Oskar Andreasson - Iptables Tutorial 1.2.2

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# Create chain for bad tcp packets

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$IPTABLES -N bad_tcp_packets

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

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$IPTABLES -N allowed

$IPTABLES -N icmp_packets

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# 4.1.3 Create content in userspecified chains

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# bad_tcp_packets chain

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$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

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# allowed chain

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$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

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# ICMP rules

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# Changed rules totally

$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

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# 4.1.4 INPUT chain

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# Bad TCP packets we don't want

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$IPTABLES -A INPUT -p tcp -j bad_tcp_packets

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# Packets from the Internet to this box

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

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# Packets from LAN, DMZ or LOCALHOST

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# From DMZ Interface to DMZ firewall IP

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$IPTABLES -A INPUT -p ALL -i $DMZ_IFACE -d $DMZ_IP -j ACCEPT

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# From LAN Interface to LAN firewall IP

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$IPTABLES -A INPUT -p ALL -i $LAN_IFACE -d $LAN_IP -j ACCEPT

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# From Localhost interface to Localhost IP's

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

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

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

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

# otherwise.

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

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# All established and related packets incoming from the internet to the

# firewall

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$IPTABLES -A INPUT -p ALL -d $INET_IP -m state --state ESTABLISHED,RELATED \

-j ACCEPT

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

# will prevent them from showing up in the logs.

#

#$IPTABLES -A INPUT -p UDP -i $INET_IFACE -d $INET_BROADCAST \

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

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# 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.

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

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

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# If you have a Microsoft Network on the outside of your firewall, you may

# also get flooded by Multicasts. We drop them so we do not get flooded by

# logs

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#$IPTABLES -A INPUT -i $INET_IFACE -d 224.0.0.0/8 -j DROP

#

# Log weird packets that don't match the above.

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$IPTABLES -A INPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \

--log-level DEBUG --log-prefix "IPT INPUT packet died: "

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# 4.1.5 FORWARD chain

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# Bad TCP packets we don't want

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$IPTABLES -A FORWARD -p tcp -j bad_tcp_packets

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# DMZ section

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# General rules

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$IPTABLES -A FORWARD -i $DMZ_IFACE -o $INET_IFACE -j ACCEPT

$IPTABLES -A FORWARD -i $INET_IFACE -o $DMZ_IFACE -m state \

--state ESTABLISHED,RELATED -j ACCEPT

$IPTABLES -A FORWARD -i $LAN_IFACE -o $DMZ_IFACE -j ACCEPT

$IPTABLES -A FORWARD -i $DMZ_IFACE -o $LAN_IFACE -m state \

--state ESTABLISHED,RELATED -j ACCEPT

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# HTTP server

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$IPTABLES -A FORWARD -p TCP -i $INET_IFACE -o $DMZ_IFACE -d $DMZ_HTTP_IP \

--dport 80 -j allowed

$IPTABLES -A FORWARD -p ICMP -i $INET_IFACE -o $DMZ_IFACE -d $DMZ_HTTP_IP \

-j icmp_packets

#

# DNS server

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$IPTABLES -A FORWARD -p TCP -i $INET_IFACE -o $DMZ_IFACE -d $DMZ_DNS_IP \

--dport 53 -j allowed

$IPTABLES -A FORWARD -p UDP -i $INET_IFACE -o $DMZ_IFACE -d $DMZ_DNS_IP \

--dport 53 -j ACCEPT

$IPTABLES -A FORWARD -p ICMP -i $INET_IFACE -o $DMZ_IFACE -d $DMZ_DNS_IP \

-j icmp_packets

#

# LAN section

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$IPTABLES -A FORWARD -i $LAN_IFACE -j ACCEPT

$IPTABLES -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

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# Log weird packets that don't match the above.

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$IPTABLES -A FORWARD -m limit --limit 3/minute --limit-burst 3 -j LOG \

--log-level DEBUG --log-prefix "IPT FORWARD packet died: "

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# 4.1.6 OUTPUT chain

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# Bad TCP packets we don't want.

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$IPTABLES -A OUTPUT -p tcp -j bad_tcp_packets

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# Special OUTPUT rules to decide which IP's to allow.

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$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 ACCEPT

#

# Log weird packets that don't match the above.

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$IPTABLES -A OUTPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \

--log-level DEBUG --log-prefix "IPT OUTPUT packet died: "

######

# 4.2 nat table

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# 4.2.1 Set policies

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# 4.2.2 Create user specified chains

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# 4.2.3 Create content in user specified chains

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# 4.2.4 PREROUTING chain

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$IPTABLES -t nat -A PREROUTING -p TCP -i $INET_IFACE -d $HTTP_IP --dport 80 \

-j DNAT --to-destination $DMZ_HTTP_IP

$IPTABLES -t nat -A PREROUTING -p TCP -i $INET_IFACE -d $DNS_IP --dport 53 \

-j DNAT --to-destination $DMZ_DNS_IP

$IPTABLES -t nat -A PREROUTING -p UDP -i $INET_IFACE -d $DNS_IP --dport 53 \

-j DNAT --to-destination $DMZ_DNS_IP

#

# 4.2.5 POSTROUTING chain

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# Enable simple IP Forwarding and Network Address Translation

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$IPTABLES -t nat -A POSTROUTING -o $INET_IFACE -j SNAT --to-source $INET_IP

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# 4.2.6 OUTPUT chain

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######

# 4.3 mangle table

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# 4.3.1 Set policies

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# 4.3.2 Create user specified chains

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# 4.3.3 Create content in user specified chains

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# 4.3.4 PREROUTING chain

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# 4.3.5 INPUT chain

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# 4.3.6 FORWARD chain

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# 4.3.7 OUTPUT chain

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# 4.3.8 POSTROUTING chain

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#!/bin/sh

#

# rc.UTIN.firewall - UTIN 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.

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#

# 1.1 Internet Configuration.