Network Working Group                                           J. Abley
Internet-Draft                                                 Dyn, Inc.
Updates: 1035 (if approved)                               O. Gudmundsson
Intended status: Standards Track                            M. Majkowski
Expires: May October 8, 2016                                 CloudFlare Inc.
                                                        November 5, 2015
                                                          April 06, 2016

    Providing Minimal-Sized Responses to DNS Queries with QTYPE=ANY
                     draft-ietf-dnsop-refuse-any-00
                     draft-ietf-dnsop-refuse-any-01

Abstract

   The Domain Name System (DNS) specifies a query type (QTYPE) "ANY".
   The operator of an authoritative DNS server might choose not to
   respond to such queries for reasons of local policy, motivated by
   security, performance or other reasons.

   The DNS specification does not include specific guidance for the
   behaviour of DNS servers or clients in this situation.  This document
   aims to provide such guidance.

Status of this 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
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   This Internet-Draft will expire on May October 8, 2016.

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Table of Contents

   1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .  3   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  4   3
   3.  Motivations . . . . . . . . . . . . . . . . . . . . . . . . .  5   3
   4.  General Approach  . . . . . . . . . . . . . . . . . . . . . . .  6   3
   5.  Behaviour of DNS Responders . . . . . . . . . . . . . . . . .  7   4
   6.  Behaviour of DNS Initiators . . . . . . . . . . . . . . . . .  8   5
   7.  HINFO Considerations  . . . . . . . . . . . . . . . . . . . . .  9   5
   8.  Changes to RFC 1035 . . . . . . . . . . . . . . . . . . . . . 10   6
   9.  Implementation experience . . . . . . . . . . . . . . . . . .   6
   10. Security Considerations . . . . . . . . . . . . . . . . . . . 11
   10.   6
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
   11.   6
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 13
   12.   7
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     12.1.   7
     13.1.  Normative References . . . . . . . . . . . . . . . . . . 14
     12.2.   7
     13.2.  Informative References . . . . . . . . . . . . . . . . . 14   7
     13.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Appendix A.  Editorial Notes  . . . . . . . . . . . . . . . . . . . 15   8
     A.1.   Venue  Change History  . . . . . . . . . . . . . . . . . . . . .   8
       A.1.1.  draft-ietf-dnsop-refuse-any-03  . . . . . 15
     A.2.   Change History . . . . . .   8
       A.1.2.  draft-ietf-dnsop-refuse-any-02  . . . . . . . . . . .   8
       A.1.3.  draft-ietf-dnsop-refuse-any-01  . . . . 15
       A.2.1.  draft-ietf-dnsop-refuse-any-00 . . . . . . .   8
       A.1.4.  draft-ietf-dnsop-refuse-any-00  . . . . . 15
       A.2.2.  draft-jabley-dnsop-refuse-any-01 . . . . . .   8
       A.1.5.  draft-jabley-dnsop-refuse-any-01  . . . . . . 15
       A.2.3.  draft-jabley-dnsop-refuse-any-00 . . . .   8
       A.1.6.  draft-jabley-dnsop-refuse-any-00  . . . . . . . . 15 . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 16   8

1.  Terminology

   This document uses terminology specific to the Domain Name System
   (DNS), descriptions of which can be found in
   [I-D.ietf-dnsop-dns-terminology]. [RFC7719].

   In this document, "ANY Query" refers to a DNS query meta-query with
   QTYPE=ANY.  An "ANY Response" is a response to such a query.

   In an exchange of DNS messages between two hosts, this document
   refers to the host sending a DNS request as the initiator, and the
   host sending a DNS response as the responder.

   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].

2.  Introduction

   The Domain Name System (DNS) specifies a query type (QTYPE) "ANY".
   The operator of an authoritative DNS server might choose not to
   respond to such queries for reasons of local policy, motivated by
   security, performance or other reasons.

   The DNS specification [RFC1034] [RFC1035] does not include specific
   guidance for the behaviour of DNS servers or clients in this
   situation.  This document aims to provide such guidance.

3.  Motivations

   ANY queries are legitimately used for debugging and checking the
   state of a DNS server for a particular owner name.  ANY queries are
   sometimes used as a attempt to reduce the number of queries needed to
   get information, e.g. to obtain MX, A and AAAA RRSets for a mail
   domain in a single query, although query.  Although there is no documented guidance
   available for this use case and some implementations have been
   observed that appear not to function as perhaps their developers
   expected.  For any developer that assumes that ANY query will be sent
   to authoritative server to fetch all RRSets, they need to include a
   fallback when that does not happen.

   ANY queries are also frequently used to exploit the amplification
   potential of DNS servers servers/resolvers using spoofed source addresses and
   UDP transport (see [RFC5358]).  Having the ability to return small
   responses to such queries makes DNS servers less attractive
   amplifiers.

