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.

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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.

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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.

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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

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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)

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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).

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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.)

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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.)

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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.

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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!