DNS Multiple QTYPEs
draft-ietf-dnssd-multi-qtypes-05

DNSSD                                                          R. Bellis
Internet-Draft                                                       ISC
Intended status: Standards Track                         7 November 2024
Expires: 11 May 2025

                          DNS Multiple QTYPEs
                    draft-ietf-dnssd-multi-qtypes-05

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
   (OpCode=0).

About This Document

   This note is to be removed before publishing as an RFC.

   The latest revision of this draft can be found at https://dnssd-
   wg.github.io/draft-ietf-dnssd-multi-qtypes/draft-ietf-dnssd-multi-
   qtypes.html.  Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-dnssd-multi-qtypes/.

   Discussion of this document takes place on the DNSSD Working Group
   mailing list (mailto:dnssd@ietf.org), which is archived at
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   https://www.ietf.org/mailman/listinfo/dnssd/.

   Source for this draft and an issue tracker can be found at
   https://github.com/dnssd-wg/draft-ietf-dnssd-multi-qtypes.

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   This Internet-Draft will expire on 11 May 2025.

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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 Options Format  . . . . . . . . . . .   3
     3.2.  Server Handling . . . . . . . . . . . . . . . . . . . . .   4
       3.2.1.  Request Parsing . . . . . . . . . . . . . . . . . . .   4
       3.2.2.  Response Generation . . . . . . . . . . . . . . . . .   4
     3.3.  Client Response Processing  . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

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 the A, AAAA and HTTPS
   records for a domain name together, rather than having to issue
   multiple queries.

   The DNS wire protocol in theory supported having multiple questions
   in a single packet, but in practise this does not work.  In
   [RFC9619], [RFC1035] is updated to only permit a single question in a
   QUERY (OpCode=0) request.

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   Sending QTYPE=ANY does not guarantee that all RRsets will be
   returned.  [RFC8482] specifies that responders may return a single
   RRset of their choosing.

   This document provides a solution for 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 the single
   QTYPE appearing in the question section.  A different EDNS option is
   used in response packets as protection against DNS middleboxes that
   echo EDNS options verbatim.

   The specification described herein is applicable both for queries
   from a stub resolver to recursive servers, and from recursive
   resolvers to authoritative servers.  It does not apply to Multicast
   DNS queries [RFC6762], which are already designed to allow requesting
   multiple records in a single query.

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 Options 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: MQTYPE-Query (TBD1) in queries and MQTYPE-Response
   (TBD2) in responses.

   OPTION-LENGTH: Size (in octets) of OPTION-DATA.

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   OPTION-DATA: Option specific, as below:

                   +0 (MSB)                            +1 (LSB)
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   0: |           QT1 (MSB)           |           QT1 (LSB)           |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   2: /              ...              |              ...              /
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      /           QTn (MSB)           |           QTn (LSB)           |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

   QT: a (potentially empty) list of 2 byte fields (QTx) in network
   order (MSB first) each specifying a DNS RRTYPE.  The RRTYPEs MUST be
   for real resource records, and MUST NOT refer to Meta RRTYPEs such as
   "OPT" and those from the reserved range 128 - 255, e.g.  "IXFR",
   "TSIG", "*", etc.

3.2.  Server Handling

3.2.1.  Request Parsing

   If MQTYPE-Query is received in any inbound DNS message with an OpCode
   other than QUERY (0) the server MUST return a FORMERR response.

   A server that receives an MQTYPE-Response option in any inbound DNS
   message MUST return a FORMERR response.

   A server that receives more than one MQTYPE-Query option in a query
   MUST return a FORMERR response.

   If MQTYPE-Query is received in a query that contains no primary
   question (i.e.  QDCOUNT=0) the server MUST return a FORMERR response.

   If any duplicate QTx (or one duplicating the primary QTYPE field) is
   contained in a query the server MUST return a FORMERR response.

   If any invalid QTx is received in the query (e.g. one corresponding
   to a Meta RRTYPE) the server MUST return a FORMERR response.

3.2.2.  Response Generation

   A conforming server that receives an MQTYPE-Query option in a query
   MUST return an MQTYPE-Response option in its response, even if that
   response is truncated (TC=1).

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   The server MUST first start constructing a response for the primary
   (QNAME, QCLASS, QTYPE) tuple specified in the Question section per
   the existing DNS sections.  The RCODE and all other flags (e.g.  AA,
   AD, etc) MUST be determined at this time.

   If this initial response results in truncation (TC=1) then the
   additional queries specified in MQTYPE-Query MUST NOT be processed.

   After the initial response is prepared, the server MUST attempt to
   combine the responses for individual (QNAME, QCLASS, QTx)
   combinations into the response for the first query.

