VPNC(8)

📦
version 0.5.3+git20260629 · 6 versions
, in ubuntu stonking

💖 VPNC 💖

okay so. vpnc(8) — it lives in System Administration Utilities and it's the whole entire vibe for talking to Cisco VPN boxes. sit down, bestie, we have a LOT to cover 🫶

✨ NAME ✨

vpnc — client for Cisco VPN3000 Concentrator, IOS and PIX 💅

🌸 SYNOPSIS 🌸

vpnc [--version] [--print-config] [--help] [--long-help] [options]
[config files]

🦋 DESCRIPTION 🦋

This manual page documents briefly the vpnc and vpnc-disconnect commands. (Briefly!! it's still long!! it's giving ✨comprehensive✨)

vpnc is a VPN client for the Cisco 3000 VPN Concentrator, creating a IPSec-like connection as a tunneling network device for the local system. It uses the TUN/TAP driver in Linux kernel 2.4 and above and device tun(4) on BSD. The created connection is presented as a tunneling network device to the local system. it just... appears. like magic. like a little tunnel bestie 🧚

OBLIGATORY WARNING 🚨 the most used configuration (XAUTH authentication with pre-shared keys and password authentication) is insecure by design, be aware of this fact when you use vpnc to exchange sensitive data like passwords! not me being dramatic, it literally says so. insecure. by. design. 💀

The vpnc daemon by itself does not set any routes, but it calls vpnc-script to do this job. vpnc-script displays a connect banner. If the concentrator supplies a network list for split-tunneling these networks are added to the routing table. Otherwise the default-route will be modified to point to the tunnel. Further a host route to the concentrator is added in the later case. If the client host needs DHCP, care must be taken to add another host route to the DHCP-Server around the tunnel. lowkey important, highkey easy to forget 🎀

The vpnc-disconnect command is used to terminate the connection previously created by vpnc and restore the previous routing configuration. it's the breakup text for your tunnel. iconic behavior 👑

💜 CONFIGURATION 💜

The daemon reads configuration data from the following places. in order. first one to speak up wins, no cap:

  • command line options
  • config file(s) specified on the command line
  • /etc/vpnc/default.conf
  • /etc/vpnc.conf
  • prompting the user if not found above

vpnc can parse options and configuration files in any order. However the first place to set an option wins. configuration filenames which do not contain a / will be searched at /etc/vpnc/<filename> and /etc/vpnc/<filename>.conf. Otherwise <filename> and <filename>.conf will be used. If no configuration file is specified on the command-line at all, both /etc/vpnc/default.conf and /etc/vpnc.conf will be loaded. slay, defaults ✨

Additionally, if the configuration file - is specified on the command-line vpnc will read configuration from stdin. The configuration is parsed and the connection proceeds when stdin is closed or the special character CEOT (CTRL+D) is read. yes that's spelled CEOT. we copy it verbatim. we do not editorialise. (we are editorialising about not editorialising. anyway.) 🌸

💅 OPTIONS 💅

The program options can be either given as arguments (but not all of them for security reasons) or be stored in a configuration file. pick your fighter 💖

