a2 computer science - computer networking problems

8/9/2019 A2 computer Science - Computer Networking Problems

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9 (c) When the computers in segment 192.168.2 were configured on the network, they wereprogrammed with a subnet mask.

What is the purpose of a subnet mask, and what would the subnet mask be in thiscase?

Purpose: ................................... ................................... ................................... ...................

............................................................................................................................................

Subnet mask: .................................. ................................... .................................... ............

............................................................................................................................................(2 marks)

9 (d) Laptop computers connect to the network wirelessly using Wi-Fi. Wirelesscommunication is less secure than communication using cables.

Explain two measures that the Wireless Access Point could use to improve the securityof the network.

Measure 1: ................................. ................................... ................................... ...................

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Measure 2: ................................ ................................... ................................... ...................

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............................................................................................................................................(2 marks)

Question 9 continues on the next page


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9 (e) The computers in segment 192.168.1 use Carrier Sense Multiple Access with CollisionDetection (CSMA/CD) to determine when to transmit data.

Explain how the CSMA/CD method is used, including what happens in the event of acollision occurring.

In this question you will also be assessed on your ability to use good English and toorganise your answer clearly in complete sentences, using specialist vocabulary whereappropriate.

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15

9 (a) (i) 192.168.0.x where x is not 0 or 255; 1

9 (a) (ii) 192.168.2.x where x is not 0 or 255 1

9 (a) (iii) 192.168.2.y where y is not 0 or 255 and the IP address isdifferent to the one in (ii)

1

9 (b) Star; 1

9 (c) Identify which other computers are on same segment // can havepackets/data sent directly to them;Identify which other computers are on a different segment // must havepackets/data sent to them via the router;R network for subnetMAX 1255.255.255.0 / FFFFFF00 / 11111111111111111111111100000000; 2

9 (d) Use of WEP/Wired Equivalent Privacy/WPA/WiFi Protected Access;(Strong) encryption of transmitted data; R encodingUser/computer must enter/send a passphrase/certificate at start ofcommunication before laptop allowed to connect; A key for passphraseA only allow password if used in correct context;

Access point checks MAC/hardware address of laptop and only allowscomputers with a MAC/hardware address in a list of approvedaddressed to connect; R IP addressDisable broadcast of SSID/identity;Reduce / limit power of transmitter;MAX 2 2


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Computing COMP3 - AQA GCE Mark Scheme 2010 June series

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9 (e) Subject-related points:(Applies to) bus (topology);Computer monitors/listens to (data signal on cable/bus);If (data) signal present // if cable/bus busy continue to wait;When no (data) signal present // when cable/bus idle start to transmit;

Whilst transmitting, computer monitors cable/bus to check for collision //to check if signal is identical to what it is sending;Collision occurs if two computers (start) sending at same time // if twopackets/frames in transit at same time;If collision detected, jamming signal/signal warning of collision sent;To ensure other (transmitting) computers aware of problem // to stopother computers sending data;Computer that detected collision also stops sending data;Then waits a random period before attempting to retransmit/repeatingtransmission/this process;Period is random to reduce likelihood of collision recurring (betweencomputers that caused collision);

If a collision occurs again then waits a longer random time beforeattempting to transmit again;Use of exponential back-off algorithm to determine wait time;

Mark Bands and Description5-6 To achieve a mark in this band, candidates must meet

the subject criterion (SUB) and 4 of the 5 quality ofwritten communication criteria (QWCx).

SUB Candidate has produced a detailed descriptionof how CSMA/CD works, including whathappens if there is a collision (at least 5 points).

QWC1 Text is legible.QWC2 There are few, if any, errors of spelling,

punctuation and grammar. Meaning is clear.QWC3 The candidate has selected and used a form

and style of writing appropriate to the purposeand has expressed ideas clearly and fluently.

QWC4 Sentences and paragraphs follow on from oneanother clearly and coherently.

QWC5 Appropriate specialist vocabulary has beenused.

3-4 To achieve a mark in this band, candidates must meetthe subject criterion (SUB) and 4 of the 5 quality of

written communication criteria (QWCx).SUB Candidate has produced a reasonabledescription which may or may not cover whathappens in the event of a collision (at least 3points).

QWC1 Text is legible.QWC2 There may be occasional errors of spelling,

punctuation and grammar. Meaning is clear.QWC3 The candidate has, in the main, used a form and

style of writing appropriate to the purpose, withoccasional lapses. The candidate hasexpressed ideas clearly and reasonably fluently.

QWC4 The candidate has used well-linked sentencesand paragraphs.

QWC5 Appropriate specialist vocabulary has been


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Internet

Segment192.168. 1

Segment192.168.2

150.14.12.88

BA

8 Figure 5 shows the topology of a particular computer Local Area Network (LAN) that isdivided up into segments.

Figure 5

8 (a) Suggest suitable IP addresses for:

8 (a) (i) the Router 2 port labelled A : ................................ ................................... ......................

8 (a) (ii) the Router 2 port labelled B : ........................................................................................ (2 marks)

8 (b) When the computers in segment 192.168.2 were configured on the LAN, they wereprogrammed with a subnet mask.

What subnet mask should have been used?

..........................................................................................................................................(1 mark)

File Server

Router 1

Segment192.168. 0

Router 2

Segment192.168.1

150.14.12.88Router andFirewall

Segment192.168.2

Internet


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8 (a) (i) 192.168.0.x where x is not 0 or 255; 1

8 (a) (ii) 192.168.2.x where x is not 0 or 255; 1

8 (b) 255.255.255.0; 1

8 (c) Reason: To reduce (network) congestion//improve throughput// to cutthe number of collisions* ; A faster operation/transmission;Explanation: by cutting the number of collisions* //by reducing thenumber of stations/computers connected to each section of cabling//because two computers in one segment can communicate at the sametime as two computers in another segment;Note: * = Do not award two marks for cutting the number of collisions only award one for either reason or explanation.

Reason: To improve security;Explanation: by localising packet transmission to one segment;

Reason: To improve reliability;Explanation: By limiting effect of cable failure to one segment;

Award marks for either:

one reason + explanation

two reasons

two explanationsMax

2

8 (d) (i) Less expensive as reduced cabling requirement;No reliance on central node as data does not all travel through onenode;A less cabling required without reference to reduced cost if candidatehas explained why less cables are neededA computer/station for nodeMust have explanation as well as advantage for mark

Max1

8 (d) (ii) Improved security as: data only travels down one link // is not sentthroughout network // is not sent to all nodes;Improved reliability as if one link fails the other links/nodes are notaffected;Speed of link remains constant // speed not affected by number ofconnections/collisions // faster connection as: no collisions/links notshared;A cable for link

R responses about terminal/computer failureMust have explanation as well as advantage for mark Max1


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M/Jun13/COMP3

Do not writeoutside the

box

(10)

5 A student is using her computer at school.

Figure 8 shows the physical topology of the Local Area Network (LAN) to which hercomputer is connected. The LAN is divided up into segments. It also shows a webserver that her computer connects to through the Internet.

The student is using computer C .

Figure 8

Internet

Segment 192.168.1

Segment192.168.0

Segment192.168.2

BA

E

Web server

C D

Switch

Router 1

Router 2

Gateway

Fileserver

5 (a) Suggest suitable IP addresses for:

5 (a) (i) the "Router 1" port labelled A ................................. ................................... ......................

5 (a) (ii) the "Router 1" port labelled B ................................. ................................... ......................

5 (a) (iii) the network adapter card in the students computer, labelled C

............................................................................................................................................(3 marks)

5 (b) What physical network topology is used within segment 192.168.1?

............................................................................................................................................(1 mark)


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5 (c) When the computers in segment 192.168.1 were configured on the network, they wereprogrammed with a subnet mask.

What subnet mask would have been used?

............................................................................................................................................(1 mark)

5 (d) The student has been accessing data from the file server computer that is labelled Don Figure 8 . This file server uses a server operating system.

Explain what a server operating system is.

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............................................................................................................................................(1 mark)

5 (e) Some other students using laptops are connected to the LAN by Wi-Fi through the

Wireless Access Point that is labelled E on Figure 8 . Wireless communication isless secure than communication using cables.

5 (e) (i) Describe one measure that could be implemented by the Wireless Access Point toimprove the security of the network.

............................................................................................................................................

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............................................................................................................................................(1 mark)

5 (e) (ii) Explain why Wi-Fi has been chosen for this connection rather than Bluetooth.

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............................................................................................................................................(1 mark)

Question 5 continues on the next page


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Figure 8 is repeated below so that you can answer question part 5 (f) without having toturn back in the question paper booklet.

Figure 8 (repeated)

Internet

Segment 192.168.1

Segment192.168.0

Segment192.168.2

BA

E

Web server

C D

Switch

Router 1

Router 2

Gateway

Fileserver

The student now uploads a file from her computer to a web server over the Internet.

5 (f) Write a detailed description of how one packet of data that the student is uploadingto the web server will be routed from her computer in the United Kingdom to the webserver that is located in Chicago in the United States of America. You may assumethat the web browser software on the students computer has already looked up, usinga domain name server, the IP address of the web server.

Your description should cover: how the packet will be routed within the LAN from the students computer to the

gateway and

how, once it has reached the gateway, the packet will be routed across the Internetto the web server that the data is being uploaded to.

In your answer you will be assessed on your ability to use good English, and toorganise your answer clearly in complete sentences, using specialist vocabulary whereappropriate. (8 marks)


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5 (g) The web server has a routable IP address.

The students computer has a non-routable IP address.

Explain two differences between routable and non-routable IP addresses.

Difference 1: ................................... ................................... .................................... ............

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Difference 2: ................................... ................................... .................................... ............

............................................................................................................................................ (2 marks)

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5 (a) (i) 192.168.0.x where x is not 0 or 255;Must be a specific IP addressR. addresses that include port numbers

1

5 (a) (ii) 192.168.1.x where x is not 0 or 255;Must be a specific IP addressR. addresses that include port numbers

1

5 (a) (iii) 192.168.1.y where y is not 0 or 255 and is notthe same as x in (ii);Must be a specific IP address

R. addresses that include port numbers

1


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MARK SCHEME A-level Computing COMP3 June 2013

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5 (b) Bus (topology/network); A Line 1

5 (c) 255.255.255.0 / FFFFFF00 /11111111 11111111 11111111 00000000; 1

5 (d) (An operating system that is optimised to)provide (one or more specialised) services to(network) clients;

A. description of examples of services e.g.logging on, sharing printers, but just the exampleof accessing files is not enough as this is in thequestion there needs to be additionalexplanation if files is used as an example, e.g.managing quotas, security of files.R. answers that imply that server does allprocessing i.e. confusion with thin client.

1

5 (e) (i) Use of Wired Equivalent Privacy/WEP/WPA/WPA2/WiFi Protected Access;(Strong) encryption of transmitted data // use of

Advanced Encryption Standard/AES; R encodingUse of Extensible Authentication Protocol/EAP;User/computer must enter/send apassphrase/certificate at start of communicationbefore laptop allowed to connect; A key forpassphrase A only allow password if used incorrect context ie for accessing network, not for

logging on to a sever or just having a password Access point checks MAC/hardware address oflaptop and only allows computers with aMAC/hardware address in a list of approvedaddresses to connect; R IP addressDisable broadcast of SSID/identity;Reduce / limit power of transmitter;Use of two/multi-factor authentication;

1

5 (e) (ii) Longer range // faster transmission speeds //higher bandwidth // more simultaneous

connections; A. reverse of points e.g. "Bluetooth only has ashort range"R. Bluetooth can only connect two devices atonce

1


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5 (f) SUBJECT MARKING POINTS:

Internal:

Students computer uses subnet mask (anddestination/web servers IP address) todetermine if destination computer/web serveris on same subnet // identify not on samesubnet

Up to two marks from description (in separatesection below) of how subnet mask is used

Packet is sent (from students computer) toRouter (1)

Router 1 identifies that destination is outsidethe LAN so forwards packet to Gateway

External:

Hierarchical organisation of routers Example of hierarchical organisation of

routers e.g. passed up to a national router,transferred internationally and then passedback down a hierarchy

Path to take selected by each router (notdetermined at start) NE passed from router torouter

Route may change as a result of e.g.congestion, technical problems

Either:

(Possible) repackaging of packet to usedifferent protocol (e.g. Gateway may changeprotocol)

Route determined using the (Network ID partof the destination) IP address (Note: can infer"IP address" if just "address" is stated, ifpreviously candidate has written about an IPaddress)

Use of router tables / criteria to determinenext hop / (step of) path

Router decrementing "time to live" of packet Source and destination MAC addresses

changed at each router // MAC addressesused for each hop

How subnet mask used (MAX 2 points):

AND operation of subnet mask with studentscomputers IP address

AND operation of subnet mask with webservers IP address

Result (of AND operation) is the network ID; Network IDs compared If they are the same, then the computers are

on the same subnet

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A interchangeable use of subnet ID and networkID

HOW TO AWARD MARKS:

Mark Bands and Descrip tion7-8 To achieve a mark in this band,candidates must meet the subject

criterion (SUB) and all 5 of the quality oflanguage criteria (QLx).

SUB Candidate has covered bothinternal and external routing indetail and has made at leastseven subject-related points.

QWC1 Text is legible.QWC2 There are few, if any, errors of

spelling, punctuation andgrammar. Meaning is clear.

