listener.ora and tnsnames.ora and SQLNET.ORA

importance of listener.ora and tnsnames.ora and
SQLNET.ORA

tnsnames.ora and listener.ora are 2 important configuration files in Oracle networking. They are used and consulted whenever someone tries to connect to oracle.
In the order of importance, listener.ora is more important than tnsnames.ora, as without listener.ora, no one can reach the database, listener.ora is the “only door to oracle database”.
Now, Listener, running on database server and listening for incoming connections, which MUST be started to reach and approach the database, runs on server side and makes use of listener.ora, a server-side file. This file is used to specify
1) The protocol used
2) The Server
3) The protocol where listener will be listening
This file does not specify and does not contain the database and the instance information unless you specify it using SID_LIST_{listener_name}. For the default listener, database automatically registers itself with the listener. My point here is that important is not the database and instance information, its the protocol, port and server information.

Now, forget about LISTENER because we are moving to tnsnames.ora.
An oracle database can operate and work successfully even if it does not exist in the database environment. Its purpose is just to ease out the work of the person working on database. How !!! Normally, when anybody wants to connect to an oracle database what he will do ? He will provide the server name, the protocol he will use and the port number of a computer. So, think about the person typing all 3 information almost 10 times a day.. .. !! :). Here tnsnames.ora comes into play. It stores all the 3 necessary things with one easy to remember single word name, and whenever user types in that names, tnsnames.ora is consulted by oracle, all 3 things are picked up and used to make connection.

SQLNET.ORA

SQLNET.ORA can be used for different purposes,
first to identify the method to connect from client like tnsnames
Second it can be used to bypass the network layer by setting the parameter automatic_ipc=on
Third, we can set to check the client whether its active after certain interval.
If sqlnet.ora is not there, then it will take the default values.