I have a 3605 Enterasys AP installed, which uses a wireless controller. The AP was working, but now the controller says its Radios are OFF. However the AP still has an address, and the controller shows it as up. Does this mean the AP isn't getting enough power, or something else?
Every AP is polling the the controller, if polls are not answered the AP will assume that the controller is not longer reachable and switch to the second controller. So the backup tunnel to the foreign controller is declared the active tunnel and the active tunnel to the local controller is moved to backup tunnel state.
Fast Failover (the name of the function) is a nice feature but not my cup of tea :-) In my opionion it's too dynamic so a small hiccup in the LAN could move your APs from the local to the foreign controller.
I never use it as it could result in some confusion by the customer.... and the switchover for the "normal" failover is fast enough in my experience. I don't think it's a big deal if the APs need a little bit more time for the switchover in case of a controller outage (1-2 pings).