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QID: NA648 Answer Query
Hi, just have query regarding answer provided for this question.

Q. What happens when computers on a private network attempt to connect to the internet through a Cisco router running PAT?

Correct answer: The router uses the same IP address but a different TCP source port number for each connection.

I understand PAT is about port translation & assigning different port numbers to connections. But PAT is also another name for NAT which is about translating private addresses to public. Here we have a private network going through a PAT router so I assume it is using private addresses - these private addresses need to be translated to public so should the answer not be the option below:

The router assigns a unique IP address from a pool of legally registered addresses for the duration of the connection.

I think you are getting NAT/PAT confused with DHCP

DHCP assigns IP addresses from a pool of pre-defined DHCP addresses for a time (set by the admin).

PAT (Port address Translation) is a form of PAT but not exactly the same, in the same way that dog is a type of animal but animal is not a type of dog.  NAT covers a wider scope.

So, concentrating on PAT only, an outgoing packet looking for a web page would be looked at by the router as "private ip: IE session", with the private IP address then being stored in the PAT table and the PAT table having an entry with "router IP:80 is translated to private IP:IE session.......the router then knows then when it comes back from the web server looking for "router IP:80 - it can easily be translated back to the private IP address because it has the entry.

The answer is therefore the one stated

Hope that helps

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