When a user interacts with the internet a series of steps take place behind the scenes to ensure the request reaches the correct server and a response is returned. It involves identifying the server using an IP address, resolving domain names through DNS, routing the request across networks to efficiently handle traffic. Understanding how a request originates from the client and reaches the server requires breaking down each of these components and how they work together in the request response cycle.
User-Response Cycle:
User initiates request
The process starts when the user enters a URL like www.wikipedia.org in the browser.
Browser checks local cache
The system first checks:
- Browser cache
- OS cache
If the IP is already known, it skips DNS lookup.
DNS query is initiated
If not found, a DNS query is triggered to find the IP address of the domain.
Local resolver (sub-resolver)
The request first goes to the local machine’s resolver which handles DNS queries.
Request goes to ISP resolver
The query is forwarded to the ISP DNS resolver.
Root Name Server
The ISP resolver contacts the Root Name Server, which doesn’t give the exact IP but directs to the correct TLD server (Top Level Domain).
TLD (Top Level Domain) server
Based on .org, .com, .in, etc., the request is sent to the respective TLD server.
Zone File
This server contains the actual records or zone file:
- A record - IPv4 address
- AAAA record - IPv6 address
- CNAME - alias
- MX - mail
It returns the correct IP address.
IP returned to client
The IP travels back:
NS - TLD - ISP - local resolver - browser
HTTP request sent
The browser sends an HTTP request to the server.
Server processes request
The backend server processes logic and fetches data.
Response sent back
The server sends an HTTP response.
Browser shows content
The browser receives the response and displays the webpage.
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