Multiple WLCs are implemented in a high-availability configuration in a mobility group.

In a high-availability configuration with multiple WLCs in a mobility group, when APs that only have a primary controller configured become orphaned (their primary WLC fails), they will by default join the controller with the lowest percentage of associated APs per license capacity. This load-based selection mechanism ensures a balanced distribution of APs across the remaining controllers in the mobility group. The WLC with the lowest percentage of AP capacity utilized is chosen because it has the most headroom to accept additional APs without becoming overloaded. This prevents a single backup controller from becoming overwhelmed while others remain underutilized. The selection is not based on absolute number of APs (Option D), available free licenses in absolute terms (Option A), or CPU utilization (Option C) — it specifically uses the percentage of license capacity occupied, which normalizes across controllers with different total AP capacities. Reference: WLSD Study Guide — N+1 Redundancy Default Behavior, AP Orphan Failover Logic, WLC Load-Based AP Assignment.