The DNS Zone Version (ZONEVERSION) Option

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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶

This Internet-Draft will expire on 18 July 2024.¶

Copyright Notice

Copyright (c) 2024 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 Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights 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

The ZONEVERSION option allows DNS queriers to request, and authoritative DNS severs to provide, a token representing the version of the zone from which a DNS response was generated. It is similar to the NSID option, which can be used to convey the identification of a name server that generates a response.¶

The Domain Name System allows data to be loosely coherent [RFC3254], because synchronization can never be instantaneous, and some uses of DNS do not require strong coherency anyway. This means that a record obtained by one response could be out-of-sync with other authoritative sources of the same data at the same point in time. This can make it difficult to debug some problems when there is a need to couple the data with the version of the zone it came from. Furthermore, in today's Internet, it is common for high volume and important DNS zones to utilize IP anycast Section 4.9 of [RFC4786] and/or load-balanced backend servers. In general, there is no way to ensure that two separate queries are delivered to the same server. The ZONEVERSION option both simplifies and improves the DNS monitoring and debugging by directly associating the data and the version together in a single response.¶

The SOA Serial field (Section 4.3.5 of [RFC1034]) is one example of zone versioning. Its purpose is to facilitate the distribution of zone data between primary and secondary name servers. It is also often useful in DNS monitoring and debugging. This document specifies the SOA Serial as one type of ZONEVERSION data.¶

Some DNS zones may use other distrubtion and synchronization mechanisms not based on the SOA Serial number, such as relational databases or other proprietary methods. In those cases the SOA Serial field may not be relevant with respect to the versioning of its content. To accomodate these use cases, new ZONEVERSION types should be defined in future specifications. Alternatively, zone operators may use one of the private use ZONEVERSION code points allocated by this specification.¶

The ZONEVERSION option is OPTIONAL to implement by DNS clients and name servers. It is designed for use only when a name server provides authoritative response data. It is intended only for hop-to-hop communication and is not transitive.¶

2. The ZONEVERSION Option

This document specifies a new EDNS(0) Section 6.1.2 of [RFC6891] option, ZONEVERSION, which can be used by DNS clients and servers to provide information regarding the version of the zone from which a response is generated.¶

                +0 (MSB)                       +1 (LSB)
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: |           LABELCOUNT          |            TYPE               |
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: |                            VERSION                            |
   /                                                               /
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

5. Example usage

A name server which (a) implements this specification, (b) receives a query with the ZONEVERSION option, (c) is authoritative for the original QNAME, and (d) utilizes the SOA serial field for versioning of said zone should include a ZONEVERSION option in its response. In the response's ZONEVERSION option the OPTION-LENGTH would be set to 6 and the OPTION-DATA would consist of the 1-octet LABELCOUNT, the 1-octet TYPE with value 0, and 4-octet SOA SERIAL value.¶

The example below demonstrates expected output of a diagnostic tool that implements the ZONEVERSION option, displaying a response from a compliant authoritative DNS server:¶

  $ dig @ns.example.com www.example.com aaaa +zoneversion

  ; <<>> DiG 9.17.14-patched <<>> @ns.example.com www.example.com aaaa +zoneversion
  ; (1 server found)
  ;; global options: +cmd
  ;; Got answer:
  ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7077
  ;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 2

  ;; OPT PSEUDOSECTION:
  ; EDNS: version: 0, flags:; udp: 1232
  ; ZONEVERSION: 02 00 78 95 a4 e9 ("SOA-SERIAL: 2023073001 (example.com.)")
  ;; QUESTION SECTION:
  ;www.example.com.    IN  AAAA

  ;; ANSWER SECTION:
  www.example.com.  43200  IN  AAAA  2001:db8::80

  ;; AUTHORITY SECTION:
  example.com.    43200  IN  NS  ns.example.com.

  ;; ADDITIONAL SECTION:
  ns.example.com.    43200  IN  AAAA  2001:db8::53

  ;; Query time: 15 msec
  ;; SERVER: 2001:db8::53#53(2001:db8::53) (UDP)
  ;; WHEN: dom jul 30 19:51:04 -04 2023
  ;; MSG SIZE  rcvd: 129

6. Acknowledgements

The authors thanks all the comments and support made in the DNSOP mailing list, chats and discussions. In special for the suggestions to generalize the option using a registry of types from Petr Špaček and Florian Obser, suggestions for implementation from Stéphane Bortzmeyer, security clarifications from George Michaelson, zone name disambiguation from Joe Abley and Brian Dickson, and reviews from Tim Wicinski and Peter Thomassen.¶

7. IANA Considerations

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 theoretically be tampered by a person-in-the-middle if the transport is made by insecure 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 trustworthiness, 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 type 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 type defined above, there's no risk on disclosure of private information, as the SERIAL of the SOA record is already publicly available.¶

Please note that the ZONEVERSION option can not be used for checking the correctness of an entire zone in a server. For such cases, the ZONEMD record [RFC8976] might be better suited at such a task. ZONEVERSION can help identify and correlate a certain specific answer with a version of a zone, but it has no special integrity or verification function besides a normal field value inside a zone, as stated above.¶

Appendix A. Implementation Considerations

With very few exceptions, EDNS options which elicit an EDNS option in the response are independent of the queried name. 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 4.7.0 with support for ZONEVERSION with an experimental opcode, with live test servers installed for compliance tests. Also there is a client command "dig" with added zoneversion support, along with test libraries in Perl, Python and Go. More information in the working document [ImplRef].¶

Authors' Addresses