See if this helps you ?

Found this in a Metalink article (DocID=1024124.6)

This is not documented in the Oracle manuals and can be useful (even required) when the init.ora parameter GLOBAL_NAMES is set to TRUE.....
Note that if GLOBAL_NAMES is set to FALSE, you can name the dblink anything you desire.

Database Links
--------------
Database links are created using the following syntax:

SQL> create database link
connect to identified by
using '';

The name of the database link should match the global name of the target
database if GLOBAL_NAMES=TRUE. This may seem restricting since then there can
be only one database link per schema to a given database if global_names is
set to true. To overcome this use database link qualifiers. For example:

SQL> create database link oradb@link1
using 'D:BOSTON-MFG';

NOTE: in this example, 'link1' is database link qualifier
and 'D:BOSTON-MFG' is the connect string

My NOTE : your select to the remote database would look like this :
select * from table_name@oradb@link1;

-Tom