Without centralized policy, OMP allows all WAN Edge routers in the same VPN to communicate in a full- mesh overlay. Cisco Catalyst SD-WAN uses OMP as the control-plane protocol between WAN Edge routers and SD-WAN controllers. WAN Edge devices advertise OMP routes, TLOC routes, and service routes to the controllers, and the controllers distribute the reachable routes back to the relevant edge devices. Cisco policy documentation describes the default unpolicied behavior as permissive: routes are accepted and advertised so sites in the same VPN learn reachability to each other. That default route distribution produces a full-mesh data-plane capability, even though control connections remain hubbed through the controllers. Hub-and- spoke, regional isolation, point-to-point restriction, or service-chained topologies require centralized control or data policy to filter routes or steer traffic. Blocking all communication is the opposite of the default behavior. Reference topics: Cisco SD-WAN OMP, default route distribution, full-mesh overlay, centralized control policy, VPN segmentation.