You press Enter and the page appears. In between, four stages run in a few hundred milliseconds — and knowing them is the difference between guessing at a slow site and finding the actual bottleneck.
1. DNS — resolves the domain name to an IP address. astmation.com → 203.0.113.42
2. CONNECT — the browser opens a network connection before any HTTP is exchanged. For HTTPS that's TCP plus a TLS handshake. For HTTP/3 it's QUIC, which runs on UDP rather than TCP. Which one you get depends on the site and the browser.
3. HTTP — the request goes out, the server responds. Note that most modern sites don't just hand back a file sitting on disk; the page is often built per request.
4. RENDER — the browser parses the HTML, pulls in CSS and JavaScript, and paints. More resources keep being fetched as it goes, and JavaScript may request still more after the first paint.
One honest caveat: no two page loads are identical. Caches skip stages entirely, redirects add round trips, connection reuse removes handshakes, and a JavaScript-heavy app may do most of its real work after the HTML arrives.
But the stages are the map. When a page feels slow, you're asking: is it DNS, the connection, the server's response time, or the rendering? Each one has different fixes.
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