vpnc(8) client for Cisco VPN3000 Concentrator, IOS and PIX


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


This manual page documents briefly the vpnc and vpnc-disconnect commands.

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.

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!

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.

The vpnc-disconnect command is used to terminate the connection previously created by vpnc and restore the previous routing configuration.


The daemon reads configuration data from the following places:
  • 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.

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.


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

--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>

(configfile only option)
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>

(configfile only option)
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>

enable interactive extended authentication (for challenge response auth)

conf-variable: Xauth interactive

--vendor <cisco/netscreen>
vendor of your IPSec gateway
Default: cisco

conf-variable: Vendor <cisco/netscreen>

--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>
name of the IKE DH Group
Default: dh2

conf-variable: IKE DH Group <dh1/dh2/dh5>

--pfs <nopfs/dh1/dh2/dh5/server>
Diffie-Hellman group to use for PFS
Default: server

conf-variable: Perfect Forward Secrecy <nopfs/dh1/dh2/dh5/server>

enables weak single DES encryption

conf-variable: Enable Single DES

enables using no encryption for data traffic (key exchanged must be encrypted)

conf-variable: Enable no encryption

--application-version <ASCII string>
Application Version to report. Note: Default string is generated at runtime.
Default: Cisco Systems VPN Client 0.5.3r550-2+b1: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 exluding authentication data.
  • 99: Dump everything INCLUDING AUTHENTICATION data (e.g. PASSWORDS).

conf-variable: Debug <0/1/2/3/99>

Don't detach from the console after login

conf-variable: No Detach

--pid-file <filename>
store the pid of background process in <filename>
Default: /var/run/vpnc.pid

conf-variable: Pidfile <filename>

--local-addr <ip/hostname>
local IP to use for ISAKMP / ESP / ... ( == automatically assign)

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: 300

conf-variable: DPD idle timeout (our side) <0,10-86400>

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

conf-variable: IPSEC target network <target network/netmask>

--password-helper <executable>
path to password program or helper name

conf-variable: Password helper <executable>

Prints your configuration; output can be used as vpnc.conf


/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.


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


This is an example vpnc.conf with pre-shared keys:

IPSec gateway vpn.example.com

IPSec ID ExampleVpnPSK

IKE Authmode psk

IPSec secret PskS3cret!

Xauth username [email protected]

Xauth password USecr3t

And another one with hybrid authentication (requires that vpnc was built with openssl support):

IPSec gateway vpn.example.com

IPSec ID ExampleVpnHybrid

IKE Authmode hybrid

CA-Dir /etc/vpnc


CA-File /etc/vpnc/vpn-example-com.pem

IPSec secret HybS3cret?

Xauth username [email protected]

Xauth password 123456

The lines begin with a keyword (no leading spaces!). The values start exactly one space after the keywords, and run to the end of line. This lets you put any kind of weird character (except CR, LF and NUL) in your strings, but it does mean you can't add comments after a string, or spaces before them.

In case the the CA-Dir option is used, your certificate needs to be named something like 722d15bd.X, where X is a manually assigned number to make sure that files with colliding hashes have different names. The number can be derived from the certificate file itself:

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

See also the --print-config option to generate a config file, and the example file in the package documentation directory where more advanced usage is demonstrated.

Advanced features like manual setting of multiple target routes and disabling /etc/resolv.conf rewriting is documented in the README of the vpnc package.


This man-page has been written by Eduard Bloch <blade(at)debian.org> and Christian Lackas <delta(at)lackas.net>, based on 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.