Learn

How the internet works

From the first ARPANET message to the Wi-Fi in your living room: packets, addresses, names, routes, the web and the encryption that protects it.

8 lessons · 51 min

  1. 1ARPANET and the packetFreeIn 1969 two computers exchanged two letters, then crashed. The idea that carried them, packet switching, still moves every byte you send.1964–1969 · 6 min
  2. 2TCP/IP: a network of networksCerf and Kahn designed a way for different networks to talk. On 1 January 1983 ARPANET switched to it, and the internet got its common language.1974–1983 · 6 min
  3. 3IP addresses and subnetsHow a 32-bit number locates every device, how a prefix splits it into network and host, and why IPv4 ran out.1993–today · 7 min
  4. 4DNS: the internet's phone bookBefore 1983 every computer kept one shared list of names. Paul Mockapetris replaced it with a distributed system that answers billions of questions a day.1983 · 6 min
  5. 5Routing and BGPHow routers pick a path, how tens of thousands of networks agree on routes, and how one command took Facebook off the internet for six hours.2021 · 7 min
  6. 6The web and HTTPA physicist at CERN wanted to share documents. The result was the web, and a protocol simple enough to read by eye: HTTP.1989–1993 · 6 min
  7. 7HTTPS and TLSHTTP was readable by anyone on the path. TLS wraps it in encryption and proves who the server is, and Let's Encrypt made that free.1999–today · 7 min
  8. 8Your home networkHow your laptop gets an address it never asked you for, and how a dozen devices at home share one public IP to reach the internet.1996–today · 6 min