 1.1+ restricts the list per default to
2606 "X25519:secp256r1:X448:secp521r1:secp384r1".
2608 If you use certificates that use non-standard curves, you might
2610 need to add them here. If you do not force the ecdh curve by us‐
2611 ing --ecdh-curve, the groups for ecdh will also be picked from
2612 this list.
2613 OpenVPN maps the curve name secp256r1 to prime256v1 to allow
2615 specifying the same tls-groups option for mbedTLS and OpenSSL.
2616 Warning: this option not only affects elliptic curve certifi‐
2618 cates but also the key exchange in TLS 1.3 and using this option
2619 improperly will disable TLS 1.3.
2620 --tls-cert-profile profile
2622 Set the allowed cryptographic algorithms for certificates ac‐
2623 cording to profile.
2624 The following profiles are supported:
2626 legacy (default)
2628 SHA1 and newer, RSA 2048-bit+, any elliptic curve.
2629 preferred
2631 SHA2 and newer, RSA 2048-bit+, any elliptic curve.
2632 suiteb SHA256/SHA384, ECDSA with P-256 or P-384.
2634 This option is only fully supported for mbed TLS builds. OpenSSL
2636 builds use the following approximation:
2637 legacy (default)
2639 sets "security level 1"
2640 preferred
2642 sets "security level 2"
2643 suiteb sets "security level 3" and --tls-cipher "SUITEB128".
2645 OpenVPN will migrate to 'preferred' as default in the future.
2647 Please ensure that your keys already comply.
2648 WARNING: --tls-ciphers, --tls-ciphersuites and tls-groups
2650 These options are expert features, which - if used correctly -
2651 can improve the security of your VPN connection. But it is also
2652 easy to unwittingly use them to carefully align a gun with your
2653 foot, or just break your connection. Use with care!
2654 --tls-cipher l
2656 A list l of allowable TLS ciphers delimited by a colon (":").
2657 These setting can be used to ensure that certain cipher suites
2659 are used (or not used) for the TLS connection. OpenVPN uses TLS
2660 to secure the control channel, over which the keys that are used
2661 to protect the actual VPN traffic are exchanged.
2662 The supplied list of ciphers is (after potential OpenSSL/IANA
2664 name translation) simply supplied to the crypto library. Please
2665 see the OpenSSL and/or mbed TLS documentation for details on the
2666 cipher list interpretation.
2667 For OpenSSL, the --tls-cipher is used for TLS 1.2 and below.
2669 Use --show-tls to see a list of TLS ciphers supported by your
2671 crypto library.
2672 The default for --tls-cipher is to use mbed TLS's default cipher
2674 list when using mbed TLS or DE‐
2675 FAULT:!EXP:!LOW:!MEDIUM:!kDH:!kECDH:!DSS:!PSK:!SRP:!kRSA when
2676 using OpenSSL.
2677 --tls-ciphersuites l
2679 Same as --tls-cipher but for TLS 1.3 and up. mbed TLS has no TLS
2680 1.3 support yet and only the --tls-cipher setting is used.
2681 The default for --tls-ciphersuites is to use the crypto li‐
2683 brary's default.
2684 --tls-client
2686 Enable TLS and assume client role during TLS handshake.
2687 --tls-crypt keyfile
2689 Encrypt and authenticate all control channel packets with the
2690 key from keyfile. (See --tls-auth for more background.)
2691 Encrypting (and authenticating) control channel packets:
2693 • provides more privacy by hiding the certificate used for the
2695 TLS connection,
2696 • makes it harder to identify OpenVPN traffic as such,
2698 • provides "poor-man's" post-quantum security, against attackers
2700 who will never know the pre-shared key (i.e. no forward se‐
2701 crecy).
2702 In contrast to --tls-auth, --tls-crypt does not require the user
2704 to set --key-direction.
2705 Security Considerations
2707 All peers use the same --tls-crypt pre-shared group key to au‐
2709 thenticate and encrypt control channel messages. To ensure that
2710 IV collisions remain unlikely, this key should not be used to
2711 encrypt more than 2^48 client-to-server or 2^48 server-to-client
2712 control channel messages. A typical initial negotiation is about
2713 10 packets in each direction. Assuming both initial negotiation
2714 and renegotiations are at most 2^16 (65536) packets (to be con‐
2715 servative), and (re)negotiations happen each minute for each
2716 user (24/7), this limits the tls-crypt key lifetime to 8171
2717 years divided by the number of users. So a setup with 1000 users
2718 should rotate the key at least once each eight years. (And a
2719 setup with 8000 users each year.)
2720 If IV collisions were to occur, this could result in the secu‐
2722 rity of --tls-crypt degrading to the same security as using
2723 --tls-auth. That is, the control channel still benefits from
2724 the extra protection against active man-in-the-middle-attacks
2725 and DoS attacks, but may no longer offer extra privacy and
2726 post-quantum security on top of what TLS itself offers.
2727 For large setups or setups where clients are not trusted, con‐
2729 sider using --tls-crypt-v2 instead. That uses per-client unique
2730 keys, and thereby improves the bounds to 'rotate a client key at
2731 least once per 8000 years'.
2732 --tls-crypt-v2 keyfile
2734 Use client-specific tls-crypt keys.
2735 For clients, keyfile is a client-specific tls-crypt key. Such a
2737 key can be generated using the --genkey tls-crypt-v2-client op‐
2738 tion.
2739 For servers, keyfile is used to unwrap client-specific keys sup‐
2741 plied by the client during connection setup. This key must be
2742 the same as the key used to generate the client-specific key
2743 (see --genkey tls-crypt-v2-client).
2744 On servers, this option can be used together with the --tls-auth
2746 or --tls-crypt option. In that case, the server will detect
2747 whether the client is using client-specific keys, and automati‐
2748 cally select the right mode.
2749 --tls-crypt-v2-verify cmd
2751 Run command cmd to verify the metadata of the client-specific
2752 tls-crypt-v2 key of a connecting client. This allows server ad‐
2753 ministrators to reject client connections, before exposing the
2754 TLS stack (including the notoriously dangerous X.509 and ASN.1
2755 stacks) to the connecting client.
2756 OpenVPN supplies the following environment variables to the com‐
2758 mand:
2759 • script_type is set to tls-crypt-v2-verify
2761 • metadata_type is set to 0 if the metadata was user supplied,
2763 or 1 if it's a 64-bit unix timestamp representing the key cre‐
2764 ation time.
2765 • metadata_file contains the filename of a temporary file that
2767 contains the client metadata.
2768 The command can reject the connection by exiting with a non-zero
2770 exit code.
2771 --tls-exit
2773 Exit on TLS negotiation failure.
2774 --tls-export-cert directory
2776 Store the certificates the clients use upon connection to this
2777 directory. This will be done before --tls-verify is called. The
2778 certificates will use a temporary name and will be deleted when
2779 the tls-verify script returns. The file name used for the cer‐
2780 tificate is available via the peer_cert environment variable.
2781 --tls-server
2783 Enable TLS and assume server role during TLS handshake. Note
2784 that OpenVPN is designed as a peer-to-peer application. The des‐
2785 ignation of client or server is only for the purpose of negoti‐
2786 ating the TLS control channel.
2787 --tls-timeout n
2789 Packet retransmit timeout on TLS control channel if no acknowl‐
2790 edgment from remote within n seconds (default 2). When OpenVPN
2791 sends a control packet to its peer, it will expect to receive an
2792 acknowledgement within n seconds or it will retransmit the
2793 packet, subject to a TCP-like exponential backoff algorithm.
2794 This parameter only applies to control channel packets. Data
2795 channel packets (which carry encrypted tunnel data) are never
2796 acknowledged, sequenced, or retransmitted by OpenVPN because the
2797 higher level network protocols running on top of the tunnel such
2798 as TCP expect this role to be left to them.
2799 --tls-version-min args
2801 Sets the minimum TLS version we will accept from the peer (de‐
2802 fault is "1.0").
2803 Valid syntax:
2805 tls-version-min version ['or-highest']
2807 Examples for version include 1.0, 1.1, or 1.2. If or-highest is
2809 specified and version is not recognized, we will only accept the
2810 highest TLS version supported by the local SSL implementation.
2811 --tls-version-max version
2813 Set the maximum TLS version we will use (default is the highest
2814 version supported). Examples for version include 1.0, 1.1, or
2815 1.2.
2816 --verify-hash args
2818 Specify SHA1 or SHA256 fingerprint for level-1 cert.
2819 Valid syntax:
2821 verify-hash hash [algo]
2823 The level-1 cert is the CA (or intermediate cert) that signs the
2825 leaf certificate, and is one removed from the leaf certificate
2826 in the direction of the root. When accepting a connection from a
2827 peer, the level-1 cert fingerprint must match hash or certifi‐
2828 cate verification will fail. Hash is specified as XX:XX:... For
2829 example:
2830 AD:B0:95:D8:09:C8:36:45:12:A9:89:C8:90:09:CB:13:72:A6:AD:16
2832 The algo flag can be either SHA1 or SHA256. If not provided, it
2834 defaults to SHA1.
2835 --verify-x509-name args
2837 Accept connections only if a host's X.509 name is equal to name.
2838 The remote host must also pass all other tests of verification.
2839 Valid syntax:
2841 verify-x509 name type
2843 Which X.509 name is compared to name depends on the setting of
2845 type. type can be subject to match the complete subject DN (de‐
2846 fault), name to match a subject RDN or name-prefix to match a
2847 subject RDN prefix. Which RDN is verified as name depends on the
2848 --x509-username-field option. But it defaults to the common name
2849 (CN), e.g. a certificate with a subject DN
2850 C=KG, ST=NA, L=Bishkek, CN=Server-1
2852 would be matched by:
2854 verify-x509-name 'C=KG, ST=NA, L=Bishkek, CN=Server-1'
2856 verify-x509-name Server-1 name
2857 verify-x509-name Server- name-prefix
2858 The last example is useful if you want a client to only accept
2860 connections to Server-1, Server-2, etc.
2861 --verify-x509-name is a useful replacement for the --tls-verify
2863 option to verify the remote host, because --verify-x509-name
2864 works in a --chroot environment without any dependencies.
2865 Using a name prefix is a useful alternative to managing a CRL
2867 (Certificate Revocation List) on the client, since it allows the
2868 client to refuse all certificates except for those associated
2869 with designated servers.
2870 NOTE: Test against a name prefix only when you are using Open‐
2872 VPN with a custom CA certificate that is under your con‐
2873 trol. Never use this option with type name-prefix when
2874 your client certificates are signed by a third party,
2875 such as a commercial web CA.
2876 --x509-track attribute
2878 Save peer X509 attribute value in environment for use by plugins
2879 and management interface. Prepend a + to attribute to save val‐
2880 ues from full cert chain. Values will be encoded as
2881 X509_<depth>_<attribute>=<value>. Multiple --x509-track options
2882 can be defined to track multiple attributes.
2883 --x509-username-field args
2885 Field in the X.509 certificate subject to be used as the user‐
2886 name (default CN).
2887 Valid syntax:
2889 x509-username-field [ext:]fieldname
2891 Typically, this option is specified with fieldname as either of
2893 the following:
2894 x509-username-field emailAddress
2896 x509-username-field ext:subjectAltName
2897 The first example uses the value of the emailAddress attribute
2899 in the certificate's Subject field as the username. The second
2900 example uses the ext: prefix to signify that the X.509 extension
2901 fieldname subjectAltName be searched for an rfc822Name (email)
2902 field to be used as the username. In cases where there are mul‐
2903 tiple email addresses in ext:fieldname, the last occurrence is
2904 chosen.
2905 When this option is used, the --verify-x509-name option will
2907 match against the chosen fieldname instead of the Common Name.
2908 Only the subjectAltName and issuerAltName X.509 extensions are
2910 supported.
2911 Please note: This option has a feature which will convert an
2913 all-lowercase fieldname to uppercase characters, e.g., ou -> OU.
2914 A mixed-case fieldname or one having the ext: prefix will be
2915 left as-is. This automatic upcasing feature is deprecated and
2916 will be removed in a future release.
2917 PKCS#11 / SmartCard options
2919 --pkcs11-cert-private args
2920 Set if access to certificate object should be performed after
2921 login. Every provider has its own setting.
2922 Valid syntaxes:
2924 pkcs11-cert-private 0
2926 pkcs11-cert-private 1
2927 --pkcs11-id name
2929 Specify the serialized certificate id to be used. The id can be
2930 gotten by the standalone --show-pkcs11-ids option.
2931 --pkcs11-id-management
2933 Acquire PKCS#11 id from management interface. In this case a
2934 NEED-STR 'pkcs11-id-request' real-time message will be trig‐
2935 gered, application may use pkcs11-id-count command to retrieve
2936 available number of certificates, and pkcs11-id-get command to
2937 retrieve certificate id and certificate body.
2938 --pkcs11-pin-cache seconds
2940 Specify how many seconds the PIN can be cached, the default is
2941 until the token is removed.
2942 --pkcs11-private-mode mode
2944 Specify which method to use in order to perform private key op‐
2945 erations. A different mode can be specified for each provider.
2946 Mode is encoded as hex number, and can be a mask one of the fol‐
2947 lowing:
2948 0 (default) Try to determine automatically.
2950 1 Use sign.
2952 2 Use sign recover.
2954 4 Use decrypt.
2956 8 Use unwrap.
2958 --pkcs11-protected-authentication args
2960 Use PKCS#11 protected authentication path, useful for biometric
2961 and external keypad devices. Every provider has its own setting.
2962 Valid syntaxes:
2964 pkcs11-protected-authentication 0
2966 pkcs11-protected-authentication 1
2967 --pkcs11-providers provider
2969 Specify an RSA Security Inc. PKCS #11 Cryptographic Token Inter‐
2970 face (Cryptoki) providers to load. This option can be used in‐
2971 stead of --cert, --key and --pkcs12.
2972 If p11-kit is present on the system, its p11-kit-proxy.so module
2974 will be loaded by default if either the --pkcs11-id or
2975 --pkcs11-id-management options are specified without
2976 --pkcs11-provider being given.
2977 --show-pkcs11-ids args
2979 (Standalone) Show PKCS#11 token object list.
2980 Valid syntax:
2982 show-pkcs11 [provider] [cert_private]
2984 Specify cert_private as 1 if certificates are stored as private
2986 objects.
2987 If p11-kit is present on the system, the provider argument is
2989 optional; if omitted the default p11-kit-proxy.so module will be
2990 queried.
2991 --verb option can be used BEFORE this option to produce debug‐
2993 ging information.
2994
2996 OpenVPN 2.4 and higher have the capability to negotiate the data cipher
2997 that is used to encrypt data packets. This section describes the mecha‐
2998 nism in more detail and the different backwards compatibility mechanism
2999 with older server and clients.
3000 OpenVPN 2.5 and higher behaviour
3002 When both client and server are at least running OpenVPN 2.5, that the
3003 order of the ciphers of the server's --data-ciphers is used to pick the
3004 the data cipher. That means that the first cipher in that list that is
3005 also in the client's --data-ciphers list is chosen. If no common cipher
3006 is found the client is rejected with a AUTH_FAILED message (as seen in
3007 client log):
3008 AUTH: Received control message: AUTH_FAILED,Data channel cipher ne‐
3009 gotiation failed (no shared cipher)
3010 OpenVPN 2.5 will only allow the ciphers specified in --data-ciphers. To
3012 ensure backwards compatibility also if a cipher is specified using the
3013 --cipher option it is automatically added to this list. If both options
3014 are unset the default is AES-256-GCM:AES-128-GCM.
