ORA-03135: connection lost contact
1) Server unexpectedly terminated or was forced to terminate.
2) Server timed out the connection
1) Check if the server session was terminated.
2) Check if the timeout parameters are set properly in sqlnet.ora.
ORA-03135 occurs when we try to connect oracle database and the connection gets time out. ORA-03135 can also be caused by the firewall when connecting remotely.
To resolve ORA-03135 exception we need to increase the value of the expire_time parameter in the SQLNET.ORA file, as mentioned in Action part. We can also set the parameters sqlnet.inbound_connect_timeout and inbound_connect_timeout_listenername to 0 can avoid the ORA-03135 error. SQLNET.ORA file is located under $ORACLE_HOME/network/admin/.
We recently faced ORA-03135 on one of our testing environment after Server Admin team did a firewall upgrade. Users were able connect to the database, but if their session was idle for some time, the connection was getting terminated.
To resolve ORA-03135 we added following to SQLNET.ORA file
SQLNET.EXPIRE_TIME = 10