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 server if client side connections are used on the server itself.

For client and server communication 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=/oracle_home)))

To configure the client add the following to tnsnames.ora

Tnsalies=(description
=address=(protocol=tcp)(host=hostname)(port=1521))(connect_data=(sid=dev)))

Listener commands:

$ lsnrctl start listenername
$ lsnrctl stop listenername
$ lsnrctl status listenername
$ lsnrctl service listenername
$ lsnrctl reload listenername
$ tnsping listenername