How DNS Works: A Step-by-Step Guide (Deep & Beginner-Friendly Explanation)
Whenever you type a website name like learncyber.in into your browser, a lot of things happen behind the scenes in just milliseconds. This entire process is handled by a system called DNS (Domain Name System).
In this detailed guide, we will break down how DNS works step by step, exactly as shown in the image above, and also explain the technical depth so learners can build a strong foundation in networking, cybersecurity, and web technologies.
What is DNS (Domain Name System)?
DNS is like the phonebook of the internet. Humans remember website names (like google.com), but computers communicate using IP addresses (like 142.250.182.14). DNS translates human-readable domain names into machine-readable IP addresses.
Without DNS, we would have to remember numerical IP addresses for every website, which is impractical.
Step 1: User Enters a Website Address
The process starts when a user types a website URL (for example, learncyber.in) into the browser’s address bar and presses Enter.
What happens at this moment?
- The browser understands that it needs to locate the server hosting this website.
- To do that, it must first find the IP address linked to the domain name.
- This triggers the DNS resolution process.
At this stage, no internet request to the website itself has been made yet — only a request to find the IP address.
Step 2: Browser Checks Its Cache
Before asking anyone else, the browser checks its internal DNS cache.
What is DNS Cache?
DNS cache is a temporary storage that keeps previously resolved domain names and their IP addresses. If you recently visited the same website, the browser may already know the IP address.
Possible Outcomes
- Cache Hit: IP address found → browser skips DNS lookup and connects directly.
- Cache Miss: IP address not found → browser asks the Operating System.
This caching mechanism improves speed and reduces unnecessary DNS traffic.
Step 3: Operating System DNS Resolver
If the browser cache does not have the IP address, it sends the request to the Operating System’s DNS Resolver.
What is a DNS Resolver?
A DNS Resolver is a service running on your device (Windows, Linux, macOS, Android, etc.) that handles DNS queries on behalf of applications.
Resolver Cache Check
- The OS checks its own DNS cache.
- If found → returns the IP to the browser.
- If not found → forwards the query to an external DNS server.
Common DNS resolvers include:
- ISP DNS Servers
- Google DNS (8.8.8.8)
- Cloudflare DNS (1.1.1.1)
Step 4: Recursive DNS Resolver (DNS Server)
Now the real DNS journey begins. The request reaches a Recursive DNS Resolver.
This server is responsible for finding the correct IP address by communicating with other DNS servers if necessary.
The Recursive Resolver Performs Multiple Queries
1. Root DNS Server
The resolver first asks the Root DNS Server:
“Where can I find information about .in domains?”
The root server does not know the IP but responds with the address of the TLD DNS server.
2. TLD (Top-Level Domain) DNS Server
The resolver now asks the .in TLD DNS server:
“Where is the authoritative server for learncyber.in?”
The TLD server replies with the address of the Authoritative DNS Server.
3. Authoritative DNS Server
This server holds the actual DNS records for the domain.
It responds with the exact IP address associated with learncyber.in.
Important DNS Records
- A Record: Maps domain to IPv4 address
- AAAA Record: Maps domain to IPv6 address
- CNAME: Alias for another domain
- MX: Mail server records
Step 5: IP Address Returned to Browser
Once the recursive resolver gets the IP address:
- It sends the IP back to the Operating System.
- The OS forwards it to the browser.
- The resolver also stores it in cache for future use.
Now the browser finally knows where the website lives.
Step 6: Browser Connects to the Web Server
Using the IP address, the browser establishes a connection with the web server.
Behind the Scenes
- TCP handshake (SYN, SYN-ACK, ACK)
- HTTPS negotiation (TLS/SSL encryption)
- HTTP request sent (GET / POST)
This ensures secure and reliable data transfer between the browser and the server.
Step 7: Website Loads
The web server responds with:
- HTML files
- CSS stylesheets
- JavaScript files
- Images and media
The browser renders the content and displays the website to the user.
🎉 The website is now fully loaded!
Why DNS is Important?
- Makes the internet user-friendly
- Improves performance with caching
- Supports load balancing
- Critical for cybersecurity monitoring
DNS in Cybersecurity (Extra Knowledge)
DNS is often targeted in cyberattacks such as:
- DNS Spoofing
- DNS Poisoning
- DDoS Attacks
Understanding DNS deeply helps security professionals detect suspicious traffic and protect networks.
Conclusion
DNS may look simple on the surface, but it is one of the most critical components of the internet. From the moment a user types a website name to the moment the page loads, DNS silently works in the background to make everything possible.
Mastering DNS is essential for anyone learning Networking, Web Development, or Cybersecurity.
Happy Learning 🚀
