Computer Network- A Complete Picture

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Arjit Sharma
02 Mins

Ever wondered what happens when you type a URL like csprimer.in into your browser and hit Enter? Beneath that simple action lies series of networking and system events. In this article lets unpack this.

Step 1: You Type csprimer.in into Chrome

Your browser is just another software application. It doesn’t yet know the IP address of csprimer.in, so it needs to ask.

Step 2: DNS Resolution

  • Chrome queries the Operating System (OS) to resolve the domain name
  • OS checks its DNS cache; if not found, it queries a configured DNS resolver
  • This may involve multiple recursive DNS queries until it reaches the authoritative server for csprimer.in
  • The resolved IP address (e.g., 142.250.190.78) is returned to the browser

Step 3: Browser Prepares an HTTP Request

  • The browser constructs a GET / HTTP/1.1 request with headers (Host, User-Agent, etc.)
  • This is application-layer data ready to be sent to the web server

Step 4: OS Assigns a Source Port & Initiates TCP Connection

  • The browser hands the HTTP request to the OS’s networking stack
  • OS chooses a source port (e.g., 49152) and uses TCP to establish a three-way handshake with the destination server’s port 80 or 443 (for HTTPS)
  • A reliable channel is now established for sending data

Step 5: Request Travels Through the Protocol Stack

The HTTP request is encapsulated in layers as it moves down:

LayerAction
ApplicationConstructs HTTP request
TransportTCP segments the data, adds port info
InternetAdds IP headers, including source and destination IPs
Network AccessConverts data into frames; moves via physical medium

The request is sent over the Internet, hopping through routers and switches.

Step 6: Server-Side Handling

  • The destination server (e.g., running Apache or Nginx) receives the packet
  • OS on the server checks the destination port, sees it’s for HTTP (port 80), and passes it to the correct application process via a socket
  • The web server reads the request and processes it (e.g., routing, templating, database queries)

Step 7: Server Sends Back an HTTP Response

  • Web server generates a response: headers + HTML body
  • This response is sent back through the same TCP connection
  • It travels up the stack from physical → data link → network → transport → application

Step 8: Browser Receives and Renders

  • Chrome receives the HTTP response
  • It parses the HTML, requests additional resources (CSS, JS, images)
  • Renders the page to the user - csprimer.in now appears fully loaded

Conclusion

This is the magic behind every click. A few milliseconds, and a cascade of layers and global collaboration help load those websites for you. Understanding this stack empowers software engineers to build better web apps, debug smarter, and optimize network-heavy systems.

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