sql*net and the listener

I'm sure this is a simple question, but I could not find the answer in any of my books.

When a message is sent into the server from a sql*net client and my listener is listening on port 1521, does it also send all replies and checks through port 1521 or does it choose another?

Which ports will I need to open for a firewall?

Thanks!!

A search on Metalink for keyword 'firewall' yields a useful article (Oracle note no. 125021.1).

The client sends a request for a connection to the listener on port 1521 (or whichever port is defined in tnsnames and listener.ora). When the listener spawns a server process, a port redirection takes place, and the spawned server tries to contact the client on a pretty much random port.

The Oracle note gives a method of verifying that the firewall is indeed what is causing the problem, and several possible solutions.

HTH

David.