How Does a WLC Achieve Stateful Switchover for APs and Clients?

350-401 By islever Editorial Last updated

Short answer

B The active WLC establishes a CAPWAP tunnel with the AP, and the standby WLC copies the AP database and the client database from the active WLC.

Question

How does a WLC achieve stateful switchover for APs and clients?
  1. The active WLC establishes a CAPWAP tunnel to the AP, and the standby WLC establishes a LWAPP tunnel to the AP.
  2. The active WLC establishes a CAPWAP tunnel with the AP, and the standby WLC copies the AP database and the client database from the active WLC. Correct Answer
  3. The active WLC establishes a CAPWAP tunnel with the AP and standby WLC to share the AP database information.
  4. The active and standby WLCs establish separate CAPWAP tunnels to the AP.

Key Takeaways

Tests the distinction between control-plane tunnel establishment versus background database replication, with the common trap being confusion over whether controllers or APs form direct HA tunnels.

This question examines how Cisco Wireless LAN Controllers maintain seamless connectivity during failover through runtime state synchronization. The community overwhelmingly confirms that the active controller continuously mirrors AP and client databases to the standby unit to enable transparent switchover.

Common mistake: Candidates frequently select Option C, incorrectly assuming the active and standby WLCs establish CAPWAP tunnels directly to each other or misinterpreting AP discovery mechanics. They often overlook that synchronization occurs over a dedicated internal HA link using proprietary protocols, not standard CAPWAP control channels.

Expert Analysis

Core Concept: WLC High Availability Architecture

In enterprise wireless deployments, High Availability (HA) ensures minimal downtime during controller failures. The architecture relies on an Active and Standby WLC pair communicating over a dedicated HA interface. For Stateful Switchover (SSO), the standby controller must maintain an exact mirror of critical runtime data so that when a failover occurs, existing sessions remain uninterrupted without requiring reauthentication.

Why Option B is Correct

Option B accurately describes the synchronization mechanism. During normal operation, the Active WLC maintains all active CAPWAP tunnels, AP configurations, client session states, and image files. It continuously replicates this AP database and client database to the Standby WLC over the internal HA connection. As highlighted by multiple candidates referencing the Official Cert Guide, this state synchronization allows the standby unit to seamlessly assume control without forcing APs to re-enter the discovery phase.

Why Other Options Are Incorrect

  • Option A suggests mixed protocol tunnels (CAPWAP vs LWAPP). Modern networks exclusively use CAPWAP, and HA failover does not rely on protocol switching or dual-tunnel maintenance.
  • Option C implies a direct CAPWAP tunnel exists between the two WLCs specifically for sharing AP DB info. While WLCs communicate extensively over the HA link, they do not form CAPWAP control/data tunnels with each other; synchronization uses proprietary HA messaging over the standby interface.
  • Option D claims both controllers establish separate CAPWAP tunnels to the AP. This violates HA design principles; APs only maintain a single active CAPWAP tunnel to the primary controller at any given time to prevent split-brain scenarios and redundant traffic overhead.

Community Insights & Verification

Multiple candidates confirmed Option B, emphasizing that the AP-manager interface remains consistent across the HA pair, enabling transparent failover. Commenters noted that the physical HA connection handles the database mirroring, ensuring zero-touch recovery for associated clients and registered access points.

Official Reference

These links open the official vendor documentation in a new tab.

Exam Strategy

When evaluating WLC high availability questions, always distinguish between control-plane tunnel establishment and background state synchronization. Remember that APs only ever hold one active CAPWAP tunnel to the primary controller, while database mirroring happens silently over the dedicated HA link—this distinction quickly eliminates tunnel-based distractors.

Community Votes

B
85%
C
15%

85% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 9 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 9

  1. outnumber_gargle024 👍 5 Answered B
    In HA mode, WLCs use the same AP-manager interface for communication with the APs. This ensures seamless failover and allows the standby controller to use the existing capwap tunnel to communicate with the AP. The AP database info is sync'd over the physical connection between the two devices.
  2. shefo1 👍 4 Answered B
    from OCG p.525 Each AP learns of the HA pair during a CAPWAP discovery phase and then builds a CAPWAP tunnel to the active controller. The active unit keeps CAPWAP tunnels, AP states, client states, configurations, and image files all in sync with the hot standby unit. The active controller also synchronizes the state of each associated client that is in the RUN state with the hot standby controller. If the active controller fails, the standby will already have the current state information for each AP and client, making the failover process transparent to the end users.
  3. Tadese 👍 3 Answered C
    The new High Availability (HA) feature (that is, AP SSO) set within the Cisco Unified Wireless Network software release version 8.0 and above allows the access point (AP) to establish a CAPWAP tunnel with the Active WLC and share a mirror copy of the AP database with the Standby WLC. The APs do not go into the Discovery state when the Active WLC fails and the Standby WLC takes over the network as the Active WLC.
  4. chiacche 👍 2 Answered B
    High availability WLC : 1. Establish a CAPWAP 2. Status synchronization 3. Transparent failover
  5. kivi_bg 👍 1
    B allows the access point (AP) to establish a CAPWAP tunnel with the Active WLC and share a mirror copy of the AP database with the Standby WLC https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-7/High_Availability_DG.html#pgfId-202764
Show 4 more comments
  1. Mizuchan 👍 1 Answered C
    During stateful switchover, the active and standby WLCs synchronize critical information, such as AP and client databases, to ensure a seamless transition. This synchronization helps in maintaining the established connections during failover events.
  2. Osama_anwar 👍 4 Answered B
    Confirmed
  3. teems5uk 👍 3 Answered B
    I'll go with B
  4. Luiggi 👍 3 Answered B
    I'ts B...

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