Hi Angela,
I pasted below the part of config guide explaining the different modes. In summary :
-Fallback off means : when 1st radius server shows dead , WLC moves to the second. And will only change again when the 2nd is dead too.
-Passive means : whent 1st radius is dead, WLC moves to the second. If there is a new authentication coming in, it will try the 1st radius server again
-Active means : WLC constantly sends radius probes to detect when primary is back up.
config radius fallback-test mode {off | passive | active}
where
•
off disables RADIUS server fallback.
•passive causes the controller to revert to a server with a lower priority from the available backup servers without using extraneous probe messages. The controller simply ignores all inactive servers for a time period and retries later when a RADIUS message needs to be sent.
•active causes the controller to revert to a server with a lower priority from the available backup servers by using RADIUS probe messages to proactively determine whether a server that has been marked inactive is back online. The controller simply ignores all inactive servers for all active RADIUS requests. Once the primary server receives a response from the recovered ACS server, the active fallback RADIUS server no longer sends probe messages to the server requesting the active probe authentication.
