Loopback database link & ORA-02082: a loopback database link must have a connection qualifier

SQL> show parameter global_names

NAME         TYPE  VALUE
------------------------------------ ----------- ------------------------------
global_names        boolean  TRUE

SQL> create database link orcl.local connect to donghua identified by donghua using 'orcl';

Database link created.

SQL> select * from dual@orcl.local;
select * from dual@orcl.local
                   *
ERROR at line 1:
ORA-02085: database link ORCL.LOCAL connects to ORCL.LAB.DBAGLOBE.COM


SQL> drop database link orcl.local;

Database link dropped.

SQL> create database link orcl.lab.dbaglobe.com connect to donghua identified by donghua using 'orcl';
create database link orcl.lab.dbaglobe.com connect to donghua identified by donghua using 'orcl'
                                           *
ERROR at line 1:
ORA-02082: a loopback database link must have a connection qualifier

SQL> create database link orcl.lab.dbaglobe.com@loopback 
  2  connect to donghua identified by donghua using 'orcl';

Database link created.

SQL> select instance_name from v$instance@orcl.lab.dbaglobe.com@loopback;

INSTANCE_NAME
----------------
orcl

SQL> drop database link orcl.lab.dbaglobe.com@loopback;

Database link dropped.

SQL> create database link orcl.lab.dbaglobe.com@l   
  2  connect to donghua identified by donghua using 'orcl';

Database link created.

SQL> select instance_name from v$instance@orcl.lab.dbaglobe.com@l;

INSTANCE_NAME
----------------
orcl

SQL> drop database link orcl.lab.dbaglobe.com@l
  2  ;

Database link dropped.