DNS Hierarchy Explained: Root to Authoritative Servers

How the internet finds your favorite websites in milliseconds

When you type a web address like www.example.com into your browser, you might imagine your computer just “knows” where to find it.
In reality, it follows a structured hierarchy of servers — like climbing down a ladder from the top level (Root) to the exact destination (Authoritative Server).

This process is the Domain Name System (DNS) hierarchy, and it ensures that billions of devices can find websites quickly and reliably.

1. The Big Picture of DNS Hierarchy

Think of DNS as a phone book of the internet — except it’s global, distributed, and updated constantly.
It is organized in levels, from the root servers at the top to authoritative servers that give the final answer.

2. Levels of the DNS Hierarchy

• (a) Root DNS Servers — The Starting Point

  • What they are: The top-level DNS servers that know where to find the servers for each Top-Level Domain (TLD).

  • Count: 13 logical root server systems (named A to M), operated by organizations like Verisign, ICANN, and NASA.

  • Job: When a resolver asks, “Where is www.example.com?” the root server responds with, “Go ask the .com TLD server.”

  • Example: Root server → Points to .com name servers for any .com domain query.

• (b) Top-Level Domain (TLD) Servers

  • What they are: Servers responsible for domains under a specific TLD like .com, .org, .net, .in, .uk.

  • Job: The TLD server says, “I know where the authoritative name server for example.com is.”

  • Example: The .com TLD server tells you to ask ns1.examplehosting.com for example.com.

• (c) Authoritative DNS Servers

  • What they are: The servers that hold the actual DNS records for a domain.

  • Job: Give the final answer — the IP address for the requested domain or subdomain.

  • Example: ns1.examplehosting.com → “www.example.com is at 93.184.216.34.”

3. How a DNS Query Flows from Root to Authoritative Server

Let’s walk through the journey when you type www.netflix.com into your browser:

1. Browser Cache Check – Your browser first checks if it already knows the IP from a previous visit.

2. Local DNS Resolver – Your ISP’s resolver checks if it has the answer cached.

3. Root Server Query – If not cached, it asks a root server, “Where can I find .com domains?”

4. TLD Server Query – The root server sends it to the .com TLD server.

5. Authoritative Server Query – The .com server sends it to Netflix’s authoritative DNS server.

6. Final Answer Returned – Netflix’s authoritative server says, “www.netflix.com is at 198.38.96.78.”

7. Connection Established – Your browser connects to Netflix’s server and starts loading the website.

4. Real-World Analogy

Imagine you want to call John in another city:

• Root server = You ask the country’s phone directory for the city directory.

• TLD server = The city directory tells you which local phone book John is listed in.

• Authoritative server = The local phone book gives you John’s exact phone number.

5. Why DNS Hierarchy Matters

• Efficiency: Keeps the internet fast by breaking the search into steps.

• Scalability: Supports billions of devices and domains.

• Reliability: Even if one server fails, the hierarchy ensures others can take over.