A campus adds SD-WAN with OSPF on the service side and OMP in the overlay. LAN subnets must be advertised into the fabric, remote site prefixes must be injected back to OSPF, and transport interfaces must stay isolated from service routes. Which underlay and overlay interaction should the engineer configure to achieve correct routing exchange?

The correct interaction requires mutual redistribution at the WAN Edge where service-side OSPF meets the overlay, with OSPF into OMP advertising campus LAN subnets as OMP routes and OMP into OSPF injecting remote-site prefixes back into OSPF, while service VPNs remain separate from transport VPN 0 to preserve segmentation and policy control. The default-only approach fails by concept because originating only a default into OSPF provides reachability but does not inject specific remote prefixes as required, limiting optimal path selection, visibility, and troubleshooting. The controller-based approach fails by concept because the SD-WAN Controller (formerly vSmart) handles OMP control plane and policy distribution but has no OSPF adjacency or service forwarding instance, so redistribution can only occur on the Edge where both protocols coexist. The merged-VPN approach fails by concept because performing redistribution inside VPN 0 places service prefixes with TLOCs and underlay next hops, breaking transport isolation and risking leaks and unintended recursion. Exam caveat is to distinguish full mutual redistribution from default-originate shortcuts and to associate VPN 0 strictly with transport, never service OSPF. Practical check is to verify LAN routes in the OMP table on a remote Edge, verify remote prefixes in the OSPF LSDB and IP routing table locally, and confirm show commands place service interfaces in service VPNs and transport links only in VPN 0.