Computer Networking (4343202) - Summer 2025 Solution

Question 1(a) [3 marks]

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List Various network Topologies of computer network and explain any one.

Answer:

Table: Network Topologies

Star Topology Explanation:

• Central Hub: All devices connect to one central point
• Easy Installation: Simple to add/remove devices
• Single Point Failure: Hub failure affects entire network

Mnemonic: “SRBMTH - Star Ring Bus Mesh Tree Hybrid”

Question 1(b) [4 marks]

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Compare LAN, WAN and MAN.

Answer:

Comparison Table:

Key Points:

• LAN: Local Area Network for small areas
• MAN: Metropolitan Area Network for cities
• WAN: Wide Area Network for large distances

Mnemonic: “LMW - Local Metropolitan Wide”

Question 1(c) [7 marks]

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Draw the layered architecture of OSI reference model and write at least two services provided by each layer of the model.

Answer:

graph TD
    A[Application Layer - 7] --> B[Presentation Layer - 6]
    B --> C[Session Layer - 5]
    C --> D[Transport Layer - 4]
    D --> E[Network Layer - 3]
    E --> F[Data Link Layer - 2]
    F --> G[Physical Layer - 1]

Services by Each Layer:

Mnemonic: “All People Seem To Need Data Processing”

Question 1(c OR) [7 marks]

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Explain Each layer of TCP/IP Model with its protocol.

Answer:

graph TD
    A[Application Layer] --> B[Transport Layer]
    B --> C[Internet Layer]
    C --> D[Network Access Layer]

TCP/IP Model Layers:

Key Features:

• Simplified Model: Only 4 layers vs OSI’s 7
• Protocol Suite: Complete networking solution
• Internet Standard: Basis of modern internet

Mnemonic: “ATIN - Application Transport Internet Network”

Question 2(a) [3 marks]

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Explain functions of following network devices: Repeater, Hub

Answer:

Device Functions:

Details:

• Repeater: Regenerates weak signals over long distances
• Hub: Connects multiple devices in star topology
• Shared Medium: Both create single collision domain

Mnemonic: “RH - Repeat Hub signals”

Question 2(b) [4 marks]

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Explain the following term 1) FDDI 2) ARP, RARP

Answer:

FDDI (Fiber Distributed Data Interface):

• Technology: 100 Mbps fiber optic network
• Topology: Dual ring for fault tolerance
• Application: Backbone networks, high reliability

ARP (Address Resolution Protocol):

• Function: Maps IP address to MAC address
• Process: Broadcasts request, receives reply

RARP (Reverse ARP):

• Function: Maps MAC address to IP address
• Usage: Diskless workstations, boot process

Mnemonic: “FAR - FDDI ARP RARP”

Question 2(c) [7 marks]

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Explain the Function of firewall in network security with principles and Kerberos-concept.

Answer:

Firewall Functions:

graph LR
    A[Internet] --> B[Firewall] --> C[Internal Network]
    B --> D[Block Threats]
    B --> E[Allow Traffic]
    B --> F[Log Activity]

Firewall Principles:

• Packet Filtering: Examines packet headers
• Stateful Inspection: Tracks connection states
• Application Gateway: Deep packet inspection

Kerberos Concept:

• Authentication Service: Secure user verification
• Ticket System: Time-limited access tokens
• Three-party Protocol: Client, Server, Key Distribution Center

Security Benefits:

• Access Control: Prevents unauthorized access
• Network Protection: Shields internal resources

Mnemonic: “FPK - Firewall Protects with Kerberos”

Question 2(a OR) [3 marks]

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Explain functions of following network devices: Switch, Router

Answer:

Device Functions:

Details:

• Switch: Creates separate collision domains per port
• Router: Connects different networks, makes routing decisions
• Intelligence: Switch learns MAC, Router maintains routing table

Mnemonic: “SR - Switch Routes intelligently”

Question 2(b OR) [4 marks]

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Explain the following term 1) CDDI 2) DHCP and BOOTP

Answer:

CDDI (Copper Distributed Data Interface):

• Technology: FDDI over copper cables
• Speed: 100 Mbps over twisted pair
• Cost: Cheaper alternative to fiber FDDI

DHCP (Dynamic Host Configuration Protocol):

• Function: Automatic IP address assignment
• Process: Discover, Offer, Request, Acknowledge
• Benefits: Centralized IP management

BOOTP (Bootstrap Protocol):

• Function: Network bootstrap for diskless clients
• Static: Fixed IP address assignment
• Predecessor: Earlier version of DHCP

Mnemonic: “CDB - CDDI DHCP BOOTP”

Question 2(c OR) [7 marks]

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Explain Software define network(SDN) with its Architecture, Application, Advantage and limitation.

