Administrative Distance (abbreviation for AD) is a value that routers/Layer 3 switches use in order to select the best path when there are more than 1 routes to the same destination from two different routing protocols.Administrative Distance (AD) is a numeric value which can range from 0 to 255 and is referred as standard for route preference across vendors.
Below table gives the default Administrative Distance for all the Routing protocols –
|Static Route out an interface||0||S|
|Static Route to Next-Hop IP||1||S|
|EIGRP Summary route||5||D|
|RIP v1 & v2||120||R|
|Exterior Gateway Protocol (EGP)||140||E|
|External EIGRP||170||D EX|