ORA-01017: invalid username/password; logon denied ORA-02063: preceding line from %sI checked the connection using sqlplus, worked. Using connection description on sqlplus, also worked fine. I even recreated the database link, but still failed.
Then I cloned again to another machine, tested the database link, worked.
What was the difference between the two machine? It was the host name settings. The first one that failed had its host name only accessible locally. The second one had its host name registered on DNS server. So the database server I tried to access using database link could resolve host name of the second machine, but not of the first one.
Then I added the host name of first machine to DNS server, tested the database link, worked.
