I have been trying to create a working link from my production database to my test database. I create a private link named the same as the global name of the target DB. I put in the owner name identified by the owner password of the owner on the target database. I put in the connect string from my tnsnames.ora file.
The link creates, but it will not work. I either get a 2019 (connection description for remote database not found) or a 12154 (TNS:could not resolve service name). I can connect over to the database using the username/password@connect string that I used in the db_link with no problems.