In an N+1 redundancy deployment, an AP ' s ability to return to its designated primary WLC after that controller recovers depends on two distinct configuration requirements working in concert. First, the AP Fallback feature (Option C) must be enabled on the WLC. AP Fallback instructs APs to monitor the availability of their configured primary controller and automatically reconnect to it when it becomes available again, rather than remaining permanently joined to the N+1 backup controller. Without AP Fallback enabled, APs stay connected to whichever controller they most recently joined. Second, the APs must have their primary WLC information correctly configured (Option D). If an AP does not have the primary controller ' s name, IP address, or FQDN correctly set, it cannot identify when its designated primary has recovered and therefore cannot initiate a return fallback. DHCP Option 43 (Option A) is used for initial AP discovery only. Secondary WLC configuration (Option B) addresses failover direction but not the return path. AP failover priority (Option E) controls which APs are moved first during a failover event, not whether fallback occurs. Reference: WLSD Study Guide — N+1 Redundancy Design, AP Fallback Configuration, Controller Primary, Secondary and Tertiary Assignment.