Administrative Distance

Administrative Distance, also seen as route preference and believability is a number that is assigned to dynamic routes, static routes, and directly-connected routes. The lower the number the more preferred the route is.

What if you had you had two different routing protocols on the same device (Also known as “ships-in-the-night”) and a learned route from both routing protocols?. That’s where administrative distance comes into play. The lower the administrative distance the more believability/trustworthy the route is.

Vendors will typically design their routers to assign a default administrative distance for each type of route source. Since we are talking Cisco here, below is table of Cisco’s default administrative distances. These values are not an industry standard.

Cisco ’s Administrative Distance Default Values

*When a static route refers to an interface instead of a next hop address, the destination is considered to be a directly connected network.

**If the administrative distance is 255, the router does not believe the source of that route and does not install the route in the routing table.