DNS stands for Domain Name System. A domain server allows users on the Internet to find a computer based on a name that has been assigned to that system. The system resolves the name of the computer within a table which stores the names and IP addresses. Once the name is requested by an end user, the table on the DNS server is queried and the results allow the user to access a particular server based on its Name and not only its IP address. This DNS table functions as a Host file would on a local machine, but it is global and resolves all IP addresses on the Internet that are registered with a DNS server.

DNS fail over provides a site with redundancy built into it. For example, if the primary DNS entry of a site is unreachable, then the DNS fail over would then query a secondary DNS entry in order to have DNS fail over and the user's request to be guided to a secondary site which would exist as backup to the primary site. In this example, the DNS entries are added as primary and secondary, but there are also appliances that can have the same functionality. Many of these appliances allow the DNS server to have one IP address; therefore, it will manage if a site is accessible or not with "heartbeat" requests. These requests allow each appliance at a primary location and a secondary location to maintain communication to one another in order to verify connectivity.