Oskar Andreasson - Iptables Tutorial 1.2.2

#

# 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

#

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

#

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

#

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

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

#

# 4.1.5 FORWARD chain

#

#

# Bad TCP packets we don't want

#

$IPTABLES -A FORWARD -p tcp -j bad_tcp_packets

#

# 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

#

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

#

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

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

#

# 4.1.6 OUTPUT chain

#

#

# Bad TCP packets we don't want.

#

$IPTABLES -A OUTPUT -p tcp -j bad_tcp_packets

#

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

#

$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 -o $INET_IFACE -j ACCEPT

#

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

#

$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

#

#

# 4.2.1 Set policies

#

#

# 4.2.2 Create user specified chains

#

#

# 4.2.3 Create content in user specified chains

#

#

# 4.2.4 PREROUTING chain

#

#

# 4.2.5 POSTROUTING chain

#

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

$IPTABLES -t nat -A POSTROUTING -p tcp --tcp-flags SYN,RST SYN \

-j TCPMSS --clamp-mss-to-pmtu

fi

$IPTABLES -t nat -A POSTROUTING -o $INET_IFACE -j MASQUERADE

#

# 4.2.6 OUTPUT chain

#

######

# 4.3 mangle table

#

#

# 4.3.1 Set policies

#

#

# 4.3.2 Create user specified chains

#

#

# 4.3.3 Create content in user specified chains

#

#

# 4.3.4 PREROUTING chain

#

#

# 4.3.5 INPUT chain

#

#

# 4.3.6 FORWARD chain

#

#

# 4.3.7 OUTPUT chain

#

#

# 4.3.8 POSTROUTING chain

#

#!/bin/sh

#

# rc.flush-iptables - Resets iptables to default values.

#

# 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

#

# Configurations

#

IPTABLES="/usr/sbin/iptables"

#

# reset the default policies in the filter table.

#

$IPTABLES -P INPUT ACCEPT

$IPTABLES -P FORWARD ACCEPT

$IPTABLES -P OUTPUT ACCEPT

#

# reset the default policies in the nat table.

#

$IPTABLES -t nat -P PREROUTING ACCEPT

$IPTABLES -t nat -P POSTROUTING ACCEPT

$IPTABLES -t nat -P OUTPUT ACCEPT

#

# reset the default policies in the mangle table.

#

$IPTABLES -t mangle -P PREROUTING ACCEPT

$IPTABLES -t mangle -P POSTROUTING ACCEPT

$IPTABLES -t mangle -P INPUT ACCEPT

$IPTABLES -t mangle -P OUTPUT ACCEPT

$IPTABLES -t mangle -P FORWARD ACCEPT

#

# flush all the rules in the filter and nat tables.

#

$IPTABLES -F

$IPTABLES -t nat -F

$IPTABLES -t mangle -F

#

# erase all chains that's not default in filter and nat table.

#

$IPTABLES -X

$IPTABLES -t nat -X

$IPTABLES -t mangle -X

#!/bin/bash

#

# rc.test-iptables - test script for iptables chains and tables.

#

# 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

#

#

# Filter table, all chains

#

iptables -t filter -A INPUT -p icmp --icmp-type echo-request \

-j LOG --log-prefix="filter INPUT:"

iptables -t filter -A INPUT -p icmp --icmp-type echo-reply \

-j LOG --log-prefix="filter INPUT:"

iptables -t filter -A OUTPUT -p icmp --icmp-type echo-request \

-j LOG --log-prefix="filter OUTPUT:"

iptables -t filter -A OUTPUT -p icmp --icmp-type echo-reply \

-j LOG --log-prefix="filter OUTPUT:"

iptables -t filter -A FORWARD -p icmp --icmp-type echo-request \

-j LOG --log-prefix="filter FORWARD:"

iptables -t filter -A FORWARD -p icmp --icmp-type echo-reply \

-j LOG --log-prefix="filter FORWARD:"

#

# NAT table, all chains except OUTPUT which don't work.

#

iptables -t nat -A PREROUTING -p icmp --icmp-type echo-request \

-j LOG --log-prefix="nat PREROUTING:"

iptables -t nat -A PREROUTING -p icmp --icmp-type echo-reply \

-j LOG --log-prefix="nat PREROUTING:"

iptables -t nat -A POSTROUTING -p icmp --icmp-type echo-request \

-j LOG --log-prefix="nat POSTROUTING:"

iptables -t nat -A POSTROUTING -p icmp --icmp-type echo-reply \

-j LOG --log-prefix="nat POSTROUTING:"

iptables -t nat -A OUTPUT -p icmp --icmp-type echo-request \

-j LOG --log-prefix="nat OUTPUT:"

iptables -t nat -A OUTPUT -p icmp --icmp-type echo-reply \

-j LOG --log-prefix="nat OUTPUT:"

#

# Mangle table, all chains

#

iptables -t mangle -A PREROUTING -p icmp --icmp-type echo-request \

-j LOG --log-prefix="mangle PREROUTING:"

iptables -t mangle -A PREROUTING -p icmp --icmp-type echo-reply \

-j LOG --log-prefix="mangle PREROUTING:"

iptables -t mangle -I FORWARD 1 -p icmp --icmp-type echo-request \

-j LOG --log-prefix="mangle FORWARD:"

iptables -t mangle -I FORWARD 1 -p icmp --icmp-type echo-reply \

-j LOG --log-prefix="mangle FORWARD:"

iptables -t mangle -I INPUT 1 -p icmp --icmp-type echo-request \

-j LOG --log-prefix="mangle INPUT:"

iptables -t mangle -I INPUT 1 -p icmp --icmp-type echo-reply \

-j LOG --log-prefix="mangle INPUT:"

iptables -t mangle -A OUTPUT -p icmp --icmp-type echo-request \

-j LOG --log-prefix="mangle OUTPUT:"