On 28 Feb 2012, at 18:40, Paul Vixie wrote:
if the EDNS option for this just had an array of additional QTYPE, such
that the real QNAME and QCLASS pertained to all of these additional
questions, then i could definitely see value in this. the response's OPT
option would include the list of qtypes which were found to be
non-empty. all of the rrsets would be in the answer section.
Yes, that's pretty much what was in the draft I wrote (but didn't publish) and
discussed with you during the last Prague IETF.
My rationale likewise was that having constant QNAME and QCLASS but multiple
QTYPEs should eliminate the need for multiple RCODEs.
However further discussion with other folks revealed issues (ISTR around
DNSSEC?) where it would be possible to get inconsistent RCODEs for different
QTYPEs.
I've attached a copy of that document. It could be resurrected if there's
sufficient interest.
Ray
Network Working Group R. Bellis
Internet-Draft Nominet UK
Intended status: Standards Track March 28, 2011
Expires: September 29, 2011
Title
draft-bellis-dnsext-multi-qtypes-00
Abstract
This document specifies a method for a DNS client to request
additional DNS record types to be delivered alongside the primary
record type specified in the question section of a DNS query.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 29, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology used in this document . . . . . . . . . . . . . . . 3
3. Description . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Multiple QTYPE EDNS Option Format . . . . . . . . . . . . . 3
3.2. Response Generation . . . . . . . . . . . . . . . . . . . . 4
3.2.1. Server Side Processing . . . . . . . . . . . . . . . . 4
3.2.2. Client Side Processing . . . . . . . . . . . . . . . . 5
3.2.3. DNSSEC . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
A commonly requested DNS [RFC1035] feature is the ability to receive
multiple related resouce records (RRs) in a single DNS response.
For example, it may be desirable to receive both the A and AAAA
records for a domain name together, rather than having to issue
multiple queries.
The DNS wire protocol in theory supports having multiple questions in
a single packet, but in practise this does not work:
o Each question consists of the tuple (QNAME, QTYPE, QCLASS). Since
each question has its own QNAME field it would be possible for one
name to exist and another to not exist, resulting in an
inconsistent response code.
o The idea that only a single question is allowed is sufficiently
entrenched that many DNS servers will simply return an error (or
fail to response at all) if they receive a query with a question
count (QDCOUNT) of more than one.
To resolve both of these issues, this document constraints the
problem to those cases where only the QTYPE varies by specifying a
new option for the Extension Mechanisms for DNS (EDNS [RFC2671]) that
contains an additional list of QTYPE values that the client wishes to
receive in addition to that in the primary question.
2. Terminology used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Description
3.1. Multiple QTYPE EDNS Option Format
The overall format of an EDNS option is shown for reference below,
per RFC 2671, followed by the option specific data:
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+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | |
/ OPTION-DATA /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
OPTION-CODE: TBD by IANA
OPTION-LENGTH: Size (in octets) of OPTION-DATA.
OPTION-DATA: Option specific, as below:
+0 (MSB) +1 (LSB)
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: |QTD| reserved | QTCOUNT | QT1 (MSB) |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | QT1 (LSB) | ... |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| ... /// QTn (MSB) |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| QTn (LSB) |
+---+---+---+---+---+---+---+---+
QTD: this bit indicates the direction of the packet. It MUST be
clear (0) in a query and set (1) in a response.
QTCOUNT: a 3 bit field with range 0 .. 7 specifying the number of QT
fields to follow.
QTn: a 2 byte field (MSB first) specifying a DNS RR type. The RR
type MUST be for a real resource record, and MUST NOT refer to a
pseudo RR type such as "IXFR", "TSIG", etc.
3.2. Response Generation
3.2.1. Server Side Processing
A conforming server that receives a Multiple QTYPE Option in a query
MUST return a Multiple QTYPE option in its response.
The QTD bit in that response MUST be set (1) as protection against
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servers which simply echo unknown EDNS options verbatim. If the QTD
bit in a response is zero the client MUST treat the response as if
this option is unsupported.
The server SHOULD attempt to return any resource records known to it
that match the additional (QTYPE, QCLASS, QTn) tuples. These records
MUST be returned in the Answer Section of the response, but the
answer for the primary question MUST be included first.
For any particular QTn in the query, if the server provides addtional
answers, or has knowledge that the RR type type does not exist for
that QNAME (a "negative answer"), it must include that QTn value in
its response.
A negative answer is therefore indicated by the combination of the
presence of a QTn value in the Multiple QTYPE Option and the absence
of a matching record in the Answer Section. This is necessary (in
the absence of DNSSEC) to differentiate between absence of the record
from the zone and absence of the record from the response.
An authoritative server receiving a Multiple QTYPE Option MUST
attempt to return all specified RR types except where that would
result in truncation in which case it may omit some (or all) of the
records for the additional RR types. Those RR types MUST then also
be omitted from the Multiple QTYPE Option in the response.
A caching recursive server receiving a Multiple QTYPE Option SHOULD
attempt to fill its positive and negative caches with all of the
specified RR types before returning its response to the client.
TODO: is there a case for mandatory answers, i.e. the client saying I
_really_ want all these?
3.2.2. Client Side Processing
Recursive resolvers MAY use this method to obtain multiple records
from an authoritative server. For the purposes of Section 5.4.1 of
[RFC2181] any authoritative answers received MUST be ranked the same
as the answer for the primary question.
3.2.3. DNSSEC
If the DNS client sets the "DNSSEC OK" (DO) bit in the query then the
server MUST also return the related DNSSEC records that would have
been returned in a standalone query for the same QTYPE.
A negative answer from a signed zone MUST contain the appropriate
authenticated denial of existence records, per RFC 3403 and RFC 5155.
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In a signed zone there is a theoretical risk of valid signatures for
one RR type and invalid signatures for another. This is the only
case known to the author where the response code for any particular
QNAME may be inconsistent across different RR types.
Should a validating resolver produce NOERROR for some RR types and
SERVFAIL for others it MUST omit the RR types that failed to validate
from its response and from the QTn fields on the Multiple QTYPE
option. The client MAY then initiate standalone queries for those RR
types.
4. Security Considerations
The method documented here does not change any of the security
properties of the DNS protocol itself.
It should however be noted that this method does increase the
potential amplification factor when the DNS protocol is used as a
vector for an denial of service attack.
5. IANA Considerations
IANA is requested to assign a new value in the DNS EDNS0 Options
regsitry.
6. Acknowledgements
The author wishes to thank the following for their feedback and
reviews during the development of this document: Michael Graff,
Matthijs Mekking, Paul Vixie.
7. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
RFC 2671, August 1999.
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Appendix A. Change Log
NB: to be removed by the RFC Editor before publication.
draft-bellis-dnsext-multi-qtypes-00
Initial draft
Author's Address
Ray Bellis
Nominet UK
Edmund Halley Road
Oxford OX4 4DQ
United Kingdom
Phone: +44 1865 332211
Email: [email protected]
URI: http://www.nominet.org.uk/
Bellis Expires September 29, 2011 [Page 7]
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