listener.ora is the name of the Oracle Net Listener configuration file and it resides under $ORACLE_HOME\network\admin.

The content of a sample listener.ora file in its simplest form is as follows:

SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(SID_NAME = XE)
(ORACLE_HOME = C:\oraclexe\app\oracle\product\11.2.0\server)
)
)
LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = amomen-PC)(PORT = 1521))
)
)

The description of the parameters is as follows:

Make the necessary changes to the preceding parameters, save the file, and restart the Windows Oracle Listener service OracleXETNSListener.

Navigate to Oracle home ($ORACLE_HOME\bin), start the listener utility (lsnrctl), enter status as shown in the following screenshot, and hit Enter.

If the listener is not started, the command displays an error message, as shown in the following screenshot:

If the listener is running, the command displays detailed listener information as shown in the following screenshot:

The listener is automatically configured when we install Oracle Database 11g XE.

Transparent Network Susbstrate (TNS) handles all remote database connections. Oracle software reads the TNS connection string to understand how to connect to the remote databases. Every Oracle database and the Oracle Client software will have this file. By default the tnsnames.ora file is located under $ORACLE_HOME\network\admin. A sample alias entry from the tnsnames.ora file is as follows:

MY_XE =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = amomen-PC)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SID = XE)
)
)

In the preceding code:

When connecting to the remote database, we will use my_xe as a connect string.