to a new domain X by D.  To allow name server at D to resolve
      simple names, the name for X must be distinct from L, E, D, C, F,
      and J.  However, allowing A to resolve simple names, X needs to be
      also distinct from A, B, K, as well as from Q, P, N, and R.

   The following observations can be made.

      Simple names along parallel trails (distinct trails leading from
      one domain to the naming universe) must be distinct, e.g., N must
      be distinct from E for B or A to properly resolve simple names.

      No universal uniqueness of simple names is called for, e.g., the
      simple name S does not have to be distinct from that of E, F, G,
      H, D, C, K, Q, B, or A.

      The lower the level at which a domain occurs, the more immune it
      is to the requirement of naming uniqueness.

   To satisfy the required distinction of simple names for proper
   resolution at all levels, a naming authority needs to ensure the
   simple name to be assigned distinct from those in the name server
   databases at the endpoint naming domains within its domain.  As an
   example, for D to assign a simple name for X, it would need to
   consult databases at A and K.  It is, however, acceptable to have
   simple names under domain A identical with those under K.  Failure of
   such distinct assignment of simple names by naming authority of one
   domain would jeopardize the capability of simple name resolution for
   entities within the subtree under that domain.
























 


RFC 819                                                     August 1982;


APPENDIX C

   Further Discussion of Name Service and Name Servers

   The name service on a system should appear to the programmer of an
   application program simply as a system call or library subroutine.
   Within that call or subroutine there may be several types of methods
   for resolving the name string into an address.

      First, a local table may be consulted.  This table may be a
      complete table and may be updated frequently, or it may simply be
      a cache of the few latest name to address mappings recently
      determined.

      Second, a call may be made to a name server to resolve the string
      into a destination address.

      Third, a call may be made to a name server to resolve the string
      into a relay address.

   Whenever a name server is called it may be a recursive server or an
   interactive server.

      If the server is recursive, the caller won't be able to tell if
      the server itself had the information to resolve the query or
      called another server recursively (except perhaps for the time it
      takes).

      If the server is iterative, the caller must be prepared for either
      the answer to its query, or a response indicating that it should
      call on a different server.

   It should be noted that the main name service discussed in this memo
   is simply a name string to address service.  For some applications
   there may be other services needed.

      For example, even within the Internet there are several procedures
      or protocols for actually transferring mail.  One need is to
      determine which mail procedures a destination host can use.
      Another need is to determine the name of a relay host if the
      source and destination hosts do not have a common mail procedure.