QWC3 The candidate has selected andused a form and style of writingappropriate to the purpose andhas expressed ideas clearly andfluently.

QWC4 Sentences (and paragraphs)follow on from one another clearlyand coherently.

QWC5 Appropriate specialist vocabularyhas been used.

5-6 To achieve a mark in this band,candidates must meet the subjectcriterion (SUB) and 4 of the 5 quality of

language criteria (QLx).SUB Candidate has covered both

internal and external routing,although one may be in moredetail than the other and hasmade at least five subject-relatedpoints.

QWC1 Text is legible.QWC2 There may be occasional errors

of spelling, punctuation andgrammar. Meaning is clear.

QWC3 The candidate has, in the main,used a form and style of writingappropriate to the purpose, withoccasional lapses. The candidatehas expressed ideas clearly andreasonably fluently.

QWC4 The candidate has used well-linked sentences (andparagraphs).

QWC5 Appropriate specialistvocabulary has been used.

1-4 To achieve a mark in this band,


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candidates must meet the subjectcriterion (SUB) and 4 of the 5 quality of

language criteria (QLx).SUB Candidate may not have covered

both internal and external routing,but has covered at least one ofthem. Up to four relevant pointshave been made.

QWC1 Most of the text is legible.QWC2 There may be some

errors of spelling, punctuation andgrammar but it should still bepossible to understand most of theresponse.

QWC3 The candidate has used aform and style of writing which hasmany deficiencies. Ideas are notalways clearly expressed.

QWC4 Sentences (andparagraphs) may not always bewell-connected.

QWC5 Specialist vocabulary hasbeen used inappropriately or notat all.

0 Candidate has made no relevant points.

Note: Even if English is perfect, candidates canonly get marks for the points made at the top ofthe mark scheme for this question.

If a candidate meets the subject criterion in aband but does not meet the quality of languagecriteria then drop mark by one band, providingthat at least 4 of the quality of language criteriaare met in the lower band. If 4 criteria are notmet then drop by two bands.


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5 (g) Any two points from the list below. Candidateonly needs to make one side of point, the othercan be implied. Do not award marks for twosides of same point.

Routable Non-Routable

(Globally)unique. Many computers/devicesmay have same address. Allocated by acentral/regionalissuing authority( A example).

Not allocated centrally //allocated by a homeuser/company/ISP.

Can beconnected todirectly over theInternet / fromoutside privatenetwork

Difficult/impossible toconnect to over Internet //from outside of network.

Owner can belooked up usingWHOIS protocol

Owner cannot be lookedup using WHOIS protocol

A. non-routable IP addresses more secure ascannot be connected to over Internet/fromoutside network

A. can identify location from a routable IPaddress

2


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Figure 6 below shows the local area network (LAN) of the supermarket chains head office.It consists of three Ethernet bus segments with IP addresses 192.80.0, 192.80.1 and 192.80.2connected together by routers.IP addresses that begin with 192 are private addresses.

The head office hosts an on-line ordering service for customers on a Web server with publicIP address 213.97.56.21. The Web server and the local area network are connected to the Internet through a router andfirewall.

The local area network is a server-based network. There is one file server and domain controller and one print server.

Figure 6

M/0104/CPT5

Router

Router

Router&

Firewall

192.80.1.5Segment File server192.80.0 192.80.1.2 192.80.1.3 192.80.1.4 & Domain

controller

Segment192.80.0.1 192.80.1.1 192.80.1

PrintServer

192.80.0.2 192.80.2.1 Segment

192.80.2.2 192.80.2.3 192.80.2.4 192.80.2.5 192.80.2

Web server

213.97.56.21

192.80.0.3 213.97.56.19 Internet
http://www.xtremepapers.net/


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(d) Draw a diagram to show how segment 192.80.1 would be wired using a switch..

(2 marks)

(e) Why must the router-firewall and the Web server have public IP addresses?

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...........................................................................................................................................(1 mark)

(f) The computer with IP address 192.80.1.3 uses the TCP/IP protocol to send a documentto be printed to the print server. Describe how the TCP/IP protocol is used to route thedocument to its destination. Your description should cover the role of the two routersand network card addresses.

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15 LEAVE MARGIN BLANK


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(g) State one purpose of the firewall in this local network.

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(h) The local area network is a server-based network . What is meant by a server-basednetwork?

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END OF QUESTIONS

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LEAVE MARGIN BLANK

Copyright 2004 AQA and its licensors. All rights reserved


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(d) One mark for central hub and one mark for computers connected tohub as shown

NB If hub incorrect answer scores zeroIf hub correct but computers incorrect answer scores one markRouter can be replaced by a computer labelled with router's IP address

2

(e) So that these are reachable from anywhere on the Internet//so thatcan be seen/reached from the world outside;R. So can be reached by another branch of supermarket 1

Don't have to labelcomputers withtheir IP addresses.A. IP addresses inplace of computers+ routerRouter

S w it ch


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(f) Document split into smaller chunks; A. segments/packets/framesDestination IP address doesnt match this segments IP address;Document chunks sent to nearest router;Using its network card address/MAC address;Router sends chunks to router connected to print server segment;Using its routing tables and;This router's network card address;This router sends chunks to print server;to max 5

(g) To block access to/from the internal private network from/to the Internet;To stop certain kinds of access to the Web server, e.g. telnet;To close ports to prevent users from connecting to them;To block connections on unwanted ports;To prevent unauthorised access to the private computers;A. Filtering

to max 1

(h) A network in which resource security/user authentication/administration/resource allocation;managed/controlled by/carried out by servers; 2

Total 15

Grand Total 65


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6 The head office of an organisation consists of several large off ices, each with manycomputers linked as a local area network (LAN). The LAN also links to the Internet via arouter and firewall. In each office, the computers are linked as a segment as shown inFigure 4 .

Figure 4

(a) IP addresses that begin with 172.31 are non-routable addresses. Why are these usedwithin the LAN?

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.............................................................................................................................................(1 mark)

(b) The network manager has registered IP address 212.99.34.23 with the Internet registrar.

Referring to Figure 4 , write suitable IP addresses for

(i) ....................................................................................................................................

(ii) ....................................................................................................................................

(iii) ....................................................................................................................................(3 marks)


M/J an08/CPT5(10)

Node A Node B Node C Node X

Node A Node B Node C Node Y

Node A Node B Node C Node Z

Internet

172.31.15.3 172.31.15.4 Segment 172.31.15

(ii) (i)

.............

.............

.............

(iii)

172.31.19.4 Segment 172.31.19

172.31.45.4 Segment 172.31.45

Router&

Firewall

Router

Router

Router

. . . . . . . . . . . . . . . . . .

Segment 172.31.1


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(c) Give two reasons for segmenting this LAN.

1...........................................................................................................................................

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2...........................................................................................................................................

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(d) (i) What would be a suitable subnet mask for this LAN?

....................................................................................................................................(1 mark)

(ii) Using addresses 172.31.15.3 and 172.31.19.5 explain how a subnet mask is usedto determine whether the computers are on the same subnet.

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8

6 (a) because machines do not need a direct presence on the Internet;more secure; A private addresses;R machines dont need access to the Internetdevices outside of the LAN cannot access them / route to them;

1

6 (b) (i) 212.99.34.23 1

6 (b) (ii) 172.31.1.1 1

6 (b) (iii) 172.31.1.x; where x can be any number between 2 and 254 1

6 (c) too much traffic if single network causing too many collisions

// network traffic too slow // to increase bandwith;

to restrict access; A to improve security;to increase the number of addresses available // too many devices toaddress on one subnet;

problems can be more easily isolated to one segment;

2

6 (d) (i) 255.255.255.0 // 1111 1111 1111 1111 1111 1111 0000 0000 ; 1

6 (d) (ii) 172.31.15.3 = 1010 1100 0001 1111 0000 1111 0000 0011

172.31.19.5 = 1010 1100 0001 1111 0001 0011 0000 0101

255.255.255.0 = 1111 1111 1111 1111 1111 1111 0000 0000

AND operation of subnet mask with each IP address; to isolatesubnet IDs/network address; (or by example)

subnet IDs compared; if same, then on same subnet;if matches NE

3 The binarynumbers are

provided soyou cancheck theanswerswhen acandidateuses them toexplain.They are notworth marks

bythemselves.
http://www.xtremepapers.net/http://www.xtremepapers.net/


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6 A school Local Area Network (LAN) uses the TCP/IP protocol to communicate betweencomputers.

(a) What is a protocol?

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.............................................................................................................................................(1 mark)

(b) Complete the diagram of the TCP/IP protocol stack below:

(iii) Give one example of a type of application found in the Application Layer.

....................................................................................................................................(1 mark)

(c) This LAN uses the Ethernet protocol as its Data Link Layer, which uses Ethernet MAC(Media Access Control) addressing to route Ethernet frames. What is an EthernetMAC address?

.............................................................................................................................................(1 mark)

(d) The school now wants to connect to the Internet. Every computer in the LAN is givenan IP address with a network ID of 192.168.4 and a subnet mask of 255.255.255.0.

