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Diagnosing the ORA-12537: TNS: connection closed error

Oracle Database Tips by Donald Burleson

Question:  I'm trying to connect to Oracle and I get the ORA-12537: TNS: connection closed error.  How do I fix an ORA-12537?

Answer: The ORA-12537 is an informational error, and the "real" error is the secondary error message.

ORA-12537 TNS:connection closed
Cause: Normal "end of file" condition has been reached; partner has disconnected.
Action: None needed; this is an information message.

The ORA-12537 error sometimes relates configuration issues in the sqlnet.ora, protocol.ora and listener.ora files.  Verify that you service names match between your listener and remote client connect strings.

This ORA-12537 can also happen if your firewall has disconnected idle connections.

Also, the ORA-12537 sometimes happens in these cases:


1. You have a path name that is too long for the Oracle TNS client. See MOSC note:263489.1.

Since the iORA-12537 ssue is caused by a large connection string there are several workarounds for the issue.

1. Install the exe in a shorter named directory.

2. Modify the TNS Names entry so that it is shorter.

3. Replace domain names with IP Addresses if that shortens and vice versa.

4. Remove any parameters from the entry that are not needed.

5. Patch the Database Listener to the most recent version.



3. Tnsping Net Service Name fails with TNS-12537: TNS:connection closed or Sqlplus connection errors out with Ora-12537


* In the Sqlnet.ora file the parameter TCP.VALIDNODE_CHECKING is enabled and TCP.INVITEDNODES is set to some specific IP's of the Client Machine.

* If trying to connect to the Apps database, by default, with Oracle Apps Installation the parameter TCP.VALIDNODE_CHECKING is enabled and TCP.INVITEDNODES is set to Server Machines IP or Hostname.


* You can disable these parameters in the Sqlnet.ora

* Or add the client machines ip address in the TCP.INVITEDNODES list.

4. For ORA-12537 relating from inter-version connections.

You can get the ORA-12537 error if you listed 10g database SID with 9i listener.

5. In Oracle Apps 11i, you can get the ORA-12537 because of an eBusiness Suite security feature (See MOSC note 291897.1).  The fix is to edit your sqlnet.ora file to include the client IP address in the tcp.invited_nodes = (x.x.x.x, hostname, ...).

If you like Oracle tuning, see the book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.



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