As mentioned before, the Administrative Distance (AD) is the belief or trustworthiness of the route being advertised. The lower the AD, the more you can trust that route to be the best path to take; in the 0-255 range, 0 is the best and 255 cannot trusted at all. Routers will always choose the network with the lowest AD, but if a router receives the same route from two different locations and has the same AD, then it will use the metric, cost, or hop count to decide which would be the better route. It will always be the smallest number that would win.
Each routing protocol has an algorithm to calculate the best route to a network, and we will get into that later in the book. The following table gives the default AD to static and dynamic routes:
|
Route source |
Administrative distance |
|
Connected Interface |
0 |
|
Static route |
0 or 1 |
|
RIP |
120... |
