Understanding Administrative Distance in Networking: A Guide for Routing Protocol Trustworthiness

Administrative Distance

Administrative distance is a term used in networking to determine the trustworthiness of routing information received from different routing protocols.

It is essentially a numerical value assigned to a routing protocol or a particular route within a protocol.

The administrative distance is used by routers to select the best route among multiple available routes for a destination network. A lower administrative distance indicates a more preferred or trustworthy route.

Here are some common default administrative distances for popular routing protocols:

– Directly connected network: 0
– Static route: 1
– Enhanced Interior Gateway Routing Protocol (EIGRP): 90
– Open Shortest Path First (OSPF): 110
– Interior Gateway Routing Protocol (IGRP): 100
– Border Gateway Protocol (BGP): 20
– Routing Information Protocol (RIP): 120

In general, if a router receives multiple routes to the same destination network from different protocols, it will select the route with the lowest administrative distance to use for forwarding traffic. If two routes have the same administrative distance, other metrics like the next-hop IP address or metric value may be used to determine the best route.

Keep in mind that the administrative distance is a local setting and may vary from one router to another. Network administrators have the ability to manually adjust the administrative distance to influence routing decisions based on their requirements and network topology.

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