Neville Iregi

Empowering Africa through secure and scalable technology solutions.

Overview

This lab used Cisco Packet Tracer (Simulation Mode) to examine how data moves through a network using the OSI and TCP/IP models. By generating HTTP and DNS traffic, the lab visualized the encapsulation process, showing how Protocol Data Units (PDUs) are built, transmitted, and processed at each layer of the network stack.

Lab Objectives

  1. Examine HTTP web traffic
  2. Identify elements of the TCP/IP protocol suite
  3. Observe encapsulation and decapsulation across OSI layers
  4. Understand the relationship between ports, protocols, and services

Tools & Environment

  • Cisco Packet Tracer (Simulation Mode)
  • Web Client and Web Server
  • HTTP, DNS, TCP
  • OSI & TCP/IP model visualizers

Part 1: HTTP Traffic Analysis

  • Generated web traffic by accessing www.osi.local from a Web Client
  • Stepped through packets using Capture/Forward
  • Inspected PDUs at each OSI layer

Key Observations by Layer:

  • Layer 7 (Application): HTTP request sent to web server
  • Layer 4 (Transport):
    • Source Port: Ephemeral (1025)
    • Destination Port: 80 (HTTP)
  • Layer 3 (Network):
    • Destination IP: 192.168.1.254
  • Layer 2 (Data Link):
    • Ethernet II frame with source and destination MAC addresses
  • Layer 1 (Physical):
    • Frame placed on the network medium

Outbound and inbound traffic analysis showed that:

  • Source and destination MAC addresses, IP addresses, and ports are reversed on return traffic
  • Encapsulation occurs outbound; decapsulation occurs inbound

Part 2: TCP/IP Protocol Suite Analysis

  • Enabled all event filters to observe additional protocols
  • Identified multiple TCP/IP suite protocols including:
    • ARP, DNS, TCP, HTTP
  • Examined DNS query and response
    • DNS query resolved www.osi.local
    • DNS response returned IP 192.168.1.254
    • DNS operates on Port 53

TCP Connection Behavior Observed:

  • TCP connection establishment (state: ESTABLISHED)
  • TCP session termination (state: CLOSED)
  • Demonstrated TCP’s role in reliable, stateful communication

Key Networking Concepts Demonstrated

  • OSI vs TCP/IP model mapping
  • Encapsulation and decapsulation
  • Port-based service identification
  • Client–server communication flow
  • TCP session establishment and teardown
  • DNS name resolution process

Challenge Question Answers

  • Web Server listening port (HTTP): Port 80
  • DNS service port: Port 53

Key Takeaways

  • OSI and TCP/IP models work together to enable reliable communication
  • Packet Tracer simulation provides visibility into otherwise invisible network processes
  • Port numbers identify application services
  • TCP ensures reliable delivery through connection management
  • DNS enables human-readable names to resolve to IP addresses

Outcome

This lab reinforced theoretical knowledge of the OSI and TCP/IP models through hands-on simulation. By inspecting PDUs at each layer, I gained practical insight into how web traffic, DNS resolution, and TCP connections function together to deliver network services reliably.

Full Technical Report

📄 Detailed Step-by-Step Lab Report

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