(i) Give one example of an IP address for this LAN.

....................................................................................................................................(1 mark)

(ii) How many different host IDs are there?

....................................................................................................................................(1 mark)


M/J an07/CPT5

Application Layer

(i)

(ii)

Data Link Layer

(1 mark)

(1 mark)


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(iii) What could the school do if it needs more host IDs?

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(1 mark)

(iv) IP addresses starting with 192.168 are private addresses. Why were privateaddresses chosen for the individual computers on the network?

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....................................................................................................................................(1 mark)

(e) The school registers the IP address 222.125.105.15 with the Internet registrar. How canthis IP address be used to connect to the Internet?

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10

6 (a) a set of rules/procedures; 1

(b) (i) Transport (Layer); 1

(ii)Network (Layer); 1

(iii) telnet;http (client) // web server // IRC Client Server;

email; internet/web browser;

FTP; snmp;

TFTP; A instant messaging / VoIP;

SMTP; https; max 1 3

(c) a (unique) address / identifier assigned to network card

// (unique) hardware address/identifier; A code R name instead of address 1

(d) (i) any IP address in the range 192.168.4.1 to 192.168.4.254

A 192.168.4.255 or 192.168.4.0

(ii) 254 A 256, 255, 253 1

(iii) change the subnet mask // get another network ID // get class A or B

network ID;

split the network into subnets; R segments max 1

(iv) for security reasons; not accessible/addressable from outside the

LAN;

avoids massive use of public addresses; max 1

Total 4

(e) use a router // use a gateway address;

assign registered IP address (222.125.105.15) to the Internet-facing NIC of

router/gateway;

assign local IP address (192.168.4.1) to LAN-facing NIC of router;

local computer sends message to (LAN-facing NIC of) router/gateway;

router/gateway sends message to Internet using registered IP address

(222.125.105.15);

router/gateway sends reply from Internet to local computers private IP

address; max 2

Total 11


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6 A small organisation, Acme Consultants, with four stand-alone computers in an office, wantto set up a peer-to-peer network in order to share the printer connected to one of thecomputers.

(a) What is peer-to-peer networking?

.............................................................................................................................................

.............................................................................................................................................(1 mark)

(b) If an Ethernet switch is used to set up the network, draw a labelled diagram of thephysical layout of the network.

(2 marks)

(c) It is decided to set the IP addresses for each computer manually and use a subnet maskof 255.255.255.0.

(i) The following IP addresses were used for the computers:Computer A: 192.168.5.2Computer B: 192.168.5.3Computer C: 192.168.4.4Computer D: 192.168.5.5

Why is this not satisfactory?

....................................................................................................................................(1 mark)

(ii) What should be the network ID of this network?

....................................................................................................................................(1 mark)

(iii) What possible values could the host IDs take?

....................................................................................................................................(1 mark)


M/J an06/CPT5


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(d) Acme Consultants now want to connect their network to the Internet using an ADSLline. A router is used to connect the network switch to the ADSL modem.

(i) What is the purpose of the router?

....................................................................................................................................

....................................................................................................................................(1 mark)

(ii) The IP addresses 192.168.5.1 and 222.125.105.15 are assigned to the router.Which of the IP addresses needs to be registered with the Internet registrar and why?

IP address: ...................................................................................................................

Reason...........................................................................................................................

......................................................................................................................................(2 marks)

Figure 4

(iii) Figure 4 above shows part of the TCP/IP configuration window displayed on themonitor of computer A. What IP address should be entered for the Defaultgateway?

......................................................................................................................................(1 mark)


10

M/J an06/CPT5 Turn over

Internet Protocol (TCP/IP) Properties X?

General

You can get IP settings assigned automatically if your network supportsthis capability. Otherwise, you need to ask your network administrator forthe appropriate IP settings.

Obtain an IP address automatically

Use the following IP address:

IP address:

Subnet mask:

Default gateway:

1925 . 21685 . 255 . 22

2555 . 22555 . 255 . 20

1925 . 21685 . 255 . 22


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AQA GCE Mark Scheme, 2006 January series CPT5

7

6 a) in a peer-to-peer network there are no dedicated servers;

in a peer-to-peer network all computers are equal / have equal status;

each computer functions as both a client and a server;

user at each computer acts both as user and administrator;

user at each computer controls what is shared with other computers;

a user logged in at one peer computer is able to use resources on any other peer computer;

R each computer directly connected to each other, so can send to each other without a server

R all computers have same rights max 1

b)

