#!/bin/bash
 
 # Set some sensible default policies
 iptables -P INPUT DROP
 iptables -P FORWARD DROP
 iptables -P OUTPUT ACCEPT
 
 # Open the loopback interface
 iptables -A INPUT -i lo -j ACCEPT
 
 # This is the rule that does the work
 iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT 
