Updating tnsnames ora
If you do not change that file as well, then whenever you start SQL*Net Easy Configuration, your changes to tns_will simply be lost!
However, if you change this file and then start SQL*Net Easy Configuration and make some dummy changes, then your changes will be interpreted as well.
The syntax for connection entries is strictly defined, so it's important to make sure they are formatted correctly.
The file is where the Oracle Client stores various network connection settings which apply to ODBC connections.
These entries contain information that allows the ODBC driver to establish network connections to an Oracle Database, including hostname and port number.
Users must create an entry in this file for each database they wish to access.
The answer you get depends on which executable you're running.
This document describes in detail how to insert those entries into the corresponding files and how to determine whether they were inserted correctly.
Sometimes I get Oracle connection problems because I can't figure out which file my database client is using. For tnsnames-based oracle networking, using the TNS_ADMIN variable is the only way to ensure you're getting a consistent file.