3015 OpenVPN 2.4 clients
3017 The negotiation support in OpenVPN 2.4 was the first iteration of the
3018 implementation and still had some quirks. Its main goal was "upgrade to
3019 AES-256-GCM when possible". An OpenVPN 2.4 client that is built
3020 against a crypto library that supports AES in GCM mode and does not
3021 have --ncp-disable will always announce support for AES-256-GCM and
3022 AES-128-GCM to a server by sending IV_NCP=2.
3023 This only causes a problem if --ncp-ciphers option has been changed
3025 from the default of AES-256-GCM:AES-128-GCM to a value that does not
3026 include these two ciphers. When a OpenVPN servers try to use
3027 AES-256-GCM or AES-128-GCM the connection will then fail. It is there‐
3028 fore recommended to always have the AES-256-GCM and AES-128-GCM ciphers
3029 to the --ncp-ciphers options to avoid this behaviour.
3030 OpenVPN 3 clients
3032 Clients based on the OpenVPN 3.x library (‐
3033 https://github.com/openvpn/openvpn3/) do not have a configurable
3034 --ncp-ciphers or --data-ciphers option. Instead these clients will an‐
3035 nounce support for all their supported AEAD ciphers (AES-256-GCM,
3036 AES-128-GCM and in newer versions also Chacha20-Poly1305).
3037 To support OpenVPN 3.x based clients at least one of these ciphers
3039 needs to be included in the server's --data-ciphers option.
3040 OpenVPN 2.3 and older clients (and clients with --ncp-disable)
3042 When a client without cipher negotiation support connects to a server
3043 the cipher specified with the --cipher option in the client configura‐
3044 tion must be included in the --data-ciphers option of the server to al‐
3045 low the client to connect. Otherwise the client will be sent the
3046 AUTH_FAILED message that indicates no shared cipher.
3047 If the client is 2.3 or older and has been configured with the --en‐
3049 able-small ./configure argument, using data-ciphers-fallback cipher in
3050 the server config file with the explicit cipher used by the client is
3051 necessary.
3052 OpenVPN 2.4 server
3054 When a client indicates support for AES-128-GCM and AES-256-GCM (with
3055 IV_NCP=2) an OpenVPN 2.4 server will send the first cipher of the
3056 --ncp-ciphers to the OpenVPN client regardless of what the cipher is.
3057 To emulate the behaviour of an OpenVPN 2.4 client as close as possible
3058 and have compatibility to a setup that depends on this quirk, adding
3059 AES-128-GCM and AES-256-GCM to the client's --data-ciphers option is
3060 required. OpenVPN 2.5+ will only announce the IV_NCP=2 flag if those
3061 ciphers are present.
3062 OpenVPN 2.3 and older servers (and servers with --ncp-disable)
3064 The cipher used by the server must be included in --data-ciphers to al‐
3065 low the client connecting to a server without cipher negotiation sup‐
3066 port. (For compatibility OpenVPN 2.5 will also accept the cipher set
3067 with --cipher)
3068 If the server is 2.3 or older and has been configured with the --en‐
3070 able-small ./configure argument, adding data-ciphers-fallback cipher to
3071 the client config with the explicit cipher used by the server is neces‐
3072 sary.
3073 Blowfish in CBC mode (BF-CBC) deprecation
3075 The --cipher option defaulted to BF-CBC in OpenVPN 2.4 and older ver‐
3076 sion. The default was never changed to ensure backwards compatibility.
3077 In OpenVPN 2.5 this behaviour has now been changed so that if the --ci‐
3078 pher is not explicitly set it does not allow the weak BF-CBC cipher any
3079 more and needs to explicitly added as --cipher BFC-CBC or added to
3080 --data-ciphers.
3081 We strongly recommend to switching away from BF-CBC to a more secure
3083 cipher as soon as possible instead.
3084
3086 OpenVPN consists of two sides of network configuration. One side is
3087 the link between the local and remote side, the other side is the vir‐
3088 tual network adapter (tun/tap device).
3089 Link Options
3091 This link options section covers options related to the connection be‐
3092 tween the local and the remote host.
3093 --bind keywords
3095 Bind to local address and port. This is the default unless any
3096 of --proto tcp-client , --http-proxy or --socks-proxy are used.
3097 If the optional ipv6only keyword is present OpenVPN will bind
3099 only to IPv6 (as opposed to IPv6 and IPv4) when a IPv6 socket is
3100 opened.
3101 --float
3103 Allow remote peer to change its IP address and/or port number,
3104 such as due to DHCP (this is the default if --remote is not
3105 used). --float when specified with --remote allows an OpenVPN
3106 session to initially connect to a peer at a known address, how‐
3107 ever if packets arrive from a new address and pass all authenti‐
3108 cation tests, the new address will take control of the session.
3109 This is useful when you are connecting to a peer which holds a
3110 dynamic address such as a dial-in user or DHCP client.
3111 Essentially, --float tells OpenVPN to accept authenticated pack‐
3113 ets from any address, not only the address which was specified
3114 in the --remote option.
3115 --fragment max
3117 Enable internal datagram fragmentation so that no UDP datagrams
3118 are sent which are larger than max bytes.
3119 The max parameter is interpreted in the same way as the
3121 --link-mtu parameter, i.e. the UDP packet size after encapsula‐
3122 tion overhead has been added in, but not including the UDP
3123 header itself.
3124 The --fragment option only makes sense when you are using the
3126 UDP protocol (--proto udp).
3127 --fragment adds 4 bytes of overhead per datagram.
3129 See the --mssfix option below for an important related option to
3131 --fragment.
3132 It should also be noted that this option is not meant to replace
3134 UDP fragmentation at the IP stack level. It is only meant as a
3135 last resort when path MTU discovery is broken. Using this option
3136 is less efficient than fixing path MTU discovery for your IP
3137 link and using native IP fragmentation instead.
3138 Having said that, there are circumstances where using OpenVPN's
3140 internal fragmentation capability may be your only option, such
3141 as tunneling a UDP multicast stream which requires fragmenta‐
3142 tion.
3143 --keepalive args
3145 A helper directive designed to simplify the expression of --ping
3146 and --ping-restart.
3147 Valid syntax:
3149 keepalive interval timeout
3151 This option can be used on both client and server side, but it
3153 is enough to add this on the server side as it will push appro‐
3154 priate --ping and --ping-restart options to the client. If used
3155 on both server and client, the values pushed from server will
3156 override the client local values.
3157 The timeout argument will be twice as long on the server side.
3159 This ensures that a timeout is detected on client side before
3160 the server side drops the connection.
3161 For example, --keepalive 10 60 expands as follows:
3163 if mode server:
3165 ping 10 # Argument: interval
3166 ping-restart 120 # Argument: timeout*2
3167 push "ping 10" # Argument: interval
3168 push "ping-restart 60" # Argument: timeout
3169 else
3170 ping 10 # Argument: interval
3171 ping-restart 60 # Argument: timeout
3172 --link-mtu n
3174 Sets an upper bound on the size of UDP packets which are sent
3175 between OpenVPN peers. It's best not to set this parameter un‐
3176 less you know what you're doing.
3177 --local host
3179 Local host name or IP address for bind. If specified, OpenVPN
3180 will bind to this address only. If unspecified, OpenVPN will
3181 bind to all interfaces.
3182 --lport port
3184 Set local TCP/UDP port number or name. Cannot be used together
3185 with --nobind option.
3186 --mark value
3188 Mark encrypted packets being sent with value. The mark value can
3189 be matched in policy routing and packetfilter rules. This option
3190 is only supported in Linux and does nothing on other operating
3191 systems.
3192 --mode m
3194 Set OpenVPN major mode. By default, OpenVPN runs in
3195 point-to-point mode (p2p). OpenVPN 2.0 introduces a new mode
3196 (server) which implements a multi-client server capability.
3197 --mssfix max
3199 Announce to TCP sessions running over the tunnel that they
3200 should limit their send packet sizes such that after OpenVPN has
3201 encapsulated them, the resulting UDP packet size that OpenVPN
3202 sends to its peer will not exceed max bytes. The default value
3203 is 1450.
3204 The max parameter is interpreted in the same way as the
3206 --link-mtu parameter, i.e. the UDP packet size after encapsula‐
3207 tion overhead has been added in, but not including the UDP
3208 header itself. Resulting packet would be at most 28 bytes
3209 larger for IPv4 and 48 bytes for IPv6 (20/40 bytes for IP header
3210 and 8 bytes for UDP header). Default value of 1450 allows IPv4
3211 packets to be transmitted over a link with MTU 1473 or higher
3212 without IP level fragmentation.
3213 The --mssfix option only makes sense when you are using the UDP
3215 protocol for OpenVPN peer-to-peer communication, i.e. --proto
3216 udp.
3217 --mssfix and --fragment can be ideally used together, where
3219 --mssfix will try to keep TCP from needing packet fragmentation
3220 in the first place, and if big packets come through anyhow (from
3221 protocols other than TCP), --fragment will internally fragment
3222 them.
3223 Both --fragment and --mssfix are designed to work around cases
3225 where Path MTU discovery is broken on the network path between
3226 OpenVPN peers.
3227 The usual symptom of such a breakdown is an OpenVPN connection
3229 which successfully starts, but then stalls during active usage.
3230 If --fragment and --mssfix are used together, --mssfix will take
3232 its default max parameter from the --fragment max option.
3233 Therefore, one could lower the maximum UDP packet size to 1300
3235 (a good first try for solving MTU-related connection problems)
3236 with the following options:
3237 --tun-mtu 1500 --fragment 1300 --mssfix
3239 --mtu-disc type
3241 Should we do Path MTU discovery on TCP/UDP channel? Only sup‐
3242 ported on OSes such as Linux that supports the necessary system
3243 call to set.
3244 Valid types:
3246 no Never send DF (Don't Fragment) frames
3248 maybe Use per-route hints
3250 yes Always DF (Don't Fragment)
3252 --mtu-test
3254 To empirically measure MTU on connection startup, add the
3255 --mtu-test option to your configuration. OpenVPN will send ping
3256 packets of various sizes to the remote peer and measure the
3257 largest packets which were successfully received. The --mtu-test
3258 process normally takes about 3 minutes to complete.
3259 --nobind
3261 Do not bind to local address and port. The IP stack will allo‐
3262 cate a dynamic port for returning packets. Since the value of
3263 the dynamic port could not be known in advance by a peer, this
3264 option is only suitable for peers which will be initiating con‐
3265 nections by using the --remote option.
3266 --passtos
3268 Set the TOS field of the tunnel packet to what the payload's TOS
3269 is.
3270 --ping n
3272 Ping remote over the TCP/UDP control channel if no packets have
3273 been sent for at least n seconds (specify --ping on both peers
3274 to cause ping packets to be sent in both directions since Open‐
3275 VPN ping packets are not echoed like IP ping packets). When used
3276 in one of OpenVPN's secure modes (where --secret, --tls-server
3277 or --tls-client is specified), the ping packet will be crypto‐
3278 graphically secure.
3279 This option has two intended uses:
3281 1. Compatibility with stateful firewalls. The periodic ping will
3283 ensure that a stateful firewall rule which allows OpenVPN UDP
3284 packets to pass will not time out.
3285 2. To provide a basis for the remote to test the existence of
3287 its peer using the --ping-exit option.
3288 --ping-exit n
3290 Causes OpenVPN to exit after n seconds pass without reception of
3291 a ping or other packet from remote. This option can be combined
3292 with --inactive, --ping and --ping-exit to create a two-tiered
3293 inactivity disconnect.
3294 For example,
3296 openvpn [options...] --inactive 3600 --ping 10 --ping-exit 60
3298 when used on both peers will cause OpenVPN to exit within 60
3300 seconds if its peer disconnects, but will exit after one hour if
3301 no actual tunnel data is exchanged.
3302 --ping-restart n
3304 Similar to --ping-exit, but trigger a SIGUSR1 restart after n
3305 seconds pass without reception of a ping or other packet from
3306 remote.
3307 This option is useful in cases where the remote peer has a dy‐
3309 namic IP address and a low-TTL DNS name is used to track the IP
3310 address using a service such as http://dyndns.org/ + a dynamic
3311 DNS client such as ddclient.
3312 If the peer cannot be reached, a restart will be triggered,
3314 causing the hostname used with --remote to be re-resolved (if
3315 --resolv-retry is also specified).
3316 In server mode, --ping-restart, --inactive or any other type of
3318 internally generated signal will always be applied to individual
3319 client instance objects, never to whole server itself. Note also
3320 in server mode that any internally generated signal which would
3321 normally cause a restart, will cause the deletion of the client
3322 instance object instead.
3323 In client mode, the --ping-restart parameter is set to 120 sec‐
3325 onds by default. This default will hold until the client pulls a
3326 replacement value from the server, based on the --keepalive set‐
3327 ting in the server configuration. To disable the 120 second de‐
3328 fault, set --ping-restart 0 on the client.
3329 See the signals section below for more information on SIGUSR1.
3331 Note that the behavior of SIGUSR1 can be modified by the --per‐
3333 sist-tun, --persist-key, --persist-local-ip and --persist-re‐
3334 mote-ip options.
3335 Also note that --ping-exit and --ping-restart are mutually ex‐
3337 clusive and cannot be used together.
3338 --ping-timer-rem
3340 Run the --ping-exit / --ping-restart timer only if we have a re‐
3341 mote address. Use this option if you are starting the daemon in
3342 listen mode (i.e. without an explicit --remote peer), and you
3343 don't want to start clocking timeouts until a remote peer con‐
3344 nects.
3345 --proto p
3347 Use protocol p for communicating with remote host. p can be udp,
3348 tcp-client, or tcp-server.
3349 The default protocol is udp when --proto is not specified.
3351 For UDP operation, --proto udp should be specified on both
3353 peers.
3354 For TCP operation, one peer must use --proto tcp-server and the
3356 other must use --proto tcp-client. A peer started with
3357 tcp-server will wait indefinitely for an incoming connection. A
3358 peer started with tcp-client will attempt to connect, and if
3359 that fails, will sleep for 5 seconds (adjustable via the --con‐
3360 nect-retry option) and try again infinite or up to N retries
3361 (adjustable via the --connect-retry-max option). Both TCP client
3362 and server will simulate a SIGUSR1 restart signal if either side
3363 resets the connection.
3364 OpenVPN is designed to operate optimally over UDP, but TCP capa‐
3366 bility is provided for situations where UDP cannot be used. In
3367 comparison with UDP, TCP will usually be somewhat less efficient
3368 and less robust when used over unreliable or congested networks.
3369 This article outlines some of problems with tunneling IP over
3371 TCP: http://sites.inka.de/sites/bigred/devel/tcp-tcp.html
3372 There are certain cases, however, where using TCP may be advan‐
3374 tageous from a security and robustness perspective, such as tun‐
3375 neling non-IP or application-level UDP protocols, or tunneling
3376 protocols which don't possess a built-in reliability layer.
3377 --port port
3379 TCP/UDP port number or port name for both local and remote (sets
3380 both --lport and --rport options to given port). The current de‐
3381 fault of 1194 represents the official IANA port number assign‐
3382 ment for OpenVPN and has been used since version 2.0-beta17.
3383 Previous versions used port 5000 as the default.
3384 --rport port
3386 Set TCP/UDP port number or name used by the --remote option. The
3387 port can also be set directly using the --remote option.
3388 --replay-window args
3390 Modify the replay protection sliding-window size and time win‐
3391 dow.
3392 Valid syntax:
3394 replay-window n [t]
3396 Use a replay protection sliding-window of size n and a time win‐
3398 dow of t seconds.
3399 By default n is 64 (the IPSec default) and t is 15 seconds.
3401 This option is only relevant in UDP mode, i.e. when either
3403 --proto udp is specified, or no --proto option is specified.
