What happens when you type a URL?

Steps 1 and 2: find the server, then say hello

Your computer can't use a name like example.com to reach a website. It needs the server's IP address, so it first asks DNS, the internet's contacts list: "what's the address for example.com?" DNS answers with a number, such as 203.0.113.10.

Next, your computer and that server do the TCP three-way handshake: your computer sends SYN, the server answers SYN-ACK, and your computer replies ACK. Now both sides know the other is there and ready to talk.

Step 3: lock the connection

If the address starts with https://, the two sides then do a TLS handshake. They check that the server is really who it says it is and agree on secret keys. From then on, everything they send is scrambled, so anyone in between (on public Wi-Fi, for example) sees only gibberish. That's what the little padlock in your browser bar means.

Steps 4 to 6: ask, receive, draw

With a safe connection open, your browser sends an HTTP request, basically "please send me this page." The simplest one is GET /, which asks for the site's home page.

The server answers with the page as code: HTML that describes what's on the page. Your browser reads that code, notices it also needs pictures and style sheets (CSS), asks for those too, and then renders the page: it works out where every heading, image and paragraph goes and draws them on your screen.

Try it yourself

Open any website, then open your browser's developer tools (F12 on Windows, Option+Command+I on a Mac) and click the Network tab. Reload the page. Every line is one request: the first is the page's HTML, and the rest are the pictures, styles and scripts the browser fetched after reading it. Click the padlock in the address bar to see the site's certificate from step 3.

Good to know

• This is a simplified overview. Steps can be skipped or combined: if your computer already has the DNS answer saved (cached), step 1 is skipped.
• Newer sites using HTTP/3 run over QUIC (on UDP), which merges the handshake and the encryption setup into one step.
• Each step gets its own episode, and the long-form video goes through them one by one.

For CCNA learners

This ties together CCNA 200-301 exam topics 1.5, compare TCP to UDP (the three-way handshake) and 4.3, explain the role of DHCP and DNS: be able to put DNS resolution, the TCP handshake and the application request in order.