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 --providers providers
315 Load the list of (OpenSSL) providers. This is mainly useful for
316 using an external provider for key management like tpm2-openssl
317 or to load the legacy provider with
318 --providers legacy default
320 Behaviour of changing this option between SIGHUP might not be
322 well behaving. If you need to change/add/remove this option,
323 fully restart OpenVPN.
324 --remap-usr1 signal
326 Control whether internally or externally generated SIGUSR1 sig‐
327 nals are remapped to SIGHUP (restart without persisting state)
328 or SIGTERM (exit).
329 signal can be set to SIGHUP or SIGTERM. By default, no remapping
331 occurs.
332 --script-security level
334 This directive offers policy-level control over OpenVPN's usage
335 of external programs and scripts. Lower level values are more
336 restrictive, higher values are more permissive. Settings for
337 level:
338 0 Strictly no calling of external programs.
340 1 (Default) Only call built-in executables such as ifcon‐
342 fig, ip, route, or netsh.
343 2 Allow calling of built-in executables and user-defined
345 scripts.
346 3 Allow passwords to be passed to scripts via environmental
348 variables (potentially unsafe).
349 OpenVPN releases before v2.3 also supported a method flag which
351 indicated how OpenVPN should call external commands and scripts.
352 This could be either execve or system. As of OpenVPN 2.3, this
353 flag is no longer accepted. In most *nix environments the ex‐
354 ecve() approach has been used without any issues.
355 Some directives such as --up allow options to be passed to the
357 external script. In these cases make sure the script name does
358 not contain any spaces or the configuration parser will choke
359 because it can't determine where the script name ends and script
360 options start.
361 To run scripts in Windows in earlier OpenVPN versions you needed
363 to either add a full path to the script interpreter which can
364 parse the script or use the system flag to run these scripts. As
365 of OpenVPN 2.3 it is now a strict requirement to have full path
366 to the script interpreter when running non-executables files.
367 This is not needed for executable files, such as .exe, .com,
368 .bat or .cmd files. For example, if you have a Visual Basic
369 script, you must use this syntax now:
370 --up 'C:\\Windows\\System32\\wscript.exe C:\\Program\ Files\\OpenVPN\\config\\my-up-script.vbs'
372 Please note the single quote marks and the escaping of the back‐
374 slashes (\) and the space character.
375 The reason the support for the system flag was removed is due to
377 the security implications with shell expansions when executing
378 scripts via the system() call.
379 --setcon context
381 Apply SELinux context after initialization. This essentially
382 provides the ability to restrict OpenVPN's rights to only net‐
383 work I/O operations, thanks to SELinux. This goes further than
384 --user and --chroot in that those two, while being great secu‐
385 rity features, unfortunately do not protect against privilege
386 escalation by exploitation of a vulnerable system call. You can
387 of course combine all three, but please note that since setcon
388 requires access to /proc you will have to provide it inside the
389 chroot directory (e.g. with mount --bind).
390 Since the setcon operation is delayed until after initializa‐
392 tion, OpenVPN can be restricted to just network-related system
393 calls, whereas by applying the context before startup (such as
394 the OpenVPN one provided in the SELinux Reference Policies) you
395 will have to allow many things required only during initializa‐
396 tion.
397 Like with chroot, complications can result when scripts or
399 restarts are executed after the setcon operation, which is why
400 you should really consider using the --persist-key and --per‐
401 sist-tun options.
402 --status args
404 Write operational status to file every n seconds.
405 Valid syntaxes:
407 status file
409 status file n
410 Status can also be written to the syslog by sending a SIGUSR2
412 signal.
413 With multi-client capability enabled on a server, the status
415 file includes a list of clients and a routing table. The output
416 format can be controlled by the --status-version option in that
417 case.
418 For clients or instances running in point-to-point mode, it will
420 contain the traffic statistics.
421 --status-version n
423 Set the status file format version number to n.
424 This only affects the status file on servers with multi-client
426 capability enabled. Valid status version values:
427 1 Traditional format (default). The client list contains
429 the following fields comma-separated: Common Name, Real
430 Address, Bytes Received, Bytes Sent, Connected Since.
431 2 A more reliable format for external processing. Compared
433 to version 1, the client list contains some additional
434 fields: Virtual Address, Virtual IPv6 Address, Username,
435 Client ID, Peer ID, Data Channel Cipher. Future versions
436 may extend the number of fields.
437 3 Identical to 2, but fields are tab-separated.
439 --test-crypto
441 Do a self-test of OpenVPN's crypto options by encrypting and de‐
442 crypting test packets using the data channel encryption options
443 specified above. This option does not require a peer to func‐
444 tion, and therefore can be specified without --dev or --remote.
445 The typical usage of --test-crypto would be something like this:
447 openvpn --test-crypto --secret key
449 or
451 openvpn --test-crypto --secret key --verb 9
453 This option is very useful to test OpenVPN after it has been
455 ported to a new platform, or to isolate problems in the com‐
456 piler, OpenSSL crypto library, or OpenVPN's crypto code. Since
457 it is a self-test mode, problems with encryption and authentica‐
458 tion can be debugged independently of network and tunnel issues.
459 --tmp-dir dir
461 Specify a directory dir for temporary files. This directory will
462 be used by openvpn processes and script to communicate temporary
463 data with openvpn main process. Note that the directory must be
464 writable by the OpenVPN process after it has dropped it's root
465 privileges.
466 This directory will be used by in the following cases:
468 • --client-connect scripts and OPENVPN_PLUGIN_CLIENT_CONNECT
470 plug-in hook to dynamically generate client-specific configu‐
471 ration client_connect_config_file and return success/failure
472 via client_connect_deferred_file when using deferred client
473 connect method
474 • OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY plug-in hooks returns
476 success/failure via auth_control_file when using deferred auth
477 method
478 • OPENVPN_PLUGIN_ENABLE_PF plugin hook to pass filtering rules
480 via pf_file
481 --use-prediction-resistance
483 Enable prediction resistance on mbed TLS's RNG.
484 Enabling prediction resistance causes the RNG to reseed in each
486 call for random. Reseeding this often can quickly deplete the
487 kernel entropy pool.
488 If you need this option, please consider running a daemon that
490 adds entropy to the kernel pool.
491 --user user
493 Change the user ID of the OpenVPN process to user after initial‐
494 ization, dropping privileges in the process. This option is use‐
495 ful to protect the system in the event that some hostile party
496 was able to gain control of an OpenVPN session. Though OpenVPN's
497 security features make this unlikely, it is provided as a second
498 line of defense.
499 By setting user to nobody or somebody similarly unprivileged,
501 the hostile party would be limited in what damage they could
502 cause. Of course once you take away privileges, you cannot re‐
503 turn them to an OpenVPN session. This means, for example, that
504 if you want to reset an OpenVPN daemon with a SIGUSR1 signal
505 (for example in response to a DHCP reset), you should make use
506 of one or more of the --persist options to ensure that OpenVPN
507 doesn't need to execute any privileged operations in order to
508 restart (such as re-reading key files or running ifconfig on the
509 TUN device).
510 --writepid file
512 Write OpenVPN's main process ID to file.
513 Log options
515 --echo parms
516 Echo parms to log output.
517 Designed to be used to send messages to a controlling applica‐
519 tion which is receiving the OpenVPN log output.
520 --errors-to-stderr
522 Output errors to stderr instead of stdout unless log output is
523 redirected by one of the --log options.
524 --log file
526 Output logging messages to file, including output to std‐
527 out/stderr which is generated by called scripts. If file already
528 exists it will be truncated. This option takes effect immedi‐
529 ately when it is parsed in the command line and will supersede
530 syslog output if --daemon or --inetd is also specified. This op‐
531 tion is persistent over the entire course of an OpenVPN instan‐
532 tiation and will not be reset by SIGHUP, SIGUSR1, or
533 --ping-restart.
534 Note that on Windows, when OpenVPN is started as a service, log‐
536 ging occurs by default without the need to specify this option.
537 --log-append file
539 Append logging messages to file. If file does not exist, it
540 will be created. This option behaves exactly like --log except
541 that it appends to rather than truncating the log file.
542 --machine-readable-output
544 Always write timestamps and message flags to log messages, even
545 when they otherwise would not be prefixed. In particular, this
546 applies to log messages sent to stdout.
547 --mute n
549 Log at most n consecutive messages in the same category. This is
550 useful to limit repetitive logging of similar message types.
551 --mute-replay-warnings
553 Silence the output of replay warnings, which are a common false
554 alarm on WiFi networks. This option preserves the security of
555 the replay protection code without the verbosity associated with
556 warnings about duplicate packets.
557 --suppress-timestamps
559 Avoid writing timestamps to log messages, even when they other‐
560 wise would be prepended. In particular, this applies to log mes‐
561 sages sent to stdout.
562 --syslog progname
564 Direct log output to system logger, but do not become a daemon.
565 See --daemon directive above for description of progname parame‐
566 ter.
567 --verb n
569 Set output verbosity to n (default 1). Each level shows all info
570 from the previous levels. Level 3 is recommended if you want a
571 good summary of what's happening without being swamped by out‐
572 put.
573 0 No output except fatal errors.
575 1 to 4 Normal usage range.
577 5 Outputs R and W characters to the console for each packet
579 read and write, uppercase is used for TCP/UDP packets and
580 lowercase is used for TUN/TAP packets.
581 6 to 11
583 Debug info range (see errlevel.h in the source code for
584 additional information on debug levels).
585 Protocol options
587 Options in this section affect features available in the OpenVPN wire
588 protocol. Many of these options also define the encryption options of
589 the data channel in the OpenVPN wire protocol. These options must be
590 configured in a compatible way between both the local and remote side.
591 --allow-compression mode
593 As described in the --compress option, compression is a poten‐
594 tially dangerous option. This option allows controlling the be‐
595 haviour of OpenVPN when compression is used and allowed.
596 Valid syntaxes:
598 allow-compression
600 allow-compression mode
601 The mode argument can be one of the following values:
603 asym (default)
605 OpenVPN will only decompress downlink packets but not
606 compress uplink packets. This also allows migrating to
607 disable compression when changing both server and client
608 configurations to remove compression at the same time is
609 not a feasible option.
610 no OpenVPN will refuse any non-stub compression.
612 yes OpenVPN will send and receive compressed packets.
614 --auth alg
616 Authenticate data channel packets and (if enabled) tls-auth con‐
617 trol channel packets with HMAC using message digest algorithm
618 alg. (The default is SHA1 ). HMAC is a commonly used message au‐
619 thentication algorithm (MAC) that uses a data string, a secure
620 hash algorithm and a key to produce a digital signature.
621 The OpenVPN data channel protocol uses encrypt-then-mac (i.e.
623 first encrypt a packet then HMAC the resulting ciphertext),
624 which prevents padding oracle attacks.
625 If an AEAD cipher mode (e.g. GCM) is chosen then the specified
627 --auth algorithm is ignored for the data channel and the authen‐
628 tication method of the AEAD cipher is used instead. Note that
629 alg still specifies the digest used for tls-auth.
630 In static-key encryption mode, the HMAC key is included in the
632 key file generated by --genkey. In TLS mode, the HMAC key is dy‐
633 namically generated and shared between peers via the TLS control
634 channel. If OpenVPN receives a packet with a bad HMAC it will
635 drop the packet. HMAC usually adds 16 or 20 bytes per packet.
636 Set alg=none to disable authentication.
637 For more information on HMAC see
639 http://www.cs.ucsd.edu/users/mihir/papers/hmac.html
640 --cipher alg
642 This option is deprecated for server-client mode. --data-ciphers
643 or possibly --data-ciphers-fallback` should be used instead.
644 Encrypt data channel packets with cipher algorithm alg.
646 The default is BF-CBC, an abbreviation for Blowfish in Cipher
648 Block Chaining mode. When cipher negotiation (NCP) is allowed,
649 OpenVPN 2.4 and newer on both client and server side will auto‐
650 matically upgrade to AES-256-GCM. See --data-ciphers and
651 --ncp-disable for more details on NCP.
652 Using BF-CBC is no longer recommended, because of its 64-bit
654 block size. This small block size allows attacks based on colli‐
655 sions, as demonstrated by SWEET32. See
656 https://community.openvpn.net/openvpn/wiki/SWEET32 for details.
657 Due to this, support for BF-CBC, DES, CAST5, IDEA and RC2 ci‐
658 phers will be removed in OpenVPN 2.6.
659 To see other ciphers that are available with OpenVPN, use the
661 --show-ciphers option.
662 Set alg to none to disable encryption.
664 --compress algorithm
666 DEPRECATED Enable a compression algorithm. Compression is gen‐
667 erally not recommended. VPN tunnels which use compression are
668 susceptible to the VORALCE attack vector.
669 The algorithm parameter may be lzo, lz4, lz4-v2, stub, stub-v2
671 or empty. LZO and LZ4 are different compression algorithms,
672 with LZ4 generally offering the best performance with least CPU
673 usage.
674 The lz4-v2 and stub-v2 variants implement a better framing that
676 does not add overhead when packets cannot be compressed. All
677 other variants always add one extra framing byte compared to no
678 compression framing.
679 If the algorithm parameter is stub, stub-v2 or empty, compres‐
681 sion will be turned off, but the packet framing for compression
682 will still be enabled, allowing a different setting to be pushed
683 later. Additionally, stub and stub-v2 wil disable announcing
684 lzo and lz4 compression support via IV_ variables to the server.
685 Note: the stub (or empty) option is NOT compatible with the
687 older option --comp-lzo no.
688 *Security Considerations*
690 Compression and encryption is a tricky combination. If an at‐
692 tacker knows or is able to control (parts of) the plain-text of
693 packets that contain secrets, the attacker might be able to ex‐
694 tract the secret if compression is enabled. See e.g. the CRIME
695 and BREACH attacks on TLS and VORACLE on VPNs which also lever‐
696 age to break encryption. If you are not entirely sure that the
697 above does not apply to your traffic, you are advised to not en‐
698 able compression.
699 --comp-lzo mode
701 DEPRECATED Enable LZO compression algorithm. Compression is
702 generally not recommended. VPN tunnels which uses compression
703 are suspectible to the VORALCE attack vector.
704 Use LZO compression -- may add up to 1 byte per packet for in‐
706 compressible data. mode may be yes, no, or adaptive (default).
707 In a server mode setup, it is possible to selectively turn com‐
709 pression on or off for individual clients.
710 First, make sure the client-side config file enables selective
712 compression by having at least one --comp-lzo directive, such as
713 --comp-lzo no. This will turn off compression by default, but
714 allow a future directive push from the server to dynamically
715 change the on/off/adaptive setting.
716 Next in a --client-config-dir file, specify the compression set‐
718 ting for the client, for example:
719 comp-lzo yes
721 push "comp-lzo yes"
722 The first line sets the comp-lzo setting for the server side of
724 the link, the second sets the client side.
725 --comp-noadapt
727 DEPRECATED When used in conjunction with --comp-lzo, this option
728 will disable OpenVPN's adaptive compression algorithm. Normally,
729 adaptive compression is enabled with --comp-lzo.
730 Adaptive compression tries to optimize the case where you have
732 compression enabled, but you are sending predominantly incom‐
733 pressible (or pre-compressed) packets over the tunnel, such as
734 an FTP or rsync transfer of a large, compressed file. With adap‐
735 tive compression, OpenVPN will periodically sample the compres‐
736 sion process to measure its efficiency. If the data being sent
737 over the tunnel is already compressed, the compression effi‐
738 ciency will be very low, triggering openvpn to disable compres‐
739 sion for a period of time until the next re-sample test.
740 --key-direction
742 Alternative way of specifying the optional direction parameter
743 for the --tls-auth and --secret options. Useful when using in‐
744 line files (See section on inline files).
745 --keysize n
747 DEPRECATED This option will be removed in OpenVPN 2.6.
748 Size of cipher key in bits (optional). If unspecified, defaults
750 to cipher-specific default. The --show-ciphers option (see be‐
751 low) shows all available OpenSSL ciphers, their default key
752 sizes, and whether the key size can be changed. Use care in
753 changing a cipher's default key size. Many ciphers have not been
754 extensively cryptanalyzed with non-standard key lengths, and a
755 larger key may offer no real guarantee of greater security, or
756 may even reduce security.
757 --data-ciphers cipher-list
759 Restrict the allowed ciphers to be negotiated to the ciphers in
760 cipher-list. cipher-list is a colon-separated list of ciphers,
761 and defaults to AES-256-GCM:AES-128-GCM.
762 For servers, the first cipher from cipher-list that is also sup‐
764 ported by the client will be pushed to clients that support ci‐
765 pher negotiation.
766 Cipher negotiation is enabled in client-server mode only. I.e.
768 if --mode is set to 'server' (server-side, implied by setting
769 --server ), or if --pull is specified (client-side, implied by
770 setting --client).
771 If no common cipher is found during cipher negotiation, the con‐
773 nection is terminated. To support old clients/old servers that
774 do not provide any cipher negotiation support see --data-ci‐
775 phers-fallback.
776 Additionally, to allow for more smooth transition, if NCP is en‐
778 abled, OpenVPN will inherit the cipher of the peer if that ci‐
779 pher is different from the local --cipher setting, but the peer
780 cipher is one of the ciphers specified in --data-ciphers. E.g. a
781 non-NCP client (<=v2.3, or with --ncp-disabled set) connecting
782 to a NCP server (v2.4+) with --cipher BF-CBC and --data-ciphers
783 AES-256-GCM:AES-256-CBC set can either specify --cipher BF-CBC
784 or --cipher AES-256-CBC and both will work.
785 Note for using NCP with an OpenVPN 2.4 peer: This list must in‐
787 clude the AES-256-GCM and AES-128-GCM ciphers.
788 This list is restricted to be 127 chars long after conversion to
790 OpenVPN ciphers.
791 This option was called --ncp-ciphers in OpenVPN 2.4 but has been
793 renamed to --data-ciphers in OpenVPN 2.5 to more accurately re‐
794 flect its meaning.
795 --data-ciphers-fallback alg
797 Configure a cipher that is used to fall back to if we could not
798 determine which cipher the peer is willing to use.
799 This option should only be needed to connect to peers that are
801 running OpenVPN 2.3 and older version, and have been configured
802 with --enable-small (typically used on routers or other embedded
803 devices).
804 --ncp-disable
806 DEPRECATED Disable "Negotiable Crypto Parameters". This com‐
807 pletely disables cipher negotiation.
808 --secret args
810 Enable Static Key encryption mode (non-TLS). Use pre-shared se‐
811 cret file which was generated with --genkey.
812 Valid syntaxes:
814 secret file
816 secret file direction
817 The optional direction parameter enables the use of 4 distinct
819 keys (HMAC-send, cipher-encrypt, HMAC-receive, cipher-decrypt),
820 so that each data flow direction has a different set of HMAC and
821 cipher keys. This has a number of desirable security properties
822 including eliminating certain kinds of DoS and message replay
823 attacks.
824 When the direction parameter is omitted, 2 keys are used bidi‐
826 rectionally, one for HMAC and the other for encryption/decryp‐
827 tion.
828 The direction parameter should always be complementary on either
830 side of the connection, i.e. one side should use 0 and the other
831 should use 1, or both sides should omit it altogether.
832 The direction parameter requires that file contains a 2048 bit
834 key. While pre-1.5 versions of OpenVPN generate 1024 bit key
835 files, any version of OpenVPN which supports the direction pa‐
836 rameter, will also support 2048 bit key file generation using
837 the --genkey option.
838 Static key encryption mode has certain advantages, the primary
840 being ease of configuration.
841 There are no certificates or certificate authorities or compli‐
843 cated negotiation handshakes and protocols. The only requirement
844 is that you have a pre-existing secure channel with your peer
845 (such as ssh) to initially copy the key. This requirement, along
846 with the fact that your key never changes unless you manually
847 generate a new one, makes it somewhat less secure than TLS mode
848 (see below). If an attacker manages to steal your key, every‐
849 thing that was ever encrypted with it is compromised. Contrast
850 that to the perfect forward secrecy features of TLS mode (using
851 Diffie Hellman key exchange), where even if an attacker was able
852 to steal your private key, he would gain no information to help
853 him decrypt past sessions.
854 Another advantageous aspect of Static Key encryption mode is
856 that it is a handshake-free protocol without any distinguishing
857 signature or feature (such as a header or protocol handshake se‐
858 quence) that would mark the ciphertext packets as being gener‐
859 ated by OpenVPN. Anyone eavesdropping on the wire would see
860 nothing but random-looking data.
861 --tran-window n
863 Transition window -- our old key can live this many seconds af‐
864 ter a new a key renegotiation begins (default 3600 seconds).
865 This feature allows for a graceful transition from old to new
866 key, and removes the key renegotiation sequence from the criti‐
867 cal path of tunnel data forwarding.
868 Client Options
870 The client options are used when connecting to an OpenVPN server con‐
871 figured to use --server, --server-bridge, or --mode server in its con‐
872 figuration.
873 --allow-pull-fqdn
875 Allow client to pull DNS names from server (rather than being
876 limited to IP address) for --ifconfig, --route, and
877 --route-gateway.
878 --allow-recursive-routing
880 When this option is set, OpenVPN will not drop incoming tun
881 packets with same destination as host.
882 --auth-token token
884 This is not an option to be used directly in any configuration
885 files, but rather push this option from a --client-connect
886 script or a --plugin which hooks into the OPEN‐
887 VPN_PLUGIN_CLIENT_CONNECT or OPENVPN_PLUGIN_CLIENT_CONNECT_V2
888 calls. This option provides a possibility to replace the clients
889 password with an authentication token during the lifetime of the
890 OpenVPN client.
891 Whenever the connection is renegotiated and the
893 --auth-user-pass-verify script or --plugin making use of the
894 OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY hook is triggered, it will
895 pass over this token as the password instead of the password the
896 user provided. The authentication token can only be reset by a
897 full reconnect where the server can push new options to the
898 client. The password the user entered is never preserved once an
899 authentication token has been set. If the OpenVPN server side
900 rejects the authentication token then the client will receive an
901 AUTH_FAILED and disconnect.
902 The purpose of this is to enable two factor authentication meth‐
904 ods, such as HOTP or TOTP, to be used without needing to re‐
905 trieve a new OTP code each time the connection is renegotiated.
906 Another use case is to cache authentication data on the client
907 without needing to have the users password cached in memory dur‐
908 ing the life time of the session.
909 To make use of this feature, the --client-connect script or
911 --plugin needs to put
912 push "auth-token UNIQUE_TOKEN_VALUE"
914 into the file/buffer for dynamic configuration data. This will
916 then make the OpenVPN server to push this value to the client,
917 which replaces the local password with the UNIQUE_TOKEN_VALUE.
918 Newer clients (2.4.7+) will fall back to the original password
920 method after a failed auth. Older clients will keep using the
921 token value and react according to --auth-retry
922 --auth-token-user base64username
924 Companion option to --auth-token. This options allows to over‐
925 ride the username used by the client when reauthenticating with
926 the auth-token. It also allows to use --auth-token in setups
927 that normally do not use username and password.
928 The username has to be base64 encoded.
930 --auth-user-pass
932 Authenticate with server using username/password.
933 Valid syntaxes:
935 auth-user-pass
937 auth-user-pass up
938 If up is present, it must be a file containing username/password
940 on 2 lines. If the password line is missing, OpenVPN will prompt
941 for one.
942 If up is omitted, username/password will be prompted from the
944 console.
945 The server configuration must specify an --auth-user-pass-verify
947 script to verify the username/password provided by the client.
948 --auth-retry type
950 Controls how OpenVPN responds to username/password verification
951 errors such as the client-side response to an AUTH_FAILED mes‐
952 sage from the server or verification failure of the private key
953 password.
954 Normally used to prevent auth errors from being fatal on the
956 client side, and to permit username/password requeries in case
957 of error.
958 An AUTH_FAILED message is generated by the server if the client
960 fails --auth-user-pass authentication, or if the server-side
961 --client-connect script returns an error status when the client
962 tries to connect.
963 type can be one of:
965 none Client will exit with a fatal error (this is the de‐
967 fault).
968 nointeract
970 Client will retry the connection without requerying for
971 an --auth-user-pass username/password. Use this option
972 for unattended clients.
973 interact
975 Client will requery for an --auth-user-pass user‐
976 name/password and/or private key password before attempt‐
977 ing a reconnection.
978 Note that while this option cannot be pushed, it can be con‐
980 trolled from the management interface.
981 --client
983 A helper directive designed to simplify the configuration of
984 OpenVPN's client mode. This directive is equivalent to:
985 pull
987 tls-client
988 --client-nat args
990 This pushable client option sets up a stateless one-to-one NAT
991 rule on packet addresses (not ports), and is useful in cases
992 where routes or ifconfig settings pushed to the client would
993 create an IP numbering conflict.
994 Examples:
996 client-nat snat 192.168.0.0/255.255.0.0
998 client-nat dnat 10.64.0.0/255.255.0.0
999 network/netmask (for example 192.168.0.0/255.255.0.0) defines
1001 the local view of a resource from the client perspective, while
1002 alias/netmask (for example 10.64.0.0/255.255.0.0) defines the
1003 remote view from the server perspective.
1004 Use snat (source NAT) for resources owned by the client and dnat
1006 (destination NAT) for remote resources.
1007 Set --verb 6 for debugging info showing the transformation of
1009 src/dest addresses in packets.
1010 --connect-retry n
1012 Wait n seconds between connection attempts (default 5). Re‐
1013 peated reconnection attempts are slowed down after 5 retries per
1014 remote by doubling the wait time after each unsuccessful at‐
1015 tempt. An optional argument max specifies the maximum value of
1016 wait time in seconds at which it gets capped (default 300).
