You are having difficulty connecting to the Oracle Listener and would like to troubleshoot connectivity between the Oracle RDBMS and Listener.
1) Make sure that the listener.ora file has the correct information in it.
The two basic elements that need to be present are the hostname and the port number. The hostname must be able to resolve to the server IP. The server IP can be used, as well as, standard loop-back IP (127.0.0.1) or "localhost" provided they resolve to the server IP.
2) Database registration with the listener.
The local_listener parameter for a DLP database should already be set to '(DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=PROTECT)))' if the installation/upgrade processes were followed. If this isn't the case, open the "Symantec DLP Oracle 11g/12c Installation Upgrade Guide" and look up 'Creating the TNS Listener'.
To actually see what's in there, log into sqlplus as sys as sysdba and:
SQL> show parameter local_listener
If it comes up blank, you can modify it to match the above entry. Here's an example:
SQL> alter system set local_listener = '(ADDRESS = (PROTOCOL=TCP)(HOST=Myhost)(PORT=1521))';
THEN do the following:
SQL> alter system register;
This will force the registration of the listener with Oracle.
3) Still, not connecting? Try this:
edit the sqlnet.ora file and change the entry for
if it's set to "NONE" try setting it to "NTS", or vice versa (the guide recommends changing this to NONE).
Either way the listener will require a bounce to load the new setting:
> lsnrctl reload