Database do NOT "listen"; period.
listener processes listen.
a single listener can listen on 1 or more IP#, on 1 or more ports to support 1 or more databases.
On Production DB server with 2 Network Interface Cards, you have have "front end" network servicing end users & "back end" network for backup & such.
What SB said is true but I can see where his statement
a single listener can listen on 1 or more IP#, on 1 or more ports to support 1 or more databases
could be misleading, causing one to believe that each database somehow requires its own port on the listener. Not so. (SB - I know that wasn't what you were saying, only that the way it was said, it could be read that way).
Just to amplify and clarify, the entire configuration of the listener is for the listener. It has nothing to do with the database.
One single listener, using the default name of LISTENER, listening on the single default port of 1521 and a single IP address, is quite capable of -- indeed was designed to, service multiple databases of multiple versions running from multiple homes.
Now, if you have a need to configure the listener to listen on multiple ports and/or multiple ip addresses, that can certainly be done. But there is no relationship between those multiple ip addresses/multiple ports and any database.
> the other is on a public IP network ( behind a firewall ) .
Besides the replies that it is the listener that listens on IP address(es).... I would like to add :
Check to see that the firewall doesn't stop SQLNet traffic between the "folks outside the facility connect across the public network" and the database and vice-versa.
Hemant K Chitale