Networking and System Administration

Pass path: Learn the definitions and operational differences between LAN, WAN, and WLAN, plus the layer-specific roles of switches, routers, and firewalls. Top path: Analyze broadcast domains vs collision domains across hubs, switches, and routers, and evaluate transport protocol trade-offs between TCP and UDP.

Part 1: Core Concepts (2 Marks)

• ★ Computer Network: A collection of autonomous computing devices interconnected by transmission media and communication protocols to facilitate resource sharing, data exchange, and distributed processing.
• ★ Router: A Layer-3 (Network Layer) internetworking device that examines destination IP addresses to forward packets across different logical subnets using dynamic routing tables.
• ★ Switch: A Layer-2 (Data Link Layer) multiport networking device that maintains a MAC Address Table (CAM table) to forward Ethernet frames selectively to destination ports, isolating collision domains.

Part 2: Structural Frameworks (10 Marks)

1. Core Network Devices and Transmission Topologies

• Introduction: Define computer networks. Categorize networks based on geographic scope (LAN: campus/building; MAN: city; WAN: telecommunications backbones spanning nations; WLAN: IEEE 802.11 wireless local networks).
• Comprehensive Device Breakdown:
  1. Hub (Layer 1 - Physical): Multiport repeater that blindly broadcasts incoming electrical signals out of all other ports. Creates one massive collision domain and one broadcast domain.
  2. Bridge / Switch (Layer 2 - Data Link):
     • Operates via hardware ASICs to build a Content Addressable Memory (CAM) table matching MAC addresses to physical ports.
     • Each port is an isolated collision domain, but all ports share a single broadcast domain (unless partitioned by VLANs).
  3. Router (Layer 3 - Network):
     • Interconnects heterogeneous network segments (e.g., LAN to WAN).
     • Breaks both collision domains AND broadcast domains.
     • Implements routing protocols (OSPF, BGP, RIP) to determine optimal paths based on metrics (cost, hop count, bandwidth).
  4. Firewall (Layer 3/4/7 - Network to Application):
     • Inspects inbound and outbound network traffic against security rule sets (Stateful Packet Inspection, Next-Gen Deep Packet Inspection).
• Core Transport Protocols:
  • TCP (RFC 793): Connection-oriented, reliable byte stream, sequence numbering, ACK packets, sliding window flow control, congestion avoidance.
  • UDP (RFC 768): Connectionless, lightweight datagram protocol, zero connection handshake overhead, ideal for DNS queries, VoIP, and real-time gaming.
• Conclusion: Emphasize that modern enterprise networks depend on switches at the access/distribution layer and redundant routers/firewalls at the core perimeter.

Part 3: Distinction Tables

Part 4: Worked Problems & Exam Traps

• Problem 1 (Easy): A network has 3 switches, each with 24 ports, connected together without VLANs. How many collision domains and broadcast domains exist?
  • Solution:
    1. Collision Domains: In an unmanaged switch environment, each active switch port constitutes a distinct collision domain. Assuming all $3 \times 24 = 72$ ports are occupied (minus interconnecting trunk links), there are 72 separate collision domains.
    2. Broadcast Domains: Switches forward Layer-2 broadcast frames (FF:FF:FF:FF:FF:FF) across all connected ports. Because all switches are linked in a single flat network without routers or VLANs, there is exactly 1 broadcast domain.
• Problem 2 (Exam-Level Analysis): Explain why a network administrator cannot simply replace a router with a fast Layer-2 switch to connect an office LAN to an external Internet Service Provider (ISP).
  • Solution:
    1. A Layer-2 switch switches frames based on local MAC addresses; it cannot interpret IP headers, determine inter-network routing paths, or manage different data-link frame encapsulations (e.g., Ethernet to PPPoE/Fiber PON).
    2. Switches do not break broadcast domains; connecting directly to an ISP network without a router would flood external ISP broadcast traffic into the internal corporate LAN.
    3. Crucially, routers perform Network Address Translation (NAT) and manage public vs private IP address translation, which a standard Layer-2 switch cannot perform.
• Problem 3 (Twist / Case Scenario): Why does streaming live video frequently utilize UDP while downloading a PDF document strictly requires TCP?
  • Solution:
    1. Streaming video prioritizes timely arrival over absolute perfection; dropped packets result in minor, imperceptible pixel flickers, whereas TCP retransmission delays would cause buffering freezes.
    2. A PDF document requires 100% bitwise data integrity; a single corrupted or missing packet in an executable or compressed PDF renders the entire file corrupt and unreadable.
  • Students lose marks here because they state that switches break broadcast domains (switches only break collision domains; routers break broadcast domains).