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5. Configure the Client

If ppp and ssh are set up on the client, and the server is ready to connect, then all we need to do on the client is create the script to bring up the link.

5.1. Install the Script

The VPN connection is initiated using the vpn-pppssh script below.

  1. Save this file on the client (it doesn't matter where -- /usr/local/bin/vpn-pppssh is a good place) and make it executable by running "chmod a+x vpn-pppssh".

  2. Fill in the settings at the top of the file with the values you decided on in Section 3.3.

    Remember that this is running under bash so you'll need to avoid whitespace around the equals sign, use quotes where necessary, and escape metacharacters such as $. See the BASH Programming Introduction or Advanced Bash Scripting Guide for more.

    SERVER_HOSTNAME=eldivino.domain.com
    SERVER_USERNAME=vpn
    SERVER_IFIPADDR=192.168.3.2
    CLIENT_IFIPADDR=192.168.3.1
    

    Run "vpn-pppssh config" to print out a list of the configuration variables. This way, you can confirm that your settings are being interpreted correctly.

5.2. The vpn-pppssh Script

Here is vpn-pppssh. All the action is on one line. (the one beginning with "PPPD" in the start clause). All the rest of this file is just support code.

#!/bin/sh
# /usr/local/bin/vpn-pppssh
#
# This script initiates a ppp-ssh vpn connection.
# see the VPN PPP-SSH HOWTO on http://www.linuxdoc.org for more information.
#
# revision history:
# 1.6 11-Nov-1996 miquels@cistron.nl
# 1.7 20-Dec-1999 bart@jukie.net
# 2.0 16-May-2001 bronson@trestle.com


#
# You will need to change these variables...
#


# The host name or IP address of the SSH server that we are
# sending the connection request to:
SERVER_HOSTNAME=eldivino.domain.com

# The username on the VPN server that will run the tunnel.
# For security reasons, this should NOT be root.  (Any user
# that can use PPP can intitiate the connection on the client)
SERVER_USERNAME=vpn

# The VPN network interface on the server should use this address:
SERVER_IFIPADDR=192.168.3.2

# ...and on the client, this address:
CLIENT_IFIPADDR=192.168.3.1


# This tells ssh to use unprivileged high ports, even though it's
# running as root.  This way, you don't have to punch custom holes
# through your firewall.
LOCAL_SSH_OPTS="-P"


#
# The rest of this file should not need to be changed.
#



PATH=/usr/local/sbin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/bin/X11/:

#
# required commands...
#

PPPD=/usr/sbin/pppd
SSH=/usr/bin/ssh

if ! test -f $PPPD  ; then echo "can't find $PPPD";  exit 3; fi
if ! test -f $SSH   ; then echo "can't find $SSH";   exit 4; fi


case "$1" in
  start)
    # echo -n "Starting vpn to $SERVER_HOSTNAME: "
    ${PPPD} updetach noauth passive pty "${SSH} ${LOCAL_SSH_OPTS} ${SERVER_HOSTNAME} -l${SERVER_USERNAME} -o Batchmode=yes sudo ${PPPD} nodetach notty noauth" ipparam vpn ${CLIENT_IFIPADDR}:${SERVER_IFIPADDR}
    # echo "connected."
    ;;

  stop)
        # echo -n "Stopping vpn to $SERVER_HOSTNAME: "
        PID=`ps ax | grep "${SSH} ${LOCAL_SSH_OPTS} ${SERVER_HOSTNAME} -l${SERVER_USERNAME} -o" | grep -v ' passive ' | grep -v 'grep ' | awk '{print $1}'`
        if [ "${PID}" != "" ]; then
          kill $PID
          echo "disconnected."
        else
          echo "Failed to find PID for the connection"
        fi
    ;;

  config)
    echo "SERVER_HOSTNAME=$SERVER_HOSTNAME"
    echo "SERVER_USERNAME=$SERVER_USERNAME"
    echo "SERVER_IFIPADDR=$SERVER_IFIPADDR"
    echo "CLIENT_IFIPADDR=$CLIENT_IFIPADDR"
  ;;

  *)
    echo "Usage: vpn {start|stop|config}"
    exit 1
    ;;
esac

exit 0