Understanding TCP/IP and OSI Models Through Packet Tracer: A Beginner-Friendly Walkthrough.

Network communication often feels abstract — layers, protocols, and technical terms that seem disconnected at first glance. But when you visualize how data moves across a network, suddenly everything starts making sense.

In this post, I walk through a hands-on Packet Tracer simulation that explores the TCP/IP and OSI models, examines HTTP web traffic, and analyzes DNS and TCP events step by step. Whether you’re a cybersecurity student, an IT beginner, or a professional refreshing foundational concepts, this guide turns theory into something you can actually see.

How This Lab Works

This Packet Tracer activity focuses on two main goals:

1. Analyzing TCP/IP and OSI models in action
2. Examining HTTP, DNS, and TCP behavior through simulation events

As the attached document states:

“This assignment involves… installation of packet tracer. The second part dives into the packet simulation mode activities for understanding the TCP/IP and relationship with the OSI model.”

Let’s break down exactly what happens inside the simulation.

https://drive.google.com/file/d/1KSijvs9JVKJ6xxq4gjFN14VSvC9yB3hH/view?usp=sharing

Part 1: Examining HTTP Web Traffic

Switching to Simulation Mode

The first step is switching Packet Tracer from Real-Time mode to Simulation mode. This allows each network event — HTTP, DNS, and TCP segments — to be captured and inspected.

The document notes:

“Yes. On the events list 4 events appeared… Far right corner the events are visible.”

These four events represent the HTTP request process.

Exploring the HTTP Packet (OSI Layers Breakdown)

When clicking the first event in the list, Packet Tracer opens the PDU Display Window, showing how the data moves through the OSI layers.

Layer 7 (Application)

“1. The HTTP client sends a HTTP request to the server.”

Layer 4 (Transport)

• Destination port: 80
• Source port: 1025

Layer 3 (Network)

• Destination IP: 192.168.1.254

Layer 2 (Data Link)

“Ethernet II Header 0060.47CA.4DEE >> 0001.96A9.401D”

This demonstrates encapsulation — how the packet gains headers as it moves from the application layer down towards the physical network.

Outbound PDU Details

The document shows how Packet Tracer maps OSI layers to TCP/IP components:

• Layer 3: Destination IP
• Layer 4:
• “source port 1025, destination port 80”
• Layer 7:
• “Host is www.osi.local”

This reinforces how each layer contributes specific information needed to deliver the request.

Important Observation: Reversed Ports

At one point, Packet Tracer shows reversed port values:

“In layer TCP src port: 1025 Dst port: 80. Out layer Dst port 1025 TCP src port: 80.”

This reflects the difference between request traffic (client → server) and response traffic (server → client). Servers respond from port 80 back to the client’s ephemeral port 1025.

Part 2: Displaying TCP/IP Protocol Suite Events

Switching the event filter to Show All Events reveals additional traffic such as DNS queries and TCP session messages.

DNS Query Analysis

From the document:

“(VARIABLE LENGTH): www.osi.local” — DNS Query Name Field

The DNS answer later returns:

“IP:192.168.1.254”

DNS resolves the domain name before the HTTP request is sent.

TCP Connection Events

Packet Tracer then displays the TCP session setup and closure.

Connection Established

“4. The TCP connection is successful.”

Connection Closed

“The device sets the connection state to CLOSED.”

This completes the full TCP lifecycle: handshake → data transfer → termination.

Clarifying the Challenge Questions

The document includes answers that are technically ambiguous:

“TCP SRC port: 1025” (as the server’s listening port) “DST port: 80” (as the DNS port)

For clarity:

• HTTP servers listen on port 80
• DNS servers listen on port 53
• Port 1025 is an ephemeral client port, not a server port

The values were quoted exactly as they appear in the document, as required.

What This Lab Demonstrates

This Packet Tracer activity helps visualize how data moves across the OSI layers and how TCP/IP protocols work together during web communication. As the document concludes:

“This simulation helped me to develop the understanding of the TCP/IP protocol suite and how vital each layer is when the goal is to have data transmitted successfully.”

Understanding packet behavior is essential for anyone entering cybersecurity — whether you’re troubleshooting, analyzing logs, or detecting threats, everything begins with packets.

Download the Full Lab PDF

You can download the full Packet Tracer assignment here:

**https://drive.google.com/file/d/1KSijvs9JVKJ6xxq4gjFN14VSvC9yB3hH/view?usp=sharing**

If you enjoyed this walkthrough and want more Packet Tracer or networking breakdowns, feel free to follow for upcoming posts.