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-token-user base64username
913 Companion option to --auth-token. This options allows to over‐
914 ride the username used by the client when reauthenticating with
915 the auth-token. It also allows to use --auth-token in setups
916 that normally do not use username and password.
917 The username has to be base64 encoded.
919 --auth-user-pass
921 Authenticate with server using username/password.
922 Valid syntaxes:
924 auth-user-pass
926 auth-user-pass up
927 If up is present, it must be a file containing username/password
929 on 2 lines. If the password line is missing, OpenVPN will prompt
930 for one.
931 If up is omitted, username/password will be prompted from the
933 console.
934 The server configuration must specify an --auth-user-pass-verify
936 script to verify the username/password provided by the client.
937 --auth-retry type
939 Controls how OpenVPN responds to username/password verification
940 errors such as the client-side response to an AUTH_FAILED mes‐
941 sage from the server or verification failure of the private key
942 password.
943 Normally used to prevent auth errors from being fatal on the
945 client side, and to permit username/password requeries in case
946 of error.
947 An AUTH_FAILED message is generated by the server if the client
949 fails --auth-user-pass authentication, or if the server-side
950 --client-connect script returns an error status when the client
951 tries to connect.
952 type can be one of:
954 none Client will exit with a fatal error (this is the de‐
956 fault).
957 nointeract
959 Client will retry the connection without requerying for
960 an --auth-user-pass username/password. Use this option
961 for unattended clients.
962 interact
964 Client will requery for an --auth-user-pass user‐
965 name/password and/or private key password before attempt‐
966 ing a reconnection.
967 Note that while this option cannot be pushed, it can be con‐
969 trolled from the management interface.
970 --client
972 A helper directive designed to simplify the configuration of
973 OpenVPN's client mode. This directive is equivalent to:
974 pull
976 tls-client
977 --client-nat args
979 This pushable client option sets up a stateless one-to-one NAT
980 rule on packet addresses (not ports), and is useful in cases
981 where routes or ifconfig settings pushed to the client would
982 create an IP numbering conflict.
983 Examples:
985 client-nat snat 192.168.0.0/255.255.0.0
987 client-nat dnat 10.64.0.0/255.255.0.0
988 network/netmask (for example 192.168.0.0/255.255.0.0) defines
990 the local view of a resource from the client perspective, while
991 alias/netmask (for example 10.64.0.0/255.255.0.0) defines the
992 remote view from the server perspective.
993 Use snat (source NAT) for resources owned by the client and dnat
995 (destination NAT) for remote resources.
996 Set --verb 6 for debugging info showing the transformation of
998 src/dest addresses in packets.
999 --connect-retry n
1001 Wait n seconds between connection attempts (default 5). Re‐
1002 peated reconnection attempts are slowed down after 5 retries per
1003 remote by doubling the wait time after each unsuccessful at‐
1004 tempt. An optional argument max specifies the maximum value of
1005 wait time in seconds at which it gets capped (default 300).
1006 --connect-retry-max n
1008 n specifies the number of times each --remote or <connection>
1009 entry is tried. Specifying n as 1 would try each entry exactly
1010 once. A successful connection resets the counter. (default un‐
1011 limited).
1012 --connect-timeout n
1014 See --server-poll-timeout.
1015 --explicit-exit-notify n
1017 In UDP client mode or point-to-point mode, send server/peer an
1018 exit notification if tunnel is restarted or OpenVPN process is
1019 exited. In client mode, on exit/restart, this option will tell
1020 the server to immediately close its client instance object
1021 rather than waiting for a timeout.
1022 The n parameter (default 1 if not present) controls the maximum
1024 number of attempts that the client will try to resend the exit
1025 notification message.
1026 In UDP server mode, send RESTART control channel command to con‐
1028 nected clients. The n parameter (default 1 if not present) con‐
1029 trols client behavior. With n = 1 client will attempt to recon‐
1030 nect to the same server, with n = 2 client will advance to the
1031 next server.
1032 OpenVPN will not send any exit notifications unless this option
1034 is enabled.
1035 --inactive args
1037 Causes OpenVPN to exit after n seconds of inactivity on the
1038 TUN/TAP device. The time length of inactivity is measured since
1039 the last incoming or outgoing tunnel packet. The default value
1040 is 0 seconds, which disables this feature.
1041 Valid syntaxes:
1043 inactive n
1045 inactive n bytes
1046 If the optional bytes parameter is included, exit if less than
1048 bytes of combined in/out traffic are produced on the tun/tap de‐
1049 vice in n seconds.
1050 In any case, OpenVPN's internal ping packets (which are just
1052 keepalives) and TLS control packets are not considered "activ‐
1053 ity", nor are they counted as traffic, as they are used inter‐
1054 nally by OpenVPN and are not an indication of actual user activ‐
1055 ity.
1056 --proto-force p
1058 When iterating through connection profiles, only consider pro‐
1059 files using protocol p (tcp | udp).
1060 --pull This option must be used on a client which is connecting to a
1062 multi-client server. It indicates to OpenVPN that it should ac‐
1063 cept options pushed by the server, provided they are part of the
1064 legal set of pushable options (note that the --pull option is
1065 implied by --client ).
1066 In particular, --pull allows the server to push routes to the
1068 client, so you should not use --pull or --client in situations
1069 where you don't trust the server to have control over the
1070 client's routing table.
1071 --pull-filter args
1073 Filter options on the client pushed by the server to the client.
1074 Valid syntaxes:
1076 pull-filter accept text
1078 pull-filter ignore text
1079 pull-filter reject text
1080 Filter options received from the server if the option starts
1082 with text. The action flag accept allows the option, ignore re‐
1083 moves it and reject flags an error and triggers a SIGUSR1
1084 restart. The filters may be specified multiple times, and each
1085 filter is applied in the order it is specified. The filtering of
1086 each option stops as soon as a match is found. Unmatched options
1087 are accepted by default.
1088 Prefix comparison is used to match text against the received op‐
1090 tion so that
1091 pull-filter ignore "route"
1093 would remove all pushed options starting with route which would
1095 include, for example, route-gateway. Enclose text in quotes to
1096 embed spaces.
1097 pull-filter accept "route 192.168.1."
1099 pull-filter ignore "route "
1100 would remove all routes that do not start with 192.168.1.
1102 Note that reject may result in a repeated cycle of failure and
1104 reconnect, unless multiple remotes are specified and connection
1105 to the next remote succeeds. To silently ignore an option pushed
1106 by the server, use ignore.
1107 --remote args
1109 Remote host name or IP address, port and protocol.
1110 Valid syntaxes:
1112 remote host
1114 remote host port
1115 remote host port proto
1116 The port and proto arguments are optional. The OpenVPN client
1118 will try to connect to a server at host:port. The proto argu‐
1119 ment indicates the protocol to use when connecting with the re‐
1120 mote, and may be tcp or udp. To enforce IPv4 or IPv6 connec‐
1121 tions add a 4 or 6 suffix; like udp4 / udp6 / tcp4 / tcp6.
1122 On the client, multiple --remote options may be specified for
1124 redundancy, each referring to a different OpenVPN server, in the
1125 order specified by the list of --remote options. Specifying mul‐
1126 tiple --remote options for this purpose is a special case of the
1127 more general connection-profile feature. See the <connection>
1128 documentation below.
1129 The client will move on to the next host in the list, in the
1131 event of connection failure. Note that at any given time, the
1132 OpenVPN client will at most be connected to one server.
1133 Examples:
1135 remote server1.example.net
1137 remote server1.example.net 1194
1138 remote server2.example.net 1194 tcp
1139 Note: Since UDP is connectionless, connection failure is de‐
1141 fined by the --ping and --ping-restart options.
1142 Also, if you use multiple --remote options, AND you are
1144 dropping root privileges on the client with --user and/or
1145 --group AND the client is running a non-Windows OS, if
1146 the client needs to switch to a different server, and
1147 that server pushes back different TUN/TAP or route set‐
1148 tings, the client may lack the necessary privileges to
1149 close and reopen the TUN/TAP interface. This could cause
1150 the client to exit with a fatal error.
1151 If --remote is unspecified, OpenVPN will listen for packets from
1153 any IP address, but will not act on those packets unless they
1154 pass all authentication tests. This requirement for authentica‐
1155 tion is binding on all potential peers, even those from known
1156 and supposedly trusted IP addresses (it is very easy to forge a
1157 source IP address on a UDP packet).
1158 When used in TCP mode, --remote will act as a filter, rejecting
1160 connections from any host which does not match host.
1161 If host is a DNS name which resolves to multiple IP addresses,
1163 OpenVPN will try them in the order that the system getaddrinfo()
1164 presents them, so priorization and DNS randomization is done by
1165 the system library. Unless an IP version is forced by the proto‐
1166 col specification (4/6 suffix), OpenVPN will try both IPv4 and
1167 IPv6 addresses, in the order getaddrinfo() returns them.
1168 --remote-random
1170 When multiple --remote address/ports are specified, or if con‐
1171 nection profiles are being used, initially randomize the order
1172 of the list as a kind of basic load-balancing measure.
1173 --remote-random-hostname
1175 Prepend a random string (6 bytes, 12 hex characters) to hostname
1176 to prevent DNS caching. For example, "foo.bar.gov" would be mod‐
1177 ified to "<random-chars>.foo.bar.gov".
1178 --resolv-retry n
1180 If hostname resolve fails for --remote, retry resolve for n sec‐
1181 onds before failing.
1182 Set n to "infinite" to retry indefinitely.
1184 By default, --resolv-retry infinite is enabled. You can disable
1186 by setting n=0.
1187 --single-session
1189 After initially connecting to a remote peer, disallow any new
1190 connections. Using this option means that a remote peer cannot
1191 connect, disconnect, and then reconnect.
1192 If the daemon is reset by a signal or --ping-restart, it will
1194 allow one new connection.
1195 --single-session can be used with --ping-exit or --inactive to
1197 create a single dynamic session that will exit when finished.
1198 --server-poll-timeout n
1200 When connecting to a remote server do not wait for more than n
1201 seconds for a response before trying the next server. The de‐
1202 fault value is 120s. This timeout includes proxy and TCP connect
1203 timeouts.
1204 --static-challenge args
1206 Enable static challenge/response protocol
1207 Valid syntax:
1209 static-challenge text echo
1211 The text challenge text is presented to the user which describes
1213 what information is requested. The echo flag indicates if the
1214 user's input should be echoed on the screen. Valid echo values
1215 are 0 or 1.
1216 See management-notes.txt in the OpenVPN distribution for a de‐
1218 scription of the OpenVPN challenge/response protocol.
1219 --show-proxy-settings
1221 Show sensed HTTP or SOCKS proxy settings. Currently, only Win‐
1222 dows clients support this option.
1223 --http-proxy args
1225 Connect to remote host through an HTTP proxy. This requires at
1226 least an address server and port argument. If HTTP Proxy-Au‐
1227 thenticate is required, a file name to an authfile file contain‐
1228 ing a username and password on 2 lines can be given, or stdin to
1229 prompt from console. Its content can also be specified in the
1230 config file with the --http-proxy-user-pass option. (See section
1231 on inline files)
1232 The last optional argument is an auth-method which should be one
1234 of none, basic, or ntlm.
1235 HTTP Digest authentication is supported as well, but only via
1237 the auto or auto-nct flags (below). This must replace the auth‐
1238 file argument.
1239 The auto flag causes OpenVPN to automatically determine the
1241 auth-method and query stdin or the management interface for
1242 username/password credentials, if required. This flag exists on
1243 OpenVPN 2.1 or higher.
1244 The auto-nct flag (no clear-text auth) instructs OpenVPN to au‐
1246 tomatically determine the authentication method, but to reject
1247 weak authentication protocols such as HTTP Basic Authentication.
1248 Examples:
1250 http-proxy proxy.example.net 3128
1252 http-proxy proxy.example.net 3128 authfile.txt
1253 http-proxy proxy.example.net 3128 stdin
1254 http-proxy proxy.example.net 3128 auto basic
1255 http-proxy proxy.example.net 3128 auto-nct ntlm
1256 --http-proxy-option args
1258 Set extended HTTP proxy options. Requires an option type as ar‐
1259 gument and an optional parameter to the type. Repeat to set
1260 multiple options.
1261 VERSION version
1263 Set HTTP version number to version (default 1.0).
1264 AGENT user-agent
1266 Set HTTP "User-Agent" string to user-agent.
1267 CUSTOM-HEADER name content
1269 Adds the custom Header with name as name and content as
1270 the content of the custom HTTP header.
1271 Examples:
1273 http-proxy-option VERSION 1.1
1275 http-proxy-option AGENT OpenVPN/2.4
1276 http-proxy-option X-Proxy-Flag some-flags
1277 --socks-proxy args
1279 Connect to remote host through a Socks5 proxy. A required
1280 server argument is needed. Optionally a port (default 1080) and
1281 authfile can be given. The authfile is a file containing a
1282 username and password on 2 lines, or stdin can be used to prompt
1283 from console.
1284 Server Options
1286 Starting with OpenVPN 2.0, a multi-client TCP/UDP server mode is sup‐
1287 ported, and can be enabled with the --mode server option. In server
1288 mode, OpenVPN will listen on a single port for incoming client connec‐
1289 tions. All client connections will be routed through a single tun or
1290 tap interface. This mode is designed for scalability and should be able
1291 to support hundreds or even thousands of clients on sufficiently fast
1292 hardware. SSL/TLS authentication must be used in this mode.
1293 --auth-gen-token args
1295 Returns an authentication token to successfully authenticated
1296 clients.
1297 Valid syntax:
1299 auth-gen-token [lifetime] [external-auth]
1301 After successful user/password authentication, the OpenVPN
1303 server will with this option generate a temporary authentication
1304 token and push that to the client. On the following renegotia‐
1305 tions, the OpenVPN client will pass this token instead of the
1306 users password. On the server side the server will do the token
1307 authentication internally and it will NOT do any additional au‐
1308 thentications against configured external user/password authen‐
1309 tication mechanisms.
1310 The tokens implemented by this mechanism include an initial
1312 timestamp and a renew timestamp and are secured by HMAC.
1313 The lifetime argument defines how long the generated token is
1315 valid. The lifetime is defined in seconds. If lifetime is not
1316 set or it is set to 0, the token will never expire.
1317 The token will expire either after the configured lifetime of
1319 the token is reached or after not being renewed for more than 2
1320 * reneg-sec seconds. Clients will be sent renewed tokens on ev‐
1321 ery TLS renogiation to keep the client's token updated. This is
1322 done to invalidate a token if a client is disconnected for a
1323 sufficently long time, while at the same time permitting much
1324 longer token lifetimes for active clients.
1325 This feature is useful for environments which are configured to
1327 use One Time Passwords (OTP) as part of the user/password au‐
1328 thentications and that authentication mechanism does not imple‐
1329 ment any auth-token support.
1330 When the external-auth keyword is present the normal authentica‐
1332 tion method will always be called even if auth-token succeeds.
1333 Normally other authentications method are skipped if auth-token
1334 verification suceeds or fails.
1335 This option postpones this decision to the external authentica‐
1337 tion methods and checks the validity of the account and do other
1338 checks.
1339 In this mode the environment will have a session_id variable
1341 that holds the session id from auth-gen-token. Also an environ‐
1342 ment variable session_state is present. This variable indicates
1343 whether the auth-token has succeeded or not. It can have the
1344 following values:
1345 Initial
1347 No token from client.
1348 Authenticated
1350 Token is valid and not expired.
1351 Expired
1353 Token is valid but has expired.
1354 Invalid
1356 Token is invalid (failed HMAC or wrong length)
1357 AuthenticatedEmptyUser / ExpiredEmptyUser
1359 The token is not valid with the username sent from the
1360 client but would be valid (or expired) if we assume an
1361 empty username was used instead. These two cases are a
1362 workaround for behaviour in OpenVPN 3. If this work‐
1363 around is not needed these two cases should be handled in
1364 the same way as Invalid.
1365 Warning: Use this feature only if you want your authentication
1367 method called on every verification. Since the external authen‐
1368 tication is called it needs to also indicate a success or fail‐
1369 ure of the authentication. It is strongly recommended to return
1370 an authentication failure in the case of the Invalid/Expired
1371 auth-token with the external-auth option unless the client could
1372 authenticate in another acceptable way (e.g. client certifi‐
1373 cate), otherwise returning success will lead to authentication
1374 bypass (as does returning success on a wrong password from a
1375 script).
1376 --auth-gen-token-secret file
1378 Specifies a file that holds a secret for the HMAC used in
1379 --auth-gen-token If file is not present OpenVPN will generate a
1380 random secret on startup. This file should be used if auth-token
1381 should validate after restarting a server or if client should be
1382 able to roam between multiple OpenVPN servers with their
1383 auth-token.
1384 --auth-user-pass-optional
1386 Allow connections by clients that do not specify a user‐
1387 name/password. Normally, when --auth-user-pass-verify or --man‐
1388 agement-client-auth are specified (or an authentication plugin
1389 module), the OpenVPN server daemon will require connecting
1390 clients to specify a username and password. This option makes
1391 the submission of a username/password by clients optional, pass‐
1392 ing the responsibility to the user-defined authentication mod‐
1393 ule/script to accept or deny the client based on other factors
1394 (such as the setting of X509 certificate fields). When this op‐
1395 tion is used, and a connecting client does not submit a user‐
1396 name/password, the user-defined authentication module/script
1397 will see the username and password as being set to empty strings
1398 (""). The authentication module/script MUST have logic to detect
1399 this condition and respond accordingly.
1400 --ccd-exclusive
1402 Require, as a condition of authentication, that a connecting
1403 client has a --client-config-dir file.
1404 --client-config-dir dir
1406 Specify a directory dir for custom client config files. After a
1407 connecting client has been authenticated, OpenVPN will look in
1408 this directory for a file having the same name as the client's
1409 X509 common name. If a matching file exists, it will be opened
1410 and parsed for client-specific configuration options. If no
1411 matching file is found, OpenVPN will instead try to open and
1412 parse a default file called "DEFAULT", which may be provided but
1413 is not required. Note that the configuration files must be read‐
1414 able by the OpenVPN process after it has dropped it's root priv‐
1415 ileges.
1416 This file can specify a fixed IP address for a given client us‐
1418 ing --ifconfig-push, as well as fixed subnets owned by the
1419 client using --iroute.
1420 One of the useful properties of this option is that it allows
1422 client configuration files to be conveniently created, edited,
1423 or removed while the server is live, without needing to restart
1424 the server.
1425 The following options are legal in a client-specific context:
1427 --push, --push-reset, --push-remove, --iroute, --ifconfig-push,
1428 --vlan-pvid and --config.
1429 --client-to-client
1431 Because the OpenVPN server mode handles multiple clients through
1432 a single tun or tap interface, it is effectively a router. The
1433 --client-to-client flag tells OpenVPN to internally route
1434 client-to-client traffic rather than pushing all client-origi‐
1435 nating traffic to the TUN/TAP interface.
1436 When this option is used, each client will "see" the other
1438 clients which are currently connected. Otherwise, each client
1439 will only see the server. Don't use this option if you want to
1440 firewall tunnel traffic using custom, per-client rules.
1441 --disable
1443 Disable a particular client (based on the common name) from con‐
1444 necting. Don't use this option to disable a client due to key
1445 or password compromise. Use a CRL (certificate revocation list)
1446 instead (see the --crl-verify option).
1447 This option must be associated with a specific client instance,
1449 which means that it must be specified either in a client in‐
1450 stance config file using --client-config-dir or dynamically gen‐
1451 erated using a --client-connect script.
1452 --connect-freq args
1454 Allow a maximum of n new connections per sec seconds from
1455 clients.
1456 Valid syntax:
1458 connect-freq n sec
1460 This is designed to contain DoS attacks which flood the server
1462 with connection requests using certificates which will ulti‐
1463 mately fail to authenticate.
1464 This is an imperfect solution however, because in a real DoS
1466 scenario, legitimate connections might also be refused.
1467 For the best protection against DoS attacks in server mode, use
1469 --proto udp and either --tls-auth or --tls-crypt.
1470 --duplicate-cn
1472 Allow multiple clients with the same common name to concurrently
1473 connect. In the absence of this option, OpenVPN will disconnect
1474 a client instance upon connection of a new client having the
1475 same common name.
1476 --ifconfig-pool args
1478 Set aside a pool of subnets to be dynamically allocated to con‐
1479 necting clients, similar to a DHCP server.
1480 Valid syntax:
1482 ifconfig-pool start-IP end-IP [netmask]
1484 For tun-style tunnels, each client will be given a /30 subnet
1486 (for interoperability with Windows clients). For tap-style tun‐
1487 nels, individual addresses will be allocated, and the optional
1488 netmask parameter will also be pushed to clients.
1489 --ifconfig-ipv6-pool args
1491 Specify an IPv6 address pool for dynamic assignment to clients.
1492 Valid args:
1494 ifconfig-ipv6-pool ipv6addr/bits
1496 The pool starts at ipv6addr and matches the offset determined
1498 from the start of the IPv4 pool. If the host part of the given
1499 IPv6 address is 0, the pool starts at ipv6addr +1.
1500 --ifconfig-pool-persist args
1502 Persist/unpersist ifconfig-pool data to file, at seconds inter‐
1503 vals (default 600), as well as on program startup and shutdown.
1504 Valid syntax:
1506 ifconfig-pool-persist file [seconds]
1508 The goal of this option is to provide a long-term association
1510 between clients (denoted by their common name) and the virtual
1511 IP address assigned to them from the ifconfig-pool. Maintaining
1512 a long-term association is good for clients because it allows
1513 them to effectively use the --persist-tun option.
1514 file is a comma-delimited ASCII file, formatted as <Com‐
1516 mon-Name>,<IP-address>.
1517 If seconds = 0, file will be treated as read-only. This is use‐
1519 ful if you would like to treat file as a configuration file.
1520 Note that the entries in this file are treated by OpenVPN as
1522 suggestions only, based on past associations between a common
1523 name and IP address. They do not guarantee that the given com‐
1524 mon name will always receive the given IP address. If you want
1525 guaranteed assignment, use --ifconfig-push
1526 --ifconfig-push args
1528 Push virtual IP endpoints for client tunnel, overriding the
1529 --ifconfig-pool dynamic allocation.
1530 Valid syntax:
1532 ifconfig-push local remote-netmask [alias]
1534 The parameters local and remote-netmask are set according to the
1536 --ifconfig directive which you want to execute on the client ma‐
1537 chine to configure the remote end of the tunnel. Note that the
1538 parameters local and remote-netmask are from the perspective of
1539 the client, not the server. They may be DNS names rather than IP
1540 addresses, in which case they will be resolved on the server at
1541 the time of client connection.
