How DNS Work
When the client try to connect to a hostname, it go through the following process
1) Check it own cache, to see if it can find it, ipconfig /displaydns can check the dns cache in window, it can also added in /etc/hosts
2) if it is not found in 1), it query for ISP dns server
3) if DNS server cannot find it under its cache, it direct the query to root server, there are 13 root server in the world
4) Root server retun the Top Level Domain Server (TLD) to ISP DNS server (e.g .com server)
5) ISP DNS server send the query to .com server
6) .com server respons it with authority name server
7) ISP DNS server send the query to the server returned in 6)
8) the server in 6) return the A name record
9) ISP DNS server add the record to cache and give it to client.
