DNS-How URLs are resolved

  1. If not, then it asks to Operating System if it has a mapping present for the URL.
  2. If not, then it goes to resolver server which are usually hosted by ISP

Resolver servers are also known as DNS resolver or recursive DNS server.

4. Resolver than checks in its own cache if a mapping is present.

5. If not, then it goes to root sever. All resolver servers must know one thing ie How to reach the root server(s).

  • At present there are 13 root servers available which are operated by 12 independent organisation
  • They are named [letter].root-servers.net where [letter] changes rom a to m.
  • This does not mean that there are just 13 physical servers ( each organisation provides multiple physical servers distributed around the globe

6. Root server directs the resolver to top level domain server.

TLDs are maintained by ICANN Internet corporation for assigned Names and Numbers

8. TLD returns the mapping if found else it redirects the resolvers to authoritative servers

  • Authoritative servers are the actual mapping container where this mapping remains permanently
  • Authoritative servers don’t cache any thing
  • Authoritative servers gets the information of mapping from domain registrar. When a domain name is purchased, domain registrar reserves the name and make a communication to the TLD registry (the authoritative name servers)
  • Authoritative servers resolved the mapping and gives the record back to resolver

9. Resolver returns the result to browser and browser shows the website.

#Whenever get a chance, resolver caches the information so that it does not need to bother the servers again and again.

#resolvers are also known as recursive server as they recurse the DNS hierarchy to get the information.



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Software Developer, Interested in Technology and Productivity