9
Figure 6 shows the topology of a particular computer network that is divided up into segments. Figure 6 File Server Segment 192.168.0 Wireless Access Point Router 1
Segment 192.168.1
C
A
B Router 2
Router and Firewall
Switch
157.44.12.3
Segment 192.168.2
Internet
9
(a)
Suggest suitable IP addresses for:
9
(a) (i)
the “Router 2” port labelled A: ............................................................................................
9
(a) (ii) the “Router 2” port labelled B: ...........................................................................................
9
(a) (iii) the computer network interface card labelled C: ............................................................... (3 marks)
9
(b)
What physical network topology is used within segment 192.168.2 to connect the computers to the switch? ............................................................................................................................................ (1 mark)
9
(c)
When the computers in segment 192.168.2 were configured on the network, they were programmed with a subnet mask. What is the purpose of a subnet mask, and what would the subnet mask be in this case? Purpose: ................................... ................................... ................................... ...................
............................................................................................................................................ Subnet mask: .................................. ................................... .................................... ............
9
............................................................................................................................................ (2 marks) (d)
Laptop computers connect to the network wirelessly using Wi-Fi. Wireless communication communicati on is less secure than communicatio communication n using cables. Explain two measures Explain two measures that the Wireless Access Point could use to improve the security of the network. Measure 1: ................................. ................................... ................................... ...................
............................................................................................................................................
............................................................................................................................................ Measure 2: ................................ ................................... ................................... ...................
............................................................................................................................................
............................................................................................................................................ (2 marks)
Question 9 continues on the next page
9
(c)
When the computers in segment 192.168.2 were configured on the network, they were programmed with a subnet mask. What is the purpose of a subnet mask, and what would the subnet mask be in this case? Purpose: ................................... ................................... ................................... ...................
............................................................................................................................................ Subnet mask: .................................. ................................... .................................... ............
9
............................................................................................................................................ (2 marks) (d)
Laptop computers connect to the network wirelessly using Wi-Fi. Wireless communication communicati on is less secure than communicatio communication n using cables. Explain two measures Explain two measures that the Wireless Access Point could use to improve the security of the network. Measure 1: ................................. ................................... ................................... ...................
............................................................................................................................................
............................................................................................................................................ Measure 2: ................................ ................................... ................................... ...................
............................................................................................................................................
............................................................................................................................................ (2 marks)
Question 9 continues on the next page
9
(e)
The computers in segment 192.168.1 use Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to determine when to transmit data. Explain how the CSMA/CD method is used, including what happens in the event of a collision occurring. In this question you will also be assessed on your ability to use good English and to organise your answer clearly in complete sentences, using specialist vocabulary where appropriate.
............................................................................................................................................
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............................................................................................................................................
............................................................................................................................................ (6 marks)
____ 14
9
(a)
(i)
192.168.0.x 192.168.0. x where x is not 0 or 255;
1
9
(a)
(ii)
192.168.2.x 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 is different to the one in (ii)
1
9
(b)
Star;
1
9
(c)
Identify which other computers are on same segment // can have packets/data sent directly to them; Identify which other computers are on a different segment // must have packets/data sent to them via the router; R network for subnet MAX 1 255.255.255.0 255.255.25 5.0 / FFFFFF00 FFFFFF0 0 / 111111111111111111 11111111111111111111111100000000; 11111100000000;
2
Use of WEP/Wired Equivalent Privacy/WPA/WiFi Protected Access; (Strong) encryption of transmitted data; R encoding User/computer must enter/send a passphrase/certificate passphrase/certificate at start of communication before laptop allowed to connect; A key for passphrase A only allow password if used in correct context; Access point checks checks MAC/hardware MAC/hardware address of laptop laptop and only allows allows computers with a MAC/hardware address in a list of approved addressed to connect; R IP address Disable broadcast of SSID/identity; Reduce / limit power of transmitter; MAX 2
2
9
(d)
15
