Catch OAuth introspection response?

For the layered VS option, you don't really need external ip/port, because traffic will never leave the bigip between the two virtual servers.

So you can use a dummy ip such as 1.0.0.1

I didn't test it with the second VS as pool member, but you can use an iRule which will route traffic to the second virtual server

Here is the reference for the virtual irule command: https://devcentral.f5.com/wiki/iRules.virtual.ashx