BSc.(Hons) Computer Science with Network Security BEng (Hons) Telecommunications Cohort: BCNS/17B/FT Examinations for 2017-2018 / Semester 2 Resit Examinations for BCNS/15A/FT, BTEL/15B/FT & BTEL/16B/FT MODULE: NETWORKS MODULE CODE: CAN1102C Duration: 2 Hours 15 Mins Instructions to Candidates: 1. This examination is open textbook(s) and open notes (hardcopy only). Students are NOT permitted to use any computing or communication devices. 2. The exam paper consists of 2 sections (A and B). Answer all questions from each section. 3. Calculators are allowed. 4. Questions may be answered in any order but your answers must show the question number clearly. 5. Always start a new question on a fresh page. 6. Questions do not carry equal marks. 7. Total marks: 100. This question paper contains 3 questions and 11 pages. Page 1 of 11
QUESTION 1 :(50 Marks) ANSWER ALL QUESTIONS SECTION A Use the Multiple Choice Answer Sheet provided to answer the following MCQs. 1. In a connectionless-oriented service, what happens next after the receiver detects errors during transmission and the segment is discarded? a. The receiver verifies sender MAC and IP address b. The sender verifies the successful delivery of the segment with the receiver c. The receiver does not notify the sender that it has discarded the data d. Another segment is sent out automatically e. The sender stops sending data 2. What is the theoretical maximum size of the data portion of an UDP segment alone? a. 65,535 bytes b. 65,515 bytes c. 1,460 bytes d. 65,527 bytes e. 65,475 bytes 3. Which of the following best describe the function of a MAC address? a. It is used to physically locate a device on a network b. It is used to resolve domain name to IP address c. It is used to route packets across networks d. It is used to logically locate a device on a network 4. Which best describe the structure of an encapsulated protocol data unit (PDU)? a. Application header, Segment header, network header, data, segment trailer b. Frame header, Segment header, network header, data, frame trailer c. Frame header, segment header, data, segment trailer, frame trailer d. Frame header, network header, segment header, data, frame trailer 5. Which of the following is (are) invalid sequence number? a. 0 b. 1 c. 2 32 d. 2 32 1 e. -1 Page 2 of 11
6. You have been assigned a Class C address range and you need at least 30 subnets with 2 hosts per subnet for your organisation. Which subnet mask can you use? a. 255.255.255.242 b. 255.255.255.248 c. 255.255.255.240 d. 255.255.255.252 e. 255.255.255.0 7. Your ISP has provided you with the following address range 132.127.0.0 /24. Which of the following statements is (are) true about the network? a. There are 254 usable hosts per subnet b. There is one usable network c. There are 255 usable hosts per subnet d. There are 254 usable subnets 8. Using the following address and subnet mask 196.197.198.0 /24. What is the total number of (sub) networks and the total number of hosts per (sub)network? a. 1 network with 254 hosts b. 2 usable subnets with 126 hosts each c. 6 usable subnets with 30 hosts each d. 14 usable subnets with 14 hosts each 9. During the encapsulation process, what happens to data at Layer 3? a. The datagram is placed into a frame containing the physical address b. It stays in the form of data with some protocol info added to it c. The segment is placed into a datagram containing the logical address d. It is encoded into bits and readied for transmission 10. Which of the following concern(s) Layer 4? a. Best path selection for packet travel b. Window Size c. Encoding and Modulation d. Which form of data encryption to use e. Error Detection 11. Which layer is responsible for the formatting of data? a. Network b. Session c. Presentation d. OSI Layer 6 e. OSI Layer 4 Page 3 of 11
12. Which statement(s) about IPv6 addresses are true? 1) Leading zeros are required; 2) Two colons (::) are used to represent successive hexadecimal fields of zeros; 3) Two colons (::) are used to separate fields; 4) A single interface will have multiple IPv6 addresses of different types. a. 1 and 3 b. 2 and 4 c. 1, 3 and 4 d. 1, 2, 3 and 4 13. An optional feature of IPv6, the jumbo payload option, allows the exchange of packets with payloads of up to: a. 65536B b. 4 GB c. 1500B d. 532B. 14. Which of the following is a valid IPv6 address? a. 4021::240E::0AC0:3428:121C b. 4021:240E::0AC0:3428:: c. 4021::0000::240E::0000::0000:0AC0::3428::121C d. 4021:0:240E::0AC0:3428:121C 15. Which IPv6 address is equivalent to FF01::1? a. FF01:0:0:1 b. FF01:1:1:1 c. FF01:0:0:0:0:0:0:1 d. FF01:1:1:1:1:1:1:1 16. Which of the following is an invalid IPv6 address? a. 3111:2e::0ac0:1212:789c b. 4021:beef:cafe:3428 c. 0000:bad:dad:dead d. None of the above 17. Having entered http://www.google.mu in a web browser, the page fails to display. This is because of: a. Improper DNS configuration on the HTTP client b. congestion on the local area network c. HTTP server is incorrectly configured d. HTTP client does not have a Flash plug-in installed e. All of the above Page 4 of 11
