Cisco Administrative distance

What is an Administrative distance

The administrative distance (AD) value is assigned by the router on a per-protocol basis. Routers, by design, should not install multiple routes into the routing table as this has the potential to cause routing loops.

While a router may run multiple routing protocols on the same device, it is necessary for the router to implement a process to ensure that multiple routes, pointing to the same destination do not simultaneously exist in the routing table.

Each process running on a router advertises its administrative distance value to the local router. The router uses this value to determine which route should be used.

The following table illustrate the default administrative distances for the routing protocols used on Cisco devices: