Which routing protocol has the highest default administrative distance?

OMP (Overlay Management Protocol) has the highest default administrative distance of 250. This high value ensures that routes learned via OMP are generally preferred over routes learned from other routing protocols, as OMP is the control plane protocol responsible for advertising reachability information within the SD-WAN fabric. IS-IS has a default administrative distance of 115. IBGP (Internal Border Gateway Protocol) has a default administrative distance of 200. External EIGRP (Enhanced Interior Gateway Routing Protocol) has a default administrative distance of 170. These lower values mean they would be preferred over OMP if a route to the same destination was learned via multiple protocols, which is not the desired behavior in an SD-WAN overlay.