ORA-609 and TNS-12537 in 11g Alert.log

Issue:  ORA-609 and TNS-12537 in 11g Alert.log


Findings:
1) lsnrctl status hanged
2) conn user/pwd@orcl hanged
3) Database is up and running
4) Error in alert log
nt OS err code: 0
Fatal NI connect error 12537, connecting to:
(LOCAL=NO)
VERSION INFORMATION:
TNS for Linux: Version 11.1.0.6.0 - Production
Oracle Bequeath NT Protocol Adapter for Linux: Version 11.1.0.6.0 - Production
TCP/IP NT Protocol Adapter for Linux: Version 11.1.0.6.0 - Production
Time: 25-JAN-2012 12:38:49
Tracing not turned on.
Tns error struct:
ORA-609 : opiodr aborting process unknown ospid (4018_47693892033648)
ns main err code: 12537
TNS-12537: TNS:connection closed
ns secondary err code: 12560
nt main err code: 0
nt secondary err code: 0
nt OS err code: 0
ORA-609 : opiodr aborting process unknown ospid (4016_47051970669680)

Cause:
The ORA-609 error is thrown when a client connection of any kind failed to complete or aborted the connection
process before the server process was completely spawned.
Beginning with 10gR2, a default value for inbound connect timeout has been set at 60 seconds.

Solution:
Increase the values for INBOUND_CONNECT_TIMEOUT at both listener and server side sqlnet.ora file as a preventive measure.
If the problem  is due to connection timeouts,an increase in the following parameters should eliminate or reduce the occurrence of the ORA-609s.

Sqlnet.ora: SQLNET.INBOUND_CONNECT_TIMEOUT=180
Listener.ora: INBOUND_CONNECT_TIMEOUT_listener_name=120


I had faced this issue on Linux Server.In may case the issue got resolved after changing one of the Kernel Parameter.
Change the value of net.ipv4.ip_forward from 0 to 1 in /etc/sysctl.conf file.
# Controls IP packet forwarding
net.ipv4.ip_forward = 1