We upgraded Oracle 10.1 to 10.2, and We found WARNING: 'inbound connection timed out (ORA-3136)' in alert.log.
When we found this error, So we opened metalink for finding what it is.
This problem can occur on any platform, When you use Oracle Net services - Version 10.2 up.
Because; The Oracle Net 10G parameter "SQLNET.INBOUND_CONNECT_TIMEOUT and INBOUND_CONNECT_TIMEOUT_listenername default to 0 in 10.1.
To address Denial of Service (DOS) issues, the parameter were set to have a default of 60 (seconds) in 10.2
The following may be seen in the alert log: WARNING: inbound connection timed out (ORA-3136)
SQLNET.INBOUND_CONNECT_TIMEOUT is set to a value in seconds and determines how long a client has to provide the necessary authentication information to a database.
INBOUND_CONNECT_TIMEOUT_listenername is set to a value in seconds and determines how long a client has to complete its connect request to the listener after the network connection has been established.
To protect both the listener and the database server, Oracle Corporation recommends setting INBOUND_CONNECT_TIMEOUT_listenername in combination with the SQLNET.INBOUND_CONNECT_TIMEOUT parameter.
Whenever default timeouts are assigned to a parameter, there may be cases where this default does not work well with a particular application. However, some type of timeout on the connection establishment is necessary to combat Denial of Service attacks on the database. In this case, SQLNET.INBOUND_CONNECT__TIMEOUT and INBOUND_CONNECT_TIMEOUT_listenername were given default values of 60 seconds in Oracle 10.2. It is these timeout values that can cause the errors described in this note.
Also note that it is possilbe the reason the database is slow to authenticate, may be due to an overloaded Oracle database or node.
Set the parameters SQLNET.INBOUND_CONNECT_TIMEOUT and INBOUND_CONNECT_TIMEOUT_listenername to 0 (indefinite) or to an approprate value for the application yet still combat DOS attacks (120 for example).
These parameters are set on the SERVER side:
Further tuning of these parameters may be needed is the problem persists.