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