3404 When OpenVPN tunnels IP packets over UDP, there is the possibil‐
3406 ity that packets might be dropped or delivered out of order. Be‐
3407 cause OpenVPN, like IPSec, is emulating the physical network
3408 layer, it will accept an out-of-order packet sequence, and will
3409 deliver such packets in the same order they were received to the
3410 TCP/IP protocol stack, provided they satisfy several con‐
3411 straints.
3412 a. The packet cannot be a replay (unless --no-replay is speci‐
3414 fied, which disables replay protection altogether).
3415 b. If a packet arrives out of order, it will only be accepted if
3417 the difference between its sequence number and the highest
3418 sequence number received so far is less than n.
3419 c. If a packet arrives out of order, it will only be accepted if
3421 it arrives no later than t seconds after any packet contain‐
3422 ing a higher sequence number.
3423 If you are using a network link with a large pipeline (meaning
3425 that the product of bandwidth and latency is high), you may want
3426 to use a larger value for n. Satellite links in particular often
3427 require this.
3428 If you run OpenVPN at --verb 4, you will see the message "Re‐
3430 play-window backtrack occurred [x]" every time the maximum se‐
3431 quence number backtrack seen thus far increases. This can be
3432 used to calibrate n.
3433 There is some controversy on the appropriate method of handling
3435 packet reordering at the security layer.
3436 Namely, to what extent should the security layer protect the en‐
3438 capsulated protocol from attacks which masquerade as the kinds
3439 of normal packet loss and reordering that occur over IP net‐
3440 works?
3441 The IPSec and OpenVPN approach is to allow packet reordering
3443 within a certain fixed sequence number window.
3444 OpenVPN adds to the IPSec model by limiting the window size in
3446 time as well as sequence space.
3447 OpenVPN also adds TCP transport as an option (not offered by
3449 IPSec) in which case OpenVPN can adopt a very strict attitude
3450 towards message deletion and reordering: Don't allow it. Since
3451 TCP guarantees reliability, any packet loss or reordering event
3452 can be assumed to be an attack.
3453 In this sense, it could be argued that TCP tunnel transport is
3455 preferred when tunneling non-IP or UDP application protocols
3456 which might be vulnerable to a message deletion or reordering
3457 attack which falls within the normal operational parameters of
3458 IP networks.
3459 So I would make the statement that one should never tunnel a
3461 non-IP protocol or UDP application protocol over UDP, if the
3462 protocol might be vulnerable to a message deletion or reordering
3463 attack that falls within the normal operating parameters of what
3464 is to be expected from the physical IP layer. The problem is
3465 easily fixed by simply using TCP as the VPN transport layer.
3466 --replay-persist file
3468 Persist replay-protection state across sessions using file to
3469 save and reload the state.
3470 This option will strengthen protection against replay attacks,
3472 especially when you are using OpenVPN in a dynamic context (such
3473 as with --inetd) when OpenVPN sessions are frequently started
3474 and stopped.
3475 This option will keep a disk copy of the current replay protec‐
3477 tion state (i.e. the most recent packet timestamp and sequence
3478 number received from the remote peer), so that if an OpenVPN
3479 session is stopped and restarted, it will reject any replays of
3480 packets which were already received by the prior session.
3481 This option only makes sense when replay protection is enabled
3483 (the default) and you are using either --secret (shared-secret
3484 key mode) or TLS mode with --tls-auth.
3485 --socket-flags flags
3487 Apply the given flags to the OpenVPN transport socket. Cur‐
3488 rently, only TCP_NODELAY is supported.
3489 The TCP_NODELAY socket flag is useful in TCP mode, and causes
3491 the kernel to send tunnel packets immediately over the TCP con‐
3492 nection without trying to group several smaller packets into a
3493 larger packet. This can result in a considerably improvement in
3494 latency.
3495 This option is pushable from server to client, and should be
3497 used on both client and server for maximum effect.
3498 --tcp-nodelay
3500 This macro sets the TCP_NODELAY socket flag on the server as
3501 well as pushes it to connecting clients. The TCP_NODELAY flag
3502 disables the Nagle algorithm on TCP sockets causing packets to
3503 be transmitted immediately with low latency, rather than waiting
3504 a short period of time in order to aggregate several packets
3505 into a larger containing packet. In VPN applications over TCP,
3506 TCP_NODELAY is generally a good latency optimization.
3507 The macro expands as follows:
3509 if mode server:
3511 socket-flags TCP_NODELAY
3512 push "socket-flags TCP_NODELAY"
3513 Virtual Network Adapter (VPN interface)
3515 Options in this section relates to configuration of the virtual tun/tap
3516 network interface, including setting the VPN IP address and network
3517 routing.
3518 --bind-dev device
3520 (Linux only) Set device to bind the server socket to a Virtual
3521 Routing and Forwarding device
3522 --block-ipv6
3524 On the client, instead of sending IPv6 packets over the VPN tun‐
3525 nel, all IPv6 packets are answered with an ICMPv6 no route host
3526 message. On the server, all IPv6 packets from clients are an‐
3527 swered with an ICMPv6 no route to host message. This options is
3528 intended for cases when IPv6 should be blocked and other options
3529 are not available. --block-ipv6 will use the remote IPv6 as
3530 source address of the ICMPv6 packets if set, otherwise will use
3531 fe80::7 as source address.
3532 For this option to make sense you actually have to route traffic
3534 to the tun interface. The following example config block would
3535 send all IPv6 traffic to OpenVPN and answer all requests with no
3536 route to host, effectively blocking IPv6 (to avoid IPv6 connec‐
3537 tions from dual-stacked clients leaking around IPv4-only VPN
3538 services).
3539 Client config
3541 --ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1
3543 --redirect-gateway ipv6
3544 --block-ipv6
3545 Server config
3547 Push a "valid" ipv6 config to the client and block on the
3548 server
3549 --push "ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1"
3551 --push "redirect-gateway ipv6"
3552 --block-ipv6
3553 Note: this option does not influence traffic sent from the
3555 server towards the client (neither on the server nor on the
3556 client side). This is not seen as necessary, as such traffic
3557 can be most easily avoided by not configuring IPv6 on the server
3558 tun, or setting up a server-side firewall rule.
3559 --dev device
3561 TUN/TAP virtual network device which can be tunX, tapX, null or
3562 an arbitrary name string (X can be omitted for a dynamic de‐
3563 vice.)
3564 See examples section below for an example on setting up a TUN
3566 device.
3567 You must use either tun devices on both ends of the connection
3569 or tap devices on both ends. You cannot mix them, as they repre‐
3570 sent different underlying network layers:
3571 tun devices encapsulate IPv4 or IPv6 (OSI Layer 3)
3573 tap devices encapsulate Ethernet 802.3 (OSI Layer 2).
3575 Valid syntaxes:
3577 dev tun2
3579 dev tap4
3580 dev ovpn
3581 When the device name starts with tun or tap, the device type is
3583 extracted automatically. Otherwise the --dev-type option needs
3584 to be added as well.
3585 --dev-node node
3587 Explicitly set the device node rather than using /dev/net/tun,
3588 /dev/tun, /dev/tap, etc. If OpenVPN cannot figure out whether
3589 node is a TUN or TAP device based on the name, you should also
3590 specify --dev-type tun or --dev-type tap.
3591 Under Mac OS X this option can be used to specify the default
3593 tun implementation. Using --dev-node utun forces usage of the
3594 native Darwin tun kernel support. Use --dev-node utunN to select
3595 a specific utun instance. To force using the tun.kext
3596 (/dev/tunX) use --dev-node tun. When not specifying a --dev-node
3597 option openvpn will first try to open utun, and fall back to
3598 tun.kext.
3599 On Windows systems, select the TAP-Win32 adapter which is named
3601 node in the Network Connections Control Panel or the raw GUID of
3602 the adapter enclosed by braces. The --show-adapters option under
3603 Windows can also be used to enumerate all available TAP-Win32
3604 adapters and will show both the network connections control
3605 panel name and the GUID for each TAP-Win32 adapter.
3606 --dev-type device-type
3608 Which device type are we using? device-type should be tun (OSI
3609 Layer 3) or tap (OSI Layer 2). Use this option only if the
3610 TUN/TAP device used with --dev does not begin with tun or tap.
3611 --dhcp-option args
3613 Set additional network parameters on supported platforms. May be
3614 specified on the client or pushed from the server. On Windows
3615 these options are handled by the tap-windows6 driver by default
3616 or directly by OpenVPN if dhcp is disabled or the wintun driver
3617 is in use. The OpenVPN for Android client also handles them in‐
3618 ternally.
3619 On all other platforms these options are only saved in the
3621 client's environment under the name foreign_options_{n} before
3622 the --up script is called. A plugin or an --up script must be
3623 used to pick up and interpret these as required. Many Linux dis‐
3624 tributions include such scripts and some third-party user inter‐
3625 faces such as tunnelblick also come with scripts that process
3626 these options.
3627 Valid syntax:
3629 dhcp-options type [parm]
3631 DOMAIN name
3633 Set Connection-specific DNS Suffix to name.
3634 ADAPTER_DOMAIN_SUFFIX name
3636 Alias to DOMAIN. This is a compatibility option, it
3637 should not be used in new deployments.
3638 DOMAIN-SEARCH name
3640 Add name to the domain search list. Repeat this option
3641 to add more entries. Up to 10 domains are supported.
3642 DNS address
3644 Set primary domain name server IPv4 or IPv6 address. Re‐
3645 peat this option to set secondary DNS server addresses.
3646 Note: DNS IPv6 servers are currently set using netsh (the
3648 existing DHCP code can only do IPv4 DHCP, and that proto‐
3649 col only permits IPv4 addresses anywhere). The option
3650 will be put into the environment, so an --up script could
3651 act upon it if needed.
3652 WINS address
3654 Set primary WINS server address (NetBIOS over TCP/IP Name
3655 Server). Repeat this option to set secondary WINS server
3656 addresses.
3657 NBDD address
3659 Set primary NBDD server address (NetBIOS over TCP/IP
3660 Datagram Distribution Server). Repeat this option to set
3661 secondary NBDD server addresses.
3662 NTP address
3664 Set primary NTP server address (Network Time Protocol).
3665 Repeat this option to set secondary NTP server addresses.
3666 NBT type
3668 Set NetBIOS over TCP/IP Node type. Possible options:
3669 1 b-node (broadcasts)
3671 2 p-node (point-to-point name queries to a WINS
3673 server)
3674 4 m-node (broadcast then query name server)
3676 8 h-node (query name server, then broadcast).
3678 NBS scope-id
3680 Set NetBIOS over TCP/IP Scope. A NetBIOS Scope ID pro‐
3681 vides an extended naming service for the NetBIOS over
3682 TCP/IP (Known as NBT) module. The primary purpose of a
3683 NetBIOS scope ID is to isolate NetBIOS traffic on a sin‐
3684 gle network to only those nodes with the same NetBIOS
3685 scope ID. The NetBIOS scope ID is a character string that
3686 is appended to the NetBIOS name. The NetBIOS scope ID on
3687 two hosts must match, or the two hosts will not be able
3688 to communicate. The NetBIOS Scope ID also allows comput‐
3689 ers to use the same computer name, as they have different
3690 scope IDs. The Scope ID becomes a part of the NetBIOS
3691 name, making the name unique. (This description of Net‐
3692 BIOS scopes courtesy of NeonSurge@abyss.com)
3693 DISABLE-NBT
3695 Disable Netbios-over-TCP/IP.
3696 --ifconfig args
3698 Set TUN/TAP adapter parameters. It requires the IP address of
3699 the local VPN endpoint. For TUN devices in point-to-point mode,
3700 the next argument must be the VPN IP address of the remote VPN
3701 endpoint. For TAP devices, or TUN devices used with --topology
3702 subnet, the second argument is the subnet mask of the virtual
3703 network segment which is being created or connected to.
3704 For TUN devices, which facilitate virtual point-to-point IP con‐
3706 nections (when used in --topology net30 or p2p mode), the proper
3707 usage of --ifconfig is to use two private IP addresses which are
3708 not a member of any existing subnet which is in use. The IP ad‐
3709 dresses may be consecutive and should have their order reversed
3710 on the remote peer. After the VPN is established, by pinging
3711 rn, you will be pinging across the VPN.
3712 For TAP devices, which provide the ability to create virtual
3714 ethernet segments, or TUN devices in --topology subnet mode
3715 (which create virtual "multipoint networks"), --ifconfig is used
3716 to set an IP address and subnet mask just as a physical ethernet
3717 adapter would be similarly configured. If you are attempting to
3718 connect to a remote ethernet bridge, the IP address and subnet
3719 should be set to values which would be valid on the the bridged
3720 ethernet segment (note also that DHCP can be used for the same
3721 purpose).
3722 This option, while primarily a proxy for the ifconfig(8) com‐
3724 mand, is designed to simplify TUN/TAP tunnel configuration by
3725 providing a standard interface to the different ifconfig imple‐
3726 mentations on different platforms.
3727 --ifconfig parameters which are IP addresses can also be speci‐
3729 fied as a DNS or /etc/hosts file resolvable name.
3730 For TAP devices, --ifconfig should not be used if the TAP inter‐
3732 face will be getting an IP address lease from a DHCP server.
3733 Examples:
3735 # tun device in net30/p2p mode
3737 ifconfig 10.8.0.2 10.8.0.1
3738 # tun/tap device in subnet mode
3740 ifconfig 10.8.0.2 255.255.255.0
3741 --ifconfig-ipv6 args
3743 Configure an IPv6 address on the tun device.
3744 Valid syntax:
3746 ifconfig-ipv6 ipv6addr/bits [ipv6remote]
3748 The ipv6addr/bits argument is the IPv6 address to use. The sec‐
3750 ond parameter is used as route target for --route-ipv6 if no
3751 gateway is specified.
3752 The --topology option has no influence with --ifconfig-ipv6
3754 --ifconfig-noexec
3756 Don't actually execute ifconfig/netsh commands, instead pass
3757 --ifconfig parameters to scripts using environmental variables.
3758 --ifconfig-nowarn
3760 Don't output an options consistency check warning if the --if‐
3761 config option on this side of the connection doesn't match the
3762 remote side. This is useful when you want to retain the overall
3763 benefits of the options consistency check (also see --dis‐
3764 able-occ option) while only disabling the ifconfig component of
3765 the check.
3766 For example, if you have a configuration where the local host
3768 uses --ifconfig but the remote host does not, use --ifcon‐
3769 fig-nowarn on the local host.
3770 This option will also silence warnings about potential address
3772 conflicts which occasionally annoy more experienced users by
3773 triggering "false positive" warnings.
3774 --lladdr address
3776 Specify the link layer address, more commonly known as the MAC
3777 address. Only applied to TAP devices.
3778 --persist-tun
3780 Don't close and reopen TUN/TAP device or run up/down scripts
3781 across SIGUSR1 or --ping-restart restarts.
3782 SIGUSR1 is a restart signal similar to SIGHUP, but which offers
3784 finer-grained control over reset options.
3785 --redirect-gateway flags
3787 Automatically execute routing commands to cause all outgoing IP
3788 traffic to be redirected over the VPN. This is a client-side op‐
3789 tion.
3790 This option performs three steps:
3792 1. Create a static route for the --remote address which forwards
3794 to the pre-existing default gateway. This is done so that [1m(3)
3795 will not create a routing loop.
3796 2. Delete the default gateway route.
3798 3. Set the new default gateway to be the VPN endpoint address
3800 (derived either from --route-gateway or the second parameter
3801 to --ifconfig when --dev tun is specified).
3802 When the tunnel is torn down, all of the above steps are re‐
3804 versed so that the original default route is restored.
3805 Option flags:
3807 local Add the local flag if both OpenVPN peers are directly
3809 connected via a common subnet, such as with wireless. The
3810 local flag will cause step [1m(1) above to be omitted.