1542 The optional alias parameter may be used in cases where NAT
1544 causes the client view of its local endpoint to differ from the
1545 server view. In this case local/remote-netmask will refer to the
1546 server view while alias/remote-netmask will refer to the client
1547 view.
1548 This option must be associated with a specific client instance,
1550 which means that it must be specified either in a client in‐
1551 stance config file using --client-config-dir or dynamically gen‐
1552 erated using a --client-connect script.
1553 Remember also to include a --route directive in the main OpenVPN
1555 config file which encloses local, so that the kernel will know
1556 to route it to the server's TUN/TAP interface.
1557 OpenVPN's internal client IP address selection algorithm works
1559 as follows:
1560 1. Use --client-connect script generated file for static IP
1562 (first choice).
1563 2. Use --client-config-dir file for static IP (next choice).
1565 3. Use --ifconfig-pool allocation for dynamic IP (last choice).
1567 --ifconfig-ipv6-push args
1569 for --client-config-dir per-client static IPv6 interface config‐
1570 uration, see --client-config-dir and --ifconfig-push for more
1571 details.
1572 Valid syntax:
1574 ifconfig-ipv6-push ipv6addr/bits ipv6remote
1576 --inetd args
1578 Valid syntaxes:
1579 inetd
1581 inetd wait
1582 inetd nowait
1583 inetd wait progname
1584 Use this option when OpenVPN is being run from the inetd or
1586 xinetd(8) server.
1587 The wait and nowait option must match what is specified in the
1589 inetd/xinetd config file. The nowait mode can only be used with
1590 --proto tcp-server The default is wait. The nowait mode can be
1591 used to instantiate the OpenVPN daemon as a classic TCP server,
1592 where client connection requests are serviced on a single port
1593 number. For additional information on this kind of configura‐
1594 tion, see the OpenVPN FAQ:
1595 https://community.openvpn.net/openvpn/wiki/325-openvpn-as-a--forking-tcp-server-which-can-service-multiple-clients-over-a-single-tcp-port
1596 This option precludes the use of --daemon, --local or --remote.
1598 Note that this option causes message and error output to be han‐
1599 dled in the same way as the --daemon option. The optional prog‐
1600 name parameter is also handled exactly as in --daemon.
1601 Also note that in wait mode, each OpenVPN tunnel requires a sep‐
1603 arate TCP/UDP port and a separate inetd or xinetd entry. See the
1604 OpenVPN 1.x HOWTO for an example on using OpenVPN with xinetd:
1605 https://openvpn.net/community-resources/1xhowto/
1606 --multihome
1608 Configure a multi-homed UDP server. This option needs to be used
1609 when a server has more than one IP address (e.g. multiple inter‐
1610 faces, or secondary IP addresses), and is not using --local to
1611 force binding to one specific address only. This option will add
1612 some extra lookups to the packet path to ensure that the UDP re‐
1613 ply packets are always sent from the address that the client is
1614 talking to. This is not supported on all platforms, and it adds
1615 more processing, so it's not enabled by default.
1616 Notes:
1618 • This option is only relevant for UDP servers.
1620 • If you do an IPv6+IPv4 dual-stack bind on a Linux ma‐
1622 chine with multiple IPv4 address, connections to IPv4
1623 addresses will not work right on kernels before 3.15,
1624 due to missing kernel support for the IPv4-mapped case
1625 (some distributions have ported this to earlier kernel
1626 versions, though).
1627 --iroute args
1629 Generate an internal route to a specific client. The netmask pa‐
1630 rameter, if omitted, defaults to 255.255.255.255.
1631 Valid syntax:
1633 iroute network [netmask]
1635 This directive can be used to route a fixed subnet from the
1637 server to a particular client, regardless of where the client is
1638 connecting from. Remember that you must also add the route to
1639 the system routing table as well (such as by using the --route
1640 directive). The reason why two routes are needed is that the
1641 --route directive routes the packet from the kernel to OpenVPN.
1642 Once in OpenVPN, the --iroute directive routes to the specific
1643 client.
1644 This option must be specified either in a client instance config
1646 file using --client-config-dir or dynamically generated using a
1647 --client-connect script.
1648 The --iroute directive also has an important interaction with
1650 --push "route ...". --iroute essentially defines a subnet which
1651 is owned by a particular client (we will call this client A). If
1652 you would like other clients to be able to reach A's subnet, you
1653 can use --push "route ..." together with --client-to-client to
1654 effect this. In order for all clients to see A's subnet, OpenVPN
1655 must push this route to all clients EXCEPT for A, since the sub‐
1656 net is already owned by A. OpenVPN accomplishes this by not not
1657 pushing a route to a client if it matches one of the client's
1658 iroutes.
1659 --iroute-ipv6 args
1661 for --client-config-dir per-client static IPv6 route configura‐
1662 tion, see --iroute for more details how to setup and use this,
1663 and how --iroute and --route interact.
1664 Valid syntax:
1666 iroute-ipv6 ipv6addr/bits
1668 --max-clients n
1670 Limit server to a maximum of n concurrent clients.
1671 --max-routes-per-client n
1673 Allow a maximum of n internal routes per client (default 256).
1674 This is designed to help contain DoS attacks where an authenti‐
1675 cated client floods the server with packets appearing to come
1676 from many unique MAC addresses, forcing the server to deplete
1677 virtual memory as its internal routing table expands. This di‐
1678 rective can be used in a --client-config-dir file or auto-gener‐
1679 ated by a --client-connect script to override the global value
1680 for a particular client.
1681 Note that this directive affects OpenVPN's internal routing ta‐
1683 ble, not the kernel routing table.
1684 --opt-verify
1686 Clients that connect with options that are incompatible with
1687 those of the server will be disconnected.
1688 Options that will be compared for compatibility include
1690 dev-type, link-mtu, tun-mtu, proto, ifconfig, comp-lzo, frag‐
1691 ment, keydir, cipher, auth, keysize, secret, no-replay,
1692 tls-auth, key-method, tls-server and tls-client.
1693 This option requires that --disable-occ NOT be used.
1695 --port-share args
1697 Share OpenVPN TCP with another service
1698 Valid syntax:
1700 port-share host port [dir]
1702 When run in TCP server mode, share the OpenVPN port with another
1704 application, such as an HTTPS server. If OpenVPN senses a con‐
1705 nection to its port which is using a non-OpenVPN protocol, it
1706 will proxy the connection to the server at host:port. Currently
1707 only designed to work with HTTP/HTTPS, though it would be theo‐
1708 retically possible to extend to other protocols such as ssh.
1709 dir specifies an optional directory where a temporary file with
1711 name N containing content C will be dynamically generated for
1712 each proxy connection, where N is the source IP:port of the
1713 client connection and C is the source IP:port of the connection
1714 to the proxy receiver. This directory can be used as a dictio‐
1715 nary by the proxy receiver to determine the origin of the con‐
1716 nection. Each generated file will be automatically deleted when
1717 the proxied connection is torn down.
1718 Not implemented on Windows.
1720 --push option
1722 Push a config file option back to the client for remote execu‐
1723 tion. Note that option must be enclosed in double quotes ("").
1724 The client must specify --pull in its config file. The set of
1725 options which can be pushed is limited by both feasibility and
1726 security. Some options such as those which would execute scripts
1727 are banned, since they would effectively allow a compromised
1728 server to execute arbitrary code on the client. Other options
1729 such as TLS or MTU parameters cannot be pushed because the
1730 client needs to know them before the connection to the server
1731 can be initiated.
1732 This is a partial list of options which can currently be pushed:
1734 --route, --route-gateway, --route-delay, --redirect-gateway,
1735 --ip-win32, --dhcp-option, --inactive, --ping, --ping-exit,
1736 --ping-restart, --setenv, --auth-token, --persist-key, --per‐
1737 sist-tun, --echo, --comp-lzo, --socket-flags, --sndbuf, --rcvbuf
1738 --push-peer-info
1740 Push additional information about the client to server. The fol‐
1741 lowing data is always pushed to the server:
1742 IV_VER=<version>
1744 The client OpenVPN version
1745 IV_PLAT=[linux|solaris|openbsd|mac|netbsd|freebsd|win]
1747 The client OS platform
1748 IV_LZO_STUB=1
1750 If client was built with LZO stub capability
1751 IV_LZ4=1
1753 If the client supports LZ4 compressions.
1754 IV_PROTO
1756 Details about protocol extensions that the peer supports.
1757 The variable is a bitfield and the bits are defined as
1758 follows (starting a bit 0 for the first (unused) bit:
1759 • bit 1: The peer supports peer-id floating mechanism
1761 • bit 2: The client expects a push-reply and the server
1763 may send this reply without waiting for a push-request
1764 first.
1765 IV_NCP=2
1767 Negotiable ciphers, client supports --cipher pushed by
1768 the server, a value of 2 or greater indicates client sup‐
1769 ports AES-GCM-128 and AES-GCM-256.
1770 IV_CIPHERS=<ncp-ciphers>
1772 The client announces the list of supported ciphers con‐
1773 figured with the --data-ciphers option to the server.
1774 IV_GUI_VER=<gui_id> <version>
1776 The UI version of a UI if one is running, for example
1777 de.blinkt.openvpn 0.5.47 for the Android app.
1778 IV_SSO=[crtext,][openurl,][proxy_url]
1780 Additional authentication methods supported by the
1781 client. This may be set by the client UI/GUI using
1782 --setenv
1783 When --push-peer-info is enabled the additional information con‐
1785 sists of the following data:
1786 IV_HWADDR=<string>
1788 This is intended to be a unique and persistent ID of the
1789 client. The string value can be any readable ASCII
1790 string up to 64 bytes. OpenVPN 2.x and some other imple‐
1791 mentations use the MAC address of the client's interface
1792 used to reach the default gateway. If this string is gen‐
1793 erated by the client, it should be consistent and pre‐
1794 served across independent session and preferably re-in‐
1795 stallations and upgrades.
1796 IV_SSL=<version string>
1798 The ssl version used by the client, e.g. OpenSSL 1.0.2f
1799 28 Jan 2016.
1800 IV_PLAT_VER=x.y
1802 The version of the operating system, e.g. 6.1 for Windows
1803 7.
1804 UV_<name>=<value>
1806 Client environment variables whose names start with UV_
1807 --push-remove opt
1809 Selectively remove all --push options matching "opt" from the
1810 option list for a client. opt is matched as a substring against
1811 the whole option string to-be-pushed to the client, so
1812 --push-remove route would remove all --push route ... and --push
1813 route-ipv6 ... statements, while --push-remove "route-ipv6
1814 2001:" would only remove IPv6 routes for 2001:... networks.
1815 --push-remove can only be used in a client-specific context,
1817 like in a --client-config-dir file, or --client-connect script
1818 or plugin -- similar to --push-reset, just more selective.
1819 NOTE: to change an option, --push-remove can be used to first
1821 remove the old value, and then add a new --push option with the
1822 new value.
1823 NOTE 2: due to implementation details, 'ifconfig' and 'ifcon‐
1825 fig-ipv6' can only be removed with an exact match on the option
1826 ( push-remove ifconfig), no substring matching and no matching
1827 on the IPv4/IPv6 address argument is possible.
1828 --push-reset
1830 Don't inherit the global push list for a specific client in‐
1831 stance. Specify this option in a client-specific context such
1832 as with a --client-config-dir configuration file. This option
1833 will ignore --push options at the global config file level.
1834 NOTE: --push-reset is very thorough: it will remove almost all
1836 options from the list of to-be-pushed options. In many cases,
1837 some of these options will need to be re-configured afterwards -
1838 specifically, --topology subnet and --route-gateway will get
1839 lost and this will break client configs in many cases. Thus,
1840 for most purposes, --push-remove is better suited to selectively
1841 remove push options for individual clients.
1842 --server args
1844 A helper directive designed to simplify the configuration of
1845 OpenVPN's server mode. This directive will set up an OpenVPN
1846 server which will allocate addresses to clients out of the given
1847 network/netmask. The server itself will take the .1 address of
1848 the given network for use as the server-side endpoint of the lo‐
1849 cal TUN/TAP interface. If the optional nopool flag is given, no
1850 dynamic IP address pool will prepared for VPN clients.
1851 Valid syntax:
1853 server network netmask [nopool]
1855 For example, --server 10.8.0.0 255.255.255.0 expands as follows:
1857 mode server
1859 tls-server
1860 push "topology [topology]"
1861 if dev tun AND (topology == net30 OR topology == p2p):
1863 ifconfig 10.8.0.1 10.8.0.2
1864 if !nopool:
1865 ifconfig-pool 10.8.0.4 10.8.0.251
1866 route 10.8.0.0 255.255.255.0
1867 if client-to-client:
1868 push "route 10.8.0.0 255.255.255.0"
1869 else if topology == net30:
1870 push "route 10.8.0.1"
1871 if dev tap OR (dev tun AND topology == subnet):
1873 ifconfig 10.8.0.1 255.255.255.0
1874 if !nopool:
1875 ifconfig-pool 10.8.0.2 10.8.0.253 255.255.255.0
1876 push "route-gateway 10.8.0.1"
1877 if route-gateway unset:
1878 route-gateway 10.8.0.2
1879 Don't use --server if you are ethernet bridging. Use
1881 --server-bridge instead.
1882 --server-bridge args
1884 A helper directive similar to --server which is designed to sim‐
1885 plify the configuration of OpenVPN's server mode in ethernet
1886 bridging configurations.
1887 Valid syntaxes:
1889 server-bridge gateway netmask pool-start-IP pool-end-IP
1891 server-bridge [nogw]
1892 If --server-bridge is used without any parameters, it will en‐
1894 able a DHCP-proxy mode, where connecting OpenVPN clients will
1895 receive an IP address for their TAP adapter from the DHCP server
1896 running on the OpenVPN server-side LAN. Note that only clients
1897 that support the binding of a DHCP client with the TAP adapter
1898 (such as Windows) can support this mode. The optional nogw flag
1899 (advanced) indicates that gateway information should not be
1900 pushed to the client.
1901 To configure ethernet bridging, you must first use your OS's
1903 bridging capability to bridge the TAP interface with the ether‐
1904 net NIC interface. For example, on Linux this is done with the
1905 brctl tool, and with Windows XP it is done in the Network Con‐
1906 nections Panel by selecting the ethernet and TAP adapters and
1907 right-clicking on "Bridge Connections".
1908 Next you you must manually set the IP/netmask on the bridge in‐
1910 terface. The gateway and netmask parameters to --server-bridge
1911 can be set to either the IP/netmask of the bridge interface, or
1912 the IP/netmask of the default gateway/router on the bridged sub‐
1913 net.
1914 Finally, set aside a IP range in the bridged subnet, denoted by
1916 pool-start-IP and pool-end-IP, for OpenVPN to allocate to con‐
1917 necting clients.
1918 For example, server-bridge 10.8.0.4 255.255.255.0 10.8.0.128
1920 10.8.0.254 expands as follows:
1921 mode server
1923 tls-server
1924 ifconfig-pool 10.8.0.128 10.8.0.254 255.255.255.0
1926 push "route-gateway 10.8.0.4"
1927 In another example, --server-bridge (without parameters) expands
1929 as follows:
1930 mode server
1932 tls-server
1933 push "route-gateway dhcp"
1935 Or --server-bridge nogw expands as follows:
1937 mode server
1939 tls-server
1940 --server-ipv6 args
1942 Convenience-function to enable a number of IPv6 related options
1943 at once, namely --ifconfig-ipv6, --ifconfig-ipv6-pool and --push
1944 tun-ipv6.
1945 Valid syntax:
1947 server-ipv6 ipv6addr/bits
1949 Pushing of the --tun-ipv6 directive is done for older clients
1951 which require an explicit --tun-ipv6 in their configuration.
1952 --stale-routes-check args
1954 Remove routes which haven't had activity for n seconds (i.e. the
1955 ageing time). This check is run every t seconds (i.e. check in‐
1956 terval).
1957 Valid syntax:
1959 stale-routes-check n [t]
1961 If t is not present it defaults to n.
1963 This option helps to keep the dynamic routing table small. See
1965 also --max-routes-per-client
1966 --username-as-common-name
1968 Use the authenticated username as the common-name, rather than
1969 the common-name from the client certificate. Requires that some
1970 form of --auth-user-pass verification is in effect. As the re‐
1971 placement happens after --auth-user-pass verification, the veri‐
1972 fication script or plugin will still receive the common-name
1973 from the certificate.
1974 The common_name environment variable passed to scripts and plug‐
1976 ins invoked after authentication (e.g, client-connect script)
1977 and file names parsed in client-config directory will match the
1978 username.
1979 --verify-client-cert mode
1981 Specify whether the client is required to supply a valid cer‐
1982 tificate.
1983 Possible mode options are:
1985 none A client certificate is not required. the client needs to
1987 authenticate using username/password only. Be aware that
1988 using this directive is less secure than requiring cer‐
1989 tificates from all clients.
1990 If you use this directive, the entire responsibility of
1992 authentication will rest on your --auth-user-pass-verify
1993 script, so keep in mind that bugs in your script could
1994 potentially compromise the security of your VPN.
1995 --verify-client-cert none is functionally equivalent to
1997 --client-cert-not-required.
1998 optional
2000 A client may present a certificate but it is not required
2001 to do so. When using this directive, you should also use
2002 a --auth-user-pass-verify script to ensure that clients
2003 are authenticated using a certificate, a username and
2004 password, or possibly even both.
2005 Again, the entire responsibility of authentication will
2007 rest on your --auth-user-pass-verify script, so keep in
2008 mind that bugs in your script could potentially compro‐
2009 mise the security of your VPN.
2010 require
2012 This is the default option. A client is required to
2013 present a certificate, otherwise VPN access is refused.
2014 If you don't use this directive (or use --verify-client-cert re‐
2016 quire) but you also specify an --auth-user-pass-verify script,
2017 then OpenVPN will perform double authentication. The client cer‐
2018 tificate verification AND the --auth-user-pass-verify script
2019 will need to succeed in order for a client to be authenticated
2020 and accepted onto the VPN.
2021 --vlan-tagging
2023 Server-only option. Turns the OpenVPN server instance into a
2024 switch that understands VLAN-tagging, based on IEEE 802.1Q.
2025 The server TAP device and each of the connecting clients is seen
2027 as a port of the switch. All client ports are in untagged mode
2028 and the server TAP device is VLAN-tagged, untagged or accepts
2029 both, depending on the --vlan-accept setting.
2030 Ethernet frames with a prepended 802.1Q tag are called "tagged".
2032 If the VLAN Identifier (VID) field in such a tag is non-zero,
2033 the frame is called "VLAN-tagged". If the VID is zero, but the
2034 Priority Control Point (PCP) field is non-zero, the frame is
2035 called "prio-tagged". If there is no 802.1Q tag, the frame is
2036 "untagged".
2037 Using the --vlan-pvid v option once per client (see
2039 --client-config-dir), each port can be associated with a certain
2040 VID. Packets can only be forwarded between ports having the
2041 same VID. Therefore, clients with differing VIDs are completely
2042 separated from one-another, even if --client-to-client is acti‐
2043 vated.
2044 The packet filtering takes place in the OpenVPN server. Clients
2046 should not have any VLAN tagging configuration applied.
2047 The --vlan-tagging option is off by default. While turned off,
2049 OpenVPN accepts any Ethernet frame and does not perform any spe‐
2050 cial processing for VLAN-tagged packets.
2051 This option can only be activated in --dev tap mode.
2053 --vlan-accept args
2055 Configure the VLAN tagging policy for the server TAP device.
2056 Valid syntax:
2058 vlan-accept all|tagged|untagged
2060 The following modes are available:
2062 tagged Admit only VLAN-tagged frames. Only VLAN-tagged packets
2064 are accepted, while untagged or priority-tagged packets
2065 are dropped when entering the server TAP device.
2066 untagged
2068 Admit only untagged and prio-tagged frames. VLAN-tagged
2069 packets are not accepted, while untagged or prior‐
2070 ity-tagged packets entering the server TAP device are
2071 tagged with the value configured for the global
2072 --vlan-pvid setting.
2073 all (default)
2075 Admit all frames. All packets are admitted and then
2076 treated like untagged or tagged mode respectively.
2077 Note: Some vendors refer to switch ports running in tagged mode
2079 as "trunk ports" and switch ports running in untagged
2080 mode as "access ports".
2081 Packets forwarded from clients to the server are VLAN-tagged
2083 with the originating client's PVID, unless the VID matches the
2084 global --vlan-pvid, in which case the tag is removed.
2085 If no PVID is configured for a given client (see --vlan-pvid)
2087 packets are tagged with 1 by default.
2088 --vlan-pvid v
2090 Specifies which VLAN identifier a "port" is associated with.
2091 Only valid when --vlan-tagging is speficied.
2092 In the client context, the setting specifies which VLAN ID a
2094 client is associated with. In the global context, the VLAN ID of
2095 the server TAP device is set. The latter only makes sense for
2096 --vlan-accept untagged and --vlan-accept all modes.
2097 Valid values for v go from 1 through to 4094. The global value
2099 defaults to 1. If no --vlan-pvid is specified in the client con‐
2100 text, the global value is inherited.
2101 In some switch implementations, the PVID is also referred to as
2103 "Native VLAN".
2104
2106 SSL Library information
2107 --show-ciphers
2108 (Standalone) Show all cipher algorithms to use with the --cipher
2109 option.
2110 --show-digests
2112 (Standalone) Show all message digest algorithms to use with the
2113 --auth option.
2114 --show-tls
2116 (Standalone) Show all TLS ciphers supported by the crypto li‐
2117 brary. OpenVPN uses TLS to secure the control channel, over
2118 which the keys that are used to protect the actual VPN traffic
2119 are exchanged. The TLS ciphers will be sorted from highest pref‐
2120 erence (most secure) to lowest.
2121 Be aware that whether a cipher suite in this list can actually
2123 work depends on the specific setup of both peers (e.g. both
2124 peers must support the cipher, and an ECDSA cipher suite will
2125 not work if you are using an RSA certificate, etc.).
2126 --show-engines
2128 (Standalone) Show currently available hardware-based crypto ac‐
2129 celeration engines supported by the OpenSSL library.
2130 --show-groups
2132 (Standalone) Show all available elliptic curves/groups to use
2133 with the --ecdh-curve and tls-groups options.
2134 Generating key material
2136 --genkey args
2137 (Standalone) Generate a key to be used of the type keytype. if
2138 keyfile is left out or empty the key will be output on stdout.
