GTM - Modifying DNS Answers Based On Source Addresses- Listener per Sub-Domain?

I'm a newbie at GTM pretty much- I need to have a sub-domain created and have our enterprise DNS delegate all look-ups to GTM for that subdomain, so I may create the logic to provide a particular DNS answer if the DNS query is sourced by a particular IP address, and a different answer for all others.

Do I need a different listener address for each sub-domain, and should it be the floating IP address?

Thanks!

Mike