[netfilter] http://www.netfilter.org/ [program and example] http://danieldegraaf.afraid.org/info/iptables/ [tutorial] http://iptables-tutorial.frozentux.net/iptables-tutorial.html [url and scripts] http://www.linuxguruz.com/iptables/ [quick] http://www.siliconvalleyccie.com/linux-hn/iptables-intro.htm http://xkr47.outerspace.dyndns.org/netfilter/packet_flow/packet_flow 9.png