IBM AIX 6.1: Number of TCP Connections Limited - ORA-12547, Tnsping Yields TNS-12547 id 1084443.1

Connections to the database via the listener (i.e. TCP)  are limited in number and testing reveals that this number is consistent.  A shutdown of database and listener will resolve the issue until   number of TCP connections is established again.  Local or bequeath connections are NOT exhibiting this problem so local connections to the database are not failing at the time that this issue is reproducible. 



Apart from the client failures at number of TCP connections, the listener appears to be functioning normally for a while.  However, in a RAC environment, the listener may be stopped by the CRS when this problem is occurring as it is unreachable using TCP/IP.

Additionally, any Oracle feature or process that relies on TCP may exhibit errors or may crash during the time of this failure.  e.g...ONS or Oracle Notification Service may crash.

Changes

This is likely a new installation of Oracle on IBM AIX 6.1 or an upgrade of the OS to IBM AIX 6.1 has recently taken place.

Cause

In this case, the IBM AIX 6.1 Traffic Regulation feature or TR was being used to restrict the number of TCP connections that were allowed for a range of TCP ports.  Traffic Regulation  was introduced in December 2009 with version 6.1 of IBM AIX.