Which routing protocol has the highest default administrative distance?

IS-IS has a default administrative distance of 115, which is lower than OMP's 250.

The Overlay Management Protocol (OMP) in Cisco SD-WAN has a default administrative distance of 250. This high value ensures that routes learned via OMP are less preferred than routes learned from other protocols like OSPF, BGP, or EIGRP, allowing the underlay network's routing to take precedence for forwarding decisions when overlaps occur.

Internal BGP (iBGP) has a default administrative distance of 200, which is lower than OMP's 250.

External EIGRP has a default administrative distance of 170, which is lower than OMP's 250.