Shared Server: Port 1521 Open on Firewall But Unable to Connect Due to Errors: ORA-12535,TNS-12203

(Doc ID 361284.1)

Last updated on OCTOBER 27, 2016

Applies to:

Oracle Net Services - Version to [Release 8.1.7 to 11.2]
Information in this document applies to any platform.
Checked for relevance on 30-SEP-2011

This document describes a situation where a recent change to SHARED SERVER has occurred the firewall is now blocking the redirected connections to the dispatcher processes.


Firewall is present between the Oracle database and the clients. Port 1521 is open in the firewall.
Client connections time out or fail to complete giving errors like ORA-12535 or TNS-12203.


  1. Firewall service has been installed between database and clients.
  2. One of these:
  • Database has been switched from dedicated mode to shared mode or client connections were restricted to shared mode.
  • Database has been migrated to RAC setup.


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