Administrative distance
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 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 | 115 |
| RIP | 120 |
| EGP | 140 |
| ODR | 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.
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