Internet DRAFT - draft-ietf-dnsext-obsolete-iquery


DNSEXT Working Group                                     David C Lawrence
INTERNET-DRAFT                                                    Nominum
<draft-ietf-dnsext-obsolete-iquery-04.txt>                      July 2002
Updates: RFC 1035

                          Obsoleting IQUERY

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC 2026.

   Internet-Drafts are working documents of the Internet Engineering
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   This draft expires on 14 January 2003.

   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 PTR queries and
   reverse-mapping records is preferable.  Consequently, this document
   deprecates the IQUERY operation and updates RFC 1035 to declare it
   entirely obsolete.

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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 onerous 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 names.

   Response packet 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 attacks.

   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 requestor 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's 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 PTR
   records in the tree and has served the community well
   for many years.

   Based on all of these factors, this draft proposes 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 RFC 2119, namely that there may exit valid reasons
   to ignore a particular item, but the full implications must be
   understood and carefully weighed before choosing a different course.

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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)"

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

   Inverse queries using the IQUERY opcode were originally described
   as the ability to look up the names that are associated with a
   particular 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 IQUERY
   request is received.

4 - Security Considerations

   Since this document obsoletes an operation that was once available,
   it is conceivable that someone was using it as the basis of a
   security policy.  However, since the most logical course for such a
   policy to take in the face of a lack of positive response from a
   server is to deny authentication/authorization, it is highly
   unlikely that removing support for IQUERY will open any new
   security holes.

   Note that if IQUERY is not obsoleted, securing the responses with
   DNSSEC is extremely difficult without out-on-the-fly digital signing.

5 - IANA Considerations

   The IQUERY opcode of 1 should be permanently retired, not to be
   assigned to any future opcode.

6 - Acknowledgments

   Olafur Gudmundsson was the instigator for this action.
   Matt Crawford, John Klensin, Erik Nordmark and Keith Moore
   contributed some improved wording as the matter of how to handle
   obsoleting functionality described by an Internet Standard.

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7 - References

[RFC1035]  P. Mockapetris, ``Domain Names - Implementation and
           Specification'', STD 13, RFC 1035, November 1987.

[RFC2026]  S. Bradner, ``The Internet Standards Process -- Revision 3'',
           BCP 9, RFC 2026, October 1996.

[RFC2119]  S. Bradner, ``Key Words for Use in RFCs to Indicate
           Requirement Levels'', BCP 14, RFC 2119, March 1997.

8 - Author's Address

      David C Lawrence
      Nominum, Inc.
      2385 Bay Rd
      Redwood City CA 94063

      Phone: +1.650.779.6042

9 - Full Copyright Statement

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

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