TNS-12535: TNS:operation timed out and TNS-00505: Operation timed out

Error Message:

TNS-12535: TNS:operation timed out and TNS-00505: Operation timed out.

Log file:

TNS-12535: TNS:operation timed out
    ns secondary err code: 12560
    nt main err code: 505

TNS-00505: Operation timed out
    nt secondary err code: 110
    nt OS err code: 0
 Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=xxx.xxx.x.xxx)(PORT=45678))

Solution:

We can identify these errors in log file frequently. This problem is due to the value of idle session timeout in firewall settings. If the client connection is idle for more than the idle session timeout then the firewall drops the connection.
The following parameter, set at the $ORACLE_HOME/network/admin/sqlnet.ora, can resolve this kind of problem.

SQLNET.EXPIRE_TIME=n  Where <n> is a non-zero value set in minutes. 

After adding this parameter no need to restart the database or listener. The new changes takes place automatically for new connections.