Stories about IP packets traveling the world (or just another Cisco blog…)
In Cisco IOS, Administrative Distance (AD) is used to determine the reliability of a routing protocol.
AD is a value between 0 and 255 and a lower value is preferred. The value 255 is considered as untrusted and a route with this value will not be placed into the routing table.
|Route Source||Default Distance Values|
|Exterior Gateway Protocol (EGP)||140|
|On-Demand routing (ODR)||160|
R1#show ip route Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP + - replicated route, % - next hop override Gateway of last resort is 192.168.128.1 to network 0.0.0.0 S* 0.0.0.0/0 [1/0] via 192.168.128.1 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks C 10.1.0.0/16 is directly connected, Vlan5 L 10.1.0.250/32 is directly connected, Vlan5 O 192.168.4.0/23 [110/2] via 192.168.128.252, 1w3d, Vlan128
Static route, AD = 1 :
R1#show ip route 0.0.0.0 Routing entry for 0.0.0.0/0, supernet Known via "static", distance 1, metric 0, candidate default path Routing Descriptor Blocks: * 192.168.128.1 Route metric is 0, traffic share count is 1
Connected interface, AD = 0 :
R1#show ip route 10.1.0.0 Routing entry for 10.1.0.0/16 Known via "connected", distance 0, metric 0 (connected, via interface) Routing Descriptor Blocks: * directly connected, via Vlan5 Route metric is 0, traffic share count is 1
OSPF route, AD = 110 :
R1#show ip route 192.168.4.0 Routing entry for 192.168.4.0/23, supernet Known via "ospf 1", distance 110, metric 2, type intra area Last update from 192.168.128.252 on Vlan128, 1w3d ago Routing Descriptor Blocks: * 192.168.128.252, from 192.168.128.252, 1w3d ago, via Vlan128 Route metric is 2, traffic share count is 1
Study notes of a swiss network engineer currently in the CCNP certification track