Answer:

graph TD
    A[SDN Controller] --> B[OpenFlow Protocol]
    B --> C[Network Switches]
    A --> D[Network Applications]
    D --> E[Traffic Engineering]
    D --> F[Security Policies]

SDN Architecture:

• Control Plane: Centralized network intelligence
• Data Plane: Packet forwarding devices
• Application Plane: Network applications and services

Applications:

• Cloud Computing: Dynamic resource allocation
• Network Virtualization: Multiple virtual networks
• Traffic Engineering: Optimized path selection

Advantages:

• Centralized Control: Simplified network management
• Programmability: Custom network behaviors
• Flexibility: Rapid service deployment

Limitations:

• Single Point Failure: Controller dependency
• Scalability: Performance bottlenecks
• Security: New attack vectors

Mnemonic: “SCAP - Software Control Application Programmable”

Question 3(a) [3 marks]

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Find the class of following IP address. 1) 01111000 00001111 10101010 11000000 2) 11101000 01010101 11111111 11000011

Answer:

IP Address Classification:

Class Ranges:

• Class A: 1-126 (0xxxxxxx)
• Class B: 128-191 (10xxxxxx)
• Class C: 192-223 (110xxxxx)
• Class D: 224-239 (1110xxxx)

Results:

• First IP: Class A (Unicast)
• Second IP: Class D (Multicast)

Mnemonic: “ABCD - A(1-126) B(128-191) C(192-223) D(224-239)”

Question 3(b) [4 marks]

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Differentiate IPv4 and IPv6.

Answer:

IPv4 vs IPv6 Comparison:

Key Differences:

• Addressing: IPv6 provides vastly more addresses
• Security: IPv6 has mandatory security features
• Performance: IPv6 has simplified header structure

Mnemonic: “IPv4 to IPv6 = More addresses, Better security”

Question 3(c) [7 marks]

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Explain Static and Dynamic Routing Algorithms.

Answer:

Static Routing:

graph TD
    A[Administrator] --> B[Manual Route Entry]
    B --> C[Routing Table]
    C --> D[Fixed Paths]

Dynamic Routing:

graph TD
    A[Routing Protocol] --> B[Route Discovery]
    B --> C[Automatic Updates]
    C --> D[Adaptive Paths]

Comparison Table:

Applications:

• Static: Small networks, specific paths
• Dynamic: Large networks, fault tolerance

Mnemonic: “SD - Static=Simple, Dynamic=Automatic”

Question 3(a OR) [3 marks]

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Explain CIDR. How does it differ from traditional IP address allocation methods?

Answer:

CIDR (Classless Inter-Domain Routing):

• Concept: Variable length subnet masking
• Notation: IP address/prefix length (e.g., 192.168.1.0/24)
• Flexibility: Subnets of any size

Traditional vs CIDR:

Benefits:

• Address Conservation: Reduces IP address waste
• Route Aggregation: Summarizes multiple routes

Mnemonic: “CIDR = Classless Intelligent Address Routing”

Question 3(b OR) [4 marks]

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Describe DSL technology with its types, advantages and limitations.

Answer:

DSL (Digital Subscriber Line):

• Technology: High-speed internet over telephone lines
• Frequency: Uses higher frequencies than voice

DSL Types:

Advantages:

• Always-on Connection: No dial-up required
• Existing Infrastructure: Uses phone lines
• Cost-effective: Affordable high-speed access

Limitations:

• Distance Dependent: Speed decreases with distance
• Line Quality: Requires good copper lines
• Availability: Not available everywhere

Mnemonic: “DSL = Digital Speed Limited by distance”

Question 3(c OR) [7 marks]

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Explain error control and flow control at data link layer in detail.

Answer:

Error Control:

graph TD
    A[Data Transmission] --> B[Error Detection]
    B --> C{Error Found?}
    C -->|Yes| D[Request Retransmission]
    C -->|No| E[Accept Data]
    D --> A

Error Control Methods:

Flow Control:

graph LR
    A[Sender] --> B[Buffer Check]
    B --> C{Buffer Full?}
    C -->|No| D[Send Data]
    C -->|Yes| E[Wait]
    E --> B

Flow Control Techniques:

• Stop-and-Wait: Send one frame, wait for ACK
• Sliding Window: Multiple frames in transit
• Buffer Management: Prevents overflow

Implementation:

• Hardware Level: Buffer status signals
• Software Level: Protocol acknowledgments

Mnemonic: “EF - Error detection, Flow regulation”

Question 4(a) [3 marks]

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Explain video over IP.

Answer:

Video over IP (VoIP):

• Technology: Transmits video signals over IP networks
• Digitization: Converts analog video to digital packets
• Real-time: Requires low latency transmission

Components:

• Encoder: Compresses video data
• Network: IP infrastructure for transport
• Decoder: Decompresses at destination

Applications:

• Video Conferencing: Business communications
• Streaming: Entertainment services
• Surveillance: Security systems

Requirements:

• Bandwidth: High data rate needs
• QoS: Quality of Service guarantees

Mnemonic: “VIP = Video Internet Protocol”

Question 4(b) [4 marks]

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Explain Electronic-Mail with its protocol.

