Internet Architecture - OSI Model, TCP/IP, Protocols, Ports & Networking Devices

In the last post, we talked about how the Internet works and how your data travels through underwater cables.

Today, let’s go one level deeper and understand the actual architecture of the internet using models, protocols, ports, and devices.

OSI Model — The 7-Layer of Networking

Think of the OSI Model (Open Systems Interconnection) like a 7-layer cake, where each layer handles a specific part of the communication process.

TCP/IP Model — The Practical Internet Model

The TCP/IP Model is what the internet actually uses in real life. It’s simpler and has 4 layers.

OSI vs TCP/IP — How They Connect

Let’s map the two models together:

• OSI is more theoretical (7 layers), TCP/IP is more practical (4 layers).

• OSI focuses on “how it should work”, TCP/IP focuses on “how it actually works on the internet.”

Common Protocols and Port Numbers You See Every Day

Here are the most used protocols and their port numbers (super useful in DevOps):

Routers vs Switches — Your Daily Network Tools

Simple Trick:

• Router = Connects you to the world 🌍

• Switch = Connects your devices locally 🖥️

Client-Server Model — How Apps Like YouTube Work

Every time you use an app like YouTube or Instagram:

• You: Client (sending requests).

• Server (Youtube’s Server): Server (responding with data).

This Client-Server Model is the backbone of the modern internet.

• Client sends request → Server processes and responds → Client receives data.

Quick Reminder on Ports & Firewalls

Ports are like apartment doors in a big building (your computer).

• Example: HTTP uses Port 80, SSH uses Port 22, etc.

• Firewalls can open/close ports to allow or block services for security.

You can check open ports using:

netstat -tulnp

Summary

• OSI Model — 7 layers explained

• TCP/IP — 4-layer practical model

• Protocols & Ports — daily internet rules

• Routers & Switches — how networks connect

• Client-Server — how apps communicate