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New Member

PAT!!!

Hi Friends!

Im a little bit confused about PAT (Port Address Translation).

Here what i think about PAT:

Lets say an inside host wanna reach www.cisco.com. Then it will send this packet to its PAT enabled gateway with a 80 port request. Then this router will add this address to its translation table as

Local address: 10.1.1.1

Port: 80

Global Address: 11.11.11.11

Assigned Port: 100

Everything is OK till now... The problem on my head comes with Assigned port in this table... It is 100 for example...

So how the receiving host knows that it is a web request.. Cuz it request to port 100 not 80...

Im not familiar with a PAT packet header...

I will thank to you if you explain me how it works and its packet structure...

Thanks in advanced...

Ahmet SAAT

2 REPLIES
Purple

Re: PAT!!!

Ahmet,

The thing to understand here is that PAT modifies the source port, not the destination port. The destination only cares about the destination port in any packets it receives so changing the source port does not really matter.

In your example, the local (source) port would be likely to be something greater than 1023 which may get translated into some similar port number greater than 1023. The destination port would remain port 80.

Hope that helps - pls do rate the post if it does.

Paresh

New Member

Re: PAT!!!

Thank you Paresh!

You saved my life... Now everything is clear!!!

Regards...

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