WARNING: INBOUND CONNECTION TIMED OUT (ORA-3136) AND ORA-03135: CONNECTION LOST CONTACT

ISSUE:

Alert log on Oracle server shows the following error: 

INBOUND CONNECTION TIMED OUT (ORA-3136) 

Example log:

Time: 21-SEP-2014 03:50:34
TNS-12535: TNS:operation timed out
TNS-12535: TNS:operation timed out
  Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=39748))
WARNING: inbound connection timed out (ORA-3136)
  Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=39750))
WARNING: inbound connection timed out (ORA-3136)

AND

Informatica SSOT load failed with below message

Message: Database driver error...
CMN_1022 [
Database driver error...
Function Name : Logon
ORA-03135: connection lost contact

Database driver error...
Function Name : Connect
Database Error: Failed to connect to database using user [OBAW_OBIA] and connection string [Database].]

REASON:

This issue occurs due to one of the following reasons:

Inbound connection was timed out by the server as the user authentication was not completed within the given time specified by SQLNET.INBOUND_CONNECT_TIMEOUT or its default value specified in sqlnet.ora.
There is a lag in the network or a layer between the database and the client is preventing the log on process from completing within the allowed time.

Solution:

By default, the SQLNET.INBOUND_CONNECT_TIMEOUT is set to 60 seconds. 

To resolve this issue, do the following:

Change the setting by adding the parameters SQLNET.INBOUND_CONNECT_TIMEOUT in $ORACLE_HOME/network/admin/sqlnet.ora and INBOUND_CONNECT_TIMEOUT_<listener name> to the $ORACLE_HOME/network/admin/listener.ora file on the database server.

Bounce the listener  and Verify the issue.

Example:

SQLNET.INBOUND_CONNECT_TIMEOUT = 300
INBOUND_CONNECT_TIMEOUT_PROD = 300