The Domain Name System (DNS) is one of the most crucial Internet protocols because it is the proverbial molasses that holds the bread together. DNS ties names, such as www.google.com, to IP addresses, such as 220.127.116.11. When we want to communicate with a networked device and we don’t know its IP address, we access that device via its DNS name.
DNS servers store a database of resource records of IP address-to-DNS name mappings, which they share with clients and other DNS servers.
Because the architecture of DNS servers is complicated, we will just look at some common types of DNS traffic. You can review the various DNS-related RFCs at http://www.isc.org/community/reference/RFCs/DNS.
As you can see ...