DNS Protocol Modifications for Delegation Extensions
draft-ietf-dnsop-delext-02

deleg                                                          R. Arends
Internet-Draft                                                     ICANN
Intended status: Standards Track                             P. van Dijk
Expires: 19 September 2026                                      PowerDNS
                                                               P. Špaček
                                                                     ISC
                                                           18 March 2026

          DNS Protocol Modifications for Delegation Extensions
                       draft-ietf-dnsop-delext-02

Abstract

   The Domain Name System (DNS) protocol permits Delegation Signer (DS)
   records at delegation points.  This document describes modifications
   to the Domain Name System (DNS) protocol to permit a range of
   resource record types at delegation points.  These modifications are
   designed to maintain compatibility with existing DNS resolution
   mechanisms and provide a secure method for processing these records
   at delegation points.

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 19 September 2026.

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   Please review these documents carefully, as they describe your rights

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   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions and Definitions . . . . . . . . . . . . . . .   3
     1.2.  Relationship with the DELEG draft . . . . . . . . . . . .   3
     1.3.  Relationship with NS and DS records . . . . . . . . . . .   3
     1.4.  Services Provided by Delegation Types . . . . . . . . . .   3
   2.  Delegation Types  . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Updates to allocation policy  . . . . . . . . . . . . . .   4
   3.  Resolver Requirements . . . . . . . . . . . . . . . . . . . .   4
     3.1.  The EDNS(0) DE Flag . . . . . . . . . . . . . . . . . . .   4
     3.2.  Referrals . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Name Server Requirements  . . . . . . . . . . . . . . . . . .   4
     4.1.  Including Delegation Types in a Referral Response . . . .   5
     4.2.  Explicit queries for Delegation Types . . . . . . . . . .   5
   5.  DNSSEC Requirements . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  The DNSKEY-ADT flag . . . . . . . . . . . . . . . . . . .   5
     5.2.  Validating a Referral . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   [RFC4034] defines the Delegation Signer (DS) resource record as
   having a unique property: it resides at a delegation as authoritative
   data.  Discussions and drafts within the DPRIVE, DNSOP, and DELEG
   working groups have highlighted interest in allowing additional types
   of data to be present at delegation points.  This document reserves a
   range of Resource Record (RR) types allowed at delegation points and
   describes the protocol modifications for DNS implementations that
   support them.

   To shield implementations that do not implement these modifications,
   a new EDNS(0) [RFC6891] option is introduced to indicate support for
   this range of RR types.

   To protect against downgrade attacks, a new DNSKEY flag is
   introduced.

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1.1.  Conventions and Definitions

   The term Delegation Types designates the set of RR types consisting
   of the range of RR types reserved in Section 2 of this document.

   *  Delegation-Extension-aware name server or resolver: A server that
      implements this specification.

   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.

1.2.  Relationship with the DELEG draft

   The DELEG draft specifies a new resource record type (DELEG) that is
   authoritative at a delegation point and proposes protocol
   modifications to support DELEG.  The purpose of this document is to
   make sure that protocol modifications are generic for a range of
   types.

1.3.  Relationship with NS and DS records

   The use of DS and delegation-point NS records is orthogonal to the
   use of Delegation Types.  Both types MAY coexist with Delegation
   Types.

1.4.  Services Provided by Delegation Types

   Services provided by Delegation Types consist of information useful
   to a resolver when connecting to servers responsible for the
   delegated namespace.  This can include, but is not limited to, secure
   transport parameters, policy information about zones, and DNSSEC
   security parameters.

2.  Delegation Types

   [RFC6895] contains three subcategories of RR type numbers: Data
   Types, Q-Types, and Meta-Types.  This specification adds a fourth
   subcategory: Delegation Types.

   Considerations for the allocation of Delegation Types are as follows:

   Decimal      Hexadecimal      Registration Procedure
   61440-61935  0xF000-0xF1EF    Expert Review or Standards Action
   61936-61951  0xF1F0-0xF1FF    Private Use

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2.1.  Updates to allocation policy

   This section is to be written with guidance from the RFC6895 Experts
   Pool.

3.  Resolver Requirements

   To indicate Delegation Types support, the resolver sets the
   Delegation Extensions (DE) flag in the EDNS(0) Flags field when
   sending a DNS request message.

3.1.  The EDNS(0) DE Flag

   The DE flag is carried in the OPT RR TTL field.

