Network Working Group S. Bortzmeyer
Internet-Draft AFNIC
Intended status: Informational March 20, 2014
Expires: September 21, 2014
DNS query name minimisation to improve privacy
draft-bortzmeyer-dns-qname-minimisation-00
Abstract
This document describes one of the techniques that could be used to
improve DNS privacy (see [I-D.bortzmeyer-dnsop-dns-privacy]), a
technique called "qname minimisation".
Discussions of the document should currently take place on the dns-
privacy mailing list [dns-privacy].
Status of This Memo
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document authors. All rights reserved.
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Internet-Draft Qname minimisation March 2014
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Table of Contents
1. Introduction and background . . . . . . . . . . . . . . . . . 2
2. Qname minimisation . . . . . . . . . . . . . . . . . . . . . 2
3. Operational considerations . . . . . . . . . . . . . . . . . 3
4. Security considerations . . . . . . . . . . . . . . . . . . . 3
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 3
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4
6.2. Informative References . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction and background
The problem statement is exposed in
[I-D.bortzmeyer-dnsop-dns-privacy]. The terminology ("qname",
"resolver", etc) is also defined in this companion document. This
specific solution is not intended to completely solve the problem,
far from it. It is better to see it as one tool among a toolbox.
It follows the principle explained in section 6.1 of [RFC6973]: the
less data you send out, the less privacy problems you'll get.
2. Qname minimisation
The idea is to minimise the amount of data sent from the DNS
resolver. When a resolver receives the query "What is the AAAA
record for www.example.com?", it sends to the root (assuming a cold
resolver, whose cache is empty) the very same question. Sending
"What are the NS records for .com?" would be sufficient (since it
will be the answer from the root anyway). To do so would be
compatible with the current DNS system and therefore could be easily
deployable, since it is an unilateral change to the resolvers.
To do such minimisation, the resolver needs to know the zone cut
[RFC2181]. There is not a zone cut at every label boundary. If we
take the name www.foo.bar.example, it is possible that there is a
zone cut between "foo" and "bar" but not between "bar" and "example".
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So, assuming the resolver already knows the name servers of .example,
when it receives the query "What is the AAAA record of
www.foo.bar.example", it does not always know if the request should
be sent to the name servers of bar.example or to those of example.
[RFC2181] suggests an algorithm to find the zone cut, so resolvers
may try it.
Note that DNSSEC-validating resolvers already have access to this
information, since they have to find the zone cut (the DNSKEY record
set is just below, the DS record set just above).
It can be noted that minimising the amount of data sent also
partially addresses the case of a wire sniffer, not just the case of
privacy invasion by the servers.
One should note that the behaviour suggested here (minimising the
amount of data sent in qnames) is NOT forbidden by the [RFC1034]
(section 5.3.3) or [RFC1035] (section 7.2). Sending the full qname
to the authoritative name server is a tradition, not a protocol
requirment.
Another note is that the answer to the NS query, unlike the referral
sent when the question is a full qname, is in the Answer section, not
in the Authoritative section. It has probably no practical
consequences.
3. Operational considerations
The administrators of the forwarders, and of the authoritative name
servers, will get less data, which will reduce the utility of the
statistics they can produce (such as the percentage of the various
qtypes). On the other hand, it will decrease their legal
responsability, in many cases.
4. Security considerations
Some broken name servers do not react properly to qtype=NS requests.
As an example, look at www.ratp.fr (not ratp.fr), which is delegated
to two name servers that reply properly to "A www.ratp.fr" queries
but send REFUSED to queries "NS www.ratp.fr". This behaviour is a
gross protocol violation and there is no need to stop improving the
DNS because of such brokenness. However, qname minimisation may
still work with such domains since they are only leaf domains (no
need to send them NS requests).
5. Acknowledgments
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Thanks to Olaf Kolkman, Mark Andrews and Francis Dupont for the
interesting discussions on this qname minimisation. Thanks to Mohsen
Souissi for proofreading.
6. References
6.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[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.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973, July
2013.
[I-D.bortzmeyer-dnsop-dns-privacy]
Bortzmeyer, S., "DNS privacy problem statement", draft-
bortzmeyer-dnsop-dns-privacy-01 (work in progress),
December 2013.
6.2. Informative References
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997.
[dns-privacy]
IETF, ., "The dns-privacy mailing list", March 2014.
Author's Address
Stephane Bortzmeyer
AFNIC
Immeuble International
Saint-Quentin-en-Yvelines 78181
France
Phone: +33 1 39 30 83 46
Email: bortzmeyer+ietf@nic.fr
URI: http://www.afnic.fr/
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