GTM: Creating a Wide IP that returns different answers to internal clients

The problem that you may have with your second solution (Return 2 DNS) is that internal users will have no true GTM load-balancing - meaning that no healthcheck or load info will be used and you could potentially have an issue later.

 

 

You could CNAME internal users to 1 WideIP and external users to another - and then use topology and LB as you wish for each WideIP. You could potentially create a small number of internal topo records using logical datacenters, as you mentioned, and then reuse them.