Oracle Tip : Override or have a local copy of TNSNAMES.ORA

Usually users don’t have access on UNIX box to modify the global TNSNAMES.ORA in the $ORACLE_HOME/network/admin. In this case all they need to do is create a .tnsnames.ora [notice the DOT before the file name] in their home directory. Next time when you login oracle notices this file and when you try to connect it looks up this file before the global tnsnames.ora is referred. In case of conflicts user’s version takes precedence.

Interested read more - http://oracledoug.com/serendipity/index.php?/archives/782-.tnsnames.ora.html

Flag for the DBA - when a user on UNIX says he is not able to connect the culprit could be his copy of .tnsnames.ora too!

And for the still curious this is possible with sqlnet.ora as well.

Oh I love Oracle :)