Iptables Tutorial 1.2.2 - Oskar Andreasson
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--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 $INET_IFACE -j icmp_packets
#
# If you have a Microsoft Network on the outside of your firewall, you may
# also get flooded by Multicasts. We drop them so we do not get flooded by
# logs
#
#$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
#
Example rc.flush-iptables script
#!/bin/sh
#
# rc.flush-iptables - Resets iptables to default values.
#
# Copyright (C) 2001 Oskar Andreasson <bluefluxATkoffeinDOTnet>
#
# 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
Example rc.test-iptables script
#!/bin/bash
#
# rc.test-iptables - test script for iptables chains and tables.
#
# Copyright (C) 2001 Oskar Andreasson <bluefluxATkoffeinDOTnet>
#
# 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:"
iptables -t mangle -A OUTPUT -p icmp --icmp-type echo-reply
-j LOG --log-prefix="mangle OUTPUT:"
iptables -t mangle -I POSTROUTING 1 -p icmp --icmp-type echo-request
-j LOG --log-prefix="mangle POSTROUTING:"
iptables -t mangle -I POSTROUTING 1 -p icmp --icmp-type echo-reply
-j LOG --log-prefix="mangle POSTROUTING:"
Index
Symbols
$INET_IP, Configuration options
$LAN_IFACE, FORWARD chain
$LAN_IP, OUTPUT chain
$LOCALHOST_IP, OUTPUT chain
$STATIC_IP, OUTPUT chain
--ahspi, AH/ESP match
--chunk-types, SCTP matches
--clamp-mss-to-pmtu, TCPMSS target
--clustermac, CLUSTERIP target
--cmd-owner, Owner match
--comment, Comment match
--ctexpire, Conntrack match
--ctorigdst, Conntrack match
--ctorigsrc, Conntrack match
--ctproto, Conntrack match
--ctrepldst, Conntrack match
--ctreplsrc, Conntrack match
--ctstate, Conntrack match
--ctstatus, Conntrack match
--destination, Generic matches
--destination-port, TCP matches, UDP matches, SCTP matches, Multiport match
--dscp, Dscp match
--dscp-class, Dscp match
--dst-range, IP range match
--dst-type, Addrtype match
--ecn, Ecn match
--ecn-ip-ect, Ecn match
--ecn-tcp-ece, Ecn match
--ecn-tcp-remove, ECN target
--espspi, AH/ESP match
--fragment, Generic matches
--gid-owner, Owner match
--hash-init, CLUSTERIP target
--hashlimit, Hashlimit match
--hashlimit-burst, Hashlimit match
--hashlimit-htable-expire, Hashlimit match
--hashlimit-htable-expire match, Hashlimit match
--hashlimit-htable-gcinterval, Hashlimit match
--hashlimit-htable-max, Hashlimit match
--hashlimit-htable-size, Hashlimit match
--hashlimit-mode, Hashlimit match
--hashlimit-name, Hashlimit match
--hashmode, CLUSTERIP target
--helper, Helper match
--hitcount, Recent match
--icmp-type, ICMP matches
--in-interface, Generic matches
--length, Length match
--limit, Limit match
--limit-burst, Limit match
--local-node, CLUSTERIP target
--log-ip-options, LOG target options
--log-level, LOG target options
--log-prefix, LOG target options
--log-tcp-options, LOG target options
--log-tcp-sequence, LOG target options
--mac-source, Mac match
--mark, Connmark match, Mark match
--mask, CONNMARK target
--match, Implicit matches
--mss, Tcpmss match
--name, Recent match
--new, CLUSTERIP target
--nodst, SAME target
--out-interface, Generic matches
--pid-owner, Owner match
--pkt-type, Packet type match
--pkt-type match, Packet type match
--port, Multiport match
--protocol, Generic matches
--queue-num, NFQUEUE target
--rcheck, Recent match
--rdest, Recent match
--realm, Realm match
--reject-with, REJECT target
--remove, Recent match
--restore, CONNSECMARK target
--restore-mark, CONNMARK target
--rsource, Recent match
--rttl, Recent match
--save, CONNSECMARK target
--save-mark, CONNMARK target
--seconds, Recent match
--selctx, SECMARK target
--set, Recent match
--set-class, CLASSIFY target
--set-dscp, DSCP target
--set-dscp-class, DSCP target
--set-mark, CONNMARK target, MARK target
--set-mss, TCPMSS target
--set-tos, TOS target
--sid-owner, Owner match
--source, Generic matches
--source-port, TCP matches, UDP matches, SCTP matches, Multiport match
--src-range, IP range match
--src-type, Addrtype match
--state, State match
--syn, TCP matches
--tcp-flags, TCP matches
--tcp-option, TCP matches
--to, NETMAP target, SAME target
--to-destination, DNAT target
--to-destination target, DNAT target
--to-ports, MASQUERADE target, REDIRECT target
--to-source, SNAT target
--tos, Tos match
--total-nodes, CLUSTERIP target
--ttl-dec, TTL target
--ttl-eq, Ttl match
--ttl-gt, Ttl match
--ttl-inc, TTL target
--ttl-lt, Ttl match
--ttl-set, TTL target
--uid-owner, Owner match
--ulog-cprange, ULOG target
