Refer to the exhibit.

The design is an IPv6 overlay carried across an existing underlay, so the correct advantages are that multiple independent logical networks can run over a shared underlay and that unsupported protocols can be transported across that underlay. Cisco describes overlay tunnels as encapsulating one protocol inside another so traffic can cross infrastructure that does not natively support the passenger protocol. For an IPv6 migration, this permits IPv6 connectivity across an IPv4-only transport while the intermediate network remains unchanged. The same overlay concept also allows separate logical networks to be created over common physical transport, which is a fundamental design principle in SD-Access, SD-WAN, GRE, and other overlay technologies. The design does not eliminate fate-sharing; if the underlay fails, the overlay fails. It also does not reduce forwarding overhead, because encapsulation adds header bytes and may affect MTU. The number of devices joining the overlay still depends on addressing, routing, tunnel scale, and control-plane design. Reference topics: IPv6 overlay tunneling, shared underlay, encapsulation overhead, protocol transport, migration design.