Administrative distance (AD) influences the decision on which routing protocol the router should trust:
- AD can be modified.
- AD is only locally significant to the router, other router’s AD of routing protocol might be modified.
- Router will use the routing protocol that has the lowest AD to make routing decision.
Default Administrative distance of various routing protocols:
Directly connected = 0
Static route = 1
EIGRP summary = 5
External BGP (eBGP) = 20
EIGRP = 90
IGRP = 100 (Still exists?)
OSPF = 110
IS-IS = 115
RIP = 120
On Demand Routing (ODR) = 160
External EIGRP = 170
Internal BGP (iBGP) = 200
Unknown = 255
cyruslab 