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What Is Administrative Distance?

Administrative distance is the feature used by routers to select the best path when there are two or more different routes to the same destination from two different routing protocols. Administrative distance defines the reliability of a routing protocol. Each routing protocol is prioritized in order of most to least reliable (believable) using an administrative distance value. | Cisco - What Is Administrative Distance Solutions U Prộtlu t Support T Partners T Training T CprporatB Tech Notes What Is Administrative Distance Introduction Most routing protocols have metric structures and algorithms that are not compatible with other protocols. In a network where multiple routing protocols are present the exchange of route information and the capability to select the best path across the multiple protocols are critical. Administrative distance is the feature used by routers to select the best path when there are two or more different routes to the same destination from two different routing protocols. Administrative distance defines the reliability of a routing protocol. Each routing protocol is prioritized in order of most to least reliable believable using an administrative distance value. Selecting the Best Path Administrative distance is the first criterion that a router uses to determine which routing protocol to use if two protocols provide route information for the same destination. Keep in mind that administrative distance has only local significance that is it is not advertised in routing updates. Note The smaller the administrative distance value the more reliable the protocol. For example if a router receives a route to a certain network from both Open Shortest Path First OSPF default administrative distance - 110 and Interior Gateway Routing Protocol IGRP default administrative distance - 100 the router will choose IGRP because it is more reliable. This means the IGRP version of the route would be added to the routing table. If you lose the source of the IGRP-derived information for example because of a power shutdown the software uses the OSPF-derived information until the IGRP-derived information reappears. The table below lists the administrative distance default values of the protocols that Cisco supports. Route Source Default Distance Values Connected interface 0 http www.cisco.com warp public 105 admin_distance.html 1 of 3 5 6