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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.

Abstract

 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
 names.

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 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
 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
 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
 course.

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)"

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 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
 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 DNS
 Security (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 instigated this action.  Matt Crawford, John
 Klensin, Erik Nordmark and Keith Moore contributed some improved
 wording in how to handle obsoleting functionality described by an
 Internet Standard.

7 - References

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

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

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

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8 - Author's Address

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

 Phone: +1.650.779.6042
 EMail: tale@nominum.com

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9 - Full Copyright Statement

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

 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.

 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.

 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

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