In a recent thread on OTN, the OP was having a difficult time understanding dynamic registration. They were confused about the interactions of settings in listener.ora, tnsnames.ora, and the local_listener parameter. After responding to the thread with a summary, I thought it might be worth repeating here, along with a few more references. I actually covered all of these points in earlier articles, “Registering the Oracle Database With the Listener” and “Exploring the Local Listener Parameter“, but sometimes a simply restating key points can help clarify things for some people.
In short, the summary of important points are as follows:
1) The listener itself doesn’t give a flying fig about what is in tnsnames.ora. That file (tnsnames.ora) is used ONLY by client processes. In the case of dynamic registration, the database IS the client process.
2) The listener is quite capable of starting with no listener.ora file at all. In this case it will start with all default values, including the default name of LISTENER and default port of 1521. For most people, most of the time, this is sufficient.
3) If the local_listener parameter is not set (null) the database will send the registration request to port 1521. Notice that 1521 is also the default port of of the listener.
4) If you choose to set local_listener, you can either use a full connect string ((ADDRESS = (PROTOCOL = TCP)(HOST = localhost.localdomain)(PORT = 1421))) or simply reference an entry in tnsnames.ora, to resolve to the address (server name and port) of the listener.
5) The SID_LIST section of listener.ora has nothing to do with dynamic registration. Quite the opposite. The SID_LIST section is how you implement static registration.
The original thread on OTN may be found here: “Oracle Net Service Configuration“. In that thread, there was also a link to a very nice explanation by Martin Beach on his blog “Martin’s Blog”, “Little things worth knowing-static and dynamic listener registration“
Ed Stevens, DBA 