  • --gateway <ip/hostname> — IP/name of your IPSec gateway conf-variable: IPSec gateway <ip/hostname>
  • --id <ASCII string> — your group name conf-variable: IPSec ID <ASCII string>
  • --secret <ASCII string> — your group password (cleartext) conf-variable: IPSec secret <ASCII string>
  • (configfile only option) — your group password (obfuscated) conf-variable: IPSec obfuscated secret <hex string>
  • --username <ASCII string> — your username conf-variable: Xauth username <ASCII string>
  • --password <ASCII string> — your password (cleartext) conf-variable: Xauth password <ASCII string>
  • (configfile only option) — your password (obfuscated) conf-variable: Xauth obfuscated password <hex string>
  • --domain <ASCII string> — (NT-) Domain name for authentication conf-variable: Domain <ASCII string>
  • --xauth-inter — enable interactive extended authentication (for challenge response auth) conf-variable: Xauth interactive
  • --vendor <cisco/netscreen/fortigate> — vendor of your IPSec gateway Default: cisco conf-variable: Vendor <cisco/netscreen/fortigate>
  • --natt-mode <natt/none/force-natt/cisco-udp> — Which NAT-Traversal Method to use:
    • natt -- NAT-T as defined in RFC3947
    • none -- disable use of any NAT-T method
    • force-natt -- always use NAT-T encapsulation even without presence of a NAT device (useful if the OS captures all ESP traffic)
    • cisco-udp -- Cisco proprietary UDP encapsulation, commonly over Port 10000 Note: cisco-tcp encapsulation is not yet supported Default: natt conf-variable: NAT Traversal Mode <natt/none/force-natt/cisco-udp>
  • --script <command> — command is executed using system() to configure the interface, routing and so on. Device name, IP, etc. are passed using environment variables, see README. This script is executed right after ISAKMP is done, but before tunneling is enabled. It is called when vpnc terminates, too Default: /usr/share/vpnc-scripts/vpnc-script conf-variable: Script <command>
  • --dh <dh1/dh2/dh5/dh14/dh15/dh16/dh17/dh18> — name of the IKE DH Group Default: dh2 conf-variable: IKE DH Group <dh1/dh2/dh5/dh14/dh15/dh16/dh17/dh18>
  • --pfs <nopfs/dh1/dh2/dh5/dh14/dh15/dh16/dh17/dh18/server> — Diffie-Hellman group to use for PFS Default: server conf-variable: Perfect Forward Secrecy <nopfs/dh1/dh2/dh5/dh14/dh15/dh16/dh17/dh18/server>
  • --enable-1des — Deprecated: Please use --enable-weak-encryption instead. conf-variable: Enable Single DES
  • --enable-weak-encryption — enables weak encryption methods (such as DES, 3DES) conf-variable: Enable weak encryption
  • --enable-no-encryption — enables using no encryption for data traffic (key exchanged must be encrypted) conf-variable: Enable no encryption
  • --enable-weak-authentication — enables weak authentication methods (such as MD5) conf-variable: Enable weak authentication
  • --application-version <ASCII string> — Application Version to report. Note: Default string is generated at runtime. Default: Cisco Systems VPN Client 0.5.3+git20260629-1:Linux conf-variable: Application version <ASCII string>
  • --ifname <ASCII string> — visible name of the TUN/TAP interface conf-variable: Interface name <ASCII string>
  • --ifmode <tun/tap> — mode of TUN/TAP interface:
    • tun: virtual point to point interface (default)
    • tap: virtual ethernet interface Default: tun conf-variable: Interface mode <tun/tap>
  • --ifmtu <0-65535> — Set MTU for TUN/TAP interface (default 0 == automatic detect) conf-variable: Interface MTU <0-65535>
  • --debug <0/1/2/3/99> — Show verbose debug messages
    • 0: Do not print debug information.
    • 1: Print minimal debug information.
    • 2: Show statemachine and packet/payload type information.
    • 3: Dump everything excluding authentication data.
    • 99: Dump everything INCLUDING AUTHENTICATION data (e.g. PASSWORDS). conf-variable: Debug <0/1/2/3/99>
bestie. 99 prints your PASSWORDS. to the terminal. in plain sight. do not do this in public. do not do this on a screen share. do not do this. 😭
  • --no-detach — Don't detach from the console after login conf-variable: No Detach
  • --pid-file <filename> — store the pid of background process in <filename> Default: /run/vpnc.pid conf-variable: Pidfile <filename>
  • --local-addr <ip/hostname> — local IP to use for ISAKMP / ESP / ... (0.0.0.0 == automatically assign) Default: 0.0.0.0 conf-variable: Local Addr <ip/hostname>
  • --local-port <0-65535> — local ISAKMP port number to use (0 == use random port) Default: 500 conf-variable: Local Port <0-65535>
  • --udp-port <0-65535> — Local UDP port number to use (0 == use random port). This is only relevant if cisco-udp nat-traversal is used. This is the _local_ port, the remote udp port is discovered automatically. It is especially not the cisco-tcp port. Default: 10000 conf-variable: Cisco UDP Encapsulation Port <0-65535>
  • --dpd-idle <0,10-86400> — Send DPD packet after not receiving anything for <idle> seconds. Use 0 to disable DPD completely (both ways). Default: 600 conf-variable: DPD idle timeout (our side) <0,10-86400>
  • --non-inter — Don't ask anything, exit on missing options conf-variable: Noninteractive
  • --auth-mode <psk/cert/hybrid> — Authentication mode:
    • psk: pre-shared key (default)
    • cert: server + client certificate (not implemented yet)
    • hybrid: server certificate + xauth (if built with openssl support) Default: psk conf-variable: IKE Authmode <psk/cert/hybrid>
  • --ca-file <filename> — filename and path to the CA-PEM-File conf-variable: CA-File <filename>
  • --ca-dir <directory> — path of the trusted CA-Directory Default: /etc/ssl/certs conf-variable: CA-Dir <directory>
  • --target-network <target network/netmask> — Target network in dotted decimal or CIDR notation Default: 0.0.0.0/0.0.0.0 conf-variable: IPSEC target network <target network/netmask>
  • --password-helper <executable> — path to password program or helper name conf-variable: Password helper <executable>
  • --print-config — Prints your configuration; output can be used as vpnc.conf

