From gbhackers.com
Domain Name System or DNS is one of the foundational elements of the entire internet; however, unless you specialize in networking, you probably don’t realize how important it is.
DNS is essentially like a phone book of numbers that computers use for communication. Specifically, these numbers are IP addresses.
This directory is stored on domain name servers around the world, and a site can have more than one IP address.
Despite the importance of DNS, it’s something that tends to be overlooked in terms of network security. DNS security tends to fall lower on the totem pole than firewalls, proxies and endpoint protection, for example.