2139 See the following sections for the different keytypes.
2140 Valid syntax:
2142 --genkey keytype keyfile
2144 Valid keytype arguments are:
2146 secret Standard OpenVPN shared secret keys
2148 tls-crypt Alias for secret
2150 tls-auth Alias for secret
2152 auth-token Key used for --auth-gen-token-key
2154 tls-crypt-v2-server TLS Crypt v2 server key
2156 tls-crypt-v2-client TLS Crypt v2 client key
2158 Examples:
2160 $ openvpn --genkey secret shared.key
2162 $ openvpn --genkey tls-crypt shared.key
2163 $ openvpn --genkey tls-auth shared.key
2164 $ openvpn --genkey tls-crypt-v2-server v2crypt-server.key
2165 $ openvpn --tls-crypt-v2 v2crypt-server.key --genkey tls-crypt-v2-client v2crypt-client-1.key
2166 • Generating Shared Secret Keys Generate a shared secret, for
2168 use with the --secret, --tls-auth or --tls-crypt options.
2169 Syntax:
2171 $ openvpn --genkey secret|tls-crypt|tls-auth keyfile
2173 The key is saved in keyfile. All three variants (--secret,
2175 tls-crypt and tls-auth) generate the same type of key. The
2176 aliases are added for convenience.
2177 If using this for --secret, this file must be shared with the
2179 peer over a pre-existing secure channel such as scp(1).
2180 • Generating TLS Crypt v2 Server key Generate a --tls-crypt-v2
2182 key to be used by an OpenVPN server. The key is stored in
2183 keyfile.
2184 Syntax:
2186 --genkey tls-crypt-v2-server keyfile
2188 • Generating TLS Crypt v2 Client key Generate a --tls-crypt-v2
2190 key to be used by OpenVPN clients. The key is stored in key‐
2191 file.
2192 Syntax
2194 --genkey tls-crypt-v2-client keyfile [metadata]
2196 If supplied, include the supplied metadata in the wrapped
2198 client key. This metadata must be supplied in base64-encoded
2199 form. The metadata must be at most 735 bytes long (980 bytes
2200 in base64).
2201 If no metadata is supplied, OpenVPN will use a 64-bit unix
2203 timestamp representing the current time in UTC, encoded in
2204 network order, as metadata for the generated key.
2205 A tls-crypt-v2 client key is wrapped using a server key. To
2207 generate a client key, the user must therefore supply the
2208 server key using the --tls-crypt-v2 option.
2209 Servers can use --tls-crypt-v2-verify to specify a metadata
2211 verification command.
2212 • Generate Authentication Token key Generate a new secret that
2214 can be used with --auth-gen-token-secret
2215 Syntax:
2217 --genkey auth-token [keyfile]
2219 Note: This file should be kept secret to the server as anyone
2221 that has access to this file will be able to generate
2222 auth tokens that the OpenVPN server will accept as
2223 valid.
2224 Data Channel Renegotiation
2226 When running OpenVPN in client/server mode, the data channel will use a
2227 separate ephemeral encryption key which is rotated at regular inter‐
2228 vals.
2229 --reneg-bytes n
2231 Renegotiate data channel key after n bytes sent or received
2232 (disabled by default with an exception, see below). OpenVPN al‐
2233 lows the lifetime of a key to be expressed as a number of bytes
2234 encrypted/decrypted, a number of packets, or a number of sec‐
2235 onds. A key renegotiation will be forced if any of these three
2236 criteria are met by either peer.
2237 If using ciphers with cipher block sizes less than 128-bits,
2239 --reneg-bytes is set to 64MB by default, unless it is explicitly
2240 disabled by setting the value to 0, but this is HIGHLY DISCOUR‐
2241 AGED as this is designed to add some protection against the
2242 SWEET32 attack vector. For more information see the --cipher op‐
2243 tion.
2244 --reneg-pkts n
2246 Renegotiate data channel key after n packets sent and received
2247 (disabled by default).
2248 --reneg-sec args
2250 Renegotiate data channel key after at most max seconds (default
2251 3600) and at least min seconds (default is 90% of max for
2252 servers, and equal to max for clients).
2253 reneg-sec max [min]
2255 The effective --reneg-sec value used is per session pseudo-uni‐
2257 form-randomized between min and max.
2258 With the default value of 3600 this results in an effective per
2260 session value in the range of 3240 .. 3600 seconds for servers,
2261 or just 3600 for clients.
2262 When using dual-factor authentication, note that this default
2264 value may cause the end user to be challenged to reauthorize
2265 once per hour.
2266 Also, keep in mind that this option can be used on both the
2268 client and server, and whichever uses the lower value will be
2269 the one to trigger the renegotiation. A common mistake is to set
2270 --reneg-sec to a higher value on either the client or server,
2271 while the other side of the connection is still using the de‐
2272 fault value of 3600 seconds, meaning that the renegotiation will
2273 still occur once per 3600 seconds. The solution is to increase
2274 --reneg-sec on both the client and server, or set it to 0 on one
2275 side of the connection (to disable), and to your chosen value on
2276 the other side.
2277 TLS Mode Options
2279 TLS mode is the most powerful crypto mode of OpenVPN in both security
2280 and flexibility. TLS mode works by establishing control and data chan‐
2281 nels which are multiplexed over a single TCP/UDP port. OpenVPN initi‐
2282 ates a TLS session over the control channel and uses it to exchange ci‐
2283 pher and HMAC keys to protect the data channel. TLS mode uses a robust
2284 reliability layer over the UDP connection for all control channel com‐
2285 munication, while the data channel, over which encrypted tunnel data
2286 passes, is forwarded without any mediation. The result is the best of
2287 both worlds: a fast data channel that forwards over UDP with only the
2288 overhead of encrypt, decrypt, and HMAC functions, and a control channel
2289 that provides all of the security features of TLS, including certifi‐
2290 cate-based authentication and Diffie Hellman forward secrecy.
2291 To use TLS mode, each peer that runs OpenVPN should have its own local
2293 certificate/key pair (--cert and --key), signed by the root certificate
2294 which is specified in --ca.
2295 When two OpenVPN peers connect, each presents its local certificate to
2297 the other. Each peer will then check that its partner peer presented a
2298 certificate which was signed by the master root certificate as speci‐
2299 fied in --ca.
2300 If that check on both peers succeeds, then the TLS negotiation will
2302 succeed, both OpenVPN peers will exchange temporary session keys, and
2303 the tunnel will begin passing data.
2304 The OpenVPN project provides a set of scripts for managing RSA certifi‐
2306 cates and keys: https://github.com/OpenVPN/easy-rsa
2307 --askpass file
2309 Get certificate password from console or file before we daemo‐
2310 nize.
2311 Valid syntaxes:
2313 askpass
2315 askpass file
2316 For the extremely security conscious, it is possible to protect
2318 your private key with a password. Of course this means that ev‐
2319 ery time the OpenVPN daemon is started you must be there to type
2320 the password. The --askpass option allows you to start OpenVPN
2321 from the command line. It will query you for a password before
2322 it daemonizes. To protect a private key with a password you
2323 should omit the -nodes option when you use the openssl command
2324 line tool to manage certificates and private keys.
2325 If file is specified, read the password from the first line of
2327 file. Keep in mind that storing your password in a file to a
2328 certain extent invalidates the extra security provided by using
2329 an encrypted key.
2330 --ca file
2332 Certificate authority (CA) file in .pem format, also referred to
2333 as the root certificate. This file can have multiple certifi‐
2334 cates in .pem format, concatenated together. You can construct
2335 your own certificate authority certificate and private key by
2336 using a command such as:
2337 openssl req -nodes -new -x509 -keyout ca.key -out ca.crt
2339 Then edit your openssl.cnf file and edit the certificate vari‐
2341 able to point to your new root certificate ca.crt.
2342 For testing purposes only, the OpenVPN distribution includes a
2344 sample CA certificate (ca.crt). Of course you should never use
2345 the test certificates and test keys distributed with OpenVPN in
2346 a production environment, since by virtue of the fact that they
2347 are distributed with OpenVPN, they are totally insecure.
2348 --capath dir
2350 Directory containing trusted certificates (CAs and CRLs). Not
2351 available with mbed TLS.
2352 CAs in the capath directory are expected to be named <hash>.<n>.
2354 CRLs are expected to be named <hash>.r<n>. See the -CApath op‐
2355 tion of openssl verify, and the -hash option of openssl x509,
2356 openssl crl and X509_LOOKUP_hash_dir()[22m(3) for more information.
2357 Similar to the --crl-verify option, CRLs are not mandatory -
2359 OpenVPN will log the usual warning in the logs if the relevant
2360 CRL is missing, but the connection will be allowed.
2361 --cert file
2363 Local peer's signed certificate in .pem format -- must be signed
2364 by a certificate authority whose certificate is in --ca file.
2365 Each peer in an OpenVPN link running in TLS mode should have its
2366 own certificate and private key file. In addition, each certifi‐
2367 cate should have been signed by the key of a certificate author‐
2368 ity whose public key resides in the --ca certificate authority
2369 file. You can easily make your own certificate authority (see
2370 above) or pay money to use a commercial service such as
2371 thawte.com (in which case you will be helping to finance the
2372 world's second space tourist :). To generate a certificate, you
2373 can use a command such as:
2374 openssl req -nodes -new -keyout mycert.key -out mycert.csr
2376 If your certificate authority private key lives on another ma‐
2378 chine, copy the certificate signing request (mycert.csr) to this
2379 other machine (this can be done over an insecure channel such as
2380 email). Now sign the certificate with a command such as:
2381 openssl ca -out mycert.crt -in mycert.csr
2383 Now copy the certificate (mycert.crt) back to the peer which
2385 initially generated the .csr file (this can be over a public
2386 medium). Note that the openssl ca command reads the location of
2387 the certificate authority key from its configuration file such
2388 as /usr/share/ssl/openssl.cnf -- note also that for certificate
2389 authority functions, you must set up the files index.txt (may be
2390 empty) and serial (initialize to 01).
2391 --crl-verify args
2393 Check peer certificate against a Certificate Revocation List.
2394 Valid syntax:
2396 crl-verify file/directory flag
2398 Examples:
2400 crl-verify crl-file.pem
2402 crl-verify /etc/openvpn/crls dir
2403 A CRL (certificate revocation list) is used when a particular
2405 key is compromised but when the overall PKI is still intact.
2406 Suppose you had a PKI consisting of a CA, root certificate, and
2408 a number of client certificates. Suppose a laptop computer con‐
2409 taining a client key and certificate was stolen. By adding the
2410 stolen certificate to the CRL file, you could reject any connec‐
2411 tion which attempts to use it, while preserving the overall in‐
2412 tegrity of the PKI.
2413 The only time when it would be necessary to rebuild the entire
2415 PKI from scratch would be if the root certificate key itself was
2416 compromised.
2417 The option is not mandatory - if the relevant CRL is missing,
2419 OpenVPN will log a warning in the logs - e.g.
2420 VERIFY WARNING: depth=0, unable to get certificate CRL
2422 but the connection will be allowed. If the optional dir flag is
2424 specified, enable a different mode where the crl-verify is
2425 pointed at a directory containing files named as revoked serial
2426 numbers (the files may be empty, the contents are never read).
2427 If a client requests a connection, where the client certificate
2428 serial number (decimal string) is the name of a file present in
2429 the directory, it will be rejected.
2430 Note: As the crl file (or directory) is read every time a peer
2432 connects, if you are dropping root privileges with
2433 --user, make sure that this user has sufficient privi‐
2434 leges to read the file.
2435 --dh file
2437 File containing Diffie Hellman parameters in .pem format (re‐
2438 quired for --tls-server only).
2439 Set file to none to disable Diffie Hellman key exchange (and use
2441 ECDH only). Note that this requires peers to be using an SSL li‐
2442 brary that supports ECDH TLS cipher suites (e.g. OpenSSL 1.0.1+,
2443 or mbed TLS 2.0+).
2444 Use openssl dhparam -out dh2048.pem 2048 to generate 2048-bit DH
2446 parameters. Diffie Hellman parameters may be considered public.
2447 --ecdh-curve name
2449 Specify the curve to use for elliptic curve Diffie Hellman.
2450 Available curves can be listed with --show-curves. The specified
2451 curve will only be used for ECDH TLS-ciphers.
2452 This option is not supported in mbed TLS builds of OpenVPN.
2454 --extra-certs file
2456 Specify a file containing one or more PEM certs (concatenated
2457 together) that complete the local certificate chain.
2458 This option is useful for "split" CAs, where the CA for server
2460 certs is different than the CA for client certs. Putting certs
2461 in this file allows them to be used to complete the local cer‐
2462 tificate chain without trusting them to verify the peer-submit‐
2463 ted certificate, as would be the case if the certs were placed
2464 in the ca file.
2465 --hand-window n
2467 Handshake Window -- the TLS-based key exchange must finalize
2468 within n seconds of handshake initiation by any peer (default 60
2469 seconds). If the handshake fails we will attempt to reset our
2470 connection with our peer and try again. Even in the event of
2471 handshake failure we will still use our expiring key for up to
2472 --tran-window seconds to maintain continuity of transmission of
2473 tunnel data.
2474 --key file
2476 Local peer's private key in .pem format. Use the private key
2477 which was generated when you built your peer's certificate (see
2478 --cert file above).
2479 --pkcs12 file
2481 Specify a PKCS #12 file containing local private key, local cer‐
2482 tificate, and root CA certificate. This option can be used in‐
2483 stead of --ca, --cert, and --key. Not available with mbed TLS.
2484 --remote-cert-eku oid
2486 Require that peer certificate was signed with an explicit ex‐
2487 tended key usage.
2488 This is a useful security option for clients, to ensure that the
2490 host they connect to is a designated server.
2491 The extended key usage should be encoded in oid notation, or
2493 OpenSSL symbolic representation.
2494 --remote-cert-ku key-usage
2496 Require that peer certificate was signed with an explicit
2497 key-usage.
2498 If present in the certificate, the keyUsage value is validated
2500 by the TLS library during the TLS handshake. Specifying this op‐
2501 tion without arguments requires this extension to be present (so
2502 the TLS library will verify it).
2503 If key-usage is a list of usage bits, the keyUsage field must
2505 have at least the same bits set as the bits in one of the values
2506 supplied in the key-usage list.
2507 The key-usage values in the list must be encoded in hex, e.g.
2509 remote-cert-ku a0
2511 --remote-cert-tls type
2513 Require that peer certificate was signed with an explicit key
2514 usage and extended key usage based on RFC3280 TLS rules.
2515 Valid syntaxes:
2517 remote-cert-tls server
2519 remote-cert-tls client
2520 This is a useful security option for clients, to ensure that the
2522 host they connect to is a designated server. Or the other way
2523 around; for a server to verify that only hosts with a client
2524 certificate can connect.
2525 The --remote-cert-tls client option is equivalent to
2527 remote-cert-ku
2529 remote-cert-eku "TLS Web Client Authentication"
2530 The --remote-cert-tls server option is equivalent to
2532 remote-cert-ku
2534 remote-cert-eku "TLS Web Server Authentication"
2535 This is an important security precaution to protect against a
2537 man-in-the-middle attack where an authorized client attempts to
2538 connect to another client by impersonating the server. The at‐
2539 tack is easily prevented by having clients verify the server
2540 certificate using any one of --remote-cert-tls, --ver‐
2541 ify-x509-name, or --tls-verify.
2542 --tls-auth args
2544 Add an additional layer of HMAC authentication on top of the TLS
2545 control channel to mitigate DoS attacks and attacks on the TLS
2546 stack.
2547 Valid syntaxes:
2549 tls-auth file
2551 tls-auth file 0
2552 tls-auth file 1
2553 In a nutshell, --tls-auth enables a kind of "HMAC firewall" on
2555 OpenVPN's TCP/UDP port, where TLS control channel packets bear‐
2556 ing an incorrect HMAC signature can be dropped immediately with‐
2557 out response.
2558 file (required) is a file in OpenVPN static key format which can
2560 be generated by --genkey.
2561 Older versions (up to OpenVPN 2.3) supported a freeform
2563 passphrase file. This is no longer supported in newer versions
2564 (v2.4+).
2565 See the --secret option for more information on the optional di‐
2567 rection parameter.
2568 --tls-auth is recommended when you are running OpenVPN in a mode
2570 where it is listening for packets from any IP address, such as
2571 when --remote is not specified, or --remote is specified with
2572 --float.
2573 The rationale for this feature is as follows. TLS requires a
2575 multi-packet exchange before it is able to authenticate a peer.
2576 During this time before authentication, OpenVPN is allocating
2577 resources (memory and CPU) to this potential peer. The potential
2578 peer is also exposing many parts of OpenVPN and the OpenSSL li‐
2579 brary to the packets it is sending. Most successful network at‐
2580 tacks today seek to either exploit bugs in programs (such as
2581 buffer overflow attacks) or force a program to consume so many
2582 resources that it becomes unusable. Of course the first line of
2583 defense is always to produce clean, well-audited code. OpenVPN
2584 has been written with buffer overflow attack prevention as a top
2585 priority. But as history has shown, many of the most widely used
2586 network applications have, from time to time, fallen to buffer
2587 overflow attacks.
2588 So as a second line of defense, OpenVPN offers this special
2590 layer of authentication on top of the TLS control channel so
2591 that every packet on the control channel is authenticated by an
2592 HMAC signature and a unique ID for replay protection. This sig‐
2593 nature will also help protect against DoS (Denial of Service)
2594 attacks. An important rule of thumb in reducing vulnerability to
2595 DoS attacks is to minimize the amount of resources a potential,
2596 but as yet unauthenticated, client is able to consume.
2597 --tls-auth does this by signing every TLS control channel packet
2599 with an HMAC signature, including packets which are sent before
2600 the TLS level has had a chance to authenticate the peer. The re‐
2601 sult is that packets without the correct signature can be
2602 dropped immediately upon reception, before they have a chance to
2603 consume additional system resources such as by initiating a TLS
2604 handshake. --tls-auth can be strengthened by adding the --re‐
2605 play-persist option which will keep OpenVPN's replay protection
2606 state in a file so that it is not lost across restarts.
2607 It should be emphasized that this feature is optional and that
2609 the key file used with --tls-auth gives a peer nothing more than
2610 the power to initiate a TLS handshake. It is not used to encrypt
2611 or authenticate any tunnel data.
2612 Use --tls-crypt instead if you want to use the key file to not
2614 only authenticate, but also encrypt the TLS control channel.
2615 --tls-groups list
2617 A list of allowable groups/curves in order of preference.
2618 Set the allowed elliptic curves/groups for the TLS session.
2620 These groups are allowed to be used in signatures and key ex‐
2621 change.
2622 mbedTLS currently allows all known curves per default.
2624 OpenSSL 1.1+ restricts the list per default to
2626 "X25519:secp256r1:X448:secp521r1:secp384r1".
2628 If you use certificates that use non-standard curves, you might
2630 need to add them here. If you do not force the ecdh curve by us‐
2631 ing --ecdh-curve, the groups for ecdh will also be picked from
2632 this list.
2633 OpenVPN maps the curve name secp256r1 to prime256v1 to allow
2635 specifying the same tls-groups option for mbedTLS and OpenSSL.
2636 Warning: this option not only affects elliptic curve certifi‐
2638 cates but also the key exchange in TLS 1.3 and using this option
2639 improperly will disable TLS 1.3.
2640 --tls-cert-profile profile
2642 Set the allowed cryptographic algorithms for certificates ac‐
2643 cording to profile.
2644 The following profiles are supported:
2646 legacy (default)
2648 SHA1 and newer, RSA 2048-bit+, any elliptic curve.
2649 preferred
2651 SHA2 and newer, RSA 2048-bit+, any elliptic curve.
2652 suiteb SHA256/SHA384, ECDSA with P-256 or P-384.
2654 This option is only fully supported for mbed TLS builds. OpenSSL
2656 builds use the following approximation:
2657 legacy (default)
2659 sets "security level 1"
2660 preferred
2662 sets "security level 2"
2663 suiteb sets "security level 3" and --tls-cipher "SUITEB128".
2665 OpenVPN will migrate to 'preferred' as default in the future.
2667 Please ensure that your keys already comply.
2668 WARNING: --tls-ciphers, --tls-ciphersuites and tls-groups
2670 These options are expert features, which - if used correctly -
2671 can improve the security of your VPN connection. But it is also
2672 easy to unwittingly use them to carefully align a gun with your
2673 foot, or just break your connection. Use with care!
2674 --tls-cipher l
2676 A list l of allowable TLS ciphers delimited by a colon (":").
2677 These setting can be used to ensure that certain cipher suites
2679 are used (or not used) for the TLS connection. OpenVPN uses TLS
2680 to secure the control channel, over which the keys that are used
2681 to protect the actual VPN traffic are exchanged.
2682 The supplied list of ciphers is (after potential OpenSSL/IANA
2684 name translation) simply supplied to the crypto library. Please
2685 see the OpenSSL and/or mbed TLS documentation for details on the
2686 cipher list interpretation.
2687 For OpenSSL, the --tls-cipher is used for TLS 1.2 and below.
2689 Use --show-tls to see a list of TLS ciphers supported by your
2691 crypto library.
2692 The default for --tls-cipher is to use mbed TLS's default cipher
2694 list when using mbed TLS or DE‐
2695 FAULT:!EXP:!LOW:!MEDIUM:!kDH:!kECDH:!DSS:!PSK:!SRP:!kRSA when
2696 using OpenSSL.
2697 --tls-ciphersuites l
2699 Same as --tls-cipher but for TLS 1.3 and up. mbed TLS has no TLS
2700 1.3 support yet and only the --tls-cipher setting is used.
2701 The default for --tls-ciphersuites is to use the crypto li‐
2703 brary's default.
2704 --tls-client
2706 Enable TLS and assume client role during TLS handshake.
2707 --tls-crypt keyfile
2709 Encrypt and authenticate all control channel packets with the
2710 key from keyfile. (See --tls-auth for more background.)
2711 Encrypting (and authenticating) control channel packets:
2713 • provides more privacy by hiding the certificate used for the
2715 TLS connection,
2716 • makes it harder to identify OpenVPN traffic as such,
2718 • provides "poor-man's" post-quantum security, against attackers
2720 who will never know the pre-shared key (i.e. no forward se‐
2721 crecy).
2722 In contrast to --tls-auth, --tls-crypt does not require the user
2724 to set --key-direction.
2725 Security Considerations
2727 All peers use the same --tls-crypt pre-shared group key to au‐
2729 thenticate and encrypt control channel messages. To ensure that
2730 IV collisions remain unlikely, this key should not be used to
2731 encrypt more than 2^48 client-to-server or 2^48 server-to-client
2732 control channel messages. A typical initial negotiation is about
2733 10 packets in each direction. Assuming both initial negotiation
2734 and renegotiations are at most 2^16 (65536) packets (to be con‐
2735 servative), and (re)negotiations happen each minute for each
2736 user (24/7), this limits the tls-crypt key lifetime to 8171
2737 years divided by the number of users. So a setup with 1000 users
2738 should rotate the key at least once each eight years. (And a
2739 setup with 8000 users each year.)