Computing COMP3 - AQA GCE Mark Scheme 2010 June series
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 two packets/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 stop other computers sending data; Computer that detected collision also stops sending data; Then waits a random period before attempting to retransmit/repeating transmission/this process; Period is random to reduce likelihood of collision recurring (between computers that caused collision); If a collision occurs again then waits a longer random time before attempting to transmit again; Use of exponential back-off algorithm to determine wait time; Mark Bands and Description 5-6 To achieve a mark in this band, candidates must meet the subject criterion (SUB) and 4 of the 5 quality of written communication criteria (QWCx). SUB Candidate has produced a detailed description of how CSMA/CD works, including what happens 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 purpose and has expressed ideas clearly and fluently. QWC4 Sentences and paragraphs follow on from one another clearly and coherently. QWC5 Appropriate specialist vocabulary has been used. 3-4 To achieve a mark in this band, candidates must meet the subject criterion (SUB) and 4 of the 5 quality of written communication criteria (QWCx). SUB Candidate has produced a reasonable description which may or may not cover what happens in the event of a collision (at least 3 points). 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, with occasional lapses. The candidate has expressed ideas clearly and reasonably fluently. QWC4 The candidate has used well-linked sentences and paragraphs. QWC5 Appropriate specialist vocabulary has been 16
8
Figure 5 shows the topology of a particular computer Local Area Network (LAN) that is divided up into segments. Figure 5 File Server Segment 192.168. 0
Router 1
A
Segment Segment 192.168.1 192.168.1
B Router 2 Segment Segment 192.168.2 192.168.2
Router and Firewall
150.14.12.88 150.14.12.88
Internet Internet
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 were programmed with a subnet mask. What subnet mask should have been used? .......................................................................................................................................... (1 mark)
8 (c)
The LAN has a bus topology and has been divided into segments. Explain why the LAN has been segmented. ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................ (2 marks)
8 (d)
Alternatively, the LAN could have been constructed using a star topology.
8 (d) (i) State one advantage of using a bus topology and explain how the advantage is achieved. ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................ (1 mark) 8 (d) (ii) State one advantage of using a star topology and explain how the advantage is achieved. ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................ (1 mark) Question 8 continues on the next page
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 cut the number of collisions* ; A faster operation/transmission; Explanation: by cutting the number of collisions* //by reducing the number of stations/computers connected to each section of cabling// because two computers in one segment can communicate at the same time 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 explanations
Max 2
Less expensive as reduced cabling requirement; No reliance on central node as data does not all travel through one node; A less cabling required without reference to reduced cost if candidate has explained why less cables are needed A computer/station for node Must have explanation as well as advantage for mark
Max 1
Improved security as: data only travels down one link // is not sent throughout network // is not sent to all nodes; Improved reliability as if one link fails the other links/nodes are not affected; Speed of link remains constant // speed not affected by number of connections/collisions // faster connection as: no collisions/links not shared; A cable for link R responses about terminal/computer failure Must have explanation as well as advantage for mark
Max 1
• • •
8
8
(d)
(d)
(i)
(ii)
10
5
Do not write outside the box
A student is using her computer at school. Figure 8 shows the physical topology of the Local Area Network (LAN) to which her computer is connected. The LAN is divided up into segments. It also shows a web server that her computer connects to through the Internet. The student is using computer C . Figure 8
Segment 192.168.0
File server
A
B
C
Router 1
D
Segment 192.168.1
E
Router 2
Segment 192.168.2
Switch
Gateway
Internet Web server
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 student’s computer, labelled C
5 (b)
(10)
............................................................................................................................................ (3 marks) What physical network topology is used within segment 192.168.1? ............................................................................................................................................ (1 mark)
M/Jun13/COMP3
Do not write outside the box
11
5 (c)
When the computers in segment 192.168.1 were configured on the network, they were programmed 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 D on Figure 8. This file server uses a server operating system. Explain what a server operating system is.
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................ (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 is less secure than communication using cables.
5 (e) (i) Describe one measure that could be implemented by the Wireless Access Point to improve the security of the network.
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................ (1 mark) 5 (e) (ii) Explain why Wi-Fi has been chosen for this connection rather than Bluetooth.
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................ (1 mark)
Question 5 continues on the next page
Turn over
(11)
M/Jun13/COMP3
12
Do not write outside the box
Figure 8 is repeated below so that you can answer question part 5 (f) without having to turn back in the question paper booklet. Figure 8 (repeated) Segment 192.168.0
File server
A
B
C
Router 1
D
Segment 192.168.1
E
Router 2
Segment 192.168.2
Switch
Gateway
Internet Web server
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 uploading to the web server will be routed from her computer in the United Kingdom to the web server that is located in Chicago in the United States of America. You may assume that the web browser software on the student’s computer has already looked up, using a 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 student’s computer to the gateway and how, once it has reached the gateway, the packet will be routed across the Internet to 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 to organise your answer clearly in complete sentences, using specialist vocabulary where (8 marks) appropriate.
