Stage 2 beginner Free
Networking Basics
How computers find and talk to each other — and how to see what's really travelling between them.
Runs in your browser. Nothing to install — the lesson and a real Linux computer open side by side.
Start Stage 2 →Lesson steps
- Welcome
- Your address
- Is anyone there?
- Names instead of numbers
- Run your own DNS server
- Ports
- Knock on a port
- Knock on every door
- Talk to a web server
- Check your own doors
- Watch the traffic
- Why HTTPS matters
- Final challenge: a new machine
- Stage complete
What this stage is
Your lab computer joins a small practice network with a few other machines on it. You'll find them, connect to their services, and watch the packets that pass between them — all from the terminal, in your browser.
It uses the commands from Linux Fundamentals, so do that stage first.
Why it matters
Every attack on a website or a server arrives over a network, and every defence starts with knowing what's on yours: which machines are there, which doors (ports) are open, and what travels in plain sight.
By the end you'll be able to
- find a computer's IP address, and tell whether another computer answers
- turn names into addresses, the way your browser does with DNS
- list the services listening on a computer, and connect to one by hand
- fetch a web page from the terminal and read its headers
- spot a service that shouldn't be running
- capture network traffic and read what's inside it — and explain why HTTPS matters
It ends with a final challenge: a new machine appears on the network, and you find out what it is.
Learn more (external)
- MDN — How does the Internet work? — A short, clear overview of networks, addresses and packets.
- How DNS works (comic) — A short comic that walks through a DNS lookup.
- Cloudflare — What is HTTPS? — What encryption protects, and what it doesn't.