Firewall

Recommended read
http://www.justlinux.com/nhf/Security/IPtables_Basics.html

http://www.netfilter.org/documentation/HOWTO//networking-concepts-HOWTO.html#toc11

http://www.netfilter.org/documentation/HOWTO//packet-filtering-HOWTO.html

http://iptables-tutorial.frozentux.net/iptables-tutorial.html

http://www.sns.ias.edu/~jns/wp/2006/01/24/iptables-how-does-it-work/

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