18. The broadcast address of the second usable subnet in Class C where 4 bits were borrowed is? a. x.x.x.41 b. x.x.x.47 c. x.x.x.43 d. x.x.x.63 e. x.x.x.31 19. Which of the following destination address (es) is (are) located on the local network, if the source IP address is: 10011001.10101010.00100101.10100011 (represented in binary) a. 10011101.10101010.00100101.10100010 b. 10101010.10011001.10100011.00100101 c. 10011101.10101011.00100101.10100010 d. 10011001.10101010.11011011.01100110 e. 10011001.10101010.10101010.10101010 20. Star topologies are very commonly implemented, this could be because: a. Star topology performs well under heavy traffic b. Fairly easy to add or remove nodes in a star topology c. Star topology is relatively cheap to implement d. Star topology provides very good redundancy e. All of the above 21. Which of the following applies to UDP? a. It stands for Unreliable Datagram Protocol b. It provides a best effort service c. It provides error detection. d. It is used for time-sensitive application as it has minimal overhead e. All of the above. 22. Which of the following is true about switch-based LAN? a. Lack of traffic isolation b. Efficiently making use of switches in a LAN c. Difficult to manage users and groups d. The LAN should not have routers 23. Subnetting with subnet mask 255.255.240.0, which of the following might NOT be a subnet ID for that subnetting? a. 160 b. 80 c. 192 d. 132 e. 48 Page 5 of 11
24. Which field is used in TCP for flow control? a. Urgent pointer b. Checksum c. Sequence Number d. Acknowledgement Number 25. An organization is granted a block of addresses with the starting address 199.34.76.64 /28. How many usable host addresses are granted? a. 62 b. 16 c. 14 d. 6 e. 30 26. How many layers are there in the TCP/IP model? a. 5 b. 4 c. 7 d. 6 27. Given a Class A address has been subnetted (9 bits borrowed). What is the subnet mask? a. 255.255.0.0 b. 255.255.255.0 c. 255.255.128.0 d. 255.192.0.0 e. 255.255.192.0 28. Which best describe the structure of an encapsulated data unit a. Segment header, network header, data, segment trailer b. Segment header, network header, frame header, data, frame trailer c. Frame header, segment header, data, segment trailer d. Frame header, network header, segment header, data, frame trailer 29. refers to the structure or format of data, the order in which they are to be presented. a. Semantics b. Syntax c. Timing d. Protocol 30. In cyclic redundancy checking, the CRC is than the divisor. a. the same as b. one bit less c. one bit more d. zero bit Page 6 of 11
31. From the following statements, which should be FALSE? a. A network arranged in a star topology performs well under heavy load. b. A client typically has one network interface and does not route datagrams c. Transport Layer is responsible for end-to-end communication. d. Session Layer is responsible for data formatting. 32. A company requires 799 IP addresses. Which of the following set of class C blocks the company can use? a. 191.47.32.0; 191.47.42.0; 191.47.52.0; 191.47.62.0 b. 191.47.32.0; 191.47.33.0; 191.47.34.0 c. 191.47.32.0; 191.47.33.0; 191.47.34.0; 191.47.35.0 d. None of the above 33. Which layer is closest to the end-user? a. Transport Layer b. Application Layer c. Network Layer d. Presentation Layer 34. If you have an IP address of 128.129.130.131 and a subnet mask of 255.0.0.0, which of the following could be correct? a. You are subnetted for a class A address b. You are subnetted for a class B address c. That is an invalid subnet mask assignment d. None of the above 35. In transmission, the channel capacity is shared by both communicating devices at all times. a. simplex b. half-duplex c. full-duplex d. half-simplex 36. defines how a particular pattern is to be interpreted, and what action is to be taken. a. Syntax b. Semantics c. Timing d. None of the above 37. Given the IP address 200.1.2.0 and the subnet mask 255.255.255.224, what could be a potential subnet id? a. 200.1.2.128 b. 200.1.1.32 c. 200.1.2.64 d. 200.1.1.96 Page 7 of 11
