What is administrative distance?
Administrative distance (AD) is an integer from 0 to 255 that rates the trustworthiness of routing information received on a router from a neighboring router. The AD is used as the tiebreaker when a router has multiple paths from different routing protocols to the same destination. The path with the lower AD is the one given priority.
What are the three classes of routing protocols?
- Distance vector
- Balanced hybrid
What is the AD for each of the following?
- Directly connected interface 0
- Static route 1
- EIGRP 90
- IGRP 100
- OSPF 110
- RIP 120
- External EIGRP 170
- Unknown 255
How do distance vector routing protocols function?
Also known as Bellman-Ford-Fulkerson algorithms, distance vector routing protocols pass complete routing tables to neighboring routers. Neighboring routers then combine the received routing table with their own routing table. Each router receives a routing table from its directly connected neighbor. Distance vector routing tables include information about the total cost and the logical address of the first router on the path to each network they know about.
How do distance vector routing protocols keep track of any changes to the internetwork?
Distance vector routing protocols keep track of an internetwork by periodically broadcasting updates out all active interfaces. This broadcast contains the entire routing table. This method is often called routing by rumor. Slow convergence of distance vector routing protocols can cause inconsistent routing tables and routing loops.