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00331 .

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Sri Lanka Institute of Information Technology

B. Sc. Special Honours Degreein Information Technology

[CSN / IT]

Final ExaminationYear 2, Semester 1 (2010)

Data Communications & Computer Networks II(206)

I Duration: 3 HoursFriday, 30th April 2010

(Time: 2.00 p. m. - 5.00 p.m.)

Instructions to Candidates:• This paper has 5 Questions.• This paper contains 5 pages and cover page.• Some useful commands are given at the end of the paper.

Final Examination - 20 I0Data Communication & Computer Networks II - 1" Semester

00331 ..

Question 1) is based on Transmission Control Protocol.

1. Following is a dump of a TCP header in the hexadecimal format.

(24 marks)

0644 0017 0000 0025 0000 0012 5012 0400 0000 0000

Source Port Number (16 Bits) Destination Port Number (16 Bits)

Sequence Number (32 Bits)

Acknowledgement Number (32 Bits)

Header U A P R S FReserved

Length R C S S Y I Window Size (16 Bits)Bits (6)

(4 bits) G K H T N N

Checksum (16 Bits) Urgent Pointer (16 Bits)

Options & Paddings

Data

FIgure J

Answer the following questions. (Mention the base, if it is not in decimal. Ex: Hex or bin)

a. Write the source port number.

b. Write the sequence number.

(J mark)

(1 mark)

c. Write the window size and briefly explain the information given by this value.

(3 marks)

d. What can you say about this TCP segment by observing the values of six

different Control fields (flags)? (2 marks)

e. What is the size (in bytes) of this TCP header? (2 marks)

2. Briefly explain any two of the following Control fields (flags) if it is set to 1.

(Ex. URG flag = 1) (4 marks)

1. URG

11. PSH

111. RST

3. Write three timers used in TCP and briefly explain any two of them. (5 marks)

4. Draw the TCP connection establishment process (3-way-handshake in a timing

diagram) and write the TCP client states and TCP server states. Assume initially TCP

client is in CLOSED state and TCP server is in LISTEN state. (6 marks)

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00331

Final Examination - 20 I0Data Communication & Computer Networks II- ]'1 Semester

Question 2) is based on addressing and routing configuration with Cisco routers. (22 marks)

1. What are the four types of memories used in a router? (4 marks)

2. Consider the following network diagram and write the commands / configurations to

the following questions. You need to mention the router prompt. (Rl, R2 - routers,

SW1, SW2 - switches, A to R - computers).

LAN 1 (192.168.10.0/24) LAN 2 (172.17.0.0/16)

192.168.10.6 172.17.0.6

n/w 10.1.0.0 /16

172.17.0.5 172.17.0.7192.168.10.5 192.168.10.7

Figure 2

a. From user mode of R2, entry to the privilege mode of R2. (1 mark)

b. Entry to the configuration mode of R2 (1 mark)

c. Change the hostname ofR2 to 'SALES'. (2 marks)

d. Configure privilege level password for R2. (2 marks)

e. Configure a suitable IP address to the 'serial 0' interface and configure the

clock rate as 64000 to the same interface in R2. (4 marks)

f. Assume that 'Ethernet 0' interface is already configured. Configure dynamic

routing in R2. Use IGRP as the routing protocol. (4 marks)

g. What is the command to verify the configuration you did? (2 marks)

h. Save the configuration to the NVRAM. (2 marks)

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Final Examination - 2010Data Communication & Computer Networks II - I" Semester

00331

Question 3) is based on Switching, Virtual LAN and Spanning Tree Protocol. (20 marks)1. Write three types of internal switching paths and mention which is the most efficient

method. (2 marks)

2. List two advantages of creating VLANs. (2 marks)

3. List two protocols used in VLAN. (1 mark)

4. Why do we need to have redundant links from one LAN segment to the other? What

sort of problems will occur with the redundant links? (2 marks)

5. The following diagram shows a switched network. Bridge IDs of each switch and the

path costs are given in the diagram. Draw this diagram in your answer booklet.

Segme t 1Segment 2 Segment 4

n2 2

19 19 IC: 100 I

I IH A: 300I

I2 4

I I19 I 0: 600 I

2

Segment 3Segment 5

4 2I II B: 500 I 4 2

! E: 400 I I F: 200 I19

419

Figure 3 Segment 6

a) Mark the Root Bridge in the diagram. (2 marks)

b) Select and name the Root Port of each bridge as RP. (2.5 marks)

c) Mark the designated Bridge for each segment. (2 marks)

d) Name the designated port in each designated bridge as DP. (2.5 marks)

e) If selected Root Bridge is not working, then which is the next root bridge?Explain the method it selects by Spanning Tree Protocol? (4 marks)

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00331.

Final Examination - 20 I0Data Communication & Computer Networks II- I" Semester

Question 4) is based on the Access Control List Security and Network security. (18 marks)

I. What are the fields of IP packet that can be checked by Extended Access ControlU~ ~~~

2. The network administrator wants to implement ACL security for the following

requirements for the network given below. (Assume IGRP has been applied as

routing protocol.) (8 marks)

LAN 1 (192.168.10.0/24) LAN 2 (172.17.0.0/16)

s

192.168.10.6 172.17.0.6

n/w 10.1.0.0 /16

172.17.0.5 172.17.0.7192.168.10.5 192.168.10.7 Figure 4

a. Host A is not allowed to telnet to the host P in LAN 2.

b. Other hosts in LAN 1 can telnet to the host P in LAN 2.

c. Host P is allowed to access any web server in LAN I.

d. Host P is not allowed to access any other servers in LANI.

e. Any unspecified communication should be not allowed.

Select the most suitable routers and configure Access Control Lists for the above

requirements. Apply them to most suitable interfaces. (Show the prompt of router in

your configuration.)

3. Write two advantages in Named Access Control Lists. (2 marks)

4. Write two types offirewalls and mention the ISO OSI layer(s) it operates. (2 marks)

5. Write two servers that can be placed in De Militarized Zone. (2 marks)

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Final Examination - 2010Data Communication & Computer Networks II - pSI Semester

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Question 5) (16 marks)

1. Explain the ARP and RARP protocols. (6 marks)

2. Briefly explain the IGMP protocol. (4 marks)

3. Briefly explain the fragmentation process in internet protocol and specify how thefragmentation offset value creates. (6 marks)

USEFUL COMMANDS FOR DATACOMMUNICATIONS AND COMPUTERNETWORKS II

Standard IP Access List and Extended Access list €onfiguration Commands

Command Configuration Mode andDescription

access-list access-list-number { deny I permit} Global command for standardsource [ source-wildcard] [ log] numbered access lists

access-list access-list-number { deny I permit} Global command for extendedsource [ source-wildcard] destination [ destination- numbered access listswildcard] [ log]

ip access-group { number I name [ in [out j} Interface subcommand to enableaccess lists

access-list access-list-number {permit I deny} Extended IP Access-list configurationprotocol source source-wildcard [operator port]destination destination-wildcard [operator port][established] [log]

ip access-group access-list-number {in lout} Activates the extended list on aninterface

End of Paper

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