inverse query:PTR RR or OPCODE=1 ?

Joseph S D Yao jsdy at
Thu Dec 3 02:58:41 UTC 2009

On Thu, Dec 03, 2009 at 10:42:38AM +0800, lipeng967 wrote:
>   when I read the RFC1035, I noticed the opcode defination in the DNS message head . It said that when opcode = 1 the message did Inverse query . but in the packet  I capatured when I used nslookup to do inverse query ,the inverse query packet use the opcode = 0 and the question segment with RR TYPE PTR. Can someone explain this ?  Am I wrong about understanding the inverse query ? Thank a lot .

Note that 6.4 (inverse queries) was optional, and read 3.5
(, which is about REVERSE (not inverse) DNS as it is used
today.  With some additions and changes: the RFCs are living documents.

RFC 3425 obsolets inverse queries entirely:

   The IQUERY method of performing inverse DNS lookups, specified in RFC
   1035, has not been generally implemented and has usually been
   operationally disabled where it has been implemented.  Both reflect a
   general view in the community that the concept was unwise and that
   the widely-used alternate approach of using pointer (PTR) queries and
   reverse-mapping records is preferable.  Consequently, this document
   deprecates the IQUERY operation, declaring it entirely obsolete.
   This document updates RFC 1035.

** Joe Yao				jsdy at - Joseph S. D. Yao

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