What is a DNS server?

A DNS server is a server that answers DNS queries and reports which IP address corresponds to a domain name.

In simpler terms: a DNS server tells the computer exactly where on the internet it needs to connect.

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#Why a DNS server is needed

When you type in the browser:

example.com

the computer does not know where this site is located. It asks the DNS server:

"What is the IP address of example.com?"

The DNS server looks for the answer and returns the IP.

Without DNS servers:

• sites would not open by name
• applications and services could not work

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#What a DNS server does

The main tasks of a DNS server:

• accepts DNS queries
• looks up the "domain -> IP" mapping
• returns the answer to the client
• may cache answers to speed things up

A DNS server does not transmit sites or data, it only reports the address.

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#How a DNS server works (simplified)

1. The client sends a DNS query
2. The DNS server:

• either finds the answer itself
• or asks other DNS servers

3. The DNS server returns the IP address
4. The client connects to the needed server by IP

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#Types of DNS servers (briefly)

For understanding in an interview, it is important to know that DNS servers come in different kinds:

#Recursive DNS server

• accepts the request from the client
• "walks" through other DNS servers itself
• returns the final answer

Usually this is:

• the provider's DNS
• public DNS (Google, Cloudflare)

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#Authoritative DNS server

• knows the exact data about the domain
• stores the domain's DNS records
• does not ask other servers

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#Important points for an interview

• a DNS server is not a single server, but part of a distributed system
• DNS servers work around the clock and automatically
• if DNS servers fail, sites become unreachable by name
• a DNS server operates at the application layer of OSI

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#Real-life example

A DNS server is like a directory assistance service:

• you give a name
• you are told a number
• then you call it yourself

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#Short interview answer

Remember this formulation:

A DNS server is a server that processes DNS queries and returns the IP address that corresponds to a domain name, allowing the client to find the right server on the network.