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Oracle Networking
Listener.ora,Tnsnames.ora
and sqlnet.ora
Listener.ora: The listener file contains server side network configuration parameters. It can
be found in the ORACLE_HOME/network/admin/ directory on the server.
Tnsnames.ora: The tnsnames.ora file contains client side network configuration parameters.
It can be found in the ORACLE_HOME/network/admin. This file will also be present on the
server if client side connections are used on the server itself.
Sqlnet.ora: The sqlnet.ora file contains client side network configuration parameter. It can be
found in the ORACLE_HOME/network/admin. This file will also be present on the serverif
client side connections are used on the server itself.

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For client and server to communicate two files must be configured:
$ORACLE_HOME/network/admin/listener.ora on server side.
$ORACLE_HOME/network/admin/tnsnames.ora on client side.
To configure the server add the following to listerner.ora
Listenername=(address_list=(address=(protocol=tcp)(host=hostname)(port=1521)))
Sid_list_listenername=(sid_list=(sid_desc=(sid_name=<instance_name>)(oracle_home=/orac
le_home)))
To configure the client add the following to tnsnames.ora
Tnsalies=(description
=address=(protocol=tcp)(host=hostname)(port=1521))(connect_data=(sid=dev)))
$ lsnrctl start listenername.
$ lsnrctl stop listenername.
$lsnrctl status listenername.
$lsnrctl service listenername
$lsnrctl reload listenername.
$tnsping listenername.

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Listener Error:
[oracle@localhost admin]$ sqlplus system/manager@rman
SQL*Plus: Release 10.2.0.1.0 – Production on Sun Feb 28 04:09:39 2010
Copyright (c) 1982, 2005, Oracle. All rights reserved.
ERROR:
ORA-28547: connection to server failed, probable Oracle Net admin error
Enter user-name: