data communication and computer networks ii 206

8/6/2019 Data Communication and Computer Networks II 206

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Sri Lanka Institute of Information Technologyte rnSLIlT~JIII~B.Sc. Special Honours Degree.In

Information TechnologyFinal Examination

Year 2, Semester 1 (2008)Data Commu~ication and Comp~ter Networks II(206)

Duration: 3 HoursFriday, 2nd May 2008

(Titne 9.00 a.nl. - 12.00 noon)Instruction to Candidates:

Calculators are allowed. This paper contains 5 questions All questions carry equal marks. Answer All Questions on the paper itself. Total Marks 100. This paper contains 14 pages excluding the cover page.


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Final ExaminationData Communication and Computer Networks II - First Semester

Question 11. A TCP client opens a connection with a server using an initial sequence number

(ISN) of 12000. The server party opens the connection with an ISN of28000.a) Show the TCP connection establishment process. Indicate the sequence number

and the acknowledgement numbers in a diagram. (3 marks)II Client Server

b) Following the question above (a), show how the following data segments aresent by the client and the server. Indica~e the sequence number and theacknowledgement numbers in a diagram. (5 marks)

Clienterver300 Bytes 200 Bytes00 Bytes

Client Server

"-

I

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C)' Show the TCP COIDlectiontermination process initiated by the client. Indicate thesequence number and the acknowledgement numbers in a diagram. (2 marks)

I Client Server

d) Explain the function of a "Retransmission Timer". (3 marks)

e) Explain how 'Error Control' is done for a corrupted segment,(2 marks)

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f) A Receiver ButTer Size is 2000 Bytes. It's window size is 200 Bytes. How muchdata is available in the buffer? (2 marks)

g) Write one of the reasons of sending a segment with an RST flag. (3 marks)



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Question 2a) An IP datagram has arrived with the following information in the header (in

hexadecimal): Use the diagram of the IP header given below. Answer thefollowing questions, you can answer in hexa decimal or decimal or binary forlarge numbers.45 00 00 54 00 03 00 00 20 06 00 00 7C 4E 03 02 B4 OEOF 02

VER HLENService type Totallengthbits 8 bits 16 bitsFlagsragmentation offsetbits3 bitsrotocolHeader checksumbits 16 bits

ress Destination IF AddressOption

1. What is the header size? (1 mark) _11. What is the fJ:agmentation offset? (1 mark) _111. Is the packet fragmented? (1 mark) _lV. What is the size of the data? (2 marks) _v. What is the transport Layer protocol of the packet? (1 mark)

VI. How many more routers can the packet travel to? (l mark) _Vll. What is the identification number of the packet? (1 mark) _

b) An original IP packet contains 6000 data bytes. The identification number is320. '1. Assuming that Ethernet is used at the Data Link Layer (supports only 1500

Bytes for the Data Field), draw how the IP packet is fragmented. Mention howmuch data is contained in fragments. The standard IP header is used on everyIP fragment. (5 marks).\ Sri Lanka Institute of Information TechnologyPage 4 of 14


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11. How many fragments are there? (1 mark)

111. (a) What is the class of 172.11.5.3 IP address (classful)? (1 mark)

(b) An IP address and subnet mask are 200.5.10.129 255.255.255.128. What isthe network address? (3 marks)

(c) You have a class B network address, 130.12.0.0. Write the most suitablesubnet mask to create 25 subnetwork addresses. (2 marks)

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Question 3Teletech is a business process outsourcing (BPO) company based in Colorado. It is nowhaving new branches in Sydney and Shanghai. Teletech has obtained the network address182.10.0.0/16 tor the company.

10.10.10.0/24 8 81 20.10.10.0/24SO

EOColarado

EO

Sydney SO

a) Using the obtained network address, assign subnets to each branch using theminimum number of host bits to the network side. (Do not use the first subnet withall Osand the last subnet with allls.)Write the subnet address given with thesub net mask in decimal.(Assign the first possible subnet to Colorado, second to Sydney and the third toShanghai.) (5 marks)

Network Subnet Addressubnet MaskSydneyhanghai

b) What is the maximum number of possible hosts per network? (1 mark

c) Assign the first IP.address of the subnet of each branch to the router interface. (1mark)Network IP Address of the Router Interface of the Network

Sydneyhanghai"

