How DNS Resolution Works

❀ Introduction :

⤷ Every time you type google.com in your browser, something important happens in the background.
Your computer does not understand website names. It only understands IP addresses.

⤑ DNS (Domain Name System) helps convert:

google.com → IP address

⤑ That is why DNS is called the internet’s phonebook.

⤑ In this blog, we will understand how DNS works step by step using a tool called dig.

❋ What is DNS and Why Do We Need It?

⤑ Humans like easy names:

• google.com

• amazon.com

• github.com

⤑ Computers like numbers:

• 142.250.185.46

⤑ Without DNS:

• You would need to remember IP addresses

• Websites changing servers would break bookmarks

⤑ DNS solves this by:

• Mapping domain names to IP addresses

• Working in a distributed way, not from one single server

• Making the internet fast, scalable, and reliable

❋ What is dig and Why Is It Used?

⤑ dig stands for Domain Information Groper.

⤑ It is a command-line tool used to:

• Check DNS records

• Understand how DNS resolution works

• Debug DNS problems

• Learn DNS deeply

Basic command:

dig google.com

Unlike browsers (which hide DNS details), dig shows exactly what is happening.

❋ DNS Works in Layers (Hierarchy)

DNS is not one server.
It works in three main layers:

Each layer only knows the next layer, not everything.

❋ Layer 1 : Root Name Servers (dig . NS)

Command:

dig . NS

This asks:

Who manages the root of DNS?

What root servers do:

• They are the top of DNS

• They do NOT know website IPs

• They only know where TLD servers are

Example response idea:

I don’t know google.com, but I know who manages .com

Important points:

• There are 13 root server names

• They are spread across the world

• Very reliable and fast

❋ Layer 2 : TLD Name Servers (dig com NS)

Command:

dig com NS

This asks:

Who manages the .com domain?

What TLD servers do:

• They manage domains like .com, .org, .net

• They do NOT know IP addresses

• They point to authoritative servers

Example response idea:

I don’t know google’s IP, but I know Google’s name servers

❋ Layer 3 : Authoritative Name Servers (dig google.com NS)

Command:

dig google.com NS

This asks:

Who is responsible for google.com?

Authoritative servers:

• Are owned by the domain owner (Google)

• Store real DNS records

• Are the source of truth

They contain:

• A records (IP address)

• MX records (email)

• TXT records (verification)

Example:

ns1.google.com
ns2.google.com

These servers finally know:

Yes, this is the IP address of google.com

❋ Full DNS Resolution (dig google.com)

Command:

dig google.com

This gives:

• IP address

• TTL (how long it can be cached)

• Which DNS server answered

⤑ What happens behind the scenes:

1. Check cache

2. Ask root server

3. Root points to .com

4. .com points to Google servers

5. Google server returns IP

6. Result is cached

TTL example:

300 seconds

Means the result can be reused for 5 minutes.

❋ What Are NS Records and Why Are They Important?

⤷ NS (Name Server) records tell:

• Who controls a domain

• Where DNS queries should go next

⤑ They are important because:

• DNS is distributed

• No single server controls everything

• Multiple servers give backup (redundancy)

If one server fails, another works.

❋ What is a Recursive Resolver?

⤷ Your computer does not talk to root servers directly.

⤑ Instead, it uses a recursive resolver, such as:

• 8.8.8.8 (Google DNS)

• 1.1.1.1 (Cloudflare DNS)

• ISP DNS

Flow:

Your PC → Recursive Resolver → Root → TLD → Authoritative

⤑ The resolver:

• Does all DNS work for you

• Caches results

• Returns final IP

❋ DNS and Real Browser Requests

⤷ When you open a website:

1. Browser checks cache

2. OS checks cache

3. Recursive resolver is asked

4. DNS resolution happens

5. IP address is returned

6. Browser connects using HTTP/HTTPS

⤑ DNS usually takes:

• 20–120 ms if not cached

• <10 ms if cached

That’s why DNS feels instant.

❋ DNS from a System Design View

⤑ DNS is designed to be:

• Distributed

• Fast

• Fault-tolerant

• Scalable

⤑ Important ideas:

• Caching improves speed

• Multiple name servers improve reliability

• DNS helps CDNs route users to nearby servers

You can watch for System Design View of DNS :