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#

# 3. /proc set up.

#

#

# 3.1 Required proc configuration

#

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

#

# 3.2 Non-Required proc configuration

#

#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

###########################################################################

#

# 4. rules set up.

#

######

# 4.1 Filter table

#

#

# 4.1.1 Set policies

#

$IPTABLES -P INPUT DROP

$IPTABLES -P OUTPUT DROP

$IPTABLES -P FORWARD DROP

#

# 4.1.2 Create userspecified chains

#

#

# Create chain for bad tcp packets

#

$IPTABLES -N bad_tcp_packets

#

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

#

$IPTABLES -N allowed

$IPTABLES -N icmp_packets

#

# 4.1.3 Create content in userspecified chains

#

#

# bad_tcp_packets chain

#

$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

#

# allowed chain

#

$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

#

# ICMP rules

#

# 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

#

# 4.1.4 INPUT chain

#

#

# Bad TCP packets we don't want

#

$IPTABLES -A INPUT -p tcp -j bad_tcp_packets

#

# Packets from the Internet to this box

#

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

#

# Packets from LAN, DMZ or LOCALHOST

#

#

# From DMZ Interface to DMZ firewall IP

#

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

#

# From LAN Interface to LAN firewall IP

#

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

#

# From Localhost interface to Localhost IP's

#

$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

#

# 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

#

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

# firewall

#

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

–j ACCEPT

#

# 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

#

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

#–destination-port 67:68 -j DROP

#

# 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

#

# DMZ section

#

# General rules

#

$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

#

# HTTP server

#

$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

#

$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

#

$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 -s $INET_IP -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

#

$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

#

#

# Enable simple IP Forwarding and Network Address Translation

#

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