(12)
M/Jun13/COMP3
Do not write outside the box
13
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............................................................................................................................................ Your answer to question 5 (f) may be continued on the next page
Turn over
(13)
M/Jun13/COMP3
14
Do not write outside the box
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5 (g)
The web server has a routable IP address. The student’s computer has a non-routable IP address.
Explain two differences between routable and non-routable IP addresses. Difference 1: ................................... ................................... .................................... ............
............................................................................................................................................ Difference 2: ................................... ................................... .................................... ............
............................................................................................................................................ (2 marks)
____ 18
(14)
M/Jun13/COMP3
5
(a)
(i)
192.168.0.x where x is not 0 or 255; Must be a specific IP address R. 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 address R. addresses that include port numbers
1
5
(a)
(iii)
192.168.1.y where y is not 0 or 255 and is not the same as x in (ii); Must be a specific IP address R. addresses that include port numbers
1
8 of 24
MARK SCHEME – A-level Computing – COMP3 – June 2013
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 example of accessing files is not enough as this is in the question there needs to be additional explanation if files is used as an example, e.g. managing quotas, security of files. R. answers that imply that server does all processing i.e. confusion with thin client.
1
Use of Wired Equivalent Privacy/WEP/ WPA/WPA2/WiFi Protected Access; (Strong) encryption of transmitted data // use of Advanced Encryption Standard/AES; R encoding Use of Extensible Authentication Protocol/EAP; User/computer must enter/send a passphrase/certificate at start of communication before laptop allowed to connect; A key for passphrase A only allow password if used in correct context ie for accessing network, not for logging on to a sever or just having a password Access point checks MAC/hardware address of laptop and only allows computers with a MAC/hardware address in a list of approved addresses to connect; R IP address Disable broadcast of SSID/identity; Reduce / limit power of transmitter; Use of two/multi-factor authentication;
1
Longer range // faster transmission speeds // higher bandwidth // more simultaneous connections; A. reverse of points e.g. "Bluetooth only has a short range" R. Bluetooth can only connect two devices at once
1
5
5
(e)
(e)
(i)
(ii)
9 of 24
MARK SCHEME – A-level Computing – COMP3 – June 2013
5
(f)
SUBJECT MARKING POINTS: Internal:
Student’s computer uses subnet mask (and destination/web server’s IP address) to determine if destination computer/web server is on same subnet // identify not on same subnet Up to two marks from description (in separate section below) of how subnet mask is used Packet is sent (from student’s computer) to Router (1) Router 1 identifies that destination is outside the 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 passed back down a hierarchy Path to take selected by each router (not determined at start) NE passed from router to router Route may change as a result of e.g. congestion, technical problems
8
Either:
(Possible) repackaging of packet to use different protocol (e.g. Gateway may change protocol) Route determined using the (Network ID part of the destination) IP address (Note: can infer "IP address" if just "address" is stated, if previously candidate has written about an IP address) Use of router tables / criteria to determine next hop / (step of) path Router decrementing "time to live" of packet Source and destination MAC addresses changed at each router // MAC addresses used for each “hop”
How subnet mask us ed (MAX 2 points):
AND operation of subnet mask with student’s computer’s IP address AND operation of subnet mask with web server’s 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
10 of 24
MARK SCHEME – A-level Computing – COMP3 – June 2013
A interchangeable use of subnet ID and network ID HOW TO AWARD MARKS: Mark Bands and Descrip tion 7-8 To achieve a mark in this band, candidates must meet the subject criterion (SUB) and all 5 of the quality of language criteria (QLx). SUB Candidate has covered both internal and external routing in detail and has made at least seven subject-related 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 purpose and has expressed ideas clearly and fluently. QWC4 Sentences (and paragraphs) follow on from one another clearly and coherently. QWC5 Appropriate specialist vocabulary has been used. 5-6 To achieve a mark in this band, candidates must meet the subject criterion (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 more detail than the other and has made at least five subject-related points. 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, with occasional lapses. The candidate has expressed ideas clearly and reasonably fluently. QWC4 The candidate has used welllinked sentences (and paragraphs). QWC5 Appropriate specialist vocabulary has been used. 1-4 To achieve a mark in this band,
11 of 24
MARK SCHEME – A-level Computing – COMP3 – June 2013
0
candidates must meet the subject criterion (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 of them. Up to four relevant points have been made. QWC1 Most of the text is legible. QWC2 There may be some errors of spelling, punctuation and grammar but it should still be possible to understand most of the response. QWC3 The candidate has used a form and style of writing which has many deficiencies. Ideas are not always clearly expressed. QWC4 Sentences (and paragraphs) may not always be well-connected. QWC5 Specialist vocabulary has been used inappropriately or not at all. Candidate has made no relevant points.
