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DNSEXT Working Group                                           R. Bellis
Internet-Draft                                                       ISC
Intended status: Standards Track                           July 03, 2017
Expires: January 4, 2018


                          DNS Multiple QTYPEs
                  draft-bellis-dnsext-multi-qtypes-04

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
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   This Internet-Draft will expire on January 4, 2018.

Copyright Notice

   Copyright (c) 2017 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
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   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   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 . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   A commonly requested DNS [RFC1035] feature is the ability to receive
   multiple related resource 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 [RFC6891]) that
   contains an additional list of QTYPE values that the client wishes to
   receive in addition to that in the primary question.

   TODO: why not "ANY" ?






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2.  Terminology used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Description

3.1.  Multiple QTYPE EDNS Option Format

   The overall format of an EDNS option is shown for reference below,
   per [RFC6891], followed by the option specific data:

      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   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.  NB: Whilst the QTCOUNT could in theory be




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   calculated based on the OPTION-LENGTH field, having it explicitly
   specified ensures a sensible constraint its value.

   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 "OPT", "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
   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 (QNAME, QTn, QCLASS) tuples.  These records
   MUST be returned in the Answer Section of the response, but the
   answer for the primary QTYPE from the Question Section 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
   the Multiple QTYPE Option of 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.

   A server that is authoritative for the specified QNAME on receipt of
   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.





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   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 [RFC4034] and
   [RFC5155].

   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 a denial of service attack.

5.  IANA Considerations

   IANA is requested to assign a new value in the DNS EDNS0 Option Codes
   registry.







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6.  Acknowledgements

   The author wishes to thank the following for their feedback and
   reviews during the initial development of this document: Michael
   Graff, Olafur Gudmundsson, Matthijs Mekking, Paul Vixie.

7.  Normative References

   [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>.

   [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
              <http://www.rfc-editor.org/info/rfc2181>.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,
              <http://www.rfc-editor.org/info/rfc4034>.

   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of
              Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
              <http://www.rfc-editor.org/info/rfc5155>.

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891, DOI 10.17487/
              RFC6891, April 2013,
              <http://www.rfc-editor.org/info/rfc6891>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <http://www.rfc-editor.org/info/rfc8174>.

Author's Address










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   Ray Bellis
   Internet Systems Consortium, Inc.
   950 Charter Street
   Redwood City  CA 94063
   USA

   Phone: +1 650 423 1200
   Email: ray@isc.org











































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