Internet Engineering Task Force                               H. Salgado
Internet-Draft                                                 NIC Chile
Intended status: Informational                         M. Vergara Ereche
Expires: 17 March 2023                                             ICANN
                                                       13 September 2022


   The "ZONEVERSION" EDNS option for the version token of a RR's zone
                    draft-ietf-dnsop-zoneversion-01

Abstract

   The "ZONEVERSION" EDNS option allows a DNS querier to request a DNS
   authoritative server to add an EDNS option in the answer of such
   query with a token field representing the version of the zone which
   contains the answered Resource Record, such as the SOA serial field
   in zones when this number corresponds to the zone version.

   This "ZONEVERSION" data allows to debug and diagnose problems by
   helping to recognize the data source of an answer in an atomic single
   query, by associating the response with a respective zone version.

Status of This Memo

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   This Internet-Draft will expire on 17 March 2023.

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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
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  The ZONEVERSION Option  . . . . . . . . . . . . . . . . . . .   3
     2.1.  The ZONEVERSION Option Presentation Format  . . . . . . .   4
   3.  ZONEVERSION Processing  . . . . . . . . . . . . . . . . . . .   4
     3.1.  Initiator . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Responder . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Flag Definition for SOA-SERIAL  . . . . . . . . . . . . . . .   4
     4.1.  Flag SOA-SERIAL Presentation Format . . . . . . . . . . .   5
   5.  Example usage . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  DNS EDNS0 Option Code Registration  . . . . . . . . . . .   6
     7.2.  ZONEVERSION Registry  . . . . . . . . . . . . . . . . . .   7
       7.2.1.  Expert Review Directives  . . . . . . . . . . . . . .   7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   8
   10. Informative References  . . . . . . . . . . . . . . . . . . .   9
   Appendix A.  Implementation Considerations  . . . . . . . . . . .   9
   Appendix B.  Implementation References  . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The "ZONEVERSION" EDNS option [RFC6891] allows a DNS querier to
   request to a DNS authoritative server to add an EDNS option in the
   answer of such query with a token field representing the version of
   the zone associated to the answered Resource Record, such as the SOA
   serial field in zones when this number corresponds to the zone
   version.

   This "ZONEVERSION" data allows to help debug by recognizing the data
   source of an answer, associating this answer with a respective zone
   version.

   DNS data is of loose coherent nature, meaning that a record obtained
   by a response could be out-of-sync with other authoritative sources
   of the same data.  This makes it difficult to debug responses,
   because you'd need to couple an answer with the same version of the
   zone used to obtain such data.  Even when in zones where the SOA
   serial field have the meaning of zone version you could use a



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   separate query to ask for the SOA RR of the zone and therefore know
   its SOA serial, such separate query is performed in a different time
   and could arrive from another authoritative source (for example, in
   the case the server is anycasted as described in Section 4.9 of
   [RFC4786]), so it's not directly correlated with the original query.

   This EDNS option is aimed to be used only on authoritative servers
   for a zone.  It's intended for hop-to-hop communication (not
   transitive).  Resolver and forwarder behavior is undefined.

   The ZONEVERSION EDNS extension can have different meaning depending
   on the semantics of the zone maintainer and implementation of
   nameservers.  This document defines one possible value, when the zone
   version corresponds to the serial field of the SOA Resource Record of
   the zone, a classic behaviour defined in Section 4.3.5 of [RFC1034].

   As the writing of this document, we recognize there are cases where
   nameservers use different backends for its data sources (like
   relational databases or by using a different off-DNS synchronicity
   among others) therefore, the SOA version field doesn't offer much
   relevance as a versioning to its content, and in those cases the
   ZONEVERSION EDNS extension SHOULD be extended with a different flag
   and have an opaque value for its data token.

1.1.  Requirements Language

   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.  The ZONEVERSION Option

   The variable part of RDATA in the OPT RR Section 6.1.2 of [RFC6891]
   for ZONEVERSION is defined as follows:

   *  The OPTION-CODE for the ZONEVERSION option is <TBD>.

   *  The OPTION-LENGTH for the ZONEVERSION option MUST have a value of
      0 for queries, and MUST have the value of length in octects for
      the next OPTION-DATA for responses.

   *  The OPTION-DATA for the ZONEVERSION option is composed of the
      concatenation of an unsigned 1 byte Flag number (FLAG-NUMBER), an
      unsigned 2 bytes number with the Length of the next field in bytes
      (FLAG-LENGTH), and the final Data value of the ZONEVERSION field
      as an opaque bit value, with the previous specified length (FLAG-
      DATA).




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   [RFC Editor: change <TBD> to the proper code when assigned by IANA.]

2.1.  The ZONEVERSION Option Presentation Format

   The presentation format of the RDATA portion is as follows:

   The OPTION-CODE field MUST be represented as the mnemonic value
   "ZONEVERSION".

