How dns (domain name system) works step by step

Step-by-Step Process of DNS Resolution

DNS (Domain Name System) is a system that translates human-readable domain names (like www.example.com) into IP addresses (like 192.0.2.1), which are necessary for devices to communicate on the internet. Here’s how DNS works step by step.

1. User Requests a Website

A user types a URL (e.g., www.example.com) into a web browser.

The browser needs to know the IP address of www.example.com to establish a connection.

2. Check Browser Cache

The browser first checks its local cache to see if it has already resolved the domain recently. If found, it uses the cached IP address, skipping the DNS lookup.

If the IP isn’t cached, the browser proceeds to the next step.

3. Check Operating System Cache

The operating system (OS) also maintains a DNS cache. The browser asks the OS if it knows the IP address of the requested domain. If the OS has it, the process ends here.

If not, the OS forwards the request to a DNS resolver.

4. Query the DNS Resolver

The OS sends a request to the DNS resolver (usually provided by the ISP or a public DNS service like Google or Cloudflare).

The resolver’s job is to find the IP address of the domain.

5. Check Resolver Cache

The DNS resolver checks its own cache. If the IP address for the domain is cached, it returns the IP to the browser.

6. Recursive Query: Request to Root DNS Server

If the resolver does not have the IP address cached, it starts a recursive query.

The resolver sends a request to a Root DNS Server. These root servers don’t know the IP of the specific domain but can point the resolver to the right Top-Level Domain (TLD) DNS Server (e.g., .com, .net, .org).

7. Request to TLD DNS Server

The resolver sends a request to the TLD DNS server (e.g., the one responsible for .com domains).

The TLD server responds with the IP address of the Authoritative Name Server for example.com.

8. Request to Authoritative Name Server

The resolver then sends a request to the Authoritative Name Server for example.com.

This server knows the actual IP address of www.example.com and returns it to the resolver.

9. Return IP Address to Browser

The resolver sends the IP address back to the OS, which then provides it to the browser.

10. Browser Connects to the Web Server

With the IP address in hand, the browser sends an HTTP request to the web server at that IP, and the web page begins to load.

Summary of DNS Lookup Components:

DNS Resolver: The server that handles the request and performs recursive queries.

Root DNS Server: Directs queries to the appropriate TLD servers.

TLD DNS Server: Directs queries to the appropriate authoritative name server.

Authoritative Name Server: Holds the actual DNS records and provides the IP address.