From tripwire.com
A popular joke among technologists says that it’s always DNS, even when it initially didn’t seem that way. DNS issues come in many shapes and forms, including some often-overlooked security issues.
DNS (short for the Domain Name System) continues to be described as “the phonebook of the Internet,” but many people, including most readers of this blog, will be more familiar with the basic workings of DNS than with the outdated phenomenon of paper phonebooks.
Moreover, DNS does a lot more than turning names (such as www.tripwire.com) into numbers (such as 192.229.182.232). It allows a domain owner to respond to questions only they can know the answer to, such as what the mail servers for the domain are or what public key is used for DKIM. Sometimes, DNS is simply used to give a specific answer, to simply prove ownership of a domain.