3811 autolocal
3813 Try to automatically determine whether to enable local
3814 flag above.
3815 def1 Use this flag to override the default gateway by using
3817 0.0.0.0/1 and 128.0.0.0/1 rather than 0.0.0.0/0. This has
3818 the benefit of overriding but not wiping out the original
3819 default gateway.
3820 bypass-dhcp
3822 Add a direct route to the DHCP server (if it is non-lo‐
3823 cal) which bypasses the tunnel (Available on Windows
3824 clients, may not be available on non-Windows clients).
3825 bypass-dns
3827 Add a direct route to the DNS server(s) (if they are
3828 non-local) which bypasses the tunnel (Available on Win‐
3829 dows clients, may not be available on non-Windows
3830 clients).
3831 block-local
3833 Block access to local LAN when the tunnel is active, ex‐
3834 cept for the LAN gateway itself. This is accomplished by
3835 routing the local LAN (except for the LAN gateway ad‐
3836 dress) into the tunnel.
3837 ipv6 Redirect IPv6 routing into the tunnel. This works similar
3839 to the def1 flag, that is, more specific IPv6 routes are
3840 added (2000::/4, 3000::/4), covering the whole IPv6 uni‐
3841 cast space.
3842 !ipv4 Do not redirect IPv4 traffic - typically used in the flag
3844 pair ipv6 !ipv4 to redirect IPv6-only.
3845 --redirect-private flags
3847 Like --redirect-gateway, but omit actually changing the default
3848 gateway. Useful when pushing private subnets.
3849 --route args
3851 Add route to routing table after connection is established. Mul‐
3852 tiple routes can be specified. Routes will be automatically torn
3853 down in reverse order prior to TUN/TAP device close.
3854 Valid syntaxes:
3856 route network/IP
3858 route network/IP netmask
3859 route network/IP netmask gateway
3860 route network/IP netmask gateway metric
3861 This option is intended as a convenience proxy for the route(8)
3863 shell command, while at the same time providing portable seman‐
3864 tics across OpenVPN's platform space.
3865 netmask
3867 defaults to 255.255.255.255 when not given
3868 gateway
3870 default taken from --route-gateway or the second parame‐
3871 ter to --ifconfig when --dev tun is specified.
3872 metric default taken from --route-metric if set, otherwise 0.
3874 The default can be specified by leaving an option blank or set‐
3876 ting it to default.
3877 The network and gateway parameters can also be specified as a
3879 DNS or /etc/hosts file resolvable name, or as one of three spe‐
3880 cial keywords:
3881 vpn_gateway
3883 The remote VPN endpoint address (derived either from
3884 --route-gateway or the second parameter to --ifconfig
3885 when --dev tun is specified).
3886 net_gateway
3888 The pre-existing IP default gateway, read from the rout‐
3889 ing table (not supported on all OSes).
3890 remote_host
3892 The --remote address if OpenVPN is being run in client
3893 mode, and is undefined in server mode.
3894 --route-delay args
3896 Valid syntaxes:
3897 route-delay
3899 route-delay n
3900 route-delay n m
3901 Delay n seconds (default 0) after connection establishment, be‐
3903 fore adding routes. If n is 0, routes will be added immediately
3904 upon connection establishment. If --route-delay is omitted,
3905 routes will be added immediately after TUN/TAP device open and
3906 --up script execution, before any --user or --group privilege
3907 downgrade (or --chroot execution.)
3908 This option is designed to be useful in scenarios where DHCP is
3910 used to set tap adapter addresses. The delay will give the DHCP
3911 handshake time to complete before routes are added.
3912 On Windows, --route-delay tries to be more intelligent by wait‐
3914 ing w seconds (default 30 by default) for the TAP-Win32 adapter
3915 to come up before adding routes.
3916 --route-ipv6 args
3918 Setup IPv6 routing in the system to send the specified IPv6 net‐
3919 work into OpenVPN's tun.
3920 Valid syntax:
3922 route-ipv6 ipv6addr/bits [gateway] [metric]
3924 The gateway parameter is only used for IPv6 routes across tap
3926 devices, and if missing, the ipv6remote field from --ifcon‐
3927 fig-ipv6 or --route-ipv6-gateway is used.
3928 --route-gateway arg
3930 Specify a default gateway for use with --route.
3931 If dhcp is specified as the parameter, the gateway address will
3933 be extracted from a DHCP negotiation with the OpenVPN
3934 server-side LAN.
3935 Valid syntaxes:
3937 route-gateway gateway
3939 route-gateway dhcp
3940 --route-ipv6-gateway gw
3942 Specify a default gateway gw for use with --route-ipv6.
3943 --route-metric m
3945 Specify a default metric m for use with --route.
3946 --route-noexec
3948 Don't add or remove routes automatically. Instead pass routes to
3949 --route-up script using environmental variables.
3950 --route-nopull
3952 When used with --client or --pull, accept options pushed by
3953 server EXCEPT for routes, block-outside-dns and dhcp options
3954 like DNS servers.
3955 When used on the client, this option effectively bars the server
3957 from adding routes to the client's routing table, however note
3958 that this option still allows the server to set the TCP/IP prop‐
3959 erties of the client's TUN/TAP interface.
3960 --topology mode
3962 Configure virtual addressing topology when running in --dev tun
3963 mode. This directive has no meaning in --dev tap mode, which al‐
3964 ways uses a subnet topology.
3965 If you set this directive on the server, the --server and
3967 --server-bridge directives will automatically push your chosen
3968 topology setting to clients as well. This directive can also be
3969 manually pushed to clients. Like the --dev directive, this di‐
3970 rective must always be compatible between client and server.
3971 mode can be one of:
3973 net30 Use a point-to-point topology, by allocating one /30 sub‐
3975 net per client. This is designed to allow point-to-point
3976 semantics when some or all of the connecting clients
3977 might be Windows systems. This is the default on OpenVPN
3978 2.0.
3979 p2p Use a point-to-point topology where the remote endpoint
3981 of the client's tun interface always points to the local
3982 endpoint of the server's tun interface. This mode allo‐
3983 cates a single IP address per connecting client. Only use
3984 when none of the connecting clients are Windows systems.
3985 subnet Use a subnet rather than a point-to-point topology by
3987 configuring the tun interface with a local IP address and
3988 subnet mask, similar to the topology used in --dev tap
3989 and ethernet bridging mode. This mode allocates a single
3990 IP address per connecting client and works on Windows as
3991 well. Only available when server and clients are OpenVPN
3992 2.1 or higher, or OpenVPN 2.0.x which has been manually
3993 patched with the --topology directive code. When used on
3994 Windows, requires version 8.2 or higher of the TAP-Win32
3995 driver. When used on *nix, requires that the tun driver
3996 supports an ifconfig(8) command which sets a subnet in‐
3997 stead of a remote endpoint IP address.
3998 Note: Using --topology subnet changes the interpretation of the
4000 arguments of --ifconfig to mean "address netmask", no longer
4001 "local remote".
4002 --tun-mtu n
4004 Take the TUN device MTU to be n and derive the link MTU from it
4005 (default 1500). In most cases, you will probably want to leave
4006 this parameter set to its default value.
4007 The MTU (Maximum Transmission Units) is the maximum datagram
4009 size in bytes that can be sent unfragmented over a particular
4010 network path. OpenVPN requires that packets on the control and
4011 data channels be sent unfragmented.
4012 MTU problems often manifest themselves as connections which hang
4014 during periods of active usage.
4015 It's best to use the --fragment and/or --mssfix options to deal
4017 with MTU sizing issues.
4018 --tun-mtu-extra n
4020 Assume that the TUN/TAP device might return as many as n bytes
4021 more than the --tun-mtu size on read. This parameter defaults to
4022 0, which is sufficient for most TUN devices. TAP devices may in‐
4023 troduce additional overhead in excess of the MTU size, and a
4024 setting of 32 is the default when TAP devices are used. This pa‐
4025 rameter only controls internal OpenVPN buffer sizing, so there
4026 is no transmission overhead associated with using a larger
4027 value.
4028 TUN/TAP standalone operations
4030 These two standalone operations will require --dev and optionally
4031 --user and/or --group.
4032 --mktun
4034 (Standalone) Create a persistent tunnel on platforms which sup‐
4035 port them such as Linux. Normally TUN/TAP tunnels exist only for
4036 the period of time that an application has them open. This op‐
4037 tion takes advantage of the TUN/TAP driver's ability to build
4038 persistent tunnels that live through multiple instantiations of
4039 OpenVPN and die only when they are deleted or the machine is re‐
4040 booted.
4041 One of the advantages of persistent tunnels is that they elimi‐
4043 nate the need for separate --up and --down scripts to run the
4044 appropriate ifconfig(8) and route(8) commands. These commands
4045 can be placed in the the same shell script which starts or ter‐
4046 minates an OpenVPN session.
4047 Another advantage is that open connections through the
4049 TUN/TAP-based tunnel will not be reset if the OpenVPN peer
4050 restarts. This can be useful to provide uninterrupted connectiv‐
4051 ity through the tunnel in the event of a DHCP reset of the
4052 peer's public IP address (see the --ipchange option above).
4053 One disadvantage of persistent tunnels is that it is harder to
4055 automatically configure their MTU value (see --link-mtu and
4056 --tun-mtu above).
4057 On some platforms such as Windows, TAP-Win32 tunnels are persis‐
4059 tent by default.
4060 --rmtun
4062 (Standalone) Remove a persistent tunnel.
4063 Virtual Routing and Forwarding
4065 Options in this section relates to configuration of virtual routing and
4066 forwarding in combination with the underlying operating system.
4067 As of today this is only supported on Linux, a kernel >= 4.9 is recom‐
4069 mended.
4070 This could come in handy when for example the external network should
4072 be only used as a means to connect to some VPN endpoints and all regu‐
4073 lar traffic should only be routed through any tunnel(s). This could be
4074 achieved by setting up a VRF and configuring the interface connected to
4075 the external network to be part of the VRF. The examples below will
4076 cover this setup.
4077 Another option would be to put the tun/tap interface into a VRF. This
4079 could be done by an up-script which uses the ip link set command shown
4080 below.
4081 VRF setup with iproute2
4083 Create VRF vrf_external and map it to routing table 1023
4084 ip link add vrf_external type vrf table 1023
4086 Move eth0 into vrf_external
4088 ip link set master vrf_external dev eth0
4090 Any prefixes configured on eth0 will be moved from the :code`main`
4092 routing table into routing table 1023
4093 VRF setup with ifupdown
4095 For Debian based Distributions ifupdown2 provides an almost drop-in re‐
4096 placement for ifupdown including VRFs and other features. A configura‐
4097 tion for an interface eth0 being part of VRF code:vrf_external could
4098 look like this:
4099 auto eth0
4101 iface eth0
4102 address 192.0.2.42/24
4103 address 2001:db8:08:15::42/64
4104 gateway 192.0.2.1
4105 gateway 2001:db8:08:15::1
4106 vrf vrf_external
4107 auto vrf_external
4109 iface vrf_external
4110 vrf-table 1023
4111 OpenVPN configuration
4113 The OpenVPN configuration needs to contain this line:
4114 bind-dev vrf_external
4116 Further reading
4118 Wikipedia has nice page one VRFs:
4119 https://en.wikipedia.org/wiki/Virtual_routing_and_forwarding
4120 This talk from the Network Track of FrOSCon 2018 provides an overview
4122 about advanced layer 2 and layer 3 features of Linux
4123 • Slides:
4125 https://www.slideshare.net/BarbarossaTM/l2l3-fr-fortgeschrittene-helle-und-dunkle-magie-im-linuxnetzwerkstack
4126 • Video (german):
4128 https://media.ccc.de/v/froscon2018-2247-l2_l3_fur_fortgeschrittene_-_helle_und_dunkle_magie_im_linux-netzwerkstack
4129
4131 OpenVPN can execute external scripts in various phases of the lifetime
4132 of the OpenVPN process.
4133 Script Order of Execution
4135 1. --up
4136 Executed after TCP/UDP socket bind and TUN/TAP open.
4138 2. --tls-verify
4140 Executed when we have a still untrusted remote peer.
4142 3. --ipchange
4144 Executed after connection authentication, or remote IP address
4146 change.
4147 4. --client-connect
4149 Executed in --mode server mode immediately after client authentica‐
4151 tion.
4152 5. --route-up
4154 Executed after connection authentication, either immediately after,
4156 or some number of seconds after as defined by the --route-delay op‐
4157 tion.
4158 6. --route-pre-down
4160 Executed right before the routes are removed.
4162 7. --client-disconnect
4164 Executed in --mode server mode on client instance shutdown.
4166 8. --down
4168 Executed after TCP/UDP and TUN/TAP close.
4170 9. --learn-address
4172 Executed in --mode server mode whenever an IPv4 address/route or
4174 MAC address is added to OpenVPN's internal routing table.
4175 10. --auth-user-pass-verify
4177 Executed in --mode server mode on new client connections, when the
4179 client is still untrusted.
4180 SCRIPT HOOKS
4182 --auth-user-pass-verify args
4183 Require the client to provide a username/password (possibly in
4184 addition to a client certificate) for authentication.
4185 Valid syntax:
4187 auth-user-pass-verify cmd method
4189 OpenVPN will run command cmd to validate the username/password
4191 provided by the client.
4192 cmd consists of a path to a script (or executable program), op‐
4194 tionally followed by arguments. The path and arguments may be
4195 single- or double-quoted and/or escaped using a backslash, and
4196 should be separated by one or more spaces.
4197 If method is set to via-env, OpenVPN will call script with the
4199 environmental variables username and password set to the user‐
4200 name/password strings provided by the client. Beware that this
4201 method is insecure on some platforms which make the environment
4202 of a process publicly visible to other unprivileged processes.
4203 If method is set to via-file, OpenVPN will write the username
4205 and password to the first two lines of a temporary file. The
4206 filename will be passed as an argument to script, and the file
4207 will be automatically deleted by OpenVPN after the script re‐
4208 turns. The location of the temporary file is controlled by the
4209 --tmp-dir option, and will default to the current directory if
4210 unspecified. For security, consider setting --tmp-dir to a
4211 volatile storage medium such as /dev/shm (if available) to pre‐
4212 vent the username/password file from touching the hard drive.
4213 The script should examine the username and password, returning a
4215 success exit code (0) if the client's authentication request is
4216 to be accepted, or a failure code (1) to reject the client.
4217 This directive is designed to enable a plugin-style interface
4219 for extending OpenVPN's authentication capabilities.
4220 To protect against a client passing a maliciously formed user‐
4222 name or password string, the username string must consist only
4223 of these characters: alphanumeric, underbar ('_'), dash ('-'),
4224 dot ('.'), or at ('@'). The password string can consist of any
4225 printable characters except for CR or LF. Any illegal characters
4226 in either the username or password string will be converted to
4227 underbar ('_').
4228 Care must be taken by any user-defined scripts to avoid creating
4230 a security vulnerability in the way that these strings are han‐
4231 dled. Never use these strings in such a way that they might be
4232 escaped or evaluated by a shell interpreter.
4233 For a sample script that performs PAM authentication, see sam‐
4235 ple-scripts/auth-pam.pl in the OpenVPN source distribution.
4236 --client-connect cmd
4238 Run command cmd on client connection.
4239 cmd consists of a path to a script (or executable program), op‐
4241 tionally followed by arguments. The path and arguments may be
4242 single- or double-quoted and/or escaped using a backslash, and
4243 should be separated by one or more spaces.
4244 The command is passed the common name and IP address of the
4246 just-authenticated client as environmental variables (see envi‐
4247 ronmental variable section below). The command is also passed
4248 the pathname of a freshly created temporary file as the last ar‐
4249 gument (after any arguments specified in cmd ), to be used by
4250 the command to pass dynamically generated config file directives
4251 back to OpenVPN.
