How to detect interface?

That's quite difficult to do. Without actually waking up the PC you have a quite hard time distinguishing the WakeOnLan case from the case of a machine that is not presently active on the network and which is refusing to talk to you.

I agree, considering to the switch it is just a mac, you would need some kind of wakeonlan discovery tool, as a switch or router would most likely have no idea the services that are available on a NIC connected to a port, other than mac/IP depending on its status.