database link

hi all,

i have oracle 11g eand oracle 12c on Windows Platform.

i have create a database link like this:

  CREATE DATABASE LINK CTM2XDS

   CONNECT TO PIPPO IDENTIFIED BY xxxx

   USING '(DESCRIPTION=

(ADDRESS=(PROTOCOL=TCP)

(HOST=HOST_NAME)(PORT=1521))

(CONNECT_DATA=(SID=MAST)))';

but if i make a query on dba_db_links the database link name appear like this:

select DB_LINK from dba_db_links;

DB_LINK

---------------

CTMX2DS.168.2.7

why my db_link name appear like this extension (.168.2.7)?