The Domain Name System (DNS) is a hierarchical, distributed database, implemented on a TCP/IP network. It is primarily used to look up IP addresses for Internet host names and host names for IP addresses. The data is distributed across the network and is located by using period-separated names that are read from right to left. DNS is also used to store other Internet-related host information, such as mail exchange routing information, location data, and available services. The hierarchical nature of the service enables the local administration of local domains, while providing international coverage of other domains that are connected to the Internet, an intranet, or both.
DNS clients request information about a host name from one or more name servers and wait for a response. DNS servers respond to requests from an information cache that was loaded from any of the following sources:
A file or a third-party database on a DNS master server
A file or a third-party database from a cooperating DNS slave server in the network
Information stored from previous queries
If no response is found and the server is not responsible for the domain in question, the service, if appropriately configured, will recursively request the host name from other servers and cache that response.