2740 If IV collisions were to occur, this could result in the secu‐
2742 rity of --tls-crypt degrading to the same security as using
2743 --tls-auth. That is, the control channel still benefits from
2744 the extra protection against active man-in-the-middle-attacks
2745 and DoS attacks, but may no longer offer extra privacy and
2746 post-quantum security on top of what TLS itself offers.
2747 For large setups or setups where clients are not trusted, con‐
2749 sider using --tls-crypt-v2 instead. That uses per-client unique
2750 keys, and thereby improves the bounds to 'rotate a client key at
2751 least once per 8000 years'.
2752 --tls-crypt-v2 keyfile
2754 Use client-specific tls-crypt keys.
2755 For clients, keyfile is a client-specific tls-crypt key. Such a
2757 key can be generated using the --genkey tls-crypt-v2-client op‐
2758 tion.
2759 For servers, keyfile is used to unwrap client-specific keys sup‐
2761 plied by the client during connection setup. This key must be
2762 the same as the key used to generate the client-specific key
2763 (see --genkey tls-crypt-v2-client).
2764 On servers, this option can be used together with the --tls-auth
2766 or --tls-crypt option. In that case, the server will detect
2767 whether the client is using client-specific keys, and automati‐
2768 cally select the right mode.
2769 --tls-crypt-v2-verify cmd
2771 Run command cmd to verify the metadata of the client-specific
2772 tls-crypt-v2 key of a connecting client. This allows server ad‐
2773 ministrators to reject client connections, before exposing the
2774 TLS stack (including the notoriously dangerous X.509 and ASN.1
2775 stacks) to the connecting client.
2776 OpenVPN supplies the following environment variables to the com‐
2778 mand:
2779 • script_type is set to tls-crypt-v2-verify
2781 • metadata_type is set to 0 if the metadata was user supplied,
2783 or 1 if it's a 64-bit unix timestamp representing the key cre‐
2784 ation time.
2785 • metadata_file contains the filename of a temporary file that
2787 contains the client metadata.
2788 The command can reject the connection by exiting with a non-zero
2790 exit code.
2791 --tls-exit
2793 Exit on TLS negotiation failure.
2794 --tls-export-cert directory
2796 Store the certificates the clients use upon connection to this
2797 directory. This will be done before --tls-verify is called. The
2798 certificates will use a temporary name and will be deleted when
2799 the tls-verify script returns. The file name used for the cer‐
2800 tificate is available via the peer_cert environment variable.
2801 --tls-server
2803 Enable TLS and assume server role during TLS handshake. Note
2804 that OpenVPN is designed as a peer-to-peer application. The des‐
2805 ignation of client or server is only for the purpose of negoti‐
2806 ating the TLS control channel.
2807 --tls-timeout n
2809 Packet retransmit timeout on TLS control channel if no acknowl‐
2810 edgment from remote within n seconds (default 2). When OpenVPN
2811 sends a control packet to its peer, it will expect to receive an
2812 acknowledgement within n seconds or it will retransmit the
2813 packet, subject to a TCP-like exponential backoff algorithm.
2814 This parameter only applies to control channel packets. Data
2815 channel packets (which carry encrypted tunnel data) are never
2816 acknowledged, sequenced, or retransmitted by OpenVPN because the
2817 higher level network protocols running on top of the tunnel such
2818 as TCP expect this role to be left to them.
2819 --tls-version-min args
2821 Sets the minimum TLS version we will accept from the peer (de‐
2822 fault is "1.0").
2823 Valid syntax:
2825 tls-version-min version ['or-highest']
2827 Examples for version include 1.0, 1.1, or 1.2. If or-highest is
2829 specified and version is not recognized, we will only accept the
2830 highest TLS version supported by the local SSL implementation.
2831 --tls-version-max version
2833 Set the maximum TLS version we will use (default is the highest
2834 version supported). Examples for version include 1.0, 1.1, or
2835 1.2.
2836 --verify-hash args
2838 Specify SHA1 or SHA256 fingerprint for level-1 cert.
2839 Valid syntax:
2841 verify-hash hash [algo]
2843 The level-1 cert is the CA (or intermediate cert) that signs the
2845 leaf certificate, and is one removed from the leaf certificate
2846 in the direction of the root. When accepting a connection from a
2847 peer, the level-1 cert fingerprint must match hash or certifi‐
2848 cate verification will fail. Hash is specified as XX:XX:... For
2849 example:
2850 AD:B0:95:D8:09:C8:36:45:12:A9:89:C8:90:09:CB:13:72:A6:AD:16
2852 The algo flag can be either SHA1 or SHA256. If not provided, it
2854 defaults to SHA1.
2855 --verify-x509-name args
2857 Accept connections only if a host's X.509 name is equal to name.
2858 The remote host must also pass all other tests of verification.
2859 Valid syntax:
2861 verify-x509 name type
2863 Which X.509 name is compared to name depends on the setting of
2865 type. type can be subject to match the complete subject DN (de‐
2866 fault), name to match a subject RDN or name-prefix to match a
2867 subject RDN prefix. Which RDN is verified as name depends on the
2868 --x509-username-field option. But it defaults to the common name
2869 (CN), e.g. a certificate with a subject DN
2870 C=KG, ST=NA, L=Bishkek, CN=Server-1
2872 would be matched by:
2874 verify-x509-name 'C=KG, ST=NA, L=Bishkek, CN=Server-1'
2876 verify-x509-name Server-1 name
2877 verify-x509-name Server- name-prefix
2878 The last example is useful if you want a client to only accept
2880 connections to Server-1, Server-2, etc.
2881 --verify-x509-name is a useful replacement for the --tls-verify
2883 option to verify the remote host, because --verify-x509-name
2884 works in a --chroot environment without any dependencies.
2885 Using a name prefix is a useful alternative to managing a CRL
2887 (Certificate Revocation List) on the client, since it allows the
2888 client to refuse all certificates except for those associated
2889 with designated servers.
2890 NOTE: Test against a name prefix only when you are using Open‐
2892 VPN with a custom CA certificate that is under your con‐
2893 trol. Never use this option with type name-prefix when
2894 your client certificates are signed by a third party,
2895 such as a commercial web CA.
2896 --x509-track attribute
2898 Save peer X509 attribute value in environment for use by plugins
2899 and management interface. Prepend a + to attribute to save val‐
2900 ues from full cert chain. Values will be encoded as
2901 X509_<depth>_<attribute>=<value>. Multiple --x509-track options
2902 can be defined to track multiple attributes.
2903 --x509-username-field args
2905 Field in the X.509 certificate subject to be used as the user‐
2906 name (default CN).
2907 Valid syntax:
2909 x509-username-field [ext:]fieldname
2911 Typically, this option is specified with fieldname as either of
2913 the following:
2914 x509-username-field emailAddress
2916 x509-username-field ext:subjectAltName
2917 The first example uses the value of the emailAddress attribute
2919 in the certificate's Subject field as the username. The second
2920 example uses the ext: prefix to signify that the X.509 extension
2921 fieldname subjectAltName be searched for an rfc822Name (email)
2922 field to be used as the username. In cases where there are mul‐
2923 tiple email addresses in ext:fieldname, the last occurrence is
2924 chosen.
2925 When this option is used, the --verify-x509-name option will
2927 match against the chosen fieldname instead of the Common Name.
2928 Only the subjectAltName and issuerAltName X.509 extensions are
2930 supported.
2931 Please note: This option has a feature which will convert an
2933 all-lowercase fieldname to uppercase characters, e.g., ou -> OU.
2934 A mixed-case fieldname or one having the ext: prefix will be
2935 left as-is. This automatic upcasing feature is deprecated and
2936 will be removed in a future release.
2937 PKCS#11 / SmartCard options
2939 --pkcs11-cert-private args
2940 Set if access to certificate object should be performed after
2941 login. Every provider has its own setting.
2942 Valid syntaxes:
2944 pkcs11-cert-private 0
2946 pkcs11-cert-private 1
2947 --pkcs11-id name
2949 Specify the serialized certificate id to be used. The id can be
2950 gotten by the standalone --show-pkcs11-ids option.
2951 --pkcs11-id-management
2953 Acquire PKCS#11 id from management interface. In this case a
2954 NEED-STR 'pkcs11-id-request' real-time message will be trig‐
2955 gered, application may use pkcs11-id-count command to retrieve
2956 available number of certificates, and pkcs11-id-get command to
2957 retrieve certificate id and certificate body.
2958 --pkcs11-pin-cache seconds
2960 Specify how many seconds the PIN can be cached, the default is
2961 until the token is removed.
2962 --pkcs11-private-mode mode
2964 Specify which method to use in order to perform private key op‐
2965 erations. A different mode can be specified for each provider.
2966 Mode is encoded as hex number, and can be a mask one of the fol‐
2967 lowing:
2968 0 (default) Try to determine automatically.
2970 1 Use sign.
2972 2 Use sign recover.
2974 4 Use decrypt.
2976 8 Use unwrap.
2978 --pkcs11-protected-authentication args
2980 Use PKCS#11 protected authentication path, useful for biometric
2981 and external keypad devices. Every provider has its own setting.
2982 Valid syntaxes:
2984 pkcs11-protected-authentication 0
2986 pkcs11-protected-authentication 1
2987 --pkcs11-providers provider
2989 Specify an RSA Security Inc. PKCS #11 Cryptographic Token Inter‐
2990 face (Cryptoki) providers to load. This option can be used in‐
2991 stead of --cert, --key and --pkcs12.
2992 If p11-kit is present on the system, its p11-kit-proxy.so module
2994 will be loaded by default if either the --pkcs11-id or
2995 --pkcs11-id-management options are specified without
2996 --pkcs11-provider being given.
2997 --show-pkcs11-ids args
2999 (Standalone) Show PKCS#11 token object list.
3000 Valid syntax:
3002 show-pkcs11 [provider] [cert_private]
3004 Specify cert_private as 1 if certificates are stored as private
3006 objects.
3007 If p11-kit is present on the system, the provider argument is
3009 optional; if omitted the default p11-kit-proxy.so module will be
3010 queried.
3011 --verb option can be used BEFORE this option to produce debug‐
3013 ging information.
3014
3016 OpenVPN 2.4 and higher have the capability to negotiate the data cipher
3017 that is used to encrypt data packets. This section describes the mecha‐
3018 nism in more detail and the different backwards compatibility mechanism
3019 with older server and clients.
3020 OpenVPN 2.5 and higher behaviour
3022 When both client and server are at least running OpenVPN 2.5, that the
3023 order of the ciphers of the server's --data-ciphers is used to pick the
3024 the data cipher. That means that the first cipher in that list that is
3025 also in the client's --data-ciphers list is chosen. If no common cipher
3026 is found the client is rejected with a AUTH_FAILED message (as seen in
3027 client log):
3028 AUTH: Received control message: AUTH_FAILED,Data channel cipher ne‐
3029 gotiation failed (no shared cipher)
3030 OpenVPN 2.5 will only allow the ciphers specified in --data-ciphers. To
3032 ensure backwards compatibility also if a cipher is specified using the
3033 --cipher option it is automatically added to this list. If both options
3034 are unset the default is AES-256-GCM:AES-128-GCM.
3035 OpenVPN 2.4 clients
3037 The negotiation support in OpenVPN 2.4 was the first iteration of the
3038 implementation and still had some quirks. Its main goal was "upgrade to
3039 AES-256-GCM when possible". An OpenVPN 2.4 client that is built
3040 against a crypto library that supports AES in GCM mode and does not
3041 have --ncp-disable will always announce support for AES-256-GCM and
3042 AES-128-GCM to a server by sending IV_NCP=2.
3043 This only causes a problem if --ncp-ciphers option has been changed
3045 from the default of AES-256-GCM:AES-128-GCM to a value that does not
3046 include these two ciphers. When a OpenVPN servers try to use
3047 AES-256-GCM or AES-128-GCM the connection will then fail. It is there‐
3048 fore recommended to always have the AES-256-GCM and AES-128-GCM ciphers
3049 to the --ncp-ciphers options to avoid this behaviour.
3050 OpenVPN 3 clients
3052 Clients based on the OpenVPN 3.x library (‐
3053 https://github.com/openvpn/openvpn3/) do not have a configurable
3054 --ncp-ciphers or --data-ciphers option. Instead these clients will an‐
3055 nounce support for all their supported AEAD ciphers (AES-256-GCM,
3056 AES-128-GCM and in newer versions also Chacha20-Poly1305).
3057 To support OpenVPN 3.x based clients at least one of these ciphers
3059 needs to be included in the server's --data-ciphers option.
3060 OpenVPN 2.3 and older clients (and clients with --ncp-disable)
3062 When a client without cipher negotiation support connects to a server
3063 the cipher specified with the --cipher option in the client configura‐
3064 tion must be included in the --data-ciphers option of the server to al‐
3065 low the client to connect. Otherwise the client will be sent the
3066 AUTH_FAILED message that indicates no shared cipher.
3067 If the client is 2.3 or older and has been configured with the --en‐
3069 able-small ./configure argument, using data-ciphers-fallback cipher in
3070 the server config file with the explicit cipher used by the client is
3071 necessary.
3072 OpenVPN 2.4 server
3074 When a client indicates support for AES-128-GCM and AES-256-GCM (with
3075 IV_NCP=2) an OpenVPN 2.4 server will send the first cipher of the
3076 --ncp-ciphers to the OpenVPN client regardless of what the cipher is.
3077 To emulate the behaviour of an OpenVPN 2.4 client as close as possible
3078 and have compatibility to a setup that depends on this quirk, adding
3079 AES-128-GCM and AES-256-GCM to the client's --data-ciphers option is
3080 required. OpenVPN 2.5+ will only announce the IV_NCP=2 flag if those
3081 ciphers are present.
3082 OpenVPN 2.3 and older servers (and servers with --ncp-disable)
3084 The cipher used by the server must be included in --data-ciphers to al‐
3085 low the client connecting to a server without cipher negotiation sup‐
3086 port. (For compatibility OpenVPN 2.5 will also accept the cipher set
3087 with --cipher)
3088 If the server is 2.3 or older and has been configured with the --en‐
3090 able-small ./configure argument, adding data-ciphers-fallback cipher to
3091 the client config with the explicit cipher used by the server is neces‐
3092 sary.
3093 Blowfish in CBC mode (BF-CBC) deprecation
3095 The --cipher option defaulted to BF-CBC in OpenVPN 2.4 and older ver‐
3096 sion. The default was never changed to ensure backwards compatibility.
3097 In OpenVPN 2.5 this behaviour has now been changed so that if the --ci‐
3098 pher is not explicitly set it does not allow the weak BF-CBC cipher any
3099 more and needs to explicitly added as --cipher BFC-CBC or added to
3100 --data-ciphers.
3101 We strongly recommend to switching away from BF-CBC to a more secure
3103 cipher as soon as possible instead.
3104
3106 OpenVPN consists of two sides of network configuration. One side is
3107 the link between the local and remote side, the other side is the vir‐
3108 tual network adapter (tun/tap device).
3109 Link Options
3111 This link options section covers options related to the connection be‐
3112 tween the local and the remote host.
3113 --bind keywords
3115 Bind to local address and port. This is the default unless any
3116 of --proto tcp-client , --http-proxy or --socks-proxy are used.
3117 If the optional ipv6only keyword is present OpenVPN will bind
3119 only to IPv6 (as opposed to IPv6 and IPv4) when a IPv6 socket is
3120 opened.
3121 --float
3123 Allow remote peer to change its IP address and/or port number,
3124 such as due to DHCP (this is the default if --remote is not
3125 used). --float when specified with --remote allows an OpenVPN
3126 session to initially connect to a peer at a known address, how‐
3127 ever if packets arrive from a new address and pass all authenti‐
3128 cation tests, the new address will take control of the session.
3129 This is useful when you are connecting to a peer which holds a
3130 dynamic address such as a dial-in user or DHCP client.
3131 Essentially, --float tells OpenVPN to accept authenticated pack‐
3133 ets from any address, not only the address which was specified
3134 in the --remote option.
3135 --fragment max
3137 Enable internal datagram fragmentation so that no UDP datagrams
3138 are sent which are larger than max bytes.
3139 The max parameter is interpreted in the same way as the
3141 --link-mtu parameter, i.e. the UDP packet size after encapsula‐
3142 tion overhead has been added in, but not including the UDP
3143 header itself.
3144 The --fragment option only makes sense when you are using the
3146 UDP protocol (--proto udp).
3147 --fragment adds 4 bytes of overhead per datagram.
3149 See the --mssfix option below for an important related option to
3151 --fragment.
3152 It should also be noted that this option is not meant to replace
3154 UDP fragmentation at the IP stack level. It is only meant as a
3155 last resort when path MTU discovery is broken. Using this option
3156 is less efficient than fixing path MTU discovery for your IP
3157 link and using native IP fragmentation instead.
3158 Having said that, there are circumstances where using OpenVPN's
3160 internal fragmentation capability may be your only option, such
3161 as tunneling a UDP multicast stream which requires fragmenta‐
3162 tion.
3163 --keepalive args
3165 A helper directive designed to simplify the expression of --ping
3166 and --ping-restart.
3167 Valid syntax:
3169 keepalive interval timeout
3171 This option can be used on both client and server side, but it
3173 is enough to add this on the server side as it will push appro‐
3174 priate --ping and --ping-restart options to the client. If used
3175 on both server and client, the values pushed from server will
3176 override the client local values.
3177 The timeout argument will be twice as long on the server side.
3179 This ensures that a timeout is detected on client side before
3180 the server side drops the connection.
3181 For example, --keepalive 10 60 expands as follows:
3183 if mode server:
3185 ping 10 # Argument: interval
3186 ping-restart 120 # Argument: timeout*2
3187 push "ping 10" # Argument: interval
3188 push "ping-restart 60" # Argument: timeout
3189 else
3190 ping 10 # Argument: interval
3191 ping-restart 60 # Argument: timeout
3192 --link-mtu n
3194 Sets an upper bound on the size of UDP packets which are sent
3195 between OpenVPN peers. It's best not to set this parameter un‐
3196 less you know what you're doing.
3197 --local host
3199 Local host name or IP address for bind. If specified, OpenVPN
3200 will bind to this address only. If unspecified, OpenVPN will
3201 bind to all interfaces.
3202 --lport port
3204 Set local TCP/UDP port number or name. Cannot be used together
3205 with --nobind option.
3206 --mark value
3208 Mark encrypted packets being sent with value. The mark value can
3209 be matched in policy routing and packetfilter rules. This option
3210 is only supported in Linux and does nothing on other operating
3211 systems.
3212 --mode m
3214 Set OpenVPN major mode. By default, OpenVPN runs in
3215 point-to-point mode (p2p). OpenVPN 2.0 introduces a new mode
3216 (server) which implements a multi-client server capability.
3217 --mssfix max
3219 Announce to TCP sessions running over the tunnel that they
3220 should limit their send packet sizes such that after OpenVPN has
3221 encapsulated them, the resulting UDP packet size that OpenVPN
3222 sends to its peer will not exceed max bytes. The default value
3223 is 1450.
3224 The max parameter is interpreted in the same way as the
3226 --link-mtu parameter, i.e. the UDP packet size after encapsula‐
3227 tion overhead has been added in, but not including the UDP
3228 header itself. Resulting packet would be at most 28 bytes
3229 larger for IPv4 and 48 bytes for IPv6 (20/40 bytes for IP header
3230 and 8 bytes for UDP header). Default value of 1450 allows IPv4
3231 packets to be transmitted over a link with MTU 1473 or higher
3232 without IP level fragmentation.
3233 The --mssfix option only makes sense when you are using the UDP
3235 protocol for OpenVPN peer-to-peer communication, i.e. --proto
3236 udp.
3237 --mssfix and --fragment can be ideally used together, where
3239 --mssfix will try to keep TCP from needing packet fragmentation
3240 in the first place, and if big packets come through anyhow (from
3241 protocols other than TCP), --fragment will internally fragment
3242 them.
3243 Both --fragment and --mssfix are designed to work around cases
3245 where Path MTU discovery is broken on the network path between
3246 OpenVPN peers.
3247 The usual symptom of such a breakdown is an OpenVPN connection
3249 which successfully starts, but then stalls during active usage.
3250 If --fragment and --mssfix are used together, --mssfix will take
3252 its default max parameter from the --fragment max option.
3253 Therefore, one could lower the maximum UDP packet size to 1300
3255 (a good first try for solving MTU-related connection problems)
3256 with the following options:
3257 --tun-mtu 1500 --fragment 1300 --mssfix
3259 --mtu-disc type
3261 Should we do Path MTU discovery on TCP/UDP channel? Only sup‐
3262 ported on OSes such as Linux that supports the necessary system
3263 call to set.
3264 Valid types:
3266 no Never send DF (Don't Fragment) frames
3268 maybe Use per-route hints
3270 yes Always DF (Don't Fragment)
3272 --mtu-test
3274 To empirically measure MTU on connection startup, add the
3275 --mtu-test option to your configuration. OpenVPN will send ping
3276 packets of various sizes to the remote peer and measure the
3277 largest packets which were successfully received. The --mtu-test
3278 process normally takes about 3 minutes to complete.
3279 --nobind
3281 Do not bind to local address and port. The IP stack will allo‐
3282 cate a dynamic port for returning packets. Since the value of
3283 the dynamic port could not be known in advance by a peer, this
3284 option is only suitable for peers which will be initiating con‐
3285 nections by using the --remote option.
3286 --passtos
3288 Set the TOS field of the tunnel packet to what the payload's TOS
3289 is.
3290 --ping n
3292 Ping remote over the TCP/UDP control channel if no packets have
3293 been sent for at least n seconds (specify --ping on both peers
3294 to cause ping packets to be sent in both directions since Open‐
3295 VPN ping packets are not echoed like IP ping packets). When used
3296 in one of OpenVPN's secure modes (where --secret, --tls-server
3297 or --tls-client is specified), the ping packet will be crypto‐
3298 graphically secure.
3299 This option has two intended uses:
3301 1. Compatibility with stateful firewalls. The periodic ping will
3303 ensure that a stateful firewall rule which allows OpenVPN UDP
3304 packets to pass will not time out.
3305 2. To provide a basis for the remote to test the existence of
3307 its peer using the --ping-exit option.
3308 --ping-exit n
3310 Causes OpenVPN to exit after n seconds pass without reception of
3311 a ping or other packet from remote. This option can be combined
3312 with --inactive, --ping and --ping-exit to create a two-tiered
3313 inactivity disconnect.