   The OPTION-LENGTH field could be ommited in presentation format, but
   if is used, MUST be represented as an unsigned decimal integer.

   The OPTION-DATA field MUST be represented following its own format,
   as specified in the corresponding Flag's specification.

3.  ZONEVERSION Processing

3.1.  Initiator

   The EDNS ZONEVERSION option MAY be included on any QUERY, by adding a
   zero-length EDNS ZONEVERSION option to the options field of the OPT
   record when the query is made.

3.2.  Responder

   If an EDNS ZONEVERSION option is sent to a server that is
   Authoritative for the zone, then a name server that understands the
   ZONEVERSION option and chooses to honor a particular ZONEVERSION
   request, MUST put in the OPTION-DATA a flag, length and value that
   corresponds to the properly semantic of such flag number, and
   corresponds to a zone versioning value of the zone that holds the
   original QNAME of the reply (as per Section 4 of [RFC8499]).

   Otherwise, the answer MUST NOT add an EDNS ZONEVERSION option to the
   response.

4.  Flag Definition for SOA-SERIAL

   The first and only ZONEVERSION Flag defined in this document for the
   ZONEVERSION Option has the FLAG-NUMBER of 0, a FLAG-LENGTH field of
   value 4, and its corresponding FLAG-DATA MUST be a copy of the
   unsigned 32 bit version number as defined in the SERIAL field of the
   "SOA RDATA Format" in Section 3.3.13 of [RFC1035].

   The FLAG-LENGTH for this ZONEVERSION Option MUST have a value of 7
   for responses.

   The mnemonic of this flag is SOA-SERIAL.



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   Note that in this case a NXDOMAIN RCODE already includes the complete
   SOA Resource Record in the AUTHORITY section, so the inclusion of a
   ZONEVERSION EDNS Option in the answer is superflous and can be
   omitted.  In the case of a SERVFAIL RCODE the responder MAY include
   the ZONEVERSION EDNS Option if the QNAME still belongs to an
   authoritative zone of the server, in which case that value MUST be
   the one included in the answer.

   Note that a NODATA response code as defined in Section 3 of [RFC8499]
   MUST also include the ZONEVERSION answer even when there's no ANSWER
   data for the QNAME, since the RCODE is NOERROR.

4.1.  Flag SOA-SERIAL Presentation Format

   The presentation format of this flag content is as follows:

   The FLAG-NUMBER field MUST be represented as the mnemonic value "SOA-
   SERIAL".

   The FLAG-LENGTH field could be ommited in presentation format, but if
   is used, MUST be represented as an unsigned decimal integer.

   The FLAG-DATA field MUST be represented as an unsigned decimal
   integer.

5.  Example usage

   A zone which utilizes the serial field of the SOA Resource Record as
   a number of the zone version release, should answer a ZONEVERSION
   request with an EDNS option code ZONEVERSION, an OPTION-DATA with a
   Flag byte with value 0, Length value 4 and a copy of the unsigned 32
   bit version number of the SERIAL field of its SOA zone Resourse
   Record, and an OPTION-LENGTH with value 7.

   An example of a proper diagnostic tool that implements ZONEVERSION
   EDNS extension towards a compliant authoritative DNS server could be:















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     $ dig @ns.example.com www.example.com AAAA +zoneversion +norec +cmd

     ; (1 server found)
     ;; global options: +cmd
     ;; Got answer:
     ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 16429
     ;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

     ;; OPT PSEUDOSECTION:
     ; EDNS: version: 0, flags:; udp: 4096
     ; ZONEVERSION: 2019073001 (SOA-SERIAL)
     ;; QUESTION SECTION:
     ;www.example.com.                    IN      AAAA

     ;; ANSWER SECTION:
     www.example.com.             900     IN      AAAA

     ;; Query time: 53 msec
     ;; SERVER: ns.example.com#53(2001:DB8::53)
     ;; WHEN: Tue Aug 07 16:54:05 -04 2018
     ;; MSG SIZE  rcvd: 71


                                  Figure 1

6.  Acknowledgements

   The authors thanks all the comments and support made in the DNSOPS
   mailing list, chats and discussions.  In special for the suggestions
   to generalize the option using a registry of flags from Petr Špaček,
   and suggestions for implementators from Stéphane Bortzmeyer.

7.  IANA Considerations

7.1.  DNS EDNS0 Option Code Registration

   This document defines a new EDNS0 option, entitled "ZONEVERSION" (see
   Section 2), and assigns a value of <TBD> from the DNS EDNS0 Option
   Codes (OPT) Option space:

           +=======+=============+==========+=================+
           | Value | Name        | Status   | Reference       |
           +=======+=============+==========+=================+
           | <TBD> | ZONEVERSION | Standard | [this document] |
           +=======+=============+==========+=================+

                                 Table 1




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   [RFC Editor: change <TBD> to the proper code when assigned by IANA.]

