QUESTION: What is NAT, and how do I know if it's taking place on my network?
Usually NAT takes place at a firewall or a gateway on your network. Today, most networks and PCs support NAT as it has come to be an essential service due to the reduced available IPs.
Basically NAT will allow all clients in a network to access the Internet using only one real IP. Every packet that enters the NAT-enabled device will have its source IP address translated to that of the real IP address the device has on the Internet. At the same time, the NAT-enabled device will keep track of the connection to ensure the translations talking place are correct and sent to the correct internal host.
There are two main types of NAT translations, that is, Static and Dynamic. Each one of these have a few variations depending on the setup.
In your network, the best way to find out if your using NAT is to gain access to your gateway/firewall and view its configuration. If you see your internal addresses I.E. 10.0.0.x being translated to something else, I.E. 192.168.0.x, then it's most likely you're using NAT.
NAT is a study in itself and extremely interesting. I'd highly advise you look into it deeper if you can. You can find a top analysis on NAT and its different modes at www.Firewall.cx/nat-intro.php. The topic is covered over nine pages using great illustrations to help answer all questions you might have on the topic.
This was first published in February 2008