DNS Resolver


  • After receiving a DNS query from a client, resolver will either respond with cached data, or send a request to Root DNS Server, followed by another request to a Top-Level Domain DNS Server, and then one last request to an Authoritative DNS Server. After receiving a response from the authoritative server containing the requested IP address, the resolver then sends a response to the client


Resolver will cache information received from authoritative nameservers.

When a client requests the IP address of a domain name that was recently requested by another client, the resolver can just deliver the client the requested record from its cache, avoid the expensive recursive query!

Root DNS Server

  • 13 root DNS Server known to every DNS Resolver, and they are the first stop in a recursive resolver’s quest for DNS Record


  • A root server accepts a recursive resolver’s query which includes a Domain Name, and the root nameserver responds by directing the recursive resolver to a Top-Level Domain DNS Server, based on the extension of that domain (.com, .net, .org, etc.)

Top-Level Domain DNS Server

Authoritative DNS Server


  • Return IP Address of Domain Name base on A Record
  • OR if the domain has a CNAME Record it will provide the recursive resolver with the Canonical Hostname (CNAME), at which point the recursive resolver will have to perform a whole new DNS lookup to procure a record from an Authoritative DNS Server (often an A record containing an IP address)