DNSEXT Working Group David Lawrence (Nominum)
INTERNET-DRAFT February 2001
<draft-ietf-dnsext-obsolete-iquery-00.txt>
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.
Internet-Drafts are working documents of the Internet Engineering
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This draft expires on August 22, 2001.
Copyright Notice
Copyright (C) The Internet Society (2001). All rights reserved.
Abstract
Based on a lack of working implementations of the IQUERY method
of performing inverse DNS lookups, and because an alternative
mechanism for doing inverse queries of address records has been
successfully used operationally for well over a decade, this
draft proposes that the IQUERY operation be entirely obsoleted.
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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.
Furthermore, many organizations would opt to disable IQUERY, if it
existed, because it could expose large blocks of names in their
zones, such as if many of those names have a common mail
exchanger.
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 would undeniably be handy at times as a
diagnostic tool, but apparently not enough so that anyone's
bothered to implement it since it was described in 1987.
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 NOT", "SHOULD", "SHOULD NOT", and "MAY" in this
document are to be interpreted as described in RFC2119.
1.2 - Updated documents and sections
RFC 1035 sections 4.1.1 and 6.4 are changed.
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2 - New text for RFC 1035.
Section 4.1.1 has the following text to describe opcode 1:
"1 an inverse query (IQUERY)"
Is is amended to read:
"1 an inverse query (IQUERY) (obsolete)"
Section 6.4, including all subsections, of RFC 1035 should be
considered obsolete and not to be implemented. It is changed to
read 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.
References:
[RFC1035] P. Mockapetris, ``Domain Names - Implementation and
Specification'', STD 13, RFC 1035, November 1987.
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Author's Address
David Lawrence
Nominum Inc.
950 Charter Street
Redwood City CA 94063
USA
+1.650.779.6042
<tale@nominum.com>
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