SQL*PLUS is a "client" application. Thus the same tnsnames.ora file is checked no matter where you try to connect. In the case where client and server are installed on the same machine, they are often installed in the same ORACLE_HOME. However, regardless of that, the tnsnames.ora that your SQL*PLUS application uses to connect to your local DB is the exact same file it will use to connect to ANY DB ANYWHERE. Simply insure the correct entries exist in that file, and that global_names is set appropriately.