Answer:

Email System Components:

graph TD
    A[User Agent] --> B[SMTP Server]
    B --> C[Internet]
    C --> D[POP3/IMAP Server]
    D --> E[Recipient]

Email Protocols:

Protocol Details:

• SMTP: Simple Mail Transfer Protocol for sending
• POP3: Downloads mail to local device
• IMAP: Keeps mail on server, multi-device access

Message Flow:

• Composition: User creates message
• Submission: SMTP sends to server
• Delivery: Server forwards to recipient
• Retrieval: POP3/IMAP downloads message

Mnemonic: “SPI - SMTP sends, POP3/IMAP receives”

Question 4(c) [7 marks]

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Explain Role of DNS- Domain Name System Describe the process of DNS resolution.

Answer:

DNS Role:

• Name Resolution: Converts domain names to IP addresses
• Hierarchical System: Distributed database structure
• Internet Navigation: Makes web browsing user-friendly

DNS Resolution Process:

sequenceDiagram
    participant C as Client
    participant L as Local DNS
    participant R as Root Server
    participant T as TLD Server
    participant A as Authoritative Server
    
    C->>L: Query www.example.com
    L->>R: Query root
    R->>L: Refer to .com TLD
    L->>T: Query .com TLD
    T->>L: Refer to example.com
    L->>A: Query example.com
    A->>L: Return IP address
    L->>C: Return IP address

Resolution Steps:

1. Local Cache Check: Check local DNS cache
2. Recursive Query: Contact local DNS server
3. Root Server: Get TLD server reference
4. TLD Server: Get authoritative server reference
5. Authoritative Server: Get final IP address
6. Response Return: IP address returned to client

DNS Record Types:

• A Record: Maps name to IPv4 address
• AAAA Record: Maps name to IPv6 address
• CNAME: Canonical name alias
• MX: Mail exchange server

Benefits:

• User Friendly: Remember names, not numbers
• Load Distribution: Multiple IP addresses
• Service Location: Find specific services

Mnemonic: “DNS = Directory Name Service”

Question 4(a OR) [3 marks]

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Explain WWW, HTML.

Answer:

WWW (World Wide Web):

• Definition: Information system of interlinked documents
• Access: Through web browsers using HTTP
• Components: Web pages, links, URLs

HTML (HyperText Markup Language):

• Purpose: Standard markup language for web pages
• Structure: Tags define document elements
• Hyperlinks: Connect different web resources

Relationship:

• WWW: The system/platform
• HTML: The content format
• Integration: HTML creates WWW content

Mnemonic: “WWW uses HTML for content”

Question 4(b OR) [4 marks]

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Explain HTTP and FTP.

Answer:

Protocol Comparison:

HTTP (HyperText Transfer Protocol):

• Function: Request-response protocol for web
• Methods: GET, POST, PUT, DELETE
• Stateless: Each request independent

FTP (File Transfer Protocol):

• Function: Upload/download files between systems
• Modes: Active and Passive
• Authentication: Username/password required

Applications:

• HTTP: Web browsing, API calls
• FTP: File sharing, website maintenance

Mnemonic: “HF - HTTP for Hypertext, FTP for Files”

Question 4(c OR) [7 marks]

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Explain TCP and UDP protocol in transport layer in relation to connection oriented and connection less network.

Answer:

Transport Layer Protocols:

graph TD
    A[Transport Layer] --> B[TCP - Connection Oriented]
    A --> C[UDP - Connectionless]
    B --> D[Reliable Delivery]
    C --> E[Fast Delivery]

Protocol Comparison:

TCP (Transmission Control Protocol):

• Three-way Handshake: SYN, SYN-ACK, ACK
• Reliable: Acknowledgment and retransmission
• Flow Control: Prevents buffer overflow
• Applications: Web browsing, email, file transfer

UDP (User Datagram Protocol):

• No Connection Setup: Direct data transmission
• Lightweight: Minimal protocol overhead
• No Guarantees: Fire-and-forget approach
• Applications: Video streaming, DNS, gaming

Connection Models:

• Connection-Oriented: Establish, transfer, terminate
• Connectionless: Direct transmission without setup

Selection Criteria:

• Use TCP: When reliability is critical
• Use UDP: When speed is more important

Mnemonic: “TCP = Thorough, UDP = Ultra-fast”

Question 5(a) [3 marks]

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Describe Hacking and its related precautions.

