300-110 Designing Cisco Enterprise Wireless Networks Questions and Answers

This question hinges on a fundamental network engineering constraint: the maximum transmission distance of copper Ethernet cabling. IEEE 802.3 standards specify a maximum segment length of 100 meters (328 feet) for all standard PoE and Ethernet over Category 5e, 6, or 6A UTP copper cabling. The parking lot light poles are approximately 200 meters from the closest wiring closet — more than double the maximum copper distance. This immediately eliminates Options A and D, which specify Category 6 UTP cabling: at 200 meters, UTP copper cannot reliably carry Ethernet at any supported speed, and PoE cannot be delivered over this distance regardless of standard. The correct solution is fiber optic connectivity between the wiring closet and the parking lot, combined with a local AC/DC power module at each pole location. Fiber optic cabling supports single-mode runs of kilometers and multi-mode runs of hundreds of meters at Gigabit speeds — easily spanning 200 meters. At the AP mounting location on the light pole, an AC/DC power module (powered from the pole ' s existing electrical supply) converts AC power to the DC power the AP requires. Option B (fiber with 802.3af) is incorrect because PoE cannot be delivered over fiber — 802.3af requires copper cabling for simultaneous power and data delivery. Reference: WLSD Study Guide — Outdoor AP Deployment, Fiber vs. Copper Distance Limitations, Outdoor Power Solutions.

For APs to be able to fail over between a primary SSO pair in one data center and a standalone WLC in a remote data center connected via WAN with firewalls, two design requirements must be met. First, a mobility tunnel must be created between the wireless controllers (Option A). The mobility tunnel enables the controllers to exchange mobility control messages, peer information, and eventually AP context when failover occurs. Without the mobility tunnel, the remote WLC is not recognized as a valid failover target by the APs through the mobility domain. Second, UDP ports 16666 and 16667 must be open through the firewalls between the controllers (Option D). UDP port 16666 is used for mobility control traffic and UDP port 16667 is used for mobility data traffic — both must be permitted through the firewalls at both data centers for the mobility tunnel to establish and function. HTTPS port 443 (Option B) is used for web management and API communication, not for mobility tunneling. A static RF group leader (Option C) is a RRM configuration unrelated to AP failover capability. Creating a mobility group with the same names (Option E) is a component of the configuration but alone is insufficient without the mobility tunnel and open firewall ports. Reference: WLSD Study Guide — Inter-Site WLC Failover Design, Mobility Tunnel Requirements, Firewall Port Planning for WAN-Separated Controllers.

The requirement for users to retain their VLAN assignment and IP address when roaming between buildings managed by different WLCs is a Layer 3 roaming scenario. In Cisco ' s wireless architecture, IP address preservation across controller boundaries is achieved through inter-controller mobility — specifically the foreign-anchor mobility tunnel mechanism. When a client roams from Building A (WLC-A) to Building B (WLC-B), WLC-B becomes the foreign controller and WLC-A becomes the anchor controller. WLC-B tunnels the client ' s traffic back to WLC-A, allowing the client to retain its original IP address even while physically associated to an AP managed by WLC-B. This requires creating a mobility group between WLC-A and WLC-B with both controllers configured with the same mobility group name — the group name is the trust identifier that permits the mobility tunnel and anchor-foreign relationship to form. An SSO cluster (Option B) creates redundancy between two WLCs operating as one logical entity, not inter-building roaming between independent controllers. 802.11r (Option C) accelerates re-association but does not preserve IP addresses across different Layer 3 subnets. AP groups (Option D) control SSID and VLAN assignments but do not enable inter-controller IP preservation. Reference: WLSD Study Guide — Inter-Controller Mobility, Layer 3 Roaming, IP Address Preservation.

Floor loss calculation is a fundamental skill in multi-floor wireless site survey methodology. The floor attenuation value represents the signal power reduction caused by penetrating through a single floor structure including the floor decking, subfloor, ceiling material, plenum space, and any structural elements. In this measurement scenario, the engineer has two data points: -45 dBm measured at the ground level of the floor containing the access point (the signal level just below the AP ' s floor) and -50 dBm measured at the ceiling level of the floor below (the signal level just after passing through the floor structure). The floor loss is simply the difference between these two measurements: (-45 dBm) - (-50 dBm) = -45 + 50 = 5 dB. The result is expressed as a positive value (5 dB) representing attenuation — signal power decreases by 5 dB when passing through the floor. Expressing it as -5 dB (Option B) would incorrectly imply a signal gain. The 95 dB values (Options A and D) result from incorrectly adding rather than subtracting the dBm values — a common error when working with negative dBm figures. This floor attenuation value (5 dB) would then be entered into Ekahau ' s floor material properties to improve predictive model accuracy. Reference: WLSD Study Guide — Multi-Floor Signal Propagation, Floor Attenuation Factor (FAF), Ekahau Floor Loss Measurement Methodology.

This question requires straightforward wireless capacity engineering calculation. The total throughput requirement is 100 users × 1 Mbps per user = 100 Mbps aggregate. Each channel in the design can support 20 Mbps of usable throughput — this is the per-cell, per-channel allocation defined in the design parameters, representing usable throughput prior to RF overhead as stated in the question. The number of channels required is therefore: total required throughput divided by throughput per channel = 100 Mbps ÷ 20 Mbps per channel = 5 channels. In practice, each channel corresponds to a non-overlapping frequency assignment in the 5 GHz band. With 5 channels and 20 Mbps per channel, the design provides exactly 100 Mbps of aggregate capacity for 100 concurrent users at 1 Mbps each. This calculation methodology is foundational to Cisco ' s high-density WLAN design approach, where the number of spatial streams, channel allocations, and AP placement are all derived from the per-user throughput requirement multiplied by the concurrent user population. Reference: WLSD Study Guide — High-Density WLAN Capacity Planning, Per-User Throughput Calculation, Channel Planning and Spatial Reuse.

In a warehouse setting, two elements with a significant negative effect on wireless performance are AP height and absorption. AP height (Option B) is critical because warehouses often have very high ceilings (25-45 feet). When APs with internal (omnidirectional) antennas are mounted too high, the signal propagates primarily in the horizontal plane and the path loss to floor-level worker devices becomes excessive. Additionally, metal shelving between the AP and users further attenuates the already weak signal at high mounting heights. Absorption (Option E) is a major challenge in warehouses because the inventory stored on metal racks, particularly liquid goods, dry goods in cardboard, and dense materials, absorbs RF energy significantly. Metal racking causes both absorption and reflection, creating RF shadows and multipath environments that degrade connection quality. Wireless channels (Option A) are a design parameter, not an environmental impediment. Client authentication (Option C) and authorization (Option D) are network security processes unrelated to RF propagation quality. Reference: WLSD Study Guide — Warehouse Wireless Design, AP Height Considerations, RF Absorption in Industrial Environments.

A brownfield deployment scenario involves an existing operational wireless network where a physical remodel will change the RF environment. The engineer ' s task is to assess the impact of new furniture and wall materials on the existing AP placement — a scenario requiring a predictive re-analysis of how changed materials will alter propagation from the existing AP locations. Using a survey tool such as Ekahau with the known AP positions superimposed on updated floor plans, the engineer can reconfigure material attenuation properties to reflect new construction materials and re-run the predictive propagation model. This produces a before/after comparison identifying coverage gaps or interference hotspots introduced by the remodel without requiring physical downtime or temporary infrastructure changes. Option A (sweep analysis) measures existing signal strength but does not model future material changes. Option B (neighbor AP statistics) evaluates the current RF environment using WLC data, not future conditions. Option C (throughput measurements) tests current performance, not future RF impact. Reference: WLSD Study Guide — Brownfield Survey Methodology, Material Attenuation Modeling, Post-Remodel RF Impact Analysis.

Receive Start of Packet (RxSOP) is a Cisco proprietary mechanism that defines the minimum received signal threshold at which an access point will acknowledge an 802.11 frame and begin processing it. In a high-density lecture hall environment with 16 APs and directional antennas on a constrained channel plan, rogue APs operating on the same or adjacent channels contribute directly to elevated channel utilization by causing unnecessary medium contention, virtual carrier sensing via NAV, and clear channel assessment deferral. By raising the RxSOP threshold on the legitimate APs, the engineer creates a higher signal floor requirement — only signals above the configured RxSOP level are processed. Signals from distant rogue APs, arriving below this threshold, are silently discarded rather than processed, preventing them from consuming airtime through CCA deferral and NAV mechanisms. Band select (Option A) encourages dual-band clients to move to 5 GHz but does not address rogue interference. 802.11w (Option B) is a management frame protection standard, not an interference mitigation tool. DFS detection (Option D) is for radar avoidance on UNII-2 channels, not rogue AP mitigation. Reference: WLSD Study Guide — High-Density WLAN Design, RxSOP Configuration, Channel Utilization Management.

When designing a wireless network for any environment, including a historic building with ornate wall coverings and aesthetic constraints, RF coverage must always be considered first when placing access points. RF coverage is the fundamental requirement — without adequate signal strength throughout the space, no other design objective can be met. The engineer must first determine AP locations that provide the required signal strength and coverage to all areas before addressing aesthetics, overlap calculations, or interference mitigation. In a historic building specifically, the ornate wall coverings and dense construction materials may cause unexpected signal attenuation, making it even more important to model RF coverage before committing to AP positions. Once RF coverage requirements are established, aesthetic concerns (Option A) can guide the choice of AP form factor, enclosures, or cabling routes. Cell overlap (Option C) is derived from coverage calculations. RF interference (Option D) analysis follows after RF coverage baseline is established. Reference: WLSD Study Guide — Site Survey Methodology, AP Placement Priority, Special Environment Wireless Design.

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.

This WGB (Workgroup Bridge) design scenario requires satisfying multiple simultaneous constraints. EAP-FAST (Flexible Authentication via Secure Tunneling) is the correct authentication protocol because it provides enterprise-grade 802.1X security using protected access credentials (PAC) without requiring a certificate to be installed on each AP or WGB device — directly satisfying the enterprise-grade security without certificates requirement. EAP-TLS (Options B and D) requires client certificates on every authenticating device, which is explicitly excluded. Mobile station mode is required rather than static mode (Options C and D) because mobile station mode enables the WGB to aggressively scan and roam to optimal mesh neighbors dynamically, evaluating neighbor signal quality and switching to better RAPs/MAPs as the truck moves along its path. Static mode fixes the WGB to a specific channel or AP, preventing the aggressive scanning and roaming required for the latency-sensitive application. The dot1q-capable switch connection supports multiple clients in different VLANs via 802.1Q VLAN tagging between the WGB and the truck ' s local network switch. Reference: WLSD Study Guide — Workgroup Bridge Design, EAP-FAST Authentication, Mobile vs. Static WGB Mode, Industrial Wireless Design.

The design challenge is enabling IEEE 802.11r Fast BSS Transition for the new iPads (the standards-based fast roaming method) while maintaining backward compatibility for legacy RF scanners that may not support 802.11r. The SSID uses WPA2 Personal (PSK), not 802.1X enterprise authentication — therefore the correct Fast Transition variant is FT PSK (pre-shared key), not FT 802.1X (Options A and B). The critical configuration parameter is setting Fast Transition to Adaptive mode rather than mandatory. Adaptive mode is a Cisco feature that allows the AP and SSID to support both 802.11r-capable clients (which will use FT PSK for fast roaming) and non-802.11r legacy clients (which will use the standard pre-FT roaming process). In Adaptive mode, legacy scanners that cannot negotiate 802.11r during association will fall back transparently to standard roaming, while the new iPads leverage FT PSK for minimal-interruption handoffs. If Fast Transition is set to mandatory, legacy clients that do not support 802.11r will fail to associate entirely. Option C uses optimized roaming globally, which is a different mechanism and does not address the iPads ' specific need for a standards-based fast roaming solution. Reference: WLSD Study Guide — 802.11r Fast BSS Transition, FT PSK Configuration, Adaptive Fast Transition for Mixed Client Environments.

In the Cisco Catalyst 9800 IOS XE WLC configuration framework, the site tag serves as the primary organizational and functional grouping element for FlexConnect APs at a given physical location. The site tag defines the FlexConnect site — a logical boundary within which APs can perform local switching and local inter-AP roaming without requiring CAPWAP tunnel traversal to the WLC for every client handoff. Within a FlexConnect site defined by the site tag, APs can exchange client roaming context information directly with each other (peer-to-peer), enabling fast Layer 2 roaming for clients moving between APs that share the same site tag — effectively defining the roaming domain for FlexConnect APs at that site. The site tag also references the flex profile (which defines VLAN mappings, local auth settings, and split tunneling parameters) and the AP join profile. Switch port configuration (Option A) is performed on the infrastructure switches, not through the WLC site tag. IP address assignment (Option B) is a DHCP function. Firewall policies (Option C) are applied through ACLs and policy tags, not site tags. Reference: WLSD Study Guide — Catalyst 9800 Tag Architecture, FlexConnect Site Tag Role, Local Roaming in FlexConnect Deployments.

On the Cisco Catalyst 9800 IOS XE WLC platform, the tag-based configuration model uses site tags to associate APs with specific profiles including a flex profile and an AP join profile. The site tag is a fundamental binding element — when any component of a site tag is modified, including renaming the flex profile associated with that tag, the WLC treats this as a material configuration change requiring the AP to re-evaluate its operational parameters. Specifically, the AP must disconnect its existing DTLS (Datagram Transport Layer Security) control plane tunnel to the WLC and re-establish it. This DTLS session disconnect and rejoin cycle is equivalent to a full AP rejoin: CAPWAP discovery, DTLS handshake, join request, configuration download, and image verification. Client service is interrupted on the affected AP during this process. Firmware updates (Option A) occur via a separate image download process. Temporary SSID disable (Option B) is not a defined behavior for profile name changes. Switching to a backup controller (Option C) requires AP failover conditions, not configuration changes. Understanding the disruptive nature of site tag modifications is essential for change management in production 9800 deployments. Reference: WLSD Study Guide — Catalyst 9800 Tag-Based Configuration Model, Site Tag Architecture, Flex Profile and AP Join Profile Management.

To support high availability with client SSO (Stateful Switchover) and no interruption to live services during failover, the design must incorporate two requirements. First, redundant WLCs (Option A) are essential — without a physical standby controller, there is no entity to take over when the primary WLC fails. In an SSO configuration, one WLC is active and one is standby, and the standby must be ready to assume the active role instantaneously. Second, the high availability pair requires one of the WLCs to have a valid AP count license (Option B). In a Cisco WLC SSO pair, the standby controller ' s AP count license applies when it becomes active — without a valid license on at least one WLC in the pair, APs cannot join after failover. A 10-second RTT maximum (Option C) is a latency requirement for the redundancy link but is not a primary design requirement that addresses the overall high availability architecture. A back-to-back direct connection (Option D) is one way to connect the redundancy ports but is not mandatory if a low-latency switch connection is used. Code version 7.5 or newer (Option E) is a requirement for specific legacy SSO platforms but not a general design principle. Reference: WLSD Study Guide — WLC SSO High Availability Design, AP License Requirements, Redundant Controller Architecture.

The Cisco Catalyst 9300-48HX is a high-density PoE switch specifically designed for Cisco Catalyst 9100 Series AP deployments. The 48HX variant features 48 Multi-Gigabit PoE ports with IEEE 802.3bt (PoE++) support, providing up to 90W per port. The Cisco 9166 Access Point is a Wi-Fi 6E AP that requires IEEE 802.3bt (PoE++) power to achieve full radio functionality — enabling all three radios including the 6 GHz radio. In a two-switch stack of 48HX units, the total PoE budget is designed and rated to support full-port utilization with Cisco 9100 series APs simultaneously. The design intent is to connect APs to all ports on all switches — maximizing the deployment density and ensuring every AP runs with full functionality. Connecting to only half the ports on one switch (Option B), half of each switch (Option C), or all ports on only one switch (Option D) would underutilize the infrastructure and fail to achieve the full deployment density that the switch stack was architected to deliver. The AP naming scheme requiring sequential area numbering requires all APs to be connected and fully operational across the entire stack. Reference: WLSD Study Guide — Catalyst 9300 PoE Infrastructure, 9166 AP Power Requirements, High-Density Wired Infrastructure Design.

Voice over WLAN (VoWLAN) deployments require a minimum SNR threshold to maintain acceptable Mean Opinion Score (MOS) values for call quality. Cisco ' s 300-110 WLSD curriculum specifies that VoWLAN requires a minimum SNR of 25 dB throughout the coverage area. In an Ekahau post-deployment survey SNR heatmap, when the heatmap displays a consistent color indicating SNR at or above this threshold across the entire surveyed area — including all rooms, corridors, and common areas such as the lobby — the conclusion is that voice service is supported in all locations. The color coding in Ekahau ' s SNR heatmap uses green tones to indicate adequate SNR (typically ≥25 dB) and shifts toward yellow and red for degraded conditions. When the exhibit heatmap shows uniform adequate coverage across all surveyed areas without yellow or red zones, it confirms the SNR requirement for VoWLAN is universally met. Options A, B, and C suggest partial or no coverage, which would be indicated by mixed or poor SNR values — conditions not present in this scenario. The post-deployment survey with Ekahau is the validation step confirming that the predictive design was accurately realized in the physical environment. Reference: WLSD Study Guide — VoWLAN Design Requirements, SNR Thresholds, Post-Deployment Survey Validation with Ekahau.

Cisco ' s WLAN location and asset tracking architecture (based on Cisco Spaces or legacy Cisco MSE/CMX) relies on the ability to receive and measure the RF signal from tagged assets at multiple APs simultaneously. For accurate location determination using triangulation or trilateration algorithms, a minimum of three APs must receive the tag ' s signal with sufficient RSSI. Monitor mode APs are dedicated to passive RF listening — they do not transmit client-serving SSIDs and focus their full radio attention on scanning all channels for signal measurement. Placing monitor mode APs specifically on the perimeter of an asset tracking area provides the spatial diversity and boundary detection capability needed to accurately triangulate assets throughout the interior, without requiring any modifications to the existing data/voice serving APs. Adding monitor mode APs at the perimeter as an overlay ensures the existing 2.4 GHz and 5 GHz voice/data design is entirely undisturbed. Adding local mode APs (Option B) would serve clients and compete for channel capacity. Grouping APs closer (Option C) reduces capacity and increases co-channel interference. Increasing transmit power (Option D) worsens hidden node conditions without improving location accuracy. Reference: WLSD Study Guide — Cisco Location Services, Monitor Mode APs, Asset Tracking and WLAN Overlay Design.

For optimized roaming across multiple Wireless LAN Controllers (WLCs) with Cisco 8821 IP phones, two critical settings must be configured. First, configuring mobility groups between WLCs (Option A) allows for seamless inter-controller roaming by establishing mobility tunnels between controllers, enabling them to share client security context, preventing re-authentication when a phone roams from an AP on one WLC to an AP on another. Second, using Cisco Centralized Key Management (CCKM) for authentication (Option B) reduces the time required for re-authentication during roaming from a full 802.1X exchange to a single-message re-key process. CCKM stores the wireless security keys at the WLC level, enabling rapid key re-derivation during roaming without contacting the RADIUS server. AP groups (Option C) control SSID and VLAN assignments per AP cluster but have no impact on inter-controller roaming. AVC profiles (Options D and E) control application visibility and QoS marking — marking voice as best effort (Option E) would actually degrade rather than improve voice quality. Reference: WLSD Study Guide — VoWLAN Mobility Optimization, CCKM Configuration, Mobility Group Design for Multi-Controller Deployments.

Raising the minimum data rate to 24 Mbps reduces the effective coverage range of each AP because clients at the cell edge operating at low data rates are effectively excluded from the cell. This shrinks cell size, reducing channel overlap between neighboring APs on the same channel. Using directional antennas limits the coverage area of some APs by focusing RF energy in specific directions rather than radiating omnidirectionally, which directly reduces the lateral overlap between adjacent APs. Increasing AP transmit power (Option B) would worsen overlap, not reduce it. Allowing UNII-2e channels (Option C) provides more channel options but does not reduce the physical cell overlap — it only provides more channels to avoid co-channel interference. Power saving mode (Option E) is a client-side power management feature unrelated to AP cell sizing during a survey. Reference: WLSD Study Guide — Channel Overlap Mitigation, Data Rate Configuration, Directional Antenna Use Cases.

Cisco ' s mobility group architecture enables seamless client roaming between WLCs by establishing a trusted peer relationship and shared mobility domain. When two Cisco Catalyst 9800-80 WLCs are placed in the same mobility group, they establish CAPWAP mobility tunnels enabling both Layer 2 and Layer 3 roaming with session continuity including IP address preservation. Within the same mobility group, WLCs exchange client state information, allowing 802.11r Fast BSS Transition, 802.11k neighbor reports, and 802.11v BSS Transition Management to function across controller boundaries. No specific primary or secondary roles are assigned within a mobility group — all members are peers with equal standing for roaming purposes, which is precisely what Option D describes. Option A incorrectly implies a hierarchical structure that does not exist in mobility group peer relationships. Option B separating the WLCs into different groups would break inter-building roaming since clients would experience a full re-authentication cycle. Option C imposing an anchor relationship is appropriate only for guest WLANs. Reference: WLSD Study Guide — Mobility Group Architecture, Inter-Controller Roaming, 802.11r/k/v Fast Roaming Design.

