routing preference

Administrative distance (AD) or route preference is a number of arbitrary unit assigned to dynamic routes, static routes and directly connected routes. The value is used in routers to rank routes from most preferred (low AD value) to least preferred (high AD value). When multiple paths to the same destination are available in its routing table, the router uses the route with the lowest administrative distance.
Router vendors typically design their routers to assign a default administrative distance to each kind of route. For example, on Cisco routers, routes issued by the Open Shortest Path First routing protocol have a lower default administrative distance than routes issued by the Routing Information Protocol. This is because, by default on Cisco routers, OSPF has a default administrative distance of 110 and RIP has a default administrative distance of 120. Administrative distance values can, however, usually be adjusted manually by a network administrator.

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