1017 --connect-retry-max n
1019 n specifies the number of times each --remote or <connection>
1020 entry is tried. Specifying n as 1 would try each entry exactly
1021 once. A successful connection resets the counter. (default un‐
1022 limited).
1023 --connect-timeout n
1025 See --server-poll-timeout.
1026 --explicit-exit-notify n
1028 In UDP client mode or point-to-point mode, send server/peer an
1029 exit notification if tunnel is restarted or OpenVPN process is
1030 exited. In client mode, on exit/restart, this option will tell
1031 the server to immediately close its client instance object
1032 rather than waiting for a timeout.
1033 The n parameter (default 1 if not present) controls the maximum
1035 number of attempts that the client will try to resend the exit
1036 notification message.
1037 In UDP server mode, send RESTART control channel command to con‐
1039 nected clients. The n parameter (default 1 if not present) con‐
1040 trols client behavior. With n = 1 client will attempt to recon‐
1041 nect to the same server, with n = 2 client will advance to the
1042 next server.
1043 OpenVPN will not send any exit notifications unless this option
1045 is enabled.
1046 --inactive args
1048 Causes OpenVPN to exit after n seconds of inactivity on the
1049 TUN/TAP device. The time length of inactivity is measured since
1050 the last incoming or outgoing tunnel packet. The default value
1051 is 0 seconds, which disables this feature.
1052 Valid syntaxes:
1054 inactive n
1056 inactive n bytes
1057 If the optional bytes parameter is included, exit if less than
1059 bytes of combined in/out traffic are produced on the tun/tap de‐
1060 vice in n seconds.
1061 In any case, OpenVPN's internal ping packets (which are just
1063 keepalives) and TLS control packets are not considered "activ‐
1064 ity", nor are they counted as traffic, as they are used inter‐
1065 nally by OpenVPN and are not an indication of actual user activ‐
1066 ity.
1067 --proto-force p
1069 When iterating through connection profiles, only consider pro‐
1070 files using protocol p (tcp | udp).
1071 Note that this specifically only filters by the transport layer
1073 protocol, i.e. UDP or TCP. This does not affect whether IPv4 or
1074 IPv6 is used as IP protocol.
1075 For implementation reasons the option accepts the 4 and 6 suf‐
1077 fixes when specifying the protocol (i.e. udp4 / udp6 / tcp4 /
1078 tcp6). However, these behave the same as without the suffix and
1079 should be avoided to prevent confusion.
1080 --pull This option must be used on a client which is connecting to a
1082 multi-client server. It indicates to OpenVPN that it should ac‐
1083 cept options pushed by the server, provided they are part of the
1084 legal set of pushable options (note that the --pull option is
1085 implied by --client ).
1086 In particular, --pull allows the server to push routes to the
1088 client, so you should not use --pull or --client in situations
1089 where you don't trust the server to have control over the
1090 client's routing table.
1091 --pull-filter args
1093 Filter options on the client pushed by the server to the client.
1094 Valid syntaxes:
1096 pull-filter accept text
1098 pull-filter ignore text
1099 pull-filter reject text
1100 Filter options received from the server if the option starts
1102 with text. The action flag accept allows the option, ignore re‐
1103 moves it and reject flags an error and triggers a SIGUSR1
1104 restart. The filters may be specified multiple times, and each
1105 filter is applied in the order it is specified. The filtering of
1106 each option stops as soon as a match is found. Unmatched options
1107 are accepted by default.
1108 Prefix comparison is used to match text against the received op‐
1110 tion so that
1111 pull-filter ignore "route"
1113 would remove all pushed options starting with route which would
1115 include, for example, route-gateway. Enclose text in quotes to
1116 embed spaces.
1117 pull-filter accept "route 192.168.1."
1119 pull-filter ignore "route "
1120 would remove all routes that do not start with 192.168.1.
1122 Note that reject may result in a repeated cycle of failure and
1124 reconnect, unless multiple remotes are specified and connection
1125 to the next remote succeeds. To silently ignore an option pushed
1126 by the server, use ignore.
1127 --push-peer-info
1129 Push additional information about the client to server. The fol‐
1130 lowing data is always pushed to the server:
1131 IV_VER=<version>
1133 The client OpenVPN version
1134 IV_PLAT=[linux|solaris|openbsd|mac|netbsd|freebsd|win]
1136 The client OS platform
1137 IV_LZO_STUB=1
1139 If client was built with LZO stub capability
1140 IV_LZ4=1
1142 If the client supports LZ4 compressions.
1143 IV_PROTO
1145 Details about protocol extensions that the peer supports.
1146 The variable is a bitfield and the bits are defined as
1147 follows (starting a bit 0 for the first (unused) bit:
1148 • bit 1: The peer supports peer-id floating mechanism
1150 • bit 2: The client expects a push-reply and the server
1152 may send this reply without waiting for a push-request
1153 first.
1154 • bit 3: The client is capable of doing key derivation
1156 using RFC5705 key material exporter.
1157 • bit 4: The client is capable of accepting additional
1159 arguments to the AUTH_PENDING message.
1160 IV_NCP=2
1162 Negotiable ciphers, client supports --cipher pushed by
1163 the server, a value of 2 or greater indicates client sup‐
1164 ports AES-GCM-128 and AES-GCM-256.
1165 IV_CIPHERS=<ncp-ciphers>
1167 The client announces the list of supported ciphers con‐
1168 figured with the --data-ciphers option to the server.
1169 IV_GUI_VER=<gui_id> <version>
1171 The UI version of a UI if one is running, for example
1172 de.blinkt.openvpn 0.5.47 for the Android app.
1173 IV_SSO=[crtext,][openurl,][proxy_url]
1175 Additional authentication methods supported by the
1176 client. This may be set by the client UI/GUI using
1177 --setenv
1178 When --push-peer-info is enabled the additional information con‐
1180 sists of the following data:
1181 IV_HWADDR=<string>
1183 This is intended to be a unique and persistent ID of the
1184 client. The string value can be any readable ASCII
1185 string up to 64 bytes. OpenVPN 2.x and some other imple‐
1186 mentations use the MAC address of the client's interface
1187 used to reach the default gateway. If this string is gen‐
1188 erated by the client, it should be consistent and pre‐
1189 served across independent session and preferably re-in‐
1190 stallations and upgrades.
1191 IV_SSL=<version string>
1193 The ssl version used by the client, e.g. OpenSSL 1.0.2f
1194 28 Jan 2016.
1195 IV_PLAT_VER=x.y
1197 The version of the operating system, e.g. 6.1 for Windows
1198 7.
1199 UV_<name>=<value>
1201 Client environment variables whose names start with UV_
1202 --remote args
1204 Remote host name or IP address, port and protocol.
1205 Valid syntaxes:
1207 remote host
1209 remote host port
1210 remote host port proto
1211 The port and proto arguments are optional. The OpenVPN client
1213 will try to connect to a server at host:port. The proto argu‐
1214 ment indicates the protocol to use when connecting with the re‐
1215 mote, and may be tcp or udp. To enforce IPv4 or IPv6 connec‐
1216 tions add a 4 or 6 suffix; like udp4 / udp6 / tcp4 / tcp6.
1217 On the client, multiple --remote options may be specified for
1219 redundancy, each referring to a different OpenVPN server, in the
1220 order specified by the list of --remote options. Specifying mul‐
1221 tiple --remote options for this purpose is a special case of the
1222 more general connection-profile feature. See the <connection>
1223 documentation below.
1224 The client will move on to the next host in the list, in the
1226 event of connection failure. Note that at any given time, the
1227 OpenVPN client will at most be connected to one server.
1228 Examples:
1230 remote server1.example.net
1232 remote server1.example.net 1194
1233 remote server2.example.net 1194 tcp
1234 Note: Since UDP is connectionless, connection failure is de‐
1236 fined by the --ping and --ping-restart options.
1237 Also, if you use multiple --remote options, AND you are
1239 dropping root privileges on the client with --user and/or
1240 --group AND the client is running a non-Windows OS, if
1241 the client needs to switch to a different server, and
1242 that server pushes back different TUN/TAP or route set‐
1243 tings, the client may lack the necessary privileges to
1244 close and reopen the TUN/TAP interface. This could cause
1245 the client to exit with a fatal error.
1246 If --remote is unspecified, OpenVPN will listen for packets from
1248 any IP address, but will not act on those packets unless they
1249 pass all authentication tests. This requirement for authentica‐
1250 tion is binding on all potential peers, even those from known
1251 and supposedly trusted IP addresses (it is very easy to forge a
1252 source IP address on a UDP packet).
1253 When used in TCP mode, --remote will act as a filter, rejecting
1255 connections from any host which does not match host.
1256 If host is a DNS name which resolves to multiple IP addresses,
1258 OpenVPN will try them in the order that the system getaddrinfo()
1259 presents them, so priorization and DNS randomization is done by
1260 the system library. Unless an IP version is forced by the proto‐
1261 col specification (4/6 suffix), OpenVPN will try both IPv4 and
1262 IPv6 addresses, in the order getaddrinfo() returns them.
1263 --remote-random
1265 When multiple --remote address/ports are specified, or if con‐
1266 nection profiles are being used, initially randomize the order
1267 of the list as a kind of basic load-balancing measure.
1268 --remote-random-hostname
1270 Prepend a random string (6 bytes, 12 hex characters) to hostname
1271 to prevent DNS caching. For example, "foo.bar.gov" would be mod‐
1272 ified to "<random-chars>.foo.bar.gov".
1273 --resolv-retry n
1275 If hostname resolve fails for --remote, retry resolve for n sec‐
1276 onds before failing.
1277 Set n to "infinite" to retry indefinitely.
1279 By default, --resolv-retry infinite is enabled. You can disable
1281 by setting n=0.
1282 --single-session
1284 After initially connecting to a remote peer, disallow any new
1285 connections. Using this option means that a remote peer cannot
1286 connect, disconnect, and then reconnect.
1287 If the daemon is reset by a signal or --ping-restart, it will
1289 allow one new connection.
1290 --single-session can be used with --ping-exit or --inactive to
1292 create a single dynamic session that will exit when finished.
1293 --server-poll-timeout n
1295 When connecting to a remote server do not wait for more than n
1296 seconds for a response before trying the next server. The de‐
1297 fault value is 120s. This timeout includes proxy and TCP connect
1298 timeouts.
1299 --static-challenge args
1301 Enable static challenge/response protocol
1302 Valid syntax:
1304 static-challenge text echo
1306 The text challenge text is presented to the user which describes
1308 what information is requested. The echo flag indicates if the
1309 user's input should be echoed on the screen. Valid echo values
1310 are 0 or 1.
1311 See management-notes.txt in the OpenVPN distribution for a de‐
1313 scription of the OpenVPN challenge/response protocol.
1314 --show-proxy-settings
1316 Show sensed HTTP or SOCKS proxy settings. Currently, only Win‐
1317 dows clients support this option.
1318 --http-proxy args
1320 Connect to remote host through an HTTP proxy. This requires at
1321 least an address server and port argument. If HTTP Proxy-Au‐
1322 thenticate is required, a file name to an authfile file contain‐
1323 ing a username and password on 2 lines can be given, or stdin to
1324 prompt from console. Its content can also be specified in the
1325 config file with the --http-proxy-user-pass option. (See section
1326 on inline files)
1327 The last optional argument is an auth-method which should be one
1329 of none, basic, or ntlm.
1330 HTTP Digest authentication is supported as well, but only via
1332 the auto or auto-nct flags (below). This must replace the auth‐
1333 file argument.
1334 The auto flag causes OpenVPN to automatically determine the
1336 auth-method and query stdin or the management interface for
1337 username/password credentials, if required. This flag exists on
1338 OpenVPN 2.1 or higher.
1339 The auto-nct flag (no clear-text auth) instructs OpenVPN to au‐
1341 tomatically determine the authentication method, but to reject
1342 weak authentication protocols such as HTTP Basic Authentication.
1343 Examples:
1345 http-proxy proxy.example.net 3128
1347 http-proxy proxy.example.net 3128 authfile.txt
1348 http-proxy proxy.example.net 3128 stdin
1349 http-proxy proxy.example.net 3128 auto basic
1350 http-proxy proxy.example.net 3128 auto-nct ntlm
1351 --http-proxy-option args
1353 Set extended HTTP proxy options. Requires an option type as ar‐
1354 gument and an optional parameter to the type. Repeat to set
1355 multiple options.
1356 VERSION version
1358 Set HTTP version number to version (default 1.0).
1359 AGENT user-agent
1361 Set HTTP "User-Agent" string to user-agent.
1362 CUSTOM-HEADER name content
1364 Adds the custom Header with name as name and content as
1365 the content of the custom HTTP header.
1366 Examples:
1368 http-proxy-option VERSION 1.1
1370 http-proxy-option AGENT OpenVPN/2.4
1371 http-proxy-option X-Proxy-Flag some-flags
1372 --socks-proxy args
1374 Connect to remote host through a Socks5 proxy. A required
1375 server argument is needed. Optionally a port (default 1080) and
1376 authfile can be given. The authfile is a file containing a
1377 username and password on 2 lines, or stdin can be used to prompt
1378 from console.
1379 Server Options
1381 Starting with OpenVPN 2.0, a multi-client TCP/UDP server mode is sup‐
1382 ported, and can be enabled with the --mode server option. In server
1383 mode, OpenVPN will listen on a single port for incoming client connec‐
1384 tions. All client connections will be routed through a single tun or
1385 tap interface. This mode is designed for scalability and should be able
1386 to support hundreds or even thousands of clients on sufficiently fast
1387 hardware. SSL/TLS authentication must be used in this mode.
1388 --auth-gen-token args
1390 Returns an authentication token to successfully authenticated
1391 clients.
1392 Valid syntax:
1394 auth-gen-token [lifetime] [external-auth]
1396 After successful user/password authentication, the OpenVPN
1398 server will with this option generate a temporary authentication
1399 token and push that to the client. On the following renegotia‐
1400 tions, the OpenVPN client will pass this token instead of the
1401 users password. On the server side the server will do the token
1402 authentication internally and it will NOT do any additional au‐
1403 thentications against configured external user/password authen‐
1404 tication mechanisms.
1405 The tokens implemented by this mechanism include an initial
1407 timestamp and a renew timestamp and are secured by HMAC.
1408 The lifetime argument defines how long the generated token is
1410 valid. The lifetime is defined in seconds. If lifetime is not
1411 set or it is set to 0, the token will never expire.
1412 The token will expire either after the configured lifetime of
1414 the token is reached or after not being renewed for more than 2
1415 * reneg-sec seconds. Clients will be sent renewed tokens on ev‐
1416 ery TLS renogiation to keep the client's token updated. This is
1417 done to invalidate a token if a client is disconnected for a
1418 sufficently long time, while at the same time permitting much
1419 longer token lifetimes for active clients.
1420 This feature is useful for environments which are configured to
1422 use One Time Passwords (OTP) as part of the user/password au‐
1423 thentications and that authentication mechanism does not imple‐
1424 ment any auth-token support.
1425 When the external-auth keyword is present the normal authentica‐
1427 tion method will always be called even if auth-token succeeds.
1428 Normally other authentications method are skipped if auth-token
1429 verification suceeds or fails.
1430 This option postpones this decision to the external authentica‐
1432 tion methods and checks the validity of the account and do other
1433 checks.
1434 In this mode the environment will have a session_id variable
1436 that holds the session id from auth-gen-token. Also an environ‐
1437 ment variable session_state is present. This variable indicates
1438 whether the auth-token has succeeded or not. It can have the
1439 following values:
1440 Initial
1442 No token from client.
1443 Authenticated
1445 Token is valid and not expired.
1446 Expired
1448 Token is valid but has expired.
1449 Invalid
1451 Token is invalid (failed HMAC or wrong length)
1452 AuthenticatedEmptyUser / ExpiredEmptyUser
1454 The token is not valid with the username sent from the
1455 client but would be valid (or expired) if we assume an
1456 empty username was used instead. These two cases are a
1457 workaround for behaviour in OpenVPN 3. If this work‐
1458 around is not needed these two cases should be handled in
1459 the same way as Invalid.
1460 Warning: Use this feature only if you want your authentication
1462 method called on every verification. Since the external authen‐
1463 tication is called it needs to also indicate a success or fail‐
1464 ure of the authentication. It is strongly recommended to return
1465 an authentication failure in the case of the Invalid/Expired
1466 auth-token with the external-auth option unless the client could
1467 authenticate in another acceptable way (e.g. client certifi‐
1468 cate), otherwise returning success will lead to authentication
1469 bypass (as does returning success on a wrong password from a
1470 script).
1471 --auth-gen-token-secret file
1473 Specifies a file that holds a secret for the HMAC used in
1474 --auth-gen-token If file is not present OpenVPN will generate a
1475 random secret on startup. This file should be used if auth-token
1476 should validate after restarting a server or if client should be
1477 able to roam between multiple OpenVPN servers with their
1478 auth-token.
1479 --auth-user-pass-optional
1481 Allow connections by clients that do not specify a user‐
1482 name/password. Normally, when --auth-user-pass-verify or --man‐
1483 agement-client-auth are specified (or an authentication plugin
1484 module), the OpenVPN server daemon will require connecting
1485 clients to specify a username and password. This option makes
1486 the submission of a username/password by clients optional, pass‐
1487 ing the responsibility to the user-defined authentication mod‐
1488 ule/script to accept or deny the client based on other factors
1489 (such as the setting of X509 certificate fields). When this op‐
1490 tion is used, and a connecting client does not submit a user‐
1491 name/password, the user-defined authentication module/script
1492 will see the username and password as being set to empty strings
1493 (""). The authentication module/script MUST have logic to detect
1494 this condition and respond accordingly.
1495 --ccd-exclusive
1497 Require, as a condition of authentication, that a connecting
1498 client has a --client-config-dir file.
1499 --client-config-dir dir
1501 Specify a directory dir for custom client config files. After a
1502 connecting client has been authenticated, OpenVPN will look in
1503 this directory for a file having the same name as the client's
1504 X509 common name. If a matching file exists, it will be opened
1505 and parsed for client-specific configuration options. If no
1506 matching file is found, OpenVPN will instead try to open and
1507 parse a default file called "DEFAULT", which may be provided but
1508 is not required. Note that the configuration files must be read‐
1509 able by the OpenVPN process after it has dropped it's root priv‐
1510 ileges.
1511 This file can specify a fixed IP address for a given client us‐
1513 ing --ifconfig-push, as well as fixed subnets owned by the
1514 client using --iroute.
1515 One of the useful properties of this option is that it allows
1517 client configuration files to be conveniently created, edited,
1518 or removed while the server is live, without needing to restart
1519 the server.
1520 The following options are legal in a client-specific context:
1522 --push, --push-reset, --push-remove, --iroute, --ifconfig-push,
1523 --vlan-pvid and --config.
1524 --client-to-client
1526 Because the OpenVPN server mode handles multiple clients through
1527 a single tun or tap interface, it is effectively a router. The
1528 --client-to-client flag tells OpenVPN to internally route
1529 client-to-client traffic rather than pushing all client-origi‐
1530 nating traffic to the TUN/TAP interface.
1531 When this option is used, each client will "see" the other
1533 clients which are currently connected. Otherwise, each client
1534 will only see the server. Don't use this option if you want to
1535 firewall tunnel traffic using custom, per-client rules.
1536 --disable
1538 Disable a particular client (based on the common name) from con‐
1539 necting. Don't use this option to disable a client due to key
1540 or password compromise. Use a CRL (certificate revocation list)
1541 instead (see the --crl-verify option).
1542 This option must be associated with a specific client instance,
1544 which means that it must be specified either in a client in‐
1545 stance config file using --client-config-dir or dynamically gen‐
1546 erated using a --client-connect script.
1547 --connect-freq args
1549 Allow a maximum of n new connections per sec seconds from
1550 clients.
1551 Valid syntax:
1553 connect-freq n sec
1555 This is designed to contain DoS attacks which flood the server
1557 with connection requests using certificates which will ulti‐
1558 mately fail to authenticate.
1559 This is an imperfect solution however, because in a real DoS
1561 scenario, legitimate connections might also be refused.
1562 For the best protection against DoS attacks in server mode, use
1564 --proto udp and either --tls-auth or --tls-crypt.
1565 --duplicate-cn
1567 Allow multiple clients with the same common name to concurrently
1568 connect. In the absence of this option, OpenVPN will disconnect
1569 a client instance upon connection of a new client having the
1570 same common name.
1571 --ifconfig-pool args
1573 Set aside a pool of subnets to be dynamically allocated to con‐
1574 necting clients, similar to a DHCP server.
1575 Valid syntax:
1577 ifconfig-pool start-IP end-IP [netmask]
1579 For tun-style tunnels, each client will be given a /30 subnet
1581 (for interoperability with Windows clients). For tap-style tun‐
1582 nels, individual addresses will be allocated, and the optional
1583 netmask parameter will also be pushed to clients.
1584 --ifconfig-ipv6-pool args
1586 Specify an IPv6 address pool for dynamic assignment to clients.
1587 Valid args:
1589 ifconfig-ipv6-pool ipv6addr/bits
1591 The pool starts at ipv6addr and matches the offset determined
1593 from the start of the IPv4 pool. If the host part of the given
1594 IPv6 address is 0, the pool starts at ipv6addr +1.
1595 --ifconfig-pool-persist args
1597 Persist/unpersist ifconfig-pool data to file, at seconds inter‐
1598 vals (default 600), as well as on program startup and shutdown.
1599 Valid syntax:
1601 ifconfig-pool-persist file [seconds]
1603 The goal of this option is to provide a long-term association
1605 between clients (denoted by their common name) and the virtual
1606 IP address assigned to them from the ifconfig-pool. Maintaining
1607 a long-term association is good for clients because it allows
1608 them to effectively use the --persist-tun option.
1609 file is a comma-delimited ASCII file, formatted as <Com‐
1611 mon-Name>,<IP-address>.
1612 If seconds = 0, file will be treated as read-only. This is use‐
1614 ful if you would like to treat file as a configuration file.
1615 Note that the entries in this file are treated by OpenVPN as
1617 suggestions only, based on past associations between a common
1618 name and IP address. They do not guarantee that the given com‐
1619 mon name will always receive the given IP address. If you want
1620 guaranteed assignment, use --ifconfig-push
1621 --ifconfig-push args
1623 Push virtual IP endpoints for client tunnel, overriding the
1624 --ifconfig-pool dynamic allocation.
1625 Valid syntax:
1627 ifconfig-push local remote-netmask [alias]
1629 The parameters local and remote-netmask are set according to the
1631 --ifconfig directive which you want to execute on the client ma‐
1632 chine to configure the remote end of the tunnel. Note that the
1633 parameters local and remote-netmask are from the perspective of
1634 the client, not the server. They may be DNS names rather than IP
1635 addresses, in which case they will be resolved on the server at
1636 the time of client connection.
1637 The optional alias parameter may be used in cases where NAT
1639 causes the client view of its local endpoint to differ from the
1640 server view. In this case local/remote-netmask will refer to the
1641 server view while alias/remote-netmask will refer to the client
1642 view.
1643 This option must be associated with a specific client instance,
1645 which means that it must be specified either in a client in‐
1646 stance config file using --client-config-dir or dynamically gen‐
1647 erated using a --client-connect script.
1648 Remember also to include a --route directive in the main OpenVPN
1650 config file which encloses local, so that the kernel will know
1651 to route it to the server's TUN/TAP interface.
1652 OpenVPN's internal client IP address selection algorithm works
1654 as follows:
1655 1. Use --client-connect script generated file for static IP
1657 (first choice).
1658 2. Use --client-config-dir file for static IP (next choice).
1660 3. Use --ifconfig-pool allocation for dynamic IP (last choice).
1662 --ifconfig-ipv6-push args
1664 for --client-config-dir per-client static IPv6 interface config‐
1665 uration, see --client-config-dir and --ifconfig-push for more
1666 details.
1667 Valid syntax:
1669 ifconfig-ipv6-push ipv6addr/bits ipv6remote
1671 --inetd args
1673 Valid syntaxes:
1674 inetd
1676 inetd wait
1677 inetd nowait
1678 inetd wait progname
1679 Use this option when OpenVPN is being run from the inetd or
1681 xinetd(8) server.
1682 The wait and nowait option must match what is specified in the
1684 inetd/xinetd config file. The nowait mode can only be used with
1685 --proto tcp-server The default is wait. The nowait mode can be
1686 used to instantiate the OpenVPN daemon as a classic TCP server,
1687 where client connection requests are serviced on a single port
1688 number. For additional information on this kind of configura‐
1689 tion, see the OpenVPN FAQ:
1690 https://community.openvpn.net/openvpn/wiki/325-openvpn-as-a--forking-tcp-server-which-can-service-multiple-clients-over-a-single-tcp-port
1691 This option precludes the use of --daemon, --local or --remote.
1693 Note that this option causes message and error output to be han‐
1694 dled in the same way as the --daemon option. The optional prog‐
1695 name parameter is also handled exactly as in --daemon.
1696 Also note that in wait mode, each OpenVPN tunnel requires a sep‐
1698 arate TCP/UDP port and a separate inetd or xinetd entry. See the
1699 OpenVPN 1.x HOWTO for an example on using OpenVPN with xinetd:
1700 https://openvpn.net/community-resources/1xhowto/
1701 --multihome
1703 Configure a multi-homed UDP server. This option needs to be used
1704 when a server has more than one IP address (e.g. multiple inter‐
1705 faces, or secondary IP addresses), and is not using --local to
1706 force binding to one specific address only. This option will add
1707 some extra lookups to the packet path to ensure that the UDP re‐
1708 ply packets are always sent from the address that the client is
1709 talking to. This is not supported on all platforms, and it adds
1710 more processing, so it's not enabled by default.
