What Happens When You Open a Website: DNS, HTTPS and How Browsers Load a Page

One page load, step by step: how DNS finds the server, what the TCP and TLS handshakes do, how a certificate authority like Let's Encrypt vouches for a site, what an HTTP request and response look like and why HTTP/3 moved to QUIC, and how the browser turns code into pixels.

0:23 Finding the address: DNS

The Domain Name System turns a name into an IP address through a resolver, a root server, a top-level domain server and an authoritative server, with caching at every level.

Sources: Cloudflare Learning Center (original) · MDN Web Docs (original)

1:45 Two handshakes: TCP and TLS

A TCP three-way handshake opens the connection; the TLS handshake agrees on keys, proves the server identity and encrypts everything after it.

Sources: MDN Web Docs (original) · IETF RFC 8446 (original)

3:27 Who vouches for the server: certificates

A certificate authority ties a public key to a domain name after the server proves it controls the domain; Let's Encrypt does it with the automated ACME protocol.

Sources: Let's Encrypt (original)

4:51 The request and the response: HTTP

HTTP is a plain, extensible, stateless request and response protocol; versions one point one, two and three changed how messages travel, not what they mean.

Sources: MDN Web Docs (original) · IETF RFC 9114 (original)

6:29 From code to pixels: rendering

The browser parses HTML and CSS into trees, builds a render tree, runs layout and paints pixels; late images without dimensions force a reflow.

Sources: MDN Web Docs (original)

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Produced by Juan Pablo.