RFC 2672 (rfc2672) - Page 2 of 9

Non-Terminal DNS Name Redirection

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RFC 2672           Non-Terminal DNS Name Redirection         August 1999


   DNAME has the following format:

         DNAME 

   The format is not class-sensitive.  All fields are required.  The
   RDATA field  is a  [DNSIS].

   The DNAME RR causes type NS additional section processing.

   The effect of the DNAME record is the substitution of the record's
    for its  as a suffix of a domain name.  A "no-
   descendants" limitation governs the use of DNAMEs in a zone file:

      If a DNAME RR is present at a node N, there may be other data at N
      (except a CNAME or another DNAME), but there MUST be no data at
      any descendant of N.  This restriction applies only to records of
      the same class as the DNAME record.

   This rule assures predictable results when a DNAME record is cached
   by a server which is not authoritative for the record's zone.  It
   MUST be enforced when authoritative zone data is loaded.  Together
   with the rules for DNS zone authority [DNSCLR] it implies that DNAME
   and NS records can only coexist at the top of a zone which has only
   one node.

   The compression scheme of [DNSIS] MUST NOT be applied to the RDATA
   portion of a DNAME record unless the sending server has some way of
   knowing that the receiver understands the DNAME record format.
   Signalling such understanding is expected to be the subject of future
   DNS Extensions.

   Naming loops can be created with DNAME records or a combination of
   DNAME and CNAME records, just as they can with CNAME records alone.
   Resolvers, including resolvers embedded in DNS servers, MUST limit
   the resources they devote to any query.  Implementors should note,
   however, that fairly lengthy chains of DNAME records may be valid.

4.  Query Processing

   To exploit the DNAME mechanism the name resolution algorithms [DNSCF]
   must be modified slightly for both servers and resolvers.

   Both modified algorithms incorporate the operation of making a
   substitution on a name (either QNAME or SNAME) under control of a
   DNAME record.  This operation will be referred to as "the DNAME
   substitution".





Crawford                    Standards Track
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