1711 Notes:
1713 • This option is only relevant for UDP servers.
1715 • If you do an IPv6+IPv4 dual-stack bind on a Linux ma‐
1717 chine with multiple IPv4 address, connections to IPv4
1718 addresses will not work right on kernels before 3.15,
1719 due to missing kernel support for the IPv4-mapped case
1720 (some distributions have ported this to earlier kernel
1721 versions, though).
1722 --iroute args
1724 Generate an internal route to a specific client. The netmask pa‐
1725 rameter, if omitted, defaults to 255.255.255.255.
1726 Valid syntax:
1728 iroute network [netmask]
1730 This directive can be used to route a fixed subnet from the
1732 server to a particular client, regardless of where the client is
1733 connecting from. Remember that you must also add the route to
1734 the system routing table as well (such as by using the --route
1735 directive). The reason why two routes are needed is that the
1736 --route directive routes the packet from the kernel to OpenVPN.
1737 Once in OpenVPN, the --iroute directive routes to the specific
1738 client.
1739 This option must be specified either in a client instance config
1741 file using --client-config-dir or dynamically generated using a
1742 --client-connect script.
1743 The --iroute directive also has an important interaction with
1745 --push "route ...". --iroute essentially defines a subnet which
1746 is owned by a particular client (we will call this client A). If
1747 you would like other clients to be able to reach A's subnet, you
1748 can use --push "route ..." together with --client-to-client to
1749 effect this. In order for all clients to see A's subnet, OpenVPN
1750 must push this route to all clients EXCEPT for A, since the sub‐
1751 net is already owned by A. OpenVPN accomplishes this by not not
1752 pushing a route to a client if it matches one of the client's
1753 iroutes.
1754 --iroute-ipv6 args
1756 for --client-config-dir per-client static IPv6 route configura‐
1757 tion, see --iroute for more details how to setup and use this,
1758 and how --iroute and --route interact.
1759 Valid syntax:
1761 iroute-ipv6 ipv6addr/bits
1763 --max-clients n
1765 Limit server to a maximum of n concurrent clients.
1766 --max-routes-per-client n
1768 Allow a maximum of n internal routes per client (default 256).
1769 This is designed to help contain DoS attacks where an authenti‐
1770 cated client floods the server with packets appearing to come
1771 from many unique MAC addresses, forcing the server to deplete
1772 virtual memory as its internal routing table expands. This di‐
1773 rective can be used in a --client-config-dir file or auto-gener‐
1774 ated by a --client-connect script to override the global value
1775 for a particular client.
1776 Note that this directive affects OpenVPN's internal routing ta‐
1778 ble, not the kernel routing table.
1779 --opt-verify
1781 Clients that connect with options that are incompatible with
1782 those of the server will be disconnected.
1783 Options that will be compared for compatibility include
1785 dev-type, link-mtu, tun-mtu, proto, ifconfig, comp-lzo, frag‐
1786 ment, keydir, cipher, auth, keysize, secret, no-replay,
1787 tls-auth, key-method, tls-server and tls-client.
1788 This option requires that --disable-occ NOT be used.
1790 --port-share args
1792 Share OpenVPN TCP with another service
1793 Valid syntax:
1795 port-share host port [dir]
1797 When run in TCP server mode, share the OpenVPN port with another
1799 application, such as an HTTPS server. If OpenVPN senses a con‐
1800 nection to its port which is using a non-OpenVPN protocol, it
1801 will proxy the connection to the server at host:port. Currently
1802 only designed to work with HTTP/HTTPS, though it would be theo‐
1803 retically possible to extend to other protocols such as ssh.
1804 dir specifies an optional directory where a temporary file with
1806 name N containing content C will be dynamically generated for
1807 each proxy connection, where N is the source IP:port of the
1808 client connection and C is the source IP:port of the connection
1809 to the proxy receiver. This directory can be used as a dictio‐
1810 nary by the proxy receiver to determine the origin of the con‐
1811 nection. Each generated file will be automatically deleted when
1812 the proxied connection is torn down.
1813 Not implemented on Windows.
1815 --push option
1817 Push a config file option back to the client for remote execu‐
1818 tion. Note that option must be enclosed in double quotes ("").
1819 The client must specify --pull in its config file. The set of
1820 options which can be pushed is limited by both feasibility and
1821 security. Some options such as those which would execute scripts
1822 are banned, since they would effectively allow a compromised
1823 server to execute arbitrary code on the client. Other options
1824 such as TLS or MTU parameters cannot be pushed because the
1825 client needs to know them before the connection to the server
1826 can be initiated.
1827 This is a partial list of options which can currently be pushed:
1829 --route, --route-gateway, --route-delay, --redirect-gateway,
1830 --ip-win32, --dhcp-option, --inactive, --ping, --ping-exit,
1831 --ping-restart, --setenv, --auth-token, --persist-key, --per‐
1832 sist-tun, --echo, --comp-lzo, --socket-flags, --sndbuf, --rcvbuf
1833 --push-remove opt
1835 Selectively remove all --push options matching "opt" from the
1836 option list for a client. opt is matched as a substring against
1837 the whole option string to-be-pushed to the client, so
1838 --push-remove route would remove all --push route ... and --push
1839 route-ipv6 ... statements, while --push-remove "route-ipv6
1840 2001:" would only remove IPv6 routes for 2001:... networks.
1841 --push-remove can only be used in a client-specific context,
1843 like in a --client-config-dir file, or --client-connect script
1844 or plugin -- similar to --push-reset, just more selective.
1845 NOTE: to change an option, --push-remove can be used to first
1847 remove the old value, and then add a new --push option with the
1848 new value.
1849 NOTE 2: due to implementation details, 'ifconfig' and 'ifcon‐
1851 fig-ipv6' can only be removed with an exact match on the option
1852 ( push-remove ifconfig), no substring matching and no matching
1853 on the IPv4/IPv6 address argument is possible.
1854 --push-reset
1856 Don't inherit the global push list for a specific client in‐
1857 stance. Specify this option in a client-specific context such
1858 as with a --client-config-dir configuration file. This option
1859 will ignore --push options at the global config file level.
1860 NOTE: --push-reset is very thorough: it will remove almost all
1862 options from the list of to-be-pushed options. In many cases,
1863 some of these options will need to be re-configured afterwards -
1864 specifically, --topology subnet and --route-gateway will get
1865 lost and this will break client configs in many cases. Thus,
1866 for most purposes, --push-remove is better suited to selectively
1867 remove push options for individual clients.
1868 --server args
1870 A helper directive designed to simplify the configuration of
1871 OpenVPN's server mode. This directive will set up an OpenVPN
1872 server which will allocate addresses to clients out of the given
1873 network/netmask. The server itself will take the .1 address of
1874 the given network for use as the server-side endpoint of the lo‐
1875 cal TUN/TAP interface. If the optional nopool flag is given, no
1876 dynamic IP address pool will prepared for VPN clients.
1877 Valid syntax:
1879 server network netmask [nopool]
1881 For example, --server 10.8.0.0 255.255.255.0 expands as follows:
1883 mode server
1885 tls-server
1886 push "topology [topology]"
1887 if dev tun AND (topology == net30 OR topology == p2p):
1889 ifconfig 10.8.0.1 10.8.0.2
1890 if !nopool:
1891 ifconfig-pool 10.8.0.4 10.8.0.251
1892 route 10.8.0.0 255.255.255.0
1893 if client-to-client:
1894 push "route 10.8.0.0 255.255.255.0"
1895 else if topology == net30:
1896 push "route 10.8.0.1"
1897 if dev tap OR (dev tun AND topology == subnet):
1899 ifconfig 10.8.0.1 255.255.255.0
1900 if !nopool:
1901 ifconfig-pool 10.8.0.2 10.8.0.253 255.255.255.0
1902 push "route-gateway 10.8.0.1"
1903 if route-gateway unset:
1904 route-gateway 10.8.0.2
1905 Don't use --server if you are ethernet bridging. Use
1907 --server-bridge instead.
1908 --server-bridge args
1910 A helper directive similar to --server which is designed to sim‐
1911 plify the configuration of OpenVPN's server mode in ethernet
1912 bridging configurations.
1913 Valid syntaxes:
1915 server-bridge gateway netmask pool-start-IP pool-end-IP
1917 server-bridge [nogw]
1918 If --server-bridge is used without any parameters, it will en‐
1920 able a DHCP-proxy mode, where connecting OpenVPN clients will
1921 receive an IP address for their TAP adapter from the DHCP server
1922 running on the OpenVPN server-side LAN. Note that only clients
1923 that support the binding of a DHCP client with the TAP adapter
1924 (such as Windows) can support this mode. The optional nogw flag
1925 (advanced) indicates that gateway information should not be
1926 pushed to the client.
1927 To configure ethernet bridging, you must first use your OS's
1929 bridging capability to bridge the TAP interface with the ether‐
1930 net NIC interface. For example, on Linux this is done with the
1931 brctl tool, and with Windows XP it is done in the Network Con‐
1932 nections Panel by selecting the ethernet and TAP adapters and
1933 right-clicking on "Bridge Connections".
1934 Next you you must manually set the IP/netmask on the bridge in‐
1936 terface. The gateway and netmask parameters to --server-bridge
1937 can be set to either the IP/netmask of the bridge interface, or
1938 the IP/netmask of the default gateway/router on the bridged sub‐
1939 net.
1940 Finally, set aside a IP range in the bridged subnet, denoted by
1942 pool-start-IP and pool-end-IP, for OpenVPN to allocate to con‐
1943 necting clients.
1944 For example, server-bridge 10.8.0.4 255.255.255.0 10.8.0.128
1946 10.8.0.254 expands as follows:
1947 mode server
1949 tls-server
1950 ifconfig-pool 10.8.0.128 10.8.0.254 255.255.255.0
1952 push "route-gateway 10.8.0.4"
1953 In another example, --server-bridge (without parameters) expands
1955 as follows:
1956 mode server
1958 tls-server
1959 push "route-gateway dhcp"
1961 Or --server-bridge nogw expands as follows:
1963 mode server
1965 tls-server
1966 --server-ipv6 args
1968 Convenience-function to enable a number of IPv6 related options
1969 at once, namely --ifconfig-ipv6, --ifconfig-ipv6-pool and --push
1970 tun-ipv6.
1971 Valid syntax:
1973 server-ipv6 ipv6addr/bits
1975 Pushing of the --tun-ipv6 directive is done for older clients
1977 which require an explicit --tun-ipv6 in their configuration.
1978 --stale-routes-check args
1980 Remove routes which haven't had activity for n seconds (i.e. the
1981 ageing time). This check is run every t seconds (i.e. check in‐
1982 terval).
1983 Valid syntax:
1985 stale-routes-check n [t]
1987 If t is not present it defaults to n.
1989 This option helps to keep the dynamic routing table small. See
1991 also --max-routes-per-client
1992 --username-as-common-name
1994 Use the authenticated username as the common-name, rather than
1995 the common-name from the client certificate. Requires that some
1996 form of --auth-user-pass verification is in effect. As the re‐
1997 placement happens after --auth-user-pass verification, the veri‐
1998 fication script or plugin will still receive the common-name
1999 from the certificate.
2000 The common_name environment variable passed to scripts and plug‐
2002 ins invoked after authentication (e.g, client-connect script)
2003 and file names parsed in client-config directory will match the
2004 username.
2005 --verify-client-cert mode
2007 Specify whether the client is required to supply a valid cer‐
2008 tificate.
2009 Possible mode options are:
2011 none A client certificate is not required. the client needs to
2013 authenticate using username/password only. Be aware that
2014 using this directive is less secure than requiring cer‐
2015 tificates from all clients.
2016 If you use this directive, the entire responsibility of
2018 authentication will rest on your --auth-user-pass-verify
2019 script, so keep in mind that bugs in your script could
2020 potentially compromise the security of your VPN.
2021 --verify-client-cert none is functionally equivalent to
2023 --client-cert-not-required.
2024 optional
2026 A client may present a certificate but it is not required
2027 to do so. When using this directive, you should also use
2028 a --auth-user-pass-verify script to ensure that clients
2029 are authenticated using a certificate, a username and
2030 password, or possibly even both.
2031 Again, the entire responsibility of authentication will
2033 rest on your --auth-user-pass-verify script, so keep in
2034 mind that bugs in your script could potentially compro‐
2035 mise the security of your VPN.
2036 require
2038 This is the default option. A client is required to
2039 present a certificate, otherwise VPN access is refused.
2040 If you don't use this directive (or use --verify-client-cert re‐
2042 quire) but you also specify an --auth-user-pass-verify script,
2043 then OpenVPN will perform double authentication. The client cer‐
2044 tificate verification AND the --auth-user-pass-verify script
2045 will need to succeed in order for a client to be authenticated
2046 and accepted onto the VPN.
2047 --vlan-tagging
2049 Server-only option. Turns the OpenVPN server instance into a
2050 switch that understands VLAN-tagging, based on IEEE 802.1Q.
2051 The server TAP device and each of the connecting clients is seen
2053 as a port of the switch. All client ports are in untagged mode
2054 and the server TAP device is VLAN-tagged, untagged or accepts
2055 both, depending on the --vlan-accept setting.
2056 Ethernet frames with a prepended 802.1Q tag are called "tagged".
2058 If the VLAN Identifier (VID) field in such a tag is non-zero,
2059 the frame is called "VLAN-tagged". If the VID is zero, but the
2060 Priority Control Point (PCP) field is non-zero, the frame is
2061 called "prio-tagged". If there is no 802.1Q tag, the frame is
2062 "untagged".
2063 Using the --vlan-pvid v option once per client (see
2065 --client-config-dir), each port can be associated with a certain
2066 VID. Packets can only be forwarded between ports having the
2067 same VID. Therefore, clients with differing VIDs are completely
2068 separated from one-another, even if --client-to-client is acti‐
2069 vated.
2070 The packet filtering takes place in the OpenVPN server. Clients
2072 should not have any VLAN tagging configuration applied.
2073 The --vlan-tagging option is off by default. While turned off,
2075 OpenVPN accepts any Ethernet frame and does not perform any spe‐
2076 cial processing for VLAN-tagged packets.
2077 This option can only be activated in --dev tap mode.
2079 --vlan-accept args
2081 Configure the VLAN tagging policy for the server TAP device.
2082 Valid syntax:
2084 vlan-accept all|tagged|untagged
2086 The following modes are available:
2088 tagged Admit only VLAN-tagged frames. Only VLAN-tagged packets
2090 are accepted, while untagged or priority-tagged packets
2091 are dropped when entering the server TAP device.
2092 untagged
2094 Admit only untagged and prio-tagged frames. VLAN-tagged
2095 packets are not accepted, while untagged or prior‐
2096 ity-tagged packets entering the server TAP device are
2097 tagged with the value configured for the global
2098 --vlan-pvid setting.
2099 all (default)
2101 Admit all frames. All packets are admitted and then
2102 treated like untagged or tagged mode respectively.
2103 Note: Some vendors refer to switch ports running in tagged mode
2105 as "trunk ports" and switch ports running in untagged
2106 mode as "access ports".
2107 Packets forwarded from clients to the server are VLAN-tagged
2109 with the originating client's PVID, unless the VID matches the
2110 global --vlan-pvid, in which case the tag is removed.
2111 If no PVID is configured for a given client (see --vlan-pvid)
2113 packets are tagged with 1 by default.
2114 --vlan-pvid v
2116 Specifies which VLAN identifier a "port" is associated with.
2117 Only valid when --vlan-tagging is speficied.
2118 In the client context, the setting specifies which VLAN ID a
2120 client is associated with. In the global context, the VLAN ID of
2121 the server TAP device is set. The latter only makes sense for
2122 --vlan-accept untagged and --vlan-accept all modes.
2123 Valid values for v go from 1 through to 4094. The global value
2125 defaults to 1. If no --vlan-pvid is specified in the client con‐
2126 text, the global value is inherited.
2127 In some switch implementations, the PVID is also referred to as
2129 "Native VLAN".
2130
2132 SSL Library information
2133 --show-ciphers
2134 (Standalone) Show all cipher algorithms to use with the --cipher
2135 option.
2136 --show-digests
2138 (Standalone) Show all message digest algorithms to use with the
2139 --auth option.
2140 --show-tls
2142 (Standalone) Show all TLS ciphers supported by the crypto li‐
2143 brary. OpenVPN uses TLS to secure the control channel, over
2144 which the keys that are used to protect the actual VPN traffic
2145 are exchanged. The TLS ciphers will be sorted from highest pref‐
2146 erence (most secure) to lowest.
2147 Be aware that whether a cipher suite in this list can actually
2149 work depends on the specific setup of both peers (e.g. both
2150 peers must support the cipher, and an ECDSA cipher suite will
2151 not work if you are using an RSA certificate, etc.).
2152 --show-engines
2154 (Standalone) Show currently available hardware-based crypto ac‐
2155 celeration engines supported by the OpenSSL library.
2156 --show-groups
2158 (Standalone) Show all available elliptic curves/groups to use
2159 with the --ecdh-curve and tls-groups options.
2160 Generating key material
2162 --genkey args
2163 (Standalone) Generate a key to be used of the type keytype. if
2164 keyfile is left out or empty the key will be output on stdout.
2165 See the following sections for the different keytypes.
2166 Valid syntax:
2168 --genkey keytype keyfile
2170 Valid keytype arguments are:
2172 secret Standard OpenVPN shared secret keys
2174 tls-crypt Alias for secret
2176 tls-auth Alias for secret
2178 auth-token Key used for --auth-gen-token-key
2180 tls-crypt-v2-server TLS Crypt v2 server key
2182 tls-crypt-v2-client TLS Crypt v2 client key
2184 Examples:
2186 $ openvpn --genkey secret shared.key
2188 $ openvpn --genkey tls-crypt shared.key
2189 $ openvpn --genkey tls-auth shared.key
2190 $ openvpn --genkey tls-crypt-v2-server v2crypt-server.key
2191 $ openvpn --tls-crypt-v2 v2crypt-server.key --genkey tls-crypt-v2-client v2crypt-client-1.key
2192 • Generating Shared Secret Keys Generate a shared secret, for
2194 use with the --secret, --tls-auth or --tls-crypt options.
2195 Syntax:
2197 $ openvpn --genkey secret|tls-crypt|tls-auth keyfile
2199 The key is saved in keyfile. All three variants (--secret,
2201 tls-crypt and tls-auth) generate the same type of key. The
2202 aliases are added for convenience.
2203 If using this for --secret, this file must be shared with the
2205 peer over a pre-existing secure channel such as scp(1).
2206 • Generating TLS Crypt v2 Server key Generate a --tls-crypt-v2
2208 key to be used by an OpenVPN server. The key is stored in
2209 keyfile.
2210 Syntax:
2212 --genkey tls-crypt-v2-server keyfile
2214 • Generating TLS Crypt v2 Client key Generate a --tls-crypt-v2
2216 key to be used by OpenVPN clients. The key is stored in key‐
2217 file.
2218 Syntax
2220 --genkey tls-crypt-v2-client keyfile [metadata]
2222 If supplied, include the supplied metadata in the wrapped
2224 client key. This metadata must be supplied in base64-encoded
2225 form. The metadata must be at most 735 bytes long (980 bytes
2226 in base64).
2227 If no metadata is supplied, OpenVPN will use a 64-bit unix
2229 timestamp representing the current time in UTC, encoded in
2230 network order, as metadata for the generated key.
2231 A tls-crypt-v2 client key is wrapped using a server key. To
2233 generate a client key, the user must therefore supply the
2234 server key using the --tls-crypt-v2 option.
2235 Servers can use --tls-crypt-v2-verify to specify a metadata
2237 verification command.
2238 • Generate Authentication Token key Generate a new secret that
2240 can be used with --auth-gen-token-secret
2241 Syntax:
2243 --genkey auth-token [keyfile]
2245 Note: This file should be kept secret to the server as anyone
2247 that has access to this file will be able to generate
2248 auth tokens that the OpenVPN server will accept as
2249 valid.
2250 Data Channel Renegotiation
2252 When running OpenVPN in client/server mode, the data channel will use a
2253 separate ephemeral encryption key which is rotated at regular inter‐
2254 vals.
2255 --reneg-bytes n
2257 Renegotiate data channel key after n bytes sent or received
2258 (disabled by default with an exception, see below). OpenVPN al‐
2259 lows the lifetime of a key to be expressed as a number of bytes
2260 encrypted/decrypted, a number of packets, or a number of sec‐
2261 onds. A key renegotiation will be forced if any of these three
2262 criteria are met by either peer.
2263 If using ciphers with cipher block sizes less than 128-bits,
2265 --reneg-bytes is set to 64MB by default, unless it is explicitly
2266 disabled by setting the value to 0, but this is HIGHLY DISCOUR‐
2267 AGED as this is designed to add some protection against the
2268 SWEET32 attack vector. For more information see the --cipher op‐
2269 tion.
2270 --reneg-pkts n
2272 Renegotiate data channel key after n packets sent and received
2273 (disabled by default).
2274 --reneg-sec args
2276 Renegotiate data channel key after at most max seconds (default
2277 3600) and at least min seconds (default is 90% of max for
2278 servers, and equal to max for clients).
2279 reneg-sec max [min]
2281 The effective --reneg-sec value used is per session pseudo-uni‐
2283 form-randomized between min and max.
2284 With the default value of 3600 this results in an effective per
2286 session value in the range of 3240 .. 3600 seconds for servers,
2287 or just 3600 for clients.
2288 When using dual-factor authentication, note that this default
2290 value may cause the end user to be challenged to reauthorize
2291 once per hour.
2292 Also, keep in mind that this option can be used on both the
2294 client and server, and whichever uses the lower value will be
2295 the one to trigger the renegotiation. A common mistake is to set
2296 --reneg-sec to a higher value on either the client or server,
2297 while the other side of the connection is still using the de‐
2298 fault value of 3600 seconds, meaning that the renegotiation will
2299 still occur once per 3600 seconds. The solution is to increase
2300 --reneg-sec on both the client and server, or set it to 0 on one
2301 side of the connection (to disable), and to your chosen value on
2302 the other side.
2303 TLS Mode Options
2305 TLS mode is the most powerful crypto mode of OpenVPN in both security
2306 and flexibility. TLS mode works by establishing control and data chan‐
2307 nels which are multiplexed over a single TCP/UDP port. OpenVPN initi‐
2308 ates a TLS session over the control channel and uses it to exchange ci‐
2309 pher and HMAC keys to protect the data channel. TLS mode uses a robust
2310 reliability layer over the UDP connection for all control channel com‐
2311 munication, while the data channel, over which encrypted tunnel data
2312 passes, is forwarded without any mediation. The result is the best of
2313 both worlds: a fast data channel that forwards over UDP with only the
2314 overhead of encrypt, decrypt, and HMAC functions, and a control channel
2315 that provides all of the security features of TLS, including certifi‐
2316 cate-based authentication and Diffie Hellman forward secrecy.
2317 To use TLS mode, each peer that runs OpenVPN should have its own local
2319 certificate/key pair (--cert and --key), signed by the root certificate
2320 which is specified in --ca.
2321 When two OpenVPN peers connect, each presents its local certificate to
2323 the other. Each peer will then check that its partner peer presented a
2324 certificate which was signed by the master root certificate as speci‐
2325 fied in --ca.
2326 If that check on both peers succeeds, then the TLS negotiation will
2328 succeed, both OpenVPN peers will exchange temporary session keys, and
2329 the tunnel will begin passing data.
2330 The OpenVPN project provides a set of scripts for managing RSA certifi‐
2332 cates and keys: https://github.com/OpenVPN/easy-rsa
2333 --askpass file
2335 Get certificate password from console or file before we daemo‐
2336 nize.
2337 Valid syntaxes:
2339 askpass
2341 askpass file
2342 For the extremely security conscious, it is possible to protect
2344 your private key with a password. Of course this means that ev‐
2345 ery time the OpenVPN daemon is started you must be there to type
2346 the password. The --askpass option allows you to start OpenVPN
2347 from the command line. It will query you for a password before
2348 it daemonizes. To protect a private key with a password you
2349 should omit the -nodes option when you use the openssl command
2350 line tool to manage certificates and private keys.
2351 If file is specified, read the password from the first line of
2353 file. Keep in mind that storing your password in a file to a
2354 certain extent invalidates the extra security provided by using
2355 an encrypted key.
2356 --ca file
2358 Certificate authority (CA) file in .pem format, also referred to
2359 as the root certificate. This file can have multiple certifi‐
2360 cates in .pem format, concatenated together. You can construct
2361 your own certificate authority certificate and private key by
2362 using a command such as:
2363 openssl req -nodes -new -x509 -keyout ca.key -out ca.crt
2365 Then edit your openssl.cnf file and edit the certificate vari‐
2367 able to point to your new root certificate ca.crt.
2368 For testing purposes only, the OpenVPN distribution includes a
2370 sample CA certificate (ca.crt). Of course you should never use
2371 the test certificates and test keys distributed with OpenVPN in
2372 a production environment, since by virtue of the fact that they
2373 are distributed with OpenVPN, they are totally insecure.
2374 --capath dir
2376 Directory containing trusted certificates (CAs and CRLs). Not
2377 available with mbed TLS.
2378 CAs in the capath directory are expected to be named <hash>.<n>.
2380 CRLs are expected to be named <hash>.r<n>. See the -CApath op‐
2381 tion of openssl verify, and the -hash option of openssl x509,
2382 openssl crl and X509_LOOKUP_hash_dir()[22m(3) for more information.
2383 Similar to the --crl-verify option, CRLs are not mandatory -
2385 OpenVPN will log the usual warning in the logs if the relevant
2386 CRL is missing, but the connection will be allowed.
2387 --cert file
2389 Local peer's signed certificate in .pem format -- must be signed
2390 by a certificate authority whose certificate is in --ca file.
