The Internet Journey

Deep Dive: What Happens When You Click on a URL?

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Shobith Kumar
·

3 min read

Introduction

We use the internet every day, clicking on links without thinking twice. But have you ever wondered what happens behind the scenes when you click on a URL? In this deep dive, we'll explore the entire journey of a URL request, from the moment you press "Enter" to the page loading on your screen.

1. The Browser Processes the URL

  • The browser first checks if the URL is valid.

  • If the URL is incomplete (e.g., missing "https://"), the browser attempts to correct it.

  • If it's a search query instead of a URL, the browser redirects it to the default search engine.

2. DNS Resolution: Finding the Server’s IP Address

  • The browser checks its cache to see if it has the IP address for the domain.

  • If not found, it sends a request to a DNS resolver (often provided by your ISP or a third-party like Google’s 8.8.8.8).

  • The DNS resolver queries multiple authoritative servers until it finds the correct IP address.

  • The IP address is returned to the browser, which now knows where to send the request.

3. Establishing a Connection (TCP & TLS Handshake)

  • The browser establishes a connection with the web server using TCP (Transmission Control Protocol).

  • If the website uses HTTPS, a TLS (Transport Layer Security) handshake occurs to encrypt the communication.

  • The handshake involves:

    • Exchanging cryptographic keys

    • Authenticating the server (via SSL certificates)

    • Agreeing on encryption protocols

4. Sending the HTTP Request

  • The browser sends an HTTP(S) request to the server.

  • The request contains:

    • HTTP method (GET, POST, etc.)

    • Headers (e.g., user-agent, cookies, authentication tokens)

    • Optional body (for POST/PUT requests)

5. The Server Processes the Request

  • The web server (e.g., Nginx, Apache) receives the request and forwards it to the backend.

  • The backend processes:

    • Business logic

    • Database queries

    • Authentication & authorization

  • Once processed, the server generates a response (typically an HTML document).

6. The Server Sends the HTTP Response

  • The response includes:

    • Status code (200 OK, 404 Not Found, 500 Internal Server Error, etc.)

    • Headers (e.g., cache-control, content-type, cookies)

    • The response body (HTML, JSON, XML, etc.)

7. The Browser Renders the Page

  • The browser receives the response and starts rendering the page.

  • The rendering process includes:

    • Parsing HTML and building the DOM (Document Object Model)

    • Fetching and applying CSS styles

    • Executing JavaScript

    • Loading external assets (images, fonts, videos, etc.)

8. Final Steps: JavaScript Execution & User Interaction

  • The browser executes JavaScript to enable dynamic behavior.

  • Event listeners, API calls, and client-side rendering occur.

  • The page is now fully interactive and ready for user input.

Conclusion

Next time you click on a URL, you'll know the incredible amount of work happening behind the scenes. From DNS lookups to rendering the final page, the journey of a URL request involves multiple layers of networking, security, and processing.

Want to learn more?

If you're interested in a deeper technical dive, check out resources on TCP/IP, DNS mechanics, and web rendering engines.

🚀 Happy coding!

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