Internet DRAFT - draft-wkumari-dnsop-cheese-shop
draft-wkumari-dnsop-cheese-shop
Network Working Group W. Kumari
Internet-Draft Google
Intended status: Informational G. Huston
Expires: August 27, 2016 APNIC
February 24, 2016
Believing NSEC records in the DNS root.
draft-wkumari-dnsop-cheese-shop-01
Abstract
This document describes a method to generate negative answers from
NSEC records for the special case of the DNS root. This improves
performance; the resolver can answer immediatly, and does not need to
query the root. It also cuts down on the so-called "junk" queries.
[ Ed note: Text inside square brackets ([]) is additional background
information, answers to frequently asked questions, general musings,
etc. They will be removed before publication.]
[ This document is being collaborated on in Github at:
https://github.com/wkumari/draft-wkumari-dnsop-cheese-shop. The most
recent version of the document, open issues, etc should all be
available here. The authors (gratefully) accept pull requests ]
Status of This Memo
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This Internet-Draft will expire on August 27, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Background . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Believing NSEC records. . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements notation . . . . . . . . . . . . . . . . . . 3
3. Generating negatives responses from NSEC . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Background
[ This section may be removed before publication... but I'd prefer
not, it provides useful context ]
If a DNS resolver queries a root zone authoritative name server with
the EDNS0 DNSSEC OK option set, for a name that does not exist in the
root zone, it gets back an NXDOMAIN response and an NSEC record,
which "proves" that the name does not exist. NSEC proves this by
providing names (and signatures) for the names which do exist on
either side of the queried name. For example, if a nameserver
queries for .belkin, it will get back an NXDOMAIN, and an NSEC record
showing that nothing exists between (currently) .beer and .bentley
[Ed note: There *probably* should be something between a beer and a
bentley. :-P ]. This means that, if the nameserver subsequently
(during the TTL of the NSEC record) gets a query for .beeswax
(alphabetically between beer and bentley) it need not attempt to
resolve this - it has already been given proof that the name does not
exist.
The title of this draft comes from a famous Monty Python skit - "The
Cheese Shop". There are some useful parallels between this problem
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and the skit - watching the skit is encouraged to understand the
problem - https://www.youtube.com/watch?v=cWDdd5KKhts
2. Believing NSEC records.
This is a simply a refinement of
[I-D.fujiwara-dnsop-nsec-aggressiveuse], for a limited use case (the
root). Full credit to the authors of the aforementioned draft, and
this draft does not replace that draft, nor remove the need for the
broader consideration of the use of NSEC records as described in
[I-D.fujiwara-dnsop-nsec-aggressiveuse].
The scope of this document is limited to the special case of
recursive DNSSEC validating resolvers querying the root zone. This
is because the root zone has some well known properties which make it
a special case - we know it is DNSSEC signed, and uses NSEC, the
majority of the queries are "junk" queries, the rate of change is
relatively slow, and there are no odd corner cases such as wildcards.
See Section 3 for more discussion.
If the (DNSSEC validated) answer to a query to a root server is an
NXDOMAIN then the resolver SHOULD cache the NSEC record provided in
the response. The resolver SHOULD NOT send further queries for names
within the range of the NSEC record for the lifetime of the cached
NSEC TTL. Instead, the resolver SHOULD answer these queries directly
with NXDOMAIN (and NSEC records if so signalled by EDNS). They
SHOULD set the AA bit and AD bits.
2.1. Requirements notation
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. Generating negatives responses from NSEC
[ This section is mainly for discussion, and is more informal. It
should be deleted before publication. ]
Section 4.5 of [RFC4035] says:
"In theory, a resolver could use wildcards or NSEC RRs to generate
positive and negative responses (respectively) until the TTL or
signatures on the records in question expire. However, it seems
prudent for resolvers to avoid blocking new authoritative data or
synthesizing new data on their own. Resolvers that follow this
recommendation will have a more consistent view of the namespace."
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and "The reason for these recommendations is that, between the
initial query and the expiration of the data from the cache, the
authoritative data might have been changed (for example, via dynamic
update)."
So, if a resolver generates negative answers from an NSEC record, it
will not send any queries for names within that NSEC range (for the
TTL). If a new name is added to the zone during this interval the
resolver will not know this.
For the limited use case of this document (the DNS root) we believe
that this is an acceptable trade off - the (current) TTL of the
"negative cache" (in the SOA) is the same as the NSEC TTL (1 day).
This means that, for a new TLD to begin resolving everywhere will
require a minimum of a day - and this is true whether or not this is
implemented (if someone had queried for the exact name, there would
be a negatively cached answer, this simply expands the range of
negative caches).
4. IANA Considerations
This document contains no IANA considerations.
[ We MAY want to add something about setting the NSEC TTL
appropriately?! ]
5. Security Considerations
The impact of resolver caching is that the resolver will not re-query
an name server for a cached response until the TTL of the cached
response expires. This may lead to cases where the resolver responds
with outdated information for a period of time for subsequent queries
for the name name.
This draft extends the scope of this vulnerability to include queries
for all names that fall within the NSEC-defined range.
6. Acknowledgements
The authors wish to thank some folk, including Stephane Bortzmeyer,
Bob Harold, Paul Vixie.
7. References
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7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
7.2. Informative References
[I-D.fujiwara-dnsop-nsec-aggressiveuse]
Fujiwara, K. and A. Kato, "Aggressive use of NSEC/NSEC3",
draft-fujiwara-dnsop-nsec-aggressiveuse-02 (work in
progress), October 2015.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
<http://www.rfc-editor.org/info/rfc4035>.
Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
From -00 to -01.
o Fairly significant rewrite - no substantive changes, only
additional information, explaination and readability.
Authors' Addresses
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: warren@kumari.net
Geoff Huston
APNIC
6 Cordelia St
South Brisbane QLD 4001
AUS
Email: gih@apnic.net
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