Obsoleting IQUERY
RFC 3425

Document Type RFC - Proposed Standard (November 2002; No errata)
Updates RFC 1035
Last updated 2015-10-14
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IESG IESG state RFC 3425 (Proposed Standard)
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Network Working Group                                        D. Lawrence
Request for Comments: 3425                                       Nominum
Updates: 1035                                              November 2002
Category: Standards Track

                           Obsoleting IQUERY

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.


   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.

1 - Introduction

   As specified in RFC 1035 (section 6.4), the IQUERY operation for DNS
   queries is used to look up the name(s) which are associated with the
   given value.  The value being sought is provided in the query's
   answer section and the response fills in the question section with
   one or more 3-tuples of type, name and class.

   As noted in [RFC1035], section 6.4.3, inverse query processing can
   put quite an arduous burden on a server.  A server would need to
   perform either an exhaustive search of its database or maintain a
   separate database that is keyed by the values of the primary
   database.  Both of these approaches could strain system resource use,
   particularly for servers that are authoritative for millions of

Lawrence                    Standards Track                     [Page 1]
RFC 3425                   Obsoleting IQUERY               November 2002

   Response packets from these megaservers could be exceptionally large,
   and easily run into megabyte sizes.  For example, using IQUERY to
   find every domain that is delegated to one of the nameservers of a
   large ISP could return tens of thousands of 3-tuples in the question
   section.  This could easily be used to launch denial of service

   Operators of servers that do support IQUERY in some form (such as
   very old BIND 4 servers) generally opt to disable it.  This is
   largely due to bugs in insufficiently-exercised code, or concerns
   about exposure of large blocks of names in their zones by probes such
   as inverse MX queries.

   IQUERY is also somewhat inherently crippled by being unable to tell a
   requester where it needs to go to get the information that was
   requested.  The answer is very specific to the single server that was
   queried.  This is sometimes a handy diagnostic tool, but apparently
   not enough so that server operators like to enable it, or request
   implementation where it is lacking.

   No known clients use IQUERY to provide any meaningful service.  The
   only common reverse mapping support on the Internet, mapping address
   records to names, is provided through the use of pointer (PTR)
   records in the in-addr.arpa tree and has served the community well
   for many years.

   Based on all of these factors, this document recommends that the
   IQUERY operation for DNS servers be officially obsoleted.

2 - Requirements

   The key word "SHOULD" in this document is to be interpreted as
   described in BCP 14, RFC 2119, namely that there may exist valid
   reasons to ignore a particular item, but the full implications must
   be understood and carefully weighed before choosing a different

3 - Effect on RFC 1035

   The effect of this document is to change the definition of opcode 1
   from that originally defined in section 4.1.1 of RFC 1035, and to
   entirely supersede section 6.4 (including subsections) of RFC 1035.

   The definition of opcode 1 is hereby changed to:

      "1               an inverse query (IQUERY) (obsolete)"

Lawrence                    Standards Track                     [Page 2]
RFC 3425                   Obsoleting IQUERY               November 2002

   The text in section 6.4 of RFC 1035 is now considered obsolete.  The
   following is an applicability statement regarding the IQUERY opcode:

   Inverse queries using the IQUERY opcode were originally described as
   the ability to look up the names that are associated with a
   particular Resource Record (RR).  Their implementation was optional
   and never achieved widespread use.  Therefore IQUERY is now obsolete,
   and name servers SHOULD return a "Not Implemented" error when an
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