Networking

Two or more computers connected so they can pass messages. That's the whole idea — everything else is detail.

On a network, somebody asks and somebody answers. The asker is the client, the answerer is the server.

Every machine on a network needs a unique number so messages can find it — like a house address for computers.

The internet is built in layers, each with one job. Stack them and a web page reaches you. The big mental model.

A message is chopped into little packets, each labelled with the destination, sent off separately, and passed router to router until it arrives.

Two ways to send packets: TCP the careful courier (checks everything arrives in order) or UDP fire-and-forget (faster, but doesn't look back).

An IP address finds the right machine, but a machine runs many programs at once — a port number says which program the message is for.

You type a name like google.com, but machines only understand numbers. DNS is the lookup that turns the name into its IP address.

HTTP is the language browsers and servers speak to ask for and send web pages. HTTPS is the same language, but locked so nobody can snoop.

TLS is the layer that locks the connection — it proves the server is real and scrambles everything you send, so snoopers see only noise. That's the padlock.

Your whole home hides behind one public address (NAT), and a guard decides which messages are allowed through (firewall).

A CDN keeps copies of popular content close to users all over the world, so a nearby server answers instead of one across the planet.

Type a URL, press enter — and seven invisible steps fire in order to put the page on your screen. The whole track, in one journey.