The requirement for users to retain their session state 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 a mobility tunnel between WLC-A and WLC-B with both controllers configured in the same mobility group name — the group name is the trust identifier that permits the mobility tunnel and anchor-foreign relationship to form. Without the same group name, the controllers will not form a trusted mobility peer relationship. AP groups (Option C) control SSID and VLAN assignments per AP cluster but have no impact on inter-controller roaming. HA cluster configuration (Option B) creates SSO redundancy, not roaming capability between separate N+1 controllers. Redundancy port connection (Option D) is used for SSO keepalive and state sync, not mobility tunneling. Reference: WLSD Study Guide — Inter-Controller Mobility, Mobility Tunnels, Layer 3 Roaming and IP Address Preservation.