While creating DBlink between any 2 servers the important thing to note after keeping the global_names=true is to keep the global_names parameter like either 'world' or 'us.oracle.com' or what ever u like on the both servers as same which is not in your case.So use the Alter database command and keep the global_names same on both the servers and then create the fresh DBlinks.Then only u can see the link as active.