Networking 101: how computers talk
Start from zero. What a host is, the OSI model, hubs, switches and routers, data centers, IP addresses and subnets, a step-by-step trace of a laptop getting its address, and the port numbers that say which program a message is for. Animated diagrams you can pause and step through, and nothing to install.
This is where networking starts. No lab to build and nothing to install: every lesson is a page with animated diagrams that show messages moving between computers. You can pause them, step forward and back one move at a time, and slow them down, so you never miss what just happened.
How each lesson works
Every lesson has the same five parts, so you always know where you are:
- Explain: the idea, in plain words, with an everyday comparison.
- Show: a picture of it, every part named.
- Follow along: step through the animation together. Each step says what to look at.
- Challenge: a puzzle to try on your own. Hints if you need them, then the answer.
- Check: a few quick questions. Pick an answer and you’ll see straight away if you got it, and why.
Using the diagrams
| Button | What it does |
|---|---|
| Play / Pause | run the steps one after another, or stop |
| ← → | one step back, one step forward (the arrow keys on your keyboard work too) |
| ↻ | play this step again |
| Slow | half speed, for the busy steps |
| the little bars | jump straight to any step |
Under some diagrams is a box that opens up a message so you can see what’s inside it, layer by layer. The highlighted parts are the ones that matter in that step.
Do the lessons in order: each one uses words from the one before. Tick mark this lesson done at the end of each to keep track; it’s saved in your browser.
Then: part 2, hands on
When you’ve done the lessons, part 2 puts them to work on a real network: you log in to a laptop, a printer, a switch and two routers, and run the commands engineers use every day to see MAC addresses, IP addresses, DHCP, routes, DNS and its port 53 for yourself.
5 chapters · 10 lessons
- 1.1 What's a host?Know what a host is, spot the hosts in a network, and find your own computer’s MAC address: the name its network card was born with.
- 1.2 The OSI model: seven layersName the seven layers of the OSI model, say what job each one does, and watch a message get wrapped up layer by layer on the way out and unwrapped on the way in.
- 2.1 Hubs, switches and routersWatch the same messages go through a hub, a switch and a router, and say what each one reads (nothing, MAC addresses, IP addresses) and where it sends things.
- 2.2 Collision domains and broadcast domainsDraw the collision domains and broadcast domains on any small network, and say which box (hub, switch or router) makes each boundary.
- 2.3 What's a data center?Say what a data center is and what’s inside it, follow a request from your phone to a server in a rack and back, and see why everything comes in twos.
- 3.1 What's an IP address?Read an IPv4 address, turn any of its numbers into binary, tell its network part from its host part, and explain why a laptop’s IP address changes when it moves but its MAC address doesn’t.
- 3.2
CIDR: what the /24 meansRead a prefix like
/24and its subnet mask255.255.255.0, and work out a network’s address, its broadcast address, its first and last host, and how many hosts fit. - 3.3 Subnetting with VLSMCut one block of addresses into subnets of different sizes with VLSM: biggest first, the smallest block that fits, no overlaps, and write down each subnet’s network, hosts and broadcast.