dblink does not connect when activated in a remote server

dblink problem:

I am connecting to a remote server and run a functions that calls
another one using db_link.
It fails with the error message is 08001 - could not establish
connection.

When the function is located in a local server - it runs fine.

The connection string is:

'hostaddr=127.0.0.1 .....'

The following were tried but did not help:
'host=localhost' and even  providing the real target server
('host=tlvl0390') did not help.

Happens on WIndows as well as Unix

Can you help?

Thanks

Danny