Switch

Computer/PC

Computer/PC PrinterComputer/PC

Computer/PC

1 mark for switch with 4 computers/PCs connected; 1 mark for printer connected to computer; 2

c) i) Computer C is in a different subnet // network ID is different; A correct IP address 1

A there are two subnets R not on the same LAN

ii) 192.168.5; A 192.168.5.0; 1

iii) 0-255; more correctly: 1-254; or any in the range 192.168.5.1 192.168.5.254

(since 0 means all addresses on subnet, and 255 is reserved as broadcast address) 1

d) i) a router is a device that receives datagrams/packets from one computer and uses the IP

addresses that they contain to pass on these packets, correctly formatted, to another computer;

a router is a device that uses IP addresses to route packets/datagrams;

router keeps LAN traffic segregated from connection to ISP; 1

ii) IP address: 222.125.105.15

Reason: router needs to have a presence on Internet so that it can be reached from anywhere;

Public address must be unique over whole Internet // must be visible on Internet // provides

identity on Internet; A because 192.168.5.1 is a private/non-routable address; 2

iii) 192.168.5.1 1 Total 10

T.O. if a server included in diagram I boxes I routers / modems

R a specificIP address


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10 Figure 4 shows the TCP/IP protocol stack applied to a LAN (Local Area Network).

Figure 4

(a) What is a protocol?

...........................................................................................................................................

...........................................................................................................................................(1 mark)

(b) What is the topology of this local area network?

...........................................................................................................................................(1 mark)

(c) State a suitable type of network cable for the physical connections of this LAN.

...........................................................................................................................................(1 mark)

14

M/0105/CPT5

LEAVE MARGIN BLANK

FTPclient FTPserver

TCP TCP

IP IP

Ethernetdriver

Ethernetdriver

FTP protocol

TCP protocol

IP protocol

Ethernet protocol

Application

Transport

Network

Link

Ethernet cable


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The IP protocol layer uses IP addressing to route packets.

(d) Give two examples of an IP address that could belong to the same LAN.

1 ........................................................................................................................................

2 ........................................................................................................................................(2 marks)

(e) Which part of your IP addresses identifies

(i) the LAN;

..................................................................................................................................(1 mark)

(ii) the host on this LAN?

..................................................................................................................................(1 mark)

(f) The Ethernet protocol layer uses Ethernet MAC (Media Access Control) addressing toroute Ethernet frames. What is an Ethernet MAC address?

...........................................................................................................................................(1 mark)

(g) Describe two tasks performed by the TCP protocol layer1 ........................................................................................................................................

1 ........................................................................................................................................

2 ........................................................................................................................................

1 ........................................................................................................................................(2 marks)

(h) Give one example of another type of application found in the Application layer.

...........................................................................................................................................(1 mark)

(i) If two local area networks are connected through the Internet each must have aregistered public IP address.Name the type of organisation responsible for recording the allocation of public IPaddresses.

...........................................................................................................................................(1 mark)

END OF QUESTIONS

15

M/0105/CPT5

LEAVE MARGIN BLANK

12


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Mark Scheme GCE - Computing

10. (a) A set of rules/procedures; 1

(b) Bus; R Ethernet on its own 1

(c) Twisted pair//coaxial (cable)//optical fibre//fibre optic;1

(d) Need first octet or first and second octet or first, second and third octet to beidentical. Also must have four octets.For example:

R without full stops192.168.0.1192.168.0.2One mark for four octets;One mark for same LAN; 2

(e) (Use candidates example from (d))

(i) 192.168.0; 1

(ii) 1 or 2; 1

(f) a (unique) address/identifier assigned to network card // (unique) hardwareaddress/identifier; 1

(g) Any two tasks @ one eachAllocation of port numbers;Routing a packet/frame/segment to correct application/service;Splitting messages/data into packets // Disassembling messages // Assembling

packets;Adding TCP headers // Adding sequence nos;Error handling // sets parity bits;Checking that transmission successful;Resending transmission if necessary;A Sets packet size; 2

(h) Any one of the following applications for one mark;

Telnet;Internet browser;

http (client) // web server;email;FTP;TFTP;SMTP;R Non-networked applications such as word processor 1

(i) Internet Registry // Internet Registrar;A I.P. Registry/Registrar 1

Total 12


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Figure 4 shows the local area network(LAN) of the company.It consists of three Ethernet bus segments with IP addresses 192.80.0. x , 192.80.1. x and192.80.2. x connected together by routers.IP addresses that begin with 192 are private addresses.

The business hosts its own web site on a Web server with public IP address 213.97.56.21. The Web server and the local area network are connected to the Internet through a router andfirewall.