4252 If the script wants to generate a dynamic config file to be ap‐
4254 plied on the server when the client connects, it should write it
4255 to the file named by the last argument.
4256 See the --client-config-dir option below for options which can
4258 be legally used in a dynamically generated config file.
4259 Note that the return value of script is significant. If script
4261 returns a non-zero error status, it will cause the client to be
4262 disconnected.
4263 If a --client-connect wants to defer the generating of the con‐
4265 figuration then the script needs to use the client_connect_de‐
4266 ferred_file and client_connect_config_file environment vari‐
4267 ables, and write status accordingly into these files. See the
4268 Environmental Variables section for more details.
4269 --client-disconnect cmd
4271 Like --client-connect but called on client instance shutdown.
4272 Will not be called unless the --client-connect script and plug‐
4273 ins (if defined) were previously called on this instance with
4274 successful (0) status returns.
4275 The exception to this rule is if the --client-disconnect command
4277 or plugins are cascaded, and at least one client-connect func‐
4278 tion succeeded, then ALL of the client-disconnect functions for
4279 scripts and plugins will be called on client instance object
4280 deletion, even in cases where some of the related client-connect
4281 functions returned an error status.
4282 The --client-disconnect command is not passed any extra argu‐
4284 ments (only those arguments specified in cmd, if any).
4285 --down cmd
4287 Run command cmd after TUN/TAP device close (post --user UID
4288 change and/or --chroot ). cmd consists of a path to script (or
4289 executable program), optionally followed by arguments. The path
4290 and arguments may be single- or double-quoted and/or escaped us‐
4291 ing a backslash, and should be separated by one or more spaces.
4292 Called with the same parameters and environmental variables as
4294 the --up option above.
4295 Note that if you reduce privileges by using --user and/or
4297 --group, your --down script will also run at reduced privilege.
4298 --down-pre
4300 Call --down cmd/script before, rather than after, TUN/TAP close.
4301 --ipchange cmd
4303 Run command cmd when our remote ip-address is initially authen‐
4304 ticated or changes.
4305 cmd consists of a path to a script (or executable program), op‐
4307 tionally followed by arguments. The path and arguments may be
4308 single- or double-quoted and/or escaped using a backslash, and
4309 should be separated by one or more spaces.
4310 When cmd is executed two arguments are appended after any argu‐
4312 ments specified in cmd , as follows:
4313 cmd ip address port number
4315 Don't use --ipchange in --mode server mode. Use a --client-con‐
4317 nect script instead.
4318 See the Environmental Variables section below for additional pa‐
4320 rameters passed as environmental variables.
4321 If you are running in a dynamic IP address environment where the
4323 IP addresses of either peer could change without notice, you can
4324 use this script, for example, to edit the /etc/hosts file with
4325 the current address of the peer. The script will be run every
4326 time the remote peer changes its IP address.
4327 Similarly if our IP address changes due to DHCP, we should con‐
4329 figure our IP address change script (see man page for dhcpcd(8))
4330 to deliver a SIGHUP or SIGUSR1 signal to OpenVPN. OpenVPN will
4331 then re-establish a connection with its most recently authenti‐
4332 cated peer on its new IP address.
4333 --learn-address cmd
4335 Run command cmd to validate client virtual addresses or routes.
4336 cmd consists of a path to a script (or executable program), op‐
4338 tionally followed by arguments. The path and arguments may be
4339 single- or double-quoted and/or escaped using a backslash, and
4340 should be separated by one or more spaces.
4341 Three arguments will be appended to any arguments in cmd as fol‐
4343 lows:
4344 $1 - [operation]
4346 "add", "update", or "delete" based on whether or not the
4347 address is being added to, modified, or deleted from
4348 OpenVPN's internal routing table.
4349 $2 - [address]
4351 The address being learned or unlearned. This can be an
4352 IPv4 address such as "198.162.10.14", an IPv4 subnet such
4353 as "198.162.10.0/24", or an ethernet MAC address (when
4354 --dev tap is being used) such as "00:FF:01:02:03:04".
4355 $3 - [common name]
4357 The common name on the certificate associated with the
4358 client linked to this address. Only present for "add" or
4359 "update" operations, not "delete".
4360 On "add" or "update" methods, if the script returns a failure
4362 code (non-zero), OpenVPN will reject the address and will not
4363 modify its internal routing table.
4364 Normally, the cmd script will use the information provided above
4366 to set appropriate firewall entries on the VPN TUN/TAP inter‐
4367 face. Since OpenVPN provides the association between virtual IP
4368 or MAC address and the client's authenticated common name, it
4369 allows a user-defined script to configure firewall access poli‐
4370 cies with regard to the client's high-level common name, rather
4371 than the low level client virtual addresses.
4372 --route-up cmd
4374 Run command cmd after routes are added, subject to --route-de‐
4375 lay.
4376 cmd consists of a path to a script (or executable program), op‐
4378 tionally followed by arguments. The path and arguments may be
4379 single- or double-quoted and/or escaped using a backslash, and
4380 should be separated by one or more spaces.
4381 See the Environmental Variables section below for additional pa‐
4383 rameters passed as environmental variables.
4384 --route-pre-down cmd
4386 Run command cmd before routes are removed upon disconnection.
4387 cmd consists of a path to a script (or executable program), op‐
4389 tionally followed by arguments. The path and arguments may be
4390 single- or double-quoted and/or escaped using a backslash, and
4391 should be separated by one or more spaces.
4392 See the Environmental Variables section below for additional pa‐
4394 rameters passed as environmental variables.
4395 --setenv args
4397 Set a custom environmental variable name=value to pass to
4398 script.
4399 Valid syntaxes:
4401 setenv name value
4403 setenv FORWARD_COMPATIBLE 1
4404 setenv opt config_option
4405 By setting FORWARD_COMPATIBLE to 1, the config file syntax
4407 checking is relaxed so that unknown directives will trigger a
4408 warning but not a fatal error, on the assumption that a given
4409 unknown directive might be valid in future OpenVPN versions.
4410 This option should be used with caution, as there are good secu‐
4412 rity reasons for having OpenVPN fail if it detects problems in a
4413 config file. Having said that, there are valid reasons for
4414 wanting new software features to gracefully degrade when encoun‐
4415 tered by older software versions.
4416 It is also possible to tag a single directive so as not to trig‐
4418 ger a fatal error if the directive isn't recognized. To do this,
4419 prepend the following before the directive: setenv opt
4420 Versions prior to OpenVPN 2.3.3 will always ignore options set
4422 with the setenv opt directive.
4423 See also --ignore-unknown-option
4425 --setenv-safe args
4427 Set a custom environmental variable OPENVPN_name to value to
4428 pass to scripts.
4429 Valid syntaxes:
4431 setenv-safe name value
4433 This directive is designed to be pushed by the server to
4435 clients, and the prepending of OPENVPN_ to the environmental
4436 variable is a safety precaution to prevent a LD_PRELOAD style
4437 attack from a malicious or compromised server.
4438 --tls-verify cmd
4440 Run command cmd to verify the X509 name of a pending TLS connec‐
4441 tion that has otherwise passed all other tests of certification
4442 (except for revocation via --crl-verify directive; the revoca‐
4443 tion test occurs after the --tls-verify test).
4444 cmd should return 0 to allow the TLS handshake to proceed, or 1
4446 to fail.
4447 cmd consists of a path to a script (or executable program), op‐
4449 tionally followed by arguments. The path and arguments may be
4450 single- or double-quoted and/or escaped using a backslash, and
4451 should be separated by one or more spaces.
4452 When cmd is executed two arguments are appended after any argu‐
4454 ments specified in cmd, as follows:
4455 cmd certificate_depth subject
4457 These arguments are, respectively, the current certificate depth
4459 and the X509 subject distinguished name (dn) of the peer.
4460 This feature is useful if the peer you want to trust has a cer‐
4462 tificate which was signed by a certificate authority who also
4463 signed many other certificates, where you don't necessarily want
4464 to trust all of them, but rather be selective about which peer
4465 certificate you will accept. This feature allows you to write a
4466 script which will test the X509 name on a certificate and decide
4467 whether or not it should be accepted. For a simple perl script
4468 which will test the common name field on the certificate, see
4469 the file verify-cn in the OpenVPN distribution.
4470 See the Environmental Variables section below for additional pa‐
4472 rameters passed as environmental variables.
4473 --up cmd
4475 Run command cmd after successful TUN/TAP device open (pre --user
4476 UID change).
4477 cmd consists of a path to a script (or executable program), op‐
4479 tionally followed by arguments. The path and arguments may be
4480 single- or double-quoted and/or escaped using a backslash, and
4481 should be separated by one or more spaces.
4482 The up command is useful for specifying route commands which
4484 route IP traffic destined for private subnets which exist at the
4485 other end of the VPN connection into the tunnel.
4486 For --dev tun execute as:
4488 cmd tun_dev tun_mtu link_mtu ifconfig_local_ip ifconfig_remote_ip [init | restart]
4490 For --dev tap execute as:
4492 cmd tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask [init | restart]
4494 See the Environmental Variables section below for additional pa‐
4496 rameters passed as environmental variables.
4497 Note that if cmd includes arguments, all OpenVPN-generated argu‐
4499 ments will be appended to them to build an argument list with
4500 which the executable will be called.
4501 Typically, cmd will run a script to add routes to the tunnel.
4503 Normally the up script is called after the TUN/TAP device is
4505 opened. In this context, the last command line parameter passed
4506 to the script will be init. If the --up-restart option is also
4507 used, the up script will be called for restarts as well. A
4508 restart is considered to be a partial reinitialization of Open‐
4509 VPN where the TUN/TAP instance is preserved (the --persist-tun
4510 option will enable such preservation). A restart can be gener‐
4511 ated by a SIGUSR1 signal, a --ping-restart timeout, or a connec‐
4512 tion reset when the TCP protocol is enabled with the --proto op‐
4513 tion. If a restart occurs, and --up-restart has been specified,
4514 the up script will be called with restart as the last parameter.
4515 NOTE: On restart, OpenVPN will not pass the full set of envi‐
4517 ronment variables to the script. Namely, everything re‐
4518 lated to routing and gateways will not be passed, as
4519 nothing needs to be done anyway - all the routing setup
4520 is already in place. Additionally, the up-restart script
4521 will run with the downgraded UID/GID settings (if config‐
4522 ured).
4523 The following standalone example shows how the --up script can
4525 be called in both an initialization and restart context. (NOTE:
4526 for security reasons, don't run the following example unless UDP
4527 port 9999 is blocked by your firewall. Also, the example will
4528 run indefinitely, so you should abort with control-c).
4529 openvpn --dev tun --port 9999 --verb 4 --ping-restart 10 \
4531 --up 'echo up' --down 'echo down' --persist-tun \
4532 --up-restart
4533 Note that OpenVPN also provides the --ifconfig option to auto‐
4535 matically ifconfig the TUN device, eliminating the need to de‐
4536 fine an --up script, unless you also want to configure routes in
4537 the --up script.
4538 If --ifconfig is also specified, OpenVPN will pass the ifconfig
4540 local and remote endpoints on the command line to the --up
4541 script so that they can be used to configure routes such as:
4542 route add -net 10.0.0.0 netmask 255.255.255.0 gw $5
4544 --up-delay
4546 Delay TUN/TAP open and possible --up script execution until af‐
4547 ter TCP/UDP connection establishment with peer.
4548 In --proto udp mode, this option normally requires the use of
4550 --ping to allow connection initiation to be sensed in the ab‐
4551 sence of tunnel data, since UDP is a "connectionless" protocol.
4552 On Windows, this option will delay the TAP-Win32 media state
4554 transitioning to "connected" until connection establishment,
4555 i.e. the receipt of the first authenticated packet from the
4556 peer.
4557 --up-restart
4559 Enable the --up and --down scripts to be called for restarts as
4560 well as initial program start. This option is described more
4561 fully above in the --up option documentation.
4562 String Types and Remapping
4564 In certain cases, OpenVPN will perform remapping of characters in
4565 strings. Essentially, any characters outside the set of permitted char‐
4566 acters for each string type will be converted to underbar ('_').
4567 Q: Why is string remapping necessary?
4569 It's an important security feature to prevent the malicious cod‐
4570 ing of strings from untrusted sources to be passed as parameters
4571 to scripts, saved in the environment, used as a common name,
4572 translated to a filename, etc.
4573 Q: Can string remapping be disabled?
4575 Yes, by using the --no-name-remapping option, however this
4576 should be considered an advanced option.
4577 Here is a brief rundown of OpenVPN's current string types and the per‐
4579 mitted character class for each string:
4580 X509 Names
4582 Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), at ('@'),
4583 colon (':'), slash ('/'), and equal ('='). Alphanumeric is de‐
4584 fined as a character which will cause the C library isalnum()
4585 function to return true.
4586 Common Names
4588 Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), and at
4589 ('@').
4590 --auth-user-pass username
4592 Same as Common Name, with one exception: starting with OpenVPN
4593 2.0.1, the username is passed to the OPEN‐
4594 VPN_PLUGIN_AUTH_USER_PASS_VERIFY plugin in its raw form, without
4595 string remapping.
4596 --auth-user-pass password
4598 Any "printable" character except CR or LF. Printable is defined
4599 to be a character which will cause the C library isprint() func‐
4600 tion to return true.
4601 --client-config-dir filename as derived from common name or`username
4603 Alphanumeric, underbar ('_'), dash ('-'), and dot ('.') except
4604 for "." or ".." as standalone strings. As of v2.0.1-rc6, the at
4605 ('@') character has been added as well for compatibility with
4606 the common name character class.
4607 Environmental variable names
4609 Alphanumeric or underbar ('_').
4610 Environmental variable values
4612 Any printable character.
4613 For all cases, characters in a string which are not members of the le‐
4615 gal character class for that string type will be remapped to underbar
4616 ('_').
4617 Environmental Variables
4619 Once set, a variable is persisted indefinitely until it is reset by a
4620 new value or a restart,
4621 As of OpenVPN 2.0-beta12, in server mode, environmental variables set
4623 by OpenVPN are scoped according to the client objects they are associ‐
4624 ated with, so there should not be any issues with scripts having access
4625 to stale, previously set variables which refer to different client in‐
4626 stances.
4627 bytes_received
4629 Total number of bytes received from client during VPN session.
4630 Set prior to execution of the --client-disconnect script.
4631 bytes_sent
4633 Total number of bytes sent to client during VPN session. Set
4634 prior to execution of the --client-disconnect script.
4635 client_connect_config_file
4637 The path to the configuration file that should be written to by
4638 the --client-connect script (optional, if per-session configura‐
4639 tion is desired). This is the same file name as passed via com‐
4640 mand line argument on the call to the --client-connect script.
4641 client_connect_deferred_file
4643 This file can be optionally written to in order to to communi‐
4644 cate a status code of the --client-connect script or plgin.
4645 Only the first character in the file is relevant. It must be
4646 either 1 to indicate normal script execution, 0 indicates an er‐
4647 ror (in the same way that a non zero exit status does) or 2 to
4648 indicate that the script deferred returning the config file.
4649 For deferred (background) handling, the script or plugin MUST
4651 write 2 to the file to indicate the deferral and then return
4652 with exit code 0 to signal deferred handler started OK.
4653 A background process or similar must then take care of writing
4655 the configuration to the file indicated by the client_con‐
4656 nect_config_file environment variable and when finished, write
4657 the a 1 to this file (or 0 in case of an error).
4658 The absence of any character in the file when the script fin‐
4660 ishes executing is interpreted the same as 1. This allows
4661 scripts that are not written to support the defer mechanism to
4662 be used unmodified.
