Confused about NAT/PAT

[vorgusa]

I have another CCNA question about PATs. If you have two computers on a network and they both try to go to www.anandtech.com at the same time how would that work? Wouldn't they both try to go to IP:80?

and who decides what port the client and server are going to communicate on, the NAT or the Server?

 

[drebo]

They both have a destination port of 80, yes, but their source ports (the ones that matter for NAT/PAT on the user-side) are different (random).

On the server side, how it processes the multiple requests to port 80 is a function of the application.

 

[jlazzaro]

it doesnt matter how many computers need access to anandtech.com on port 80 because it tracks the translations via source ports (randomized from 1024 - 65535) in the PAT table.

high level run down...

if one computer requests information from anandtech.com with a source of 192.168.1.101:16112, the PAT device will for example translate this pair to source 1.2.3.4:17882 and make an entry in its PAT table. when the packets arrive on the public interface for 1.2.3.4:17882 the PAT device will reference its table and forward traffic to host 192.168.1.101 with a destination port of 16112.

 

[vorgusa]

ohhhh ok.. its amazing how simple some things are once you get that one piece of info.. I keep forgetting about the source info and how it can be used to help narrow things down