Track 02: Networking from Zero

How the internet really carries your data, explained for someone who has written a little code but never studied networks. Thirty lessons, from "what is a network?" to the timeouts behind a random 502, each with a video of seven to ten minutes and a written lesson here that says the same thing in the same words, with the same pictures and the same numbers.

Why this series

Networking questions come up in every system design interview, and they are where many people get lost: a diagram full of SYN, ACK, TTL and TLS, with no idea what any of it is for. This series starts from nothing and goes one idea at a time.

• Every term is explained the first time it appears, in plain words, before it is used. Each lesson opens with a short list of the words you'll meet.
• An everyday picture first, such as a letter by post, a flat number in a building or a parcel tracking page, and then the real thing mapped onto it, part by part.
• One message at a time, slowly, in numbered steps, with one worked example in real numbers.
• What goes wrong, and how the design copes: a lost packet, a timeout, ports running out.
• A pause-and-think question in every lesson, and at the end the sentences to say in an interview.
• The same colours mean the same thing in every picture: blue is the client (your phone, the sender), green is the server (the receiver), red is loss or an error.

The lessons

Lessons are being published one at a time. Those not yet out are listed so you can see where the series is going.

How to use it

1. Go in order. Each lesson uses only the words taught before it, and the number of a lesson here is its number in the video.
2. Watch, then read (or the other way round). The written lesson follows the video step by step, so you can slow down on the part that did not click.
3. Stop at the pause-and-think question and answer it before you open the answer. If you get it right, you have understood the lesson.
4. Say the interview answer out loud. Every lesson ends with the sentences to use in 30 seconds.
5. Keep the free PDF notes. Every lesson has a printable PDF with the same pictures, linked at the bottom of its page.

Start here → 01-what-is-a-network/README.md, lesson 1.

Back to the course index: ../README.md