4663 common_name
4665 The X509 common name of an authenticated client. Set prior to
4666 execution of --client-connect, --client-disconnect and
4667 --auth-user-pass-verify scripts.
4668 config Name of first --config file. Set on program initiation and reset
4670 on SIGHUP.
4671 daemon Set to "1" if the --daemon directive is specified, or "0" other‐
4673 wise. Set on program initiation and reset on SIGHUP.
4674 daemon_log_redirect
4676 Set to "1" if the --log or --log-append directives are speci‐
4677 fied, or "0" otherwise. Set on program initiation and reset on
4678 SIGHUP.
4679 dev The actual name of the TUN/TAP device, including a unit number
4681 if it exists. Set prior to --up or --down script execution.
4682 dev_idx
4684 On Windows, the device index of the TUN/TAP adapter (to be used
4685 in netsh.exe calls which sometimes just do not work right with
4686 interface names). Set prior to --up or --down script execution.
4687 foreign_option_{n}
4689 An option pushed via --push to a client which does not natively
4690 support it, such as --dhcp-option on a non-Windows system, will
4691 be recorded to this environmental variable sequence prior to
4692 --up script execution.
4693 ifconfig_broadcast
4695 The broadcast address for the virtual ethernet segment which is
4696 derived from the --ifconfig option when --dev tap is used. Set
4697 prior to OpenVPN calling the ifconfig or netsh (windows version
4698 of ifconfig) commands which normally occurs prior to --up script
4699 execution.
4700 ifconfig_ipv6_local
4702 The local VPN endpoint IPv6 address specified in the --ifcon‐
4703 fig-ipv6 option (first parameter). Set prior to OpenVPN calling
4704 the ifconfig or code:netsh (windows version of ifconfig) com‐
4705 mands which normally occurs prior to --up script execution.
4706 ifconfig_ipv6_netbits
4708 The prefix length of the IPv6 network on the VPN interface. De‐
4709 rived from the /nnn parameter of the IPv6 address in the --if‐
4710 config-ipv6 option (first parameter). Set prior to OpenVPN call‐
4711 ing the ifconfig or netsh (windows version of ifconfig) commands
4712 which normally occurs prior to --up script execution.
4713 ifconfig_ipv6_remote
4715 The remote VPN endpoint IPv6 address specified in the --ifcon‐
4716 fig-ipv6 option (second parameter). Set prior to OpenVPN calling
4717 the ifconfig or netsh (windows version of ifconfig) commands
4718 which normally occurs prior to --up script execution.
4719 ifconfig_local
4721 The local VPN endpoint IP address specified in the --ifconfig
4722 option (first parameter). Set prior to OpenVPN calling the if‐
4723 config or netsh (windows version of ifconfig) commands which
4724 normally occurs prior to --up script execution.
4725 ifconfig_remote
4727 The remote VPN endpoint IP address specified in the --ifconfig
4728 option (second parameter) when --dev tun is used. Set prior to
4729 OpenVPN calling the ifconfig or netsh (windows version of ifcon‐
4730 fig) commands which normally occurs prior to --up script execu‐
4731 tion.
4732 ifconfig_netmask
4734 The subnet mask of the virtual ethernet segment that is speci‐
4735 fied as the second parameter to --ifconfig when --dev tap is be‐
4736 ing used. Set prior to OpenVPN calling the ifconfig or netsh
4737 (windows version of ifconfig) commands which normally occurs
4738 prior to --up script execution.
4739 ifconfig_pool_local_ip
4741 The local virtual IP address for the TUN/TAP tunnel taken from
4742 an --ifconfig-push directive if specified, or otherwise from the
4743 ifconfig pool (controlled by the --ifconfig-pool config file di‐
4744 rective). Only set for --dev tun tunnels. This option is set on
4745 the server prior to execution of the --client-connect and
4746 --client-disconnect scripts.
4747 ifconfig_pool_netmask
4749 The virtual IP netmask for the TUN/TAP tunnel taken from an
4750 --ifconfig-push directive if specified, or otherwise from the
4751 ifconfig pool (controlled by the --ifconfig-pool config file di‐
4752 rective). Only set for --dev tap tunnels. This option is set on
4753 the server prior to execution of the --client-connect and
4754 --client-disconnect scripts.
4755 ifconfig_pool_remote_ip
4757 The remote virtual IP address for the TUN/TAP tunnel taken from
4758 an --ifconfig-push directive if specified, or otherwise from the
4759 ifconfig pool (controlled by the --ifconfig-pool config file di‐
4760 rective). This option is set on the server prior to execution of
4761 the --client-connect and --client-disconnect scripts.
4762 link_mtu
4764 The maximum packet size (not including the IP header) of tunnel
4765 data in UDP tunnel transport mode. Set prior to --up or --down
4766 script execution.
4767 local The --local parameter. Set on program initiation and reset on
4769 SIGHUP.
4770 local_port
4772 The local port number or name, specified by --port or --lport.
4773 Set on program initiation and reset on SIGHUP.
4774 password
4776 The password provided by a connecting client. Set prior to
4777 --auth-user-pass-verify script execution only when the via-env
4778 modifier is specified, and deleted from the environment after
4779 the script returns.
4780 proto The --proto parameter. Set on program initiation and reset on
4782 SIGHUP.
4783 remote_{n}
4785 The --remote parameter. Set on program initiation and reset on
4786 SIGHUP.
4787 remote_port_{n}
4789 The remote port number, specified by --port or --rport. Set on
4790 program initiation and reset on SIGHUP.
4791 route_net_gateway
4793 The pre-existing default IP gateway in the system routing table.
4794 Set prior to --up script execution.
4795 route_vpn_gateway
4797 The default gateway used by --route options, as specified in ei‐
4798 ther the --route-gateway option or the second parameter to --if‐
4799 config when --dev tun is specified. Set prior to --up script ex‐
4800 ecution.
4801 route_{parm}_{n}
4803 A set of variables which define each route to be added, and are
4804 set prior to --up script execution.
4805 parm will be one of network, netmask", gateway, or metric.
4807 n is the OpenVPN route number, starting from 1.
4809 If the network or gateway are resolvable DNS names, their IP ad‐
4811 dress translations will be recorded rather than their names as
4812 denoted on the command line or configuration file.
4813 route_ipv6_{parm}_{n}
4815 A set of variables which define each IPv6 route to be added, and
4816 are set prior to --up script execution.
4817 parm will be one of network, gateway or metric. route_ipv6_net‐
4819 work_{n} contains netmask as /nnn, unlike IPv4 where it is
4820 passed in a separate environment variable.
4821 n is the OpenVPN route number, starting from 1.
4823 If the network or gateway are resolvable DNS names, their IP ad‐
4825 dress translations will be recorded rather than their names as
4826 denoted on the command line or configuration file.
4827 peer_cert
4829 Temporary file name containing the client certificate upon con‐
4830 nection. Useful in conjunction with --tls-verify.
4831 script_context
4833 Set to "init" or "restart" prior to up/down script execution.
4834 For more information, see documentation for --up.
4835 script_type
4837 Prior to execution of any script, this variable is set to the
4838 type of script being run. It can be one of the following: up,
4839 down, ipchange, route-up, tls-verify, auth-user-pass-verify,
4840 client-connect, client-disconnect or learn-address. Set prior to
4841 execution of any script.
4842 signal The reason for exit or restart. Can be one of sigusr1, sighup,
4844 sigterm, sigint, inactive (controlled by --inactive option),
4845 ping-exit (controlled by --ping-exit option), ping-restart (con‐
4846 trolled by --ping-restart option), connection-reset (triggered
4847 on TCP connection reset), error or unknown (unknown signal).
4848 This variable is set just prior to down script execution.
4849 time_ascii
4851 Client connection timestamp, formatted as a human-readable time
4852 string. Set prior to execution of the --client-connect script.
4853 time_duration
4855 The duration (in seconds) of the client session which is now
4856 disconnecting. Set prior to execution of the --client-disconnect
4857 script.
4858 time_unix
4860 Client connection timestamp, formatted as a unix integer
4861 date/time value. Set prior to execution of the --client-connect
4862 script.
4863 tls_digest_{n} / tls_digest_sha256_{n}
4865 Contains the certificate SHA1 / SHA256 fingerprint, where n is
4866 the verification level. Only set for TLS connections. Set prior
4867 to execution of --tls-verify script.
4868 tls_id_{n}
4870 A series of certificate fields from the remote peer, where n is
4871 the verification level. Only set for TLS connections. Set prior
4872 to execution of --tls-verify script.
4873 tls_serial_{n}
4875 The serial number of the certificate from the remote peer, where
4876 n is the verification level. Only set for TLS connections. Set
4877 prior to execution of --tls-verify script. This is in the form
4878 of a decimal string like "933971680", which is suitable for do‐
4879 ing serial-based OCSP queries (with OpenSSL, do not prepend "0x"
4880 to the string) If something goes wrong while reading the value
4881 from the certificate it will be an empty string, so your code
4882 should check that. See the contrib/OCSP_check/OCSP_check.sh
4883 script for an example.
4884 tls_serial_hex_{n}
4886 Like tls_serial_{n}, but in hex form (e.g. 12:34:56:78:9A).
4887 tun_mtu
4889 The MTU of the TUN/TAP device. Set prior to --up or --down
4890 script execution.
4891 trusted_ip / trusted_ip6)
4893 Actual IP address of connecting client or peer which has been
4894 authenticated. Set prior to execution of --ipchange,
4895 --client-connect and --client-disconnect scripts. If using ipv6
4896 endpoints (udp6, tcp6), trusted_ip6 will be set instead.
4897 trusted_port
4899 Actual port number of connecting client or peer which has been
4900 authenticated. Set prior to execution of --ipchange,
4901 --client-connect and --client-disconnect scripts.
4902 untrusted_ip / untrusted_ip6
4904 Actual IP address of connecting client or peer which has not
4905 been authenticated yet. Sometimes used to nmap the connecting
4906 host in a --tls-verify script to ensure it is firewalled prop‐
4907 erly. Set prior to execution of --tls-verify and
4908 --auth-user-pass-verify scripts. If using ipv6 endpoints (udp6,
4909 tcp6), untrusted_ip6 will be set instead.
4910 untrusted_port
4912 Actual port number of connecting client or peer which has not
4913 been authenticated yet. Set prior to execution of --tls-verify
4914 and --auth-user-pass-verify scripts.
4915 username
4917 The username provided by a connecting client. Set prior to
4918 --auth-user-pass-verify script execution only when the via-env
4919 modifier is specified.
4920 X509_{n}_{subject_field}
4922 An X509 subject field from the remote peer certificate, where n
4923 is the verification level. Only set for TLS connections. Set
4924 prior to execution of --tls-verify script. This variable is sim‐
4925 ilar to tls_id_{n} except the component X509 subject fields are
4926 broken out, and no string remapping occurs on these field values
4927 (except for remapping of control characters to "_"). For exam‐
4928 ple, the following variables would be set on the OpenVPN server
4929 using the sample client certificate in sample-keys (client.crt).
4930 Note that the verification level is 0 for the client certificate
4931 and 1 for the CA certificate.
4932 X509_0_emailAddress=me@myhost.mydomain
4934 X509_0_CN=Test-Client
4935 X509_0_O=OpenVPN-TEST
4936 X509_0_ST=NA
4937 X509_0_C=KG
4938 X509_1_emailAddress=me@myhost.mydomain
4939 X509_1_O=OpenVPN-TEST
4940 X509_1_L=BISHKEK
4941 X509_1_ST=NA
4942 X509_1_C=KG
4943 Management Interface Options
4945 OpenVPN provides a feature rich socket based management interface for
4946 both server and client mode operations.
4947 --management args
4949 Enable a management server on a socket-name Unix socket on those
4950 platforms supporting it, or on a designated TCP port.
4951 Valid syntaxes:
4953 management socket-name unix #
4955 management socket-name unix pw-file # (recommended)
4956 management IP port # (INSECURE)
4957 management IP port pw-file #
4958 pw-file, if specified, is a password file where the password
4960 must be on first line. Instead of a filename it can use the key‐
4961 word stdin which will prompt the user for a password to use when
4962 OpenVPN is starting.
4963 For unix sockets, the default behaviour is to create a unix do‐
4965 main socket that may be connected to by any process. Use the
4966 --management-client-user and --management-client-group direc‐
4967 tives to restrict access.
4968 The management interface provides a special mode where the TCP
4970 management link can operate over the tunnel itself. To enable
4971 this mode, set IP to tunnel. Tunnel mode will cause the manage‐
4972 ment interface to listen for a TCP connection on the local VPN
4973 address of the TUN/TAP interface.
4974 *BEWARE* of enabling the management interface over TCP. In these
4976 cases you should ALWAYS make use of pw-file to password protect
4977 the management interface. Any user who can connect to this TCP
4978 IP:port will be able to manage and control (and interfere with)
4979 the OpenVPN process. It is also strongly recommended to set IP
4980 to 127.0.0.1 (localhost) to restrict accessibility of the man‐
4981 agement server to local clients.
4982 While the management port is designed for programmatic control
4984 of OpenVPN by other applications, it is possible to telnet to
4985 the port, using a telnet client in "raw" mode. Once connected,
4986 type help for a list of commands.
4987 For detailed documentation on the management interface, see the
4989 management-notes.txt file in the management folder of the Open‐
4990 VPN source distribution.
4991 --management-client
4993 Management interface will connect as a TCP/unix domain client to
4994 IP:port specified by --management rather than listen as a TCP
4995 server or on a unix domain socket.
4996 If the client connection fails to connect or is disconnected, a
4998 SIGTERM signal will be generated causing OpenVPN to quit.
4999 --management-client-auth
5001 Gives management interface client the responsibility to authen‐
5002 ticate clients after their client certificate has been verified.
5003 See management-notes.txt in OpenVPN distribution for detailed
5004 notes.
5005 --management-client-group g
5007 When the management interface is listening on a unix domain
5008 socket, only allow connections from group g.
5009 --management-client-pf
5011 Management interface clients must specify a packet filter file
5012 for each connecting client. See management-notes.txt in OpenVPN
5013 distribution for detailed notes.
5014 --management-client-user u
5016 When the management interface is listening on a unix domain
5017 socket, only allow connections from user u.
5018 --management-external-cert certificate-hint
5020 Allows usage for external certificate instead of --cert option
5021 (client-only). certificate-hint is an arbitrary string which is
5022 passed to a management interface client as an argument of
5023 NEED-CERTIFICATE notification. Requires --management-exter‐
5024 nal-key.
5025 --management-external-key args
5027 Allows usage for external private key file instead of --key op‐
5028 tion (client-only).
5029 Valid syntaxes:
5031 management-external-key
5033 management-external-key nopadding
5034 management-external-key pkcs1
5035 management-external-key nopadding pkcs1
5036 The optional parameters nopadding and pkcs1 signal support for
5038 different padding algorithms. See doc/mangement-notes.txt for a
5039 complete description of this feature.
5040 --management-forget-disconnect
5042 Make OpenVPN forget passwords when management session discon‐
5043 nects.
5044 This directive does not affect the --http-proxy username/pass‐
5046 word. It is always cached.
5047 --management-hold
5049 Start OpenVPN in a hibernating state, until a client of the man‐
5050 agement interface explicitly starts it with the hold release
5051 command.
5052 --management-log-cache n
5054 Cache the most recent n lines of log file history for usage by
5055 the management channel.
5056 --management-query-passwords
5058 Query management channel for private key password and
5059 --auth-user-pass username/password. Only query the management
5060 channel for inputs which ordinarily would have been queried from
5061 the console.
5062 --management-query-proxy
5064 Query management channel for proxy server information for a spe‐
5065 cific --remote (client-only).
5066 --management-query-remote
5068 Allow management interface to override --remote directives
5069 (client-only).
