the refresh.  In special situations, very short intervals can
     be specified, or the owner can prohibit copies.

   - In any system that has a distributed database, a particular
     name server may be presented with a query that can only be
     answered by some other server.  The two general approaches to
     dealing with this problem are "recursive", in which the first
     server pursues the query for the client at another server, and
     "iterative", in which the server refers the client to another
     server and lets the client pursue the query.  Both approaches
     have advantages and disadvantages, but the iterative approach
     is preferred for the datagram style of access.  The domain
     system requires implementation of the iterative approach, but
     allows the recursive approach as an option.






 
RFC 1034             Domain Concepts and Facilities        November 1987


The domain system assumes that all data originates in master files
scattered through the hosts that use the domain system.  These master
files are updated by local system administrators.  Master files are text
files that are read by a local name server, and hence become available
through the name servers to users of the domain system.  The user
programs access name servers through standard programs called resolvers.

The standard format of master files allows them to be exchanged between
hosts (via FTP, mail, or some other mechanism); this facility is useful
when an organization wants a domain, but doesn't want to support a name
server.  The organization can maintain the master files locally using a
text editor, transfer them to a foreign host which runs a name server,
and then arrange with the system administrator of the name server to get
the files loaded.

Each host's name servers and resolvers are configured by a local system
administrator [RFC-1033].  For a name server, this configuration data
includes the identity of local master files and instructions on which
non-local master files are to be loaded from foreign servers.  The name
server uses the master files or copies to load its zones.  For
resolvers, the configuration data identifies the name servers which
should be the primary sources of information.

The domain system defines procedures for accessing the data and for
referrals to other name servers.  The domain system also defines
procedures for caching retrieved data and for periodic refreshing of
data defined by the system administrator.

The system administrators provide:

   - The definition of zone boundaries.

   - Master files of data.

   - Updates to master files.

   - Statements of the refresh policies desired.

The domain system provides:

   - Standard formats for resource data.

   - Standard methods for querying the database.

   - Standard methods for name servers to refresh local data from
     foreign name servers.






 
RFC 1034             Domain Concepts and Facilities        November 1987


2.4. Elements of the DNS

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,