Administrative Distance

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Summary

Administrative distance (AD) or route preference[1] is a number of arbitrary unit assigned to dynamic routes, static routes and directly-connected routes.

Highlights

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. ([View Highlight] (https://read.readwise.io/read/01jbfygbjxsbvvwrxc6662sf35))

The administrative distance (AD) value is assigned by the router on a per-protocol basis. Routers, by design, should not install multiple routes into the routing table as this has the potential to cause routing loops. ([View Highlight] (https://read.readwise.io/read/01jbfygff4337fx1091f7qnqpy))