Imagine you are looking for someone's house, but all you have is their name. You would probably rely on a friend who knows which neighborhood they live in. That friend directs you to someone in that area who can tell you the exact address. This multi-step process which is similar to how the DNS works.

The Domain Name System (DNS) is a system that translates human-readable website names (like www.example.com) into IP addresses (like 192.0.2.1) that computers use to identify each other on the internet. When you type a website's domain name (like www.example.com) into your browser , your computer needs to find the corresponding IP address (like 192.0.2.1) to connect to the website's server. But how does your browser know where to look?

This is where the DNS hierarchy comes in - a step-by-step system that starts at the top-level root servers and works its way down to the authoritative DNS server. Let's break it down, using example.

What is the DNS Hierarchy?

The DNS hierarchy is a multi-layered system of servers that work together to translate human readable domain names like www.example.com into machine-readable IP addresses, such as 192.168.1.1

It has four primary components:

1. Root DNS Servers

2. TLD (Top-Level Domain) DNS Servers

3. Authoritative DNS Servers

4. Caching Resolvers

Each layer has a specific role, narrowing down the search for the requested domain until the exact IP address is found.

Root DNS Servers:

Root DNS Servers are the highest level DNS Servers in the hierarchy. They don't know specific IP addresses but act as a directory for Top-Level Domain(TLD) servers like .com, .org, .net, and country-specific TLDs like .uk.

When a DNS resolver asks the root server where to find a domain, the root server responds with the location of the appropriate TLD DNS server.

Example:
When you type www.example.com, the root server directs your resolver to the .com TLD server, saying,

“This domain belongs to the .com neighborhood. Go there for more details.”

Do you Know?

There are 13 logical root servers worldwide, operated by different organizations. These servers are named from A to M (e.g., A.ROOT-SERVERS.NET). you can read about all these root servers here.

TLD DNS Servers:

The TLD Servers are responsible for managing domains within their respective top-level domain. For example, the .com TLD server manages all domains ending with .com, while the .org TLD server manages domains like example.org.

When a resolver contacts a TLD Server, it gets the location of the authoritative DNS server for the specific domain.

Example:

The .com TLD server might say,

“I don’t know the IP for example.com, but I know the authoritative server that does. Here’s its address.”

Authoritative DNS Servers:

Authoritative DNS servers are the final stop in the DNS hierarchy. These servers store the actual DNS records for a domain, including its IP address, mail server information (MX records), and other data. Providers like GoDaddy, Cloudflare, etc offer authoritative DNS services.

When the resolver contacts the authoritative DNS server, it receives the definitive IP address for the requested domain.

Example:

When asked about www.example.com, the authoritative DNS server responds,

“The IP address is 192.168.1.1.”

Caching Resolvers:

Caching resolvers are DNS servers that temporarily store the results of previous queries. This caching speeds up the process by allowing repeated queries to skip the entire hierarchy and go directly to the IP address.

Example:

If you’ve visited example.com recently, the resolver might say,

“I already know the IP address is 192.168.1.1. No need to ask the hierarchy again.”

How They Work Together?

When you enter a domain name in your browser, the following steps occur:

Caching Resolver: Your device sends the query to a caching resolver, which checks its cache for the answer.

Root DNS Server: If the answer is not cached, the resolver queries a root DNS server.

TLD DNS Server: The root server directs the resolver to the appropriate TLD DNS server.

Authoritative DNS Server: The TLD server directs the resolver to the authoritative DNS server, which provides the final IP address.

Response: The resolver returns the IP address to your device, which can then access the website.

This multi-step process ensures efficient and accurate resolution of domain names to IP addresses.

The DNS hierarchy may seem complex at first, but it’s a fascinating and elegant system that ensures the internet works smoothly. From the global root servers to the local authoritative servers, every layer plays a critical role in translating domain names into IP addresses.

Next time you type a URL into your browser, remember the journey your query takes—it’s like asking for directions, but on a global scale.