NAT, Network Address Translation

Last night or early this morning I had to stay my and work on a new network connectivity with a financial institution.  I am not going to name the institution but will only say that it is one of the largest financial institution in the USA.

At the scheduled 1 a.m. eatern time, I dialed into the conference bridge and connected with 3 other parties.  This was a new circuit we were trying to implement from Phoenix to New Jersey.  I am in Toronto, Ontario and the rest of the people were in the US.  The circuit was a frame-relay circuit, CIR of 64k and burstable to 128k, good old reliable frame-relay but pain in the behind to implement and configure.

Anyhow, what I really wanted to discuss here is NAT (network address translation).  NAT hides the real source of IP address and converts it to a different IP.  For excample if you have multiple computers that want to share one single internet connection, you can do this with NAT.  Your ISP assigns you one public IP, but you have more than one computer that accesses the internet.  You will need to purchase a router to share the internet connection, if you do not have a router there are other ways to do this as well. 

How does NAT work?  Well in the above example, say computer A is and computer B is  The router is connected to the internet and has a public ip of  When computer A accessing, via the router, the router will translate the ip address to and direct the connection to  If computer B accessing the internet at the same time a computer A, the router will translate the IP to as well.