2391 Each peer in an OpenVPN link running in TLS mode should have its
2392 own certificate and private key file. In addition, each certifi‐
2393 cate should have been signed by the key of a certificate author‐
2394 ity whose public key resides in the --ca certificate authority
2395 file. You can easily make your own certificate authority (see
2396 above) or pay money to use a commercial service such as
2397 thawte.com (in which case you will be helping to finance the
2398 world's second space tourist :). To generate a certificate, you
2399 can use a command such as:
2400 openssl req -nodes -new -keyout mycert.key -out mycert.csr
2402 If your certificate authority private key lives on another ma‐
2404 chine, copy the certificate signing request (mycert.csr) to this
2405 other machine (this can be done over an insecure channel such as
2406 email). Now sign the certificate with a command such as:
2407 openssl ca -out mycert.crt -in mycert.csr
2409 Now copy the certificate (mycert.crt) back to the peer which
2411 initially generated the .csr file (this can be over a public
2412 medium). Note that the openssl ca command reads the location of
2413 the certificate authority key from its configuration file such
2414 as /usr/share/ssl/openssl.cnf -- note also that for certificate
2415 authority functions, you must set up the files index.txt (may be
2416 empty) and serial (initialize to 01).
2417 --crl-verify args
2419 Check peer certificate against a Certificate Revocation List.
2420 Valid syntax:
2422 crl-verify file/directory flag
2424 Examples:
2426 crl-verify crl-file.pem
2428 crl-verify /etc/openvpn/crls dir
2429 A CRL (certificate revocation list) is used when a particular
2431 key is compromised but when the overall PKI is still intact.
2432 Suppose you had a PKI consisting of a CA, root certificate, and
2434 a number of client certificates. Suppose a laptop computer con‐
2435 taining a client key and certificate was stolen. By adding the
2436 stolen certificate to the CRL file, you could reject any connec‐
2437 tion which attempts to use it, while preserving the overall in‐
2438 tegrity of the PKI.
2439 The only time when it would be necessary to rebuild the entire
2441 PKI from scratch would be if the root certificate key itself was
2442 compromised.
2443 The option is not mandatory - if the relevant CRL is missing,
2445 OpenVPN will log a warning in the logs - e.g.
2446 VERIFY WARNING: depth=0, unable to get certificate CRL
2448 but the connection will be allowed. If the optional dir flag is
2450 specified, enable a different mode where the crl-verify is
2451 pointed at a directory containing files named as revoked serial
2452 numbers (the files may be empty, the contents are never read).
2453 If a client requests a connection, where the client certificate
2454 serial number (decimal string) is the name of a file present in
2455 the directory, it will be rejected.
2456 Note: As the crl file (or directory) is read every time a peer
2458 connects, if you are dropping root privileges with
2459 --user, make sure that this user has sufficient privi‐
2460 leges to read the file.
2461 --dh file
2463 File containing Diffie Hellman parameters in .pem format (re‐
2464 quired for --tls-server only).
2465 Set file to none to disable Diffie Hellman key exchange (and use
2467 ECDH only). Note that this requires peers to be using an SSL li‐
2468 brary that supports ECDH TLS cipher suites (e.g. OpenSSL 1.0.1+,
2469 or mbed TLS 2.0+).
2470 Use openssl dhparam -out dh2048.pem 2048 to generate 2048-bit DH
2472 parameters. Diffie Hellman parameters may be considered public.
2473 --ecdh-curve name
2475 Specify the curve to use for elliptic curve Diffie Hellman.
2476 Available curves can be listed with --show-curves. The specified
2477 curve will only be used for ECDH TLS-ciphers.
2478 This option is not supported in mbed TLS builds of OpenVPN.
2480 --extra-certs file
2482 Specify a file containing one or more PEM certs (concatenated
2483 together) that complete the local certificate chain.
2484 This option is useful for "split" CAs, where the CA for server
2486 certs is different than the CA for client certs. Putting certs
2487 in this file allows them to be used to complete the local cer‐
2488 tificate chain without trusting them to verify the peer-submit‐
2489 ted certificate, as would be the case if the certs were placed
2490 in the ca file.
2491 --hand-window n
2493 Handshake Window -- the TLS-based key exchange must finalize
2494 within n seconds of handshake initiation by any peer (default 60
2495 seconds). If the handshake fails we will attempt to reset our
2496 connection with our peer and try again. Even in the event of
2497 handshake failure we will still use our expiring key for up to
2498 --tran-window seconds to maintain continuity of transmission of
2499 tunnel data.
2500 --key file
2502 Local peer's private key in .pem format. Use the private key
2503 which was generated when you built your peer's certificate (see
2504 --cert file above).
2505 --pkcs12 file
2507 Specify a PKCS #12 file containing local private key, local cer‐
2508 tificate, and root CA certificate. This option can be used in‐
2509 stead of --ca, --cert, and --key. Not available with mbed TLS.
2510 --remote-cert-eku oid
2512 Require that peer certificate was signed with an explicit ex‐
2513 tended key usage.
2514 This is a useful security option for clients, to ensure that the
2516 host they connect to is a designated server.
2517 The extended key usage should be encoded in oid notation, or
2519 OpenSSL symbolic representation.
2520 --remote-cert-ku key-usage
2522 Require that peer certificate was signed with an explicit
2523 key-usage.
2524 If present in the certificate, the keyUsage value is validated
2526 by the TLS library during the TLS handshake. Specifying this op‐
2527 tion without arguments requires this extension to be present (so
2528 the TLS library will verify it).
2529 If key-usage is a list of usage bits, the keyUsage field must
2531 have at least the same bits set as the bits in one of the values
2532 supplied in the key-usage list.
2533 The key-usage values in the list must be encoded in hex, e.g.
2535 remote-cert-ku a0
2537 --remote-cert-tls type
2539 Require that peer certificate was signed with an explicit key
2540 usage and extended key usage based on RFC3280 TLS rules.
2541 Valid syntaxes:
2543 remote-cert-tls server
2545 remote-cert-tls client
2546 This is a useful security option for clients, to ensure that the
2548 host they connect to is a designated server. Or the other way
2549 around; for a server to verify that only hosts with a client
2550 certificate can connect.
2551 The --remote-cert-tls client option is equivalent to
2553 remote-cert-ku
2555 remote-cert-eku "TLS Web Client Authentication"
2556 The --remote-cert-tls server option is equivalent to
2558 remote-cert-ku
2560 remote-cert-eku "TLS Web Server Authentication"
2561 This is an important security precaution to protect against a
2563 man-in-the-middle attack where an authorized client attempts to
2564 connect to another client by impersonating the server. The at‐
2565 tack is easily prevented by having clients verify the server
2566 certificate using any one of --remote-cert-tls, --ver‐
2567 ify-x509-name, or --tls-verify.
2568 --tls-auth args
2570 Add an additional layer of HMAC authentication on top of the TLS
2571 control channel to mitigate DoS attacks and attacks on the TLS
2572 stack.
2573 Valid syntaxes:
2575 tls-auth file
2577 tls-auth file 0
2578 tls-auth file 1
2579 In a nutshell, --tls-auth enables a kind of "HMAC firewall" on
2581 OpenVPN's TCP/UDP port, where TLS control channel packets bear‐
2582 ing an incorrect HMAC signature can be dropped immediately with‐
2583 out response.
2584 file (required) is a file in OpenVPN static key format which can
2586 be generated by --genkey.
2587 Older versions (up to OpenVPN 2.3) supported a freeform
2589 passphrase file. This is no longer supported in newer versions
2590 (v2.4+).
2591 See the --secret option for more information on the optional di‐
2593 rection parameter.
2594 --tls-auth is recommended when you are running OpenVPN in a mode
2596 where it is listening for packets from any IP address, such as
2597 when --remote is not specified, or --remote is specified with
2598 --float.
2599 The rationale for this feature is as follows. TLS requires a
2601 multi-packet exchange before it is able to authenticate a peer.
2602 During this time before authentication, OpenVPN is allocating
2603 resources (memory and CPU) to this potential peer. The potential
2604 peer is also exposing many parts of OpenVPN and the OpenSSL li‐
2605 brary to the packets it is sending. Most successful network at‐
2606 tacks today seek to either exploit bugs in programs (such as
2607 buffer overflow attacks) or force a program to consume so many
2608 resources that it becomes unusable. Of course the first line of
2609 defense is always to produce clean, well-audited code. OpenVPN
2610 has been written with buffer overflow attack prevention as a top
2611 priority. But as history has shown, many of the most widely used
2612 network applications have, from time to time, fallen to buffer
2613 overflow attacks.
2614 So as a second line of defense, OpenVPN offers this special
2616 layer of authentication on top of the TLS control channel so
2617 that every packet on the control channel is authenticated by an
2618 HMAC signature and a unique ID for replay protection. This sig‐
2619 nature will also help protect against DoS (Denial of Service)
2620 attacks. An important rule of thumb in reducing vulnerability to
2621 DoS attacks is to minimize the amount of resources a potential,
2622 but as yet unauthenticated, client is able to consume.
2623 --tls-auth does this by signing every TLS control channel packet
2625 with an HMAC signature, including packets which are sent before
2626 the TLS level has had a chance to authenticate the peer. The re‐
2627 sult is that packets without the correct signature can be
2628 dropped immediately upon reception, before they have a chance to
2629 consume additional system resources such as by initiating a TLS
2630 handshake. --tls-auth can be strengthened by adding the --re‐
2631 play-persist option which will keep OpenVPN's replay protection
2632 state in a file so that it is not lost across restarts.
2633 It should be emphasized that this feature is optional and that
2635 the key file used with --tls-auth gives a peer nothing more than
2636 the power to initiate a TLS handshake. It is not used to encrypt
2637 or authenticate any tunnel data.
2638 Use --tls-crypt instead if you want to use the key file to not
2640 only authenticate, but also encrypt the TLS control channel.
2641 --tls-groups list
2643 A list of allowable groups/curves in order of preference.
2644 Set the allowed elliptic curves/groups for the TLS session.
2646 These groups are allowed to be used in signatures and key ex‐
2647 change.
2648 mbedTLS currently allows all known curves per default.
2650 OpenSSL 1.1+ restricts the list per default to
2652 "X25519:secp256r1:X448:secp521r1:secp384r1".
2654 If you use certificates that use non-standard curves, you might
2656 need to add them here. If you do not force the ecdh curve by us‐
2657 ing --ecdh-curve, the groups for ecdh will also be picked from
2658 this list.
2659 OpenVPN maps the curve name secp256r1 to prime256v1 to allow
2661 specifying the same tls-groups option for mbedTLS and OpenSSL.
2662 Warning: this option not only affects elliptic curve certifi‐
2664 cates but also the key exchange in TLS 1.3 and using this option
2665 improperly will disable TLS 1.3.
2666 --tls-cert-profile profile
2668 Set the allowed cryptographic algorithms for certificates ac‐
2669 cording to profile.
2670 The following profiles are supported:
2672 insecure
2674 Identical for mbed TLS to legacy
2675 legacy (default)
2677 SHA1 and newer, RSA 2048-bit+, any elliptic curve.
2678 preferred
2680 SHA2 and newer, RSA 2048-bit+, any elliptic curve.
2681 suiteb SHA256/SHA384, ECDSA with P-256 or P-384.
2683 This option is only fully supported for mbed TLS builds. OpenSSL
2685 builds use the following approximation:
2686 insecure
2688 sets "security level 0"
2689 legacy (default)
2691 sets "security level 1"
2692 preferred
2694 sets "security level 2"
2695 suiteb sets "security level 3" and --tls-cipher "SUITEB128".
2697 OpenVPN will migrate to 'preferred' as default in the future.
2699 Please ensure that your keys already comply.
2700 WARNING: --tls-ciphers, --tls-ciphersuites and tls-groups
2702 These options are expert features, which - if used correctly -
2703 can improve the security of your VPN connection. But it is also
2704 easy to unwittingly use them to carefully align a gun with your
2705 foot, or just break your connection. Use with care!
2706 --tls-cipher l
2708 A list l of allowable TLS ciphers delimited by a colon (":").
2709 These setting can be used to ensure that certain cipher suites
2711 are used (or not used) for the TLS connection. OpenVPN uses TLS
2712 to secure the control channel, over which the keys that are used
2713 to protect the actual VPN traffic are exchanged.
2714 The supplied list of ciphers is (after potential OpenSSL/IANA
2716 name translation) simply supplied to the crypto library. Please
2717 see the OpenSSL and/or mbed TLS documentation for details on the
2718 cipher list interpretation.
2719 For OpenSSL, the --tls-cipher is used for TLS 1.2 and below.
2721 Use --show-tls to see a list of TLS ciphers supported by your
2723 crypto library.
2724 The default for --tls-cipher is to use mbed TLS's default cipher
2726 list when using mbed TLS or DE‐
2727 FAULT:!EXP:!LOW:!MEDIUM:!kDH:!kECDH:!DSS:!PSK:!SRP:!kRSA when
2728 using OpenSSL.
2729 --tls-ciphersuites l
2731 Same as --tls-cipher but for TLS 1.3 and up. mbed TLS has no TLS
2732 1.3 support yet and only the --tls-cipher setting is used.
2733 The default for --tls-ciphersuites is to use the crypto li‐
2735 brary's default.
2736 --tls-client
2738 Enable TLS and assume client role during TLS handshake.
2739 --tls-crypt keyfile
2741 Encrypt and authenticate all control channel packets with the
2742 key from keyfile. (See --tls-auth for more background.)
2743 Encrypting (and authenticating) control channel packets:
2745 • provides more privacy by hiding the certificate used for the
2747 TLS connection,
2748 • makes it harder to identify OpenVPN traffic as such,
2750 • provides "poor-man's" post-quantum security, against attackers
2752 who will never know the pre-shared key (i.e. no forward se‐
2753 crecy).
2754 In contrast to --tls-auth, --tls-crypt does not require the user
2756 to set --key-direction.
2757 Security Considerations
2759 All peers use the same --tls-crypt pre-shared group key to au‐
2761 thenticate and encrypt control channel messages. To ensure that
2762 IV collisions remain unlikely, this key should not be used to
2763 encrypt more than 2^48 client-to-server or 2^48 server-to-client
2764 control channel messages. A typical initial negotiation is about
2765 10 packets in each direction. Assuming both initial negotiation
2766 and renegotiations are at most 2^16 (65536) packets (to be con‐
2767 servative), and (re)negotiations happen each minute for each
2768 user (24/7), this limits the tls-crypt key lifetime to 8171
2769 years divided by the number of users. So a setup with 1000 users
2770 should rotate the key at least once each eight years. (And a
2771 setup with 8000 users each year.)
2772 If IV collisions were to occur, this could result in the secu‐
2774 rity of --tls-crypt degrading to the same security as using
2775 --tls-auth. That is, the control channel still benefits from
2776 the extra protection against active man-in-the-middle-attacks
2777 and DoS attacks, but may no longer offer extra privacy and
2778 post-quantum security on top of what TLS itself offers.
2779 For large setups or setups where clients are not trusted, con‐
2781 sider using --tls-crypt-v2 instead. That uses per-client unique
2782 keys, and thereby improves the bounds to 'rotate a client key at
2783 least once per 8000 years'.
2784 --tls-crypt-v2 keyfile
2786 Use client-specific tls-crypt keys.
2787 For clients, keyfile is a client-specific tls-crypt key. Such a
2789 key can be generated using the --genkey tls-crypt-v2-client op‐
2790 tion.
2791 For servers, keyfile is used to unwrap client-specific keys sup‐
2793 plied by the client during connection setup. This key must be
2794 the same as the key used to generate the client-specific key
2795 (see --genkey tls-crypt-v2-client).
2796 On servers, this option can be used together with the --tls-auth
2798 or --tls-crypt option. In that case, the server will detect
2799 whether the client is using client-specific keys, and automati‐
2800 cally select the right mode.
2801 --tls-crypt-v2-verify cmd
2803 Run command cmd to verify the metadata of the client-specific
2804 tls-crypt-v2 key of a connecting client. This allows server ad‐
2805 ministrators to reject client connections, before exposing the
2806 TLS stack (including the notoriously dangerous X.509 and ASN.1
2807 stacks) to the connecting client.
2808 OpenVPN supplies the following environment variables to the com‐
2810 mand:
2811 • script_type is set to tls-crypt-v2-verify
2813 • metadata_type is set to 0 if the metadata was user supplied,
2815 or 1 if it's a 64-bit unix timestamp representing the key cre‐
2816 ation time.
2817 • metadata_file contains the filename of a temporary file that
2819 contains the client metadata.
2820 The command can reject the connection by exiting with a non-zero
2822 exit code.
2823 --tls-exit
2825 Exit on TLS negotiation failure.
2826 --tls-export-cert directory
2828 Store the certificates the clients use upon connection to this
2829 directory. This will be done before --tls-verify is called. The
2830 certificates will use a temporary name and will be deleted when
2831 the tls-verify script returns. The file name used for the cer‐
2832 tificate is available via the peer_cert environment variable.
2833 --tls-server
2835 Enable TLS and assume server role during TLS handshake. Note
2836 that OpenVPN is designed as a peer-to-peer application. The des‐
2837 ignation of client or server is only for the purpose of negoti‐
2838 ating the TLS control channel.
2839 --tls-timeout n
2841 Packet retransmit timeout on TLS control channel if no acknowl‐
2842 edgment from remote within n seconds (default 2). When OpenVPN
2843 sends a control packet to its peer, it will expect to receive an
2844 acknowledgement within n seconds or it will retransmit the
2845 packet, subject to a TCP-like exponential backoff algorithm.
2846 This parameter only applies to control channel packets. Data
2847 channel packets (which carry encrypted tunnel data) are never
2848 acknowledged, sequenced, or retransmitted by OpenVPN because the
2849 higher level network protocols running on top of the tunnel such
2850 as TCP expect this role to be left to them.
2851 --tls-version-min args
2853 Sets the minimum TLS version we will accept from the peer (de‐
2854 fault is "1.0").
2855 Valid syntax:
2857 tls-version-min version ['or-highest']
2859 Examples for version include 1.0, 1.1, or 1.2. If or-highest is
2861 specified and version is not recognized, we will only accept the
2862 highest TLS version supported by the local SSL implementation.
2863 --tls-version-max version
2865 Set the maximum TLS version we will use (default is the highest
2866 version supported). Examples for version include 1.0, 1.1, or
2867 1.2.
2868 --verify-hash args
2870 Specify SHA1 or SHA256 fingerprint for level-1 cert.
2871 Valid syntax:
2873 verify-hash hash [algo]
2875 The level-1 cert is the CA (or intermediate cert) that signs the
2877 leaf certificate, and is one removed from the leaf certificate
2878 in the direction of the root. When accepting a connection from a
2879 peer, the level-1 cert fingerprint must match hash or certifi‐
2880 cate verification will fail. Hash is specified as XX:XX:... For
2881 example:
2882 AD:B0:95:D8:09:C8:36:45:12:A9:89:C8:90:09:CB:13:72:A6:AD:16
2884 The algo flag can be either SHA1 or SHA256. If not provided, it
2886 defaults to SHA1.
2887 --verify-x509-name args
2889 Accept connections only if a host's X.509 name is equal to name.
2890 The remote host must also pass all other tests of verification.
2891 Valid syntax:
2893 verify-x509 name type
2895 Which X.509 name is compared to name depends on the setting of
2897 type. type can be subject to match the complete subject DN (de‐
2898 fault), name to match a subject RDN or name-prefix to match a
2899 subject RDN prefix. Which RDN is verified as name depends on the
2900 --x509-username-field option. But it defaults to the common name
2901 (CN), e.g. a certificate with a subject DN
2902 C=KG, ST=NA, L=Bishkek, CN=Server-1
2904 would be matched by:
2906 verify-x509-name 'C=KG, ST=NA, L=Bishkek, CN=Server-1'
2908 verify-x509-name Server-1 name
2909 verify-x509-name Server- name-prefix
2910 The last example is useful if you want a client to only accept
2912 connections to Server-1, Server-2, etc.
2913 --verify-x509-name is a useful replacement for the --tls-verify
2915 option to verify the remote host, because --verify-x509-name
2916 works in a --chroot environment without any dependencies.
2917 Using a name prefix is a useful alternative to managing a CRL
2919 (Certificate Revocation List) on the client, since it allows the
2920 client to refuse all certificates except for those associated
2921 with designated servers.
2922 NOTE: Test against a name prefix only when you are using Open‐
2924 VPN with a custom CA certificate that is under your con‐
2925 trol. Never use this option with type name-prefix when
2926 your client certificates are signed by a third party,
2927 such as a commercial web CA.
2928 --x509-track attribute
2930 Save peer X509 attribute value in environment for use by plugins
2931 and management interface. Prepend a + to attribute to save val‐
2932 ues from full cert chain. Values will be encoded as
2933 X509_<depth>_<attribute>=<value>. Multiple --x509-track options
2934 can be defined to track multiple attributes.
2935 --x509-username-field args
2937 Field in the X.509 certificate subject to be used as the user‐
2938 name (default CN).
2939 Valid syntax:
2941 x509-username-field [ext:]fieldname
2943 Typically, this option is specified with fieldname as either of
2945 the following:
2946 x509-username-field emailAddress
2948 x509-username-field ext:subjectAltName
2949 The first example uses the value of the emailAddress attribute
2951 in the certificate's Subject field as the username. The second
2952 example uses the ext: prefix to signify that the X.509 extension
2953 fieldname subjectAltName be searched for an rfc822Name (email)
2954 field to be used as the username. In cases where there are mul‐
2955 tiple email addresses in ext:fieldname, the last occurrence is
2956 chosen.
2957 When this option is used, the --verify-x509-name option will
2959 match against the chosen fieldname instead of the Common Name.
2960 Only the subjectAltName and issuerAltName X.509 extensions are
2962 supported.
2963 Please note: This option has a feature which will convert an
2965 all-lowercase fieldname to uppercase characters, e.g., ou -> OU.
2966 A mixed-case fieldname or one having the ext: prefix will be
2967 left as-is. This automatic upcasing feature is deprecated and
2968 will be removed in a future release.
2969 PKCS#11 / SmartCard options
2971 --pkcs11-cert-private args
2972 Set if access to certificate object should be performed after
2973 login. Every provider has its own setting.
2974 Valid syntaxes:
2976 pkcs11-cert-private 0
2978 pkcs11-cert-private 1
2979 --pkcs11-id name
2981 Specify the serialized certificate id to be used. The id can be
2982 gotten by the standalone --show-pkcs11-ids option.
2983 --pkcs11-id-management
2985 Acquire PKCS#11 id from management interface. In this case a
2986 NEED-STR 'pkcs11-id-request' real-time message will be trig‐
2987 gered, application may use pkcs11-id-count command to retrieve
2988 available number of certificates, and pkcs11-id-get command to
2989 retrieve certificate id and certificate body.
2990 --pkcs11-pin-cache seconds
2992 Specify how many seconds the PIN can be cached, the default is
2993 until the token is removed.
2994 --pkcs11-private-mode mode
2996 Specify which method to use in order to perform private key op‐
2997 erations. A different mode can be specified for each provider.
2998 Mode is encoded as hex number, and can be a mask one of the fol‐
2999 lowing:
3000 0 (default) Try to determine automatically.
3002 1 Use sign.
3004 2 Use sign recover.
3006 4 Use decrypt.
3008 8 Use unwrap.
3010 --pkcs11-protected-authentication args
3012 Use PKCS#11 protected authentication path, useful for biometric
3013 and external keypad devices. Every provider has its own setting.
3014 Valid syntaxes:
3016 pkcs11-protected-authentication 0
3018 pkcs11-protected-authentication 1
3019 --pkcs11-providers provider
3021 Specify an RSA Security Inc. PKCS #11 Cryptographic Token Inter‐
3022 face (Cryptoki) providers to load. This option can be used in‐
3023 stead of --cert, --key and --pkcs12.
3024 If p11-kit is present on the system, its p11-kit-proxy.so module
3026 will be loaded by default if either the --pkcs11-id or
3027 --pkcs11-id-management options are specified without
3028 --pkcs11-provider being given.
3029 --show-pkcs11-ids args
3031 (Standalone) Show PKCS#11 token object list.
3032 Valid syntax:
3034 show-pkcs11 [provider] [cert_private]
3036 Specify cert_private as 1 if certificates are stored as private
3038 objects.
3039 If p11-kit is present on the system, the provider argument is
3041 optional; if omitted the default p11-kit-proxy.so module will be
3042 queried.
3043 --verb option can be used BEFORE this option to produce debug‐
3045 ging information.
3046
3048 OpenVPN 2.4 and higher have the capability to negotiate the data cipher
3049 that is used to encrypt data packets. This section describes the mecha‐
3050 nism in more detail and the different backwards compatibility mechanism
3051 with older server and clients.
3052 OpenVPN 2.5 and higher behaviour
3054 When both client and server are at least running OpenVPN 2.5, that the
3055 order of the ciphers of the server's --data-ciphers is used to pick the
3056 the data cipher. That means that the first cipher in that list that is
3057 also in the client's --data-ciphers list is chosen. If no common cipher
3058 is found the client is rejected with a AUTH_FAILED message (as seen in
3059 client log):
3060 AUTH: Received control message: AUTH_FAILED,Data channel cipher ne‐
3061 gotiation failed (no shared cipher)
3062 OpenVPN 2.5 will only allow the ciphers specified in --data-ciphers. To
3064 ensure backwards compatibility also if a cipher is specified using the
3065 --cipher option it is automatically added to this list. If both options
3066 are unset the default is AES-256-GCM:AES-128-GCM.