   For each individual combination the server MUST evaluate the
   resulting RCODE and other flags and check that they all match the
   values generated from the primary query.

   If any mismatch is detected the mismatching additional response MUST
   NOT be included in the final combined response and its QTx value MUST
   NOT be included in the MQTYPE-Response list.  This might happen, for
   example, if the primary query resulted in a NOERROR response but a
   QTx query resulted in a SERVFAIL, or if the primary response has AA=0
   but a QTx response has AA=1, such as might happen if the NS and DS
   records were both requested at the parent side of a zone cut.

   If no mismatches are detected the server MUST attempt to combine the
   individual RRs into their respective sections.  The server MUST
   detect duplicate RRs and keep only a single copy of each RR in its
   respective section.  Duplicates can occur e.g. in Answer section if a
   CNAME chain is involved, or e.g.  Authority section if multiple
   QTYPEs don't exist etc.  Note that RRs can be legitimately duplicated
   in different sections, e.g. for (SOA, TYPE12345) combination on apex
   where TYPE12345 is not present.

   If message size (or other) limits do not allow all of the data
   obtained by querying for an additional QTx to be included in the
   final response then the server MUST NOT include the respective QTx in
   the MQTYPE-Response list and MAY stop processing further QTx
   combinations.

   If all RRs for a single QTx combination fit into the message then the
   server MUST include the respective QTx in the MQTYPE-Response list to
   indicate that the given query type was completely processed.

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3.3.  Client Response 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.

   If the response to a query containing an MQTYPE-Query option does not
   contain an MQTYPE-Response option, or if it erroneously contains an
   MQTYPE-Query option, the client MUST treat the response as if this
   option is unsupported by the server and SHOULD process the response
   as if the MQTYPE-Query option had not been used.

   If the MQTYPE-Response option is present more than once or if a QTx
   value is duplicated (or duplicates the primary QTYPE field) the
   client MUST treat the answer as invalid (equivalent to FORMERR)

   The Question section and the list of types present in the MQTYPE-
   Response option indicates the list of (QNAME, QCLASS, qtypes)
   combinations which are completely contained within the received
   response.  The answers to all query combinations share the same RCODE
   and all other flags.

   All RRs required by existing DNS specifications are expected to be
   present in the respective sections of the DNS message, including
   proofs of nonexistence where required.  The client MUST NOT rely on
   any particular order of RRs in the message sections.

   Clients MUST take into account that individual RRs might originate
   from different DNS zones and that proofs of non-existence might have
   been produced by different signers.

   Absence of QTx values which were requested by client but are not
   present in MQTYPE-Response option indicates that:

   *  the server was unwilling to process the request (e.g. because a
      limit was exceeded), and/or

   *  the individual responses could not be combined into one message
      because of RCODE or other flag mismatches, and/or

   *  the message size limit would be exceeded

   The client SHOULD subsequently initiate standalone queries (e.g.
   without using the MQTYPE-Query option) for any QTx value which was
   requested but is missing in the response.

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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

   NB: to be rewritten once assignments have been made.

   IANA is requested to assign two new values (TBD1 and TBD2) in the DNS
   EDNS0 Option Codes registry for MQTYPE-Query and MQTYPE-Response.
   They should be consecutive, with the -Query option being an even
   number.

6.  References

6.1.  Normative References

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

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

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

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

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

   [RFC9619]  Bellis, R. and J. Abley, "In the DNS, QDCOUNT Is (Usually)
              One", RFC 9619, DOI 10.17487/RFC9619, July 2024,
              <https://www.rfc-editor.org/rfc/rfc9619>.

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6.2.  Informative References

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              DOI 10.17487/RFC6762, February 2013,
              <https://www.rfc-editor.org/rfc/rfc6762>.

   [RFC8482]  Abley, J., Gudmundsson, O., Majkowski, M., and E. Hunt,
              "Providing Minimal-Sized Responses to DNS Queries That
              Have QTYPE=ANY", RFC 8482, DOI 10.17487/RFC8482, January
              2019, <https://www.rfc-editor.org/rfc/rfc8482>.

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, and Paul Vixie.

   In addition the author wishes to thank the following for subsequent
   review during discussion in the DNSSD Working Group: Chris Box,
   Stuart Cheshire, Esko Dijk, Ted Lemon, David Schinazi and Petr
   Spacek.

Author's Address

   Ray Bellis
   Internet Systems Consortium, Inc.
   PO Box 360
   Newmarket,  NH 03857
   United States of America
   Phone: +1 650 423 1300
   Email: ray@isc.org

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