#!/bin/sh
#
# rc.firewall - Initial SIMPLE IP Firewall test script for 2.4.x
#
# Author: Oskar Andreasson <blueflux@koffein.net>
# (c) of BoingWorld.com, use at your own risk, do whatever you please with
# it as long as you don't distribute this without due credits to
# BoingWorld.com
#

###########
# Configuration options, these will speed you up getting this script to
# work with your own setup.

#
# your LAN's IP range and localhost IP. /24 means to only use the first 24 
# bits of the 32 bit IP adress. the same as netmask 255.255.255.0
#
# INET_IP is used by me to allow myself to do anything to myself, might
# be a security risc but sometimes I want this. If you don't have a static
# IP, I suggest not using this option at all for now but it's stil
# enabled per default and will add some really nifty security bugs for all
# those who skips reading the documentation=)

LAN_IP="192.168.1.2"
LAN_IP_RANGE="192.168.1.0/24"
LAN_BCAST_ADRESS="192.168.1.255"
LAN_IFACE="eth0"

LO_IFACE="lo"
LO_IP="127.0.0.1"

INET_IP="213.237.89.99"
INET_IFACE="eth0"

IPTABLES="/sbin/iptables"

#########
# Load all required IPTables modules
#
/sbin/depmod -a

#
# Adds some iptables targets like LOG and MASQUARADE.
#
#/sbin/modprobe ipt_LOG
#/sbin/modprobe ipt_MASQUERADE
/sbin/modprobe ip_tables
/sbin/modprobe ip_conntrack
/sbin/modprobe iptable_filter
/sbin/modprobe iptable_mangle
/sbin/modprobe iptable_nat
/sbin/modprobe ipt_LOG
/sbin/modprobe ipt_limit
/sbin/modprobe ipt_state

#########
#
# Enable ip_forward, this is critical since it is turned off as default in 
# Linux.
#
echo "1" > /proc/sys/net/ipv4/ip_forward

#
# Dynamic IP users:
#
#echo "1" > /proc/sys/net/ipv4/ip_dynaddr

#########
#
# Enable simple IP Forwarding and Network Address Translation
#
$IPTABLES -t nat -A POSTROUTING -o $INET_IFACE -j SNAT --to-source $INET_IP

#
# Bad TCP packets we don't want
#
$IPTABLES -A FORWARD -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "IPT FORWARD New not syn:"
$IPTABLES -A FORWARD -p tcp ! --syn -m state --state NEW -j DROP

#
# Accept the packets we actually want to forward
#
$IPTABLES -A FORWARD -i $LAN_IFACE -j ACCEPT
$IPTABLES -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT 
$IPTABLES -A FORWARD -m limit --limit 3/minute --limit-burst 3 -j LOG --log-level DEBUG --log-prefix "IPT FORWARD packet died: "

#########
#
# Set default policies for the INPUT, FORWARD and OUTPUT chains
#
$IPTABLES -P INPUT DROP
$IPTABLES -P OUTPUT DROP
$IPTABLES -P FORWARD DROP

#
# Create chain for bad tcp packets
# 
$IPTABLES -N bad_tcp_packets

#########
#
# Create separate chains for ICMP, TCP and UDP to traverse
#
$IPTABLES -N icmp_packets
$IPTABLES -N tcp_packets
$IPTABLES -N udpincoming_packets

#
# bad_tcp_packets chain
# $IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "New not syn:"
$IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j DROP

#
# The allowed chain for TCP connections
#
$IPTABLES -N allowed
$IPTABLES -A allowed -p TCP --syn -j ACCEPT
$IPTABLES -A allowed -p TCP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A allowed -p TCP -j DROP

#
# ICMP rules
#
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 0 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 3 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 5 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT

#
# TCP rules
#
$IPTABLES -A tcp_packets -p TCP -s 0/0 -j LOG --log-prefix "IPT tcp_packets :"
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 22 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 25 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 80 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 113 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 1810 -j allowed

#
# UDP ports
#
$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 25 -j ACCEPT
$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 53 -j ACCEPT
$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 123 -j ACCEPT
$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 2074 -j ACCEPT
$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 4000 -j ACCEPT

#########
#
# PREROUTING chain.
#
# Do some checks for obviously spoofed IP's 
#
#$IPTABLES -t nat -A PREROUTING -i $INET_IFACE -s 192.168.1.0/16 -j DROP
#$IPTABLES -t nat -A PREROUTING -i $INET_IFACE -s 10.0.0.0/8 -j DROP
#$IPTABLES -t nat -A PREROUTING -i $INET_IFACE -s 172.16.0.0/12 -j DROP

#########
#
# INPUT chain
#
# Take care of bad TCP packets that we don't want
#
$IPTABLES -A INPUT -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "IPT INPUT New not syn:"
$IPTABLES -A INPUT -p tcp ! --syn -m state --state NEW -j DROP

#
# Rules for incoming packets from the internet
#
$IPTABLES -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets
$IPTABLES -A INPUT -p TCP -i $INET_IFACE -j tcp_packets
$IPTABLES -A INPUT -p UDP -i $INET_IFACE -j udpincoming_packets

#
# Rules for special networks not part of the Internet
#
$IPTABLES -A INPUT -p ALL -i $LAN_IFACE -d $LAN_BCAST_ADRESS -j ACCEPT
$IPTABLES -A INPUT -p ALL -i $LO_IFACE -d $LO_IP -j ACCEPT
$IPTABLES -A INPUT -p ALL -i $LO_IFACE -d $LAN_IP -j ACCEPT
$IPTABLES -A INPUT -p ALL -i $LAN_IFACE -d $LAN_IP -j ACCEPT
$IPTABLES -A INPUT -p ALL -d $INET_IP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A INPUT -m limit --limit 3/minute --limit-burst 3 -j LOG --log-level DEBUG --log-prefix "IPT INPUT packet died: "

#
# OUTPUT chain
#
$IPTABLES -A OUTPUT -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "IPT OUTPUT New not syn:"
$IPTABLES -A OUTPUT -p tcp ! --syn -m state --state NEW -j DROP

$IPTABLES -A OUTPUT -p ALL -s $LO_IP -j ACCEPT
$IPTABLES -A OUTPUT -p ALL -s $LAN_IP -j ACCEPT
$IPTABLES -A OUTPUT -p ALL -s $INET_IP -j LOG --log-prefix "IPT OUTPUT $INET_IP: "
$IPTABLES -A OUTPUT -p ALL -s $INET_IP -j ACCEPT
$IPTABLES -A OUTPUT -m limit --limit 3/minute --limit-burst 3 -j LOG --log-level DEBUG --log-prefix "IPT OUTPUT packet died: "