3067 OpenVPN 2.4 clients
3069 The negotiation support in OpenVPN 2.4 was the first iteration of the
3070 implementation and still had some quirks. Its main goal was "upgrade to
3071 AES-256-GCM when possible". An OpenVPN 2.4 client that is built
3072 against a crypto library that supports AES in GCM mode and does not
3073 have --ncp-disable will always announce support for AES-256-GCM and
3074 AES-128-GCM to a server by sending IV_NCP=2.
3075 This only causes a problem if --ncp-ciphers option has been changed
3077 from the default of AES-256-GCM:AES-128-GCM to a value that does not
3078 include these two ciphers. When a OpenVPN servers try to use
3079 AES-256-GCM or AES-128-GCM the connection will then fail. It is there‐
3080 fore recommended to always have the AES-256-GCM and AES-128-GCM ciphers
3081 to the --ncp-ciphers options to avoid this behaviour.
3082 OpenVPN 3 clients
3084 Clients based on the OpenVPN 3.x library (‐
3085 https://github.com/openvpn/openvpn3/) do not have a configurable
3086 --ncp-ciphers or --data-ciphers option. Instead these clients will an‐
3087 nounce support for all their supported AEAD ciphers (AES-256-GCM,
3088 AES-128-GCM and in newer versions also Chacha20-Poly1305).
3089 To support OpenVPN 3.x based clients at least one of these ciphers
3091 needs to be included in the server's --data-ciphers option.
3092 OpenVPN 2.3 and older clients (and clients with --ncp-disable)
3094 When a client without cipher negotiation support connects to a server
3095 the cipher specified with the --cipher option in the client configura‐
3096 tion must be included in the --data-ciphers option of the server to al‐
3097 low the client to connect. Otherwise the client will be sent the
3098 AUTH_FAILED message that indicates no shared cipher.
3099 If the client is 2.3 or older and has been configured with the --en‐
3101 able-small ./configure argument, using data-ciphers-fallback cipher in
3102 the server config file with the explicit cipher used by the client is
3103 necessary.
3104 OpenVPN 2.4 server
3106 When a client indicates support for AES-128-GCM and AES-256-GCM (with
3107 IV_NCP=2) an OpenVPN 2.4 server will send the first cipher of the
3108 --ncp-ciphers to the OpenVPN client regardless of what the cipher is.
3109 To emulate the behaviour of an OpenVPN 2.4 client as close as possible
3110 and have compatibility to a setup that depends on this quirk, adding
3111 AES-128-GCM and AES-256-GCM to the client's --data-ciphers option is
3112 required. OpenVPN 2.5+ will only announce the IV_NCP=2 flag if those
3113 ciphers are present.
3114 OpenVPN 2.3 and older servers (and servers with --ncp-disable)
3116 The cipher used by the server must be included in --data-ciphers to al‐
3117 low the client connecting to a server without cipher negotiation sup‐
3118 port. (For compatibility OpenVPN 2.5 will also accept the cipher set
3119 with --cipher)
3120 If the server is 2.3 or older and has been configured with the --en‐
3122 able-small ./configure argument, adding data-ciphers-fallback cipher to
3123 the client config with the explicit cipher used by the server is neces‐
3124 sary.
3125 Blowfish in CBC mode (BF-CBC) deprecation
3127 The --cipher option defaulted to BF-CBC in OpenVPN 2.4 and older ver‐
3128 sion. The default was never changed to ensure backwards compatibility.
3129 In OpenVPN 2.5 this behaviour has now been changed so that if the --ci‐
3130 pher is not explicitly set it does not allow the weak BF-CBC cipher any
3131 more and needs to explicitly added as --cipher BFC-CBC or added to
3132 --data-ciphers.
3133 We strongly recommend to switching away from BF-CBC to a more secure
3135 cipher as soon as possible instead.
3136
3138 OpenVPN consists of two sides of network configuration. One side is
3139 the link between the local and remote side, the other side is the vir‐
3140 tual network adapter (tun/tap device).
3141 Link Options
3143 This link options section covers options related to the connection be‐
3144 tween the local and the remote host.
3145 --bind keywords
3147 Bind to local address and port. This is the default unless any
3148 of --proto tcp-client , --http-proxy or --socks-proxy are used.
3149 If the optional ipv6only keyword is present OpenVPN will bind
3151 only to IPv6 (as opposed to IPv6 and IPv4) when a IPv6 socket is
3152 opened.
3153 --float
3155 Allow remote peer to change its IP address and/or port number,
3156 such as due to DHCP (this is the default if --remote is not
3157 used). --float when specified with --remote allows an OpenVPN
3158 session to initially connect to a peer at a known address, how‐
3159 ever if packets arrive from a new address and pass all authenti‐
3160 cation tests, the new address will take control of the session.
3161 This is useful when you are connecting to a peer which holds a
3162 dynamic address such as a dial-in user or DHCP client.
3163 Essentially, --float tells OpenVPN to accept authenticated pack‐
3165 ets from any address, not only the address which was specified
3166 in the --remote option.
3167 --fragment max
3169 Enable internal datagram fragmentation so that no UDP datagrams
3170 are sent which are larger than max bytes.
3171 The max parameter is interpreted in the same way as the
3173 --link-mtu parameter, i.e. the UDP packet size after encapsula‐
3174 tion overhead has been added in, but not including the UDP
3175 header itself.
3176 The --fragment option only makes sense when you are using the
3178 UDP protocol (--proto udp).
3179 --fragment adds 4 bytes of overhead per datagram.
3181 See the --mssfix option below for an important related option to
3183 --fragment.
3184 It should also be noted that this option is not meant to replace
3186 UDP fragmentation at the IP stack level. It is only meant as a
3187 last resort when path MTU discovery is broken. Using this option
3188 is less efficient than fixing path MTU discovery for your IP
3189 link and using native IP fragmentation instead.
3190 Having said that, there are circumstances where using OpenVPN's
3192 internal fragmentation capability may be your only option, such
3193 as tunneling a UDP multicast stream which requires fragmenta‐
3194 tion.
3195 --keepalive args
3197 A helper directive designed to simplify the expression of --ping
3198 and --ping-restart.
3199 Valid syntax:
3201 keepalive interval timeout
3203 This option can be used on both client and server side, but it
3205 is enough to add this on the server side as it will push appro‐
3206 priate --ping and --ping-restart options to the client. If used
3207 on both server and client, the values pushed from server will
3208 override the client local values.
3209 The timeout argument will be twice as long on the server side.
3211 This ensures that a timeout is detected on client side before
3212 the server side drops the connection.
3213 For example, --keepalive 10 60 expands as follows:
3215 if mode server:
3217 ping 10 # Argument: interval
3218 ping-restart 120 # Argument: timeout*2
3219 push "ping 10" # Argument: interval
3220 push "ping-restart 60" # Argument: timeout
3221 else
3222 ping 10 # Argument: interval
3223 ping-restart 60 # Argument: timeout
3224 --link-mtu n
3226 Sets an upper bound on the size of UDP packets which are sent
3227 between OpenVPN peers. It's best not to set this parameter un‐
3228 less you know what you're doing.
3229 --local host
3231 Local host name or IP address for bind. If specified, OpenVPN
3232 will bind to this address only. If unspecified, OpenVPN will
3233 bind to all interfaces.
3234 --lport port
3236 Set local TCP/UDP port number or name. Cannot be used together
3237 with --nobind option.
3238 --mark value
3240 Mark encrypted packets being sent with value. The mark value can
3241 be matched in policy routing and packetfilter rules. This option
3242 is only supported in Linux and does nothing on other operating
3243 systems.
3244 --mode m
3246 Set OpenVPN major mode. By default, OpenVPN runs in
3247 point-to-point mode (p2p). OpenVPN 2.0 introduces a new mode
3248 (server) which implements a multi-client server capability.
3249 --mssfix max
3251 Announce to TCP sessions running over the tunnel that they
3252 should limit their send packet sizes such that after OpenVPN has
3253 encapsulated them, the resulting UDP packet size that OpenVPN
3254 sends to its peer will not exceed max bytes. The default value
3255 is 1450.
3256 The max parameter is interpreted in the same way as the
3258 --link-mtu parameter, i.e. the UDP packet size after encapsula‐
3259 tion overhead has been added in, but not including the UDP
3260 header itself. Resulting packet would be at most 28 bytes
3261 larger for IPv4 and 48 bytes for IPv6 (20/40 bytes for IP header
3262 and 8 bytes for UDP header). Default value of 1450 allows IPv4
3263 packets to be transmitted over a link with MTU 1473 or higher
3264 without IP level fragmentation.
3265 The --mssfix option only makes sense when you are using the UDP
3267 protocol for OpenVPN peer-to-peer communication, i.e. --proto
3268 udp.
3269 --mssfix and --fragment can be ideally used together, where
3271 --mssfix will try to keep TCP from needing packet fragmentation
3272 in the first place, and if big packets come through anyhow (from
3273 protocols other than TCP), --fragment will internally fragment
3274 them.
3275 Both --fragment and --mssfix are designed to work around cases
3277 where Path MTU discovery is broken on the network path between
3278 OpenVPN peers.
3279 The usual symptom of such a breakdown is an OpenVPN connection
3281 which successfully starts, but then stalls during active usage.
3282 If --fragment and --mssfix are used together, --mssfix will take
3284 its default max parameter from the --fragment max option.
3285 Therefore, one could lower the maximum UDP packet size to 1300
3287 (a good first try for solving MTU-related connection problems)
3288 with the following options:
3289 --tun-mtu 1500 --fragment 1300 --mssfix
3291 --mtu-disc type
3293 Should we do Path MTU discovery on TCP/UDP channel? Only sup‐
3294 ported on OSes such as Linux that supports the necessary system
3295 call to set.
3296 Valid types:
3298 no Never send DF (Don't Fragment) frames
3300 maybe Use per-route hints
3302 yes Always DF (Don't Fragment)
3304 --mtu-test
3306 To empirically measure MTU on connection startup, add the
3307 --mtu-test option to your configuration. OpenVPN will send ping
3308 packets of various sizes to the remote peer and measure the
3309 largest packets which were successfully received. The --mtu-test
3310 process normally takes about 3 minutes to complete.
3311 --nobind
3313 Do not bind to local address and port. The IP stack will allo‐
3314 cate a dynamic port for returning packets. Since the value of
3315 the dynamic port could not be known in advance by a peer, this
3316 option is only suitable for peers which will be initiating con‐
3317 nections by using the --remote option.
3318 --passtos
3320 Set the TOS field of the tunnel packet to what the payload's TOS
3321 is.
3322 --ping n
3324 Ping remote over the TCP/UDP control channel if no packets have
3325 been sent for at least n seconds (specify --ping on both peers
3326 to cause ping packets to be sent in both directions since Open‐
3327 VPN ping packets are not echoed like IP ping packets). When used
3328 in one of OpenVPN's secure modes (where --secret, --tls-server
3329 or --tls-client is specified), the ping packet will be crypto‐
3330 graphically secure.
3331 This option has two intended uses:
3333 1. Compatibility with stateful firewalls. The periodic ping will
3335 ensure that a stateful firewall rule which allows OpenVPN UDP
3336 packets to pass will not time out.
3337 2. To provide a basis for the remote to test the existence of
3339 its peer using the --ping-exit option.
3340 --ping-exit n
3342 Causes OpenVPN to exit after n seconds pass without reception of
3343 a ping or other packet from remote. This option can be combined
3344 with --inactive, --ping and --ping-exit to create a two-tiered
3345 inactivity disconnect.
3346 For example,
3348 openvpn [options...] --inactive 3600 --ping 10 --ping-exit 60
3350 when used on both peers will cause OpenVPN to exit within 60
3352 seconds if its peer disconnects, but will exit after one hour if
3353 no actual tunnel data is exchanged.
3354 --ping-restart n
3356 Similar to --ping-exit, but trigger a SIGUSR1 restart after n
3357 seconds pass without reception of a ping or other packet from
3358 remote.
3359 This option is useful in cases where the remote peer has a dy‐
3361 namic IP address and a low-TTL DNS name is used to track the IP
3362 address using a service such as https://www.nsupdate.info/ + a
3363 dynamic DNS client such as ddclient.
3364 If the peer cannot be reached, a restart will be triggered,
3366 causing the hostname used with --remote to be re-resolved (if
3367 --resolv-retry is also specified).
3368 In server mode, --ping-restart, --inactive or any other type of
3370 internally generated signal will always be applied to individual
3371 client instance objects, never to whole server itself. Note also
3372 in server mode that any internally generated signal which would
3373 normally cause a restart, will cause the deletion of the client
3374 instance object instead.
3375 In client mode, the --ping-restart parameter is set to 120 sec‐
3377 onds by default. This default will hold until the client pulls a
3378 replacement value from the server, based on the --keepalive set‐
3379 ting in the server configuration. To disable the 120 second de‐
3380 fault, set --ping-restart 0 on the client.
3381 See the signals section below for more information on SIGUSR1.
3383 Note that the behavior of SIGUSR1 can be modified by the --per‐
3385 sist-tun, --persist-key, --persist-local-ip and --persist-re‐
3386 mote-ip options.
3387 Also note that --ping-exit and --ping-restart are mutually ex‐
3389 clusive and cannot be used together.
3390 --ping-timer-rem
3392 Run the --ping-exit / --ping-restart timer only if we have a re‐
3393 mote address. Use this option if you are starting the daemon in
3394 listen mode (i.e. without an explicit --remote peer), and you
3395 don't want to start clocking timeouts until a remote peer con‐
3396 nects.
3397 --proto p
3399 Use protocol p for communicating with remote host. p can be udp,
3400 tcp-client, or tcp-server. You can also limit OpenVPN to use
3401 only IPv4 or only IPv6 by specifying p as udp4, tcp4-client,
3402 tcp4-server or udp6, tcp6-client, tcp6-server, respectively.
3403 The default protocol is udp when --proto is not specified.
3405 For UDP operation, --proto udp should be specified on both
3407 peers.
3408 For TCP operation, one peer must use --proto tcp-server and the
3410 other must use --proto tcp-client. A peer started with
3411 tcp-server will wait indefinitely for an incoming connection. A
3412 peer started with tcp-client will attempt to connect, and if
3413 that fails, will sleep for 5 seconds (adjustable via the --con‐
3414 nect-retry option) and try again infinite or up to N retries
3415 (adjustable via the --connect-retry-max option). Both TCP client
3416 and server will simulate a SIGUSR1 restart signal if either side
3417 resets the connection.
3418 OpenVPN is designed to operate optimally over UDP, but TCP capa‐
3420 bility is provided for situations where UDP cannot be used. In
3421 comparison with UDP, TCP will usually be somewhat less efficient
3422 and less robust when used over unreliable or congested networks.
3423 This article outlines some of problems with tunneling IP over
3425 TCP: http://sites.inka.de/sites/bigred/devel/tcp-tcp.html
3426 There are certain cases, however, where using TCP may be advan‐
3428 tageous from a security and robustness perspective, such as tun‐
3429 neling non-IP or application-level UDP protocols, or tunneling
3430 protocols which don't possess a built-in reliability layer.
3431 --port port
3433 TCP/UDP port number or port name for both local and remote (sets
3434 both --lport and --rport options to given port). The current de‐
3435 fault of 1194 represents the official IANA port number assign‐
3436 ment for OpenVPN and has been used since version 2.0-beta17.
3437 Previous versions used port 5000 as the default.
3438 --rport port
3440 Set TCP/UDP port number or name used by the --remote option. The
3441 port can also be set directly using the --remote option.
3442 --replay-window args
3444 Modify the replay protection sliding-window size and time win‐
3445 dow.
3446 Valid syntax:
3448 replay-window n [t]
3450 Use a replay protection sliding-window of size n and a time win‐
3452 dow of t seconds.
3453 By default n is 64 (the IPSec default) and t is 15 seconds.
3455 This option is only relevant in UDP mode, i.e. when either
3457 --proto udp is specified, or no --proto option is specified.
3458 When OpenVPN tunnels IP packets over UDP, there is the possibil‐
3460 ity that packets might be dropped or delivered out of order. Be‐
3461 cause OpenVPN, like IPSec, is emulating the physical network
3462 layer, it will accept an out-of-order packet sequence, and will
3463 deliver such packets in the same order they were received to the
3464 TCP/IP protocol stack, provided they satisfy several con‐
3465 straints.
3466 a. The packet cannot be a replay (unless --no-replay is speci‐
3468 fied, which disables replay protection altogether).
3469 b. If a packet arrives out of order, it will only be accepted if
3471 the difference between its sequence number and the highest
3472 sequence number received so far is less than n.
3473 c. If a packet arrives out of order, it will only be accepted if
3475 it arrives no later than t seconds after any packet contain‐
3476 ing a higher sequence number.
3477 If you are using a network link with a large pipeline (meaning
3479 that the product of bandwidth and latency is high), you may want
3480 to use a larger value for n. Satellite links in particular often
3481 require this.
3482 If you run OpenVPN at --verb 4, you will see the message
3484 "PID_ERR replay-window backtrack occurred [x]" every time the
3485 maximum sequence number backtrack seen thus far increases. This
3486 can be used to calibrate n.
3487 There is some controversy on the appropriate method of handling
3489 packet reordering at the security layer.
3490 Namely, to what extent should the security layer protect the en‐
3492 capsulated protocol from attacks which masquerade as the kinds
3493 of normal packet loss and reordering that occur over IP net‐
3494 works?
3495 The IPSec and OpenVPN approach is to allow packet reordering
3497 within a certain fixed sequence number window.
3498 OpenVPN adds to the IPSec model by limiting the window size in
3500 time as well as sequence space.
3501 OpenVPN also adds TCP transport as an option (not offered by
3503 IPSec) in which case OpenVPN can adopt a very strict attitude
3504 towards message deletion and reordering: Don't allow it. Since
3505 TCP guarantees reliability, any packet loss or reordering event
3506 can be assumed to be an attack.
3507 In this sense, it could be argued that TCP tunnel transport is
3509 preferred when tunneling non-IP or UDP application protocols
3510 which might be vulnerable to a message deletion or reordering
3511 attack which falls within the normal operational parameters of
3512 IP networks.
3513 So I would make the statement that one should never tunnel a
3515 non-IP protocol or UDP application protocol over UDP, if the
3516 protocol might be vulnerable to a message deletion or reordering
3517 attack that falls within the normal operating parameters of what
3518 is to be expected from the physical IP layer. The problem is
3519 easily fixed by simply using TCP as the VPN transport layer.
3520 --replay-persist file
3522 Persist replay-protection state across sessions using file to
3523 save and reload the state.
3524 This option will strengthen protection against replay attacks,
3526 especially when you are using OpenVPN in a dynamic context (such
3527 as with --inetd) when OpenVPN sessions are frequently started
3528 and stopped.
3529 This option will keep a disk copy of the current replay protec‐
3531 tion state (i.e. the most recent packet timestamp and sequence
3532 number received from the remote peer), so that if an OpenVPN
3533 session is stopped and restarted, it will reject any replays of
3534 packets which were already received by the prior session.
3535 This option only makes sense when replay protection is enabled
3537 (the default) and you are using either --secret (shared-secret
3538 key mode) or TLS mode with --tls-auth.
3539 --socket-flags flags
3541 Apply the given flags to the OpenVPN transport socket. Cur‐
3542 rently, only TCP_NODELAY is supported.
3543 The TCP_NODELAY socket flag is useful in TCP mode, and causes
3545 the kernel to send tunnel packets immediately over the TCP con‐
3546 nection without trying to group several smaller packets into a
3547 larger packet. This can result in a considerably improvement in
3548 latency.
3549 This option is pushable from server to client, and should be
3551 used on both client and server for maximum effect.
3552 --tcp-nodelay
3554 This macro sets the TCP_NODELAY socket flag on the server as
3555 well as pushes it to connecting clients. The TCP_NODELAY flag
3556 disables the Nagle algorithm on TCP sockets causing packets to
3557 be transmitted immediately with low latency, rather than waiting
3558 a short period of time in order to aggregate several packets
3559 into a larger containing packet. In VPN applications over TCP,
3560 TCP_NODELAY is generally a good latency optimization.
3561 The macro expands as follows:
3563 if mode server:
3565 socket-flags TCP_NODELAY
3566 push "socket-flags TCP_NODELAY"
3567 Virtual Network Adapter (VPN interface)
3569 Options in this section relates to configuration of the virtual tun/tap
3570 network interface, including setting the VPN IP address and network
3571 routing.
3572 --bind-dev device
3574 (Linux only) Set device to bind the server socket to a Virtual
3575 Routing and Forwarding device
3576 --block-ipv6
3578 On the client, instead of sending IPv6 packets over the VPN tun‐
3579 nel, all IPv6 packets are answered with an ICMPv6 no route host
3580 message. On the server, all IPv6 packets from clients are an‐
3581 swered with an ICMPv6 no route to host message. This options is
3582 intended for cases when IPv6 should be blocked and other options
3583 are not available. --block-ipv6 will use the remote IPv6 as
3584 source address of the ICMPv6 packets if set, otherwise will use
3585 fe80::7 as source address.
3586 For this option to make sense you actually have to route traffic
3588 to the tun interface. The following example config block would
3589 send all IPv6 traffic to OpenVPN and answer all requests with no
3590 route to host, effectively blocking IPv6 (to avoid IPv6 connec‐
3591 tions from dual-stacked clients leaking around IPv4-only VPN
3592 services).
3593 Client config
3595 --ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1
3597 --redirect-gateway ipv6
3598 --block-ipv6
3599 Server config
3601 Push a "valid" ipv6 config to the client and block on the
3602 server
3603 --push "ifconfig-ipv6 fd15:53b6:dead::2/64 fd15:53b6:dead::1"
3605 --push "redirect-gateway ipv6"
3606 --block-ipv6
3607 Note: this option does not influence traffic sent from the
3609 server towards the client (neither on the server nor on the
3610 client side). This is not seen as necessary, as such traffic
3611 can be most easily avoided by not configuring IPv6 on the server
3612 tun, or setting up a server-side firewall rule.
3613 --dev device
3615 TUN/TAP virtual network device which can be tunX, tapX, null or
3616 an arbitrary name string (X can be omitted for a dynamic de‐
3617 vice.)
3618 See examples section below for an example on setting up a TUN
3620 device.
3621 You must use either tun devices on both ends of the connection
3623 or tap devices on both ends. You cannot mix them, as they repre‐
3624 sent different underlying network layers:
3625 tun devices encapsulate IPv4 or IPv6 (OSI Layer 3)
3627 tap devices encapsulate Ethernet 802.3 (OSI Layer 2).
3629 Valid syntaxes:
3631 dev tun2
3633 dev tap4
3634 dev ovpn
3635 When the device name starts with tun or tap, the device type is
3637 extracted automatically. Otherwise the --dev-type option needs
3638 to be added as well.
3639 --dev-node node
3641 Explicitly set the device node rather than using /dev/net/tun,
3642 /dev/tun, /dev/tap, etc. If OpenVPN cannot figure out whether
3643 node is a TUN or TAP device based on the name, you should also
3644 specify --dev-type tun or --dev-type tap.
3645 Under Mac OS X this option can be used to specify the default
3647 tun implementation. Using --dev-node utun forces usage of the
3648 native Darwin tun kernel support. Use --dev-node utunN to select
3649 a specific utun instance. To force using the tun.kext
3650 (/dev/tunX) use --dev-node tun. When not specifying a --dev-node
3651 option openvpn will first try to open utun, and fall back to
3652 tun.kext.
3653 On Windows systems, select the TAP-Win32 adapter which is named
3655 node in the Network Connections Control Panel or the raw GUID of
3656 the adapter enclosed by braces. The --show-adapters option under
3657 Windows can also be used to enumerate all available TAP-Win32
3658 adapters and will show both the network connections control
3659 panel name and the GUID for each TAP-Win32 adapter.
3660 --dev-type device-type
3662 Which device type are we using? device-type should be tun (OSI
3663 Layer 3) or tap (OSI Layer 2). Use this option only if the
3664 TUN/TAP device used with --dev does not begin with tun or tap.
3665 --dhcp-option args
3667 Set additional network parameters on supported platforms. May be
3668 specified on the client or pushed from the server. On Windows
3669 these options are handled by the tap-windows6 driver by default
3670 or directly by OpenVPN if dhcp is disabled or the wintun driver
3671 is in use. The OpenVPN for Android client also handles them in‐
3672 ternally.
3673 On all other platforms these options are only saved in the
3675 client's environment under the name foreign_option_{n} before
3676 the --up script is called. A plugin or an --up script must be
3677 used to pick up and interpret these as required. Many Linux dis‐
3678 tributions include such scripts and some third-party user inter‐
3679 faces such as tunnelblick also come with scripts that process
3680 these options.
3681 Valid syntax:
3683 dhcp-options type [parm]
3685 DOMAIN name
3687 Set Connection-specific DNS Suffix to name.
3688 ADAPTER_DOMAIN_SUFFIX name
3690 Alias to DOMAIN. This is a compatibility option, it
3691 should not be used in new deployments.
3692 DOMAIN-SEARCH name
3694 Add name to the domain search list. Repeat this option
3695 to add more entries. Up to 10 domains are supported.
3696 DNS address
3698 Set primary domain name server IPv4 or IPv6 address. Re‐
3699 peat this option to set secondary DNS server addresses.
3700 Note: DNS IPv6 servers are currently set using netsh (the
3702 existing DHCP code can only do IPv4 DHCP, and that proto‐
3703 col only permits IPv4 addresses anywhere). The option
3704 will be put into the environment, so an --up script could
3705 act upon it if needed.
3706 WINS address
3708 Set primary WINS server address (NetBIOS over TCP/IP Name
3709 Server). Repeat this option to set secondary WINS server
3710 addresses.