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e) ,What is an Autonomous System? (1 mark)

1) Write the commands for configuring IGRP on 'Sydney' router. Indicate the promptsas well. (3 marks)

g) Explain the following topics briefly.

i. Link State Routing (2 marks)

11. Static Routing (2 marks)

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111. Split Horizon (2 marks)

IV. Route Poisoning (2 marks)



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Question 41. Write the two protocols used in VLAN Tagging? State one difference between those

two protocols. (3 marks)Two Protocols:DitJerence:

L2. What is the purpose o[having a trunk E0rl? (1 mark)3. Implement a VLAN solution for the following scenario. Network consists with 3

switches (CISCO 1912/2950) with 24 Fast Ethernet ports. You have to configure theSWI switch with following details Write the relevant commands. Useful commandsare attached at the end of the paper.

VLANs in SW1Create foIl1. VLAN name is Accounting and VLAN Number is 2 (1 mark)

2. VLAN name 1S Sales and VLAN Number is 3 (1 mark)

3. VLAN name is Production and VLAN Number is 4 (1 mark)

2. Switch port 3 and 13 for the VLAN 3 (1 mark)

3. Switch port 4 and 14 for the VLAN 4 (1 mark)

c.) Contlgure the switch port 1 as a trunk port (1 mark)



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Final ExaminationData Communication and Computer Networks 11- First Semester

4. Bridge IDs of each bridge and the path costs are given in the diagram.a) Highlight the Root Bridge. (1 mark)b) Select and highlight the Root Port of every bridge. (3 marks)c) Select the designated Bridges for each segment (2.5 marks)d) Show the designated port in each designated bridge. (2.5 marks)

Semnent 1 SeQment 2 4 SeQment 3100

~:10019

100

19

4

c: 1504

2

D: 250

2

19

2

4

2

Segment 419

Segment 5



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Question 54. State two differences between Standard Access Control List and Extended AccessControl List. Useful commandfj are attached at the end of the paper.1. (4 marks)

2. The network administrator of the following network wants to implement ACLsecurity to the network.Galle

.:t192.168.15.6/24TomRoulJlr-PTO Roiler2

Kandy

"172.10.0.6/16Mary

a) Write standard ACL statements for the following criteria. State the prompts as well.L Tony can access the Galle Network. (2 marks)

ii. But any other traffic from the Kandy network should be denied. (2 marks)

b) Apply the above access-list on a suitable router interface. Write the command.Indicate the prompt as well. (1 mark)



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Final ExaminationData Communication and Computer Networks Il-First Semester

c) Write extended ACL statements for the following criteria. Indicate the prompts aswell.i. Telnet traffic to John from the Colombo network should be denied (3.5 marks)

11. IP packets with TCP protocol, traveling from the 'Colombo' network to anydestination with a destination port less than 1023 should be permitted. (3.5marks)

d) Apply the above access-list on a suitable router interface. Write the command.Indicate the prompt as well. (1 mark)

e) Write 2 functions of a firewall. (2 marks)

______l) Give an example of a server that is placed in the DMZ. (1 mark)Sri Lanka Institute ofInformation Technology

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USEFUL COMMANDS FOR DATACOMMUNICATIONS AND COMPUTERNETWORKS IICommands for Catalvst 1900 Switch Confieuration

Command Descriptionets the IP address for in-bandmanagement of the switch

Sets the default gateway so that themanagement interface can be reachedrom a remote networkhow interfaces . Displays interface informationSets a permanent MAC addressmac-ad dress-table restricted static mac-address

Sets a restricted static MAC addressport secure [max-mae-count count]

Sets port securityisplays the MAC address table: thesecurity option displays infonnationbout ths::restricted or static settings

Sets the action to be taken by theswitch if there is a security addressiolation

Displays version information

VLAN Command Listvlan vlan [name vlan-name] IDisplays VLAN informationAssigns a port to VLAN- Displays VLAN membership

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Standard IP Access List and Extended Access list Confie:uration Commands

Command Configuration Mode andDescription

Global command for standardumbered access listsI access-list access-list-number { deny I permit}

Global command for extendednumbered access lists

ip access-group { number I name [ in lout]}

Interface subcommand to enableaccess lists

Extended IP Access-list configurationdestination 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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data communication and computer networks ii 206

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