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.
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. The smaller the administrative distance value, the more reliable the protocol. This means the IGRP version of the route would be added to the routing table. The table below lists the administrative distance default values of the protocols that Cisco supports.