\          \
                 --------       /          /      --------
   Remote ______| Client |______\ Internet \_____| Server |______ Private
   Network      | Router |      /          /     | Router |       Network
                 --------       \          \      --------
                                /          /


                         Client Router
               ----------------------------------------------------
              |   /->    10.0.0.0/255.0.0.0   \                    |
  Remote      |  |-->  172.16.0.0/255.240.0.0  |--> Tunnel >---\   |
  Network >---|--|--> 192.168.0.0/255.255.0.0 /                 |--|----> Internet
 192.168.12.0 |  |                                              |  |
              |   \-----> 0.0.0.0/0.0.0.0 --> IP Masquerade >--/   |
               ----------------------------------------------------


                        Server Router
             ----------------------------------------------------
            |                   /->    10.0.0.0/255.0.0.0    \   |
            |   /--> Tunnel >--|-->  172.16.0.0/255.240.0.0   |--|----> Private
Internet >--|--|                \--> 192.168.0.0/255.255.0.0 /   |      Network
            |  |                                                 |     172.16.0.0/12
            |   \-----> 0.0.0.0/0.0.0.0 -----> /dev/null         |    192.168.0.0/16
             ----------------------------------------------------

# /usr/sbin/pty-redir /usr/bin/ssh -t -e none -o 'Batchmode yes' -c blowfish -i /root/.ssh/identity.vpn -l joe > /tmp/vpn-device
# sleep 10

# /usr/sbin/pppd `cat /tmp/vpn-device`
# sleep 15

# /sbin/route add -net 172.16.0.0 gw vpn-internal.mycompany.com netmask 255.240.0.0
# /sbin/route add -net 192.168.0.0 gw vpn-internal.mycompany.com netmask 255.255.0.0

#! /bin/bash
#
# vpnd: Monitor the tunnel, bring it up and down as necessary
#

USERNAME=vpn-username
IDENTITY=/root/.ssh/identity.vpn

VPN_DIR=/usr/local/vpn
LOCK_DIR=/var/run
VPN_EXTERNAL=vpn.mycompany.com
VPN_INTERNAL=vpn-internal.mycompany.com
PTY_REDIR=${VPN_DIR}/pty-redir
SSH=${VPN_DIR}/${VPN_EXTERNAL}
PPPD=/usr/sbin/pppd
ROUTE=/sbin/route
CRYPTO=blowfish
PPP_OPTIONS="noipdefault ipcp-accept-local ipcp-accept-remote local noauth nocrtscts lock nodefaultroute"
ORIG_SSH=/usr/bin/ssh


starttunnel () {
   $PTY_REDIR $SSH -t -e none -o 'Batchmode yes' -c $CRYPTO -i $IDENTITY -l $USERNAME > /tmp/vpn-device
   sleep 15

   $PPPD `cat /tmp/vpn-device` $PPP_OPTIONS
   sleep 15

   # Add routes (modify these lines as necessary)
   /sbin/route add -net 10.0.0.0 gw $VPN_INTERNAL netmask 255.0.0.0
   /sbin/route add -net 172.16.0.0 gw $VPN_INTERNAL netmask 255.240.0.0
   /sbin/route add -net 192.168.0.0 gw $VPN_INTERNAL netmask 255.255.0.0
}

stoptunnel () {
   kill `ps ax | grep $SSH | grep -v grep | awk '{print $1}'`
}

resettunnel () {
   echo "reseting tunnel."
   date >> ${VPN_DIR}/restart.log
   eval stoptunnel
   sleep 5
   eval starttunnel
}

checktunnel () {
   ping -c 4 $VPN_EXTERNAL 2>/dev/null 1>/dev/null

   if [ $? -eq 0 ]; then
      ping -c 4 $VPN_INTERNAL 2>/dev/null 1>/dev/null
      if [ $? -ne 0 ]; then
         eval resettunnel
      fi
   fi
}

