Different routing protocols including the static routing may learn different routes to the same destination, but not all these routes are optimal. At a certain moment, only one routing protocol determines the current route to a certain destination. Therefore, each of these routing protocols including the static routing has a preference. When multiple routing information sources are available, the route learned by the routing protocol with the highest preference is used. The smaller the default value, the higher the preference, as shown in Table 1. Table 1 Preferences of routing protocols Routing Protocol or Route Type Route Preference DIRECT 0 OSPF 10 IS-IS 15 STATIC 60 RIP 100 OSPF ASE 150 OSPF NSSA 150 IBGP 255 EBGP 255 UNKNOWN 256 0 indicates a direct route and 255 indicates a route learned from an unreliable source.