NAT Overload on the same TCP and UDP port

[spinellicisco]

Hi,

following my LAB scenario:

- my router is configured with NAT Overload for outgoing traffic;

- one LAN client generate two session, one TCP and one UDP using the port 5000 for both protocols, to an Internet client port  63000;

- during the translation the port of the TCP session remain that used by the LAN client, the port 5000.

- during the translation the port of the UDP session does not remain that used by the LAN client, the port 5000, but is used the port 1024.

I wanted know if is normal that the Cisco router change the port of the UDP session generated by the LAN client, using the port 1024 instead of the port 5000, since the two session use two different protocols, TCP and UDP.

Thanks.

Fabio

[Giuseppe Larosa]

Hello Fabio,

yes for efficiency in implementation this is the reason behind this so that the port can be used as a key to access the NAT table

(addressIN, portIN ) ---- >  (addressOUT, portOUT)

this doesn't cause issues normally as SNMP has no socket concept.

Hope to help

Giuseppe