networking questions (part 2)

[jes]

I am having difficulty understanding the difference between Network Address Translation and Port Address Translation. I think that PAT is just like NAT but PAT connects to actual ports rather than IP addresses. Is that right?

[Paul Komski]

It seems that PAT is a subset of NAT.

http://en.wikipedia.org/wiki/Port_address_translation

[Variable]

NAT translates only network addresses, PAT does both network and ports because it uses NAT.

Without PAT you could not have one public IP connecting various applications to different machines on your internal network. Using PAT you could have one Public IP and separate internal Web, Mail and application servers because they all listen on different ports. When home users talk about NAT they are really talking about PAT.

[jes]

It sounds to me like PAT is far superior to NAT. Does anyone use NAT?

[Variable]

Everyone uses NAT. They are not two separate things per se. PAT translates ports, NAT translates IP's. But if your doing PAT your also doing NAT. You can use NAT and not PAT but not the other way around. Think about it. If your using PAT it is because you have more internal machines than public IP's and you want to split the ports inbound to various machines. Parsing HTTP to a web server, SMTP to a mail server, etc. These machines are not using the same IP's are they? No, you cannot have 5 machines with one IP. Think of your network as a street. Your IP addresses dictate which house people will go to. The port is which door of the house people will use. You may have a side door for delivery, your garage is for your car and your back door is for your daughters boyfriend. NAT is the house number, PAT is the entry point to the house proper.

[jes]

Then, if you use NAT the host sorts out the port mappings and with PAT the router does that?