draft-ietf-dnsext-obsolete-iquery-03.txt   draft-ietf-dnsext-obsolete-iquery-04.txt 
DNSEXT Working Group David C Lawrence A new Request for Comments is now available in online RFC libraries.
<draft-ietf-dnsext-obsolete-iquery-03.txt> January 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 RFC2026.
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This draft expires on 14 July 2002. RFC 3425
Copyright Notice Title: Obsoleting IQUERY
Author(s): D. Lawrence
Status: Standards Track
Date: November 2002
Mailbox: tale@nominum.com
Pages: 5
Characters: 8615
Updates: 1035
Copyright (C) The Internet Society (2002). All rights reserved. I-D Tag: draft-ietf-dnsext-obsolete-iquery-04.txt
Abstract URL: ftp://ftp.rfc-editor.org/in-notes/rfc3425.txt
The IQUERY method of performing inverse DNS lookups, specified in The IQUERY method of performing inverse DNS lookups, specified in
RFC 1035, has not been generally implemented and has usually been RFC 1035, has not been generally implemented and has usually been
operationally disabled where it has been implemented. Both reflect operationally disabled where it has been implemented. Both reflect
a general view in the community that the concept was unwise and a general view in the community that the concept was unwise and
that the widely-used alternate approach of using PTR queries and that the widely-used alternate approach of using pointer (PTR) queries
reverse-mapping records is preferable. Consequently, this document and reverse-mapping records is preferable. Consequently, this
deprecates the IQUERY operation and updates RFC 1035 to declare it document deprecates the IQUERY operation, declaring it entirely
entirely obsolete. 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 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 in-addr.arpa 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.
1.1 - Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
document are to be interpreted as described in RFC 2119.
1.2 - Updated documents and sections
In RFC 1035, sections 4.1.1 is updated in part and section 6.4 is
entirely superseded.
2 - New text for RFC 1035.
Section 4.1.1 has the following text to describe opcode 1:
"1 an inverse query (IQUERY)"
It is now considered to read as follows:
"1 an inverse query (IQUERY) (obsolete)"
Section 6.4, including all subsections, of RFC 1035 should be
considered obsolete and not to be implemented. The section
effectively now reads as follows:
"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 and Erik Nordmark contributed some
improved wording.
[RFC1035] P. Mockapetris, ``Domain Names - Implementation and
Specification'', STD 13, RFC 1035, November 1987.
[RFC2119] S. Bradner, ``Key Words for Use in RFCs to Indicate
Requirement Levels'', BCP 14, RFC 2119, March 1997.
7 - Author's Address This document is a product of the DNS Extensions Working Group of the
David Lawrence This is now a Proposed Standard Protocol.
Nominum, Inc.
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