name space itself, and resources that are described using
         domain names and no nonstandard data.

         We also want the name server transactions to be independent of
         the communications system that carries them. Some systems may
         wish to use datagrams for simple queries and responses, and
         only establish virtual circuits for transactions that need the
         reliability (e.g. database updates, long transactions); other
         systems will use virtual circuits exclusively.






 

RFC 882                                                    November 1983
                                  Domain Names - Concepts and Facilities


   Elements of the solution

      The proposed solution has three major components:

         The DOMAIN NAME SPACE, which is a specification for a tree
         structured name space.  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 ARPA Internet uses some of
         its domain names to identify hosts; queries for address
         resources return ARPA Internet host addresses.  However, to
         preserve the generality of the domain mechanism, domain names
         are not required to have a one-to-one correspondence with host
         names, host addresses, or any other type of information.

         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; these parts are called ZONEs; a name server is an
         AUTHORITY for these parts of the name space.

         RESOLVERS are programs that extract information from name
         servers in response to user 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.

      These three components roughly correspond to the three layers or
      views of the domain system:

         From the user's point of view, the domain system is accessed
         through simple procedure or OS calls to resolvers.  The domain
         space consists of a single tree and the user can request
         information from any section of the tree.

         From the resolver's point of view, the domain system is
         composed of an unknown number of name servers.  Each name
         server has one or more pieces of the whole domain tree's data,




 

RFC 882                                                    November 1983
                                  Domain Names - Concepts and Facilities


         but the resolver views each of these databases as essentially
         static.

         From a name server's point of view, the domain system consists
         of separate sets of local information called zones.  The name
         server has local copies of some of the zones.  The name server
         must periodically refresh its zones from master copies in local
         files or foreign name servers.  The name server must
         concurrently process queries that arrive from resolvers using
         the local zones.

      In the interests of performance, these layers blur a bit.  For
      example, resolvers on the same machine as a name server may share
      a database and may also introduce foreign information for use in
      later queries.  This cached information is treated differently
      from the authoritative data in zones.

   Database model

      The organization of the domain system derives from some
      assumptions about the needs and usage patterns of its user