NAME SERVERS

   Introduction

      Name servers store a distributed database consisting of the
      structure of the domain name space, the resource sets associated
      with domain names, and other information used to coordinate
      actions between name servers.

      In general, a name server will be an authority for all or part of
      a particular domain.  The region covered by this authority is
      called a zone.  Name servers may be responsible for no
      authoritative data, and hence have no zones, or may have several
      zones.  When a name server has multiple zones, the zones may have
      no common borders or zones may be contiguous.

      While administrators should not construct overlapping zones, and
      name servers must defend against overlapping zones, overlapping is
      regarded as a non-fatal flaw in the database.  Hence the measures
      taken to protect against it are omitted for the remainder of this
      memo.  A detailed discussion can be found in [14].

      When presented with a query for a domain name over which it has
      authority, a name server returns the desired resource information
      or an indication that the query refers to a domain name or
      resource that does not exist.  If a name server is presented with
      a query for a domain name that is not within its authority, it may
      have the desired information, but it will also return a response
      that points toward an authoritative name server.  If a name server
      is not an authority for a query, it can never return a negative
      response.

      There is no requirement that a name server for a domain reside in
      a host which has a name in the same domain, although this will
      usually be the case.  There is also no restriction on the number
      of name servers that can have authority over a particular domain;
      most domains will have redundant authoritative name servers.  The
      assumption is that different authoritative copies are identical,
      even though inconsistencies are possible as updates are made.

      Name server functions are designed to allow for very simple
      implementations of name servers.  The simplest name server has a
      static set of information and uses datagrams to receive queries
      and return responses.

      More sophisticated name server implementations can improve the
      performance of their clients by caching information from other
      domains.  Although this information can be acquired in a number of
      ways, the normal method is to store the information acquired by a



 

RFC 882                                                    November 1983
                                  Domain Names - Concepts and Facilities


      resolver when the resolver consults other name servers.  In a
      sophisticated host, the resolver and name server will coordinate
      their actions and use a shared database.  This cooperation
      requires the incorporation of a time-to-live (TTL) field in all
      cached resource records.  Caching is discussed in the resolver
      section of this memo; this section is devoted to the actions of a
      name servers that don't cache.

      In order to free simple name servers of the requirement of
      managing these timeouts, simple name servers should only contain
      resource records that are expected to remain constant over very
      long periods or resource records for which the name server is an
      authority.  In the following discussion, the TTL field is assumed
      to be stored in the resource record but is omitted in descriptions
      of databases and responses in the interest of clarity.

   Authority and administrative control of domains

      Although we want to have the potential of delegating the
      privileges of name space management at every node, we don't want
      such delegation to be required.

      Hence we introduce the concept of authority.  Authority is vested
      in name servers.  A name server has authority over all of its
      domain until it delegates authority for a subdomain to some other
      name server.

      Any administrative entity that wishes to establish its own domain
      must provide a name server, and have that server accepted by the
      parent name server (i.e. the name server that has authority over
      the place in the domain name space that will hold the new domain).
      While the principles of authority allow acceptance to be at the
      discretion of parent name servers, the following criteria are used
      by the root, and are recommended to all name servers because they
      are responsible for their children's actions:

         1.  It must register with the parent administrator of domains.

         2.  It must identify a responsible person.

         3.  In must provide redundant name servers.