How the internet works.

Type a URL, press Enter, and a dozen systems spring into action to get bytes from a server thousands of miles away onto your screen in a heartbeat. This is the whole journey in one map — the rest of the course zooms into each stop.

Computers route by numbers, not names. DNS is the internet's phone book: it turns google.com into an IP address by walking a chain of nameservers — root, TLD, authoritative — with caching at every step so the lookup stays fast.

Your data isn't sent as one blob — it's chopped into thousands of small packets, each stamped with a destination and routed independently across the network, then reassembled at the far end. It's why the internet is resilient: no single path has to survive.

Packets get lost, duplicated and arrive out of order — yet your page renders perfectly. TCP is the layer that turns an unreliable packet network into an ordered, guaranteed byte stream, using sequence numbers, acknowledgements and retransmits.

Under the web is just text: a request naming a method and a path, and a response with a status code and a body. Once you see that a web page starts as a plain-text conversation, HTTP stops being mysterious and status codes start making sense.

How do two strangers agree on a secret key while everyone is listening? The TLS handshake uses public-key cryptography to establish an encrypted channel and verify who you're talking to — so ordinary HTTP rides safely inside HTTPS.

The finale ties the journey off: a server 8,000 miles away still feels instant because a CDN keeps copies of the content close to you. Edge caching, anycast routing and cache invalidation are how the web scales to a planet of users without melting the origin.