Domain Name Server (DNS) is the phone book of the internet which has the job to translate domain name into ip addresses so that computers on the internet can communicate with one another.
The flow of dns query is:
Client -> DNS Recursive Resolver -> DNS Root Nameserver ->
DNS TLD Name Server -> DNS Authoritative Server
DNS Recursive resolver: This serves the client requests by communicating with other DNS servers to resolve client requests.
DNS root name server: This creates first level of domain indexes and knows which TLD name server to query for request.
Top level domain server (TLD): This server hosts the last portion of the host, I,e for www.google.com, it will host ‘.com’
Authoritative name server: This is the final destination and will return the ip address corresponding to the host if it has the record.
DNS Caching : The purpose of dns caching is so that the dns to ip translation requests can be processed quickly. DNS caching is done by the browser and in the OS.