An AirDefense primary appliance cannot have more that one associated standby AirDefense appliance.
AirDefense Primary to Standby Appliance association is 1:1
The AirDefense standby appliance must have the same exact license base installed / resident as its associated primary in order for proper fail over functionality.
There is no cost associated with licensing a standby AirDefense appliance to its associated primary appliance.
Please contact Extreme Networks GTAC Support to request AirDefense standby appliance licensing if needed:How to contact Extreme Networks Global Technical Assistance Center (GTAC)