settraps () {
   trap "eval stoptunnel; exit 0" INT TERM
   trap "eval resettunnel" HUP
   trap "eval checktunnel" USR1
}

runchecks () {
   if [ -f ${LOCK_DIR}/tunnel.pid ]; then
      OLD_PID=`cat ${LOCK_DIR}/vpnd.pid`
      if [ -d /proc/${OLD_PID} ]; then
         echo "vpnd is already running on process ${OLD_PID}."
         exit 1
      else
         echo "removing stale pid file."
         rm -rf ${LOCK_DIR}/vpnd.pid
         echo $$ > ${LOCK_DIR}/vpnd.pid
         echo "checking tunnel state."
         eval checktunnel
      fi
   else
      echo $$ > ${LOCK_DIR}/vpnd.pid
      eval starttunnel
   fi
}

case $1 in
    check)  if [ -d /proc/`cat ${LOCK_DIR}/vpnd.pid` ]; then
               kill -USR1 `cat ${LOCK_DIR}/vpnd.pid`
               exit 0
            else
               echo "vpnd is not running."
               exit 1
            fi ;;

    reset)  if [ -d /proc/`cat ${LOCK_DIR}/vpnd.pid` ]; then
               kill -HUP `cat ${LOCK_DIR}/vpnd.pid`
               exit 0
            else
               echo "vpnd is not running."
               exit 1
            fi ;;

   --help | -h)
            echo "Usage: vpnd [ check | reset ]"
            echo "Options:"
            echo "     check    Sends running vpnd a USR1 signal, telling it to check"
            echo "              the tunnel state, and restart if neccesary."
            echo "     reset    Sends running vpnd a HUP signal, telling it to reset"
            echo "              it's tunnel connection." ;; 
esac

ln -sf $ORIG_SSH $SSH
settraps
runchecks

while true; do
   i=0
   while [ $i -lt 600 ]; do
      i=((i+1))
      sleep 1
   done
   eval checktunnel
done

# This is the ssh server system wide configuration file.

Port 22
ListenAddress 0.0.0.0
HostKey /etc/ssh_host_key
RandomSeed /etc/ssh_random_seed
ServerKeyBits 768
LoginGraceTime 600
KeyRegenerationInterval 3600
PermitRootLogin yes
IgnoreRhosts yes
StrictModes yes
QuietMode no
FascistLogging yes
CheckMail no
IdleTimeout 3d
X11Forwarding no
PrintMotd no
KeepAlive yes
SyslogFacility DAEMON
RhostsAuthentication no
RhostsRSAAuthentication no
RSAAuthentication yes
PasswordAuthentication no
PermitEmptyPasswords no
UseLogin no

# /usr/sbin/groupadd vpn-users

# mkdir /home/vpn-users

# mkdir /home/vpn-users/.ssh

...
nobody:x:65534:100:nobody:/dev/null:
mwilson:x:1000:100:Matthew Wilson,,,:/home/mwilson:/bin/bash
joe:*:1020:101:Joe Mode (home),,,:/home/vpn-users:/usr/sbin/pppd
bill:*:1020:101:Bill Smith (home),,,:/home/vpn-users:/usr/sbin/pppd
frank:*:1020:101:Frank Jones (home),,,:/home/vpn-users:/usr/sbin/pppd
...

# mkdir /root/.ssh
# ssh-keygen -f /root/.ssh/identity.vpn -P ""

1024 35 1430723736674162619588314275167.......250872101150654839 root@vpn-client.mycompany.com

# ssh vpn.mycompany.com

# /usr/sbin/pty-redir /usr/bin/ssh -t -e none -o 'Batchmode yes' -c blowfish -i /root/.ssh/identity.vpn -l vpn-user vpn.mycompany.com > /tmp/vpn-device

	(now wait about 10 seconds)

# /usr/sbin/pppd `cat /tmp/vpn-device` 192.168.10.254:192.168.40.254

# /sbin/route add -net 192.168.0.0 gw vpn-internal.mycompany.com netmask 255.255.0.0