5070 --management-signal
5072 Send SIGUSR1 signal to OpenVPN if management session discon‐
5073 nects. This is useful when you wish to disconnect an OpenVPN
5074 session on user logoff. For --management-client this option is
5075 not needed since a disconnect will always generate a SIGTERM.
5076 --management-up-down
5078 Report tunnel up/down events to management interface.
5079 Plug-in Interface Options
5081 OpenVPN can be extended by loading external plug-in modules at runtime.
5082 These plug-ins must be prebuilt and adhere to the OpenVPN Plug-In API.
5083 --plugin args
5085 Loads an OpenVPN plug-in module.
5086 Valid syntax:
5088 plugin module-name
5090 plugin module-name "arguments"
5091 The module-name needs to be the first argument, indicating the
5093 plug-in to load. The second argument is an optional init string
5094 which will be passed directly to the plug-in. If the init con‐
5095 sists of multiple arguments it must be enclosed in double-quotes
5096 ("). Multiple plugin modules may be loaded into one OpenVPN
5097 process.
5098 The module-name argument can be just a filename or a filename
5100 with a relative or absolute path. The format of the filename and
5101 path defines if the plug-in will be loaded from a default
5102 plug-in directory or outside this directory.
5103 --plugin path Effective directory used
5105 ===================== =============================
5106 myplug.so DEFAULT_DIR/myplug.so
5107 subdir/myplug.so DEFAULT_DIR/subdir/myplug.so
5108 ./subdir/myplug.so CWD/subdir/myplug.so
5109 /usr/lib/my/plug.so /usr/lib/my/plug.so
5110 DEFAULT_DIR is replaced by the default plug-in directory, which
5112 is configured at the build time of OpenVPN. CWD is the current
5113 directory where OpenVPN was started or the directory OpenVPN
5114 have switched into via the --cd option before the --plugin op‐
5115 tion.
5116 For more information and examples on how to build OpenVPN
5118 plug-in modules, see the README file in the plugin folder of the
5119 OpenVPN source distribution.
5120 If you are using an RPM install of OpenVPN, see /usr/share/open‐
5122 vpn/plugin. The documentation is in doc and the actual plugin
5123 modules are in lib.
5124 Multiple plugin modules can be cascaded, and modules can be used
5126 in tandem with scripts. The modules will be called by OpenVPN in
5127 the order that they are declared in the config file. If both a
5128 plugin and script are configured for the same callback, the
5129 script will be called last. If the return code of the mod‐
5130 ule/script controls an authentication function (such as tls-ver‐
5131 ify, auth-user-pass-verify, or client-connect), then every mod‐
5132 ule and script must return success (0) in order for the connec‐
5133 tion to be authenticated.
5134 Windows-Specific Options
5136 --allow-nonadmin TAP-adapter
5137 (Standalone) Set TAP-adapter to allow access from non-adminis‐
5138 trative accounts. If TAP-adapter is omitted, all TAP adapters on
5139 the system will be configured to allow non-admin access. The
5140 non-admin access setting will only persist for the length of
5141 time that the TAP-Win32 device object and driver remain loaded,
5142 and will need to be re-enabled after a reboot, or if the driver
5143 is unloaded and reloaded. This directive can only be used by an
5144 administrator.
5145 --block-outside-dns
5147 Block DNS servers on other network adapters to prevent DNS
5148 leaks. This option prevents any application from accessing TCP
5149 or UDP port 53 except one inside the tunnel. It uses Windows
5150 Filtering Platform (WFP) and works on Windows Vista or later.
5151 This option is considered unknown on non-Windows platforms and
5153 unsupported on Windows XP, resulting in fatal error. You may
5154 want to use --setenv opt or --ignore-unknown-option (not suit‐
5155 able for Windows XP) to ignore said error. Note that pushing un‐
5156 known options from server does not trigger fatal errors.
5157 --cryptoapicert select-string
5159 (Windows/OpenSSL Only) Load the certificate and private key from
5160 the Windows Certificate System Store.
5161 Use this option instead of --cert and --key.
5163 This makes it possible to use any smart card, supported by Win‐
5165 dows, but also any kind of certificate, residing in the Cert
5166 Store, where you have access to the private key. This option has
5167 been tested with a couple of different smart cards (GemSAFE,
5168 Cryptoflex, and Swedish Post Office eID) on the client side, and
5169 also an imported PKCS12 software certificate on the server side.
5170 To select a certificate, based on a substring search in the cer‐
5172 tificate's subject:
5173 cryptoapicert "SUBJ:Peter Runestig"
5175 To select a certificate, based on certificate's thumbprint:
5177 cryptoapicert "THUMB:f6 49 24 41 01 b4 ..."
5179 The thumbprint hex string can easily be copy-and-pasted from the
5181 Windows Certificate Store GUI.
5182 --dhcp-release
5184 Ask Windows to release the TAP adapter lease on shutdown. This
5185 option has no effect now, as it is enabled by default starting
5186 with OpenVPN 2.4.1.
5187 --dhcp-renew
5189 Ask Windows to renew the TAP adapter lease on startup. This op‐
5190 tion is normally unnecessary, as Windows automatically triggers
5191 a DHCP renegotiation on the TAP adapter when it comes up, how‐
5192 ever if you set the TAP-Win32 adapter Media Status property to
5193 "Always Connected", you may need this flag.
5194 --ip-win32 method
5196 When using --ifconfig on Windows, set the TAP-Win32 adapter IP
5197 address and netmask using method. Don't use this option unless
5198 you are also using --ifconfig.
5199 manual Don't set the IP address or netmask automatically. In‐
5201 stead output a message to the console telling the user to
5202 configure the adapter manually and indicating the IP/net‐
5203 mask which OpenVPN expects the adapter to be set to.
5204 dynamic [offset] [lease-time]
5206 Automatically set the IP address and netmask by replying
5207 to DHCP query messages generated by the kernel. This
5208 mode is probably the "cleanest" solution for setting the
5209 TCP/IP properties since it uses the well-known DHCP pro‐
5210 tocol. There are, however, two prerequisites for using
5211 this mode:
5212 1. The TCP/IP properties for the TAP-Win32 adapter must
5214 be set to "Obtain an IP address automatically", and
5215 2. OpenVPN needs to claim an IP address in the subnet for
5217 use as the virtual DHCP server address.
5218 By default in --dev tap mode, OpenVPN will take the nor‐
5220 mally unused first address in the subnet. For example, if
5221 your subnet is 192.168.4.0 netmask 255.255.255.0, then
5222 OpenVPN will take the IP address 192.168.4.0 to use as
5223 the virtual DHCP server address. In --dev tun mode,
5224 OpenVPN will cause the DHCP server to masquerade as if it
5225 were coming from the remote endpoint.
5226 The optional offset parameter is an integer which is >
5228 -256 and < 256 and which defaults to -1. If offset is
5229 positive, the DHCP server will masquerade as the IP ad‐
5230 dress at network address + offset. If offset is negative,
5231 the DHCP server will masquerade as the IP address at
5232 broadcast address + offset.
5233 The Windows ipconfig /all command can be used to show
5235 what Windows thinks the DHCP server address is. OpenVPN
5236 will "claim" this address, so make sure to use a free ad‐
5237 dress. Having said that, different OpenVPN instantia‐
5238 tions, including different ends of the same connection,
5239 can share the same virtual DHCP server address.
5240 The lease-time parameter controls the lease time of the
5242 DHCP assignment given to the TAP-Win32 adapter, and is
5243 denoted in seconds. Normally a very long lease time is
5244 preferred because it prevents routes involving the
5245 TAP-Win32 adapter from being lost when the system goes to
5246 sleep. The default lease time is one year.
5247 netsh Automatically set the IP address and netmask using the
5249 Windows command-line "netsh" command. This method appears
5250 to work correctly on Windows XP but not Windows 2000.
5251 ipapi Automatically set the IP address and netmask using the
5253 Windows IP Helper API. This approach does not have ideal
5254 semantics, though testing has indicated that it works
5255 okay in practice. If you use this option, it is best to
5256 leave the TCP/IP properties for the TAP-Win32 adapter in
5257 their default state, i.e. "Obtain an IP address automati‐
5258 cally."
5259 adaptive (Default)
5261 Try dynamic method initially and fail over to netsh if
5262 the DHCP negotiation with the TAP-Win32 adapter does not
5263 succeed in 20 seconds. Such failures have been known to
5264 occur when certain third-party firewall packages in‐
5265 stalled on the client machine block the DHCP negotiation
5266 used by the TAP-Win32 adapter. Note that if the netsh
5267 failover occurs, the TAP-Win32 adapter TCP/IP properties
5268 will be reset from DHCP to static, and this will cause
5269 future OpenVPN startups using the adaptive mode to use
5270 netsh immediately, rather than trying dynamic first.
5271 To "unstick" the adaptive mode from using netsh, run
5273 OpenVPN at least once using the dynamic mode to restore
5274 the TAP-Win32 adapter TCP/IP properties to a DHCP config‐
5275 uration.
5276 --pause-exit
5278 Put up a "press any key to continue" message on the console
5279 prior to OpenVPN program exit. This option is automatically used
5280 by the Windows explorer when OpenVPN is run on a configuration
5281 file using the right-click explorer menu.
5282 --register-dns
5284 Run ipconfig /flushdns and ipconfig /registerdns on connection
5285 initiation. This is known to kick Windows into recognizing
5286 pushed DNS servers.
5287 --route-method m
5289 Which method m to use for adding routes on Windows?
5290 adaptive (default)
5292 Try IP helper API first. If that fails, fall back to the
5293 route.exe shell command.
5294 ipapi Use IP helper API.
5296 exe Call the route.exe shell command.
5298 --service args
5300 Should be used when OpenVPN is being automatically executed by
5301 another program in such a context that no interaction with the
5302 user via display or keyboard is possible.
5303 Valid syntax:
5305 service exit-event [0|1]
5307 In general, end-users should never need to explicitly use this
5309 option, as it is automatically added by the OpenVPN service
5310 wrapper when a given OpenVPN configuration is being run as a
5311 service.
5312 exit-event is the name of a Windows global event object, and
5314 OpenVPN will continuously monitor the state of this event object
5315 and exit when it becomes signaled.
5316 The second parameter indicates the initial state of exit-event
5318 and normally defaults to 0.
5319 Multiple OpenVPN processes can be simultaneously executed with
5321 the same exit-event parameter. In any case, the controlling
5322 process can signal exit-event, causing all such OpenVPN pro‐
5323 cesses to exit.
5324 When executing an OpenVPN process using the --service directive,
5326 OpenVPN will probably not have a console window to output sta‐
5327 tus/error messages, therefore it is useful to use --log or
5328 --log-append to write these messages to a file.
5329 --show-adapters
5331 (Standalone) Show available TAP-Win32 adapters which can be se‐
5332 lected using the --dev-node option. On non-Windows systems, the
5333 ifconfig(8) command provides similar functionality.
5334 --show-net
5336 (Standalone) Show OpenVPN's view of the system routing table and
5337 network adapter list.
5338 --show-net-up
5340 Output OpenVPN's view of the system routing table and network
5341 adapter list to the syslog or log file after the TUN/TAP adapter
5342 has been brought up and any routes have been added.
5343 --show-valid-subnets
5345 (Standalone) Show valid subnets for --dev tun emulation. Since
5346 the TAP-Win32 driver exports an ethernet interface to Windows,
5347 and since TUN devices are point-to-point in nature, it is neces‐
5348 sary for the TAP-Win32 driver to impose certain constraints on
5349 TUN endpoint address selection.
5350 Namely, the point-to-point endpoints used in TUN device emula‐
5352 tion must be the middle two addresses of a /30 subnet (netmask
5353 255.255.255.252).
5354 --tap-sleep n
5356 Cause OpenVPN to sleep for n seconds immediately after the
5357 TAP-Win32 adapter state is set to "connected".
5358 This option is intended to be used to troubleshoot problems with
5360 the --ifconfig and --ip-win32 options, and is used to give the
5361 TAP-Win32 adapter time to come up before Windows IP Helper API
5362 operations are applied to it.
5363 --win-sys path
5365 Set the Windows system directory pathname to use when looking
5366 for system executables such as route.exe and netsh.exe. By de‐
5367 fault, if this directive is not specified, OpenVPN will use the
5368 SystemRoot environment variable.
5369 This option has changed behaviour since OpenVPN 2.3. Earlier you
5371 had to define --win-sys env to use the SystemRoot environment
5372 variable, otherwise it defaulted to C:\\WINDOWS. It is not
5373 needed to use the env keyword any more, and it will just be ig‐
5374 nored. A warning is logged when this is found in the configura‐
5375 tion file.
5376 --windows-driver drv
5378 Specifies which tun driver to use. Values are tap-windows6 (de‐
5379 fault) and wintun. This is a Windows-only option. wintun" re‐
5380 quires --dev tun and the OpenVPN process to run elevated, or be
5381 invoked using the Interactive Service.
5382 Standalone Debug Options
5384 --show-gateway args
5385 (Standalone) Show current IPv4 and IPv6 default gateway and in‐
5386 terface towards the gateway (if the protocol in question is en‐
5387 abled).
5388 Valid syntax:
5390 --show-gateway
5392 --show-gateway IPv6-target
5393 For IPv6 this queries the route towards ::/128, or the specified
5395 IPv6 target address if passed as argument. For IPv4 on Linux,
5396 Windows, MacOS and BSD it looks for a 0.0.0.0/0 route. If there
5397 are more specific routes, the result will not always be matching
5398 the route of the IPv4 packets to the VPN gateway.
5399 Advanced Expert Options
5401 These are options only required when special tweaking is needed, often
5402 used when debugging or testing out special usage scenarios.
5403 --hash-size args
5405 Set the size of the real address hash table to r and the virtual
5406 address table to v.
5407 Valid syntax:
5409 hash-size r v
5411 By default, both tables are sized at 256 buckets.
5413 --bcast-buffers n
5415 Allocate n buffers for broadcast datagrams (default 256).
5416 --persist-local-ip
5418 Preserve initially resolved local IP address and port number
5419 across SIGUSR1 or --ping-restart restarts.
5420 --persist-remote-ip
5422 Preserve most recently authenticated remote IP address and port
5423 number across SIGUSR1 or --ping-restart restarts.
5424 --prng args
5426 (Advanced) Change the PRNG (Pseudo-random number generator) pa‐
5427 rameters
5428 Valid syntaxes:
5430 prng alg
5432 prng alg nsl
5433 Changes the PRNG to use digest algorithm alg (default sha1), and
5435 set nsl (default 16) to the size in bytes of the nonce secret
5436 length (between 16 and 64).
5437 Set alg to none to disable the PRNG and use the OpenSSL
5439 RAND_bytes function instead for all of OpenVPN's pseudo-random
5440 number needs.
5441 --rcvbuf size
5443 Set the TCP/UDP socket receive buffer size. Defaults to operat‐
5444 ing system default.
5445 --shaper n
5447 Limit bandwidth of outgoing tunnel data to n bytes per second on
5448 the TCP/UDP port. Note that this will only work if mode is set
5449 to p2p. If you want to limit the bandwidth in both directions,
5450 use this option on both peers.
5451 OpenVPN uses the following algorithm to implement traffic shap‐
5453 ing: Given a shaper rate of n bytes per second, after a datagram
5454 write of b bytes is queued on the TCP/UDP port, wait a minimum
5455 of (b / n) seconds before queuing the next write.
5456 It should be noted that OpenVPN supports multiple tunnels be‐
5458 tween the same two peers, allowing you to construct full-speed
5459 and reduced bandwidth tunnels at the same time, routing low-pri‐
5460 ority data such as off-site backups over the reduced bandwidth
5461 tunnel, and other data over the full-speed tunnel.