3711 NBDD address
3713 Set primary NBDD server address (NetBIOS over TCP/IP
3714 Datagram Distribution Server). Repeat this option to set
3715 secondary NBDD server addresses.
3716 NTP address
3718 Set primary NTP server address (Network Time Protocol).
3719 Repeat this option to set secondary NTP server addresses.
3720 NBT type
3722 Set NetBIOS over TCP/IP Node type. Possible options:
3723 1 b-node (broadcasts)
3725 2 p-node (point-to-point name queries to a WINS
3727 server)
3728 4 m-node (broadcast then query name server)
3730 8 h-node (query name server, then broadcast).
3732 NBS scope-id
3734 Set NetBIOS over TCP/IP Scope. A NetBIOS Scope ID pro‐
3735 vides an extended naming service for the NetBIOS over
3736 TCP/IP (Known as NBT) module. The primary purpose of a
3737 NetBIOS scope ID is to isolate NetBIOS traffic on a sin‐
3738 gle network to only those nodes with the same NetBIOS
3739 scope ID. The NetBIOS scope ID is a character string that
3740 is appended to the NetBIOS name. The NetBIOS scope ID on
3741 two hosts must match, or the two hosts will not be able
3742 to communicate. The NetBIOS Scope ID also allows comput‐
3743 ers to use the same computer name, as they have different
3744 scope IDs. The Scope ID becomes a part of the NetBIOS
3745 name, making the name unique. (This description of Net‐
3746 BIOS scopes courtesy of NeonSurge@abyss.com)
3747 DISABLE-NBT
3749 Disable Netbios-over-TCP/IP.
3750 --ifconfig args
3752 Set TUN/TAP adapter parameters. It requires the IP address of
3753 the local VPN endpoint. For TUN devices in point-to-point mode,
3754 the next argument must be the VPN IP address of the remote VPN
3755 endpoint. For TAP devices, or TUN devices used with --topology
3756 subnet, the second argument is the subnet mask of the virtual
3757 network segment which is being created or connected to.
3758 For TUN devices, which facilitate virtual point-to-point IP con‐
3760 nections (when used in --topology net30 or p2p mode), the proper
3761 usage of --ifconfig is to use two private IP addresses which are
3762 not a member of any existing subnet which is in use. The IP ad‐
3763 dresses may be consecutive and should have their order reversed
3764 on the remote peer. After the VPN is established, by pinging
3765 rn, you will be pinging across the VPN.
3766 For TAP devices, which provide the ability to create virtual
3768 ethernet segments, or TUN devices in --topology subnet mode
3769 (which create virtual "multipoint networks"), --ifconfig is used
3770 to set an IP address and subnet mask just as a physical ethernet
3771 adapter would be similarly configured. If you are attempting to
3772 connect to a remote ethernet bridge, the IP address and subnet
3773 should be set to values which would be valid on the the bridged
3774 ethernet segment (note also that DHCP can be used for the same
3775 purpose).
3776 This option, while primarily a proxy for the ifconfig(8) com‐
3778 mand, is designed to simplify TUN/TAP tunnel configuration by
3779 providing a standard interface to the different ifconfig imple‐
3780 mentations on different platforms.
3781 --ifconfig parameters which are IP addresses can also be speci‐
3783 fied as a DNS or /etc/hosts file resolvable name.
3784 For TAP devices, --ifconfig should not be used if the TAP inter‐
3786 face will be getting an IP address lease from a DHCP server.
3787 Examples:
3789 # tun device in net30/p2p mode
3791 ifconfig 10.8.0.2 10.8.0.1
3792 # tun/tap device in subnet mode
3794 ifconfig 10.8.0.2 255.255.255.0
3795 --ifconfig-ipv6 args
3797 Configure an IPv6 address on the tun device.
3798 Valid syntax:
3800 ifconfig-ipv6 ipv6addr/bits [ipv6remote]
3802 The ipv6addr/bits argument is the IPv6 address to use. The sec‐
3804 ond parameter is used as route target for --route-ipv6 if no
3805 gateway is specified.
3806 The --topology option has no influence with --ifconfig-ipv6
3808 --ifconfig-noexec
3810 Don't actually execute ifconfig/netsh commands, instead pass
3811 --ifconfig parameters to scripts using environmental variables.
3812 --ifconfig-nowarn
3814 Don't output an options consistency check warning if the --if‐
3815 config option on this side of the connection doesn't match the
3816 remote side. This is useful when you want to retain the overall
3817 benefits of the options consistency check (also see --dis‐
3818 able-occ option) while only disabling the ifconfig component of
3819 the check.
3820 For example, if you have a configuration where the local host
3822 uses --ifconfig but the remote host does not, use --ifcon‐
3823 fig-nowarn on the local host.
3824 This option will also silence warnings about potential address
3826 conflicts which occasionally annoy more experienced users by
3827 triggering "false positive" warnings.
3828 --lladdr address
3830 Specify the link layer address, more commonly known as the MAC
3831 address. Only applied to TAP devices.
3832 --persist-tun
3834 Don't close and reopen TUN/TAP device or run up/down scripts
3835 across SIGUSR1 or --ping-restart restarts.
3836 SIGUSR1 is a restart signal similar to SIGHUP, but which offers
3838 finer-grained control over reset options.
3839 --redirect-gateway flags
3841 Automatically execute routing commands to cause all outgoing IP
3842 traffic to be redirected over the VPN. This is a client-side op‐
3843 tion.
3844 This option performs three steps:
3846 1. Create a static route for the --remote address which forwards
3848 to the pre-existing default gateway. This is done so that [1m(3)
3849 will not create a routing loop.
3850 2. Delete the default gateway route.
3852 3. Set the new default gateway to be the VPN endpoint address
3854 (derived either from --route-gateway or the second parameter
3855 to --ifconfig when --dev tun is specified).
3856 When the tunnel is torn down, all of the above steps are re‐
3858 versed so that the original default route is restored.
3859 Option flags:
3861 local Add the local flag if both OpenVPN peers are directly
3863 connected via a common subnet, such as with wireless. The
3864 local flag will cause step [1m(1) above to be omitted.
3865 autolocal
3867 Try to automatically determine whether to enable local
3868 flag above.
3869 def1 Use this flag to override the default gateway by using
3871 0.0.0.0/1 and 128.0.0.0/1 rather than 0.0.0.0/0. This has
3872 the benefit of overriding but not wiping out the original
3873 default gateway.
3874 bypass-dhcp
3876 Add a direct route to the DHCP server (if it is non-lo‐
3877 cal) which bypasses the tunnel (Available on Windows
3878 clients, may not be available on non-Windows clients).
3879 bypass-dns
3881 Add a direct route to the DNS server(s) (if they are
3882 non-local) which bypasses the tunnel (Available on Win‐
3883 dows clients, may not be available on non-Windows
3884 clients).
3885 block-local
3887 Block access to local LAN when the tunnel is active, ex‐
3888 cept for the LAN gateway itself. This is accomplished by
3889 routing the local LAN (except for the LAN gateway ad‐
3890 dress) into the tunnel.
3891 ipv6 Redirect IPv6 routing into the tunnel. This works similar
3893 to the def1 flag, that is, more specific IPv6 routes are
3894 added (2000::/4, 3000::/4), covering the whole IPv6 uni‐
3895 cast space.
3896 !ipv4 Do not redirect IPv4 traffic - typically used in the flag
3898 pair ipv6 !ipv4 to redirect IPv6-only.
3899 --redirect-private flags
3901 Like --redirect-gateway, but omit actually changing the default
3902 gateway. Useful when pushing private subnets.
3903 --route args
3905 Add route to routing table after connection is established. Mul‐
3906 tiple routes can be specified. Routes will be automatically torn
3907 down in reverse order prior to TUN/TAP device close.
3908 Valid syntaxes:
3910 route network/IP
3912 route network/IP netmask
3913 route network/IP netmask gateway
3914 route network/IP netmask gateway metric
3915 This option is intended as a convenience proxy for the route(8)
3917 shell command, while at the same time providing portable seman‐
3918 tics across OpenVPN's platform space.
3919 netmask
3921 defaults to 255.255.255.255 when not given
3922 gateway
3924 default taken from --route-gateway or the second parame‐
3925 ter to --ifconfig when --dev tun is specified.
3926 metric default taken from --route-metric if set, otherwise 0.
3928 The default can be specified by leaving an option blank or set‐
3930 ting it to default.
3931 The network and gateway parameters can also be specified as a
3933 DNS or /etc/hosts file resolvable name, or as one of three spe‐
3934 cial keywords:
3935 vpn_gateway
3937 The remote VPN endpoint address (derived either from
3938 --route-gateway or the second parameter to --ifconfig
3939 when --dev tun is specified).
3940 net_gateway
3942 The pre-existing IP default gateway, read from the rout‐
3943 ing table (not supported on all OSes).
3944 remote_host
3946 The --remote address if OpenVPN is being run in client
3947 mode, and is undefined in server mode.
3948 --route-delay args
3950 Valid syntaxes:
3951 route-delay
3953 route-delay n
3954 route-delay n m
3955 Delay n seconds (default 0) after connection establishment, be‐
3957 fore adding routes. If n is 0, routes will be added immediately
3958 upon connection establishment. If --route-delay is omitted,
3959 routes will be added immediately after TUN/TAP device open and
3960 --up script execution, before any --user or --group privilege
3961 downgrade (or --chroot execution.)
3962 This option is designed to be useful in scenarios where DHCP is
3964 used to set tap adapter addresses. The delay will give the DHCP
3965 handshake time to complete before routes are added.
3966 On Windows, --route-delay tries to be more intelligent by wait‐
3968 ing w seconds (default 30 by default) for the TAP-Win32 adapter
3969 to come up before adding routes.
3970 --route-ipv6 args
3972 Setup IPv6 routing in the system to send the specified IPv6 net‐
3973 work into OpenVPN's tun.
3974 Valid syntax:
3976 route-ipv6 ipv6addr/bits [gateway] [metric]
3978 The gateway parameter is only used for IPv6 routes across tap
3980 devices, and if missing, the ipv6remote field from --ifcon‐
3981 fig-ipv6 or --route-ipv6-gateway is used.
3982 --route-gateway arg
3984 Specify a default gateway for use with --route.
3985 If dhcp is specified as the parameter, the gateway address will
3987 be extracted from a DHCP negotiation with the OpenVPN
3988 server-side LAN.
3989 Valid syntaxes:
3991 route-gateway gateway
3993 route-gateway dhcp
3994 --route-ipv6-gateway gw
3996 Specify a default gateway gw for use with --route-ipv6.
3997 --route-metric m
3999 Specify a default metric m for use with --route.
4000 --route-noexec
4002 Don't add or remove routes automatically. Instead pass routes to
4003 --route-up script using environmental variables.
4004 --route-nopull
4006 When used with --client or --pull, accept options pushed by
4007 server EXCEPT for routes, block-outside-dns and dhcp options
4008 like DNS servers.
4009 When used on the client, this option effectively bars the server
4011 from adding routes to the client's routing table, however note
4012 that this option still allows the server to set the TCP/IP prop‐
4013 erties of the client's TUN/TAP interface.
4014 --topology mode
4016 Configure virtual addressing topology when running in --dev tun
4017 mode. This directive has no meaning in --dev tap mode, which al‐
4018 ways uses a subnet topology.
4019 If you set this directive on the server, the --server and
4021 --server-bridge directives will automatically push your chosen
4022 topology setting to clients as well. This directive can also be
4023 manually pushed to clients. Like the --dev directive, this di‐
4024 rective must always be compatible between client and server.
4025 mode can be one of:
4027 net30 Use a point-to-point topology, by allocating one /30 sub‐
4029 net per client. This is designed to allow point-to-point
4030 semantics when some or all of the connecting clients
4031 might be Windows systems. This is the default on OpenVPN
4032 2.0.
4033 p2p Use a point-to-point topology where the remote endpoint
4035 of the client's tun interface always points to the local
4036 endpoint of the server's tun interface. This mode allo‐
4037 cates a single IP address per connecting client. Only use
4038 when none of the connecting clients are Windows systems.
4039 subnet Use a subnet rather than a point-to-point topology by
4041 configuring the tun interface with a local IP address and
4042 subnet mask, similar to the topology used in --dev tap
4043 and ethernet bridging mode. This mode allocates a single
4044 IP address per connecting client and works on Windows as
4045 well. Only available when server and clients are OpenVPN
4046 2.1 or higher, or OpenVPN 2.0.x which has been manually
4047 patched with the --topology directive code. When used on
4048 Windows, requires version 8.2 or higher of the TAP-Win32
4049 driver. When used on *nix, requires that the tun driver
4050 supports an ifconfig(8) command which sets a subnet in‐
4051 stead of a remote endpoint IP address.
4052 Note: Using --topology subnet changes the interpretation of the
4054 arguments of --ifconfig to mean "address netmask", no longer
4055 "local remote".
4056 --tun-mtu n
4058 Take the TUN device MTU to be n and derive the link MTU from it
4059 (default 1500). In most cases, you will probably want to leave
4060 this parameter set to its default value.
4061 The MTU (Maximum Transmission Units) is the maximum datagram
4063 size in bytes that can be sent unfragmented over a particular
4064 network path. OpenVPN requires that packets on the control and
4065 data channels be sent unfragmented.
4066 MTU problems often manifest themselves as connections which hang
4068 during periods of active usage.
4069 It's best to use the --fragment and/or --mssfix options to deal
4071 with MTU sizing issues.
4072 --tun-mtu-extra n
4074 Assume that the TUN/TAP device might return as many as n bytes
4075 more than the --tun-mtu size on read. This parameter defaults to
4076 0, which is sufficient for most TUN devices. TAP devices may in‐
4077 troduce additional overhead in excess of the MTU size, and a
4078 setting of 32 is the default when TAP devices are used. This pa‐
4079 rameter only controls internal OpenVPN buffer sizing, so there
4080 is no transmission overhead associated with using a larger
4081 value.
4082 TUN/TAP standalone operations
4084 These two standalone operations will require --dev and optionally
4085 --user and/or --group.
4086 --mktun
4088 (Standalone) Create a persistent tunnel on platforms which sup‐
4089 port them such as Linux. Normally TUN/TAP tunnels exist only for
4090 the period of time that an application has them open. This op‐
4091 tion takes advantage of the TUN/TAP driver's ability to build
4092 persistent tunnels that live through multiple instantiations of
4093 OpenVPN and die only when they are deleted or the machine is re‐
4094 booted.
4095 One of the advantages of persistent tunnels is that they elimi‐
4097 nate the need for separate --up and --down scripts to run the
4098 appropriate ifconfig(8) and route(8) commands. These commands
4099 can be placed in the the same shell script which starts or ter‐
4100 minates an OpenVPN session.
4101 Another advantage is that open connections through the
4103 TUN/TAP-based tunnel will not be reset if the OpenVPN peer
4104 restarts. This can be useful to provide uninterrupted connectiv‐
4105 ity through the tunnel in the event of a DHCP reset of the
4106 peer's public IP address (see the --ipchange option above).
4107 One disadvantage of persistent tunnels is that it is harder to
4109 automatically configure their MTU value (see --link-mtu and
4110 --tun-mtu above).
4111 On some platforms such as Windows, TAP-Win32 tunnels are persis‐
4113 tent by default.
4114 --rmtun
4116 (Standalone) Remove a persistent tunnel.
4117 Virtual Routing and Forwarding
4119 Options in this section relates to configuration of virtual routing and
4120 forwarding in combination with the underlying operating system.
4121 As of today this is only supported on Linux, a kernel >= 4.9 is recom‐
4123 mended.
4124 This could come in handy when for example the external network should
4126 be only used as a means to connect to some VPN endpoints and all regu‐
4127 lar traffic should only be routed through any tunnel(s). This could be
4128 achieved by setting up a VRF and configuring the interface connected to
4129 the external network to be part of the VRF. The examples below will
4130 cover this setup.
4131 Another option would be to put the tun/tap interface into a VRF. This
4133 could be done by an up-script which uses the ip link set command shown
4134 below.
4135 VRF setup with iproute2
4137 Create VRF vrf_external and map it to routing table 1023
4138 ip link add vrf_external type vrf table 1023
4140 Move eth0 into vrf_external
4142 ip link set master vrf_external dev eth0
4144 Any prefixes configured on eth0 will be moved from the :code`main`
4146 routing table into routing table 1023
4147 VRF setup with ifupdown
4149 For Debian based Distributions ifupdown2 provides an almost drop-in re‐
4150 placement for ifupdown including VRFs and other features. A configura‐
4151 tion for an interface eth0 being part of VRF code:vrf_external could
4152 look like this:
4153 auto eth0
4155 iface eth0
4156 address 192.0.2.42/24
4157 address 2001:db8:08:15::42/64
4158 gateway 192.0.2.1
4159 gateway 2001:db8:08:15::1
4160 vrf vrf_external
4161 auto vrf_external
4163 iface vrf_external
4164 vrf-table 1023
4165 OpenVPN configuration
4167 The OpenVPN configuration needs to contain this line:
4168 bind-dev vrf_external
4170 Further reading
4172 Wikipedia has nice page one VRFs:
4173 https://en.wikipedia.org/wiki/Virtual_routing_and_forwarding
4174 This talk from the Network Track of FrOSCon 2018 provides an overview
4176 about advanced layer 2 and layer 3 features of Linux
4177 • Slides:
4179 https://www.slideshare.net/BarbarossaTM/l2l3-fr-fortgeschrittene-helle-und-dunkle-magie-im-linuxnetzwerkstack
4180 • Video (german):
4182 https://media.ccc.de/v/froscon2018-2247-l2_l3_fur_fortgeschrittene_-_helle_und_dunkle_magie_im_linux-netzwerkstack
4183
4185 OpenVPN can execute external scripts in various phases of the lifetime
4186 of the OpenVPN process.
4187 Script Order of Execution
4189 1. --up
4190 Executed after TCP/UDP socket bind and TUN/TAP open.
4192 2. --tls-verify
4194 Executed when we have a still untrusted remote peer.
4196 3. --ipchange
4198 Executed after connection authentication, or remote IP address
4200 change.
4201 4. --client-connect
4203 Executed in --mode server mode immediately after client authentica‐
4205 tion.
4206 5. --route-up
4208 Executed after connection authentication, either immediately after,
4210 or some number of seconds after as defined by the --route-delay op‐
4211 tion.
4212 6. --route-pre-down
4214 Executed right before the routes are removed.
4216 7. --client-disconnect
4218 Executed in --mode server mode on client instance shutdown.
4220 8. --down
4222 Executed after TCP/UDP and TUN/TAP close.
4224 9. --learn-address
4226 Executed in --mode server mode whenever an IPv4 address/route or
4228 MAC address is added to OpenVPN's internal routing table.
4229 10. --auth-user-pass-verify
4231 Executed in --mode server mode on new client connections, when the
4233 client is still untrusted.
4234 SCRIPT HOOKS
4236 --auth-user-pass-verify args
4237 Require the client to provide a username/password (possibly in
4238 addition to a client certificate) for authentication.
4239 Valid syntax:
4241 auth-user-pass-verify cmd method
4243 OpenVPN will run command cmd to validate the username/password
4245 provided by the client.
4246 cmd consists of a path to a script (or executable program), op‐
4248 tionally followed by arguments. The path and arguments may be
4249 single- or double-quoted and/or escaped using a backslash, and
4250 should be separated by one or more spaces.
4251 If method is set to via-env, OpenVPN will call script with the
4253 environmental variables username and password set to the user‐
4254 name/password strings provided by the client. Beware that this
4255 method is insecure on some platforms which make the environment
4256 of a process publicly visible to other unprivileged processes.
4257 If method is set to via-file, OpenVPN will write the username
4259 and password to the first two lines of a temporary file. The
4260 filename will be passed as an argument to script, and the file
4261 will be automatically deleted by OpenVPN after the script re‐
4262 turns. The location of the temporary file is controlled by the
4263 --tmp-dir option, and will default to the current directory if
4264 unspecified. For security, consider setting --tmp-dir to a
4265 volatile storage medium such as /dev/shm (if available) to pre‐
4266 vent the username/password file from touching the hard drive.
4267 The script should examine the username and password, returning a
4269 success exit code (0) if the client's authentication request is
4270 to be accepted, or a failure code (1) to reject the client.
4271 This directive is designed to enable a plugin-style interface
4273 for extending OpenVPN's authentication capabilities.
4274 To protect against a client passing a maliciously formed user‐
4276 name or password string, the username string must consist only
4277 of these characters: alphanumeric, underbar ('_'), dash ('-'),
4278 dot ('.'), or at ('@'). The password string can consist of any
4279 printable characters except for CR or LF. Any illegal characters
4280 in either the username or password string will be converted to
4281 underbar ('_').
4282 Care must be taken by any user-defined scripts to avoid creating
4284 a security vulnerability in the way that these strings are han‐
4285 dled. Never use these strings in such a way that they might be
4286 escaped or evaluated by a shell interpreter.
4287 For a sample script that performs PAM authentication, see sam‐
4289 ple-scripts/auth-pam.pl in the OpenVPN source distribution.
4290 --client-connect cmd
4292 Run command cmd on client connection.
4293 cmd consists of a path to a script (or executable program), op‐
4295 tionally followed by arguments. The path and arguments may be
4296 single- or double-quoted and/or escaped using a backslash, and
4297 should be separated by one or more spaces.
4298 The command is passed the common name and IP address of the
4300 just-authenticated client as environmental variables (see envi‐
4301 ronmental variable section below). The command is also passed
4302 the pathname of a freshly created temporary file as the last ar‐
4303 gument (after any arguments specified in cmd ), to be used by
4304 the command to pass dynamically generated config file directives
4305 back to OpenVPN.
4306 If the script wants to generate a dynamic config file to be ap‐
4308 plied on the server when the client connects, it should write it
4309 to the file named by the last argument.
4310 See the --client-config-dir option below for options which can
4312 be legally used in a dynamically generated config file.
4313 Note that the return value of script is significant. If script
4315 returns a non-zero error status, it will cause the client to be
4316 disconnected.
4317 If a --client-connect wants to defer the generating of the con‐
4319 figuration then the script needs to use the client_connect_de‐
4320 ferred_file and client_connect_config_file environment vari‐
4321 ables, and write status accordingly into these files. See the
4322 Environmental Variables section for more details.
4323 --client-disconnect cmd
4325 Like --client-connect but called on client instance shutdown.
4326 Will not be called unless the --client-connect script and plug‐
4327 ins (if defined) were previously called on this instance with
4328 successful (0) status returns.
4329 The exception to this rule is if the --client-disconnect command
4331 or plugins are cascaded, and at least one client-connect func‐
4332 tion succeeded, then ALL of the client-disconnect functions for
4333 scripts and plugins will be called on client instance object
4334 deletion, even in cases where some of the related client-connect
4335 functions returned an error status.
4336 The --client-disconnect command is not passed any extra argu‐
4338 ments (only those arguments specified in cmd, if any).
4339 --down cmd
4341 Run command cmd after TUN/TAP device close (post --user UID
4342 change and/or --chroot ). cmd consists of a path to script (or
4343 executable program), optionally followed by arguments. The path
4344 and arguments may be single- or double-quoted and/or escaped us‐
4345 ing a backslash, and should be separated by one or more spaces.
4346 Called with the same parameters and environmental variables as
4348 the --up option above.
4349 Note that if you reduce privileges by using --user and/or
4351 --group, your --down script will also run at reduced privilege.
4352 --down-pre
4354 Call --down cmd/script before, rather than after, TUN/TAP close.
4355 --ipchange cmd
4357 Run command cmd when our remote ip-address is initially authen‐
4358 ticated or changes.
4359 cmd consists of a path to a script (or executable program), op‐
4361 tionally followed by arguments. The path and arguments may be
4362 single- or double-quoted and/or escaped using a backslash, and
4363 should be separated by one or more spaces.
4364 When cmd is executed two arguments are appended after any argu‐
4366 ments specified in cmd , as follows:
4367 cmd ip address port number
4369 Don't use --ipchange in --mode server mode. Use a --client-con‐
4371 nect script instead.
4372 See the Environmental Variables section below for additional pa‐
4374 rameters passed as environmental variables.
4375 If you are running in a dynamic IP address environment where the
4377 IP addresses of either peer could change without notice, you can
4378 use this script, for example, to edit the /etc/hosts file with
4379 the current address of the peer. The script will be run every
4380 time the remote peer changes its IP address.
4381 Similarly if our IP address changes due to DHCP, we should con‐
4383 figure our IP address change script (see man page for dhcpcd(8))
4384 to deliver a SIGHUP or SIGUSR1 signal to OpenVPN. OpenVPN will
4385 then re-establish a connection with its most recently authenti‐
4386 cated peer on its new IP address.
4387 --learn-address cmd
4389 Run command cmd to validate client virtual addresses or routes.
4390 cmd consists of a path to a script (or executable program), op‐
4392 tionally followed by arguments. The path and arguments may be
4393 single- or double-quoted and/or escaped using a backslash, and
4394 should be separated by one or more spaces.
4395 Three arguments will be appended to any arguments in cmd as fol‐
4397 lows:
4398 $1 - [operation]
4400 "add", "update", or "delete" based on whether or not the
4401 address is being added to, modified, or deleted from
4402 OpenVPN's internal routing table.
4403 $2 - [address]
4405 The address being learned or unlearned. This can be an
4406 IPv4 address such as "198.162.10.14", an IPv4 subnet such
4407 as "198.162.10.0/24", or an ethernet MAC address (when
4408 --dev tap is being used) such as "00:FF:01:02:03:04".
4409 $3 - [common name]
4411 The common name on the certificate associated with the
4412 client linked to this address. Only present for "add" or
4413 "update" operations, not "delete".
