Behind the Browser: Decoding the Web

What Happens When You Enter a URL? A Deep Dive

Junaid Mohd's photo
Junaid Mohd
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3 min read

1. You Type the URL and Press Enter

  • The journey begins when you type a URL (e.g., https://www.example.com) into your browser’s address bar and press Enter.

2. Browser Parses the URL

  • The browser parses the URL to understand its components:

    • Protocol: https:// (Hypertext Transfer Protocol Secure)

    • Domain: www.example.com

    • Path: /blog/post (if applicable)

    • Query Parameters: ?search=query (if applicable)

3. DNS Lookup: Translating the Domain to an IP Address

  • The browser needs to find the IP address of the server hosting the website. It does this through a DNS (Domain Name System) lookup.

  • The browser checks its cache, the operating system’s cache, and then queries DNS servers to resolve the domain name into an IP address.

4. Establishing a Connection: TCP Handshake

  • Once the browser has the IP address, it initiates a TCP (Transmission Control Protocol) handshake with the server to establish a secure connection.

  • This involves a three-step process: SYN, SYN-ACK, and ACK.

  • If the connection uses HTTPS (secure), an additional TLS/SSL handshake occurs to encrypt the data.

5. Sending an HTTP Request

  • The browser sends an HTTP GET request to the server, asking for the specific resource (e.g., a webpage).

  • The request includes headers with information like the browser type, accepted languages, and cookies.

6. Server Processes the Request

  • The server receives the request and processes it. This may involve:

    • Querying a database for dynamic content.

    • Running server-side scripts (e.g., PHP, Node.js).

    • Retrieving static files (e.g., HTML, CSS, JavaScript).

7. Server Sends an HTTP Response

  • The server sends back an HTTP response, which includes:

    • A status code (e.g., 200 OK for success, 404 Not Found for missing resources).

    • Response headers (e.g., content type, caching instructions).

    • The requested content (e.g., HTML, images, videos).

8. Browser Renders the Page

  • The browser receives the response and begins rendering the page:

    • Parses the HTML to create the DOM (Document Object Model).

    • Parses the CSS to create the CSSOM (CSS Object Model).

    • Combines the DOM and CSSOM to create the render tree.

    • Executes JavaScript to add interactivity.

    • Displays the final rendered page on the screen.

9. Loading Additional Resources

  • The page may require additional resources like images, fonts, or scripts. The browser sends additional HTTP requests to fetch these resources.

10. Page Fully Loaded

  • Once all resources are loaded and the page is fully rendered, the browser fires the load event, indicating the page is ready.

Conclusion

Entering a URL may seem like a simple action, but it triggers a sophisticated chain of events involving multiple technologies and systems. From DNS resolution to rendering, each step plays a crucial role in delivering the webpage to your screen. Understanding this process not only demystifies how the web works but also highlights the importance of optimizing each step for faster, more efficient browsing.

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