3314 For example,
3316 openvpn [options...] --inactive 3600 --ping 10 --ping-exit 60
3318 when used on both peers will cause OpenVPN to exit within 60
3320 seconds if its peer disconnects, but will exit after one hour if
3321 no actual tunnel data is exchanged.
3322 --ping-restart n
3324 Similar to --ping-exit, but trigger a SIGUSR1 restart after n
3325 seconds pass without reception of a ping or other packet from
3326 remote.
3327 This option is useful in cases where the remote peer has a dy‐
3329 namic IP address and a low-TTL DNS name is used to track the IP
3330 address using a service such as http://dyndns.org/ + a dynamic
3331 DNS client such as ddclient.
3332 If the peer cannot be reached, a restart will be triggered,
3334 causing the hostname used with --remote to be re-resolved (if
3335 --resolv-retry is also specified).
3336 In server mode, --ping-restart, --inactive or any other type of
3338 internally generated signal will always be applied to individual
3339 client instance objects, never to whole server itself. Note also
3340 in server mode that any internally generated signal which would
3341 normally cause a restart, will cause the deletion of the client
3342 instance object instead.
3343 In client mode, the --ping-restart parameter is set to 120 sec‐
3345 onds by default. This default will hold until the client pulls a
3346 replacement value from the server, based on the --keepalive set‐
3347 ting in the server configuration. To disable the 120 second de‐
3348 fault, set --ping-restart 0 on the client.
3349 See the signals section below for more information on SIGUSR1.
3351 Note that the behavior of SIGUSR1 can be modified by the --per‐
3353 sist-tun, --persist-key, --persist-local-ip and --persist-re‐
3354 mote-ip options.
3355 Also note that --ping-exit and --ping-restart are mutually ex‐
3357 clusive and cannot be used together.
3358 --ping-timer-rem
3360 Run the --ping-exit / --ping-restart timer only if we have a re‐
3361 mote address. Use this option if you are starting the daemon in
3362 listen mode (i.e. without an explicit --remote peer), and you
3363 don't want to start clocking timeouts until a remote peer con‐
3364 nects.
3365 --proto p
3367 Use protocol p for communicating with remote host. p can be udp,
3368 tcp-client, or tcp-server.
3369 The default protocol is udp when --proto is not specified.
3371 For UDP operation, --proto udp should be specified on both
3373 peers.
3374 For TCP operation, one peer must use --proto tcp-server and the
3376 other must use --proto tcp-client. A peer started with
3377 tcp-server will wait indefinitely for an incoming connection. A
3378 peer started with tcp-client will attempt to connect, and if
3379 that fails, will sleep for 5 seconds (adjustable via the --con‐
3380 nect-retry option) and try again infinite or up to N retries
3381 (adjustable via the --connect-retry-max option). Both TCP client
3382 and server will simulate a SIGUSR1 restart signal if either side
3383 resets the connection.
3384 OpenVPN is designed to operate optimally over UDP, but TCP capa‐
3386 bility is provided for situations where UDP cannot be used. In
3387 comparison with UDP, TCP will usually be somewhat less efficient
3388 and less robust when used over unreliable or congested networks.
3389 This article outlines some of problems with tunneling IP over
3391 TCP: http://sites.inka.de/sites/bigred/devel/tcp-tcp.html
3392 There are certain cases, however, where using TCP may be advan‐
3394 tageous from a security and robustness perspective, such as tun‐
3395 neling non-IP or application-level UDP protocols, or tunneling
3396 protocols which don't possess a built-in reliability layer.
3397 --port port
3399 TCP/UDP port number or port name for both local and remote (sets
3400 both --lport and --rport options to given port). The current de‐
3401 fault of 1194 represents the official IANA port number assign‐
3402 ment for OpenVPN and has been used since version 2.0-beta17.
3403 Previous versions used port 5000 as the default.
3404 --rport port
3406 Set TCP/UDP port number or name used by the --remote option. The
3407 port can also be set directly using the --remote option.
3408 --replay-window args
3410 Modify the replay protection sliding-window size and time win‐
3411 dow.
3412 Valid syntax:
3414 replay-window n [t]
3416 Use a replay protection sliding-window of size n and a time win‐
3418 dow of t seconds.
3419 By default n is 64 (the IPSec default) and t is 15 seconds.
3421 This option is only relevant in UDP mode, i.e. when either
3423 --proto udp is specified, or no --proto option is specified.
3424 When OpenVPN tunnels IP packets over UDP, there is the possibil‐
3426 ity that packets might be dropped or delivered out of order. Be‐
3427 cause OpenVPN, like IPSec, is emulating the physical network
3428 layer, it will accept an out-of-order packet sequence, and will
3429 deliver such packets in the same order they were received to the
3430 TCP/IP protocol stack, provided they satisfy several con‐
3431 straints.
3432 a. The packet cannot be a replay (unless --no-replay is speci‐
3434 fied, which disables replay protection altogether).
3435 b. If a packet arrives out of order, it will only be accepted if
3437 the difference between its sequence number and the highest
3438 sequence number received so far is less than n.
3439 c. If a packet arrives out of order, it will only be accepted if
3441 it arrives no later than t seconds after any packet contain‐
3442 ing a higher sequence number.
3443 If you are using a network link with a large pipeline (meaning
3445 that the product of bandwidth and latency is high), you may want
3446 to use a larger value for n. Satellite links in particular often
3447 require this.
3448 If you run OpenVPN at --verb 4, you will see the message "Re‐
3450 play-window backtrack occurred [x]" every time the maximum se‐
3451 quence number backtrack seen thus far increases. This can be
3452 used to calibrate n.
3453 There is some controversy on the appropriate method of handling
3455 packet reordering at the security layer.
3456 Namely, to what extent should the security layer protect the en‐
3458 capsulated protocol from attacks which masquerade as the kinds
3459 of normal packet loss and reordering that occur over IP net‐
3460 works?
3461 The IPSec and OpenVPN approach is to allow packet reordering
3463 within a certain fixed sequence number window.
3464 OpenVPN adds to the IPSec model by limiting the window size in
3466 time as well as sequence space.
3467 OpenVPN also adds TCP transport as an option (not offered by
3469 IPSec) in which case OpenVPN can adopt a very strict attitude
3470 towards message deletion and reordering: Don't allow it. Since
3471 TCP guarantees reliability, any packet loss or reordering event
3472 can be assumed to be an attack.
3473 In this sense, it could be argued that TCP tunnel transport is
3475 preferred when tunneling non-IP or UDP application protocols
3476 which might be vulnerable to a message deletion or reordering
3477 attack which falls within the normal operational parameters of
3478 IP networks.
3479 So I would make the statement that one should never tunnel a
3481 non-IP protocol or UDP application protocol over UDP, if the
3482 protocol might be vulnerable to a message deletion or reordering
3483 attack that falls within the normal operating parameters of what
3484 is to be expected from the physical IP layer. The problem is
3485 easily fixed by simply using TCP as the VPN transport layer.
3486 --replay-persist file
3488 Persist replay-protection state across sessions using file to
3489 save and reload the state.
3490 This option will strengthen protection against replay attacks,
3492 especially when you are using OpenVPN in a dynamic context (such
3493 as with --inetd) when OpenVPN sessions are frequently started
3494 and stopped.
3495 This option will keep a disk copy of the current replay protec‐
3497 tion state (i.e. the most recent packet timestamp and sequence
3498 number received from the remote peer), so that if an OpenVPN
3499 session is stopped and restarted, it will reject any replays of
3500 packets which were already received by the prior session.
3501 This option only makes sense when replay protection is enabled
3503 (the default) and you are using either --secret (shared-secret
3504 key mode) or TLS mode with --tls-auth.
3505 --socket-flags flags
3507 Apply the given flags to the OpenVPN transport socket. Cur‐
3508 rently, only TCP_NODELAY is supported.
3509 The TCP_NODELAY socket flag is useful in TCP mode, and causes
3511 the kernel to send tunnel packets immediately over the TCP con‐
3512 nection without trying to group several smaller packets into a
3513 larger packet. This can result in a considerably improvement in
3514 latency.
3515 This option is pushable from server to client, and should be
3517 used on both client and server for maximum effect.
3518 --tcp-nodelay
3520 This macro sets the TCP_NODELAY socket flag on the server as
3521 well as pushes it to connecting clients. The TCP_NODELAY flag
3522 disables the Nagle algorithm on TCP sockets causing packets to
3523 be transmitted immediately with low latency, rather than waiting
3524 a short period of time in order to aggregate several packets
3525 into a larger containing packet. In VPN applications over TCP,
3526 TCP_NODELAY is generally a good latency optimization.
3527 The macro expands as follows:
3529 if mode server:
3531 socket-flags TCP_NODELAY
3532 push "socket-flags TCP_NODELAY"
3533 Virtual Network Adapter (VPN interface)
3535 Options in this section relates to configuration of the virtual tun/tap
3536 network interface, including setting the VPN IP address and network
3537 routing.
3538 --bind-dev device
3540 (Linux only) Set device to bind the server socket to a Virtual
3541 Routing and Forwarding device
3542 --block-ipv6
3544 On the client, instead of sending IPv6 packets over the VPN tun‐
3545 nel, all IPv6 packets are answered with an ICMPv6 no route host
3546 message. On the server, all IPv6 packets from clients are an‐
3547 swered with an ICMPv6 no route to host message. This options is
3548 intended for cases when IPv6 should be blocked and other options
3549 are not available. --block-ipv6 will use the remote IPv6 as
3550 source address of the ICMPv6 packets if set, otherwise will use
3551 fe80::7 as source address.
3552 For this option to make sense you actually have to route traffic
3554 to the tun interface. The following example config block would
3555 send all IPv6 traffic to OpenVPN and answer all requests with no
3556 route to host, effectively blocking IPv6 (to avoid IPv6 connec‐
3557 tions from dual-stacked clients leaking around IPv4-only VPN
3558 services).
3559 Client config
3561 --ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1
3563 --redirect-gateway ipv6
3564 --block-ipv6
3565 Server config
3567 Push a "valid" ipv6 config to the client and block on the
3568 server
3569 --push "ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1"
3571 --push "redirect-gateway ipv6"
3572 --block-ipv6
3573 Note: this option does not influence traffic sent from the
3575 server towards the client (neither on the server nor on the
3576 client side). This is not seen as necessary, as such traffic
3577 can be most easily avoided by not configuring IPv6 on the server
3578 tun, or setting up a server-side firewall rule.
3579 --dev device
3581 TUN/TAP virtual network device which can be tunX, tapX, null or
3582 an arbitrary name string (X can be omitted for a dynamic de‐
3583 vice.)
3584 See examples section below for an example on setting up a TUN
3586 device.
3587 You must use either tun devices on both ends of the connection
3589 or tap devices on both ends. You cannot mix them, as they repre‐
3590 sent different underlying network layers:
3591 tun devices encapsulate IPv4 or IPv6 (OSI Layer 3)
3593 tap devices encapsulate Ethernet 802.3 (OSI Layer 2).
3595 Valid syntaxes:
3597 dev tun2
3599 dev tap4
3600 dev ovpn
3601 When the device name starts with tun or tap, the device type is
3603 extracted automatically. Otherwise the --dev-type option needs
3604 to be added as well.
3605 --dev-node node
3607 Explicitly set the device node rather than using /dev/net/tun,
3608 /dev/tun, /dev/tap, etc. If OpenVPN cannot figure out whether
3609 node is a TUN or TAP device based on the name, you should also
3610 specify --dev-type tun or --dev-type tap.
3611 Under Mac OS X this option can be used to specify the default
3613 tun implementation. Using --dev-node utun forces usage of the
3614 native Darwin tun kernel support. Use --dev-node utunN to select
3615 a specific utun instance. To force using the tun.kext
3616 (/dev/tunX) use --dev-node tun. When not specifying a --dev-node
3617 option openvpn will first try to open utun, and fall back to
3618 tun.kext.
3619 On Windows systems, select the TAP-Win32 adapter which is named
3621 node in the Network Connections Control Panel or the raw GUID of
3622 the adapter enclosed by braces. The --show-adapters option under
3623 Windows can also be used to enumerate all available TAP-Win32
3624 adapters and will show both the network connections control
3625 panel name and the GUID for each TAP-Win32 adapter.
3626 --dev-type device-type
3628 Which device type are we using? device-type should be tun (OSI
3629 Layer 3) or tap (OSI Layer 2). Use this option only if the
3630 TUN/TAP device used with --dev does not begin with tun or tap.
3631 --dhcp-option args
3633 Set additional network parameters on supported platforms. May be
3634 specified on the client or pushed from the server. On Windows
3635 these options are handled by the tap-windows6 driver by default
3636 or directly by OpenVPN if dhcp is disabled or the wintun driver
3637 is in use. The OpenVPN for Android client also handles them in‐
3638 ternally.
3639 On all other platforms these options are only saved in the
3641 client's environment under the name foreign_options_{n} before
3642 the --up script is called. A plugin or an --up script must be
3643 used to pick up and interpret these as required. Many Linux dis‐
3644 tributions include such scripts and some third-party user inter‐
3645 faces such as tunnelblick also come with scripts that process
3646 these options.
3647 Valid syntax:
3649 dhcp-options type [parm]
3651 DOMAIN name
3653 Set Connection-specific DNS Suffix to name.
3654 ADAPTER_DOMAIN_SUFFIX name
3656 Alias to DOMAIN. This is a compatibility option, it
3657 should not be used in new deployments.
3658 DOMAIN-SEARCH name
3660 Add name to the domain search list. Repeat this option
3661 to add more entries. Up to 10 domains are supported.
3662 DNS address
3664 Set primary domain name server IPv4 or IPv6 address. Re‐
3665 peat this option to set secondary DNS server addresses.
3666 Note: DNS IPv6 servers are currently set using netsh (the
3668 existing DHCP code can only do IPv4 DHCP, and that proto‐
3669 col only permits IPv4 addresses anywhere). The option
3670 will be put into the environment, so an --up script could
3671 act upon it if needed.
3672 WINS address
3674 Set primary WINS server address (NetBIOS over TCP/IP Name
3675 Server). Repeat this option to set secondary WINS server
3676 addresses.
3677 NBDD address
3679 Set primary NBDD server address (NetBIOS over TCP/IP
3680 Datagram Distribution Server). Repeat this option to set
3681 secondary NBDD server addresses.
3682 NTP address
3684 Set primary NTP server address (Network Time Protocol).
3685 Repeat this option to set secondary NTP server addresses.
3686 NBT type
3688 Set NetBIOS over TCP/IP Node type. Possible options:
3689 1 b-node (broadcasts)
3691 2 p-node (point-to-point name queries to a WINS
3693 server)
3694 4 m-node (broadcast then query name server)
3696 8 h-node (query name server, then broadcast).
3698 NBS scope-id
3700 Set NetBIOS over TCP/IP Scope. A NetBIOS Scope ID pro‐
3701 vides an extended naming service for the NetBIOS over
3702 TCP/IP (Known as NBT) module. The primary purpose of a
3703 NetBIOS scope ID is to isolate NetBIOS traffic on a sin‐
3704 gle network to only those nodes with the same NetBIOS
3705 scope ID. The NetBIOS scope ID is a character string that
3706 is appended to the NetBIOS name. The NetBIOS scope ID on
3707 two hosts must match, or the two hosts will not be able
3708 to communicate. The NetBIOS Scope ID also allows comput‐
3709 ers to use the same computer name, as they have different
3710 scope IDs. The Scope ID becomes a part of the NetBIOS
3711 name, making the name unique. (This description of Net‐
3712 BIOS scopes courtesy of NeonSurge@abyss.com)
3713 DISABLE-NBT
3715 Disable Netbios-over-TCP/IP.
3716 --ifconfig args
3718 Set TUN/TAP adapter parameters. It requires the IP address of
3719 the local VPN endpoint. For TUN devices in point-to-point mode,
3720 the next argument must be the VPN IP address of the remote VPN
3721 endpoint. For TAP devices, or TUN devices used with --topology
3722 subnet, the second argument is the subnet mask of the virtual
3723 network segment which is being created or connected to.
3724 For TUN devices, which facilitate virtual point-to-point IP con‐
3726 nections (when used in --topology net30 or p2p mode), the proper
3727 usage of --ifconfig is to use two private IP addresses which are
3728 not a member of any existing subnet which is in use. The IP ad‐
3729 dresses may be consecutive and should have their order reversed
3730 on the remote peer. After the VPN is established, by pinging
3731 rn, you will be pinging across the VPN.
3732 For TAP devices, which provide the ability to create virtual
3734 ethernet segments, or TUN devices in --topology subnet mode
3735 (which create virtual "multipoint networks"), --ifconfig is used
3736 to set an IP address and subnet mask just as a physical ethernet
3737 adapter would be similarly configured. If you are attempting to
3738 connect to a remote ethernet bridge, the IP address and subnet
3739 should be set to values which would be valid on the the bridged
3740 ethernet segment (note also that DHCP can be used for the same
3741 purpose).
3742 This option, while primarily a proxy for the ifconfig(8) com‐
3744 mand, is designed to simplify TUN/TAP tunnel configuration by
3745 providing a standard interface to the different ifconfig imple‐
3746 mentations on different platforms.
3747 --ifconfig parameters which are IP addresses can also be speci‐
3749 fied as a DNS or /etc/hosts file resolvable name.
3750 For TAP devices, --ifconfig should not be used if the TAP inter‐
3752 face will be getting an IP address lease from a DHCP server.
3753 Examples:
3755 # tun device in net30/p2p mode
3757 ifconfig 10.8.0.2 10.8.0.1
3758 # tun/tap device in subnet mode
3760 ifconfig 10.8.0.2 255.255.255.0
3761 --ifconfig-ipv6 args
3763 Configure an IPv6 address on the tun device.
3764 Valid syntax:
3766 ifconfig-ipv6 ipv6addr/bits [ipv6remote]
3768 The ipv6addr/bits argument is the IPv6 address to use. The sec‐
3770 ond parameter is used as route target for --route-ipv6 if no
3771 gateway is specified.
3772 The --topology option has no influence with --ifconfig-ipv6
3774 --ifconfig-noexec
3776 Don't actually execute ifconfig/netsh commands, instead pass
3777 --ifconfig parameters to scripts using environmental variables.
3778 --ifconfig-nowarn
3780 Don't output an options consistency check warning if the --if‐
3781 config option on this side of the connection doesn't match the
3782 remote side. This is useful when you want to retain the overall
3783 benefits of the options consistency check (also see --dis‐
3784 able-occ option) while only disabling the ifconfig component of
3785 the check.
3786 For example, if you have a configuration where the local host
3788 uses --ifconfig but the remote host does not, use --ifcon‐
3789 fig-nowarn on the local host.
3790 This option will also silence warnings about potential address
3792 conflicts which occasionally annoy more experienced users by
3793 triggering "false positive" warnings.
3794 --lladdr address
3796 Specify the link layer address, more commonly known as the MAC
3797 address. Only applied to TAP devices.
3798 --persist-tun
3800 Don't close and reopen TUN/TAP device or run up/down scripts
3801 across SIGUSR1 or --ping-restart restarts.
3802 SIGUSR1 is a restart signal similar to SIGHUP, but which offers
3804 finer-grained control over reset options.
3805 --redirect-gateway flags
3807 Automatically execute routing commands to cause all outgoing IP
3808 traffic to be redirected over the VPN. This is a client-side op‐
3809 tion.
3810 This option performs three steps:
3812 1. Create a static route for the --remote address which forwards
3814 to the pre-existing default gateway. This is done so that [1m(3)
3815 will not create a routing loop.
3816 2. Delete the default gateway route.
3818 3. Set the new default gateway to be the VPN endpoint address
3820 (derived either from --route-gateway or the second parameter
3821 to --ifconfig when --dev tun is specified).
3822 When the tunnel is torn down, all of the above steps are re‐
3824 versed so that the original default route is restored.
3825 Option flags:
3827 local Add the local flag if both OpenVPN peers are directly
3829 connected via a common subnet, such as with wireless. The
3830 local flag will cause step [1m(1) above to be omitted.
3831 autolocal
3833 Try to automatically determine whether to enable local
3834 flag above.
3835 def1 Use this flag to override the default gateway by using
3837 0.0.0.0/1 and 128.0.0.0/1 rather than 0.0.0.0/0. This has
3838 the benefit of overriding but not wiping out the original
3839 default gateway.
3840 bypass-dhcp
3842 Add a direct route to the DHCP server (if it is non-lo‐
3843 cal) which bypasses the tunnel (Available on Windows
3844 clients, may not be available on non-Windows clients).
3845 bypass-dns
3847 Add a direct route to the DNS server(s) (if they are
3848 non-local) which bypasses the tunnel (Available on Win‐
3849 dows clients, may not be available on non-Windows
3850 clients).
3851 block-local
3853 Block access to local LAN when the tunnel is active, ex‐
3854 cept for the LAN gateway itself. This is accomplished by
3855 routing the local LAN (except for the LAN gateway ad‐
3856 dress) into the tunnel.
3857 ipv6 Redirect IPv6 routing into the tunnel. This works similar
3859 to the def1 flag, that is, more specific IPv6 routes are
3860 added (2000::/4, 3000::/4), covering the whole IPv6 uni‐
3861 cast space.
3862 !ipv4 Do not redirect IPv4 traffic - typically used in the flag
3864 pair ipv6 !ipv4 to redirect IPv6-only.
3865 --redirect-private flags
3867 Like --redirect-gateway, but omit actually changing the default
3868 gateway. Useful when pushing private subnets.
3869 --route args
3871 Add route to routing table after connection is established. Mul‐
3872 tiple routes can be specified. Routes will be automatically torn
3873 down in reverse order prior to TUN/TAP device close.
3874 Valid syntaxes:
3876 route network/IP
3878 route network/IP netmask
3879 route network/IP netmask gateway
3880 route network/IP netmask gateway metric
3881 This option is intended as a convenience proxy for the route(8)
3883 shell command, while at the same time providing portable seman‐
3884 tics across OpenVPN's platform space.
3885 netmask
3887 defaults to 255.255.255.255 when not given
3888 gateway
3890 default taken from --route-gateway or the second parame‐
3891 ter to --ifconfig when --dev tun is specified.
3892 metric default taken from --route-metric if set, otherwise 0.
3894 The default can be specified by leaving an option blank or set‐
3896 ting it to default.
3897 The network and gateway parameters can also be specified as a
3899 DNS or /etc/hosts file resolvable name, or as one of three spe‐
3900 cial keywords:
3901 vpn_gateway
3903 The remote VPN endpoint address (derived either from
3904 --route-gateway or the second parameter to --ifconfig
3905 when --dev tun is specified).
3906 net_gateway
3908 The pre-existing IP default gateway, read from the rout‐
3909 ing table (not supported on all OSes).
