What is Administrative Distance?

This covers administrative distance in terms of routing within computer networking.

THE NEED FOR ADMINISTRATIVE DISTANCE

When routing, there may be lots of possible best routes. Say you you were going to Network B, OSPF will determine the best route to there, EIGRP will determine a best route as well, IS-IS would too and maybe you have a static route to Network B. There's 4 different best paths to Network B but which one will be put into the routing table as the main route? This is what administrative distance handles.

Administrative Distance gives each routing method a score, this score rates how reliable and trustworth the route is. The lower the score the better. So if there's two routes to a network, one from OSPF and one from a static route, then the administrative distance score will be used to decide which route to use.

The list below shows the administrative distance scores for different routing protocols and methods of routing traffic. So in the case of OSPF vs a static route, the static route is trusted more and will be used over OSPF.

Route Protcol / Source	Administrative Distance Score
Connected Devices	0
Static Routes	1
EIGRP Summary Route	5
External BGP	20
EIGRP	90
OSPF	110
IS-IS	115
RIP	120
External EIGRP	170
Internal BGP	200