WARNING: inbound connection timed out (ORA-3136)

Symptoms:

Mon Feb  8 15:31:31 2010
WARNING: inbound connection timed out (ORA-3136)
Mon Feb  8 15:31:32 2010
WARNING: inbound connection timed out (ORA-3136)
Mon Feb  8 15:31:33 2010
WARNING: inbound connection timed out (ORA-3136)
Mon Feb  8 15:31:34 2010
WARNING: inbound connection timed out (ORA-3136)
Mon Feb  8 15:31:36 2010
WARNING: inbound connection timed out (ORA-3136)
Mon Feb  8 15:31:41 2010
Mon Feb  8 15:33:25 2010
WARNING: inbound connection timed out (ORA-3136)
Mon Feb  8 15:34:44 2010
WARNING: inbound connection timed out (ORA-3136)

Knowledge Base:

The "WARNING: inbound connection timed out (ORA-3136)" in the alert log indicates that the client was not able to complete it's authentication within the period of time specified by parameter SQLNET.INBOUND_CONNECT_TIMEOUT.

From 10.2.0.1 onwards the default value of parameter SQLNET.INBOUND_CONNECT_TIMEOUT is 60 seconds, hence if the client is not able authenticate within 60 secs , the warning would appear in the alert log and the client connection will be terminated.

Root Cause:

$ORACLE_HOME/network/log/sqlnet.log (xxx.xxx.xxx.xxx is the masked IP)

***********************************************************************
Fatal NI connect error 12170.

  VERSION INFORMATION:
        TNS for Linux: Version 10.2.0.4.0 - Production
        Oracle Bequeath NT Protocol Adapter for Linux: Version 10.2.0.4.0 - Production
        TCP/IP NT Protocol Adapter for Linux: Version 10.2.0.4.0 - Production
  Time: 08-FEB-2010 15:33:25
  Tracing not turned on.
  Tns error struct:
    ns main err code: 12535
    TNS-12535: TNS:operation timed out
    ns secondary err code: 12606
    nt main err code: 0
    nt secondary err code: 0
    nt OS err code: 0
  Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=xxx.xxx.xxx.xxx)(PORT=10961))

Solution:

Shutdown these Oracle clients/Application Servers. In above case, it's x10 in-memory database cache.