Oracle: Does a 10g oracle client work with an 11g server?

I would certainly say it should. The SQL*Net protocol it uses is essentially unchanged. Here's an example of me connecting an Oracle 9 to an Oracle 10 server.

oracle@cammi:~$ sqlplus "urs/urs@THANOS_URS"

SQL*Plus: Release 9.2.0.8.0 - Production on Thu Jun 25 05:55:57 2009

Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.

Connected to:Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit ProductionWith the Partitioning, Data Mining and Real Application Testing options

According to the guys at "http://www.experts-exchange.com/"...

11 can talk to 11,10,910 can talk to 11,10,9,89 can talk to 11,10,9,8,78 can talk to 10,9,8,77 can talk to 9,8,7

According to Oracle forums, this is defined in Metalink DocID 207303.1, which provides a comprehensive client/ server compatibility matrix. I don't have Metalink access sadly, so I can't confirm this.

If you are having connection troubles, I suggest you start with the Oracle alert log on your server machine. To find the location of your oracle alert log:

SQL> select value from v$parameter where name = 'background_dump_dest';

Also, you'll probably get something useful out of enabling listener tracing:

$ lsnrctlLSNRCTL> set trc_level ADMIN

The trace file on my Solaris Oracle 10 install is found in:

$ORACLE_HOME/network/trace/listener.trc

You can view it directly or use the trcasst program to "format" it. Note that ALL of this is on the server, not your client side.

Hope this helps.

Normally this should just work. Here I sometimes have to connect to a 10g DB with a 9er client. Works flawless.

It should work. I have never had problems with upwards compatiblity of Oracle Client.Test:

myclient{oracle}# sqlplus system@rac11gSQL*Plus: Release 10.2.0.3.0 - Production on Thu Jun 25 08:44:09 2009Copyright (c) 1982, 2006, Oracle.  All Rights Reserved.Enter password:Connected to:Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - ProductionWith the Partitioning, Real Application Clusters, OLAP, Data Miningand Real Application Testing optionsSQL> select * from v$version;BANNER--------------------------------------------------------------------------------Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - ProductionPL/SQL Release 11.1.0.7.0 - ProductionCORE    11.1.0.7.0      ProductionTNS for Linux: Version 11.1.0.7.0 - ProductionNLSRTL Version 11.1.0.7.0 - Production