tufkal@tux:~$ cat /etc/init.d/custom-firewall4
echo "   Loading Firewall"

IPTABLES=/sbin/iptables

EXTIF="eth1"
INTIF="eth0"
echo "   External Interface:  $EXTIF"
echo "   Internal Interface:  $INTIF"

echo "   Enabling forwarding.."
echo "1" > /proc/sys/net/ipv4/ip_forward

echo "   Enabling DynamicAddr.."
echo "1" > /proc/sys/net/ipv4/ip_dynaddr

echo "   Clearing any existing rules and setting default policy.."
$IPTABLES -P INPUT ACCEPT
$IPTABLES -F INPUT
$IPTABLES -P OUTPUT ACCEPT
$IPTABLES -F OUTPUT
$IPTABLES -P FORWARD DROP
$IPTABLES -F FORWARD
$IPTABLES -t nat -F



echo "   FWD: Allow all connections OUT and only existing and related ones IN"
$IPTABLES -A FORWARD -i $EXTIF -o $INTIF -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A FORWARD -i $INTIF -o $EXTIF -j ACCEPT
$IPTABLES -A FORWARD -j LOG


echo "   Enabling SNAT (MASQUERADE) functionality on $EXTIF"
$IPTABLES -t nat -A POSTROUTING -o $EXTIF -j MASQUERADE

echo "    Done"