BSc (Hons) Business Information Systems, BSc (Hons) Computer Science with Network Security. Cohort: BIS/16B/FT & BCNS/16B/FT

Transcription

1 BSc (Hons) Business Information Systems, BSc (Hons) Computer Science with Network Security Cohort: BIS/16B/FT & BCNS/16B/FT Examinations for Semester 2, 2017 Semester 1 Resit Examinations for BCNS/16A/FT, BIS/14B/FT, BIS/15A/FT & BIS/15B/FT MODULE: NETWORKS MODULE CODE: CAN1101C Duration: 2 Hours Instructions to Candidates: 1. Answer ALL questions. 2. Questions may be answered in any order but your answers must show the question number clearly. 3. Always start a new question on a fresh page. 4. Use of calculator is allowed. 5. Total marks 100. This question paper contains 4 questions and 5 pages. Page 1 of 5

2 ANSWER ALL QUESTIONS QUESTION 1: (25 MARKS) a) Figure 1 shows an extract from a network packet sniffer. Figure 1 (i) Name the Transport protocol in use. Hence, list the features of this Transport protocol. Give the destination port and source port of the message? Why do we have both a source and a destination port number? To which IP address is the message sent? To which device does this address refer to? Give the purpose of this message. ( marks) b) Answer the following questions in relation to the extract from a network packet sniffer in figure 2. (i) Give the purpose of the Sequence number 5793 and the Acknowledgement number 234. (v) (vi) What does the checksum represent? Explain the purpose of the line Window size value 939. Hence, explain the use of this feature. What does the line 5 Reassembled TCP Segments mean? Name the application protocol of this message. Is this a request or a reply message? Explain your answer. ( marks) Page 2 of 5

3 Figure 2 QUESTION 2: (25 MARKS) a) List the layers of the OSI Model. Why is the model layered? b) Describe briefly the three important network layer functions. c) In a distance vector algorithm, such as RIP, routers calculate the least cost path in an iterative, distributed manner and builds up a routing table. In the following diagram, give the routing table for node B. (Show your workings) Page 3 of 5

4 d) UDP and TCP use 1's complement for their checksums. Suppose you have the following three 8-bit words: , , and Calculate the checksum that is sent along with the data, showing your workings. e) A datagram of 3750 bytes has to travel over a network with a MTU size of 1400 bytes. Describe how fragmentation can address this issue. You should give the value of the 3 key fields used in fragmentation for each fragment created. QUESTION 3: (25 MARKS) a) Each host on the Internet is currently assigned an IP address 32 bits long (Ipv4). Ipv4 addresses are usually written as a series of four decimal numbers. IPv4 addresses traditionally belong to one of five classes of address, depending on the type of network. There are two hosts A and B with addresses and with subnet mask (i) What is the purpose behind subnetting? Show all the range of hosts and IP addresses for this subnet mask. Can the two devices communicate directly? Give your reasons. Assuming they cannot communicate directly, propose a solution to allow the two devices to communicate. ( marks) b) One of the main features of a network is security. Encryption such as the Caesar cypher can be used to improve security. Explain, with an example, how Caesar cypher works. Name its advantages, and explain why it is not used. ( marks) Page 4 of 5

5 c) A bridge is a link layer device that stores and forwards Ethernet frames. One of its characteristics is that a bridge is self-learning. Bridges also do not offer protection against broadcast storms. (i) Show, by means of a diagram, how a bridge learns. Explain what is a broadcast storm is and how it can take place. (4 + 2 marks) d) Briefly describe two advantages and two disadvantages of fiber optics over copper cables. QUESTION 4: (25 MARKS) You have been appointed as the Security Consultant of a retail shop selling automotive spare parts. The staff of the shop uses a server to share resources and use the POS system. The staff provides free Wi-Fi to customers, but the connections must be monitored and limited. An IP camera system of 10 cameras covers the whole shop and parking. Your task is to describe the necessary infrastructure, topology and configuration required to provide resources and Wi-Fi to staff and customers, and identify the risks associated with a Wi-Fi connection to the shop s network. Hence, describe the steps to mitigate and test these risks, to prevent compromising the shop s data security. Your answer should be around 300 words and include all necessary diagrams. (25 marks) *** END OF QUESTION PAPER *** Page 5 of 5