3910 remote_host
3912 The --remote address if OpenVPN is being run in client
3913 mode, and is undefined in server mode.
3914 --route-delay args
3916 Valid syntaxes:
3917 route-delay
3919 route-delay n
3920 route-delay n m
3921 Delay n seconds (default 0) after connection establishment, be‐
3923 fore adding routes. If n is 0, routes will be added immediately
3924 upon connection establishment. If --route-delay is omitted,
3925 routes will be added immediately after TUN/TAP device open and
3926 --up script execution, before any --user or --group privilege
3927 downgrade (or --chroot execution.)
3928 This option is designed to be useful in scenarios where DHCP is
3930 used to set tap adapter addresses. The delay will give the DHCP
3931 handshake time to complete before routes are added.
3932 On Windows, --route-delay tries to be more intelligent by wait‐
3934 ing w seconds (default 30 by default) for the TAP-Win32 adapter
3935 to come up before adding routes.
3936 --route-ipv6 args
3938 Setup IPv6 routing in the system to send the specified IPv6 net‐
3939 work into OpenVPN's tun.
3940 Valid syntax:
3942 route-ipv6 ipv6addr/bits [gateway] [metric]
3944 The gateway parameter is only used for IPv6 routes across tap
3946 devices, and if missing, the ipv6remote field from --ifcon‐
3947 fig-ipv6 or --route-ipv6-gateway is used.
3948 --route-gateway arg
3950 Specify a default gateway for use with --route.
3951 If dhcp is specified as the parameter, the gateway address will
3953 be extracted from a DHCP negotiation with the OpenVPN
3954 server-side LAN.
3955 Valid syntaxes:
3957 route-gateway gateway
3959 route-gateway dhcp
3960 --route-ipv6-gateway gw
3962 Specify a default gateway gw for use with --route-ipv6.
3963 --route-metric m
3965 Specify a default metric m for use with --route.
3966 --route-noexec
3968 Don't add or remove routes automatically. Instead pass routes to
3969 --route-up script using environmental variables.
3970 --route-nopull
3972 When used with --client or --pull, accept options pushed by
3973 server EXCEPT for routes, block-outside-dns and dhcp options
3974 like DNS servers.
3975 When used on the client, this option effectively bars the server
3977 from adding routes to the client's routing table, however note
3978 that this option still allows the server to set the TCP/IP prop‐
3979 erties of the client's TUN/TAP interface.
3980 --topology mode
3982 Configure virtual addressing topology when running in --dev tun
3983 mode. This directive has no meaning in --dev tap mode, which al‐
3984 ways uses a subnet topology.
3985 If you set this directive on the server, the --server and
3987 --server-bridge directives will automatically push your chosen
3988 topology setting to clients as well. This directive can also be
3989 manually pushed to clients. Like the --dev directive, this di‐
3990 rective must always be compatible between client and server.
3991 mode can be one of:
3993 net30 Use a point-to-point topology, by allocating one /30 sub‐
3995 net per client. This is designed to allow point-to-point
3996 semantics when some or all of the connecting clients
3997 might be Windows systems. This is the default on OpenVPN
3998 2.0.
3999 p2p Use a point-to-point topology where the remote endpoint
4001 of the client's tun interface always points to the local
4002 endpoint of the server's tun interface. This mode allo‐
4003 cates a single IP address per connecting client. Only use
4004 when none of the connecting clients are Windows systems.
4005 subnet Use a subnet rather than a point-to-point topology by
4007 configuring the tun interface with a local IP address and
4008 subnet mask, similar to the topology used in --dev tap
4009 and ethernet bridging mode. This mode allocates a single
4010 IP address per connecting client and works on Windows as
4011 well. Only available when server and clients are OpenVPN
4012 2.1 or higher, or OpenVPN 2.0.x which has been manually
4013 patched with the --topology directive code. When used on
4014 Windows, requires version 8.2 or higher of the TAP-Win32
4015 driver. When used on *nix, requires that the tun driver
4016 supports an ifconfig(8) command which sets a subnet in‐
4017 stead of a remote endpoint IP address.
4018 Note: Using --topology subnet changes the interpretation of the
4020 arguments of --ifconfig to mean "address netmask", no longer
4021 "local remote".
4022 --tun-mtu n
4024 Take the TUN device MTU to be n and derive the link MTU from it
4025 (default 1500). In most cases, you will probably want to leave
4026 this parameter set to its default value.
4027 The MTU (Maximum Transmission Units) is the maximum datagram
4029 size in bytes that can be sent unfragmented over a particular
4030 network path. OpenVPN requires that packets on the control and
4031 data channels be sent unfragmented.
4032 MTU problems often manifest themselves as connections which hang
4034 during periods of active usage.
4035 It's best to use the --fragment and/or --mssfix options to deal
4037 with MTU sizing issues.
4038 --tun-mtu-extra n
4040 Assume that the TUN/TAP device might return as many as n bytes
4041 more than the --tun-mtu size on read. This parameter defaults to
4042 0, which is sufficient for most TUN devices. TAP devices may in‐
4043 troduce additional overhead in excess of the MTU size, and a
4044 setting of 32 is the default when TAP devices are used. This pa‐
4045 rameter only controls internal OpenVPN buffer sizing, so there
4046 is no transmission overhead associated with using a larger
4047 value.
4048 TUN/TAP standalone operations
4050 These two standalone operations will require --dev and optionally
4051 --user and/or --group.
4052 --mktun
4054 (Standalone) Create a persistent tunnel on platforms which sup‐
4055 port them such as Linux. Normally TUN/TAP tunnels exist only for
4056 the period of time that an application has them open. This op‐
4057 tion takes advantage of the TUN/TAP driver's ability to build
4058 persistent tunnels that live through multiple instantiations of
4059 OpenVPN and die only when they are deleted or the machine is re‐
4060 booted.
4061 One of the advantages of persistent tunnels is that they elimi‐
4063 nate the need for separate --up and --down scripts to run the
4064 appropriate ifconfig(8) and route(8) commands. These commands
4065 can be placed in the the same shell script which starts or ter‐
4066 minates an OpenVPN session.
4067 Another advantage is that open connections through the
4069 TUN/TAP-based tunnel will not be reset if the OpenVPN peer
4070 restarts. This can be useful to provide uninterrupted connectiv‐
4071 ity through the tunnel in the event of a DHCP reset of the
4072 peer's public IP address (see the --ipchange option above).
4073 One disadvantage of persistent tunnels is that it is harder to
4075 automatically configure their MTU value (see --link-mtu and
4076 --tun-mtu above).
4077 On some platforms such as Windows, TAP-Win32 tunnels are persis‐
4079 tent by default.
4080 --rmtun
4082 (Standalone) Remove a persistent tunnel.
4083 Virtual Routing and Forwarding
4085 Options in this section relates to configuration of virtual routing and
4086 forwarding in combination with the underlying operating system.
4087 As of today this is only supported on Linux, a kernel >= 4.9 is recom‐
4089 mended.
4090 This could come in handy when for example the external network should
4092 be only used as a means to connect to some VPN endpoints and all regu‐
4093 lar traffic should only be routed through any tunnel(s). This could be
4094 achieved by setting up a VRF and configuring the interface connected to
4095 the external network to be part of the VRF. The examples below will
4096 cover this setup.
4097 Another option would be to put the tun/tap interface into a VRF. This
4099 could be done by an up-script which uses the ip link set command shown
4100 below.
4101 VRF setup with iproute2
4103 Create VRF vrf_external and map it to routing table 1023
4104 ip link add vrf_external type vrf table 1023
4106 Move eth0 into vrf_external
4108 ip link set master vrf_external dev eth0
4110 Any prefixes configured on eth0 will be moved from the :code`main`
4112 routing table into routing table 1023
4113 VRF setup with ifupdown
4115 For Debian based Distributions ifupdown2 provides an almost drop-in re‐
4116 placement for ifupdown including VRFs and other features. A configura‐
4117 tion for an interface eth0 being part of VRF code:vrf_external could
4118 look like this:
4119 auto eth0
4121 iface eth0
4122 address 192.0.2.42/24
4123 address 2001:db8:08:15::42/64
4124 gateway 192.0.2.1
4125 gateway 2001:db8:08:15::1
4126 vrf vrf_external
4127 auto vrf_external
4129 iface vrf_external
4130 vrf-table 1023
4131 OpenVPN configuration
4133 The OpenVPN configuration needs to contain this line:
4134 bind-dev vrf_external
4136 Further reading
4138 Wikipedia has nice page one VRFs:
4139 https://en.wikipedia.org/wiki/Virtual_routing_and_forwarding
4140 This talk from the Network Track of FrOSCon 2018 provides an overview
4142 about advanced layer 2 and layer 3 features of Linux
4143 • Slides:
4145 https://www.slideshare.net/BarbarossaTM/l2l3-fr-fortgeschrittene-helle-und-dunkle-magie-im-linuxnetzwerkstack
4146 • Video (german):
4148 https://media.ccc.de/v/froscon2018-2247-l2_l3_fur_fortgeschrittene_-_helle_und_dunkle_magie_im_linux-netzwerkstack
4149
4151 OpenVPN can execute external scripts in various phases of the lifetime
4152 of the OpenVPN process.
4153 Script Order of Execution
4155 1. --up
4156 Executed after TCP/UDP socket bind and TUN/TAP open.
4158 2. --tls-verify
4160 Executed when we have a still untrusted remote peer.
4162 3. --ipchange
4164 Executed after connection authentication, or remote IP address
4166 change.
4167 4. --client-connect
4169 Executed in --mode server mode immediately after client authentica‐
4171 tion.
4172 5. --route-up
4174 Executed after connection authentication, either immediately after,
4176 or some number of seconds after as defined by the --route-delay op‐
4177 tion.
4178 6. --route-pre-down
4180 Executed right before the routes are removed.
4182 7. --client-disconnect
4184 Executed in --mode server mode on client instance shutdown.
4186 8. --down
4188 Executed after TCP/UDP and TUN/TAP close.
4190 9. --learn-address
4192 Executed in --mode server mode whenever an IPv4 address/route or
4194 MAC address is added to OpenVPN's internal routing table.
4195 10. --auth-user-pass-verify
4197 Executed in --mode server mode on new client connections, when the
4199 client is still untrusted.
4200 SCRIPT HOOKS
4202 --auth-user-pass-verify args
4203 Require the client to provide a username/password (possibly in
4204 addition to a client certificate) for authentication.
4205 Valid syntax:
4207 auth-user-pass-verify cmd method
4209 OpenVPN will run command cmd to validate the username/password
4211 provided by the client.
4212 cmd consists of a path to a script (or executable program), op‐
4214 tionally followed by arguments. The path and arguments may be
4215 single- or double-quoted and/or escaped using a backslash, and
4216 should be separated by one or more spaces.
4217 If method is set to via-env, OpenVPN will call script with the
4219 environmental variables username and password set to the user‐
4220 name/password strings provided by the client. Beware that this
4221 method is insecure on some platforms which make the environment
4222 of a process publicly visible to other unprivileged processes.
4223 If method is set to via-file, OpenVPN will write the username
4225 and password to the first two lines of a temporary file. The
4226 filename will be passed as an argument to script, and the file
4227 will be automatically deleted by OpenVPN after the script re‐
4228 turns. The location of the temporary file is controlled by the
4229 --tmp-dir option, and will default to the current directory if
4230 unspecified. For security, consider setting --tmp-dir to a
4231 volatile storage medium such as /dev/shm (if available) to pre‐
4232 vent the username/password file from touching the hard drive.
4233 The script should examine the username and password, returning a
4235 success exit code (0) if the client's authentication request is
4236 to be accepted, or a failure code (1) to reject the client.
4237 This directive is designed to enable a plugin-style interface
4239 for extending OpenVPN's authentication capabilities.
4240 To protect against a client passing a maliciously formed user‐
4242 name or password string, the username string must consist only
4243 of these characters: alphanumeric, underbar ('_'), dash ('-'),
4244 dot ('.'), or at ('@'). The password string can consist of any
4245 printable characters except for CR or LF. Any illegal characters
4246 in either the username or password string will be converted to
4247 underbar ('_').
4248 Care must be taken by any user-defined scripts to avoid creating
4250 a security vulnerability in the way that these strings are han‐
4251 dled. Never use these strings in such a way that they might be
4252 escaped or evaluated by a shell interpreter.
4253 For a sample script that performs PAM authentication, see sam‐
4255 ple-scripts/auth-pam.pl in the OpenVPN source distribution.
4256 --client-connect cmd
4258 Run command cmd on client connection.
4259 cmd consists of a path to a script (or executable program), op‐
4261 tionally followed by arguments. The path and arguments may be
4262 single- or double-quoted and/or escaped using a backslash, and
4263 should be separated by one or more spaces.
4264 The command is passed the common name and IP address of the
4266 just-authenticated client as environmental variables (see envi‐
4267 ronmental variable section below). The command is also passed
4268 the pathname of a freshly created temporary file as the last ar‐
4269 gument (after any arguments specified in cmd ), to be used by
4270 the command to pass dynamically generated config file directives
4271 back to OpenVPN.
4272 If the script wants to generate a dynamic config file to be ap‐
4274 plied on the server when the client connects, it should write it
4275 to the file named by the last argument.
4276 See the --client-config-dir option below for options which can
4278 be legally used in a dynamically generated config file.
4279 Note that the return value of script is significant. If script
4281 returns a non-zero error status, it will cause the client to be
4282 disconnected.
4283 If a --client-connect wants to defer the generating of the con‐
4285 figuration then the script needs to use the client_connect_de‐
4286 ferred_file and client_connect_config_file environment vari‐
4287 ables, and write status accordingly into these files. See the
4288 Environmental Variables section for more details.
4289 --client-disconnect cmd
4291 Like --client-connect but called on client instance shutdown.
4292 Will not be called unless the --client-connect script and plug‐
4293 ins (if defined) were previously called on this instance with
4294 successful (0) status returns.
4295 The exception to this rule is if the --client-disconnect command
4297 or plugins are cascaded, and at least one client-connect func‐
4298 tion succeeded, then ALL of the client-disconnect functions for
4299 scripts and plugins will be called on client instance object
4300 deletion, even in cases where some of the related client-connect
4301 functions returned an error status.
4302 The --client-disconnect command is not passed any extra argu‐
4304 ments (only those arguments specified in cmd, if any).
4305 --down cmd
4307 Run command cmd after TUN/TAP device close (post --user UID
4308 change and/or --chroot ). cmd consists of a path to script (or
4309 executable program), optionally followed by arguments. The path
4310 and arguments may be single- or double-quoted and/or escaped us‐
4311 ing a backslash, and should be separated by one or more spaces.
4312 Called with the same parameters and environmental variables as
4314 the --up option above.
4315 Note that if you reduce privileges by using --user and/or
4317 --group, your --down script will also run at reduced privilege.
4318 --down-pre
4320 Call --down cmd/script before, rather than after, TUN/TAP close.
4321 --ipchange cmd
4323 Run command cmd when our remote ip-address is initially authen‐
4324 ticated or changes.
4325 cmd consists of a path to a script (or executable program), op‐
4327 tionally followed by arguments. The path and arguments may be
4328 single- or double-quoted and/or escaped using a backslash, and
4329 should be separated by one or more spaces.
4330 When cmd is executed two arguments are appended after any argu‐
4332 ments specified in cmd , as follows:
4333 cmd ip address port number
4335 Don't use --ipchange in --mode server mode. Use a --client-con‐
4337 nect script instead.
4338 See the Environmental Variables section below for additional pa‐
4340 rameters passed as environmental variables.
4341 If you are running in a dynamic IP address environment where the
4343 IP addresses of either peer could change without notice, you can
4344 use this script, for example, to edit the /etc/hosts file with
4345 the current address of the peer. The script will be run every
4346 time the remote peer changes its IP address.
4347 Similarly if our IP address changes due to DHCP, we should con‐
4349 figure our IP address change script (see man page for dhcpcd(8))
4350 to deliver a SIGHUP or SIGUSR1 signal to OpenVPN. OpenVPN will
4351 then re-establish a connection with its most recently authenti‐
4352 cated peer on its new IP address.
4353 --learn-address cmd
4355 Run command cmd to validate client virtual addresses or routes.
4356 cmd consists of a path to a script (or executable program), op‐
4358 tionally followed by arguments. The path and arguments may be
4359 single- or double-quoted and/or escaped using a backslash, and
4360 should be separated by one or more spaces.
4361 Three arguments will be appended to any arguments in cmd as fol‐
4363 lows:
4364 $1 - [operation]
4366 "add", "update", or "delete" based on whether or not the
4367 address is being added to, modified, or deleted from
4368 OpenVPN's internal routing table.
4369 $2 - [address]
4371 The address being learned or unlearned. This can be an
4372 IPv4 address such as "198.162.10.14", an IPv4 subnet such
4373 as "198.162.10.0/24", or an ethernet MAC address (when
4374 --dev tap is being used) such as "00:FF:01:02:03:04".
4375 $3 - [common name]
4377 The common name on the certificate associated with the
4378 client linked to this address. Only present for "add" or
4379 "update" operations, not "delete".
4380 On "add" or "update" methods, if the script returns a failure
4382 code (non-zero), OpenVPN will reject the address and will not
4383 modify its internal routing table.
4384 Normally, the cmd script will use the information provided above
4386 to set appropriate firewall entries on the VPN TUN/TAP inter‐
4387 face. Since OpenVPN provides the association between virtual IP
4388 or MAC address and the client's authenticated common name, it
4389 allows a user-defined script to configure firewall access poli‐
4390 cies with regard to the client's high-level common name, rather
4391 than the low level client virtual addresses.
4392 --route-up cmd
4394 Run command cmd after routes are added, subject to --route-de‐
4395 lay.
4396 cmd consists of a path to a script (or executable program), op‐
4398 tionally followed by arguments. The path and arguments may be
4399 single- or double-quoted and/or escaped using a backslash, and
4400 should be separated by one or more spaces.
4401 See the Environmental Variables section below for additional pa‐
4403 rameters passed as environmental variables.
4404 --route-pre-down cmd
4406 Run command cmd before routes are removed upon disconnection.
4407 cmd consists of a path to a script (or executable program), op‐
4409 tionally followed by arguments. The path and arguments may be
4410 single- or double-quoted and/or escaped using a backslash, and
4411 should be separated by one or more spaces.
4412 See the Environmental Variables section below for additional pa‐
4414 rameters passed as environmental variables.
4415 --setenv args
4417 Set a custom environmental variable name=value to pass to
4418 script.
4419 Valid syntaxes:
4421 setenv name value
4423 setenv FORWARD_COMPATIBLE 1
4424 setenv opt config_option
4425 By setting FORWARD_COMPATIBLE to 1, the config file syntax
4427 checking is relaxed so that unknown directives will trigger a
4428 warning but not a fatal error, on the assumption that a given
4429 unknown directive might be valid in future OpenVPN versions.
4430 This option should be used with caution, as there are good secu‐
4432 rity reasons for having OpenVPN fail if it detects problems in a
4433 config file. Having said that, there are valid reasons for
4434 wanting new software features to gracefully degrade when encoun‐
4435 tered by older software versions.
4436 It is also possible to tag a single directive so as not to trig‐
4438 ger a fatal error if the directive isn't recognized. To do this,
4439 prepend the following before the directive: setenv opt
4440 Versions prior to OpenVPN 2.3.3 will always ignore options set
4442 with the setenv opt directive.
4443 See also --ignore-unknown-option
4445 --setenv-safe args
4447 Set a custom environmental variable OPENVPN_name to value to
4448 pass to scripts.
4449 Valid syntaxes:
4451 setenv-safe name value
4453 This directive is designed to be pushed by the server to
4455 clients, and the prepending of OPENVPN_ to the environmental
4456 variable is a safety precaution to prevent a LD_PRELOAD style
4457 attack from a malicious or compromised server.
4458 --tls-verify cmd
4460 Run command cmd to verify the X509 name of a pending TLS connec‐
4461 tion that has otherwise passed all other tests of certification
4462 (except for revocation via --crl-verify directive; the revoca‐
4463 tion test occurs after the --tls-verify test).
4464 cmd should return 0 to allow the TLS handshake to proceed, or 1
4466 to fail.
4467 cmd consists of a path to a script (or executable program), op‐
4469 tionally followed by arguments. The path and arguments may be
4470 single- or double-quoted and/or escaped using a backslash, and
4471 should be separated by one or more spaces.
4472 When cmd is executed two arguments are appended after any argu‐
4474 ments specified in cmd, as follows:
4475 cmd certificate_depth subject
4477 These arguments are, respectively, the current certificate depth
4479 and the X509 subject distinguished name (dn) of the peer.
4480 This feature is useful if the peer you want to trust has a cer‐
4482 tificate which was signed by a certificate authority who also
4483 signed many other certificates, where you don't necessarily want
4484 to trust all of them, but rather be selective about which peer
4485 certificate you will accept. This feature allows you to write a
4486 script which will test the X509 name on a certificate and decide
4487 whether or not it should be accepted. For a simple perl script
4488 which will test the common name field on the certificate, see
4489 the file verify-cn in the OpenVPN distribution.
4490 See the Environmental Variables section below for additional pa‐
4492 rameters passed as environmental variables.
4493 --up cmd
4495 Run command cmd after successful TUN/TAP device open (pre --user
4496 UID change).
4497 cmd consists of a path to a script (or executable program), op‐
4499 tionally followed by arguments. The path and arguments may be
4500 single- or double-quoted and/or escaped using a backslash, and
4501 should be separated by one or more spaces.
4502 The up command is useful for specifying route commands which
4504 route IP traffic destined for private subnets which exist at the
4505 other end of the VPN connection into the tunnel.
4506 For --dev tun execute as:
4508 cmd tun_dev tun_mtu link_mtu ifconfig_local_ip ifconfig_remote_ip [init | restart]
4510 For --dev tap execute as:
4512 cmd tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask [init | restart]
4514 See the Environmental Variables section below for additional pa‐
4516 rameters passed as environmental variables.
4517 Note that if cmd includes arguments, all OpenVPN-generated argu‐
4519 ments will be appended to them to build an argument list with
4520 which the executable will be called.
4521 Typically, cmd will run a script to add routes to the tunnel.
4523 Normally the up script is called after the TUN/TAP device is
4525 opened. In this context, the last command line parameter passed
4526 to the script will be init. If the --up-restart option is also
4527 used, the up script will be called for restarts as well. A
4528 restart is considered to be a partial reinitialization of Open‐
4529 VPN where the TUN/TAP instance is preserved (the --persist-tun
4530 option will enable such preservation). A restart can be gener‐
4531 ated by a SIGUSR1 signal, a --ping-restart timeout, or a connec‐
4532 tion reset when the TCP protocol is enabled with the --proto op‐
4533 tion. If a restart occurs, and --up-restart has been specified,
4534 the up script will be called with restart as the last parameter.
