2. Definition

   An "RR of unknown type" is an RR whose RDATA format is not known to
   the DNS implementation at hand, and whose type is not an assigned
   QTYPE or Meta-TYPE as specified in [RFC2929] (section 3.1) nor
   within the range reserved in that section for assignment only to
   QTYPEs and Meta-TYPEs.  Such an RR cannot be converted to a type-
   specific text format, compressed, or otherwise handled in a type-
   specific way.

   In the case of a type whose RDATA format is class specific, an RR is
   considered to be of unknown type when the RDATA format for that
   combination of type and class is not known.