WLC AP Fallback Design for N+1 Redundancy

300-425 By islever Editorial Last updated

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Short answer

DE Enable AP Fallback on the WLCs and ensure the APs have their primary WLC information configured correctly.

Question

A customer has multiple WLCs running in N+1 redundancy with APs load balanced between the WLCs. The customer performs AP failover testing between the WLCs and notices that some of the APs do not move back to their primary WLC after it recovers. What are two points that must be addressed in the design? (Choose two.)
  1. DHCP Option 43 information is incorrect.
  2. APs do not have their secondary WLC information configured correctly.
  3. APs failover priorities are set to Low.
  4. AP Fallback is not enabled on one of the WLCs. Correct Answer
  5. APs do not have their primary WLC information configured correctly. Correct Answer

Key Takeaways

The exam tests the specific mechanism of AP reassociation, highlighting the common trap of assuming APs automatically roam back; in reality, explicit configuration of AP Fallback and accurate Primary WLC settings are required.

This question addresses the design requirements for ensuring Access Points return to their primary Wireless LAN Controller after a failover event in an N+1 redundancy architecture. It establishes that both the fallback feature and correct primary controller configuration are essential for proper behavior.

Common mistake: Many learners incorrectly select options related to DHCP Option 43 or Secondary WLC configuration, confusing initial discovery/joining mechanics with post-failover recovery logic.

Expert Analysis

Why the Answer Is Correct

AP Fallback is a feature that allows an AP to leave its current active controller and return to its preferred primary controller once it becomes available again. Without this feature explicitly enabled on the controllers, APs may remain associated with the secondary (backup) controller indefinitely. Furthermore, for the AP to successfully reconnect to the primary controller, the primary controller's information must be correctly configured in the AP's settings (or via DHCP/Proxy DHCP). If the primary WLC information is incorrect, the AP cannot identify or reach its home controller even if fallback is enabled.

Why the Other Options Are Wrong

DHCP Option 43 is used for initial controller discovery during boot-up, not for managing reassociation after a failure has occurred. Similarly, while the secondary WLC must be reachable for the failover itself, the issue described is about returning to the primary, not joining the secondary. Setting priorities to 'Low' might affect which controller is chosen first but does not prevent the return process if fallback is enabled. The core issue is the lack of a directed path back to the primary.

Community Comment Notes

Community consensus strongly supports options D and E. As Jonycici noted, "If AP Fallback is not enabled... only the APs connected to WLCs with this feature enabled will return." This confirms that fallback is the enabling mechanism. Another commenter reinforced that "DE are the right choices," aligning with the official understanding that both the feature toggle and the target address (Primary WLC info) are necessary conditions.

Exam Strategy

When designing high-availability wireless networks, always verify that 'AP Fallback' is enabled if you require deterministic placement of APs on their primary controllers. Remember that failover is one-way by default; returning requires explicit configuration of both the action (fallback) and the destination (primary IP/DNS).

Frequently Asked Questions

Does AP Fallback happen automatically without configuration?

No, AP Fallback is a feature that must be explicitly enabled on the Wireless LAN Controllers. If disabled, APs will stay on the backup controller.

Why isn't Secondary WLC configuration the issue here?

Secondary WLC config ensures the AP can join during a failure. The problem is returning to the primary, which depends on Fallback being enabled and Primary info being correct.

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Community Votes

DE
100%

100% of anonymous learners picked answer DE. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 5 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 5

  1. Jonycici 👍 2
    If AP Fallback is not enabled on all WLCs, only the APs connected to WLCs with this feature enabled will return to their primary WLC once it recovers.
  2. AlmightKas 👍 1
    I chose C and E. The secondary WLC would have to have been configured correctly or the APs would have never joined the secondary WLC after failover occurred. Also, the AP Fallback has to be enabled because most of the APs did fall back and some didn't. If it wasn't enabled, all APs would not fallback to the primary AP. Lastly, I'm totally unsure of this but I believe the DHCP Option 43 information doesn't supply the APs with failover information. So that only leaves us with two answers. I fully believe E is one of the answers. I'm not totally sold on C but I don't have any other choice.
  3. e9cc965 👍 2
    Should be D and E
  4. Farhad123 👍 1
    DE are the right choices
  5. Jonycici 👍 1
    DE is correct

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