Sometimes You can get “TNS-12561: TNS:unknown error ” error.
Details of error are as follows.
TNS-12561: TNS:unknown error
1. If there is connectivity with SSL via the TNS Listener to the Database locally, this indicates something on the “AWS” side is at fault.
2. If a program is scanning the Listener, it should not be making connection attempts or pings as a non-Oracle (Listener) user.
1. Check with the AWS (Amazon) technical vendor as to what may be wrong.
2. Make sure non-Oracle Client programs or processes are attempting to ping or “connect” to a secure Listener.
As a reference for fault finding any “<unknown connect data>” listener log entries, see the following:
Listener Log Intermittently Reports: <unknown connect data> and either * 12537 or * 12569 errors (Doc ID 1664901.1)
Do you want to learn more details about RMAN, then read the following articles.