B.Sc. (Hons.) Computer Science with Network Security B.Eng. (Hons) Telecommunications B.Sc. (Hons) Business Information Systems Bridge BTEL/PT BCNS/14/FT BIS/14/FT BTEL/14/FT Examinations for 2014-2015 / Semester 2 MODULE: NETWORKS MODULE CODE: CAN1102C DURATION: 2¼ HOURS Instructions to Candidates 1. Attempt Section A and any one question each from Section B, C and D. 2. Always start a new section on a fresh page. 3. Questions carry unequal marks. 4. Maximum marks achievable: 100 5. Use of silent calculators is permitted in the Examination Room. 6. Appendix is provided This question paper contains a MCQ Section and 6 questions and 8 pages. Page 1 of 8
SECTION A (30 marks) Attempt the 15 Multiple Choice Questions in this Section There is only one correct response per multiple choice question. 1. How many responses does a host expect to get when it sends an ARP request? a) Unlimited, because it broadcasts the message b) One, because only the destination reply c) None, if the destination is not available at that moment to reply d) b and c 2. If you have an IP address of 17.0.0.0 and a subnet mask of 255.255.0.0, which of the following could be correct? a) You are subnetting for a class C address b) You are subnetting for a class A address c) You are subnetting for a class B address d) That is an invalid address assignment 3. In a connectionless-oriented service, what happens next after the destination computer detects errors during transmission and thus discards the data? a) The destination device verifies source MAC address b) The source device verifies the successful data delivery with the destination c) The destination device does not notify the source that it has discarded data d) None of the above 4. What is the theoretical maximum size of an IPv4 datagram? a) 65,535 bytes b) 32,787 bytes c) 32 bits d) 32 bytes 5. 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 6. Which best describe the structure of an encapsulated data packet a) Segment header, network header, data, segment trailer b) Segment header, network header, data, frame trailer c) Frame header, network header, segment header, data, frame trailer d) None of the above 7. Which one does not apply to UDP? a) Stands for User Datagram Protocol b) Is a best-effort delivery system c) Uses software to reassemble segments when they reach destination d) It is a connectionless-oriented protocol Page 2 of 8
8. Which field is used in TCP for error detection? a) Checksum b) Sequence Number c) Acknowledgement Number d) Source Port 9. Which of the following is the correct bit pattern of the first octet for a Class C IP address? a) 0xxx xxxx b) 10xx xxxx c) 110x xxxx d) 1110 xxxx 10.Which one of the following is the function to be made by the Transport layer? a) Best path selection for packet travel b) Encoding and Modulation c) Data Encryption d) Reliable Data Transfer 11. Which layer is closest to the end-user? a) Transport Layer b) Network Layer c) Application Layer d) Physical Layer 12. From the following statement, which one is FALSE? a) A client typically has one network interface and does not route datagrams b) Transport Layer is responsible for end-to-end communication. c) Session Layer is responsible for data formatting d) None of the above 13.In a Class C address where 4 bits have been borrowed for subnetting. bits are left for host addresses. a) 24 b) 20 c) 16 d) 4 14. The source and destination address appear in an IP s packet. a) Footer b) Header c) Field d) Trailer 15.Using a Class C address, you need five subnets with a maximum of 18 hosts on each of those subnets. Which subnet mask would you use? a) 255.255.255.192 b) 255.255.255.224 c) 255.255.255.240 d) 255.255.255.248 Page 3 of 8
SECTION B (30 marks) ANSWER ONLY ONE QUESTION IN THIS SECTION QUESTION 2 (a) HTTP is stateless. Discuss this statement. (2 marks) (b) What are the three main ways of authenticating a person? Provide an example of each method. (c) What are the principles for congestion control? (3 marks) (d) FTP is protocol used for the delivery of files across networks. Describe how FTP works. (5 marks) (e) FTP is said to have an out-of-band connection. Explain what it means. (2 marks) (f) List the mechanisms for web site to identify users? Give examples for suitable use of the mechanism. (2 marks) (g) Describe the difference between the network and transport layers. (2 marks) (h) Describe the difference between multiplexing and demultiplexing. (4 marks) (i) Why are both source port number and destination port number required for communication? (2 marks) (j) How does a host get its IP Address? (2 marks) Page 4 of 8
QUESTION 3 (a) HTTP and DNS are two very important application layer protocols for the Internet. i. Explain the difference in operation between HTTP v1.0 and HTTP v1.1. ii. Explain why the DNS protocol is important and how it works. iii. Give a sample HTTP response message with at least 4 main header lines that is sent by the web server. iv. Determine whether HTTP and DNS protocols are connection-oriented or connectionless-oriented and state the port numbers used by both protocols.. (3+4+2+2 marks) (b) Authentication and Authorization are two important network security services. i. Explain what you understand by authentication. ii. Describe one mechanism that you could use to enforce authorization. (4+1 marks) (c) FTP is a popular protocol used to transfer files from one host to another. i. Explain briefly how it works. ii. Give three distinct advantages that it has over HTTP for files transfer. (4+3 marks) (d) In respect of the ISO/OSI Reference model, i. Give three important functions handled by Layer 6. ii. Explain what is meant by 'encapsulation'. iii. Which protocol data unit has both a header and a trailer and state the layer at which it operate. (3+2+2 marks) Page 5 of 8
SECTION C (20 marks) ANSWER ONLY ONE QUESTION IN THIS SECTION QUESTION 4 (a) Describe how TCP connection management works. (3.5 marks) (b) What you understand by flow control and describe how it works in relation to TCP. (2 marks) (c) 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. i. Give the address range for a Class C network. ii. What are Class C network addresses commonly used for? iii. Can two hosts A and B with addresses 17.27.37.47 and 17.57.67.77 respectively communicate directly with each other if they share a subnet mask of 255.240.0.0? iv. Give three main differences between IPv4 and IPv6. (1+1+4+1.5 marks) (d) i. Explain what do you understand by datagram fragmentation. ii. A datagram of 4200 bytes has to travel over a network with a MTU size of 1560 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. (1+6 marks) Page 6 of 8
QUESTION 5 (a) Name the 3 fields present in IPv4 no longer present in IPv6. Why are these 3 fields no longer required? (b) What is the difference between an active and a passive intruder? (2 marks) (c) Describe briefly the difference between flow control and congestion control in relation to a connection-oriented protocol such as TCP. (d) Consider sending a 5000-byte datagram into a link that has a MTU of 1500 bytes. Suppose the original datagram is stamped with the identification number 256. How many fragments are generated? What are their characteristics? (You should give the value of the 3 key fields used in fragmentation for each fragment created.) Page 7 of 8
SECTION D (20 marks) ANSWER ONLY ONE QUESTION IN THIS SECTION QUESTION 6 (a) Describe how the following protocols work: i. ARP ii. DHCP iii. POP iv. SMTP (4+4+2+2 marks) (b) The IEEE 802.11x standard is popular in extending wired networks. i. Outline two popular flavours of this wireless standard. Elaborate on the operating frequency, range and speed of each flavour. ii. What are the two modes of operation of this standard and explain the difference between them. iii. Mention one security issue with this wireless technology and give two ways how this issue can be addressed. (3+2+3 marks) QUESTION 7 (a) Explain the Virtual Circuit Service Model. (b) Show by means of a diagram the UDP segment structure. (3 marks) (c) Explain the concept of IP Fragmentation and Re-assembly. (8 marks) (d) Compare the bridge and the router. (3 marks) *** End of Exam Paper *** Page 8 of 8