Which consideration applies when designing the Cisco SD-Access underlay network?

The underlay network in Cisco SD-Access is the physical network infrastructure that provides IP connectivity between network devices. Therefore, the underlay switches are responsible for the physical connection of end-user devices to the network. While the underlay can support IPv4 and IPv6, it's not a strict requirement for both to be present simultaneously; many deployments are IPv4-only. End-user subnets and endpoints are part of the overlay network, which is built on top of the underlay using VXLAN. Static routing is not a requirement; dynamic routing protocols like OSPF or IS-IS are commonly used for scalability and resilience in the underlay.