11g and Newer: ORA-609 TNS-12537 and TNS-12547 or TNS-12170 in DB Alert.log |
Problem :
The following errors are intermittently posted to the alert.log of a database instance that is at or newer than 11gR1. All releases that are newer than 11g would be affected.
The ORA-609 might be accompanied by either the TNS-12537, TNS-12637 or the TNS-12547 and might also include the following timeout messages:
Fatal NI connect error 12170.
TNS-12535: TNS:operation timed out
ns secondary err code: 12560
nt main err code: 505
Solution: 
The simplest solution to this problem is to increase the setting for INBOUND CONNECT TIMEOUT at the server (database) sqlnet.ora.
The default directory location for this parameter file is in $RDBMS_HOME/network/admin and NOT the Grid home.
The default setting for the SQLNET.INBOUND_CONNECT_TIMEOUT parameter is 60 seconds. When an intermittent ORA-609
is occurring, we generally recommend increasing the setting to 120.
e.g.
Sqlnet.ora at RDBMS_HOME/network/admin (not GRID)
SQLNET.INBOUND_CONNECT_TIMEOUT=120
There is NO need to restart either the database or the listener after this change has been made.
The next server process that is spawned will reference the change.