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General Internet Engineering Task Force zoneversion 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 Star Of Authority ("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.

The "ZONEVERSION" EDNS option 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 separate query to ask for the SOA Resource Record ("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 ), 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). 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 . 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.

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 .

The variable part of RDATA in the OPT RR 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 octets for the next OPTION-DATA for responses.
• The OPTION-DATA for the ZONEVERSION option is composed of the concatenation of an unsigned 1 byte Label Count number (FLAG-LABELS) indicating the number of labels in the QNAME owner name that this answer's zone name refers to, 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).

Diagram with the OPTION-DATA format for ZONEVERSION option

The FLAG-LABELS number helps to disambiguate the name of the zone that this ZONEVERSION refers to. For example, if the response is a downward referral, the server is authoritative for some portion of the QNAME that differs from a server that is below the zone cut and is completely authoritative for a longer match of labels in the QNAME. Also, if the ANSWER section has more than one RR set with different zones (like a CNAME and a target name in another zone), the number of labels in the QNAME disambiguate such situation. The value of the FLAG-LABELS field MUST NOT count the null (root) label that terminates the QNAME owner name. The value of the FLAG-LABELS field MUST be less than or equal to the number of labels in the QNAME owner name. For example, a QNAME "www.example.com." inside a "example.com." zone, has a FLAG-LABELS field value of 2. Root zone (".") has a FLAG-LABELS field value of 0. [RFC Editor: change <TBD> to the proper code when assigned by IANA.]

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 omitted in presentation format, but if it's used, MUST be represented as an unsigned decimal integer. The FLAG-LABELS value of OPTION-DATA field COULD be omitted in presentation format, but if it's used, MUST be represented as an unsigned decimal integer. It's recommended to display the zone name that represents this number of labels of the QNAME owner name, for a simpler human consumption. The FLAG-NUMBER, FLAG-LENGTH and FLAG-DATA values of OPTION-DATA field should be represented following its own format, as specified in the corresponding Flag's specification.

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.

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 ). Otherwise, the answer MUST NOT add an EDNS ZONEVERSION option to the response. In case of a downward referral response, even when the Authoritative Answer bit is not set, this specification considers that the Answer holds data that is authoritative for some portion of the QNAME (see "Referrals" in ). Given this, a ZONEVERSION option MUST be present as indicated in the paragraph above, with the zone versioning value that holds that portion of the QNAME where it is completely authoritative.

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 . The mnemonic of this flag is SOA-SERIAL. The OPTION-LENGTH for this ZONEVERSION Option MUST have a value of 8 for responses. Note that 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 MUST also include the ZONEVERSION answer even when there's no ANSWER data for the QNAME, since the RCODE is NOERROR.

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 omitted 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.

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-LABELS 1-byte, FLAG-NUMBER 1-byte with value 0, FLAG-LENGTH 1byte with 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 8. An example of a proper diagnostic tool that implements ZONEVERSION EDNS extension towards a compliant authoritative DNS server could be:

> 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 00 04 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 ]]>

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 flags from , suggestions for implementation from , security clarifications from George Michaelson, zone name disambiguation from Joe Abley and Brian Dickson, and review from Tim Wicinski.

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

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

[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.]

The ZONEVERSION option also defines a 8-bit FLAG-NUMBER field, for which IANA is to create and maintain a new registry entitled "DNS EDNS0 ZONEVERSION FLAG-NUMBER values" (abbreviation "ZONEVERSION") used by the ZONEVERSION option, inside the "Domain Name System (DNS) Parameters" group. Initial values for the DNS EDNS0 ZONEVERSION FLAG-NUMBER values registry are given below; future assignments in the 1-245 values are to be made through Specification Required Review . Assignments consist of a FLAG-NUMBER 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-NUMBER	Mnemonic	Reference
0	SOA-SERIAL	[this document]
1-245	Unassigned
246-254	Reserved for Local/Experimental Use	[this document]
255	Reserved for future expansion	[this document]

[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.

Allocation procedures for new code points in the ZONEVERSION FLAG-NUMBER registry require Specification Required review, and so it requires Expert Reviews as stated in . The expert should consider the following points:

• 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-NUMBER 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.

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 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 . 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. 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 might be better suited at such 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.

This RFC is the revised basic definition of The Domain Name System. It obsoletes RFC-882. This memo describes the domain style names and their used for host address look up and electronic mail forwarding. It discusses the clients and servers in the domain name system and the protocol used between them. This RFC is the revised specification of the protocol and format used in the implementation of the Domain Name System. It obsoletes RFC-883. This memo documents the details of the domain name client - server communication. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. The Domain Name System's wire protocol includes a number of fixed fields whose range has been or soon will be exhausted and does not allow requestors to advertise their capabilities to responders. This document describes backward-compatible mechanisms for allowing the protocol to grow. This document updates the Extension Mechanisms for DNS (EDNS(0)) specification (and obsoletes RFC 2671) based on feedback from deployment experience in several implementations. It also obsoletes RFC 2673 ("Binary Labels in the Domain Name System") and adds considerations on the use of extended labels in the DNS. Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. As the Internet has grown, and as systems and networked services within enterprises have become more pervasive, many services with high availability requirements have emerged. These requirements have increased the demands on the reliability of the infrastructure on which those services rely. Various techniques have been employed to increase the availability of services deployed on the Internet. This document presents commentary and recommendations for distribution of services using anycast. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. The Domain Name System (DNS) is defined in literally dozens of different RFCs. The terminology used by implementers and developers of DNS protocols, and by operators of DNS systems, has sometimes changed in the decades since the DNS was first defined. This document gives current definitions for many of the terms used in the DNS in a single document. This document obsoletes RFC 7719 and updates RFC 2308.

With very few exceptions, EDNS options which elicit an EDNS option in the response are independent 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.

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 .