Net Service Names and the tnsnames.ora File

6.12.2 Net Service Names and the tnsnames.ora File

The installation process creates a tnsnames.ora file on each node.

The tnsnames.ora file acts as a repository of net service names. Each net service name is associated with a connect identifier. A connect identifier is an identifier that maps a user-defined name to a connect descriptor. A connect descriptor contains the following information:

The network route to the service, including the location of the listener through a protocol address
The SERVICE_NAME parameter, with the value set to the name of a database service

Note:

The SERVICE_NAME parameter you use in the tnsnames.ora file is singular, because you can specify only one service name. The SERVICE_NAME parameter is different from the service_names database initialization parameter. The service_names database parameter defaults to the global database name, a name comprising the db_name and db_domain parameters in the initialization parameter file. When you add service names using SRVCTL or Oracle Enterprise Manager Cloud Control, it lists additional cluster-managed services for the database.

The tnsnames.ora file is located in both the Grid_home\network\admin and Oracle_home\network\admin directories. By default, the tnsnames.ora file is read from the Grid home when Oracle Grid Infrastructure is installed.

With Oracle Clusterware 11g Release 2 and later, the listener association no longer requires tnsnames.ora file entries. The listener associations are configured as follows:

Oracle Database Configuration Assistant (DBCA) no longer sets the LOCAL_LISTENER parameter. The Oracle Clusterware agent that starts the database sets the LOCAL_LISTENER parameter dynamically, and it sets it to the actual value, not an alias. So listener_alias entries are no longer needed in the tnsnames.ora file.
The REMOTE_LISTENER parameter is configured by DBCA to reference the SCAN and SCAN port, without any need for a tnsnames.ora entry. Oracle Clusterware uses the Easy Connect naming method with scanname:scanport, so no listener associations for the REMOTE_LISTENER parameter are needed in the tnsnames.ora file.

Example 6-2 Adding a Second Listener to an Oracle RAC Database

If you created a database named orcl1, to add a second listener, listening on port 2012, use a command similar to the following command to have the database register with both listeners on startup:

SQL> alter system set local_listener='(DESCRIPTION=(
ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.0.61)(PORT=1521))
(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.0.61)(PORT=2012))))' 
scope=BOTH SID='OCRL1';