Re: Problems with sqlnet through a firewall

(Emailed and posted.)

SQL*Net V2, when connecting to an Oracle server that's running MTS and shared servers, will connect as follows:

1. Client opens a connection to the listener on port 1526 (or whatever).
2. Listener accepts connection, and identifies a dispatcher that's not busy. That dispatcher is listening on some arbitrary port that you don't know in advance.
3. Listener sends a redirection message to the client, telling it to connect to the dispatcher's port.
4. Client opens a connection to the dispatcher.

This means that although your firewall is configured to pass connections to the listener's port, connections to the database will fail when they attempt to get through to the dispatcher's port. TNSPING will probably still work because it doesn't attempt to open a full connection; it probably just contacts the listener.

Solutions:

1. (Best solution.) Buy a firewall that supports SQL*Net.
2. (Not such a good solution.) Connect with dedicated server processes instead of MTS. You can specify this in TNSNAMES.ORA. Prespawning server processes is a good idea if you choose this option.