



Domain Name System Operations                                W. Hardaker
Internet-Draft                                                 W. Kumari
Intended status: Standards Track                            Google, Inc.
Expires: 3 December 2026                                         J. Reid
                                                                RTFM llp
                                                               G. Huston
                                                                   APNIC
                                                             1 June 2026


                        The DNS XFR URI Schemes
                 draft-hardaker-dnsop-dns-xfr-scheme-01

Abstract

   The DNS protocol provides an in-band mechanism for transferring the
   contents of a zone from a server to a client.  This is most
   frequently used when secondary servers are transferring the DNS zone
   content from their configured primary server.

   This document defines a Uniform Resource Identifier (URI) scheme for
   referencing DNS servers from which DNS zone contents can be
   transferred.

About This Document

   This note is to be removed before publishing as an RFC.

   The latest revision of this draft can be found at
   https://github.io/hardker/draft-hardaker-dnsop-dns-xfr-scheme/draft-
   hardaker-dnsop-dns-xfr-scheme.html.  Status information for this
   document may be found at https://datatracker.ietf.org/doc/draft-
   hardaker-dnsop-dns-xfr-scheme/.

   Discussion of this document takes place on the Domain Name System
   Operations Working Group mailing list (mailto:dnsop@ietf.org), which
   is archived at https://mailarchive.ietf.org/arch/browse/dnsop/.
   Subscribe at https://www.ietf.org/mailman/listinfo/dnsop/.

   Source for this draft and an issue tracker can be found at
   https://github.com/https://github.com/hardaker/draft-hardaker-dnsop-
   dns-xfr-scheme.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.




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Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Syntax of a DNS Transfer Protocol URI . . . . . . . . . . . .   3
   4.  URI Scheme Semantics  . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  "axfr" URI Registration . . . . . . . . . . . . . . . . .   4
     6.2.  "ixfr" URI Registration . . . . . . . . . . . . . . . . .   5
     6.3.  "xot" URI Registration  . . . . . . . . . . . . . . . . .   5
     6.4.  "xoh" URI Registration  . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8







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1.  Introduction

   The DNS protocol provides an in-band mechanism for transferring the
   contents of a zone from a server to a client.  This is most
   frequently used when secondary servers are transferring the DNS zone
   content from their configured primary server.

   This document defines a Uniform Resource Identifier (URI) [RFC3986]
   scheme for referencing DNS servers from which DNS zone contents can
   be transferred.

2.  Conventions and Definitions

   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.

3.  Syntax of a DNS Transfer Protocol URI

   Current DNS transfer protocols exist in three fundamental forms:
   Authoratative Transfers (AXFR) [RFC5936], Incremental Zone Transfers
   (IXFR) [RFC5936] and XFR over TLS (XoT) [RFC9103].  This document
   defines URI schemes for all three of these DNS transfer protocols.

   This document uses the Augmented Backus-Naur Form (ABNF) of
   [RFC5234].

       xfr-URI = scheme ":" host [ ":" port ] "/" zone

       scheme = "axfr" / "ixfr" / "xot"

       zone = TBD

   host and port are specified in [RFC3986].

   The 'scheme' signifies which DNS zone transfer protocol should be
   used (AXFR [RFC5936], IXFR [RFC5936] or XoT [RFC9103]).  While these
   two ABNF productions are defined in [RFC3986] as components of the
   generic hierarchical URI, this does not imply that the "axfr", "ixfr"
   and "xot" URI schemes are hierarchical URIs.  Developers MUST NOT use
   a generic hierarchical URI parser to parse a "axfr", "ixfr" or "xot"
   URI.







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4.  URI Scheme Semantics

   The "axfr", "ixfr" or "xot" URI schemes are used to refer to a DNS
   server that offers zone transfer support.  These three protocols each
   specify the details of how transfers are performed within their
   respective specifications and are beyond the scope of this document.

   The required 'host' part of the xfr URI denotes the DNS server host.

   As specified in each transfer protocols specifications, the 'port'
   part, if present, denotes the port on which the DNS server is
   awaiting requests.  If absent for the axfr and ixfr transfer
   protocols, this SHOULD be TCP port 53.  If absent for the xot
   transfer protocol, the default port SHOULD be TCP port 853.

   The 'zone' signifies the zone to be transferred and MUST be a fully
   qualified domain name.  Note that 'zone' MAY be "." to refer to the
   DNS root zone.  When not referring to the root zone, the 'zone'
   SHOULD have a trailing "." (for example "zone.example.").

