#
# 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 tcp_packets
$IPTABLES -N udp_packets
$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
#
# TCP rules
#
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 21 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 22 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 80 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 113 -j allowed
#
# UDP ports
#
#$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 -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 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 $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
#
# Rules for incoming packets from anywhere.
#
$IPTABLES -A INPUT -p ALL -d $INET_IP -m state --state ESTABLISHED,RELATED \
-j ACCEPT
$IPTABLES -A INPUT -p TCP -j tcp_packets
$IPTABLES -A INPUT -p UDP -j udp_packets
$IPTABLES -A INPUT -p ICMP -j icmp_packets
#
# If you have a Microsoft Network on the outside of your firewall, you may
# also get flooded by Multicasts. We drop them so we do not get flooded by
# logs
#
#$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 -p tcp --dport 21 -i $LAN_IFACE -j ACCEPT
$IPTABLES -A FORWARD -p tcp --dport 80 -i $LAN_IFACE -j ACCEPT
$IPTABLES -A FORWARD -p tcp --dport 110 -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
#
#
# 4.2.5 POSTROUTING chain
#
#
# Enable simple IP Forwarding and Network Address Translation
#