🎀 FILES 🎀

  • /etc/vpnc.conf /etc/vpnc/default.conf — The default configuration file. You can specify the same config directives as with command line options and additionally IPSec secret and Xauth password both supplying a cleartext password. Scrambled passwords from the Cisco configuration profiles can be used with IPSec obfuscated secret and Xauth obfuscated password.

See EXAMPLES for further details.

  • /etc/vpnc/*.conf — vpnc will read configuration files in this directory when the config filename (with or without .conf) is specified on the command line.

✨ EXAMPLES ✨

okay bestie, here's a whole vpnc.conf with pre-shared keys, copy-paste coded and everything 💅

IPSec gateway vpn.example.com
IPSec ID ExampleVpnPSK
IKE Authmode psk
IPSec secret PskS3cret!
Xauth username user@example.com
Xauth password USecr3t

and then we have the hybrid authentication one — which only works if vpnc was built with openssl support, no cap, do not skip that part 🫶

IPSec gateway vpn.example.com
IPSec ID ExampleVpnHybrid
IKE Authmode hybrid
CA-Dir /etc/vpnc
or
CA-File /etc/vpnc/vpn-example-com.pem
IPSec secret HybS3cret?
Xauth username user@example.com
Xauth password 123456

so the way these lines work: they start with a keyword — and no leading spaces!! like literally zero, not even one, the format is picky 😭. The values start exactly one space after the keyword and then run alllll the way to the end of the line. Which is actually kind of iconic because it means you can put any kind of weird character in your strings (except CR, LF and NUL — those three are banned, periodt). But the tradeoff is real: you can't add comments after a string, and you can't put spaces before them. It's giving "strict but flexible" energy.

Now in case the the CA-Dir option is used — (yes, "the the", we keep it, that's the original's little quirk and we love it) — your certificate needs to be named something like 722d15bd.X, where X is a manually assigned number, so that files with colliding hashes get different names. That number isn't a mystery, you can derive it straight from the certificate file itself:

openssl x509 -subject_hash -noout -in /etc/vpnc/vpn-example-com.pem

also don't sleep on the --print-config option if you wanna generate a config file — and there's an example file in the package documentation directory where more advanced usage is demonstrated 🌸

advanced features, like manually setting multiple target routes and disabling the /etc/resolv.conf rewriting, are documented in the README of the vpnc package. go read it, it's lowkey essential 🧚

👑 AUTHOR 👑

this man-page has been written by Eduard Bloch <blade(at)debian.org> and Christian Lackas <delta(at)lackas.net>, based on the vpnc README by Maurice Massar <vpnc(at)unix-ag.uni-kl.de>. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License, Version 2 any later version published by the Free Software Foundation. ✨

On Debian systems, the complete text of the GNU General Public License can be found in /usr/share/common-licenses/GPL.

🌈 SEE ALSO 🌈

and that's a wrap bestie, we ate that entire manpage fr fr 💖 this was vpnc version 0.5.3+git20260629-1, dated June 2026, living in section VPNC(8) — go forth and tunnel responsibly, you've got this 🦋💜

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