Administrative distance
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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. 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 | 0 |
| Static route | 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 |
| Unknown | 255 |
Notes:
- A static route with a next-hop gateway will have an admin distance of 1, a route with a directly connected interface will had a distance of 0.
- An administrative disance of 255 will cause the router to disbelieve the route entirely, and not use it.
