IPTables

http://www.cyberciti.biz/faq/centos-rhel-linux-openvz-hardware-node-iptables-firewall/

http://wiki.openvz.org/Setting_up_an_iptables_firewall

http://www.linuxhomenetworking.com/wiki/index.php/Quick_HOWTO_:_Ch14_:_Linux_Firewalls_Using_iptables

http://www.guiaubuntupt.org/wiki/index.php?title=Iptables

http://www.aboutdebian.com/firewall.htm

Ferramenta para gerar IPTables

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