1. (6 marks) Distance Vector protocol's convergence around routing failures

tends to be slow. During the course of time, several modifications were made

to the protocol to address this issue. Identify and briefly explain 3 such

modifications which aim to improve the convergence property of this class of

protocols. [250-300 words]

2. (6 marks) The flooding mechanism in OSPF is considered to be reliable enough

to withstand errors such as link and router failures. Give and explain two

reasons why it is so. [250-300 words]

3. (5 marks) Does the aging mechanism used in the OSPF protocol require the

use of clocks that are synchronized? Explain why or why not with suitable

examples. [250-300 words]

4. (4 marks) Summarize the following range of IP addresses given below.

(Starting with X.Y.96.0 and ending with X.Y.159.0). Explain clearly how you

arrive at the solution showing all relevant steps.

194.1.96.0/24

194.1.97.0/24

194.1.98.0/24 : :

: :

194.1.126.0/24

194.1.127.0/24

194.1.128.0/24

: :

: :

194.1.158.0/24

194.1.159.0/24

5. (9 marks) Consider the Backbone network topology shown in figure 1 below

consisting of a backbone and an aggregation layer. The backbone layer forms

an Autonomous System (AS) - AS1000 and the aggregation layer forms an

Autonomous System - AS2000. The two ASes communicate with each other

using BGP (external BGP) routes. The IGP protocol deployed within the two

ASs is OSPF. Explain how the following requirements can be met:

o (3 marks) Devices on the aggregation layer are not expected to know

internal route details of the backbone layer.

Low end performance devices reside in the aggregation layer and

consequently these devices are not expected to process a large

number of BGP routes emanating from the backbone layer. [50-

100 words]

o (3 marks) High-End performance devices reside in the backbone and

are expected to know and process internal route details of the

aggregation layer. [50-100 words]

o (3 marks) There must be a provision to install appropriate route

backups between the two ASes to improve reliability. [50-100 words]

Figure 1: BGP between Backbone and Aggregation Layers. 6. (10 marks) Consider the Network topology shown in figure 2 below. The

topology consists of 4 autonomous systems AS10, AS20, AS30 and AS40.

AS10 internally uses an IBGP route reflection topology which consists of two

clusters 1 and 2. Cluster 1 has one route reflector (RR1) with two clients (C1

and C2) whereas cluster 2 contains one Route Reflector (RR2) with one client

(C3). AS10 peers with AS20 and AS30 via C1, C2 and C3 as shown in the

figure. A target network N (which resides in AS40) is being advertised to AS10

by both AS20 and AS30.

Table 1 given below depicts the route attributes of network N as seen by

routers C1, C2 and C3 when they initially receive the route for N. In figure 2

below, the MED values for routes over the inter-AS links are shown in bold

text, and the link costs for various internal links in AS10 are shown next to

the figure. In this situation, explain using an example, why the two RRs will

keep exchanging routes indefinitely, instead of settling on a stable

configuration to start with. [300-400 words]