What happens when we type a URL?

A Uniform Resource Locator (URL) is a web address that specifies the location of a web resource on a computer network and defines how to access it. URLs are most commonly used to reference web pages, but they can also point to files, email addresses, databases, and other network resources.

A URL consists of several components: a protocol (like HTTP or HTTPS), a domain name, an optional port number, a path to the specific resource, and sometimes additional parameters or fragments. When you type a URL into your browser's address bar or click a hyperlink, a complex series of steps occurs behind the scenes to retrieve and display the requested content.

URL Structure

Every URL follows a standardized format with these components in order:

• Scheme/Protocol − Defines how to access the resource (http, https, ftp, etc.)

• Domain name − Human-readable address that maps to an IP address

• Port − Optional network port number (defaults to 80 for HTTP, 443 for HTTPS)

• Path − Specifies the location of the resource on the server

• Query parameters − Optional data passed to the server

• Fragment − References a specific section within the resource

What Happens When We Type a URL?

When you enter a URL and press Enter, your browser initiates a complex process involving multiple network protocols and systems:

Step 1: DNS Resolution

The browser first checks its cache for a DNS (Domain Name System) entry to find the corresponding IP address. If not found locally, it queries the ISP's DNS server to resolve the domain name to an IP address.

Step 2: TCP Connection

Once the IP address is obtained, the browser establishes a TCP connection with the web server using a three-way handshake (SYN, SYN-ACK, ACK messages).

Step 3: HTTP Request

The browser sends an HTTP request to the server, specifying the requested resource, headers, and any additional data.

Step 4: Server Processing

The web server processes the request, retrieves the requested resource (HTML page, image, file, etc.), and prepares an HTTP response.

Step 5: Response and Rendering

The server sends the HTTP response back to the browser, which then parses and renders the content, displaying the webpage to the user.

Key Components Involved

Conclusion

When you type a URL, your browser performs DNS resolution, establishes a TCP connection, sends an HTTP request, and renders the received response. This multi-step process involving DNS servers, network protocols, and web servers happens seamlessly within seconds to deliver the requested web content to your screen.