5462 Also note that for low bandwidth tunnels (under 1000 bytes per
5464 second), you should probably use lower MTU values as well (see
5465 above), otherwise the packet latency will grow so large as to
5466 trigger timeouts in the TLS layer and TCP connections running
5467 over the tunnel.
5468 OpenVPN allows n to be between 100 bytes/sec and 100 Mbytes/sec.
5470 --sndbuf size
5472 Set the TCP/UDP socket send buffer size. Defaults to operating
5473 system default.
5474 --tcp-queue-limit n
5476 Maximum number of output packets queued before TCP (default 64).
5477 When OpenVPN is tunneling data from a TUN/TAP device to a remote
5479 client over a TCP connection, it is possible that the TUN/TAP
5480 device might produce data at a faster rate than the TCP connec‐
5481 tion can support. When the number of output packets queued be‐
5482 fore sending to the TCP socket reaches this limit for a given
5483 client connection, OpenVPN will start to drop outgoing packets
5484 directed at this client.
5485 --txqueuelen n
5487 (Linux only) Set the TX queue length on the TUN/TAP interface.
5488 Currently defaults to operating system default.
5489
5491 Options listed in this section have been removed from OpenVPN and are
5492 no longer supported
5493 --client-cert-not-required
5495 Removed in OpenVPN 2.5. This should be replaxed with --ver‐
5496 ify-client-cert none.
5497 --ifconfig-pool-linear
5499 Removed in OpenVPN 2.5. This should be replaced with --topology
5500 p2p.
5501 --key-method
5503 Removed in OpenVPN 2.5. This option should not be used, as us‐
5504 ing the old key-method weakens the VPN tunnel security. The old
5505 key-method was also only needed when the remote side was older
5506 than OpenVPN 2.0.
5507 --no-iv
5509 Removed in OpenVPN 2.5. This option should not be used as it
5510 weakens the VPN tunnel security. This has been a NOOP option
5511 since OpenVPN 2.4.
5512 --no-replay
5514 Removed in OpenVPN 2.5. This option should not be used as it
5515 weakens the VPN tunnel security.
5516 --ns-cert-type
5518 Removed in OpenVPN 2.5. The nsCertType field is no longer sup‐
5519 ported in recent SSL/TLS libraries. If your certificates does
5520 not include key usage and extended key usage fields, they must
5521 be upgraded and the --remote-cert-tls option should be used in‐
5522 stead.
5523
5525 Client configuration files may contain multiple remote servers which it
5526 will attempt to connect against. But there are some configuration op‐
5527 tions which are related to specific --remote options. For these use
5528 cases, connection profiles are the solution.
5529 By enacpulating the --remote option and related options within <connec‐
5531 tion> and </connection>, these options are handled as a group.
5532 An OpenVPN client will try each connection profile sequentially until
5534 it achieves a successful connection.
5535 --remote-random can be used to initially "scramble" the connection
5537 list.
5538 Here is an example of connection profile usage:
5540 client
5542 dev tun
5543 <connection>
5545 remote 198.19.34.56 1194 udp
5546 </connection>
5547 <connection>
5549 remote 198.19.34.56 443 tcp
5550 </connection>
5551 <connection>
5553 remote 198.19.34.56 443 tcp
5554 http-proxy 192.168.0.8 8080
5555 </connection>
5556 <connection>
5558 remote 198.19.36.99 443 tcp
5559 http-proxy 192.168.0.8 8080
5560 </connection>
5561 persist-key
5563 persist-tun
5564 pkcs12 client.p12
5565 remote-cert-tls server
5566 verb 3
5567 First we try to connect to a server at 198.19.34.56:1194 using UDP. If
5569 that fails, we then try to connect to 198.19.34.56:443 using TCP. If
5570 that also fails, then try connecting through an HTTP proxy at
5571 192.168.0.8:8080 to 198.19.34.56:443 using TCP. Finally, try to connect
5572 through the same proxy to a server at 198.19.36.99:443 using TCP.
5573 The following OpenVPN options may be used inside of a <connection>
5575 block:
5576 bind, connect-retry, connect-retry-max, connect-timeout, ex‐
5578 plicit-exit-notify, float, fragment, http-proxy, http-proxy-option,
5579 key-direction, link-mtu, local, lport, mssfix, mtu-disc, nobind, port,
5580 proto, remote, rport, socks-proxy, tls-auth, tls-crypt, tun-mtu and,
5581 tun-mtu-extra.
5582 A defaulting mechanism exists for specifying options to apply to all
5584 <connection> profiles. If any of the above options (with the exception
5585 of remote ) appear outside of a <connection> block, but in a configura‐
5586 tion file which has one or more <connection> blocks, the option setting
5587 will be used as a default for <connection> blocks which follow it in
5588 the configuration file.
5589 For example, suppose the nobind option were placed in the sample con‐
5591 figuration file above, near the top of the file, before the first <con‐
5592 nection> block. The effect would be as if nobind were declared in all
5593 <connection> blocks below it.
5594
5596 OpenVPN allows including files in the main configuration for the --ca,
5597 --cert, --dh, --extra-certs, --key, --pkcs12, --secret, --crl-verify,
5598 --http-proxy-user-pass, --tls-auth, --auth-gen-token-secret,
5599 --tls-crypt and --tls-crypt-v2 options.
5600 Each inline file started by the line <option> and ended by the line
5602 </option>
5603 Here is an example of an inline file usage
5605 <cert>
5607 -----BEGIN CERTIFICATE-----
5608 [...]
5609 -----END CERTIFICATE-----
5610 </cert>
5611 When using the inline file feature with --pkcs12 the inline file has to
5613 be base64 encoded. Encoding of a .p12 file into base64 can be done for
5614 example with OpenSSL by running openssl base64 -in input.p12
5615
5617 SIGHUP Cause OpenVPN to close all TUN/TAP and network connections,
5618 restart, re-read the configuration file (if any), and reopen
5619 TUN/TAP and network connections.
5620 SIGUSR1
5622 Like SIGHUP`, except don't re-read configuration file, and pos‐
5623 sibly don't close and reopen TUN/TAP device, re-read key files,
5624 preserve local IP address/port, or preserve most recently au‐
5625 thenticated remote IP address/port based on --persist-tun,
5626 --persist-key, --persist-local-ip and --persist-remote-ip op‐
5627 tions respectively (see above).
5628 This signal may also be internally generated by a timeout condi‐
5630 tion, governed by the --ping-restart option.
5631 This signal, when combined with --persist-remote-ip, may be sent
5633 when the underlying parameters of the host's network interface
5634 change such as when the host is a DHCP client and is assigned a
5635 new IP address. See --ipchange for more information.
5636 SIGUSR2
5638 Causes OpenVPN to display its current statistics (to the syslog
5639 file if --daemon is used, or stdout otherwise).
5640 SIGINT, SIGTERM
5642 Causes OpenVPN to exit gracefully.
5643
5645 Prior to running these examples, you should have OpenVPN installed on
5646 two machines with network connectivity between them. If you have not
5647 yet installed OpenVPN, consult the INSTALL file included in the OpenVPN
5648 distribution.
5649 Firewall Setup:
5651 If firewalls exist between the two machines, they should be set to for‐
5652 ward the port OpenVPN is configured to use, in both directions. The
5653 default for OpenVPN is 1194/udp. If you do not have control over the
5654 firewalls between the two machines, you may still be able to use Open‐
5655 VPN by adding --ping 15 to each of the openvpn commands used below in
5656 the examples (this will cause each peer to send out a UDP ping to its
5657 remote peer once every 15 seconds which will cause many stateful fire‐
5658 walls to forward packets in both directions without an explicit fire‐
5659 wall rule).
5660 Please see your operating system guides for how to configure the fire‐
5662 wall on your systems.
5663 VPN Address Setup:
5665 For purposes of our example, our two machines will be called bob.exam‐
5666 ple.com and alice.example.com. If you are constructing a VPN over the
5667 internet, then replace bob.example.com and alice.example.com with the
5668 internet hostname or IP address that each machine will use to contact
5669 the other over the internet.
5670 Now we will choose the tunnel endpoints. Tunnel endpoints are private
5672 IP addresses that only have meaning in the context of the VPN. Each ma‐
5673 chine will use the tunnel endpoint of the other machine to access it
5674 over the VPN. In our example, the tunnel endpoint for bob.example.com
5675 will be 10.4.0.1 and for alice.example.com, 10.4.0.2.
5676 Once the VPN is established, you have essentially created a secure al‐
5678 ternate path between the two hosts which is addressed by using the tun‐
5679 nel endpoints. You can control which network traffic passes between the
5680 hosts (a) over the VPN or (b) independently of the VPN, by choosing
5681 whether to use (a) the VPN endpoint address or (b) the public internet
5682 address, to access the remote host. For example if you are on bob.exam‐
5683 ple.com and you wish to connect to alice.example.com via ssh without
5684 using the VPN (since ssh has its own built-in security) you would use
5685 the command ssh alice.example.com. However in the same scenario, you
5686 could also use the command telnet 10.4.0.2 to create a telnet session
5687 with alice.example.com over the VPN, that would use the VPN to secure
5688 the session rather than ssh.
5689 You can use any address you wish for the tunnel endpoints but make sure
5691 that they are private addresses (such as those that begin with 10 or
5692 192.168) and that they are not part of any existing subnet on the net‐
5693 works of either peer, unless you are bridging. If you use an address
5694 that is part of your local subnet for either of the tunnel endpoints,
5695 you will get a weird feedback loop.
5696 Example 1: A simple tunnel without security
5698 On bob:
5699 openvpn --remote alice.example.com --dev tun1 \
5701 --ifconfig 10.4.0.1 10.4.0.2 --verb 9
5702 On alice:
5704 openvpn --remote bob.example.com --dev tun1 \
5706 --ifconfig 10.4.0.2 10.4.0.1 --verb 9
5707 Now verify the tunnel is working by pinging across the tunnel.
5709 On bob:
5711 ping 10.4.0.2
5713 On alice:
5715 ping 10.4.0.1
5717 The --verb 9 option will produce verbose output, similar to the tcp‐
5719 dump(8) program. Omit the --verb 9 option to have OpenVPN run quietly.
5720 Example 2: A tunnel with static-key security (i.e. using a pre-shared se‐
5722 cret)
5723 First build a static key on bob.
5724 openvpn --genkey --secret key
5726 This command will build a key file called key (in ascii format). Now
5728 copy key to alice.example.com over a secure medium such as by using the
5729 scp(1) program.
5730 On bob:
5732 openvpn --remote alice.example.com --dev tun1 \
5734 --ifconfig 10.4.0.1 10.4.0.2 --verb 5 \
5735 --secret key
5736 On alice:
5738 openvpn --remote bob.example.com --dev tun1 \
5740 --ifconfig 10.4.0.2 10.4.0.1 --verb 5 \
5741 --secret key
5742 Now verify the tunnel is working by pinging across the tunnel.
5744 On bob:
5746 ping 10.4.0.2
5748 On alice:
5750 ping 10.4.0.1
5752 Example 3: A tunnel with full TLS-based security
5754 For this test, we will designate bob as the TLS client and alice as the
5755 TLS server.
5756 Note: The client or server designation only has meaning for the TLS
5758 subsystem. It has no bearing on OpenVPN's peer-to-peer,
5759 UDP-based communication model.*
5760 First, build a separate certificate/key pair for both bob and alice
5762 (see above where --cert is discussed for more info). Then construct
5763 Diffie Hellman parameters (see above where --dh is discussed for more
5764 info). You can also use the included test files client.crt, client.key,
5765 server.crt, server.key and ca.crt. The .crt files are certificates/pub‐
5766 lic-keys, the .key files are private keys, and ca.crt is a certifica‐
5767 tion authority who has signed both client.crt and server.crt. For
5768 Diffie Hellman parameters you can use the included file dh2048.pem.
5769 WARNING:
5771 All client, server, and certificate authority certificates and
5772 keys included in the OpenVPN distribution are totally insecure
5773 and should be used for testing only.
5774 On bob:
5776 openvpn --remote alice.example.com --dev tun1 \
5778 --ifconfig 10.4.0.1 10.4.0.2 \
5779 --tls-client --ca ca.crt \
5780 --cert client.crt --key client.key \
5781 --reneg-sec 60 --verb 5
5782 On alice:
5784 openvpn --remote bob.example.com --dev tun1 \
5786 --ifconfig 10.4.0.2 10.4.0.1 \
5787 --tls-server --dh dh1024.pem --ca ca.crt \
5788 --cert server.crt --key server.key \
5789 --reneg-sec 60 --verb 5
5790 Now verify the tunnel is working by pinging across the tunnel.
5792 On bob:
5794 ping 10.4.0.2
5796 On alice:
5798 ping 10.4.0.1
5800 Notice the --reneg-sec 60 option we used above. That tells OpenVPN to
5802 renegotiate the data channel keys every minute. Since we used --verb 5
5803 above, you will see status information on each new key negotiation.
5804 For production operations, a key renegotiation interval of 60 seconds
5806 is probably too frequent. Omit the --reneg-sec 60 option to use Open‐
5807 VPN's default key renegotiation interval of one hour.
5808 Routing:
5810 Assuming you can ping across the tunnel, the next step is to route a
5811 real subnet over the secure tunnel. Suppose that bob and alice have two
5812 network interfaces each, one connected to the internet, and the other
5813 to a private network. Our goal is to securely connect both private net‐
5814 works. We will assume that bob's private subnet is 10.0.0.0/24 and al‐
5815 ice's is 10.0.1.0/24.
5816 First, ensure that IP forwarding is enabled on both peers. On Linux,
5818 enable routing:
5819 echo 1 > /proc/sys/net/ipv4/ip_forward
5821 This setting is not persistent. Please see your operating systems doc‐
5823 umentation how to properly configure IP forwarding, which is also per‐
5824 sistent through system boots.
5825 If your system is configured with a firewall. Please see your operat‐
5827 ing systems guide on how to configure the firewall. You typically want
5828 to allow traffic coming from and going to the tun/tap adapter OpenVPN
5829 is configured to use.
5830 On bob:
5832 route add -net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2
5834 On alice:
5836 route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1
5838 Now any machine on the 10.0.0.0/24 subnet can access any machine on the
5840 10.0.1.0/24 subnet over the secure tunnel (or vice versa).
5841 In a production environment, you could put the route command(s) in a
5843 script and execute with the --up option.
5844
5846 https://community.openvpn.net/openvpn/wiki/FAQ
5847
5849 For a more comprehensive guide to setting up OpenVPN in a production
5850 setting, see the OpenVPN HOWTO at
5851 https://openvpn.net/community-resources/how-to/
5852
5854 For a description of OpenVPN's underlying protocol, see
5855 https://openvpn.net/community-resources/openvpn-protocol/
5856
5858 OpenVPN's web site is at https://openvpn.net/
5859 Go here to download the latest version of OpenVPN, subscribe to the
5861 mailing lists, read the mailing list archives, or browse the SVN repos‐
5862 itory.
5863
5865 Report all bugs to the OpenVPN team info@openvpn.net
5866
5868 dhcpcd(8), ifconfig(8), openssl(1), route(8), scp(1) ssh(1)
5869
5871 This product includes software developed by the OpenSSL Project (‐
5872 https://www.openssl.org/)
5873 For more information on the TLS protocol, see
5875 http://www.ietf.org/rfc/rfc2246.txt
5876 For more information on the LZO real-time compression library see
5878 https://www.oberhumer.com/opensource/lzo/
5879
5881 Copyright (C) 2002-2020 OpenVPN Inc This program is free software; you
5882 can redistribute it and/or modify it under the terms of the GNU General
5883 Public License version 2 as published by the Free Software Foundation.
5884
5886 James Yonan james@openvpn.net
5887 OPENVPN(8)