The DNS has three major components:

- The DOMAIN NAME SPACE and RESOURCE RECORDS, which are

specifications for a tree structured name space and data

associated with the names. Conceptually, each node and leaf

of the domain name space tree names a set of information, and

query operations are attempts to extract specific types of

information from a particular set. A query names the domain

name of interest and describes the type of resource

information that is desired. For example, the Internet

uses some of its domain names to identify hosts; queries for

address resources return Internet host addresses.

- NAME SERVERS are server programs which hold information about

the domain tree's structure and set information. A name

server may cache structure or set information about any part

of the domain tree, but in general a particular name server

has complete information about a subset of the domain space,

and pointers to other name servers that can be used to lead to

information from any part of the domain tree. Name servers

know the parts of the domain tree for which they have complete

information; a name server is said to be an AUTHORITY for

these parts of the name space. Authoritative information is

organized into units called ZONEs, and these zones can be

automatically distributed to the name servers which provide

redundant service for the data in a zone.

- RESOLVERS are programs that extract information from name

servers in response to client requests. Resolvers must be

able to access at least one name server and use that name

server's information to answer a query directly, or pursue the

query using referrals to other name servers. A resolver will

typically be a system routine that is directly accessible to

user programs; hence no protocol is necessary between the

resolver and the user program