As Monitis introduced a new check type – Advanced DNS, in this article I would like to provide a brief description of DNS and how it works in general. On the internet DNS(Domain Name System) associates various sorts of information with domain names and translates human-readable computer hostnames into the IP addresses that networking equipment needs for delivering information. The most basic use of DNS is to translate hostnames to IP addresses.
The domain name space consists of a tree of domain names. Each node or leaf in the tree has one or more resource records, which hold information associated with the domain name. The tree sub-divides into zones, which consists of a collection of connected nodes authoritatively served by an authoritative DNS nameserver, the one that publishes information about that domain and the name servers of any domains “beneath” it. A resolver looks up the information associated with nodes and knows how to communicate with name servers by sending DNS requests, and heeding DNS responses. Resolving usually entails iterating through several name servers to find the needed information.
Users generally do not communicate directly with a DNS resolver, instead DNS-resolution takes place transparently in client-applications such as web-browsers, mail-clients, and other Internet applications.
You can refer to the following link http://en.wikipedia.org/wiki/Domain_name_system in case you would like to go in more details with DNS mechanism.