              +0 (MSB)                            +1 (LSB)
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   0: |         EXTENDED-RCODE        |            VERSION            |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   2: | DO| CO| DE|                   Z                               |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

3.2.  Referrals

   Delegation Types in the authority section of a DNS response message
   indicate that the response contains a referral.  Delegation Types are
   expected to contain all the information needed for a resolver to act
   on.  Therefore, NS records that appear in addition to Delegation
   Types MUST be ignored.  These NS records MUST NOT be validated or
   cached.

   The purpose of this restriction is to avoid leakage of DNS messages
   over unencrypted transport when servers, indicated by Delegation
   Types, fail to respond.

   When no Delegation Types exist, the resolver MAY use NS records.
   Note that the use of DNSSEC can prove the presence and absence of
   Delegation Types for a delegation.

4.  Name Server Requirements

   Delegation-Extension-aware name servers MUST copy the value of the
   EDNS(0) DE flag from the request to the response.

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4.1.  Including Delegation Types in a Referral Response

   When the DE flag is set, the server includes Delegation Types in
   referrals and ignores NS types.  When there are no Delegation Types
   for a referral, it includes NS types.  The proof of existence of
   types for the delegated name MUST be included.

   When the DE flag is clear, and no NS records exist for a referral,
   there is no facility for the resolver to continue resolving the
   delegated namespace.  A name error SHOULD be returned in this case.
   While this may seem counterintuitive, since the name does exist, it
   is the only response code that stops the resolver from asking other
   authoritative name servers for the same information.  Authoritative
   servers SHOULD include an Extended DNS Error [RFC8914] to clarify the
   reason.

4.2.  Explicit queries for Delegation Types

   When the DE flag is set, a query for a Delegation Type SHOULD result
   in an authoritative answer if the Delegation Type exists, or a NODATA
   response (AA flag set, RCODE=0, empty answer section).

   When the DE flag is clear, a query for a Delegation Type SHOULD
   result in an authoritative answer if the Delegation Type exists; in a
   referral with NS types if NS types exist, or in a NODATA response if
   other Delegation Types exist.

5.  DNSSEC Requirements

   In a DNSSEC-signed zone, Delegation Type RRsets MUST be signed.

   To avoid a downgrade attack, where the Delegation Types and NSEC (or
   NSEC3) records can be replaced by unsigned NS records, causing the
   resolver to use unencrypted transport, a secure signal in the form of
   a DNSKEY flag is introduced.  This secure signal indicates that NSEC
   or NSEC3 records MUST be present in a referral response.

5.1.  The DNSKEY-ADT flag

   The DNSKEY Flags field consists of 16 bits:

                                             1   1   1   1   1   1
     0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
   |                           |Zon|Rev|                   |ADT|SEP|
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

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   Bit 14 is the Authoritative Delegation Types (ADT) flag.  It
   indicates to a validator that a referral MUST contain an NSEC or
   NSEC3 record to prove presence or absence of types for the delegated
   name.

5.2.  Validating a Referral

   When the DNSKEY-ADT flag is set in any DNSKEY from the DNSKEY RRset
   of the delegating zone, the validator MUST check the Delegation Types
   in the authority section of the referral against the Type Bit Maps of
   the NSEC or NSEC3 record that matches the delegated name.  If any are
   absent, the referral MUST be considered tampered with, and the
   response MUST be ignored.

6.  Security Considerations

   This section discusses security considerations, including downgrade
   attacks and resolver behavior.  Further details will be added.

7.  IANA Considerations

   IANA is requested to change reservations in the DNS Parameters RR
   types registry, with this document as the Reference.

   *  Range 0xF000-0xF1EF to Registration Procedure "Expert Review or
      Standards Action"
   *  Range 0xF1F0-0xF1FF to Registration Procedure "Private Use"

8.  Acknowledgments

   This idea was initially proposed by Petr Špaček, and independently by
   Paul Wouters.

9.  References

9.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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,
              <https://www.rfc-editor.org/info/rfc4034>.

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   [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/info/rfc6891>.

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

   [RFC8914]  Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
              Lawrence, "Extended DNS Errors", RFC 8914,
              DOI 10.17487/RFC8914, October 2020,
              <https://www.rfc-editor.org/info/rfc8914>.

9.2.  Informative References

   [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/info/rfc8174>.

Authors' Addresses

   Roy Arends
   ICANN
   Guernsey
   Email: roy.arends@icann.org

   Peter van Dijk
   PowerDNS
   Den Haag
   Netherlands
   Email: peter.van.dijk@powerdns.com

   Petr Špaček
   ISC
   Brno
   Czech Republic
   Email: pspacek@isc.org

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