In Cisco SD-Access, which protocol provides the data-plane encapsulation between fabric nodes?

VXLAN (Virtual Extensible LAN) is the correct answer because it is the fundamental data-plane encapsulation protocol used in Cisco SD-Access. It extends Layer 2 segments over a Layer 3 underlay network, allowing for scalable and flexible network virtualization. VXLAN encapsulates original Ethernet frames within UDP packets, adding a VXLAN header that includes a Virtual Network Identifier (VNI) to differentiate virtual networks. This enables the creation of multiple independent virtual networks over a shared physical infrastructure. IS-IS and OSPF are routing protocols used in the underlay network to establish reachability between fabric nodes, not for data-plane encapsulation. LISP (Locator/ID Separation Protocol) is used in SD-Access for control-plane functions, specifically for endpoint identity and location mapping, not for encapsulating data traffic itself.