Playgrounds

Here are all the pieces of the course you can play with, with nothing to install. There are two kinds:

• Labs: step-by-step simulations of the hardest things to see, like the TCP handshake or a DNS lookup. You move at your own pace and can cause errors to see what happens.
• Playgrounds: real tools that run inside your browser, like the cryptography that protects HTTPS.

Each one lives in a lesson, in its “Try it” section, which explains what you are looking at. If something doesn’t add up, start with the lesson.

Phase 0 · How the internet works

• ▶The TCP handshake, step by step// lab

  Open a TCP connection, send data and drop packets on purpose to see how TCP recovers them. Then do the same with UDP and compare.

  in 06-tcp-vs-udp.md

• ▶A real DNS lookup// lab

  Type a domain and follow, server by server, how it becomes an IP address. The lookups are real: try A, AAAA, CNAME and MX records.

  in 07-dns.md

• ▶Public and private keys in your browser// playground

  Generate a key pair, encrypt with the public key and decrypt with the private one. Then sign a message and see what happens if someone changes it.

  in 08-tls-and-https.md