How the Internet Works

Before domains, DNS, or hosting make sense, you need the layer underneath: how two computers anywhere on Earth find each other and exchange bytes.

⏱ ~12 min · 🟢 Beginner · Prerequisite: none

🎯 What you’ll be able to do

Explain the difference between an IP address, a port, and a socket
Describe why data travels as packets and when to use TCP vs UDP
Walk an interviewer through everything between “typing a URL” and “seeing the page”

The mental model

The internet is just computers mailing small packages to each other’s addresses. That’s the whole thing. Websites, email, video calls — all built on that one idea.

Two questions must be answered for any communication:

Where is the other computer? → its IP address
How do the bytes get there reliably? → TCP/IP

IP addresses — the “where”

Every device on a network has an IP address: its location on the internet.

Type	Looks like	Notes
IPv4	`104.21.45.12`	32-bit, ~4.3 billion addresses — we ran out
IPv6	`2606:4700:3033::6815:2d0c`	128-bit, effectively unlimited — the future

Humans can’t remember 104.21.45.12, so we invented domain names (ayrisglobal.com) plus a phonebook to translate them — that’s DNS (lecture 3). For now: a domain name ultimately resolves to an IP address.

Ports — the “which program”

One server (one IP) runs many programs. A port number says which program the bytes are for.

104.21.45.12 : 443   →  web server (HTTPS)
104.21.45.12 : 25    →  mail server (SMTP)
104.21.45.12 : 22    →  SSH (remote login)

Port	Service
80	HTTP (insecure web)
443	HTTPS (secure web) — the one you live on
25 / 587 / 465	SMTP (sending email)
143 / 993	IMAP (reading email)
22	SSH

Key term: socket

Address + port = a socket. 104.21.45.12:443 is a complete “deliver here” instruction — the exact program on the exact machine.

Packets — the “how”, part 1

Your data isn’t sent as one blob. It’s chopped into packets — small chunks, each stamped with source + destination IP. They travel independently across many routers (possibly via different paths) and are reassembled at the other end.

"Hello world"  →  [He][llo][ wo][rld]  →  cross the internet  →  reassembled  →  "Hello world"

Why chunks? If one is lost, you resend that one — not the whole message.

TCP vs UDP — the “how”, part 2

	TCP	UDP
Guarantees delivery?	Yes — resends lost packets, keeps order	No — fire and forget
Speed	Slightly slower (handshake + checks)	Faster
Used for	Web, email, file transfer — must be exact	Video calls, gaming, DNS — fast beats perfect

The TCP 3-way handshake — the “are you there?” before any real talk. You’ll hear this term forever:

Client → SYN      ("can we talk?")
Server → SYN-ACK  ("yes — can you hear me?")
Client → ACK      ("yes, let's go")

This round trip happens before every normal web request. It’s why latency (distance to the server) matters so much — and why CDNs (lecture 6) put servers physically close to users.

The full request lifecycle

What actually happens when you visit a site:

1. DNS:       ayrisglobal.com → 104.21.45.12        (phonebook lookup)
2. TCP:       open connection to 104.21.45.12:443   (3-way handshake)
3. TLS:       agree on encryption keys              (the 🔒 — lecture 6)
4. HTTP:      "GET /  please"                        (the actual request)
5. Response:  server returns HTML                    (your page)
6. Render:    browser draws it, fetches CSS/JS/imgs  (repeat 1–5 per asset)

Every visit, every time. Internalize these 6 steps — most of this whole track is just expanding one of them.

Steps 4–5 are the HTTP exchange itself — the request your browser sends and the response the server returns. Press ▶ Play to watch the whole journey of one page load: