Question: How do you use those Raspberry things as a router? Those have got only one network interface. Do you use USB network card with that?
Or you can use VLAN tags on the single interface, and set them on your switch/AP. I have mine trunked to a Linksys access point, and I configured the WAN and LAN to both be tagged on the port on the Linksys which the Pi is plugged into, with matching tagged interfaces for WAN and LAN.