Patent ID: 7450585

Claim:
A method to use in a first router connected on one hand to a first private Internet Protocol (IP) network and on another hand to a public IP network, for translating in a datagram a source private IP address into a public IP address so that said private IP address can be translated back into the same private IP address by a second router connected to a second private network, said method comprising the steps of: receiving an IP datagram from a source within a first private IP network, comprising a header including: a source private IP address; an IP option field; a source TCP/UDP port number; replacing in the IP datagram header, the source private IP address by the public IP address of the first router; replacing in the IP datagram header the source TCP/UDP port number by the two least significant bytes of the source private IP address; copying in the IP option field, information related to the first and the second highest significant bytes of the source private IP address so that said first and the second highest significant bytes can be deduced from said information, forwarding the IP datagram on the public IP network.