4414 On "add" or "update" methods, if the script returns a failure
4416 code (non-zero), OpenVPN will reject the address and will not
4417 modify its internal routing table.
4418 Normally, the cmd script will use the information provided above
4420 to set appropriate firewall entries on the VPN TUN/TAP inter‐
4421 face. Since OpenVPN provides the association between virtual IP
4422 or MAC address and the client's authenticated common name, it
4423 allows a user-defined script to configure firewall access poli‐
4424 cies with regard to the client's high-level common name, rather
4425 than the low level client virtual addresses.
4426 --route-up cmd
4428 Run command cmd after routes are added, subject to --route-de‐
4429 lay.
4430 cmd consists of a path to a script (or executable program), op‐
4432 tionally followed by arguments. The path and arguments may be
4433 single- or double-quoted and/or escaped using a backslash, and
4434 should be separated by one or more spaces.
4435 See the Environmental Variables section below for additional pa‐
4437 rameters passed as environmental variables.
4438 --route-pre-down cmd
4440 Run command cmd before routes are removed upon disconnection.
4441 cmd consists of a path to a script (or executable program), op‐
4443 tionally followed by arguments. The path and arguments may be
4444 single- or double-quoted and/or escaped using a backslash, and
4445 should be separated by one or more spaces.
4446 See the Environmental Variables section below for additional pa‐
4448 rameters passed as environmental variables.
4449 --setenv args
4451 Set a custom environmental variable name=value to pass to
4452 script.
4453 Valid syntaxes:
4455 setenv name value
4457 setenv FORWARD_COMPATIBLE 1
4458 setenv opt config_option
4459 By setting FORWARD_COMPATIBLE to 1, the config file syntax
4461 checking is relaxed so that unknown directives will trigger a
4462 warning but not a fatal error, on the assumption that a given
4463 unknown directive might be valid in future OpenVPN versions.
4464 This option should be used with caution, as there are good secu‐
4466 rity reasons for having OpenVPN fail if it detects problems in a
4467 config file. Having said that, there are valid reasons for
4468 wanting new software features to gracefully degrade when encoun‐
4469 tered by older software versions.
4470 It is also possible to tag a single directive so as not to trig‐
4472 ger a fatal error if the directive isn't recognized. To do this,
4473 prepend the following before the directive: setenv opt
4474 Versions prior to OpenVPN 2.3.3 will always ignore options set
4476 with the setenv opt directive.
4477 See also --ignore-unknown-option
4479 --setenv-safe args
4481 Set a custom environmental variable OPENVPN_name to value to
4482 pass to scripts.
4483 Valid syntaxes:
4485 setenv-safe name value
4487 This directive is designed to be pushed by the server to
4489 clients, and the prepending of OPENVPN_ to the environmental
4490 variable is a safety precaution to prevent a LD_PRELOAD style
4491 attack from a malicious or compromised server.
4492 --tls-verify cmd
4494 Run command cmd to verify the X509 name of a pending TLS connec‐
4495 tion that has otherwise passed all other tests of certification
4496 (except for revocation via --crl-verify directive; the revoca‐
4497 tion test occurs after the --tls-verify test).
4498 cmd should return 0 to allow the TLS handshake to proceed, or 1
4500 to fail.
4501 cmd consists of a path to a script (or executable program), op‐
4503 tionally followed by arguments. The path and arguments may be
4504 single- or double-quoted and/or escaped using a backslash, and
4505 should be separated by one or more spaces.
4506 When cmd is executed two arguments are appended after any argu‐
4508 ments specified in cmd, as follows:
4509 cmd certificate_depth subject
4511 These arguments are, respectively, the current certificate depth
4513 and the X509 subject distinguished name (dn) of the peer.
4514 This feature is useful if the peer you want to trust has a cer‐
4516 tificate which was signed by a certificate authority who also
4517 signed many other certificates, where you don't necessarily want
4518 to trust all of them, but rather be selective about which peer
4519 certificate you will accept. This feature allows you to write a
4520 script which will test the X509 name on a certificate and decide
4521 whether or not it should be accepted. For a simple perl script
4522 which will test the common name field on the certificate, see
4523 the file verify-cn in the OpenVPN distribution.
4524 See the Environmental Variables section below for additional pa‐
4526 rameters passed as environmental variables.
4527 --up cmd
4529 Run command cmd after successful TUN/TAP device open (pre --user
4530 UID change).
4531 cmd consists of a path to a script (or executable program), op‐
4533 tionally followed by arguments. The path and arguments may be
4534 single- or double-quoted and/or escaped using a backslash, and
4535 should be separated by one or more spaces.
4536 The up command is useful for specifying route commands which
4538 route IP traffic destined for private subnets which exist at the
4539 other end of the VPN connection into the tunnel.
4540 For --dev tun execute as:
4542 cmd tun_dev tun_mtu link_mtu ifconfig_local_ip ifconfig_remote_ip [init | restart]
4544 For --dev tap execute as:
4546 cmd tap_dev tap_mtu link_mtu ifconfig_local_ip ifconfig_netmask [init | restart]
4548 See the Environmental Variables section below for additional pa‐
4550 rameters passed as environmental variables.
4551 Note that if cmd includes arguments, all OpenVPN-generated argu‐
4553 ments will be appended to them to build an argument list with
4554 which the executable will be called.
4555 Typically, cmd will run a script to add routes to the tunnel.
4557 Normally the up script is called after the TUN/TAP device is
4559 opened. In this context, the last command line parameter passed
4560 to the script will be init. If the --up-restart option is also
4561 used, the up script will be called for restarts as well. A
4562 restart is considered to be a partial reinitialization of Open‐
4563 VPN where the TUN/TAP instance is preserved (the --persist-tun
4564 option will enable such preservation). A restart can be gener‐
4565 ated by a SIGUSR1 signal, a --ping-restart timeout, or a connec‐
4566 tion reset when the TCP protocol is enabled with the --proto op‐
4567 tion. If a restart occurs, and --up-restart has been specified,
4568 the up script will be called with restart as the last parameter.
4569 NOTE: On restart, OpenVPN will not pass the full set of envi‐
4571 ronment variables to the script. Namely, everything re‐
4572 lated to routing and gateways will not be passed, as
4573 nothing needs to be done anyway - all the routing setup
4574 is already in place. Additionally, the up-restart script
4575 will run with the downgraded UID/GID settings (if config‐
4576 ured).
4577 The following standalone example shows how the --up script can
4579 be called in both an initialization and restart context. (NOTE:
4580 for security reasons, don't run the following example unless UDP
4581 port 9999 is blocked by your firewall. Also, the example will
4582 run indefinitely, so you should abort with control-c).
4583 openvpn --dev tun --port 9999 --verb 4 --ping-restart 10 \
4585 --up 'echo up' --down 'echo down' --persist-tun \
4586 --up-restart
4587 Note that OpenVPN also provides the --ifconfig option to auto‐
4589 matically ifconfig the TUN device, eliminating the need to de‐
4590 fine an --up script, unless you also want to configure routes in
4591 the --up script.
4592 If --ifconfig is also specified, OpenVPN will pass the ifconfig
4594 local and remote endpoints on the command line to the --up
4595 script so that they can be used to configure routes such as:
4596 route add -net 10.0.0.0 netmask 255.255.255.0 gw $5
4598 --up-delay
4600 Delay TUN/TAP open and possible --up script execution until af‐
4601 ter TCP/UDP connection establishment with peer.
4602 In --proto udp mode, this option normally requires the use of
4604 --ping to allow connection initiation to be sensed in the ab‐
4605 sence of tunnel data, since UDP is a "connectionless" protocol.
4606 On Windows, this option will delay the TAP-Win32 media state
4608 transitioning to "connected" until connection establishment,
4609 i.e. the receipt of the first authenticated packet from the
4610 peer.
4611 --up-restart
4613 Enable the --up and --down scripts to be called for restarts as
4614 well as initial program start. This option is described more
4615 fully above in the --up option documentation.
4616 String Types and Remapping
4618 In certain cases, OpenVPN will perform remapping of characters in
4619 strings. Essentially, any characters outside the set of permitted char‐
4620 acters for each string type will be converted to underbar ('_').
4621 Q: Why is string remapping necessary?
4623 It's an important security feature to prevent the malicious cod‐
4624 ing of strings from untrusted sources to be passed as parameters
4625 to scripts, saved in the environment, used as a common name,
4626 translated to a filename, etc.
4627 Q: Can string remapping be disabled?
4629 Yes, by using the --no-name-remapping option, however this
4630 should be considered an advanced option.
4631 Here is a brief rundown of OpenVPN's current string types and the per‐
4633 mitted character class for each string:
4634 X509 Names
4636 Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), at ('@'),
4637 colon (':'), slash ('/'), and equal ('='). Alphanumeric is de‐
4638 fined as a character which will cause the C library isalnum()
4639 function to return true.
4640 Common Names
4642 Alphanumeric, underbar ('_'), dash ('-'), dot ('.'), and at
4643 ('@').
4644 --auth-user-pass username
4646 Same as Common Name, with one exception: starting with OpenVPN
4647 2.0.1, the username is passed to the OPEN‐
4648 VPN_PLUGIN_AUTH_USER_PASS_VERIFY plugin in its raw form, without
4649 string remapping.
4650 --auth-user-pass password
4652 Any "printable" character except CR or LF. Printable is defined
4653 to be a character which will cause the C library isprint() func‐
4654 tion to return true.
4655 --client-config-dir filename as derived from common name or`username
4657 Alphanumeric, underbar ('_'), dash ('-'), and dot ('.') except
4658 for "." or ".." as standalone strings. As of v2.0.1-rc6, the at
4659 ('@') character has been added as well for compatibility with
4660 the common name character class.
4661 Environmental variable names
4663 Alphanumeric or underbar ('_').
4664 Environmental variable values
4666 Any printable character.
4667 For all cases, characters in a string which are not members of the le‐
4669 gal character class for that string type will be remapped to underbar
4670 ('_').
4671 Environmental Variables
4673 Once set, a variable is persisted indefinitely until it is reset by a
4674 new value or a restart,
4675 As of OpenVPN 2.0-beta12, in server mode, environmental variables set
4677 by OpenVPN are scoped according to the client objects they are associ‐
4678 ated with, so there should not be any issues with scripts having access
4679 to stale, previously set variables which refer to different client in‐
4680 stances.
4681 bytes_received
4683 Total number of bytes received from client during VPN session.
4684 Set prior to execution of the --client-disconnect script.
4685 bytes_sent
4687 Total number of bytes sent to client during VPN session. Set
4688 prior to execution of the --client-disconnect script.
4689 client_connect_config_file
4691 The path to the configuration file that should be written to by
4692 the --client-connect script (optional, if per-session configura‐
4693 tion is desired). This is the same file name as passed via com‐
4694 mand line argument on the call to the --client-connect script.
4695 client_connect_deferred_file
4697 This file can be optionally written to in order to to communi‐
4698 cate a status code of the --client-connect script or plgin.
4699 Only the first character in the file is relevant. It must be
4700 either 1 to indicate normal script execution, 0 indicates an er‐
4701 ror (in the same way that a non zero exit status does) or 2 to
4702 indicate that the script deferred returning the config file.
4703 For deferred (background) handling, the script or plugin MUST
4705 write 2 to the file to indicate the deferral and then return
4706 with exit code 0 to signal deferred handler started OK.
4707 A background process or similar must then take care of writing
4709 the configuration to the file indicated by the client_con‐
4710 nect_config_file environment variable and when finished, write
4711 the a 1 to this file (or 0 in case of an error).
4712 The absence of any character in the file when the script fin‐
4714 ishes executing is interpreted the same as 1. This allows
4715 scripts that are not written to support the defer mechanism to
4716 be used unmodified.
4717 common_name
4719 The X509 common name of an authenticated client. Set prior to
4720 execution of --client-connect, --client-disconnect and
4721 --auth-user-pass-verify scripts.
4722 config Name of first --config file. Set on program initiation and reset
4724 on SIGHUP.
4725 daemon Set to "1" if the --daemon directive is specified, or "0" other‐
4727 wise. Set on program initiation and reset on SIGHUP.
4728 daemon_log_redirect
4730 Set to "1" if the --log or --log-append directives are speci‐
4731 fied, or "0" otherwise. Set on program initiation and reset on
4732 SIGHUP.
4733 dev The actual name of the TUN/TAP device, including a unit number
4735 if it exists. Set prior to --up or --down script execution.
4736 dev_idx
4738 On Windows, the device index of the TUN/TAP adapter (to be used
4739 in netsh.exe calls which sometimes just do not work right with
4740 interface names). Set prior to --up or --down script execution.
4741 foreign_option_{n}
4743 An option pushed via --push to a client which does not natively
4744 support it, such as --dhcp-option on a non-Windows system, will
4745 be recorded to this environmental variable sequence prior to
4746 --up script execution.
4747 ifconfig_broadcast
4749 The broadcast address for the virtual ethernet segment which is
4750 derived from the --ifconfig option when --dev tap is used. Set
4751 prior to OpenVPN calling the ifconfig or netsh (windows version
4752 of ifconfig) commands which normally occurs prior to --up script
4753 execution.
4754 ifconfig_ipv6_local
4756 The local VPN endpoint IPv6 address specified in the --ifcon‐
4757 fig-ipv6 option (first parameter). Set prior to OpenVPN calling
4758 the ifconfig or code:netsh (windows version of ifconfig) com‐
4759 mands which normally occurs prior to --up script execution.
4760 ifconfig_ipv6_netbits
4762 The prefix length of the IPv6 network on the VPN interface. De‐
4763 rived from the /nnn parameter of the IPv6 address in the --if‐
4764 config-ipv6 option (first parameter). Set prior to OpenVPN call‐
4765 ing the ifconfig or netsh (windows version of ifconfig) commands
4766 which normally occurs prior to --up script execution.
4767 ifconfig_ipv6_remote
4769 The remote VPN endpoint IPv6 address specified in the --ifcon‐
4770 fig-ipv6 option (second parameter). Set prior to OpenVPN calling
4771 the ifconfig or netsh (windows version of ifconfig) commands
4772 which normally occurs prior to --up script execution.
4773 ifconfig_local
4775 The local VPN endpoint IP address specified in the --ifconfig
4776 option (first parameter). Set prior to OpenVPN calling the if‐
4777 config or netsh (windows version of ifconfig) commands which
4778 normally occurs prior to --up script execution.
4779 ifconfig_remote
4781 The remote VPN endpoint IP address specified in the --ifconfig
4782 option (second parameter) when --dev tun is used. Set prior to
4783 OpenVPN calling the ifconfig or netsh (windows version of ifcon‐
4784 fig) commands which normally occurs prior to --up script execu‐
4785 tion.
4786 ifconfig_netmask
4788 The subnet mask of the virtual ethernet segment that is speci‐
4789 fied as the second parameter to --ifconfig when --dev tap is be‐
4790 ing used. Set prior to OpenVPN calling the ifconfig or netsh
4791 (windows version of ifconfig) commands which normally occurs
4792 prior to --up script execution.
4793 ifconfig_pool_local_ip
4795 The local virtual IP address for the TUN/TAP tunnel taken from
4796 an --ifconfig-push directive if specified, or otherwise from the
4797 ifconfig pool (controlled by the --ifconfig-pool config file di‐
4798 rective). Only set for --dev tun tunnels. This option is set on
4799 the server prior to execution of the --client-connect and
4800 --client-disconnect scripts.
4801 ifconfig_pool_netmask
4803 The virtual IP netmask for the TUN/TAP tunnel taken from an
4804 --ifconfig-push directive if specified, or otherwise from the
4805 ifconfig pool (controlled by the --ifconfig-pool config file di‐
4806 rective). Only set for --dev tap tunnels. This option is set on
4807 the server prior to execution of the --client-connect and
4808 --client-disconnect scripts.
4809 ifconfig_pool_remote_ip
4811 The remote virtual IP address for the TUN/TAP tunnel taken from
4812 an --ifconfig-push directive if specified, or otherwise from the
4813 ifconfig pool (controlled by the --ifconfig-pool config file di‐
4814 rective). This option is set on the server prior to execution of
4815 the --client-connect and --client-disconnect scripts.
4816 link_mtu
4818 The maximum packet size (not including the IP header) of tunnel
4819 data in UDP tunnel transport mode. Set prior to --up or --down
4820 script execution.
4821 local The --local parameter. Set on program initiation and reset on
4823 SIGHUP.
4824 local_port
4826 The local port number or name, specified by --port or --lport.
4827 Set on program initiation and reset on SIGHUP.
4828 password
4830 The password provided by a connecting client. Set prior to
4831 --auth-user-pass-verify script execution only when the via-env
4832 modifier is specified, and deleted from the environment after
4833 the script returns.
4834 proto The --proto parameter. Set on program initiation and reset on
4836 SIGHUP.
4837 remote_{n}
4839 The --remote parameter. Set on program initiation and reset on
4840 SIGHUP.
4841 remote_port_{n}
4843 The remote port number, specified by --port or --rport. Set on
4844 program initiation and reset on SIGHUP.
4845 route_net_gateway
4847 The pre-existing default IP gateway in the system routing table.
4848 Set prior to --up script execution.
4849 route_vpn_gateway
4851 The default gateway used by --route options, as specified in ei‐
4852 ther the --route-gateway option or the second parameter to --if‐
4853 config when --dev tun is specified. Set prior to --up script ex‐
4854 ecution.
4855 route_{parm}_{n}
4857 A set of variables which define each route to be added, and are
4858 set prior to --up script execution.
4859 parm will be one of network, netmask", gateway, or metric.
4861 n is the OpenVPN route number, starting from 1.
4863 If the network or gateway are resolvable DNS names, their IP ad‐
4865 dress translations will be recorded rather than their names as
4866 denoted on the command line or configuration file.
4867 route_ipv6_{parm}_{n}
4869 A set of variables which define each IPv6 route to be added, and
4870 are set prior to --up script execution.
4871 parm will be one of network, gateway or metric. route_ipv6_net‐
4873 work_{n} contains netmask as /nnn, unlike IPv4 where it is
4874 passed in a separate environment variable.
4875 n is the OpenVPN route number, starting from 1.
4877 If the network or gateway are resolvable DNS names, their IP ad‐
4879 dress translations will be recorded rather than their names as
4880 denoted on the command line or configuration file.
4881 peer_cert
4883 Temporary file name containing the client certificate upon con‐
4884 nection. Useful in conjunction with --tls-verify.
4885 script_context
4887 Set to "init" or "restart" prior to up/down script execution.
4888 For more information, see documentation for --up.
4889 script_type
4891 Prior to execution of any script, this variable is set to the
4892 type of script being run. It can be one of the following: up,
4893 down, ipchange, route-up, tls-verify, auth-user-pass-verify,
4894 client-connect, client-disconnect or learn-address. Set prior to
4895 execution of any script.
4896 signal The reason for exit or restart. Can be one of sigusr1, sighup,
4898 sigterm, sigint, inactive (controlled by --inactive option),
4899 ping-exit (controlled by --ping-exit option), ping-restart (con‐
4900 trolled by --ping-restart option), connection-reset (triggered
4901 on TCP connection reset), error or unknown (unknown signal).
4902 This variable is set just prior to down script execution.
4903 time_ascii
4905 Client connection timestamp, formatted as a human-readable time
4906 string. Set prior to execution of the --client-connect script.
4907 time_duration
4909 The duration (in seconds) of the client session which is now
4910 disconnecting. Set prior to execution of the --client-disconnect
4911 script.
4912 time_unix
4914 Client connection timestamp, formatted as a unix integer
4915 date/time value. Set prior to execution of the --client-connect
4916 script.
4917 tls_digest_{n} / tls_digest_sha256_{n}
4919 Contains the certificate SHA1 / SHA256 fingerprint, where n is
4920 the verification level. Only set for TLS connections. Set prior
4921 to execution of --tls-verify script.
4922 tls_id_{n}
4924 A series of certificate fields from the remote peer, where n is
4925 the verification level. Only set for TLS connections. Set prior
4926 to execution of --tls-verify script.
4927 tls_serial_{n}
4929 The serial number of the certificate from the remote peer, where
4930 n is the verification level. Only set for TLS connections. Set
4931 prior to execution of --tls-verify script. This is in the form
4932 of a decimal string like "933971680", which is suitable for do‐
4933 ing serial-based OCSP queries (with OpenSSL, do not prepend "0x"
4934 to the string) If something goes wrong while reading the value
4935 from the certificate it will be an empty string, so your code
4936 should check that. See the contrib/OCSP_check/OCSP_check.sh
4937 script for an example.
4938 tls_serial_hex_{n}
4940 Like tls_serial_{n}, but in hex form (e.g. 12:34:56:78:9A).
4941 tun_mtu
4943 The MTU of the TUN/TAP device. Set prior to --up or --down
4944 script execution.
4945 trusted_ip / trusted_ip6)
4947 Actual IP address of connecting client or peer which has been
4948 authenticated. Set prior to execution of --ipchange,
4949 --client-connect and --client-disconnect scripts. If using ipv6
4950 endpoints (udp6, tcp6), trusted_ip6 will be set instead.
4951 trusted_port
4953 Actual port number of connecting client or peer which has been
4954 authenticated. Set prior to execution of --ipchange,
4955 --client-connect and --client-disconnect scripts.
4956 untrusted_ip / untrusted_ip6
4958 Actual IP address of connecting client or peer which has not
4959 been authenticated yet. Sometimes used to nmap the connecting
4960 host in a --tls-verify script to ensure it is firewalled prop‐
4961 erly. Set prior to execution of --tls-verify and
4962 --auth-user-pass-verify scripts. If using ipv6 endpoints (udp6,
4963 tcp6), untrusted_ip6 will be set instead.
4964 untrusted_port
4966 Actual port number of connecting client or peer which has not
4967 been authenticated yet. Set prior to execution of --tls-verify
4968 and --auth-user-pass-verify scripts.
4969 username
4971 The username provided by a connecting client. Set prior to
4972 --auth-user-pass-verify script execution only when the via-env
4973 modifier is specified.
4974 X509_{n}_{subject_field}
4976 An X509 subject field from the remote peer certificate, where n
4977 is the verification level. Only set for TLS connections. Set
4978 prior to execution of --tls-verify script. This variable is sim‐
4979 ilar to tls_id_{n} except the component X509 subject fields are
4980 broken out, and no string remapping occurs on these field values
4981 (except for remapping of control characters to "_"). For exam‐
4982 ple, the following variables would be set on the OpenVPN server
4983 using the sample client certificate in sample-keys (client.crt).
4984 Note that the verification level is 0 for the client certificate
4985 and 1 for the CA certificate.
4986 X509_0_emailAddress=me@myhost.mydomain
4988 X509_0_CN=Test-Client
4989 X509_0_O=OpenVPN-TEST
4990 X509_0_ST=NA
4991 X509_0_C=KG
4992 X509_1_emailAddress=me@myhost.mydomain
4993 X509_1_O=OpenVPN-TEST
4994 X509_1_L=BISHKEK
4995 X509_1_ST=NA
4996 X509_1_C=KG
4997 Management Interface Options
4999 OpenVPN provides a feature rich socket based management interface for
5000 both server and client mode operations.
5001 --management args
5003 Enable a management server on a socket-name Unix socket on those
5004 platforms supporting it, or on a designated TCP port.
5005 Valid syntaxes:
5007 management socket-name unix #
5009 management socket-name unix pw-file # (recommended)
5010 management IP port # (INSECURE)
5011 management IP port pw-file #
5012 pw-file, if specified, is a password file where the password
5014 must be on first line. Instead of a filename it can use the key‐
5015 word stdin which will prompt the user for a password to use when
5016 OpenVPN is starting.
5017 For unix sockets, the default behaviour is to create a unix do‐
5019 main socket that may be connected to by any process. Use the
5020 --management-client-user and --management-client-group direc‐
5021 tives to restrict access.
5022 The management interface provides a special mode where the TCP
5024 management link can operate over the tunnel itself. To enable
5025 this mode, set IP to tunnel. Tunnel mode will cause the manage‐
5026 ment interface to listen for a TCP connection on the local VPN
5027 address of the TUN/TAP interface.
5028 *BEWARE* of enabling the management interface over TCP. In these
5030 cases you should ALWAYS make use of pw-file to password protect
5031 the management interface. Any user who can connect to this TCP
5032 IP:port will be able to manage and control (and interfere with)
5033 the OpenVPN process. It is also strongly recommended to set IP
5034 to 127.0.0.1 (localhost) to restrict accessibility of the man‐
5035 agement server to local clients.
5036 While the management port is designed for programmatic control
5038 of OpenVPN by other applications, it is possible to telnet to
5039 the port, using a telnet client in "raw" mode. Once connected,
5040 type help for a list of commands.
5041 For detailed documentation on the management interface, see the
5043 management-notes.txt file in the management folder of the Open‐
5044 VPN source distribution.
5045 --management-client
5047 Management interface will connect as a TCP/unix domain client to
5048 IP:port specified by --management rather than listen as a TCP
5049 server or on a unix domain socket.
5050 If the client connection fails to connect or is disconnected, a
5052 SIGTERM signal will be generated causing OpenVPN to quit.
5053 --management-client-auth
5055 Gives management interface client the responsibility to authen‐
5056 ticate clients after their client certificate has been verified.
5057 See management-notes.txt in OpenVPN distribution for detailed
5058 notes.
5059 --management-client-group g
5061 When the management interface is listening on a unix domain
5062 socket, only allow connections from group g.
5063 --management-client-pf
5065 Management interface clients must specify a packet filter file
5066 for each connecting client. See management-notes.txt in OpenVPN
5067 distribution for detailed notes.
5068 --management-client-user u
5070 When the management interface is listening on a unix domain
5071 socket, only allow connections from user u.
