Oskar Andreasson - Iptables Tutorial 1.2.2

#

#

# 4.3.6 FORWARD chain

#

#

# 4.3.7 OUTPUT chain

#

#

# 4.3.8 POSTROUTING chain

#

#!/bin/sh

#

# rc.DHCP.firewall - DHCP IP Firewall script for Linux 2.4.x and iptables

#

# Copyright (C) 2001 Oskar Andreasson

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; version 2 of the License.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program or from the site that you downloaded it

# from; if not, write to the Free Software Foundation, Inc., 59 Temple

# Place, Suite 330, Boston, MA 02111-1307 USA

#

###########################################################################

#

# 1. Configuration options.

#

#

# 1.1 Internet Configuration.

#

INET_IFACE="eth0"

#

# 1.1.1 DHCP

#

#

# Information pertaining to DHCP over the Internet, if needed.

#

# Set DHCP variable to no if you don't get IP from DHCP. If you get DHCP

# over the Internet set this variable to yes, and set up the proper IP

# address for the DHCP server in the DHCP_SERVER variable.

#

DHCP="no"

DHCP_SERVER="195.22.90.65"

#

# 1.1.2 PPPoE

#

# Configuration options pertaining to PPPoE.

#

# If you have problem with your PPPoE connection, such as large mails not

# getting through while small mail get through properly etc, you may set

# this option to "yes" which may fix the problem. This option will set a

# rule in the PREROUTING chain of the mangle table which will clamp

# (resize) all routed packets to PMTU (Path Maximum Transmit Unit).

#

# Note that it is better to set this up in the PPPoE package itself, since

# the PPPoE configuration option will give less overhead.

#

PPPOE_PMTU="no"

#

# 1.2 Local Area Network configuration.

#

# your LAN's IP range and localhost IP. /24 means to only use the first 24

# bits of the 32 bit IP address. the same as netmask 255.255.255.0

#

LAN_IP="192.168.0.2"

LAN_IP_RANGE="192.168.0.0/16"

LAN_IFACE="eth1"

#

# 1.3 DMZ Configuration.

#

#

# 1.4 Localhost Configuration.

#

LO_IFACE="lo"

LO_IP="127.0.0.1"

#

# 1.5 IPTables Configuration.

#

IPTABLES="/usr/sbin/iptables"

#

# 1.6 Other Configuration.

#

###########################################################################

#

# 2. Module loading.

#

#

# Needed to initially load modules

#

/sbin/depmod -a

#

# 2.1 Required modules

#

/sbin/modprobe ip_conntrack

/sbin/modprobe ip_tables

/sbin/modprobe iptable_filter

/sbin/modprobe iptable_mangle

/sbin/modprobe iptable_nat

/sbin/modprobe ipt_LOG

/sbin/modprobe ipt_limit

/sbin/modprobe ipt_MASQUERADE

#

# 2.2 Non-Required modules

#

#/sbin/modprobe ipt_owner

#/sbin/modprobe ipt_REJECT

#/sbin/modprobe ip_conntrack_ftp

#/sbin/modprobe ip_conntrack_irc

#/sbin/modprobe ip_nat_ftp

#/sbin/modprobe ip_nat_irc

###########################################################################

#

# 3. /proc set up.

#

#

# 3.1 Required proc configuration

#

echo "1" > /proc/sys/net/ipv4/ip_forward

#

# 3.2 Non-Required proc configuration

#

#echo "1" > /proc/sys/net/ipv4/conf/all/rp_filter

#echo "1" > /proc/sys/net/ipv4/conf/all/proxy_arp

#echo "1" > /proc/sys/net/ipv4/ip_dynaddr

###########################################################################

#

# 4. rules set up.

#

######

# 4.1 Filter table

#

#

# 4.1.1 Set policies

#

$IPTABLES -P INPUT DROP

$IPTABLES -P OUTPUT DROP

$IPTABLES -P FORWARD DROP

#

# 4.1.2 Create userspecified chains

#

#

# Create chain for bad tcp packets

#

$IPTABLES -N bad_tcp_packets

#

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

#

$IPTABLES -N allowed

$IPTABLES -N tcp_packets

$IPTABLES -N udp_packets

$IPTABLES -N icmp_packets

#

# 4.1.3 Create content in userspecified chains

#

#

# bad_tcp_packets chain

#

$IPTABLES -A bad_tcp_packets -p tcp --tcp-flags SYN,ACK SYN,ACK \

-m state --state NEW -j REJECT --reject-with tcp-reset

$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

#

# allowed chain

#

$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

#

$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 21 -j allowed

$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 22 -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

#

# UDP ports

#

$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 53 -j ACCEPT

if [ $DHCP == "yes" ] ; then

$IPTABLES -A udp_packets -p UDP -s $DHCP_SERVER --sport 67 \

--dport 68 -j ACCEPT

fi

#$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 53 -j ACCEPT

#$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 123 -j ACCEPT

#$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 2074 -j ACCEPT

#$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 4000 -j ACCEPT

#

# In Microsoft Networks you will be swamped by broadcasts. These lines

# will prevent them from showing up in the logs.

#

#$IPTABLES -A udp_packets -p UDP -i $INET_IFACE \

#--destination-port 135:139 -j DROP

#

# If we get DHCP requests from the Outside of our network, our logs will

# be swamped as well. This rule will block them from getting logged.

#

#$IPTABLES -A udp_packets -p UDP -i $INET_IFACE -d 255.255.255.255 \

#--destination-port 67:68 -j DROP

#

# ICMP rules

#

$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

#

# 4.1.4 INPUT chain

#

#

# Bad TCP packets we don't want.

#

$IPTABLES -A INPUT -p tcp -j bad_tcp_packets

#

# Rules for special networks not part of the Internet

#

$IPTABLES -A INPUT -p ALL -i $LAN_IFACE -s $LAN_IP_RANGE -j ACCEPT

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

#

# Special rule for DHCP requests from LAN, which are not caught properly

# otherwise.

#

$IPTABLES -A INPUT -p UDP -i $LAN_IFACE --dport 67 --sport 68 -j ACCEPT

#

# Rules for incoming packets from the internet.

#

$IPTABLES -A INPUT -p ALL -i $INET_IFACE -m state --state ESTABLISHED,RELATED \

-j ACCEPT

$IPTABLES -A INPUT -p TCP -i $INET_IFACE -j tcp_packets

$IPTABLES -A INPUT -p UDP -i $INET_IFACE -j udp_packets

$IPTABLES -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets