Pre-Order Your Designing Cisco Enterprise Wireless Networks 300-110

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.

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.