



Network Working Group                                        K. Fujiwara
Internet-Draft                                                      JPRS
Updates: 2181 (if approved)                                    W. Toorop
Intended status: Standards Track                              NLnet Labs
Expires: 3 September 2026                                   2 March 2026


                 Clarifications to the DNS Ranking Data
                  draft-fujiwara-dnsop-ranking-data-01

Abstract

   This document obsoletes Section 5.4.1 (Ranking data) of RFC 2181, and
   specifies directives whereby the source of the data determines for
   what purposes it may be used.

Status of This Memo

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   This Internet-Draft will expire on 3 September 2026.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   2
   4.  Directives  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Additional Considerations . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The DNS server assumed in Section 5.4.1 (Ranking data) of [RFC2181]
   is considered to be a model with a shared database described in
   Section 2.2 (Common configurations) of [RFC1035] that has both
   Authoritative server and Recursive Resolver functions.  It is assumed
   that information obtained from zone files, zone transfers, and name
   resolution will be mixed together.

   However, at the time of writing, this is no longer the practice of
   name servers and resolvers.  Zone transfers transfer the same data
   from primaries to secondary servers without any modification.  An
   authoritative name server function does not mix and return
   information obtained from name resolution.

2.  Terminology

   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.

   Many of the specialized terms used in this document are defined in
   DNS Terminology [RFC9499].

3.  Problem Statement

   In the past, recursive resolvers would return data from referral
   responses, such as delegation information or glue, in the answer
   section of responses; however, modern recursive resolvers complete
   name resolution with an authoritative response from an authoritative
   server that has authority through delegation.  However, there is no
   clear documentation of this.





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   "The Ranking Data" only indicates the priority among data, not its
   validity.  Attacks using responses that do not correspond to queries
   and additional data that is not required have been considered and
   reported, so unnecessary data should be discarded.

   [RFC1034] already describes resolver's answer as follows.

   "The ideal answer is one from a server authoritative for the query
   which either gives the required data or a name error.  The data is
   passed back to the user and entered in the cache for future use if
   its TTL is greater than zero."  (Quoted from RFC 1034, Section 5.3.3)

   "The simplest mode for the client is recursive, since in this mode
   the name server acts in the role of a resolver and returns either an
   error or the answer, but never referrals."  (Quoted from RFC 1034,
   Section 4.3.1)

   Currently, responses from authoritative servers are considered to
   include authoritative name resolution results (NXDOMAIN, NODATA, the
   RRSet requested), non-authoritative delegation information,
   unnecessary data, and other types of errors, and each of these is
   considered to affect how resolvers handle the data.  Therefore,
   directives on how to handle the data are needed.

4.  Directives

   1.  Authoritative servers MUST NOT merge zone data. (zone data should
       be retrieved from a source (zone file, internal database, zone
       transfer)

   2.  Name resolution results (Answer section, or NXDOMAIN, NODATA)
       MUST be authoritative responses from authoritative servers that
       has authority through delegation.

   3.  Non-authoritative responses (referral/delegation responses) from
       authoritative servers MUST only be used to query the delegated
       authoritative server during the name resolution.

   4.  Names and IP addresses of the authoritative name servers for
       zones (such as the root zone) that are built-in or loaded from
       "hints" files, MUST only be used for priming a resolver for those
       zones [RFC9609].

   5.  Multi-function name server







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       Name servers with multiple functions will act as an
       Authoritative, Recursive Resolver (Full-Service Resolver), or
       Forwarder depending on the namespace to which the query name
       belongs, the server IP address, the "Recursion Desired" bit, etc.
       The data handled by each function MUST be separated.

5.  Additional Considerations

   [ Further directives could be made, they may be DNS software
   implementation guidelines, which would be large in scale, so it is
   necessary to consider whether to proceed with them. ]

   *  If a DNS server plays different roles for different namespaces
      (authoritative server, recursive resolver, forwarder), it MUST NOT
      merge DNS data for each role.

      For example, a recursive resolver that returns a fixed zone as a
      split-horizon DNS can be interpreted as acting as an authoritative
      server below a certain domain name, but as a recursive resolver
      otherwise.

   *  The Additional Section returned as the result of name resolution
      MUST be exactly the same as the Additional Section that came from
      the authoritative response from the authoritative server, or a
      separate authoritative response resulting from name resolution.

   *  Full-service resolvers SHOULD only accept the following data from
      authoritative servers:

      -  NS and DS RRSets (+RRSIG) in the Authority Section of the
         delegation response and Glue A/AAAA in the Additional Section,

      -  SOA RRs (+RRSIG) in the Authority Section of authoritative
         NXDOMAIN and NODATA responses in response to the query,

      -  the Answer Section (+RRSIG) of the authoritative response in
         response to the query, and

      -  any additional sections allowed by type (delegated domain
         name),

      and SHOULD NOT accept any other information.

6.  IANA Considerations

   This document requests no IANA actions.





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7.  Security Considerations

8.  Normative References

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

   [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>.

   [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>.

   [RFC9499]  Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
              RFC 9499, DOI 10.17487/RFC9499, March 2024,
              <https://www.rfc-editor.org/rfc/rfc9499>.

   [RFC9609]  Koch, P., Larson, M., and P. Hoffman, "Initializing a DNS
              Resolver with Priming Queries", BCP 209, RFC 9609,
              DOI 10.17487/RFC9609, February 2025,
              <https://www.rfc-editor.org/rfc/rfc9609>.

Authors' Addresses

   Kazunori Fujiwara
   Japan Registry Services Co., Ltd.
   Japan
   Email: fujiwara@jprs.co.jp


   Willem Toorop
   NLnet Labs
   Science Park 400
   1098 XH Amsterdam
   Netherlands
   Email: willem@nlnetlabs.nl



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