The local area network is a server-based network. There is one file server and domain controller, and one database and application server.

Figure 4

14

M/0205/CPT5

LEAVE MARGIN BLANK


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(b) Draw a diagram to show how segment 192.80.2. x would be wired using a hub.

(2 marks)

(c) Why must the router-firewall and the Web server have public IP addresses?

...........................................................................................................................................

...........................................................................................................................................(1 mark)

(d) The computer with IP address 192.80.2.4 uses the TCP/IP protocol to send a web pageto the Web server. Describe how the TCP/IP protocol is used to route the web page to

the Web server. Your description should cover the role of the two routers and networkcard addresses.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................(5 marks)



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(e) State one purpose of the firewall in this local network.

...........................................................................................................................................

...........................................................................................................................................(1 mark)

(f) The local area network is a server-based network . What is a server-based network?

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................(2 marks)

(g) What is a database server?...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................(1 mark)

END OF QUESTIONS

Copyright 2005 AQA and its licensors. All rights reserved.

16

M/0105/CPT5

LEAVE MARGIN BLANK

15


40/43


41/43

14

(d) Document(Web page) split into smaller chunks; A. segments/packets/framesDestination IP address doesnt match this segments IP address so document chunkssent to nearest router/default router/gateway;Using nearest router's network card address/MAC address;Router sends chunks to router connected to web server segment using its routing tables;

And using network card address of router connected to web server;This router sends chunks to Web Server;Web server rebuilds document;End to end connection established//port/socket connections made; max 5

(e) To block access to/from the internal private network from/to the Internet/world outside;To stop/limit/block/restrict certain kinds of access to the Web server, e.g. telnet;To close ports to prevent users from connecting to them;To block connections on unwanted ports;To prevent unauthorised access to the private computers;A. FilteringR To stop hackers (must state more than this = one of the above answers)

max 1(f) A network in which resource security/user authentication/ administration/resource

allocation;managed/controlled by/carried out by servers;ORA network in which servers provide specialist services (A. specific servers e.g. webservers) ;for client computers;ORShared information stored on servers;rather than individual PCs/client computers; 2

(g) A database server is software/computer that processes SQL requests from clientcomputers returning results to the clients across a network or using network protocols(the data resides on the same machine as the database server);Client requests data from server, server responds with data (require request, data andresponse); max 1

Total 15

Databaseserverlistens ona

particular port forclientrequests.TCP/IP

protocolused.


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8 The diagram shows a Local Area Network consisting of two subnets. A, F and G are desktopPCs.

8 (a) (i) Name the networking devices labelled C and E.

C ................................................................................................................................

E ................................................................................................................................ (2 marks)

8 (a) (ii) If the network ID of subnet L is 192.168.7 and the network ID of subnet R is192.168.8, what are the IP addresses at ports B and D?

B ................................................................................................................................

D ................................................................................................................................(1 mark)

8 (a) (iii) What would be a suitable subnet mask for this network?

....................................................................................................................................(1 mark)

8 (a) (iv) Give a suitable IP address for the desktop PC labelled G.

....................................................................................................................................(1 mark)

8 (b) (i) How many different host IDs does subnet L support?

....................................................................................................................................(1 mark)

8 (b) (ii) Explain your answer.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................(2 marks)

END OF QUESTIONS

Copyright 2008 AQA and its licensors. All rights reserved.

C E

A

Subnet L Subnet R

B D

F G

8 Areas outside the box wil l not be scanned

for marking

8

M/J un08/CPT5(08)


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8 a (ii) B 192.168.7.1

D 192.168.8.1

A

other numbers between 2 and 254 inclusive as last byte

(not 0 or 255) 1

8 a (iii) 255.255.255.0 R 255.255.255 R 255.255.255.x(where x is anything else) 1

8 a (iv) any in the range 192.168.8.2 to 192.168.8.254allow 192.168.8.1 if not used in (ii)R if same as 8a(ii) for D

1

8 b (i) 1

8 b (ii) 2

*Beca se onl the final b te is a ailable for hosts is eq i alent to there are 256 possible

(i) (ii)

253; Because only the final byte is available for hosts;*

But 0, 1 and 255 are reserved;


But 0 and 255 are reserved

// 1 and 255 are reserved

// 0 and 1 are reserved;


But 0/ 1 / 255 is reserved;

256; Because only the final byte is available for hosts;

1 mark

8 a (i) C Router; A Brouter; A Gateway;

E Switch/hub ; 2

a2 computer science - computer networking problems

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