+----------+--------+--------+-----------------------------+

      The SOA record marks the start of a zone when it is present in a
      database; the NS record both marks the end of a zone started by an
      SOA (if a higher SOA is present) and also points to a name server
      that has a copy of the zone specified by the <owner. field of the
      NS record.

      The <domain name, etc> in the SOA record specifies the original
      source of the information in the zone and other information used
      by name servers to organize their activities.  SOA records are
      never cached (otherwise they would create false zones); they can
      only be created in special name server maintenance operations.

      The NS record says that a name server which is authoritative for
      records of the given CLASS can be found at <domain name>.

   Queries

      Queries to a name server must include a domain name which
      identifies the target resource set (QNAME), and the type and class
      of desired resource records.  The type and class fields in a query
      can include any of the corresponding type and class fields that
      are defined for resource records; in addition, the query type
      (QTYPE) and query class (QCLASS) fields may contain special values
      that match more than one of the corresponding fields in RRs.

      For example, the QTYPE field may contain:

         MAILA - matches all mail agent RRs (e.g. MD and MF).

         *     - matches any RR type.





 

RFC 882                                                    November 1983
                                  Domain Names - Concepts and Facilities


      The QCLASS field may contain:

         *    - matches any RR class.

      Using the query domain name, QTYPE, and QCLASS, the name server
      looks for matching RRs.  In addition to relevant records, the name
      server may return RRs that point toward a name server that has the
      desired information or RRs that are expected to be useful in
      interpreting the relevant RRs.  For example a name server that
      doesn't have the requested information may know a name server that
      does; a name server that returns a domain name in a relevant RR
      may also return the RR that binds that domain name to an address.

      Note that the QCLASS=* construct requires special interpretation
      regarding authority.  Since a name server may not know all of the
      classes available in the domain system, it can never know if it is
      authoritative for all classes.  Hence responses to QCLASS=*
      queries can never be authoritative.

   Example space

      For purposes of exposition, the following name space is used for
      the remainder of this memo:

                                    |                            
                 +------------------+------------------+         
                 |                  |                  |         
                DDN               ARPA               CSNET       
                 |                  |                  |         
           +-----+-----+            |            +-----+-----+   
           |     |     |            |            |           |   
          JCS  ARMY  NAVY           |           UDEL        UCI  
                                    |                            
           +--------+---------------+---------------+--------+   
           |        |               |               |        |   
          DTI      MIT             ISI             UDEL     NBS  
                    |               |                            
                +---+---+       +---+---+                        
                |       |       |   |   |                        
               DMS     AI       A   B   F                        












 

RFC 882                                                    November 1983
                                  Domain Names - Concepts and Facilities