Note: Even if English is perfect, candidates can only get marks for the points made at the top of the mark scheme for this question. If a candidate meets the subject criterion in a band but does not meet the quality of language criteria then drop mark by one band, providing that at least 4 of the quality of language criteria are met in the lower band. If 4 criteria are not met then drop by two bands.
12 of 24
MARK SCHEME – A-level Computing – COMP3 – June 2013
5
(g)
Any two points from the list below. Candidate only needs to make one side of point, the other can be implied. Do not award marks for two sides of same point. Routable Non-Routable (Globally) Many computers/devices unique. may have same address. Allocated by a Not allocated centrally // central/regional allocated by a home issuing authority user/company/ISP. ( A example). Can be Difficult/impossible to connected to connect to over Internet // directly over the from outside of network. Internet / from outside private network Owner can be Owner cannot be looked looked up using up using WHOIS protocol WHOIS protocol A. non-routable IP addresses more secure as cannot be connected to over Internet/from outside network A. can identify location from a routable IP address
2
13 of 24
Figure 6below shows the local area network (LAN) of the supermarket chain’s head office. It consists of three Ethernet bus segments with IP addresses 192.80.0, 192.80.1 and 192.80.2 connected 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 public IP address 213.97.56.21. The Web server and the local area network are connected to the Internet through a router and firewall. The local area network is a server-based network. There is one file server and domain controller and one print server. 192.80.1.5 Segment 192.80.0
192.80.0.1
192.80.1.2
192.80.1.3
File server & Domain controller
192.80.1.4
Segment 192.80.1
Router 192.80.1.1
Print Server 192.80.0.2
Router 192.80.2.1 192.80.2.2 192.80.2.3
192.80.2.4 192.80.2.5
Web server
213.97.56.21
192.80.0.3
Router 213.97.56.19 & Firewall
Internet
Figure 6
M/0104/CPT5
Segment 192.80.2
LEAVE MARGIN BLANK
15 (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 theWeb server have public IP addresses? ........................................................................................................................................... ........................................................................................................................................... (1 mark)
(f) The computer with IP address 192.80.1.3 uses the TCP/IP protocol to send a document to be printed to the print server. Describe how theTCP/IP protocol is used to route the document to its destination. Your description should cover the role of the two routers and network card addresses. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (5 marks)
LEAVE MARGIN BLANK
16 (g) Stateonepurpose of the firewall in this local network. ........................................................................................................................................... ........................................................................................................................................... (1 mark)
(h) The local area network is a ser ver-based network . What is meant by a server-based network? ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (2 marks) 15
END OF QUESTIONS
Copyright © 2004 AQA and its licensors. All rights reserved
(d)
One mark for central hub and one mark for computers connected to hub as shown NB If hub incorrect answer scores zero If hub correct but computers incorrect answer scores one mark Router can be replaced by a computer labelled with router's IP address
Router
Don't have to label computers with their IP addresses. A. IP addresses in place of computers + router
Switch
2
(e)
So that these are reachable from anywhere on the Internet//so that can be seen/reached from the world outside; R. So can be reached by another branch of supermarket
1
(f)
(g)
(h)
Document split into smaller chunks; A. segments/packets/frames Destination IP address doesn’t match this segment’s 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
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
A network in which resource security/user authentication/ administration/resource allocation; managed/controlled by/carried out by servers;
2 Total
15
Grand Total
65
10
LEAVE MARGIN BLANK
6 The head office of an organisation consists of several large off ices, each with many computers linked as a local area network (LAN). The LAN also links to the Internet via a router and firewall. In each office, the computers are linked as a segment as shown in Figure 4. Figure 4
(ii)
Router & Firewall
Node A
(iii)
Router
Node B
172.31.15.3
Node A
Internet
(i)
Node B
Router
Node C
.............
