**Introduction to Computer Networking - Exam
2018/2019 ACADEMIC YEAR (SECOND SEMESTER)
THE UNIVERSITY OF DODOMA
COLLEGE OF INFORMATICS AND VIRTUAL EDUCATION
SCHOOL OF INFORMATICS
UNDERGRADUATE UNIVERSITY EXAMINATIONS
SECOND SEMESTER 2018/2019
TN 122: INTRODUCTION TO NETWORKING
Date: 3rd July, 2019
Time Allocated: 3 Hours
Instructions:
- This examination consists of six questions.
- Answer only FOUR questions; Section A is compulsory and any other three (3) questions from section B.
- All University of Dodoma examination regulations apply.
SECTION A (40 Marks)
Question One
A: Multiple Choice questions (1 Mark Each)
1. In TCP/IP, port addresses are of length
- A) 4 Bits
- B) 16 Bits
- C) 32 Bits
- D) 48 Bits
Answer (Click to show)
B) 16 Bits
2. What is the hexadecimal equivalent of the Ethernet address 01011010 00010001 01010101 00011000 10101010 00001111?
- A) 5A-11-55-18-AA-OF
- B) 5A-11-55-18-AC-OF
- C) 5A-14-55-18-AA-OF
- D) 5A-11-55-18-BA-OF
Answer (Click to show)
A) 5A-11-55-18-AA-OF
3. Loss in signal power as light travels down the fiber is called?
- A) Propagation
- B) Attenuation
- C) Scattering
- D) Interruption
Answer (Click to show)
B) Attenuation
4. Which of the following is correct regarding class B address of IP address
- A) Network bit - 14 Host bit -16
- B) Network bit - 16 Host bit - 14
- C) Network bit - 16 Host bit -16
- D) Network bit - 18 Host bit - 16
Answer (Click to show)
A) Network bit - 14 Host bit -16
5. Message ______ means that the data must arrive at the receiver exactly as sent.
- A) Confidentiality
- B) Availability
- C) Authentication
- D) Integrity
Answer (Click to show)
D) Integrity
6. Which of the following layer of the OSI model is also called Process to Process layer?
- A) Session
- B) Transport
- C) Data Link
- D) Network
Answer (Click to show)
B) Transport
7. What is the network address of the block in which this IP address 215.100.123.256 belong?
- A) 225.100.0.0
- B) 225.100.123.72
- C) 225.100.123.0
- D) No answer
Answer (Click to show)
D) No answer (Invalid IP address - 256 is out of range)
8. A protocol named TCP, divides a stream of data into smaller units that are called
- A) Packets
- B) Segments
- C) Frames
- D) Chunks
Answer (Click to show)
B) Segments
9. Which of the following is not true about Subnetting?
- A) It can be applied only for single network
- B) Bits are borrowed off network ID portion
- C) It is used to improve security portion
- D) Bits are borrowed off host ID portion
Answer (Click to show)
B) Bits are borrowed off network ID portion
10. If a class B network on the Internet has a subnet mask of 255.255.248.0, what is the maximum number of hosts per subnet?
- A) 1022
- B) 1023
- C) 2046
- D) 2048
Answer (Click to show)
C) 2046
B: True and False Questions: (Write T for True and F for False) (1 Mark Each)
1. The OSI model protocol is the standard against which protocols are judged.
Answer (Click to show)
True
2. Peer-to-peer networks have computers that are permanently assigned as network servers.
Answer (Click to show)
False
3. A switch broadcasts all the packets it receives to all the computers that are connected to the switch.
Answer (Click to show)
False
4. Like a virus, a worm needs the user to perform an action such as starting a program or opening an e-mail attachment to start the infection.
Answer (Click to show)
False
5. LANs provide global connections for thousands of computers.
Answer (Click to show)
False
6. A hub connects two different LANs.
Answer (Click to show)
False
7. In Circuit switching type of network; data is broken up into packets before it’s sent over the network.
Answer (Click to show)
False
8. The number of addresses in class C is smaller than the needs of most organizations.
Answer (Click to show)
True
9. The most fundamental differences between SM and MM Optic Fibers are the size of the fiber’s core and the associated attenuation or loss and bandwidth of the fiber
Answer (Click to show)
True
10. An IPv4 packet sent to all workstations on the network is called a Multicast.
Answer (Click to show)
False (It is a Broadcast)
C: Short Answers Questions (1 Mark Each)
1. An organization has a class B network and wishes to form subnets for 64 departments. What would be the subnet mask?
Answer (Click to show)
255.255.252.0 (or /22)
2. Mention the topology in which each computer on the network connects to every other, creating a point-to-point connection between every device on the network.
