#!/bin/sh
#
# rc.firewall - Initial SIMPLE IP Firewall test script for 2.4.x
#
# Author: David Whitmarsh
# (c) 2001, 2002 Sparkle Computer Co ltd.
# based on rc.firewall by Oskar Andreasson <blueflux@koffein.net>
# parts (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 and Sparkle Computer Co Ltd
#

###########
# 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
#
# BR_IP is used to access the firewall accross the network
# For maxium security don't set one up - but then you must do
# everything directly on the firewall.

BR_IP="xxx.xxx.xxx.57"
BR_IFACE=br0

LAN_BCAST_ADDRESS="xxx.xxx.xxx.63"
INTERNAL_ADDRESS_RANGE="xxx.xxx.xxx.56/29"

INET_IFACE="eth1"
LAN_IFACE="eth0"

LO_IFACE="lo"
LO_IP="127.0.0.1"

IPTABLES="/sbin/iptables"

#########
# Load all required IPTables modules
#

#
# Needed to initially load modules
#
/sbin/depmod -a

#
# Adds some iptables targets like LOG, REJECT
#
/sbin/modprobe ipt_LOG
/sbin/modprobe ipt_REJECT

#
# Support for connection tracking of FTP and IRC.
#
/sbin/modprobe ip_conntrack_ftp
/sbin/modprobe ip_conntrack_irc

#
# Take down the interfaces before setting up the bridge
#

ifdown $INET_IFACE
ifdown $LAN_IFACE
ifconfig $INET_IFACE 0.0.0.0
ifconfig $LAN_IFACE 0.0.0.0

# Clean up for a restart

$IPTABLES -F 
$IPTABLES -X
#
# Set default policies for the INPUT, FORWARD and OUTPUT chains
#

$IPTABLES -P INPUT DROP
$IPTABLES -P OUTPUT ACCEPT
$IPTABLES -P FORWARD DROP

# Our interfaces don't have IP addresses so we have to start with the mangle
# PREROUTING table

$IPTABLES -t mangle -P PREROUTING DROP

# Now we are pretty secure, let's start the bridge
# This will create a new interface

brctl addbr $BR_IFACE

# and add the interfaces to it
brctl addif $BR_IFACE $INET_IFACE
brctl addif $BR_IFACE $LAN_IFACE

# make us visible to the network again (optional)
if [ "$BR_IP" != "" ] ; then
    ifconfig $BR_IFACE $BR_IP
else
# otherwise we must at least bring the interface up for the bridge to work.
    ifconfig $BR_IFACE up
fi

# Block obvious spoofs

$IPTABLES -t mangle -A PREROUTING -s 192.168.0.0/16 -j DROP
$IPTABLES -t mangle -A PREROUTING -s 10.0.0.0/8 -j DROP
$IPTABLES -t mangle -A PREROUTING -s 172.16.0.0/12 -j DROP

# Accept internal packets on the internal i/f
$IPTABLES -t mangle -A PREROUTING -i $LAN_IFACE -s $INTERNAL_ADDRESS_RANGE -j ACCEPT

# Accept external packets on the external i/f

$IPTABLES -t mangle -A PREROUTING -i $INET_IFACE ! -s $INTERNAL_ADDRESS_RANGE -j ACCEPT

#
# Accept the packets we actually want to forward
#

$IPTABLES -A FORWARD -p ALL -s $INTERNAL_ADDRESS_RANGE -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 7 --log-prefix "IPT FORWARD packet died: "

#
# Create separate chains for ICMP, TCP and UDP to traverse
#

$IPTABLES -N icmp_packets
#
# ICMP rules
#

$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 0 -j ACCEPT	# echo reply
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 3 -j ACCEPT	# dest unreachable
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 5 -j ACCEPT	# redirect
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT	# time exceeded
$IPTABLES -A FORWARD -p ICMP -j icmp_packets

#
# UDP ports
#
$IPTABLES -N udpincoming_packets

$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 53 -j ACCEPT	# DNS
$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 123 -j ACCEPT	# ntp
#$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 2074 -j ACCEPT	# speakfreely
#$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 4000 -j ACCEPT	#icq

$IPTABLES -A FORWARD -p UDP -j udpincoming_packets

#

$IPTABLES -N tcp_packets

#
# 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

# TCP rules
#

#
# Bad TCP packets we don't want
#

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

$IPTABLES -A tcp_packets -p TCP -s 0/0 -d springfield.sparkle-cc.co.uk --dport 80 -j allowed # smtp
$IPTABLES -A tcp_packets -p TCP -s 0/0 -d lisa.sparkle-cc.co.uk --dport 6346 -j allowed # gnutella
$IPTABLES -A tcp_packets -p TCP -s 0/0 -d springfield.sparkle-cc.co.uk --dport 25 -j allowed # smtp

$IPTABLES -A FORWARD -p TCP -j tcp_packets

#
# Input to the firewall itself. Leave these out if you don't want the firewall
# to be visible on the network at all.
# Note that the PREROUTING restrictions above mean that only packets form inside
# the firewall can fulfill the source condition. So the firewall machine should not be
# visible to the internet.
#

$IPTABLES -A INPUT -p ALL -i $BR_IFACE -s $INTERNAL_ADDRESS_RANGE -d $LAN_BCAST_ADDRESS -j ACCEPT
$IPTABLES -A INPUT -p ALL -i $BR_IFACE -s $INTERNAL_ADDRESS_RANGE -d $BR_IP -j ACCEPT

# But you *will* need this

$IPTABLES -A INPUT -p ALL -i $LO_IFACE -d $LO_IP -j ACCEPT

$IPTABLES -A INPUT -m limit --limit 3/minute --limit-burst 3 -j LOG --log-level 7 --log-prefix "IPT INPUT packet died: "

#
# OUTPUT chain
#

$IPTABLES -A OUTPUT -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "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 $BR_IP -j ACCEPT
$IPTABLES -A OUTPUT -m limit --limit 3/minute --limit-burst 3 -j LOG --log-level 7 --log-prefix "IPT OUTPUT packet died: "