Enabling AP fallback globally on the WLC allows access points to reconnect to their primary controller after they have connected to a secondary controller due to the primary being offline. This is the exact behavior described in the scenario — APs successfully fail over to the secondary WLC but do not return to the primary WLC when it recovers. AP Fallback is a WLC-level setting that monitors the availability of each AP ' s configured primary controller and initiates a reconnection when the primary becomes reachable again. Without AP Fallback enabled, APs remain on whatever controller they most recently joined — in this case, the secondary — even after the primary recovers. The CAPWAP AP Controller IP Address command (Option A) permanently changes the primary controller configuration on the AP, which is not the intended solution — the AP already has the correct primary configured. DHCP Option 43 (Option B) is used for initial AP discovery, not fallback. AP Failover Priority (Option D) controls which APs are processed first during a failover event, not whether APs return to their primary controller. Reference: WLSD Study Guide — AP Fallback Configuration, N+1 Redundancy Recovery, Controller Primary/Secondary Hierarchy.