IPTables

#!/bin/sh
#
# iptables firewall generated 14-11-2007
#

# set a few variables
echo ""
echo "  Setting global variables"
echo ""
export PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin
iptables="/sbin/iptables"

# adjust /proc
echo "  applying general security settings to /proc filesystem"
echo ""
if [ -e /proc/sys/net/ipv4/tcp_syncookies ]; then echo 1 > /proc/sys/net/ipv4/tcp_syncookies; fi
if [ -e /proc/sys/net/ipv4/conf/all/rp_filter ]; then echo 1 > /proc/sys/net/ipv4/conf/all/rp_filter; fi
if [ -e /proc/sys/net/ipv4/ip_forward ]; then echo 1 > /proc/sys/net/ipv4/ip_forward; fi

# load some modules
if [ -e /lib/modules/`uname -r`/kernel/net/ipv4/netfilter/ip_nat_irc.o ]; then modprobe ip_nat_irc; fi
if [ -e /lib/modules/`uname -r`/kernel/net/ipv4/netfilter/ip_conntrack_irc.o ]; then modprobe ip_conntrack_irc; fi

# flush any existing chains and set default policies
$iptables -F INPUT
$iptables -F OUTPUT
$iptables -P INPUT DROP
$iptables -P OUTPUT ACCEPT

# setup nat
echo "  Applying NAT rules"
echo ""
$iptables -F FORWARD
$iptables -F -t nat
$iptables -P FORWARD DROP
$iptables -A FORWARD -i eth0 -j ACCEPT
$iptables -A INPUT -i eth0 -j ACCEPT
$iptables -A OUTPUT -o eth0 -j ACCEPT
$iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
$iptables -t nat -A POSTROUTING -s 192.168.1.1/2 -o eth0 -j SNAT --to-source 192.168.1.2

# allow all packets on the loopback interface
$iptables -A INPUT -i lo -j ACCEPT
$iptables -A OUTPUT -o lo -j ACCEPT

# allow established and related packets back in
$iptables -A INPUT -i eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT

# icmp
echo "  Applying ICMP rules"
echo ""
$iptables -A OUTPUT -p icmp -m state --state NEW -j ACCEPT
$iptables -A INPUT -p icmp -m state --state ESTABLISHED,RELATED -j ACCEPT
$iptables -A INPUT -p icmp --icmp-type echo-request -m limit --limit 1/s -i eth0 -j ACCEPT

# open ports to the firewall
echo "  Applying the open port(s) to the firewall rules"
echo ""
$iptables -A INPUT -p tcp --dport 22 -j ACCEPT
$iptables -A INPUT -p tcp --dport 80 -j ACCEPT

# drop all other packets
echo "  Applying default drop policies"
echo ""
$iptables -A INPUT -i eth0 -p tcp --dport 0:65535 -j DROP
$iptables -A INPUT -i eth0 -p udp --dport 0:65535 -j DROP

echo "### FIREWALL is loaded ###"
echo ""