What is a DNS Resolver?

About

The resolver ¹⁾ or recursive resolver is a method (class/interface) that:

• transforms:
  • a user request (DNS query)
  • into multiple name servers query that can provide the information.
• process the response
• using or not a cache

They must be able to access at least one name server and use that name server's information to answer a query directly, or pursue the query using referrals to other name servers.

A resolver is typically directly accessible to user programs; hence no protocol is necessary between the resolver and the user program.

Resolver and Dns server

Resolver is also another name for a nameserver that can handles recursive queries.

Example: DNS Lookup

The resolver starts from the root and goes all the way down to find the authoritative nameserver of the name.

Example: when a user asks the website dns name datacadamia.com, the web browser performs a query with the resolver.

• The resolver:
  • queries the DNS root nameserver (.) to know the authoritative nameserver of the com. TLD
  • get a response from the root server with the ip address of a Top Level Domain (TLD) DNS server
• The resolver:
  • queries the TLD nameserver to get the authoritative nameserver of the apex domain datacadamia.com..
  • get a response from the TLD server with the ip address of the authoritative nameserver for datacadamia.com..
• The resolver:
  • sends a query to the final domain authority nameserver.
  • get a response
  • and give it back to the application