Iptables Tutorial 1.1.19

Andreasson Oskar

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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.

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#$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

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# 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

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# 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

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# 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

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# 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

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# 4.2.5 POSTROUTING chain

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# Enable simple IP Forwarding and Network Address Translation