Configuring a high availability SSO pair on Cisco Catalyst 9800 IOS XE WLCs has specific technical prerequisites that must be satisfied for the SSO relationship to form and function correctly. The two critical requirements are: each WLC must have a unique Redundancy Management Interface (RMI) IP address (Option B), and both WLCs must run identical IOS XE software versions (Option D). The Redundancy Management Interface is the dedicated in-band control channel over which the active and standby WLCs exchange state synchronization information, keepalive messages, and configuration updates. Each controller requires its own unique RMI IP address within the same subnet — the active uses one address and the standby uses another. If they shared the same RMI IP (Option C), there would be an IP address conflict preventing the interface from functioning. Identical software versions (Option D) are mandatory because the SSO state synchronization protocol and data structures must be version-compatible between the active and standby controllers. Any mismatch in IOS XE version will prevent SSO formation. License count (Option A) does not need to be identical for SSO. Service port IP addresses (Option E) must be unique per controller, not identical. Reference: WLSD Study Guide — Catalyst 9800 SSO Prerequisites, Redundancy Management Interface Configuration, High Availability Pair Formation Requirements.