I'm having a problem connecting to a remote database. I have added the info from a valid tnsnames.ora file used at the server site into my own tnsnames.ora, their firewall has been opened for port 1521 from the IP address of my PC, a tnsping from a command prompt responds with OK (xxx msec) as expected, but all attempts to establish a connection to the database result in: ERROR: ORA-12203: TNS:unable to connect to destination Any clues?
If you have verified that all of your parameters for the TNS entry are correct, then I suspect that the firewall may be your issue. When you contact the listener for a database connection, the server creates a server process for you (typically a dedicated server process). It is only contacting the listener that uses port 1521. Any communications between the client application and the server process occur on a different, random port. This can cause problems with certain firewall systems. To solve this, you can force all application/process communications through the listener's port by adding USE_SHARED_SOCKETS=TRUE in your registry. Then, restart the database server. Metalink has tons more information on Oracle databases and firewalls.
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