Iptables Tutorial 1.1.19

/sbin/modprobe ipt_LOG

/sbin/modprobe ipt_limit

/sbin/modprobe ipt_state

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# 2.2 Non-Required modules

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#/sbin/modprobe ipt_owner

#/sbin/modprobe ipt_REJECT

#/sbin/modprobe ipt_MASQUERADE

#/sbin/modprobe ip_conntrack_ftp

#/sbin/modprobe ip_conntrack_irc

#/sbin/modprobe ip_nat_ftp

#/sbin/modprobe ip_nat_irc

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# 3. /proc set up.

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# 3.1 Required proc configuration

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

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# 3.2 Non-Required proc configuration

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#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

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# 4. rules set up.

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# 4.1 Filter table

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# 4.1.1 Set policies

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$IPTABLES -P INPUT DROP

$IPTABLES -P OUTPUT DROP

$IPTABLES -P FORWARD DROP

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# 4.1.2 Create userspecified chains

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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.

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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

#

# 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