man secvpn.conf (1): Configuration file for the Secure Virtual Private Network

SYNOPSIS

/etc/network/secvpn.conf

DESCRIPTION

The configuration file for the Secure Virtual Private Network is expected to be a valid shell script defining variables and functions. The script is sourced by the other programs and scripts maintaining the SVPN and therefore must be handled with care!

The file is composed of two parts, a variable definition section and a function definition section (in the sense of the shell syntax).

Variables

The variables are used to define global variables for the SVPN:

THIS_IS

identifies the current hostname.

VPNS

is used to specifiy the relationship of SVPN hosts, i.e. which SVPNs should be started by secvpn and which role do the host play in this relationship.

The syntax is ActiveHost->PassiveHost, i.e. the active host is responsible to establish the secure channel to the passive host (using ssh) by starting the pppd connection and setting routes on the active and the passive host.

Multiple relationships are separated by a blank, the identifiers used for the ActiveHost and the PassiveHost must match the contents of the variable THIS_IS in the corresponding configuration files.

CRYPT_MASK

is the network mask used for the real connection via the T_CRYPT_IP IP addresses.

SSHPORT

is currently not used. In future releases, this variable may be used to identify the port to which the ssh connection should be made.

Functions

Functions are used to define the specific attributes of the SVPN hosts and the SVPN relationships.

First, a function for each SVPN host has to be defined. The name of the function must match the hostname of the SVPN host (i.e. the contents of the variable THIS_IS in the corresponding configuration file). The SVPN host specific functions are used to set the following, host specific variables:

GOOD_ONES: specifies the official, good network address (together with the network mask given as the number of contiguous bits separated with a slash) of this SVPN host. This network is the secure subnet which is represented by this SVPN host.
GOOD_IP: identifies the official, good IP address of the SVPN host. This IP address must be used for all secure communications with this host.

Next, a function for each SVPN relationship has to be defined. The names of these functions are listed in the VPNS variable (see above) and receive a prefix of vpn_ These relationship defining functions are used to set the following connection specific variables:

T_GOOD_ONES: is an optional variable used to specify the list (blank separated) of secure networks which are directly or indirectly reachable via the active SVPN host of this SVPN connection ( this good IP addresses ). The networks are identified by their IP address and their attached network mask specified by the number of contiguous bits and separated by a slash. Note that the own network must not be listed in this variable, because it is specified in the GOOD_ONES variable in the SVPN host function of the active member of the current connection.
T_BAD_IP: is the IP address of the active SVPN host which is used to establish the secure channel to the passive SVPN host. This IP address might be attached to a second interface on the active SVPN host (if a multi homed system is used) or the same IP address as for the GOOD_IP might be used (if the active SVPN host is a single homed system).
T_CRYPT_IP: is the IP address on the active SVPN host which is used for the secure ppp connection to the corresponding pppd on the passive SVPN host -- a new ppp interface will be added by secvpn for this ip.
O_CRYPT_IP: is the IP address on the passive SVPN host which is used for the secure ppp connection to the corresponding pppd on the active SVPN host -- a new ppp interface will be added by secvpn for this ip.
O_BAD_IP: is the IP address of the passive SVPN host which is used to establish the secure channel to the active SVPN host. This IP address might be attached to a second interface on the passive SVPN host (if a multi homed system is used) or the same IP address as for the GOOD_IP might be used (if the passive SVPN host is a single homed system).
O_GOOD_ONES: is an optional variable used to specify the list (blank separated) of secure networks which are directly or indirectly reachable via the passive SVPN host of this SVPN connection ( other good IP addresses ). The networks are identified by their IP address and their attached network mask specified by the number of contiguous bits and separated by a slash. Note that the own network must not be listed in this variable, because it is specified in the GOOD_ONES variable in the SVPN host function of the passive member of the current connection.

Example

# The SVPN acts as a router connecting 2 subnets.
# Each subnet itself is secure. But the Internet is unsecure.
#
#     Secure Subnet 1        /          /    Secure Subnet 2
#                            / Unsecure /
#  [hosts1]   [secvpn1]      / Internet /  [secvpn2]      [hosts2]
#  X.X.X.n    eth0:X.X.X.1   / ISDN     /  eth0:Y.Y.Y.1   Y.Y.Y.n
#             eth1:I.I.I.1   /          /  eth1:J.J.J.1
#
# ToDo:
#   The hosts1 should be able to communicate secure with hosts2 
#   over an unsecure network. 
#   secvpn1/secvpn2 are used as routers that connect the secure 
#   subnet to the internet.
#   Hosts1/hosts2 have routing entries using secvpn1/secvpn2 to 
#   reach hosts2/hosts1.
#
#
# Global variables
#
THIS_IS="`hostname`"
VPNS="secvpn1->secvpn2"
CRYPT_MASK="255.255.255.0"
SSHPORT="22"
#
# SVPN host specifications
#
# this is for the system with hostname 'secvpn1'
secvpn1() { GOOD_ONES="X.X.X.0/24"; GOOD_IP="X.X.X.1" }
# this is for the system with hostname 'secvpn2'
secvpn2() { GOOD_ONES="Y.Y.Y.0/24"; GOOD_IP="Y.Y.Y.1" }
#
# SVPN connection specifications
#
# this is for the connection from 'secvpn1' (active) to
# 'secvpn2' (passive)
vpn_secvpn1_secvpn2()
{
#         -----------
#         | secvpn1 |----------------+
#         -----------                |
#              |                     |
               |               # ppp-DEV
   T_BAD_IP="I.I.I.1";         T_CRYPT_IP="10.1.1.1"
#              |                     |  
               |               # ppp-DEV
   O_BAD_IP="J.J.J.1";         O_CRYPT_IP="10.1.1.2"
#              |                     |                       
#         -----------                |
#         | secvpn2 |----------------+
#         -----------
}

OTHER

To have real security it is necessary to secure each secvpn host and to have firewalls on each secvpn host allowing only selected IP-Adresses and Ports to pass through the VPN.

AUTHOR

Bernd Schumacher, HP Consulting, HEWLETT-PACKARD GmbH, Bad Homburg, 2000

COPYRIGHT

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