L5 - Hierarchical Routing

Question 1

What are the 2 incorrect assumptions we make in Link State and Distance Vector internet routing algorithms?

Answer 1

The internet is flat -> Contrary, consist of nested networks with local authorities.

Routers are identical

Question 2

How do we overcome our assumption that the earth is flat and routers are identical?

Answer 2

Aggregate routers into clusters (Autonomous Systems). For example, uni of Exeter is an AS, Routers in Exeter is an encapsulating AS etc.

Question 3

What is the different between Intra and Inter Autonomous Systems Routing Protocol?

Answer 3

Intra-AS Routing Protocol is used when routers in the cluster follow the same protocol. I.e they all trust each other.

Inter-AS Routing Protocol is used when the gateway routers run both intra and inter-AS routing protocols.

Question 4

What are the policies for Intra-AS Routing Protocol?

Answer 4

Autonomous Group has a single admin, all routers trust each other thus no policy is needed. For example, all routers in the Uni of Exeter.

Question 5

What are the policies for Inter-AS Routing Protocol?

Answer 5

An admin control who routes through the network and how they do it.

Question 6

What are the advantages of using Autonomous Systems?

Answer 6

Smaller routing table size, reduced traffic.

Question 7

What does Intra-AS Routing Protocol focus on?

Answer 7

Performance of the Autonomous System

Question 8

What does Inter-AS Routing Protocol focus on?

Answer 8

The routing policy of the Autonomous System.

Question 9

Which 2 intra-AS routing protocols use Dijkstra’s algorithm?

Answer 9

1. Open Shortest Path First
2. Routing Information Protocol

Question 10

What inter-AS routing protocol uses Dijkstra’s algorithm?

Answer 10

Broader Gateway Protocol.

Question 11

Explain the Routing Information Protocol…

Answer 11

Is a distance vector algorithm, and hops from the source to the destination subnet are counted. DV’s are exchanged with neighbours every 30 second.