4535 NOTE: On restart, OpenVPN will not pass the full set of envi‐
4537 ronment variables to the script. Namely, everything re‐
4538 lated to routing and gateways will not be passed, as
4539 nothing needs to be done anyway - all the routing setup
4540 is already in place. Additionally, the up-restart script
4541 will run with the downgraded UID/GID settings (if config‐
4542 ured).
4543 The following standalone example shows how the --up script can
4545 be called in both an initialization and restart context. (NOTE:
4546 for security reasons, don't run the following example unless UDP
4547 port 9999 is blocked by your firewall. Also, the example will
4548 run indefinitely, so you should abort with control-c).
4549 openvpn --dev tun --port 9999 --verb 4 --ping-restart 10 \
4551 --up 'echo up' --down 'echo down' --persist-tun \
4552 --up-restart
4553 Note that OpenVPN also provides the --ifconfig option to auto‐
4555 matically ifconfig the TUN device, eliminating the need to de‐
4556 fine an --up script, unless you also want to configure routes in
4557 the --up script.
4558 If --ifconfig is also specified, OpenVPN will pass the ifconfig
4560 local and remote endpoints on the command line to the --up
4561 script so that they can be used to configure routes such as:
4562 route add -net 10.0.0.0 netmask 255.255.255.0 gw $5
4564 --up-delay
4566 Delay TUN/TAP open and possible --up script execution until af‐
4567 ter TCP/UDP connection establishment with peer.
4568 In --proto udp mode, this option normally requires the use of
4570 --ping to allow connection initiation to be sensed in the ab‐
4571 sence of tunnel data, since UDP is a "connectionless" protocol.
4572 On Windows, this option will delay the TAP-Win32 media state
4574 transitioning to "connected" until connection establishment,
4575 i.e. the receipt of the first authenticated packet from the
4576 peer.
4577 --up-restart
4579 Enable the --up and --down scripts to be called for restarts as
4580 well as initial program start. This option is described more
4581 fully above in the --up option documentation.
4582 String Types and Remapping
4584 In certain cases, OpenVPN will perform remapping of characters in
4585 strings. Essentially, any characters outside the set of permitted char‐
4586 acters for each string type will be converted to underbar ('_').
4587 Q: Why is string remapping necessary?
4589 It's an important security feature to prevent the malicious cod‐
4590 ing of strings from untrusted sources to be passed as parameters
4591 to scripts, saved in the environment, used as a common name,
4592 translated to a filename, etc.
4593 Q: Can string remapping be disabled?
4595 Yes, by using the --no-name-remapping option, however this
4596 should be considered an advanced option.
4597 Here is a brief rundown of OpenVPN's current string types and the per‐
4599 mitted character class for each string:
4600 X509 Names
4602 Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), at ('@'),
4603 colon (':'), slash ('/'), and equal ('='). Alphanumeric is de‐
4604 fined as a character which will cause the C library isalnum()
4605 function to return true.
4606 Common Names
4608 Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), and at
4609 ('@').
4610 --auth-user-pass username
4612 Same as Common Name, with one exception: starting with OpenVPN
4613 2.0.1, the username is passed to the OPEN‐
4614 VPN_PLUGIN_AUTH_USER_PASS_VERIFY plugin in its raw form, without
4615 string remapping.
4616 --auth-user-pass password
4618 Any "printable" character except CR or LF. Printable is defined
4619 to be a character which will cause the C library isprint() func‐
4620 tion to return true.
4621 --client-config-dir filename as derived from common name or`username
4623 Alphanumeric, underbar ('_'), dash ('-'), and dot ('.') except
4624 for "." or ".." as standalone strings. As of v2.0.1-rc6, the at
4625 ('@') character has been added as well for compatibility with
4626 the common name character class.
4627 Environmental variable names
4629 Alphanumeric or underbar ('_').
4630 Environmental variable values
4632 Any printable character.
4633 For all cases, characters in a string which are not members of the le‐
4635 gal character class for that string type will be remapped to underbar
4636 ('_').
4637 Environmental Variables
4639 Once set, a variable is persisted indefinitely until it is reset by a
4640 new value or a restart,
4641 As of OpenVPN 2.0-beta12, in server mode, environmental variables set
4643 by OpenVPN are scoped according to the client objects they are associ‐
4644 ated with, so there should not be any issues with scripts having access
4645 to stale, previously set variables which refer to different client in‐
4646 stances.
4647 bytes_received
4649 Total number of bytes received from client during VPN session.
4650 Set prior to execution of the --client-disconnect script.
4651 bytes_sent
4653 Total number of bytes sent to client during VPN session. Set
4654 prior to execution of the --client-disconnect script.
4655 client_connect_config_file
4657 The path to the configuration file that should be written to by
4658 the --client-connect script (optional, if per-session configura‐
4659 tion is desired). This is the same file name as passed via com‐
4660 mand line argument on the call to the --client-connect script.
4661 client_connect_deferred_file
4663 This file can be optionally written to in order to to communi‐
4664 cate a status code of the --client-connect script or plgin.
4665 Only the first character in the file is relevant. It must be
4666 either 1 to indicate normal script execution, 0 indicates an er‐
4667 ror (in the same way that a non zero exit status does) or 2 to
4668 indicate that the script deferred returning the config file.
4669 For deferred (background) handling, the script or plugin MUST
4671 write 2 to the file to indicate the deferral and then return
4672 with exit code 0 to signal deferred handler started OK.
4673 A background process or similar must then take care of writing
4675 the configuration to the file indicated by the client_con‐
4676 nect_config_file environment variable and when finished, write
4677 the a 1 to this file (or 0 in case of an error).
4678 The absence of any character in the file when the script fin‐
4680 ishes executing is interpreted the same as 1. This allows
4681 scripts that are not written to support the defer mechanism to
4682 be used unmodified.
4683 common_name
4685 The X509 common name of an authenticated client. Set prior to
4686 execution of --client-connect, --client-disconnect and
4687 --auth-user-pass-verify scripts.
4688 config Name of first --config file. Set on program initiation and reset
4690 on SIGHUP.
4691 daemon Set to "1" if the --daemon directive is specified, or "0" other‐
4693 wise. Set on program initiation and reset on SIGHUP.
4694 daemon_log_redirect
4696 Set to "1" if the --log or --log-append directives are speci‐
4697 fied, or "0" otherwise. Set on program initiation and reset on
4698 SIGHUP.
4699 dev The actual name of the TUN/TAP device, including a unit number
4701 if it exists. Set prior to --up or --down script execution.
4702 dev_idx
4704 On Windows, the device index of the TUN/TAP adapter (to be used
4705 in netsh.exe calls which sometimes just do not work right with
4706 interface names). Set prior to --up or --down script execution.
4707 foreign_option_{n}
4709 An option pushed via --push to a client which does not natively
4710 support it, such as --dhcp-option on a non-Windows system, will
4711 be recorded to this environmental variable sequence prior to
4712 --up script execution.
4713 ifconfig_broadcast
4715 The broadcast address for the virtual ethernet segment which is
4716 derived from the --ifconfig option when --dev tap is used. Set
4717 prior to OpenVPN calling the ifconfig or netsh (windows version
4718 of ifconfig) commands which normally occurs prior to --up script
4719 execution.
4720 ifconfig_ipv6_local
4722 The local VPN endpoint IPv6 address specified in the --ifcon‐
4723 fig-ipv6 option (first parameter). Set prior to OpenVPN calling
4724 the ifconfig or code:netsh (windows version of ifconfig) com‐
4725 mands which normally occurs prior to --up script execution.
4726 ifconfig_ipv6_netbits
4728 The prefix length of the IPv6 network on the VPN interface. De‐
4729 rived from the /nnn parameter of the IPv6 address in the --if‐
4730 config-ipv6 option (first parameter). Set prior to OpenVPN call‐
4731 ing the ifconfig or netsh (windows version of ifconfig) commands
4732 which normally occurs prior to --up script execution.
4733 ifconfig_ipv6_remote
4735 The remote VPN endpoint IPv6 address specified in the --ifcon‐
4736 fig-ipv6 option (second parameter). Set prior to OpenVPN calling
4737 the ifconfig or netsh (windows version of ifconfig) commands
4738 which normally occurs prior to --up script execution.
4739 ifconfig_local
4741 The local VPN endpoint IP address specified in the --ifconfig
4742 option (first parameter). Set prior to OpenVPN calling the if‐
4743 config or netsh (windows version of ifconfig) commands which
4744 normally occurs prior to --up script execution.
4745 ifconfig_remote
4747 The remote VPN endpoint IP address specified in the --ifconfig
4748 option (second parameter) when --dev tun is used. Set prior to
4749 OpenVPN calling the ifconfig or netsh (windows version of ifcon‐
4750 fig) commands which normally occurs prior to --up script execu‐
4751 tion.
4752 ifconfig_netmask
4754 The subnet mask of the virtual ethernet segment that is speci‐
4755 fied as the second parameter to --ifconfig when --dev tap is be‐
4756 ing used. Set prior to OpenVPN calling the ifconfig or netsh
4757 (windows version of ifconfig) commands which normally occurs
4758 prior to --up script execution.
4759 ifconfig_pool_local_ip
4761 The local virtual IP address for the TUN/TAP tunnel taken from
4762 an --ifconfig-push directive if specified, or otherwise from the
4763 ifconfig pool (controlled by the --ifconfig-pool config file di‐
4764 rective). Only set for --dev tun tunnels. This option is set on
4765 the server prior to execution of the --client-connect and
4766 --client-disconnect scripts.
4767 ifconfig_pool_netmask
4769 The virtual IP netmask for the TUN/TAP tunnel taken from an
4770 --ifconfig-push directive if specified, or otherwise from the
4771 ifconfig pool (controlled by the --ifconfig-pool config file di‐
4772 rective). Only set for --dev tap tunnels. This option is set on
4773 the server prior to execution of the --client-connect and
4774 --client-disconnect scripts.
4775 ifconfig_pool_remote_ip
4777 The remote virtual IP address for the TUN/TAP tunnel taken from
4778 an --ifconfig-push directive if specified, or otherwise from the
4779 ifconfig pool (controlled by the --ifconfig-pool config file di‐
4780 rective). This option is set on the server prior to execution of
4781 the --client-connect and --client-disconnect scripts.
4782 link_mtu
4784 The maximum packet size (not including the IP header) of tunnel
4785 data in UDP tunnel transport mode. Set prior to --up or --down
4786 script execution.
4787 local The --local parameter. Set on program initiation and reset on
4789 SIGHUP.
4790 local_port
4792 The local port number or name, specified by --port or --lport.
4793 Set on program initiation and reset on SIGHUP.
4794 password
4796 The password provided by a connecting client. Set prior to
4797 --auth-user-pass-verify script execution only when the via-env
4798 modifier is specified, and deleted from the environment after
4799 the script returns.
4800 proto The --proto parameter. Set on program initiation and reset on
4802 SIGHUP.
4803 remote_{n}
4805 The --remote parameter. Set on program initiation and reset on
4806 SIGHUP.
4807 remote_port_{n}
4809 The remote port number, specified by --port or --rport. Set on
4810 program initiation and reset on SIGHUP.
4811 route_net_gateway
4813 The pre-existing default IP gateway in the system routing table.
4814 Set prior to --up script execution.
4815 route_vpn_gateway
4817 The default gateway used by --route options, as specified in ei‐
4818 ther the --route-gateway option or the second parameter to --if‐
4819 config when --dev tun is specified. Set prior to --up script ex‐
4820 ecution.
4821 route_{parm}_{n}
4823 A set of variables which define each route to be added, and are
4824 set prior to --up script execution.
4825 parm will be one of network, netmask", gateway, or metric.
4827 n is the OpenVPN route number, starting from 1.
4829 If the network or gateway are resolvable DNS names, their IP ad‐
4831 dress translations will be recorded rather than their names as
4832 denoted on the command line or configuration file.
4833 route_ipv6_{parm}_{n}
4835 A set of variables which define each IPv6 route to be added, and
4836 are set prior to --up script execution.
4837 parm will be one of network, gateway or metric. route_ipv6_net‐
4839 work_{n} contains netmask as /nnn, unlike IPv4 where it is
4840 passed in a separate environment variable.
4841 n is the OpenVPN route number, starting from 1.
4843 If the network or gateway are resolvable DNS names, their IP ad‐
4845 dress translations will be recorded rather than their names as
4846 denoted on the command line or configuration file.
4847 peer_cert
4849 Temporary file name containing the client certificate upon con‐
4850 nection. Useful in conjunction with --tls-verify.
4851 script_context
4853 Set to "init" or "restart" prior to up/down script execution.
4854 For more information, see documentation for --up.
4855 script_type
4857 Prior to execution of any script, this variable is set to the
4858 type of script being run. It can be one of the following: up,
4859 down, ipchange, route-up, tls-verify, auth-user-pass-verify,
4860 client-connect, client-disconnect or learn-address. Set prior to
4861 execution of any script.
4862 signal The reason for exit or restart. Can be one of sigusr1, sighup,
4864 sigterm, sigint, inactive (controlled by --inactive option),
4865 ping-exit (controlled by --ping-exit option), ping-restart (con‐
4866 trolled by --ping-restart option), connection-reset (triggered
4867 on TCP connection reset), error or unknown (unknown signal).
4868 This variable is set just prior to down script execution.
4869 time_ascii
4871 Client connection timestamp, formatted as a human-readable time
4872 string. Set prior to execution of the --client-connect script.
4873 time_duration
4875 The duration (in seconds) of the client session which is now
4876 disconnecting. Set prior to execution of the --client-disconnect
4877 script.
4878 time_unix
4880 Client connection timestamp, formatted as a unix integer
4881 date/time value. Set prior to execution of the --client-connect
4882 script.
4883 tls_digest_{n} / tls_digest_sha256_{n}
4885 Contains the certificate SHA1 / SHA256 fingerprint, where n is
4886 the verification level. Only set for TLS connections. Set prior
4887 to execution of --tls-verify script.
4888 tls_id_{n}
4890 A series of certificate fields from the remote peer, where n is
4891 the verification level. Only set for TLS connections. Set prior
4892 to execution of --tls-verify script.
4893 tls_serial_{n}
4895 The serial number of the certificate from the remote peer, where
4896 n is the verification level. Only set for TLS connections. Set
4897 prior to execution of --tls-verify script. This is in the form
4898 of a decimal string like "933971680", which is suitable for do‐
4899 ing serial-based OCSP queries (with OpenSSL, do not prepend "0x"
4900 to the string) If something goes wrong while reading the value
4901 from the certificate it will be an empty string, so your code
4902 should check that. See the contrib/OCSP_check/OCSP_check.sh
4903 script for an example.
4904 tls_serial_hex_{n}
4906 Like tls_serial_{n}, but in hex form (e.g. 12:34:56:78:9A).
4907 tun_mtu
4909 The MTU of the TUN/TAP device. Set prior to --up or --down
4910 script execution.
4911 trusted_ip / trusted_ip6)
4913 Actual IP address of connecting client or peer which has been
4914 authenticated. Set prior to execution of --ipchange,
4915 --client-connect and --client-disconnect scripts. If using ipv6
4916 endpoints (udp6, tcp6), trusted_ip6 will be set instead.
4917 trusted_port
4919 Actual port number of connecting client or peer which has been
4920 authenticated. Set prior to execution of --ipchange,
4921 --client-connect and --client-disconnect scripts.
4922 untrusted_ip / untrusted_ip6
4924 Actual IP address of connecting client or peer which has not
4925 been authenticated yet. Sometimes used to nmap the connecting
4926 host in a --tls-verify script to ensure it is firewalled prop‐
4927 erly. Set prior to execution of --tls-verify and
4928 --auth-user-pass-verify scripts. If using ipv6 endpoints (udp6,
4929 tcp6), untrusted_ip6 will be set instead.
4930 untrusted_port
4932 Actual port number of connecting client or peer which has not
4933 been authenticated yet. Set prior to execution of --tls-verify
4934 and --auth-user-pass-verify scripts.
4935 username
4937 The username provided by a connecting client. Set prior to
4938 --auth-user-pass-verify script execution only when the via-env
4939 modifier is specified.
4940 X509_{n}_{subject_field}
4942 An X509 subject field from the remote peer certificate, where n
4943 is the verification level. Only set for TLS connections. Set
4944 prior to execution of --tls-verify script. This variable is sim‐
4945 ilar to tls_id_{n} except the component X509 subject fields are
4946 broken out, and no string remapping occurs on these field values
4947 (except for remapping of control characters to "_"). For exam‐
4948 ple, the following variables would be set on the OpenVPN server
4949 using the sample client certificate in sample-keys (client.crt).
4950 Note that the verification level is 0 for the client certificate
4951 and 1 for the CA certificate.
4952 X509_0_emailAddress=me@myhost.mydomain
4954 X509_0_CN=Test-Client
4955 X509_0_O=OpenVPN-TEST
4956 X509_0_ST=NA
4957 X509_0_C=KG
4958 X509_1_emailAddress=me@myhost.mydomain
4959 X509_1_O=OpenVPN-TEST
4960 X509_1_L=BISHKEK
4961 X509_1_ST=NA
4962 X509_1_C=KG
4963 Management Interface Options
4965 OpenVPN provides a feature rich socket based management interface for
4966 both server and client mode operations.
4967 --management args
4969 Enable a management server on a socket-name Unix socket on those
4970 platforms supporting it, or on a designated TCP port.
4971 Valid syntaxes:
4973 management socket-name unix #
4975 management socket-name unix pw-file # (recommended)
4976 management IP port # (INSECURE)
4977 management IP port pw-file #
4978 pw-file, if specified, is a password file where the password
4980 must be on first line. Instead of a filename it can use the key‐
4981 word stdin which will prompt the user for a password to use when
4982 OpenVPN is starting.
4983 For unix sockets, the default behaviour is to create a unix do‐
4985 main socket that may be connected to by any process. Use the
4986 --management-client-user and --management-client-group direc‐
4987 tives to restrict access.
4988 The management interface provides a special mode where the TCP
4990 management link can operate over the tunnel itself. To enable
4991 this mode, set IP to tunnel. Tunnel mode will cause the manage‐
4992 ment interface to listen for a TCP connection on the local VPN
4993 address of the TUN/TAP interface.
4994 *BEWARE* of enabling the management interface over TCP. In these
4996 cases you should ALWAYS make use of pw-file to password protect
4997 the management interface. Any user who can connect to this TCP
4998 IP:port will be able to manage and control (and interfere with)
4999 the OpenVPN process. It is also strongly recommended to set IP
5000 to 127.0.0.1 (localhost) to restrict accessibility of the man‐
5001 agement server to local clients.
5002 While the management port is designed for programmatic control
5004 of OpenVPN by other applications, it is possible to telnet to
5005 the port, using a telnet client in "raw" mode. Once connected,
5006 type help for a list of commands.
5007 For detailed documentation on the management interface, see the
5009 management-notes.txt file in the management folder of the Open‐
5010 VPN source distribution.
5011 --management-client
5013 Management interface will connect as a TCP/unix domain client to
5014 IP:port specified by --management rather than listen as a TCP
5015 server or on a unix domain socket.
5016 If the client connection fails to connect or is disconnected, a
5018 SIGTERM signal will be generated causing OpenVPN to quit.
5019 --management-client-auth
5021 Gives management interface client the responsibility to authen‐
5022 ticate clients after their client certificate has been verified.
5023 See management-notes.txt in OpenVPN distribution for detailed
5024 notes.
5025 --management-client-group g
5027 When the management interface is listening on a unix domain
5028 socket, only allow connections from group g.
5029 --management-client-pf
5031 Management interface clients must specify a packet filter file
5032 for each connecting client. See management-notes.txt in OpenVPN
5033 distribution for detailed notes.
5034 --management-client-user u
5036 When the management interface is listening on a unix domain
5037 socket, only allow connections from user u.
5038 --management-external-cert certificate-hint
5040 Allows usage for external certificate instead of --cert option
5041 (client-only). certificate-hint is an arbitrary string which is
5042 passed to a management interface client as an argument of
5043 NEED-CERTIFICATE notification. Requires --management-exter‐
5044 nal-key.
5045 --management-external-key args
5047 Allows usage for external private key file instead of --key op‐
5048 tion (client-only).
5049 Valid syntaxes:
5051 management-external-key
5053 management-external-key nopadding
5054 management-external-key pkcs1
5055 management-external-key nopadding pkcs1
5056 The optional parameters nopadding and pkcs1 signal support for
5058 different padding algorithms. See doc/mangement-notes.txt for a
5059 complete description of this feature.
5060 --management-forget-disconnect
5062 Make OpenVPN forget passwords when management session discon‐
5063 nects.
5064 This directive does not affect the --http-proxy username/pass‐
5066 word. It is always cached.
5067 --management-hold
5069 Start OpenVPN in a hibernating state, until a client of the man‐
5070 agement interface explicitly starts it with the hold release
5071 command.
5072 --management-log-cache n
5074 Cache the most recent n lines of log file history for usage by
5075 the management channel.
5076 --management-query-passwords
5078 Query management channel for private key password and
5079 --auth-user-pass username/password. Only query the management
5080 channel for inputs which ordinarily would have been queried from
5081 the console.
5082 --management-query-proxy
5084 Query management channel for proxy server information for a spe‐
5085 cific --remote (client-only).
5086 --management-query-remote
5088 Allow management interface to override --remote directives
5089 (client-only).
5090 --management-signal
5092 Send SIGUSR1 signal to OpenVPN if management session discon‐
5093 nects. This is useful when you wish to disconnect an OpenVPN
5094 session on user logoff. For --management-client this option is
5095 not needed since a disconnect will always generate a SIGTERM.
5096 --management-up-down
5098 Report tunnel up/down events to management interface.
5099 Plug-in Interface Options
5101 OpenVPN can be extended by loading external plug-in modules at runtime.
5102 These plug-ins must be prebuilt and adhere to the OpenVPN Plug-In API.
5103 --plugin args
5105 Loads an OpenVPN plug-in module.
5106 Valid syntax:
5108 plugin module-name
5110 plugin module-name "arguments"
5111 The module-name needs to be the first argument, indicating the
5113 plug-in to load. The second argument is an optional init string
5114 which will be passed directly to the plug-in. If the init con‐
5115 sists of multiple arguments it must be enclosed in double-quotes
5116 ("). Multiple plugin modules may be loaded into one OpenVPN
5117 process.
5118 The module-name argument can be just a filename or a filename
5120 with a relative or absolute path. The format of the filename and
5121 path defines if the plug-in will be loaded from a default
5122 plug-in directory or outside this directory.
