Question about conntrack

[Michele Petrazzo - Unipex <michele.petrazzo@unipex.it>]

Hi list,
I have a server that nat a network lan where there are some pcs. My
provider say me that I'm uploading contents from an high (5XXXX)
external udp port. For see if it's true :) and which lan ip do the
upload (of course excluding the server) I "tcpdump" the connection and I
see that yes, there is an upload that goes out from the wan (that has a
public IP) at that specific port, but no corresponding lan traffic on
the lan port.

Here are my question: why I see the traffic on that port only on the
external port? nat does also port translation?
Is there another, better, solution for look for the data that I need?

Thanks,
Michele