Cisco Routers use administrative distance when using more than one routing protocol. This topic describes the concept and use of administrative distance in terms of routing protocols.
| Route Sourece | Default Distance |
| Connected Interface | 0 |
| Static Route | 1 |
| EIGRP summary route | 5 |
| External BGP | 20 |
| Internal EIGRP | 90 |
| IGRP | 100 |
| OSPF | 110 |
| IS-IS | 115 |
| RIPv1, RIPv2 | 120 |
| External EIGRP | 170 |
| Internal BGP | 200 |
| Unknown | 225 |
Most routing protocols have metric structures and algorithms that are not compatible with other protocols. It is critical for a network using multiple routing protocols to have the seamless exchange of route information and the ability to select the best path across multiple protocols. Cisco routers use a value called administrative distance to select the best path when they learn two or more routers to the same distination from different routing protocols.
Administrative distance rates the believability of a routing protocols. Cisco has assigned a default administrative distance value to each routing protocols supported on its routers. Each routing protocol is prioritized in the order of most-to-least believable. Some examples of prioritization are as follows:
In the figure, the table lists the default administrative distance of the protocols supported by Cisco routers. It is a vale between 0 and 255. The lower the administrative distance value, the higher the reliablility of the protocol.