December 1999
NI222 : NETWORKS AND THE INTERNET

QUESTION 4

Total Marks: 15 Marks

• Question 1
• Question 2
• Question 3
• Question 5
• Cover Page

SUGGESTED SOLUTIONS
Solutions and allocated marks are indicated in green.
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What are the two primary services provided by the Internet protocol?

Internet Protocol is responsible for providing addressing (1)and routing (1).

Distinguish between the Bellman Ford routing algorithm and Dijkstra ’s routing algorithm.Of what sort of routing algorithm are they both examples?

Bellman Ford:Uses static and decentralised routing strategy.(1)Searches forward
from the source for the shortest path to a destination (1).
Dijkstra’s:Uses static and centralised routing strategy (1).Searches backward from the destination for the shortest path to a source (1).
plus:
They are both shortest-path algorithms (1).

Explain how flooding routing technique works.What is meant by selective .ooding?In general under what circumstances is this technique useful?

Router forwards packets to all ports except the incoming port (1)by generating large number of duplicate packets (1).
Selective flooding only forwards packets in the ‘right direction ’rather than to all neighbours (1).
Useful in military applications,where large number of nodes can get destroyed at any time (1)OR useful in any application where robustness is important (1).

IP addresses are divided into class A,B,and C types of addresses:

(i)What class of IP address do you suggest for a LAN with less than 250 computers connected together and why?[2 marks ]

Class C (1),because host address has a total of 8 bits, hence =256 which is sufficient to support 250 computers (1).

(ii)How do you identify a class B IP address?[1 mark ]

Class B IP address always has the first two bits set to ‘10 ’.

(iii)In the class AIP address 125.100.10.1,identify the network part and host part of the address.Explain your answer.[2 marks ]

Network part of the address is allocated 1 byte,hence network address is 125 (1). Host part of the address is also allocated 3 bytes,hence host address is 100.10.1 (1).
No mark for answer without suitable explanation.Other valid explanations are acceptable.