5072 --management-external-cert certificate-hint
5074 Allows usage for external certificate instead of --cert option
5075 (client-only). certificate-hint is an arbitrary string which is
5076 passed to a management interface client as an argument of
5077 NEED-CERTIFICATE notification. Requires --management-exter‐
5078 nal-key.
5079 --management-external-key args
5081 Allows usage for external private key file instead of --key op‐
5082 tion (client-only).
5083 Valid syntaxes:
5085 management-external-key
5087 management-external-key nopadding
5088 management-external-key pkcs1
5089 management-external-key nopadding pkcs1
5090 The optional parameters nopadding and pkcs1 signal support for
5092 different padding algorithms. See doc/mangement-notes.txt for a
5093 complete description of this feature.
5094 --management-forget-disconnect
5096 Make OpenVPN forget passwords when management session discon‐
5097 nects.
5098 This directive does not affect the --http-proxy username/pass‐
5100 word. It is always cached.
5101 --management-hold
5103 Start OpenVPN in a hibernating state, until a client of the man‐
5104 agement interface explicitly starts it with the hold release
5105 command.
5106 --management-log-cache n
5108 Cache the most recent n lines of log file history for usage by
5109 the management channel.
5110 --management-query-passwords
5112 Query management channel for private key password and
5113 --auth-user-pass username/password. Only query the management
5114 channel for inputs which ordinarily would have been queried from
5115 the console.
5116 --management-query-proxy
5118 Query management channel for proxy server information for a spe‐
5119 cific --remote (client-only).
5120 --management-query-remote
5122 Allow management interface to override --remote directives
5123 (client-only).
5124 --management-signal
5126 Send SIGUSR1 signal to OpenVPN if management session discon‐
5127 nects. This is useful when you wish to disconnect an OpenVPN
5128 session on user logoff. For --management-client this option is
5129 not needed since a disconnect will always generate a SIGTERM.
5130 --management-up-down
5132 Report tunnel up/down events to management interface.
5133 Plug-in Interface Options
5135 OpenVPN can be extended by loading external plug-in modules at runtime.
5136 These plug-ins must be prebuilt and adhere to the OpenVPN Plug-In API.
5137 --plugin args
5139 Loads an OpenVPN plug-in module.
5140 Valid syntax:
5142 plugin module-name
5144 plugin module-name "arguments"
5145 The module-name needs to be the first argument, indicating the
5147 plug-in to load. The second argument is an optional init string
5148 which will be passed directly to the plug-in. If the init con‐
5149 sists of multiple arguments it must be enclosed in double-quotes
5150 ("). Multiple plugin modules may be loaded into one OpenVPN
5151 process.
5152 The module-name argument can be just a filename or a filename
5154 with a relative or absolute path. The format of the filename and
5155 path defines if the plug-in will be loaded from a default
5156 plug-in directory or outside this directory.
5157 --plugin path Effective directory used
5159 ===================== =============================
5160 myplug.so DEFAULT_DIR/myplug.so
5161 subdir/myplug.so DEFAULT_DIR/subdir/myplug.so
5162 ./subdir/myplug.so CWD/subdir/myplug.so
5163 /usr/lib/my/plug.so /usr/lib/my/plug.so
5164 DEFAULT_DIR is replaced by the default plug-in directory, which
5166 is configured at the build time of OpenVPN. CWD is the current
5167 directory where OpenVPN was started or the directory OpenVPN
5168 have switched into via the --cd option before the --plugin op‐
5169 tion.
5170 For more information and examples on how to build OpenVPN
5172 plug-in modules, see the README file in the plugin folder of the
5173 OpenVPN source distribution.
5174 If you are using an RPM install of OpenVPN, see /usr/share/open‐
5176 vpn/plugin. The documentation is in doc and the actual plugin
5177 modules are in lib.
5178 Multiple plugin modules can be cascaded, and modules can be used
5180 in tandem with scripts. The modules will be called by OpenVPN in
5181 the order that they are declared in the config file. If both a
5182 plugin and script are configured for the same callback, the
5183 script will be called last. If the return code of the mod‐
5184 ule/script controls an authentication function (such as tls-ver‐
5185 ify, auth-user-pass-verify, or client-connect), then every mod‐
5186 ule and script must return success (0) in order for the connec‐
5187 tion to be authenticated.
5188 WARNING:
5190 Plug-ins may do deferred execution, meaning the plug-in
5191 will return the control back to the main OpenVPN process
5192 and provide the plug-in result later on via a different
5193 thread or process. OpenVPN does NOT support multiple au‐
5194 thentication plug-ins where more than one plugin tries to
5195 do deferred authentication. If this behaviour is de‐
5196 tected, OpenVPN will shut down upon first authentication.
5197 Windows-Specific Options
5199 --allow-nonadmin TAP-adapter
5200 (Standalone) Set TAP-adapter to allow access from non-adminis‐
5201 trative accounts. If TAP-adapter is omitted, all TAP adapters on
5202 the system will be configured to allow non-admin access. The
5203 non-admin access setting will only persist for the length of
5204 time that the TAP-Win32 device object and driver remain loaded,
5205 and will need to be re-enabled after a reboot, or if the driver
5206 is unloaded and reloaded. This directive can only be used by an
5207 administrator.
5208 --block-outside-dns
5210 Block DNS servers on other network adapters to prevent DNS
5211 leaks. This option prevents any application from accessing TCP
5212 or UDP port 53 except one inside the tunnel. It uses Windows
5213 Filtering Platform (WFP) and works on Windows Vista or later.
5214 This option is considered unknown on non-Windows platforms and
5216 unsupported on Windows XP, resulting in fatal error. You may
5217 want to use --setenv opt or --ignore-unknown-option (not suit‐
5218 able for Windows XP) to ignore said error. Note that pushing un‐
5219 known options from server does not trigger fatal errors.
5220 --cryptoapicert select-string
5222 (Windows/OpenSSL Only) Load the certificate and private key from
5223 the Windows Certificate System Store.
5224 Use this option instead of --cert and --key.
5226 This makes it possible to use any smart card, supported by Win‐
5228 dows, but also any kind of certificate, residing in the Cert
5229 Store, where you have access to the private key. This option has
5230 been tested with a couple of different smart cards (GemSAFE,
5231 Cryptoflex, and Swedish Post Office eID) on the client side, and
5232 also an imported PKCS12 software certificate on the server side.
5233 To select a certificate, based on a substring search in the cer‐
5235 tificate's subject:
5236 cryptoapicert "SUBJ:Peter Runestig"
5238 To select a certificate, based on certificate's thumbprint:
5240 cryptoapicert "THUMB:f6 49 24 41 01 b4 ..."
5242 The thumbprint hex string can easily be copy-and-pasted from the
5244 Windows Certificate Store GUI.
5245 --dhcp-release
5247 Ask Windows to release the TAP adapter lease on shutdown. This
5248 option has no effect now, as it is enabled by default starting
5249 with OpenVPN 2.4.1.
5250 --dhcp-renew
5252 Ask Windows to renew the TAP adapter lease on startup. This op‐
5253 tion is normally unnecessary, as Windows automatically triggers
5254 a DHCP renegotiation on the TAP adapter when it comes up, how‐
5255 ever if you set the TAP-Win32 adapter Media Status property to
5256 "Always Connected", you may need this flag.
5257 --ip-win32 method
5259 When using --ifconfig on Windows, set the TAP-Win32 adapter IP
5260 address and netmask using method. Don't use this option unless
5261 you are also using --ifconfig.
5262 manual Don't set the IP address or netmask automatically. In‐
5264 stead output a message to the console telling the user to
5265 configure the adapter manually and indicating the IP/net‐
5266 mask which OpenVPN expects the adapter to be set to.
5267 dynamic [offset] [lease-time]
5269 Automatically set the IP address and netmask by replying
5270 to DHCP query messages generated by the kernel. This
5271 mode is probably the "cleanest" solution for setting the
5272 TCP/IP properties since it uses the well-known DHCP pro‐
5273 tocol. There are, however, two prerequisites for using
5274 this mode:
5275 1. The TCP/IP properties for the TAP-Win32 adapter must
5277 be set to "Obtain an IP address automatically", and
5278 2. OpenVPN needs to claim an IP address in the subnet for
5280 use as the virtual DHCP server address.
5281 By default in --dev tap mode, OpenVPN will take the nor‐
5283 mally unused first address in the subnet. For example, if
5284 your subnet is 192.168.4.0 netmask 255.255.255.0, then
5285 OpenVPN will take the IP address 192.168.4.0 to use as
5286 the virtual DHCP server address. In --dev tun mode,
5287 OpenVPN will cause the DHCP server to masquerade as if it
5288 were coming from the remote endpoint.
5289 The optional offset parameter is an integer which is >
5291 -256 and < 256 and which defaults to 0. If offset is pos‐
5292 itive, the DHCP server will masquerade as the IP address
5293 at network address + offset. If offset is negative, the
5294 DHCP server will masquerade as the IP address at broad‐
5295 cast address + offset.
5296 The Windows ipconfig /all command can be used to show
5298 what Windows thinks the DHCP server address is. OpenVPN
5299 will "claim" this address, so make sure to use a free ad‐
5300 dress. Having said that, different OpenVPN instantia‐
5301 tions, including different ends of the same connection,
5302 can share the same virtual DHCP server address.
5303 The lease-time parameter controls the lease time of the
5305 DHCP assignment given to the TAP-Win32 adapter, and is
5306 denoted in seconds. Normally a very long lease time is
5307 preferred because it prevents routes involving the
5308 TAP-Win32 adapter from being lost when the system goes to
5309 sleep. The default lease time is one year.
5310 netsh Automatically set the IP address and netmask using the
5312 Windows command-line "netsh" command. This method appears
5313 to work correctly on Windows XP but not Windows 2000.
5314 ipapi Automatically set the IP address and netmask using the
5316 Windows IP Helper API. This approach does not have ideal
5317 semantics, though testing has indicated that it works
5318 okay in practice. If you use this option, it is best to
5319 leave the TCP/IP properties for the TAP-Win32 adapter in
5320 their default state, i.e. "Obtain an IP address automati‐
5321 cally."
5322 adaptive (Default)
5324 Try dynamic method initially and fail over to netsh if
5325 the DHCP negotiation with the TAP-Win32 adapter does not
5326 succeed in 20 seconds. Such failures have been known to
5327 occur when certain third-party firewall packages in‐
5328 stalled on the client machine block the DHCP negotiation
5329 used by the TAP-Win32 adapter. Note that if the netsh
5330 failover occurs, the TAP-Win32 adapter TCP/IP properties
5331 will be reset from DHCP to static, and this will cause
5332 future OpenVPN startups using the adaptive mode to use
5333 netsh immediately, rather than trying dynamic first.
5334 To "unstick" the adaptive mode from using netsh, run
5336 OpenVPN at least once using the dynamic mode to restore
5337 the TAP-Win32 adapter TCP/IP properties to a DHCP config‐
5338 uration.
5339 --pause-exit
5341 Put up a "press any key to continue" message on the console
5342 prior to OpenVPN program exit. This option is automatically used
5343 by the Windows explorer when OpenVPN is run on a configuration
5344 file using the right-click explorer menu.
5345 --register-dns
5347 Run ipconfig /flushdns and ipconfig /registerdns on connection
5348 initiation. This is known to kick Windows into recognizing
5349 pushed DNS servers.
5350 --route-method m
5352 Which method m to use for adding routes on Windows?
5353 adaptive (default)
5355 Try IP helper API first. If that fails, fall back to the
5356 route.exe shell command.
5357 ipapi Use IP helper API.
5359 exe Call the route.exe shell command.
5361 --service args
5363 Should be used when OpenVPN is being automatically executed by
5364 another program in such a context that no interaction with the
5365 user via display or keyboard is possible.
5366 Valid syntax:
5368 service exit-event [0|1]
5370 In general, end-users should never need to explicitly use this
5372 option, as it is automatically added by the OpenVPN service
5373 wrapper when a given OpenVPN configuration is being run as a
5374 service.
5375 exit-event is the name of a Windows global event object, and
5377 OpenVPN will continuously monitor the state of this event object
5378 and exit when it becomes signaled.
5379 The second parameter indicates the initial state of exit-event
5381 and normally defaults to 0.
5382 Multiple OpenVPN processes can be simultaneously executed with
5384 the same exit-event parameter. In any case, the controlling
5385 process can signal exit-event, causing all such OpenVPN pro‐
5386 cesses to exit.
5387 When executing an OpenVPN process using the --service directive,
5389 OpenVPN will probably not have a console window to output sta‐
5390 tus/error messages, therefore it is useful to use --log or
5391 --log-append to write these messages to a file.
5392 --show-adapters
5394 (Standalone) Show available TAP-Win32 adapters which can be se‐
5395 lected using the --dev-node option. On non-Windows systems, the
5396 ifconfig(8) command provides similar functionality.
5397 --show-net
5399 (Standalone) Show OpenVPN's view of the system routing table and
5400 network adapter list.
5401 --show-net-up
5403 Output OpenVPN's view of the system routing table and network
5404 adapter list to the syslog or log file after the TUN/TAP adapter
5405 has been brought up and any routes have been added.
5406 --show-valid-subnets
5408 (Standalone) Show valid subnets for --dev tun emulation. Since
5409 the TAP-Win32 driver exports an ethernet interface to Windows,
5410 and since TUN devices are point-to-point in nature, it is neces‐
5411 sary for the TAP-Win32 driver to impose certain constraints on
5412 TUN endpoint address selection.
5413 Namely, the point-to-point endpoints used in TUN device emula‐
5415 tion must be the middle two addresses of a /30 subnet (netmask
5416 255.255.255.252).
5417 --tap-sleep n
5419 Cause OpenVPN to sleep for n seconds immediately after the
5420 TAP-Win32 adapter state is set to "connected".
5421 This option is intended to be used to troubleshoot problems with
5423 the --ifconfig and --ip-win32 options, and is used to give the
5424 TAP-Win32 adapter time to come up before Windows IP Helper API
5425 operations are applied to it.
5426 --win-sys path
5428 Set the Windows system directory pathname to use when looking
5429 for system executables such as route.exe and netsh.exe. By de‐
5430 fault, if this directive is not specified, OpenVPN will use the
5431 SystemRoot environment variable.
5432 This option has changed behaviour since OpenVPN 2.3. Earlier you
5434 had to define --win-sys env to use the SystemRoot environment
5435 variable, otherwise it defaulted to C:\\WINDOWS. It is not
5436 needed to use the env keyword any more, and it will just be ig‐
5437 nored. A warning is logged when this is found in the configura‐
5438 tion file.
5439 --windows-driver drv
5441 Specifies which tun driver to use. Values are tap-windows6 (de‐
5442 fault) and wintun. This is a Windows-only option. wintun" re‐
5443 quires --dev tun and the OpenVPN process to run elevated, or be
5444 invoked using the Interactive Service.
5445 Standalone Debug Options
5447 --show-gateway args
5448 (Standalone) Show current IPv4 and IPv6 default gateway and in‐
5449 terface towards the gateway (if the protocol in question is en‐
5450 abled).
5451 Valid syntax:
5453 --show-gateway
5455 --show-gateway IPv6-target
5456 For IPv6 this queries the route towards ::/128, or the specified
5458 IPv6 target address if passed as argument. For IPv4 on Linux,
5459 Windows, MacOS and BSD it looks for a 0.0.0.0/0 route. If there
5460 are more specific routes, the result will not always be matching
5461 the route of the IPv4 packets to the VPN gateway.
5462 Advanced Expert Options
5464 These are options only required when special tweaking is needed, often
5465 used when debugging or testing out special usage scenarios.
5466 --hash-size args
5468 Set the size of the real address hash table to r and the virtual
5469 address table to v.
5470 Valid syntax:
5472 hash-size r v
5474 By default, both tables are sized at 256 buckets.
5476 --bcast-buffers n
5478 Allocate n buffers for broadcast datagrams (default 256).
5479 --persist-local-ip
5481 Preserve initially resolved local IP address and port number
5482 across SIGUSR1 or --ping-restart restarts.
5483 --persist-remote-ip
5485 Preserve most recently authenticated remote IP address and port
5486 number across SIGUSR1 or --ping-restart restarts.
5487 --prng args
5489 (Advanced) Change the PRNG (Pseudo-random number generator) pa‐
5490 rameters
5491 Valid syntaxes:
5493 prng alg
5495 prng alg nsl
5496 Changes the PRNG to use digest algorithm alg (default sha1), and
5498 set nsl (default 16) to the size in bytes of the nonce secret
5499 length (between 16 and 64).
5500 Set alg to none to disable the PRNG and use the OpenSSL
5502 RAND_bytes function instead for all of OpenVPN's pseudo-random
5503 number needs.
5504 --rcvbuf size
5506 Set the TCP/UDP socket receive buffer size. Defaults to operat‐
5507 ing system default.
5508 --shaper n
5510 Limit bandwidth of outgoing tunnel data to n bytes per second on
5511 the TCP/UDP port. Note that this will only work if mode is set
5512 to p2p. If you want to limit the bandwidth in both directions,
5513 use this option on both peers.
5514 OpenVPN uses the following algorithm to implement traffic shap‐
5516 ing: Given a shaper rate of n bytes per second, after a datagram
5517 write of b bytes is queued on the TCP/UDP port, wait a minimum
5518 of (b / n) seconds before queuing the next write.
5519 It should be noted that OpenVPN supports multiple tunnels be‐
5521 tween the same two peers, allowing you to construct full-speed
5522 and reduced bandwidth tunnels at the same time, routing low-pri‐
5523 ority data such as off-site backups over the reduced bandwidth
5524 tunnel, and other data over the full-speed tunnel.
5525 Also note that for low bandwidth tunnels (under 1000 bytes per
5527 second), you should probably use lower MTU values as well (see
5528 above), otherwise the packet latency will grow so large as to
5529 trigger timeouts in the TLS layer and TCP connections running
5530 over the tunnel.
5531 OpenVPN allows n to be between 100 bytes/sec and 100 Mbytes/sec.
5533 --sndbuf size
5535 Set the TCP/UDP socket send buffer size. Defaults to operating
5536 system default.
5537 --tcp-queue-limit n
5539 Maximum number of output packets queued before TCP (default 64).
5540 When OpenVPN is tunneling data from a TUN/TAP device to a remote
5542 client over a TCP connection, it is possible that the TUN/TAP
5543 device might produce data at a faster rate than the TCP connec‐
5544 tion can support. When the number of output packets queued be‐
5545 fore sending to the TCP socket reaches this limit for a given
5546 client connection, OpenVPN will start to drop outgoing packets
5547 directed at this client.
5548 --txqueuelen n
5550 (Linux only) Set the TX queue length on the TUN/TAP interface.
5551 Currently defaults to operating system default.
5552
5554 Options listed in this section have been removed from OpenVPN and are
5555 no longer supported
5556 --client-cert-not-required
5558 Removed in OpenVPN 2.5. This should be replaxed with --ver‐
5559 ify-client-cert none.
5560 --ifconfig-pool-linear
5562 Removed in OpenVPN 2.5. This should be replaced with --topology
5563 p2p.
5564 --key-method
5566 Removed in OpenVPN 2.5. This option should not be used, as us‐
5567 ing the old key-method weakens the VPN tunnel security. The old
5568 key-method was also only needed when the remote side was older
5569 than OpenVPN 2.0.
5570 --no-iv
5572 Removed in OpenVPN 2.5. This option should not be used as it
5573 weakens the VPN tunnel security. This has been a NOOP option
5574 since OpenVPN 2.4.
5575 --no-replay
5577 Removed in OpenVPN 2.5. This option should not be used as it
5578 weakens the VPN tunnel security.
5579 --ns-cert-type
5581 Removed in OpenVPN 2.5. The nsCertType field is no longer sup‐
5582 ported in recent SSL/TLS libraries. If your certificates does
5583 not include key usage and extended key usage fields, they must
5584 be upgraded and the --remote-cert-tls option should be used in‐
5585 stead.
5586
5588 Client configuration files may contain multiple remote servers which it
5589 will attempt to connect against. But there are some configuration op‐
5590 tions which are related to specific --remote options. For these use
5591 cases, connection profiles are the solution.
5592 By enacpulating the --remote option and related options within <connec‐
5594 tion> and </connection>, these options are handled as a group.
5595 An OpenVPN client will try each connection profile sequentially until
5597 it achieves a successful connection.
5598 --remote-random can be used to initially "scramble" the connection
5600 list.
5601 Here is an example of connection profile usage:
5603 client
5605 dev tun
5606 <connection>
5608 remote 198.19.34.56 1194 udp
5609 </connection>
5610 <connection>
5612 remote 198.19.34.56 443 tcp
5613 </connection>
5614 <connection>
5616 remote 198.19.34.56 443 tcp
5617 http-proxy 192.168.0.8 8080
5618 </connection>
5619 <connection>
5621 remote 198.19.36.99 443 tcp
5622 http-proxy 192.168.0.8 8080
5623 </connection>
5624 persist-key
5626 persist-tun
5627 pkcs12 client.p12
5628 remote-cert-tls server
5629 verb 3
5630 First we try to connect to a server at 198.19.34.56:1194 using UDP. If
5632 that fails, we then try to connect to 198.19.34.56:443 using TCP. If
5633 that also fails, then try connecting through an HTTP proxy at
5634 192.168.0.8:8080 to 198.19.34.56:443 using TCP. Finally, try to connect
5635 through the same proxy to a server at 198.19.36.99:443 using TCP.
5636 The following OpenVPN options may be used inside of a <connection>
5638 block:
5639 bind, connect-retry, connect-retry-max, connect-timeout, ex‐
5641 plicit-exit-notify, float, fragment, http-proxy, http-proxy-option,
5642 key-direction, link-mtu, local, lport, mssfix, mtu-disc, nobind, port,
5643 proto, remote, rport, socks-proxy, tls-auth, tls-crypt, tun-mtu and,
5644 tun-mtu-extra.
5645 A defaulting mechanism exists for specifying options to apply to all
5647 <connection> profiles. If any of the above options (with the exception
5648 of remote ) appear outside of a <connection> block, but in a configura‐
5649 tion file which has one or more <connection> blocks, the option setting
5650 will be used as a default for <connection> blocks which follow it in
5651 the configuration file.
5652 For example, suppose the nobind option were placed in the sample con‐
5654 figuration file above, near the top of the file, before the first <con‐
5655 nection> block. The effect would be as if nobind were declared in all
5656 <connection> blocks below it.
5657
5659 OpenVPN allows including files in the main configuration for the --ca,
5660 --cert, --dh, --extra-certs, --key, --pkcs12, --secret, --crl-verify,
5661 --http-proxy-user-pass, --tls-auth, --auth-gen-token-secret,
5662 --tls-crypt and --tls-crypt-v2 options.
5663 Each inline file started by the line <option> and ended by the line
5665 </option>
5666 Here is an example of an inline file usage
5668 <cert>
5670 -----BEGIN CERTIFICATE-----
5671 [...]
5672 -----END CERTIFICATE-----
5673 </cert>
5674 When using the inline file feature with --pkcs12 the inline file has to
5676 be base64 encoded. Encoding of a .p12 file into base64 can be done for
5677 example with OpenSSL by running openssl base64 -in input.p12
5678
5680 SIGHUP Cause OpenVPN to close all TUN/TAP and network connections,
5681 restart, re-read the configuration file (if any), and reopen
5682 TUN/TAP and network connections.
5683 SIGUSR1
5685 Like SIGHUP`, except don't re-read configuration file, and pos‐
5686 sibly don't close and reopen TUN/TAP device, re-read key files,
5687 preserve local IP address/port, or preserve most recently au‐
5688 thenticated remote IP address/port based on --persist-tun,
5689 --persist-key, --persist-local-ip and --persist-remote-ip op‐
5690 tions respectively (see above).
5691 This signal may also be internally generated by a timeout condi‐
5693 tion, governed by the --ping-restart option.
5694 This signal, when combined with --persist-remote-ip, may be sent
5696 when the underlying parameters of the host's network interface
5697 change such as when the host is a DHCP client and is assigned a
5698 new IP address. See --ipchange for more information.
5699 SIGUSR2
5701 Causes OpenVPN to display its current statistics (to the syslog
5702 file if --daemon is used, or stdout otherwise).
5703 SIGINT, SIGTERM
5705 Causes OpenVPN to exit gracefully.
5706
5708 https://community.openvpn.net/openvpn/wiki/FAQ
5709
5711 For a more comprehensive guide to setting up OpenVPN in a production
5712 setting, see the OpenVPN HOWTO at
5713 https://openvpn.net/community-resources/how-to/
5714
5716 For a description of OpenVPN's underlying protocol, see
5717 https://openvpn.net/community-resources/openvpn-protocol/
5718
5720 OpenVPN's web site is at https://openvpn.net/
5721 Go here to download the latest version of OpenVPN, subscribe to the
5723 mailing lists, read the mailing list archives, or browse the SVN repos‐
5724 itory.
5725
5727 Report all bugs to the OpenVPN team info@openvpn.net
5728
5730 openvpn-examples(5), dhcpcd(8), ifconfig(8), openssl(1), route(8),
5731 scp(1) ssh(1)
5732
5734 This product includes software developed by the OpenSSL Project (‐
5735 https://www.openssl.org/)
5736 For more information on the TLS protocol, see
5738 http://www.ietf.org/rfc/rfc2246.txt
5739 For more information on the LZO real-time compression library see
5741 https://www.oberhumer.com/opensource/lzo/
5742
5744 Copyright (C) 2002-2020 OpenVPN Inc This program is free software; you
5745 can redistribute it and/or modify it under the terms of the GNU General
5746 Public License version 2 as published by the Free Software Foundation.
5747
5749 James Yonan james@openvpn.net
5750 OPENVPN(8)