examples/firewall

#!/bin/sh
#
# Firewall script for GGSN
#
# Uses $IFGN (eth0) as the Gn interface (Gn) and
# $IFGI (eth1) as the Gi interface.
#
# SUMMARY
# * All connections originating from GGSN are allowed.
# * Incoming ssh, GTPv0 and GTPv1 is allowed on the Gn interface.
# * Incoming ssh is allowed on the Gi interface.
# * Forwarding is allowed to and from the Gi interface, but disallowed
#   to and from the Gn interface.
# * Masquerede on Gi interface.

IPTABLES="/sbin/iptables"
IFGN="eth0"
IFGI="eth1"

$IPTABLES -P INPUT DROP
$IPTABLES -P FORWARD ACCEPT
$IPTABLES -P OUTPUT ACCEPT

#Allow related and established on all interfaces (input)
$IPTABLES -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

#Allow releated, established, GTP and ssh on $IFGN. Reject everything else.
$IPTABLES -A INPUT -i $IFGN -p tcp -m tcp --dport 22 --syn -j ACCEPT
$IPTABLES -A INPUT -i $IFGN -p udp -m udp --dport 2123 -j ACCEPT
$IPTABLES -A INPUT -i $IFGN -p udp -m udp --dport 2152 -j ACCEPT
$IPTABLES -A INPUT -i $IFGN -p udp -m udp --dport 3386 -j ACCEPT
$IPTABLES -A INPUT -i $IFGN -j REJECT

#Allow related, established and ssh. Drop everything else.
$IPTABLES -A INPUT -i $IFGI -p tcp -m tcp --dport 22 --syn -j ACCEPT
$IPTABLES -A INPUT -i $IFGI -j DROP

# Masquerade everything going out on $IFGI
$IPTABLES -t nat -A POSTROUTING -o $IFGI -j MASQUERADE

#Allow everything on loopback interface.
$IPTABLES -A INPUT -i lo -j ACCEPT

# Drop everything to and from $IFGN (forward)
$IPTABLES -A FORWARD -i $IFGN -j DROP
$IPTABLES -A FORWARD -o $IFGN -j DROP