   ANY queries are sometimes used to help mine authoritative-only DNS
   servers for zone data, since they are expected to return all RRSets
   for a particular
   owner query name.  A DNS zone maintainer might operator MAY prefer not to send full
   large ANY responses to reduce the potential for such information leaks.

   Some authoritative-only DNS server implementations require additional
   processing in order to send a conventional ANY response, and avoiding
   that processing expense may might be desirable.

4.  General Approach

   This proposal provides a mechanism for an authority server to signal
   that conventional ANY queries are not supported for a particular
   QNAME, and to do so in such a way that is both compatible with and
   triggers desirable behaviour by unmodified clients (e.g.  DNS
   resolvers).

   Alternative proposals for dealing with ANY queries have been
   discussed.  One approach proposed using a new RCODE to signal that an
   authortitaive
   authoritative server did not answer ANY queries in the standard way.
   This approach was found to have an undesirable effect on both
   resolvers and authoritative-only servers; resolvers receiving an
   unknown RCODE caused them to re-send the same query to all available
   authoritative servers, rather than suppress future such ANY queries
   for the same QNAME.

   This proposal avoids that outcome by returning a non-empty RRSet in
   the ANY response, providing resolvers with something to cache and
   effectively suppressing repeat queries to the same or different
   authority servers.

   This proposal specifies two different modes of behaviour by DNS
   responders, and operators for names that exists.  Operators/Implementers are free
   to choose whichever mechanism best suits their environment.

   1.  A DNS responder may can choose to search for an owner name that
       matches the QNAME and, if that name owns multiple RRSets, return
       just select one or subset of them. RRSets at
       the QNAME.

   2.  A DNS responder for whom a search for an owner name with an
       existing resource record is expensive may can return instead synthesise an synthesised HINFO resource record and return that instead.
       record.  See Section 7 for discussion of the use of HINFO.

5.  Behaviour of DNS Responders

   A DNS responder which receives an ANY query MAY decline to provide a
   conventional response, and MAY instead send a response with a single
   RRSet in the answer section.

   The RRSet returned in the answer section of the response MAY be a
   single RRSet owned by the name specified in the QNAME.  Where
   multiple RRSets exist, the responder MAY SHOULD choose a small one one(s) to
   reduce its amplification potential.

   If there is no CNAME present at the owner name matching the QNAME,
   the resource record returned in the response MAY instead be
   synthesised, in which case a single HINFO resource record should SHOULD be
   returned.  The CPU field of the HINFO RDATA SHOULD be set to RFCXXXX
   [note to RFC Editor, replace with RFC number assigned to this
   document].  The OS field of the HINFO RDATA SHOULD be set to the null
   string to minimise minimize the size of the response.

   The TTL encoded for a synthesised RR SHOULD be chosen by the operator
   of the DNS responder to be large enough to suppress frequent
   subsequent ANY queries from the same initiator with the same QNAME,
   understanding that a TTL that is too long might make policy changes
   relating to ANY queries difficult to change in the future.  The
   specific value used is hence a familiar balance when choosing TTLs TTL for
   any RR in any zone, and should be specified according to local policy.

   If the DNS query includes DO=1 and the QNAME corresponds to a zone
   that is known by the responder to be signed, a valid RRSIG for the
   RRSets in the answer (or authority if answer is empty) section MUST
   be returned.  In case DO=0 RRSIG SHOULD be omitted.

   Except as described in this section, the DNS responder MUST follow
   the standard algorithms when constructing a response.

6.  Behaviour of DNS Initiators

   XXX consider whether separate text here is required depending on
   whether the initiator is a non-caching stub resolver or a caching
   recursive resolver.

   A DNS initator initiator which sends a query with QTYPE=ANY and receives a
   response containing an HINFO, as described in Section 5, MAY cache
   the HINFO response in the normal way.  Such cached HINFO resource
   records SHOULD be retained in the cache following normal caching
   semantics, as it would with any other response received from a DNS
   responder.

   A DNS initiator MAY suppress queries with QTYPE=ANY in the event that
   the local cache contains a matching HINFO resource record with
   RDATA.CPU field, as described in Section 5.

7.  HINFO Considerations

   In the case where a zone that contains HINFO RRSets is served from an
   authority server that does not provide conventional ANY responses, it
   is possible that the HINFO RRSet in an ANY response, once cached by
   the initiator, might suppress subsequent queries from the same
   initiator with QTYPE=HINFO.  The use of HINFO in this proposal would
   hence have effectively masked mask the HINFO RRSet present in the zone.

   Authority-server operators who serve zones that rely upon
   conventional use of the HINFO RRType might RRTYPE MAY sensibly choose not to
   deploy the mechanism described in this document. document or select other type.

