Types of DNS server

All DNS servers fall into one of four categories: Recursive resolvers, root nameservers, TLD nameservers, and authoritative nameservers.

Recursive resolver / DNS resolver

  • First stop in a DNS query
  • It either respond with cached data, or send a request to a root nameserver, followed by another request to a TLD nameserver, and then one last request to an authoritative nameserver. 
  • After receiving a response from the authoritative nameserver with the requested IP address, the recursive resolver then sends a response to the client.
  • It will cache information received from authoritative name servers.
  • Most internet users use a recursive resolver provided by their ISP.

DNS Root Server

  • Accepts a domain name and responds by directing the recursive resolver to a TLD nameserver, based on the extension of that domain (.com, .net, .org, etc.).
  • 13 type root nameserver from ICANN. multiple copies of each one all over the world (632 in 2016)

TLD nameserver

  • Maintains information for all the domain names that share a common domain extension.
  • Respond by pointing to the authoritative nameserver
  • Management of TLD nameservers is handled by IANA, which breaks up the TLD servers into two main groups
  • Generic top-level domains: not country specific (.com, .org, .net, .edu, and .gov.)
  • Country code top-level domains: domains that are specific to a country or state (.uk, .us, .ru, and .jp)

Authoritative nameserver

  • Provide a recursive resolver with the IP address of that server found in the DNS A record
  • If the domain has a CNAME record (alias) it will provide the recursive resolver with an alias domain, which point the recursive resolver will have to perform a whole new DNS lookup