38. A network has a host at IP address 1.9.2.192 with subnet mask 255.255.248.0. How many host addresses are usable? a. 254 b. 4,094 c. 8,190 d. None of the above 39. The layer is responsible for the delivery of a message from one process to another. a. application b. transport c. network d. physical 40. Which of the following is/are true about switches and routers? a. Both are store-and-forward devices b. Both have forwarding tables c. Switches have routing tables d. a, b and c are correct answers 41. The size of IP address in IPv6 is a. 4 bytes b. 128 bits c. 16 bytes d. 8 bytes e. 100 bits 42. The header length of an IPv6 datagram is a. 10 bytes b. 25 bytes c. 30 bytes d. 32 bytes e. 40 bytes 43. In the IPv6 header, the traffic class field is similar to which field in the IPv4 header? a. Fragmentation field b. Fast-switching c. ACK number d. ToS field e. Option field 44. IPv6 does not use type of address a. Broadcast b. Multicast c. Anycast d. Unicast e. None of the mentioned Page 8 of 11
45. These are the features present in IPv4 but not in IPv6. a. Fragmentation b. Header checksum c. Options d. a and b only e. a, b and c are correct answers 46. The field determines the lifetime of IPv6 datagram a. Hop limit b. TTL c. Flow label d. Next header e. None of the mentioned 47. Dual-stack approach refers to a. Implementing Ipv4 with 2 stacks b. Implementing Ipv6 with 2 stacks c. Node has both IPv4 and IPv6 support d. Synonym to Tunneling approach e. None of the mentione 48. Suppose two IPv6 nodes want to interoperate using IPv6 datagrams but are connected to each other by intervening IPv4 routers. The best solution here is a. Use dual-stack approach b. Tunneling c. No solution d. Replace the system 49. Which of the following is true when describing a multicast address? a. Packets addressed to a unicast address are delivered to a single interface. b. Packets are delivered to all interfaces identified by the address. This is also called a one-to-many address. c. Identifies multiple interfaces and is only delivered to one address. This address can also be called one-to-one-of-many. d. These addresses are meant for non-routing purposes, but they are almost globally unique so it is unlikely they will have an address overlap. 50. Which of the following is true when describing a unicast address? a. Packets addressed to a unicast address are delivered to a single interface. b. These are your typical publicly routable addresses, just like a regular publicly routable address in IPv4. c. These are like private addresses in IPv4 in that they are not meant to be routed. d. These addresses are meant for non-routing purposes, but they are almost globally unique so it is unlikely they will have an address overlap. Page 9 of 11
SECTION B QUESTION 2 :(25 Marks) (a) A user enters the following valid URL of the 2018 blockbuster movie http://www.marvel.com/avengersinfinitywar/index.html in a modern web browser and is unable to display the said web page. (i) Suggest one way how you could test whether there is some problem with your DNS server. (ii) Suggest one way how you could test whether there is some problem with the HTTP server itself. (iii) Suggest two other possible causes that might prevent the web page from displaying. (b) Suppose you have just joined a company as a network technician. You are been given some tasks to accomplish by the system engineer as well as to test your knowledge. (i) The system engineer requests you to configure a host with IP address: 192.168.13.175 on a network with subnet mask of 255.255.255.240. Is there a problem? If so, what is it? (ii) Secondly, you are given an IP Host address of 15.16.193.6 with a subnet mask of 255.255.248.0. Calculate the subnet address, broadcast address and host addresses of the subnet. Show all details. (10 Marks) (5 Marks) (10 Marks) Page 10 of 11
QUESTION 3 :(25 Marks) (c) A router performing the fragmentation follows a specific algorithm to divide the message into fragments for transmission. The exact implementation of the fragmentation process depends on the type of router. For this example, an IP message 12,000 bytes long (including the 20-byte IP header) needs to be sent via router R1 with a MTU of 3,300 bytes for network A while router R2 will fragment incoming frames at a MTU of 1,300 bytes for network B. Describe the M bit [More Fragment] and the Offset field for IP fragments passing over Network A and Network B via routers R1 and R2 respectively. Determine the size of each fragment formed. (10 + 15 Marks) ***END OF QUESTION PAPER*** Page 11 of 11