#!/bin/sh
 
PATH=/usr/sbin:/sbin:/bin:/usr/bin
 
#
# delete all existing rules.
#
iptables -F
iptables -t nat -F
iptables -t mangle -F
iptables -X
 
# Always accept loopback traffic
iptables -A INPUT -i lo -j ACCEPT
 
# Allow established connections, and those not coming from the outside
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -m state --state NEW -i ! eth1 -j ACCEPT
iptables -A FORWARD -i eth1 -o eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT
 
# Allow outgoing connections from the LAN side.
iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT
 
# Masquerade.
iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE
 
# Don't forward from the outside to the inside.
iptables -A FORWARD -i eth1 -o eth1 -j REJECT
 
# Enable routing.
echo 1 > /proc/sys/net/ipv4/ip_forward