172.31.15.4
Node C
.............
172.31.19.4
Node X
Segment 172.31.15
NodeY
Segment 172.31.19
. . . . . . . . . Segment 172.31.1 . . . . . . . . .
Node A Router
Node B
Node C
.............
172.31.45.4
Node Z
Segment 172.31.45
(a) IP addresses that begin with 172.31 are non-routable addresses. Why are these used within the LAN? ............................................................................................................................................. ............................................................................................................................................. (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)
(10)
M/J an08/CPT5
11
LEAVE MARGIN BLANK
(c) Give two reasons for segmenting this LAN. 1........................................................................................................................................... ............................................................................................................................................. 2........................................................................................................................................... ............................................................................................................................................. (2 marks)
(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 used to determine whether the computers are on the same subnet. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (3 marks)
10
(11)
M/J an08/CPT5
6
(a)
because machines do not need a direct presence on the Internet; more secure; A private addresses; R machines don’t need access to the Internet devices 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;
6 6
(d) (d)
(i) (ii)
to restrict access; A to improve security; to increase the number of addresses available // too many devices to address on one subnet; problems can be more easily isolated to one segment;
2
255.255.255.0 // 1111 1111 1111 1111 1111 1111 0000 0000 ;
1
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 isolate subnet IDs/network address; (or by example) subnet IDs compared; if same, then on same subnet; if matches NE
8
3
The binary numbers are provided so you can check the answers when a candidate uses them to explain. They are not worth marks by themselves.
10
LEAVE MARGIN BLANK
6
A school Local Area Network (LAN) uses the TCP/IP protocol to communicate between computers. (a) What is a protocol? ............................................................................................................................................. ............................................................................................................................................. (1 mark)
(b) Complete the diagram of theTCP/IP protocol stack below: Application Layer
(i)
(1 mark)
(ii)
(1 mark)
Data Link Layer
(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 Ethernet MAC address? ............................................................................................................................................. (1 mark)
(d) The school now wants to connect to the Internet. Every computer in the LAN is given an 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)
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(iii) What could the school do if it needs more host IDs? .................................................................................................................................... .................................................................................................................................... (1 mark)
(iv) IP addresses starting with 192.168 are private addresses. Why were private addresses chosen for the individual computers on the network? .................................................................................................................................... .................................................................................................................................... (1 mark)
(e) The school registers the IP address 222.125.105.15 with the Internet registrar. How can this IP address be used to connect to the Internet? ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. (2 marks)
11
M/J an07/CPT5
Turn over
▲
6
(a)
a set of rules/procedures;
(b)
(i)
Transport (Layer);
1
(ii)
Network (Layer);
1
(iii)
telnet; http (client) // web server // IRC Client Server;
(c)
1
email;
internet/web browser;
FTP;
snmp;
TFTP;
A instant
SMTP;
https;
max 1
3
a (unique) address / identifier assigned to network card // (unique) hardware address/identifier;
(d)
messaging / VoIP;
(i)
A code R name
instead of address
1
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
(iii)
change the subnet mask // get another network ID // get class A or B
A
256, 255, 253
1
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
(e)
4
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 computer’s private IP address;
max 2 Total
10
11
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6 A small organisation, Acme Consultants, with four stand-alone computers in an office, want to set up a peer-to-peer network in order to share the printer connected to one of the computers. (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 the physical layout of the network.
(2 marks)
(c) It is decided to set the IP addresses for each computer manually and use a subnet mask of 255.255.255.0. (i) The following IP addresses were used for the computers: Computer A: 192.168.5.2 Computer B: 192.168.5.3 Computer C: 192.168.4.4 Computer 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 ADSL line. 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 Internet Protocol (TCP/IP) Properties
?