   [RFC Editor: change "this document" with the proper RFC number for
   this document when assigned by IANA.]

7.2.  ZONEVERSION Registry

   The ZONEVERSION option also defines a 8-bit Flag field, for which
   IANA is to create and maintain a new registry entitled "DNS EDNS0
   ZONEVERSION Flags values" (abbreviation "ZONEVERSION") used by the
   ZONEVERSION option, inside the "Domain Name System (DNS) Parameters"
   group.  Initial values for the DNS EDNS0 ZONEVERSION Flags values
   registry are given below; future assignments in the 1-245 values are
   to be made through Specification Required Review [BCP26].
   Assignments consist of a Flag value as an unsigned 8-bit integer
   recorded in decimal, a Mnemonic name as an uppercase ASCII string
   with maximum length of 15 characters, and the required document
   reference.

       +==================+=====================+=================+
       | ZONEVERSION Flag | Mnemonic            | Reference       |
       +==================+=====================+=================+
       | 0                | SOA-SERIAL          | [this document] |
       +==================+=====================+=================+
       | 1-245            | Unassigned          |                 |
       +==================+=====================+=================+
       | 246-254          | Reserved for Local/ | [this document] |
       |                  | Experimental Use    |                 |
       +==================+=====================+=================+
       | 255              | Reserved for future | [this document] |
       |                  | expansion           |                 |
       +==================+=====================+=================+

                                 Table 2

   [RFC Editor: change "this document" with the proper RFC number for
   this document when assigned by IANA.]

   The change control for this registry should be my means of an
   Standard action.

7.2.1.  Expert Review Directives

   Allocation procedures for new code points in the ZONEVERSION Flag
   registry require Specification Required review, and so it requires
   Expert Reviews as stated in [BCP26].

   The expert should consider the following points:



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   *  Duplication of code point allocations should be avoided.

   *  A Presentation Format section should be provided, with a clear
      code point mnemonic.

   *  The referenced document and stated use of the new code point
      should be appropriate for the intended use of a ZONEVERSION Flag
      assignment.  In particular the reference should state clear
      instructions for implementers about the syntax and semantic of the
      data.  Also the Length of the Data must have proper limits.

   The expert reviewing the request MUST approve or disapprove the
   request within 10 business days from when he or she received the
   expert review request.

8.  Security Considerations

   The EDNS extension data it's not covered by RRSIG records, so there's
   no way to verify its authenticity nor integrity using DNSSEC and
   could theoricatelly be tampered by a person-in-the-middle if the
   transport is made by unsecure means.  Caution should be taken to use
   the EDNS ZONEVERSION data for any means besides troubleshooting and
   debugging.

   If there's a need to certify the ZONEVERSION trustwortiness, it will
   be necessary to use an encrypted and authenticated DNS transport.

   If there's a need to authenticate data origin for the ZONEVERSION
   value, an answer with the SOA-SERIAL flag as defined above could be
   compared to a separate regular SOA query with DO flag, whose answer
   shall be DNSSEC signed, with the cautions about Anycast and others as
   already stated in Introduction.

   With the SOA-SERIAL flag defined above, there's no risk on disclosure
   of private information, as the SERIAL of the SOA record is already
   publicly available.

9.  Normative References

   [BCP26]    Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

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




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   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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>.

10.  Informative References

   [RFC4786]  Abley, J. and K. Lindqvist, "Operation of Anycast
              Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786,
              December 2006, <https://www.rfc-editor.org/info/rfc4786>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
              January 2019, <https://www.rfc-editor.org/info/rfc8499>.

Appendix A.  Implementation Considerations

   With very few exceptions, EDNS options which elicit an EDNS option in
   the response are independant of the QNAME.  This is not the case of
   ZONEVERSION, so its implementation may be more or less difficult
   depending on how EDNS options are handled in the name server.

Appendix B.  Implementation References

   There's a patched NSD server version 4.3.7 with support for
   ZONEVERSION with the experimental opcode 65024 maintained in
   https://github.com/huguei/nsd/tree/rrserial with SOA-SERIAL flag
   support, and installed for live testing in 200.1.122.30 address with
   configured zones dateserial.example.com. and incserial.example.com.;
   with MX, TXT and AAAA apex records.

Authors' Addresses

   Hugo Salgado
   NIC Chile
   Miraflores 222, piso 14
   CP 8320198 Santiago
   Chile
   Phone: +56 2 29407700



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   Email: hsalgado@nic.cl


   Mauricio Vergara Ereche
   ICANN
   Email: mauricio.vergara@icann.org













































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