   The HINFO RRType RRTYPE is believed to be rarely used in the DNS at the time
   of writing, based on observations made both at recursive servers and
   authority servers.

8.  Changes to RFC 1035

   It is important to note that returning a subset of available RRSets
   when processing an ANY query is legitimate and consistent with
   [RFC1035]; ANY does not mean ALL.

   This document describes optional behaviour for both DNS initators initiators
   and responders, and implementation of the guidance provided by this
   document is OPTIONAL.

9.  Implementation experience

   In October 2015 CloudFlare Authoritative Nameserver implementation
   implemented the HINFO response.  Few minor problems have been
   reported and worked out.  NSD has for a while implemented a sub-set
   response.  A Bind user implemented this draft suggestion of returning
   only single RRset during an attack.

10.  Security Considerations

   Queries with QTYPE=ANY are frequently observed as part of reflection
   attacks, since a relatively small query can be used to elicit a large
   response; this is a desirable characteristic if the goal is to
   maximise
   maximize the amplification potential of a DNS server as part of a
   volumetric attack.  The ability of a DNS operator to suppress such
   responses on a particular server makes that server a less useful
   amplifier.

   The optional behaviour described in this document to reduce the size
   of responses to queries with QTYPE=ANY is compatible with the use of
   DNSSEC by both initiator and responder.

10.

11.  IANA Considerations

   This document has no

   The IANA actions.

11. is requested to update the Resource Record (RR) TYPEs
   Registry [1] entry as follows:

   +------+-------+-------------------------------+--------------------+
   | Type | Value | Meaning                       | Reference          |
   +------+-------+-------------------------------+--------------------+
   | *    | 255   | A request for some or all     | [RFC1035][RFC6895] |
   |      |       | records the server has        | [This Document]    |
   |      |       | available                     |                    |
   +------+-------+-------------------------------+--------------------+

12.  Acknowledgements

   Evan Hunt and David Lawrence provided valuable observations.

12. observations and
   concrete suggestions.  Jeremy Laidman helped make the document
   better.  Tony Finch realized that this document was valuable and
   implemented it while under attack.  A large number of people have
   provided comments and suggestions we thank them all for the feedback.

13.  References

12.1.

13.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <http://www.rfc-editor.org/info/rfc1034>.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <http://www.rfc-editor.org/info/rfc1035>.

   [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>.

12.2.

13.2.  Informative References

   [I-D.ietf-dnsop-dns-terminology]
              Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", draft-ietf-dnsop-dns-terminology-05 (work in
              progress), September 2015.

   [RFC5358]  Damas, J. and F. Neves, "Preventing Use of Recursive
              Nameservers in Reflector Attacks", BCP 140, RFC 5358, DOI
              10.17487/RFC5358, October 2008,
              <http://www.rfc-editor.org/info/rfc5358>.

   [RFC6895]  Eastlake 3rd, D., "Domain Name System (DNS) IANA
              Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895,
              April 2013, <http://www.rfc-editor.org/info/rfc6895>.

   [RFC7719]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", RFC 7719, DOI 10.17487/RFC7719, December
              2015, <http://www.rfc-editor.org/info/rfc7719>.

13.3.  URIs

   [1] http://www.iana.org/assignments/dns-parameters/dns-
       parameters.xhtml#dns-parameters-4

Appendix A.  Editorial Notes

   This section (and sub-sections) to be removed prior to publication.

A.1.  Venue

   An appropriate forum for discussion of this draft is the dnsop
   working group.

A.2.  Change History

A.2.1.

A.1.1.  draft-ietf-dnsop-refuse-any-03

   Text clarifications, reflecting experience, added implementation
   experience.

A.1.2.  draft-ietf-dnsop-refuse-any-02

   Added suggestion to call out RRSIG is optional when DO=0.

   Number of text suggestions from Jeremy Laidman

A.1.3.  draft-ietf-dnsop-refuse-any-01

   Add IANA Considerations

A.1.4.  draft-ietf-dnsop-refuse-any-00

   Re-submitted with a different name following adoption at the dnsop wg
   meeting convened at IETF 94.

A.2.2.

A.1.5.  draft-jabley-dnsop-refuse-any-01

   Make signing of RRSets in answers from signed zones mandatory.

   Document the option of returning an existing RRSet in place of a
   synthesised one.

A.2.3.

A.1.6.  draft-jabley-dnsop-refuse-any-00

   Initial draft circulated for comment.

Authors' Addresses

   Joe Abley
   Dyn, Inc.
   103-186 Albert Street
   London, ON  N6A 1M1
   Canada

   Phone: +1 519 670 9327
   Email: jabley@dyn.com
   Olafur Gudmundsson
   CloudFlare Inc.

   Email: olafur@cloudflare.com

   Marek Majkowski
   CloudFlare Inc.

   Email: marek@cloudflare.com