When designing a wireless network to support diverse services — including data, voice, video, and location tracking — across a distributed enterprise with a main office and 10 branch locations, the two primary design factors directly shaping the RF and capacity architecture are the number of wireless devices requiring access and the type of site where the survey will be performed. The device count (Option B) drives AP density, channel reuse planning, capacity modeling, and controller licensing requirements. Each service type — particularly VoWLAN and video — imposes strict per-client throughput and latency constraints that must be multiplied across the concurrent device population. The type of site (Option C) determines the survey approach, attenuation characteristics, coverage requirements, and antenna selection. A warehouse, hospital, or open-plan office each demands a fundamentally different RF design. Options A and D are organizational considerations, not technical RF design inputs. Option E (power sockets) is an installation logistics concern, not a wireless design factor. Reference: WLSD Study Guide — Requirements Gathering, Site Survey Planning, Capacity and Coverage Design Methodology.

Cisco ' s Embedded Wireless Controller (EWC) architecture is the ideal solution for small deployments with strict budget constraints where only the access points can be replaced. EWC is a controller function that runs directly within the Cisco Catalyst 9100 Series access point itself — eliminating the need for a dedicated physical or virtual WLC appliance. The APs serve dual roles as both the wireless radio infrastructure and the controller platform. The unified model (Option B) requires a dedicated hardware WLC such as the 9800 series, exceeding the customer ' s budget. Fabric (Option C) requires Cisco DNA Center and SD-Access infrastructure, making it cost-prohibitive for a small deployment. Cloud (Option D) requires ongoing subscription fees that may not fit a fixed one-time budget. EWC provides enterprise-grade features including centralized SSID management, RRM, and client mobility within the AP cluster — all without additional controller hardware investment. This makes it the canonical solution for SMB migrations from autonomous deployments. Reference: WLSD Study Guide — Controller Deployment Models, Embedded Wireless Controller Architecture, SMB and Branch Wireless Design.

In a Cisco Catalyst 9800 SSO deployment using Link Aggregation Group (LAG) for network interface redundancy, the SSO pair — WLC1 (active) and WLC2 (standby) — must both have their physical interfaces connected to the network infrastructure as part of the LAG bundle. LAG on the 9800 in an SSO configuration is implemented as a multi-chassis LAG across both the active and standby controllers. This means both WLC1 and WLC2 contribute physical member links to the port channel, and the connected switches must have LACP or PAgP bundle members from both controllers in the same port channel group. When an SSO failover occurs — WLC1 fails and WLC2 takes over as active — the LAG remains operational because WLC2 ' s physical links are already established members of the bundle and continue forwarding traffic without any link renegotiation. If only WLC1 had LAG connectivity and WLC2 had independent links, an SSO failover would cause a LAG topology change requiring re-convergence, introducing downtime. WLC3 is a separate N+1 backup controller joined via a mobility tunnel — not part of the SSO pair and its LAG configuration is independent. Reference: WLSD Study Guide — Catalyst 9800 SSO with LAG, Multi-Chassis Link Aggregation, High Availability Network Redundancy Design.

In a mixed deployment where a Cisco Catalyst 9800 IOS XE WLC operating in SSO is required to establish a mobility peer relationship with a legacy AireOS WLC, the critical configuration requirement is that the 9800 SSO pair presents a single, consistent mobility MAC address to all peer WLCs. When the 9800 is in SSO mode, the active and standby controllers function as a single logical entity, but AireOS WLCs identify mobility peers by MAC address. If the MAC address changes during an SSO switchover, the AireOS peer will detect the change and tear down the mobility tunnel, disrupting inter-controller client roaming. The command ' wireless mobility mac-address < MAC > ' configures a static, persistent mobility MAC address on the 9800 SSO pair that remains constant regardless of which physical unit is active. This ensures the AireOS WLC always identifies the 9800 pair by the same MAC address, maintaining the mobility tunnel and enabling seamless client roaming. Option A configures the HA interface for SSO synchronization but not for AireOS mobility interoperability. Option B sets a default gateway. Option D enables management gateway failover, unrelated to mobility peer identification. Reference: WLSD Study Guide — IOS XE WLC SSO Configuration, AireOS to 9800 Migration, Mobility Peer MAC Address Management.