The border node is part of the Cisco SD-Access overlay architecture. In the SD-Access fabric, the overlay consists of fabric roles and services that provide endpoint connectivity, segmentation, policy, and external reachability over the routed underlay. Border nodes connect the fabric overlay to external Layer 3 networks, shared services, WAN, Internet, or other fabric/transit domains. They perform the fabric boundary function, including routing between virtual networks and external routing domains as designed. Spine and leaf are generic data center or fabric topology terms and are not the named SD-Access fabric overlay roles in this question. Cisco DNA Center, now Cisco Catalyst Center, is central to management, automation, assurance, and policy deployment, but it is not itself an overlay forwarding component. The forwarding overlay is built from roles such as edge, border, control-plane, and intermediate nodes. Therefore, the correct component from the options is the border node. The design should select border placement based on external connectivity, scale, route control, redundancy, and whether the border is internal, external, or anywhere border. Reference topics: SD-Access overlay, border node, fabric roles, external connectivity, virtual networks.
