Which feature enables Layer 2 client roaming across wireless controllers?

Mobility groups enable Layer 2 client roaming across wireless controllers by allowing controllers to share client context and coordinate handoffs. When a client roams from an access point (AP) associated with one controller to an AP associated with another controller within the same mobility group, the client's IP address and session are maintained, preventing reauthentication and re-IP addressing. N+1 high availability is a redundancy model for controllers, not a roaming mechanism. RF grouping is used for radio resource management and interference mitigation, not client roaming. SSO (Single Sign-On) is an authentication mechanism, not a feature for Layer 2 roaming across controllers.