Selecting interface for DNS forwarding

Hello, I'm trying to forward some DNS requests on test interface I created.
But I'm not quite sure how to limit this to just that one interface, without messing up my other LAN. If I exclude my LAN from listening, would it be affected by any other change I make to this DNS.

Aditionally, this will just affect devices that use my router as their DNS , right?

Have you read about multiple DNS instances?