3299264 - Oracle sessions disconnecting

Symptom 1:

The DBCO connection to remote DB failed with ORA-12547, and we can see the following error in listener.log:

07-FEB-2023 10:45:16 * <unknown connect data> * (ADDRESS=(PROTOCOL=tcp)(HOST=172.17.64.83)(PORT=53112)) * establish * <unknown sid> * 12525
TNS-12525: TNS:listener has not received client's request in time allowed
 TNS-12535: TNS:operation timed out
  TNS-12606: TNS: Application timeout occurred

Symptom 2:

Sessions getting abruptly disconnected with error ORA-03113.

In the alert.log there's:

Fatal NI connect error 12170, connecting to:
 (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=<IP_ADDRESS|HOSTNAME>)(PORT=1521))(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=<SERVICE_NAME>)(CID=(PROGRAM=<program>)(HOST=<hostname>)(USER=<user_id>))))

[...]
  Tracing not turned on.
  Tns error struct:
    ns main err code: 12535
    
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: 0
    nt OS err code: 0

• Not restricted to any application
• Oracle any version
• Not restricted to any platform

ORA-12547, firewall, timeout,TNS-12535,TNS-12525 , KBA , BC-DB-ORA , Oracle , Problem