Administrative distance is the measure used by Cisco 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. A lower numerical value is preferred, e.g. an OSPF route with an administrative distance of 110 will be chosen over a RIP route with an administrative distance of 120.

The following tables gives the default administrative distances used by Cisco

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 routers.

Protocol	Administrative distance
Directly connected route	0
Static route out an interface	1°
Static route to next-hop address	1
EIGRP summary route	5
External BGP	20
Internal EIGRP	90
IGRP	100
OSPF	110
IS-IS IS-IS Intermediate System To Intermediate System , is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices....	115
RIP Routing Information Protocol The Routing Information Protocol is a distance-vector routing protocol, which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a destination. The maximum number of hops allowed for RIP is 15....	120
EGP Exterior Gateway Protocol The Exterior Gateway Protocol is a now obsolete routing protocol for the Internet originally specified in 1982 by Eric C. Rosen of Bolt, Beranek and Newman, and David L. Mills. It was first described in RFC 827 and formally specified in RFC 904...	140
ODR On Demand Routing On-Demand Routing is an enhancement to Cisco Discovery Protocol , a protocol used to discover other Cisco devices on either broadcast or non-broadcast media....	160
External EIGRP	170
Internal BGP	200
DHCP-learned	254
Unknown	255

Notes:

• An administrative distance of 255 will cause the router to disbelieve the route entirely and not use it.
• Since IOS 12.2, the administrative distance of a static route with an exit interface is 1. Prior to the release of 12.2 it was in fact 0.

° Actual administrative distance is recognized somewhere between 0 and 1. This AD is more trustworthy than 1 but less trustworthy than 0.

External links

• Cisco - What is Administrative Distance? [Ref. Mr. Praveen Suvarna Mundkur]