[1]Linux Advanced Routing & Traffic Control HOWTO
http://www.tldp.org/HOWTO/Adv-Routing-HOWTO/
[2]Linux Advanced Routing & Traffic Control
http://www.lartc.org/
[3]The official IPsec Howto for Linux
http://www.ipsec-howto.org/
[4]Iptables Tutorial 1.2.2
https://www.frozentux.net/iptables-tutorial/iptables-tutorial.html
[5]The Double NAT MINI-HOWTO
http://www.netfilter.org/documentation/HOWTO//netfilter-double-nat-HOWTO.html
[6]Linux 2.4 NAT HOWTO
http://www.netfilter.org/documentation/HOWTO//NAT-HOWTO.html
http://www.tldp.org/HOWTO/Adv-Routing-HOWTO/
[2]Linux Advanced Routing & Traffic Control
http://www.lartc.org/
[3]The official IPsec Howto for Linux
http://www.ipsec-howto.org/
[4]Iptables Tutorial 1.2.2
https://www.frozentux.net/iptables-tutorial/iptables-tutorial.html
[5]The Double NAT MINI-HOWTO
http://www.netfilter.org/documentation/HOWTO//netfilter-double-nat-HOWTO.html
[6]Linux 2.4 NAT HOWTO
http://www.netfilter.org/documentation/HOWTO//NAT-HOWTO.html