X
General You can get IP settings assigned automatically if your network supports this capability. Otherwise, you need to ask your network administrator for the appropriate IP settings. Obtain an IP address automatically Use the following IP address: IP address:
1925 . 21685 . 255 . 22
Subnet mask:
2555 . 22555 . 255 . 20
Default gateway:
1925 . 21685 . 255 . 22
(iii) Figure 4above shows part of theTCP/IP configuration window displayed on the monitor of computer A. What IP address should be entered for the Default gateway? ...................................................................................................................................... (1 mark)
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M/J an06/CPT5
Turn over
▲
AQA GCE Mark Scheme, 2006 January series – CPT5
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) Computer/PC
Computer/PC
T.O. if
a server included in diagram boxes I routers / modems I
Switch
Computer/PC
Computer/PC
Printer
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; iii) 0-255; more correctly: 1-254;
1 R a specific IP address
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
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14
10 Figure4 shows the TCP/IP protocol stack applied to a LAN (Local Area Network). Application
FTP protocol FTP client
FTP server
Transport TCP protocol TCP
TCP
Network IP protocol IP
Link
IP
Ethernet protocol Ethernet driver
Ethernet driver Ethernet cable
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)
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15 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 to route Ethernet frames. What is an Ethernet MAC address? ........................................................................................................................................... (1 mark)
(g) Describe two tasks performed by the TCP protocol layer 1 ........................................................................................................................................ 1 ........................................................................................................................................ 2 ........................................................................................................................................ 1 ........................................................................................................................................ (2 marks)
(h) Give oneexample 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 a registered public IP address. Name the type of organisation responsible for recording the allocation of public IP addresses. ........................................................................................................................................... (1 mark)
END OF QUESTIONS
M/0105/CPT5
12
Mark Scheme
10.
GCE -
Computing
(a)
A set
of rules/procedures;
(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 be identical. Also must have four octets. For example: R without
192.168.0.1 192.168.0.2 One mark for four octets; One mark for same LAN;
(g)
(h)
(i)
full stops
2
(Use candidate’s example from (d))
(e)
(f)
1
(i)
192.168.0;
1
(ii)
1 or 2;
1
a (unique) address/identifier assigned to network card // (unique) hardware address/identifier;
1
Any two tasks @ one each Allocation 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
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
Internet Registry // Internet Registrar; A I.P. Registry/Registrar
1 Total
12
14 Figure 4shows the local area network(L AN) of the company. It consists of three Ethernet bus segments with IP addresses 192.80.0.x , 192.80.1.x and 192.80.2.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 and firewall. 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
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15 (b) Draw a diagramto 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 page to the Web server. Describe how the TCP/I P protocol is used to route the web page to the Web server. Your description should cover the role of the two routers and network card addresses. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (5 marks)
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16 (e) Stateonepurpose of the firewall in this local network. ........................................................................................................................................... ........................................................................................................................................... (1 mark)
(f) The local area network is aser ver-based network . What is a server-based network? ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (2 marks)
(g) What is a database server? ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (1 mark)
15
END OF QUESTIONS
Copyright ©2005 AQA and its licensors. All rights reserved.
M/0105/CPT5
(b) One mark for central hub and one mark for computers connected to hub as shown NB If hub incorrect answer scores zero If hub correct but computers incorrect answer scores one mark Don't have to label Router can be replaced by a computer labelled with router's computers with IP address their IP addresses. Router
Switch
A. IP addresses in place of computers + router
Don't have to label server if drawn as shown
2 (c) So that these are reachable from anywhere on the Internet//so that can be seen/reached from the world outside; A. So that they can be uniquely identified. R. So can be reached by another branch of company 1
13
(d) Document(Web page) split into smaller chunks; A. segments/packets/frames Destination IP address doesn’t match this segment’s IP address so document chunks sent 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. Filtering R 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; OR A network in which servers provide specialist services (A. specific servers e.g. web servers) ; for client computers; OR Shared information stored on servers; rather than individual PCs/client computers; 2 (g) A database server is software/computer that processes SQL requests from client computers returning results to the clients across a network or using network protocols Database (the data resides on the same machine as the database server); server Client requests data from server, server responds with data (require request, data and listens on response); max 1 a particular port for Total 15 client requests. TCP/IP protocol used.
14
8
Areas outside the box wil l not be scanned for marking
8 The diagramshows a Local Area Network consisting of two subnets. A, F and G are desktop
PCs. Subnet L
Subnet R
D B
E
C
A F 8
(a)
G
(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 is 192.168.8, 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
8
Copyright ©2008 AQA and its licensors. All rights reserved.
(08)
M/J un08/CPT5
