Which Cisco WLC feature allows a wireless device to perform a Layer 3 roam between two separate controllers without changing the client IP address?

A mobility tunnel is established between the anchor (original) WLC and the foreign (new) WLC when a client performs a Layer 3 roam, allowing the anchor WLC to tunnel the client's traffic to the foreign WLC, thus maintaining the client's IP address and connectivity.

Mobile IP is a separate networking standard for host mobility that is not the primary mechanism Cisco WLCs use for Layer 3 roaming.

LWAPP (Lightweight Access Point Protocol) is a protocol used for communication between WLCs and lightweight access points, not for client Layer 3 roaming between controllers.

GRE (Generic Routing Encapsulation) is a general tunneling protocol; while mobility tunnels may utilize GRE, 'mobility tunnel' refers to the specific WLC feature that implements this functionality for client roaming.