The Cisco SD-Access fabric data plane leverages VXLAN-style MAC-in-IP encapsulation to transport endpoint traffic across the Layer 3 fabric. In SD-Access, the underlay provides IP reachability between fabric nodes, while the overlay uses encapsulation to carry user traffic and policy context across that underlay. Cisco fabric edge nodes encapsulate traffic before forwarding it through intermediate nodes and decapsulate it when it reaches the destination edge or border. LISP is used by the control plane to resolve endpoint-to-location mappings, so option A describes the mapping function rather than the data plane. IS-IS provides underlay routing reachability and is not the overlay data-plane mechanism. BGP can be used outside the fabric or in other overlay designs, but it is not the SD-Access fabric data plane. The exam option describes the essential encapsulation function, even though VXLAN is technically MAC-in-UDP over IP. Reference topics: SD- Access data plane, VXLAN encapsulation, fabric edge forwarding, underlay and overlay separation, policy transport.