Answer:

Hacking Definition:

• Unauthorized Access: Breaking into computer systems
• Malicious Intent: Steal, modify, or destroy data
• Security Breach: Exploit system vulnerabilities

Types of Hacking:

• Ethical Hacking: Authorized security testing
• Malicious Hacking: Criminal activities
• Social Engineering: Manipulate human behavior

Precautions:

Mnemonic: “HSPFAB - Hacking Stopped by Passwords, Firewalls, Antivirus, Backups”

Question 5(b) [4 marks]

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Explain IPSec architecture.

Answer:

IPSec (Internet Protocol Security):

graph TD
    A[IPSec Architecture] --> B[Authentication Header - AH]
    A --> C[Encapsulating Security Payload - ESP]
    A --> D[Security Association - SA]
    A --> E[Internet Key Exchange - IKE]

IPSec Components:

Operating Modes:

• Transport Mode: Protects payload only
• Tunnel Mode: Protects entire IP packet

Security Services:

• Authentication: Verify sender identity
• Integrity: Ensure data unchanged
• Confidentiality: Encrypt data content
• Anti-replay: Prevent packet replay attacks

Mnemonic: “AISE - AH, IPSec, SA, ESP”

Question 5(c) [7 marks]

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Explain network Security topologies.

Answer:

Network Security Topologies:

graph TD
    A[Internet] --> B[Firewall]
    B --> C[DMZ]
    C --> D[Web Server]
    C --> E[Mail Server]
    B --> F[Internal Network]
    F --> G[Workstations]
    F --> H[Database Server]

Security Zones:

Topology Components:

• Perimeter Security: Firewalls, IDS/IPS
• Network Segmentation: VLANs, subnets
• Access Control: Authentication, authorization
• Monitoring: Logging, SIEM systems

Security Principles:

• Defense in Depth: Multiple security layers
• Least Privilege: Minimum required access
• Network Isolation: Separate critical systems

Implementation Strategies:

• Firewall Rules: Control traffic flow
• VPN Access: Secure remote connections
• Network Monitoring: Detect threats
• Incident Response: Handle security events

Benefits:

• Risk Reduction: Minimize attack surface
• Compliance: Meet regulatory requirements
• Business Continuity: Protect operations

Mnemonic: “NST = Network Security Through topology design”

Question 5(a OR) [3 marks]

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Explain ISO and how it contributes to information security?

Answer:

ISO (International Organization for Standardization):

• Global Standards: Develops international standards
• Quality Assurance: Ensures consistent practices
• Best Practices: Provides framework for implementation

ISO 27001 - Information Security:

• ISMS: Information Security Management System
• Risk Management: Systematic approach to security
• Continuous Improvement: Regular review and updates

Contributions to Information Security:

• Framework: Structured approach to security
• Compliance: Meet regulatory requirements
• Risk Assessment: Identify and mitigate threats

Benefits:

• Standardization: Common security language
• Credibility: International recognition
• Improvement: Ongoing security enhancement

Mnemonic: “ISO = International Security Organization”

Question 5(b OR) [4 marks]

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Give Difference between symmetric and asymmetric encryption algorithms.

Answer:

Encryption Algorithm Comparison:

Symmetric Encryption:

• Examples: AES, DES, 3DES
• Process: Same key encrypts and decrypts
• Challenge: Secure key distribution

Asymmetric Encryption:

• Examples: RSA, ECC, Diffie-Hellman
• Process: Public key encrypts, private key decrypts
• Advantage: No key distribution problem

Hybrid Approach:

• Combination: Use both types together
• Method: Asymmetric for key exchange, symmetric for data

Applications:

• Symmetric: Bulk data encryption
• Asymmetric: Digital signatures, key exchange

Mnemonic: “SA = Symmetric Shared, Asymmetric Apart”

Question 5(c OR) [7 marks]

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Explain Email security with its standards.

Answer:

Email Security Challenges:

graph TD
    A[Email Threats] --> B[Phishing]
    A --> C[Malware]
    A --> D[Spam]
    A --> E[Data Interception]
    A --> F[Identity Spoofing]

Email Security Standards:

Security Mechanisms:

• Encryption: Protect message content
• Digital Signatures: Verify sender identity
• Authentication: Confirm message origin
• Integrity: Ensure message unchanged

Implementation Layers:

• Transport Layer: TLS/SSL encryption
• Message Layer: S/MIME, PGP encryption
• Policy Layer: SPF, DKIM, DMARC

Best Practices:

• User Education: Recognize phishing attempts
• Gateway Filtering: Block malicious emails
• Regular Updates: Keep security software current
• Backup Systems: Protect against data loss

Benefits:

• Confidentiality: Private communications
• Authentication: Verified senders
• Compliance: Meet regulatory requirements
• Trust: Secure business communications

Mnemonic: “SPTSD = S/MIME, PGP, TLS, SPF, DKIM protect email”