Answer (Click to show)
Mesh Topology
3. When it comes to Port Address, which port number does HTTP use?
Answer (Click to show)
Port 80
4. What is the subnetwork address if the destination address is 203.145.4.56 and the subnet mask is 255.255.240.0?
Answer (Click to show)
203.145.0.0
5. How Many Devices Can Be Connected To One USB Port?
Answer (Click to show)
127 devices (theoretical maximum)
6. How long is an IPv6 address as far as bits are concerned?
Answer (Click to show)
128 bits
7. Mention four “versions” of Ethernet available for commercial use.
Answer (Click to show)
10Base-T, 100Base-TX, 1000Base-T, 10GBase-T
8. Given a class C IP address, you need to subnet a network that has 12 subnets, each with at least 10 hosts. Which subnet mask would you use?
Answer (Click to show)
255.255.255.240
9. Name the authority that oversees global IP address allocation.
Answer (Click to show)
IANA (Internet Assigned Numbers Authority)
10. If 10 nodes are communicating using a Hub on a 10-Mbps network and 8 of them are active, then what will each node get as far as bandwidth is concerned?
Answer (Click to show)
1.25 Mbps (10 Mbps ÷ 8 active nodes)
Question Two
a) Convert listed IP address into the stated notation; in your conversion include the class where each address belongs. (1 Marks Each)
i. 149.30.211.99 to Binary notation
Answer (Click to show)
Class B Binary: 10010101.00011110.11010011.01100011
ii. 10001111 11111101 00011001 00011101 to Decimal notation
Answer (Click to show)
Class B Decimal: 143.253.25.29
iii. 201.45.178.89 to Hexadecimal notation
Answer (Click to show)
Class C Hexadecimal: C9.2D.B2.59
b) An Organization has been granted an IP address 219.200.37.0 and has 12 separate departments of which each of the department is supposed to have its own network. Design the subnets. In your network design show the following
i. The subnet mask (1 Marks)
Answer (Click to show)
255.255.255.240 (or /28)
ii. The number of host addresses in each subnet (1 Marks)
Answer (Click to show)
16 addresses per subnet, 14 usable hosts
iii. The first available host address in the second subnet (2 Marks)
Answer (Click to show)
219.200.37.17
iv. The range of available addresses in the fourth subnet. (3 Marks)
Answer (Click to show)
219.200.37.49 to 219.200.37.62
SECTION B (60 Marks)
Question Three
a) (i) Define Computer Networking; (1 Mark)
Answer (Click to show)
Computer Networking is the practice of connecting computers and other devices to share resources and exchange information.
(ii) Provide two arguments in favor of the use of a computer network in an organization and one argument against. (3 Marks)
Answer (Click to show)
Arguments in Favor:
- Resource Sharing: Enables sharing of expensive hardware and software resources
- Enhanced Communication: Facilitates fast and efficient data exchange Argument Against:
- Security Risks: Increases vulnerability to unauthorized access and data breaches
b) Based on their definitions, differentiate between LAN, MAN & WAN (include example of each case). (6 Marks)
Answer (Click to show)
- LAN (Local Area Network): Covers small geographical area like a building or campus. Example: University computer lab network
- MAN (Metropolitan Area Network): Spans a city or large campus. Example: City-wide bank network
- WAN (Wide Area Network): Covers large geographical areas like countries/continents. Example: The Internet
c) List only four (4) design factors to be looked at when choosing a networking media. (4 Marks)
Answer (Click to show)
- Bandwidth
- Cost
- Distance
- Security
d) Write short notes about the listed topologies (include diagram for each in your notes) (2 Marks Each)
i. Star Topology
Answer (Click to show)
All devices connect to central hub/switch Diagram:
[PC1] [PC2] \ / [Hub] / \ [PC3] [PC4]
ii. Mesh Topology
Answer (Click to show)
Every device connected to every other device Diagram:
[PC1] ----- [PC2] | \ / | | \ / | | [PC3] | | / \ | | / \ | [PC4] ----- [PC5]
iii. Ring Topology
Answer (Click to show)
Devices connected in circular fashion Diagram:
[PC1] → [PC2] ↑ ↓ [PC4] ← [PC3]
Question Four
a) Why do we have protocols in computer networking? (2 Marks)
Answer (Click to show)
Protocols establish rules for communication, ensuring devices can understand each other and exchange data reliably and efficiently.
