TNS and Listener related issues

Oracle TNS issues(tnasnames.ora)

One of the most common error while connecting to Oracle Database is this one. There are plenty of options that needs to be checked and sometime it takes quite a few hours to figure out the exact issue. In my career, I have seen this so many times and each time I have explored new area of this error.

This is mainly due to tns and listener configuration.

There are couple of other error code as well, related to this.

Like : TNS Could not resolve ,ORA-28040: No matching authentication protocol etc..

In this scenario,  we have to look into below possibilities.

•   Need to check $TNS_ADMIN is properly set to folder $ORACLE_HOME/network/admin or $ORACLE_HOME/network/admin/<context_name>
• check tnsnames.ora, listener.ora and sqlnet.ora is configured properly and the content are well formatted
• check lsnrctl status <dbname> is resolving and showing status as active up and running
• check sqlnet.ora file and see the ifile is referring to correct location.
• there are several properties of sqlnet.ora file those needs to be validated.

few example of issue and solution will be added here as well. which will be containing some reference parameters and content of these mentioned files.