URL to Page Load: The Complete Story

1. DNS Resolution: Finding the IP Address

• The browser first checks its own DNS cache for the IP address of the requested URL.

• If not found, it checks the operating system’s DNS cache.

• If the OS also doesn't have the entry, the browser initiates a recursive DNS lookup using a DNS resolver (usually provided by the ISP or a public DNS like Google or Cloudflare).

2. Establishing a TCP Connection

• After resolving the IP address, the browser establishes a TCP connection to the server using that IP.

• Modern browsers use a persistent connection (via keep-alive) to reduce the overhead of repeatedly opening new connections.

3. SSL/TLS Handshake (for HTTPS)

• If the protocol is HTTPS, a TLS/SSL handshake is performed:

  • Validates server identity via certificates.

  • Negotiates encryption methods.

  • Establishes an encrypted connection between the browser and the server.

4. Sending the HTTP Request

• The browser compiles the request according to HTTP specifications.

• Since the user just enters a URL, the browser fires an HTTP GET request to the server.

• The request includes:

  • Headers: Metadata and instructions for the server (e.g., Accept, User-Agent, Host, etc.).

  • Cookies: (if any) are also sent.

  • Query parameters like ?q=home to pass additional information.

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5. Anatomy of the URL

Example:
https://example.com/products/item?q=home

• Scheme: Defines the protocol (e.g., https)

• Domain: Human-readable address (e.g., example.com)

• Path: Specific resource being requested (e.g., /products/item)

• Query Parameters: Key-value pairs providing extra data (?q=home)

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6.Receiving the Response

• The server receives the HTTP request and parses it to understand the action required.

• The server may:

  • Load a static file from disk.

  • Perform a database query and return dynamic content.

  • Return an error response (e.g., 400 Bad Request) if the request is malformed.

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7. Rendering the Page

• The browser receives the HTTP response, usually containing HTML.

• The browser starts rendering the page, constructing the DOM tree.

8. Loading Additional Resources

• As the HTML is parsed, the browser detects other resources:

  • JavaScript files

  • CSS stylesheets

  • Images and fonts

• For each, a similar request cycle (DNS lookup → TCP → HTTP GET) is repeated if those resources are not cached.