5123 --plugin path Effective directory used
5125 ===================== =============================
5126 myplug.so DEFAULT_DIR/myplug.so
5127 subdir/myplug.so DEFAULT_DIR/subdir/myplug.so
5128 ./subdir/myplug.so CWD/subdir/myplug.so
5129 /usr/lib/my/plug.so /usr/lib/my/plug.so
5130 DEFAULT_DIR is replaced by the default plug-in directory, which
5132 is configured at the build time of OpenVPN. CWD is the current
5133 directory where OpenVPN was started or the directory OpenVPN
5134 have switched into via the --cd option before the --plugin op‐
5135 tion.
5136 For more information and examples on how to build OpenVPN
5138 plug-in modules, see the README file in the plugin folder of the
5139 OpenVPN source distribution.
5140 If you are using an RPM install of OpenVPN, see /usr/share/open‐
5142 vpn/plugin. The documentation is in doc and the actual plugin
5143 modules are in lib.
5144 Multiple plugin modules can be cascaded, and modules can be used
5146 in tandem with scripts. The modules will be called by OpenVPN in
5147 the order that they are declared in the config file. If both a
5148 plugin and script are configured for the same callback, the
5149 script will be called last. If the return code of the mod‐
5150 ule/script controls an authentication function (such as tls-ver‐
5151 ify, auth-user-pass-verify, or client-connect), then every mod‐
5152 ule and script must return success (0) in order for the connec‐
5153 tion to be authenticated.
5154 Windows-Specific Options
5156 --allow-nonadmin TAP-adapter
5157 (Standalone) Set TAP-adapter to allow access from non-adminis‐
5158 trative accounts. If TAP-adapter is omitted, all TAP adapters on
5159 the system will be configured to allow non-admin access. The
5160 non-admin access setting will only persist for the length of
5161 time that the TAP-Win32 device object and driver remain loaded,
5162 and will need to be re-enabled after a reboot, or if the driver
5163 is unloaded and reloaded. This directive can only be used by an
5164 administrator.
5165 --block-outside-dns
5167 Block DNS servers on other network adapters to prevent DNS
5168 leaks. This option prevents any application from accessing TCP
5169 or UDP port 53 except one inside the tunnel. It uses Windows
5170 Filtering Platform (WFP) and works on Windows Vista or later.
5171 This option is considered unknown on non-Windows platforms and
5173 unsupported on Windows XP, resulting in fatal error. You may
5174 want to use --setenv opt or --ignore-unknown-option (not suit‐
5175 able for Windows XP) to ignore said error. Note that pushing un‐
5176 known options from server does not trigger fatal errors.
5177 --cryptoapicert select-string
5179 (Windows/OpenSSL Only) Load the certificate and private key from
5180 the Windows Certificate System Store.
5181 Use this option instead of --cert and --key.
5183 This makes it possible to use any smart card, supported by Win‐
5185 dows, but also any kind of certificate, residing in the Cert
5186 Store, where you have access to the private key. This option has
5187 been tested with a couple of different smart cards (GemSAFE,
5188 Cryptoflex, and Swedish Post Office eID) on the client side, and
5189 also an imported PKCS12 software certificate on the server side.
5190 To select a certificate, based on a substring search in the cer‐
5192 tificate's subject:
5193 cryptoapicert "SUBJ:Peter Runestig"
5195 To select a certificate, based on certificate's thumbprint:
5197 cryptoapicert "THUMB:f6 49 24 41 01 b4 ..."
5199 The thumbprint hex string can easily be copy-and-pasted from the
5201 Windows Certificate Store GUI.
5202 --dhcp-release
5204 Ask Windows to release the TAP adapter lease on shutdown. This
5205 option has no effect now, as it is enabled by default starting
5206 with OpenVPN 2.4.1.
5207 --dhcp-renew
5209 Ask Windows to renew the TAP adapter lease on startup. This op‐
5210 tion is normally unnecessary, as Windows automatically triggers
5211 a DHCP renegotiation on the TAP adapter when it comes up, how‐
5212 ever if you set the TAP-Win32 adapter Media Status property to
5213 "Always Connected", you may need this flag.
5214 --ip-win32 method
5216 When using --ifconfig on Windows, set the TAP-Win32 adapter IP
5217 address and netmask using method. Don't use this option unless
5218 you are also using --ifconfig.
5219 manual Don't set the IP address or netmask automatically. In‐
5221 stead output a message to the console telling the user to
5222 configure the adapter manually and indicating the IP/net‐
5223 mask which OpenVPN expects the adapter to be set to.
5224 dynamic [offset] [lease-time]
5226 Automatically set the IP address and netmask by replying
5227 to DHCP query messages generated by the kernel. This
5228 mode is probably the "cleanest" solution for setting the
5229 TCP/IP properties since it uses the well-known DHCP pro‐
5230 tocol. There are, however, two prerequisites for using
5231 this mode:
5232 1. The TCP/IP properties for the TAP-Win32 adapter must
5234 be set to "Obtain an IP address automatically", and
5235 2. OpenVPN needs to claim an IP address in the subnet for
5237 use as the virtual DHCP server address.
5238 By default in --dev tap mode, OpenVPN will take the nor‐
5240 mally unused first address in the subnet. For example, if
5241 your subnet is 192.168.4.0 netmask 255.255.255.0, then
5242 OpenVPN will take the IP address 192.168.4.0 to use as
5243 the virtual DHCP server address. In --dev tun mode,
5244 OpenVPN will cause the DHCP server to masquerade as if it
5245 were coming from the remote endpoint.
5246 The optional offset parameter is an integer which is >
5248 -256 and < 256 and which defaults to -1. If offset is
5249 positive, the DHCP server will masquerade as the IP ad‐
5250 dress at network address + offset. If offset is negative,
5251 the DHCP server will masquerade as the IP address at
5252 broadcast address + offset.
5253 The Windows ipconfig /all command can be used to show
5255 what Windows thinks the DHCP server address is. OpenVPN
5256 will "claim" this address, so make sure to use a free ad‐
5257 dress. Having said that, different OpenVPN instantia‐
5258 tions, including different ends of the same connection,
5259 can share the same virtual DHCP server address.
5260 The lease-time parameter controls the lease time of the
5262 DHCP assignment given to the TAP-Win32 adapter, and is
5263 denoted in seconds. Normally a very long lease time is
5264 preferred because it prevents routes involving the
5265 TAP-Win32 adapter from being lost when the system goes to
5266 sleep. The default lease time is one year.
5267 netsh Automatically set the IP address and netmask using the
5269 Windows command-line "netsh" command. This method appears
5270 to work correctly on Windows XP but not Windows 2000.
5271 ipapi Automatically set the IP address and netmask using the
5273 Windows IP Helper API. This approach does not have ideal
5274 semantics, though testing has indicated that it works
5275 okay in practice. If you use this option, it is best to
5276 leave the TCP/IP properties for the TAP-Win32 adapter in
5277 their default state, i.e. "Obtain an IP address automati‐
5278 cally."
5279 adaptive (Default)
5281 Try dynamic method initially and fail over to netsh if
5282 the DHCP negotiation with the TAP-Win32 adapter does not
5283 succeed in 20 seconds. Such failures have been known to
5284 occur when certain third-party firewall packages in‐
5285 stalled on the client machine block the DHCP negotiation
5286 used by the TAP-Win32 adapter. Note that if the netsh
5287 failover occurs, the TAP-Win32 adapter TCP/IP properties
5288 will be reset from DHCP to static, and this will cause
5289 future OpenVPN startups using the adaptive mode to use
5290 netsh immediately, rather than trying dynamic first.
5291 To "unstick" the adaptive mode from using netsh, run
5293 OpenVPN at least once using the dynamic mode to restore
5294 the TAP-Win32 adapter TCP/IP properties to a DHCP config‐
5295 uration.
5296 --pause-exit
5298 Put up a "press any key to continue" message on the console
5299 prior to OpenVPN program exit. This option is automatically used
5300 by the Windows explorer when OpenVPN is run on a configuration
5301 file using the right-click explorer menu.
5302 --register-dns
5304 Run ipconfig /flushdns and ipconfig /registerdns on connection
5305 initiation. This is known to kick Windows into recognizing
5306 pushed DNS servers.
5307 --route-method m
5309 Which method m to use for adding routes on Windows?
5310 adaptive (default)
5312 Try IP helper API first. If that fails, fall back to the
5313 route.exe shell command.
5314 ipapi Use IP helper API.
5316 exe Call the route.exe shell command.
5318 --service args
5320 Should be used when OpenVPN is being automatically executed by
5321 another program in such a context that no interaction with the
5322 user via display or keyboard is possible.
5323 Valid syntax:
5325 service exit-event [0|1]
5327 In general, end-users should never need to explicitly use this
5329 option, as it is automatically added by the OpenVPN service
5330 wrapper when a given OpenVPN configuration is being run as a
5331 service.
5332 exit-event is the name of a Windows global event object, and
5334 OpenVPN will continuously monitor the state of this event object
5335 and exit when it becomes signaled.
5336 The second parameter indicates the initial state of exit-event
5338 and normally defaults to 0.
5339 Multiple OpenVPN processes can be simultaneously executed with
5341 the same exit-event parameter. In any case, the controlling
5342 process can signal exit-event, causing all such OpenVPN pro‐
5343 cesses to exit.
5344 When executing an OpenVPN process using the --service directive,
5346 OpenVPN will probably not have a console window to output sta‐
5347 tus/error messages, therefore it is useful to use --log or
5348 --log-append to write these messages to a file.
5349 --show-adapters
5351 (Standalone) Show available TAP-Win32 adapters which can be se‐
5352 lected using the --dev-node option. On non-Windows systems, the
5353 ifconfig(8) command provides similar functionality.
5354 --show-net
5356 (Standalone) Show OpenVPN's view of the system routing table and
5357 network adapter list.
5358 --show-net-up
5360 Output OpenVPN's view of the system routing table and network
5361 adapter list to the syslog or log file after the TUN/TAP adapter
5362 has been brought up and any routes have been added.
5363 --show-valid-subnets
5365 (Standalone) Show valid subnets for --dev tun emulation. Since
5366 the TAP-Win32 driver exports an ethernet interface to Windows,
5367 and since TUN devices are point-to-point in nature, it is neces‐
5368 sary for the TAP-Win32 driver to impose certain constraints on
5369 TUN endpoint address selection.
5370 Namely, the point-to-point endpoints used in TUN device emula‐
5372 tion must be the middle two addresses of a /30 subnet (netmask
5373 255.255.255.252).
5374 --tap-sleep n
5376 Cause OpenVPN to sleep for n seconds immediately after the
5377 TAP-Win32 adapter state is set to "connected".
5378 This option is intended to be used to troubleshoot problems with
5380 the --ifconfig and --ip-win32 options, and is used to give the
5381 TAP-Win32 adapter time to come up before Windows IP Helper API
5382 operations are applied to it.
5383 --win-sys path
5385 Set the Windows system directory pathname to use when looking
5386 for system executables such as route.exe and netsh.exe. By de‐
5387 fault, if this directive is not specified, OpenVPN will use the
5388 SystemRoot environment variable.
5389 This option has changed behaviour since OpenVPN 2.3. Earlier you
5391 had to define --win-sys env to use the SystemRoot environment
5392 variable, otherwise it defaulted to C:\\WINDOWS. It is not
5393 needed to use the env keyword any more, and it will just be ig‐
5394 nored. A warning is logged when this is found in the configura‐
5395 tion file.
5396 --windows-driver drv
5398 Specifies which tun driver to use. Values are tap-windows6 (de‐
5399 fault) and wintun. This is a Windows-only option. wintun" re‐
5400 quires --dev tun and the OpenVPN process to run elevated, or be
5401 invoked using the Interactive Service.
5402 Standalone Debug Options
5404 --show-gateway args
5405 (Standalone) Show current IPv4 and IPv6 default gateway and in‐
5406 terface towards the gateway (if the protocol in question is en‐
5407 abled).
5408 Valid syntax:
5410 --show-gateway
5412 --show-gateway IPv6-target
5413 For IPv6 this queries the route towards ::/128, or the specified
5415 IPv6 target address if passed as argument. For IPv4 on Linux,
5416 Windows, MacOS and BSD it looks for a 0.0.0.0/0 route. If there
5417 are more specific routes, the result will not always be matching
5418 the route of the IPv4 packets to the VPN gateway.
5419 Advanced Expert Options
5421 These are options only required when special tweaking is needed, often
5422 used when debugging or testing out special usage scenarios.
5423 --hash-size args
5425 Set the size of the real address hash table to r and the virtual
5426 address table to v.
5427 Valid syntax:
5429 hash-size r v
5431 By default, both tables are sized at 256 buckets.
5433 --bcast-buffers n
5435 Allocate n buffers for broadcast datagrams (default 256).
5436 --persist-local-ip
5438 Preserve initially resolved local IP address and port number
5439 across SIGUSR1 or --ping-restart restarts.
5440 --persist-remote-ip
5442 Preserve most recently authenticated remote IP address and port
5443 number across SIGUSR1 or --ping-restart restarts.
5444 --prng args
5446 (Advanced) Change the PRNG (Pseudo-random number generator) pa‐
5447 rameters
5448 Valid syntaxes:
5450 prng alg
5452 prng alg nsl
5453 Changes the PRNG to use digest algorithm alg (default sha1), and
5455 set nsl (default 16) to the size in bytes of the nonce secret
5456 length (between 16 and 64).
5457 Set alg to none to disable the PRNG and use the OpenSSL
5459 RAND_bytes function instead for all of OpenVPN's pseudo-random
5460 number needs.
5461 --rcvbuf size
5463 Set the TCP/UDP socket receive buffer size. Defaults to operat‐
5464 ing system default.
5465 --shaper n
5467 Limit bandwidth of outgoing tunnel data to n bytes per second on
5468 the TCP/UDP port. Note that this will only work if mode is set
5469 to p2p. If you want to limit the bandwidth in both directions,
5470 use this option on both peers.
5471 OpenVPN uses the following algorithm to implement traffic shap‐
5473 ing: Given a shaper rate of n bytes per second, after a datagram
5474 write of b bytes is queued on the TCP/UDP port, wait a minimum
5475 of (b / n) seconds before queuing the next write.
5476 It should be noted that OpenVPN supports multiple tunnels be‐
5478 tween the same two peers, allowing you to construct full-speed
5479 and reduced bandwidth tunnels at the same time, routing low-pri‐
5480 ority data such as off-site backups over the reduced bandwidth
5481 tunnel, and other data over the full-speed tunnel.
5482 Also note that for low bandwidth tunnels (under 1000 bytes per
5484 second), you should probably use lower MTU values as well (see
5485 above), otherwise the packet latency will grow so large as to
5486 trigger timeouts in the TLS layer and TCP connections running
5487 over the tunnel.
5488 OpenVPN allows n to be between 100 bytes/sec and 100 Mbytes/sec.
5490 --sndbuf size
5492 Set the TCP/UDP socket send buffer size. Defaults to operating
5493 system default.
5494 --tcp-queue-limit n
5496 Maximum number of output packets queued before TCP (default 64).
5497 When OpenVPN is tunneling data from a TUN/TAP device to a remote
5499 client over a TCP connection, it is possible that the TUN/TAP
5500 device might produce data at a faster rate than the TCP connec‐
5501 tion can support. When the number of output packets queued be‐
5502 fore sending to the TCP socket reaches this limit for a given
5503 client connection, OpenVPN will start to drop outgoing packets
5504 directed at this client.
5505 --txqueuelen n
5507 (Linux only) Set the TX queue length on the TUN/TAP interface.
5508 Currently defaults to operating system default.
5509
5511 Options listed in this section have been removed from OpenVPN and are
5512 no longer supported
5513 --client-cert-not-required
5515 Removed in OpenVPN 2.5. This should be replaxed with --ver‐
5516 ify-client-cert none.
5517 --ifconfig-pool-linear
5519 Removed in OpenVPN 2.5. This should be replaced with --topology
5520 p2p.
5521 --key-method
5523 Removed in OpenVPN 2.5. This option should not be used, as us‐
5524 ing the old key-method weakens the VPN tunnel security. The old
5525 key-method was also only needed when the remote side was older
5526 than OpenVPN 2.0.
5527 --no-iv
5529 Removed in OpenVPN 2.5. This option should not be used as it
5530 weakens the VPN tunnel security. This has been a NOOP option
5531 since OpenVPN 2.4.
5532 --no-replay
5534 Removed in OpenVPN 2.5. This option should not be used as it
5535 weakens the VPN tunnel security.
5536 --ns-cert-type
5538 Removed in OpenVPN 2.5. The nsCertType field is no longer sup‐
5539 ported in recent SSL/TLS libraries. If your certificates does
5540 not include key usage and extended key usage fields, they must
5541 be upgraded and the --remote-cert-tls option should be used in‐
5542 stead.
5543
5545 Client configuration files may contain multiple remote servers which it
5546 will attempt to connect against. But there are some configuration op‐
5547 tions which are related to specific --remote options. For these use
5548 cases, connection profiles are the solution.
5549 By enacpulating the --remote option and related options within <connec‐
5551 tion> and </connection>, these options are handled as a group.
5552 An OpenVPN client will try each connection profile sequentially until
5554 it achieves a successful connection.
5555 --remote-random can be used to initially "scramble" the connection
5557 list.
5558 Here is an example of connection profile usage:
5560 client
5562 dev tun
5563 <connection>
5565 remote 198.19.34.56 1194 udp
5566 </connection>
5567 <connection>
5569 remote 198.19.34.56 443 tcp
5570 </connection>
5571 <connection>
5573 remote 198.19.34.56 443 tcp
5574 http-proxy 192.168.0.8 8080
5575 </connection>
5576 <connection>
5578 remote 198.19.36.99 443 tcp
5579 http-proxy 192.168.0.8 8080
5580 </connection>
5581 persist-key
5583 persist-tun
5584 pkcs12 client.p12
5585 remote-cert-tls server
5586 verb 3
5587 First we try to connect to a server at 198.19.34.56:1194 using UDP. If
5589 that fails, we then try to connect to 198.19.34.56:443 using TCP. If
5590 that also fails, then try connecting through an HTTP proxy at
5591 192.168.0.8:8080 to 198.19.34.56:443 using TCP. Finally, try to connect
5592 through the same proxy to a server at 198.19.36.99:443 using TCP.
5593 The following OpenVPN options may be used inside of a <connection>
5595 block:
5596 bind, connect-retry, connect-retry-max, connect-timeout, ex‐
5598 plicit-exit-notify, float, fragment, http-proxy, http-proxy-option,
5599 key-direction, link-mtu, local, lport, mssfix, mtu-disc, nobind, port,
5600 proto, remote, rport, socks-proxy, tls-auth, tls-crypt, tun-mtu and,
5601 tun-mtu-extra.
5602 A defaulting mechanism exists for specifying options to apply to all
5604 <connection> profiles. If any of the above options (with the exception
5605 of remote ) appear outside of a <connection> block, but in a configura‐
5606 tion file which has one or more <connection> blocks, the option setting
5607 will be used as a default for <connection> blocks which follow it in
5608 the configuration file.
5609 For example, suppose the nobind option were placed in the sample con‐
5611 figuration file above, near the top of the file, before the first <con‐
5612 nection> block. The effect would be as if nobind were declared in all
5613 <connection> blocks below it.
5614
5616 OpenVPN allows including files in the main configuration for the --ca,
5617 --cert, --dh, --extra-certs, --key, --pkcs12, --secret, --crl-verify,
5618 --http-proxy-user-pass, --tls-auth, --auth-gen-token-secret,
5619 --tls-crypt and --tls-crypt-v2 options.
5620 Each inline file started by the line <option> and ended by the line
5622 </option>
5623 Here is an example of an inline file usage
5625 <cert>
5627 -----BEGIN CERTIFICATE-----
5628 [...]
5629 -----END CERTIFICATE-----
5630 </cert>
5631 When using the inline file feature with --pkcs12 the inline file has to
5633 be base64 encoded. Encoding of a .p12 file into base64 can be done for
5634 example with OpenSSL by running openssl base64 -in input.p12
5635
5637 SIGHUP Cause OpenVPN to close all TUN/TAP and network connections,
5638 restart, re-read the configuration file (if any), and reopen
5639 TUN/TAP and network connections.
5640 SIGUSR1
5642 Like SIGHUP`, except don't re-read configuration file, and pos‐
5643 sibly don't close and reopen TUN/TAP device, re-read key files,
5644 preserve local IP address/port, or preserve most recently au‐
5645 thenticated remote IP address/port based on --persist-tun,
5646 --persist-key, --persist-local-ip and --persist-remote-ip op‐
5647 tions respectively (see above).
5648 This signal may also be internally generated by a timeout condi‐
5650 tion, governed by the --ping-restart option.
5651 This signal, when combined with --persist-remote-ip, may be sent
5653 when the underlying parameters of the host's network interface
5654 change such as when the host is a DHCP client and is assigned a
5655 new IP address. See --ipchange for more information.
5656 SIGUSR2
5658 Causes OpenVPN to display its current statistics (to the syslog
5659 file if --daemon is used, or stdout otherwise).
5660 SIGINT, SIGTERM
5662 Causes OpenVPN to exit gracefully.
5663
5665 https://community.openvpn.net/openvpn/wiki/FAQ
5666
5668 For a more comprehensive guide to setting up OpenVPN in a production
5669 setting, see the OpenVPN HOWTO at
5670 https://openvpn.net/community-resources/how-to/
5671
5673 For a description of OpenVPN's underlying protocol, see
5674 https://openvpn.net/community-resources/openvpn-protocol/
5675
5677 OpenVPN's web site is at https://openvpn.net/
5678 Go here to download the latest version of OpenVPN, subscribe to the
5680 mailing lists, read the mailing list archives, or browse the SVN repos‐
5681 itory.
5682
5684 Report all bugs to the OpenVPN team info@openvpn.net
5685
5687 openvpn-examples(5), dhcpcd(8), ifconfig(8), openssl(1), route(8),
5688 scp(1) ssh(1)
5689
5691 This product includes software developed by the OpenSSL Project (‐
5692 https://www.openssl.org/)
5693 For more information on the TLS protocol, see
5695 http://www.ietf.org/rfc/rfc2246.txt
5696 For more information on the LZO real-time compression library see
5698 https://www.oberhumer.com/opensource/lzo/
5699
5701 Copyright (C) 2002-2020 OpenVPN Inc This program is free software; you
5702 can redistribute it and/or modify it under the terms of the GNU General
5703 Public License version 2 as published by the Free Software Foundation.
5704
5706 James Yonan james@openvpn.net
5707 OPENVPN(8)