Listener for dataguard config, how?

Hi!
Can somebody please give me a hint about where to start? Given 10g (linux), a working dataguard configuration and tnsnames as the addressing means for clients how does it normally go?
So far we switch the tnsnames file and have clients reconnect. I'd like to use the same tnsnames file regardless of which instance is primary.
Now, the listener control file specifies a host and a port, so I presume I can just run the listener on a separate machine. But the remote listener parameter just expects a hostname. But what I'd like to do is for the listener to connect a given service name to one or another instance, depending on status.
Where do I start looking for this?

Lots of Greetings!
Volker

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