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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

   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 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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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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.

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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