UDP nat question

Filipe Abrantes fla at inescporto.pt
Wed Apr 20 18:11:49 CEST 2005

First of all, thanks for replying, it's clear now.

I have one more question related to this:

Imagine a host behind NAT with IP which has an application 
on port 5060 ( a sip client) and opens a connection to a server outside 
the NAT (the sip registrar with IP on port 5060), and 
consider that the NAT box translates the SIP client src_ip to and src_prt to 5054, for this communication.

The SIP registrar is able to reach the SIP client running on by using, but what about other 
hosts on the Internet? Will they also be able to reach the SIP client 
using the pair, or only packets coming from the SIP 
registrar be accepted?

Thanks again

Filipe Abrantes

Filipe Lameiro Abrantes
Campus da FEUP
Rua Dr. Roberto Frias, 378
4200-465 Porto

Phone: +351 22 209 4266
E-mail: fla at inescporto.pt

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