Mailbox binding.................................................54
   Appendix 1 - Domain Name Syntax Specification......................56
   Appendix 2 - Field formats and encodings...........................57
      TYPE values.....................................................57
      QTYPE values....................................................57
      CLASS values....................................................58
      QCLASS values...................................................58
      Standard resource record formats................................59
   Appendix 3 - Internet specific field formats and operations........67
   REFERENCES and BIBLIOGRAPHY........................................72
   INDEX..............................................................73
   


Mockapetris                                                    [Page ii]
 

RFC 883                                                    November 1983
                         Domain Names - Implementation and Specification


INTRODUCTION

   Overview

      The goal of domain names is to provide a mechanism for naming
      resources in such a way that the names are usable in different
      hosts, networks, protocol families, internets, and administrative
      organizations.

      From the user's point of view, domain names are useful as
      arguments to a local agent, called a resolver, which retrieves
      information associated with the domain name.  Thus a user might
      ask for the host address or mail information associated with a
      particular domain name.  To enable the user to request a
      particular type of information, an appropriate query type is
      passed to the resolver with the domain name.  To the user, the
      domain tree is a single information space.

      From the resolver's point of view, the database that makes up the
      domain space is distributed among various name servers.  Different
      parts of the domain space are stored in different name servers,
      although a particular data item will usually be stored redundantly
      in two or more name servers.  The resolver starts with knowledge
      of at least one name server.  When the resolver processes a user
      query it asks a known name server for the information; in return,
      the resolver either receives the desired information or a referral
      to another name server.  Using these referrals, resolvers learn
      the identities and contents of other name servers.  Resolvers are
      responsible for dealing with the distribution of the domain space
      and dealing with the effects of name server failure by consulting
      redundant databases in other servers.

      Name servers manage two kinds of data.  The first kind of data
      held in sets called zones; each zone is the complete database for
      a particular subtree of the domain space.  This data is called
      authoritative.  A name server periodically checks to make sure
      that its zones are up to date, and if not obtains a new copy of
      updated zones from master files stored locally or in another name
      server.  The second kind of data is cached data which was acquired
      by a local resolver.  This data may be incomplete but improves the
      performance of the retrieval process when non-local data is
      repeatedly accessed.  Cached data is eventually discarded by a
      timeout mechanism.

      This functional structure isolates the problems of user interface,
      failure recovery, and distribution in the resolvers and isolates
      the database update and refresh problems in the name servers.





 

RFC 883                                                    November 1983
                         Domain Names - Implementation and Specification


   Implementation components

      A host can participate in the domain name system in a number of
      ways, depending on whether the host runs programs that retrieve
      information from the domain system, name servers that answer
      queries from other hosts, or various combinations of both
      functions.  The simplest, and perhaps most typical, configuration
      is shown below:

                   Local Host                        |  Foreign   
                                                     |            
      +---------+               +----------+         |  +--------+
      |         | user queries  |          |queries  |  |        |
      |  User   |-------------->|          |---------|->|Foreign |
      | Program |               | Resolver |         |  |  Name  |
      |         |<--------------|          |<--------|--| Server |
      |         | user responses|          |responses|  |        |
      +---------+               +----------+         |  +--------+
                                  |     A            |            
                  cache additions |     | references |            
                                  V     |            |