OSPF

Question 1

Suppose a company was using the RIP dynamic routing protocol on its routers. What reasons would you gvie to persuade them to change to OSPF instead? In this context explain the difference between the Distance Vector and Link State Routing

Answer 1

RIP has slow convergence. If a node in a network goes down it will route packets poorly until its algorithm has reconverged.

Distance Vector Routing does not take line bandwidth into account.

This is due to Distance Vector Routing. Each node only knows about its immediate neighbours.

With Link state routing each node has a map of the entire topology and each node can recalculate the map if there are any changes.

Question 2

Describe the format of an OSPF Link State Anouncement.

Answer 2

Split into a Header and body
Header:
Link Age
Link Type
Link State ID
Advertising Router
Sequence 
Checksum 
Length

Body depends on Link Type

Question 3

Explain how a Link state announcement would be disseminated throughout the network.

Answer 3

LSA Updates are distributed to all other routers using relaible flooding.

The router floods an LSA Update if there are topology or link cost changes. (Won’t flood if it receives no new information in an Update)

Also floods every 30 minutes

Question 4

What is an Autonomous System?

Answer 4

An Autonomous system is a region of the internet adminsiterd by a single entity.

Question 5

Type of routing within an Autonomous system?

Between ASs?

Answer 5

Intra-domain routing

Inter-domain routing

Question 6

What is a gateway in terms of Border Gateway Protocol?

Answer 6

It is just an IP router that connects ASs.