Routing protocols (including static routing) may discover different routes to the same destination, but not all routes are optimal. Only one routing protocol at a time determines the optimal route to a destination. To select the optimal route, each routing protocol (including static routing) is assigned a preference (a smaller value indicates a higher preference). When multiple routing information sources coexist, the route discovered by the routing protocol with the highest preference is selected as the optimal route and added to the local routing table.
Routers define external preference and internal preference. External preference is manually configured for each routing protocol, lists the default external preferences of routing protocols.
