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Network Working Group                                        D. LawrenceRequest for Comments: 3425                                       NominumUpdates:1035                                              November 2002Category: Standards TrackObsoleting IQUERYStatus 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 inRFC1035, 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 updatesRFC 1035.1 - Introduction   As specified inRFC 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.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   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 inBCP 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 onRFC 1035   The effect of this document is to change the definition of opcode 1   from that originally defined insection 4.1.1 of RFC 1035, and to   entirely supersedesection 6.4 (including subsections) ofRFC 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 insection 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.Lawrence                    Standards Track                     [Page 3]

RFC 3425                   Obsoleting IQUERY               November 20028 - Author's Address   David C Lawrence   Nominum, Inc.   2385 Bay Rd   Redwood City CA 94063   USA   Phone: +1.650.779.6042   EMail: tale@nominum.comLawrence                    Standards Track                     [Page 4]

RFC 3425                   Obsoleting IQUERY               November 20029 - 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.Lawrence                    Standards Track                     [Page 5]