b) Why the OSI model was formulated in layers? Provide 4 reasons. (4 Marks)
Answer (Click to show)
- Modular Design: Easy to modify one layer without affecting others
- Interoperability: Enables multi-vendor compatibility
- Easier Learning: Breaks complex process into manageable parts
- Standardization: Provides framework for protocol development
c) List the seven layers of ISO’s OSI model starting from layer number 1, when listing briefly explain the function of each layer (the order of arrangement should be adhered) (8 Marks)
Answer (Click to show)
- Physical: Transmits raw bit stream over physical medium
- Data Link: Provides node-to-node delivery, framing, error control
- Network: Handles source-to-destination packet delivery, routing
- Transport: Ensures end-to-end message delivery, error recovery
- Session: Establishes, manages, terminates connections
- Presentation: Handles translation, encryption, compression
- Application: Provides interface for user applications
d) Briefly explain how the collision is avoided in the below listed LAN technologies: (3 Marks Each)
i. Ethernet
Answer (Click to show)
Uses CSMA/CD (Carrier Sense Multiple Access with Collision Detection):
- Listens before transmitting
- Detects collisions during transmission
- Backs off and retransmits after random delay
ii. Token Ring
Answer (Click to show)
Uses token passing mechanism:
- Special token circulates network
- Only device with token can transmit
- Prevents collisions by controlled access
Question Five
a) Is worm the same as virus? Provide briefly explanation (2 Mark)
Answer (Click to show)
No. A virus requires host program and user action to spread, while a worm is standalone and self-replicating across networks without user intervention.
b) Define the following i. Security Attack (1 Mark)
Answer (Click to show)
Any action that compromises security of information owned by an organization
ii. Security mechanism (1 Mark)
Answer (Click to show)
A mechanism designed to detect, prevent, or recover from security attack
iii. Security service (1 Mark)
Answer (Click to show)
A service that enhances security of data processing systems and information transfers
c) Give brief explanation on why do we need Computer Network Security. (3 Marks)
Answer (Click to show)
To protect confidentiality, maintain data integrity, ensure availability of resources, and prevent financial losses and reputation damage from security breaches.
d) With diagrams, list the four types of security attacks and alongside them mention each security service does it affect. (6 Marks)
Answer (Click to show)
- Interruption (Availability): Sender ---X-⇒ Receiver
- Interception (Confidentiality): Sender —⇒ [Attacker] —⇒ Receiver
- Modification (Integrity): Sender —⇒ [Attacker alters] —⇒ Receiver
- Fabrication (Authenticity): [Attacker forges] —⇒ Receiver
e) Briefly explain four (4) ways one can implement security defense mechanism. (6 Marks)
Answer (Click to show)
- Access Control: Restrict access using passwords, biometrics
- Encryption: Convert data to unreadable format
- Firewalls: Filter network traffic
- Intrusion Detection Systems: Monitor for suspicious activity
Question Six
a) Briefly explain two environments where layer 3 switches come into use. (4 Marks)
Answer (Click to show)
- Large LANs with multiple VLANs requiring inter-VLAN routing
- Network backbones where high-speed routing between subnets is needed
b) Why do we configure switches? Briefly explain three reasons. (6 Marks)
Answer (Click to show)
- VLAN Configuration: To segment network for security and performance
- Security Settings: To control port access and prevent unauthorized connections
- Performance Optimization: To manage traffic flow and prevent bottlenecks
c) When you move the NIC cards from one PC to another PC, does the MAC address gets transferred as well? Briefly explain. (4 Marks)
Answer (Click to show)
Yes, because MAC address is hard-coded into the NIC hardware, not the computer. The address moves with the physical card.
d) Mention two advantages and 2 disadvantages of twisted pair. (4 Marks)
Answer (Click to show)
Advantages:
- Low cost
- Easy installation Disadvantages:
- Susceptible to interference
- Limited distance
e) Outline the two limitations of star topology. (2 Marks)
Answer (Click to show)
- Single point of failure at central device
- Requires more cabling than bus topology
END OF EXAMINATION