5.  Security Considerations

   The "axfr", "ixfr" or "xot" URI schemes do not introduce new security
   considerations beyond what is specified in their respective RFCs
   (AXFR [RFC5936], IXFR [RFC5936] or XoT [RFC9103]).  These schemes are
   intended for use in documentation and configuration files that refer
   to servers offering DNS zone transfers.  Documentation and
   configuration files should carefully consider which protocol is most
   suitable for use, and if possible the "xot" protocol should be
   preferred if privacy or integrity of the zone contents are a concern.

6.  IANA Considerations

   This section contains the registration information for the "axfr",
   "ixfr" or "xot" URI schemes (in accordance with [RFC4395]).

6.1.  "axfr" URI Registration

   URI scheme name: axfr

   Status: permanent

   URI scheme syntax: See Section Section 3

   URI scheme semantics: See Section Section 4

   Encoding considerations: There are no encoding considerations beyond
   those in [RFC3986].



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   Applications/protocols that use this URI scheme name:

   The "axfr" URI scheme is intended to be used by applications with a
   need to identify a DNS server supporting authoritative transfer over
   DNS using the AXFR protocol for a zone.

   Interoperability considerations: N/A

   Security considerations: See Section Section 5

   Contact: Wes Hardaker ietf@hardakers.net (mailto:ietf@hardakers.net)

6.2.  "ixfr" URI Registration

   URI scheme name: ixfr

   Status: permanent

   URI scheme syntax: See Section Section 3

   URI scheme semantics: See Section Section 4

   Encoding considerations: There are no encoding considerations beyond
   those in [RFC3986].

   Applications/protocols that use this URI scheme name:

   The "ixfr" URI scheme is intended to be used by applications with a
   need to identify a DNS server supporting authoritative transfer over
   DNS using the IXFR protocol for a zone.

   Interoperability considerations: N/A

   Security considerations: See Section Section 5

   Contact: Wes Hardaker ietf@hardakers.net (mailto:ietf@hardakers.net)

6.3.  "xot" URI Registration

   URI scheme name: xot

   Status: permanent

   URI scheme syntax: See Section Section 3

   URI scheme semantics: See Section Section 4





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   Encoding considerations: There are no encoding considerations beyond
   those in [RFC3986].

   Applications/protocols that use this URI scheme name:

   The "xot" URI scheme is intended to be used by applications with a
   need to identify a DNS server supporting authoritative transfer over
   DNS using the XoT protocol for a zone.

   Interoperability considerations: N/A

   Security considerations: See Section Section 5

   Contact: Wes Hardaker ietf@hardakers.net (mailto:ietf@hardakers.net)

6.4.  "xoh" URI Registration

   URI scheme name: xoh

   Status: permanent

   URI scheme syntax: See Section Section 3

   URI scheme semantics: See Section Section 4

   Encoding considerations: There are no encoding considerations beyond
   those in [RFC3986].

   Applications/protocols that use this URI scheme name:

   The "xoh" URI scheme is intended to be used by applications with a
   need to identify a DNS server supporting authoritative transfer over
   DNS over the HTTPS protocol for a zone.

   Interoperability considerations: N/A

   Security considerations: See Section Section 5

   Contact: Wes Hardaker ietf@hardakers.net (mailto:ietf@hardakers.net)

7.  References

7.1.  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/rfc/rfc2119>.



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   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/rfc/rfc3986>.

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", RFC 4395,
              DOI 10.17487/RFC4395, February 2006,
              <https://www.rfc-editor.org/rfc/rfc4395>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/rfc/rfc5234>.

   [RFC5936]  Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
              (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
              <https://www.rfc-editor.org/rfc/rfc5936>.

   [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>.

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

   [RFC9103]  Toorop, W., Dickinson, S., Sahib, S., Aras, P., and A.
              Mankin, "DNS Zone Transfer over TLS", RFC 9103,
              DOI 10.17487/RFC9103, August 2021,
              <https://www.rfc-editor.org/rfc/rfc9103>.

7.2.  Informative References

   [RFC7766]  Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and
              D. Wessels, "DNS Transport over TCP - Implementation
              Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016,
              <https://www.rfc-editor.org/rfc/rfc7766>.

Acknowledgments

Examples

   The following are example XFR URIs specifying an 'axfr' URI for the
   DNS root zone, an 'ixfr' URI for example.com, and a 'xot' URI for
   zone.example on port 8853:

   *  axfr:b.root-servers.net/.



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   *  ixfr:ns.example.com/example.com.

   *  xot:ns.zone.example:8853/zone.example.

   *  xoh:ns.zone.example/zone.example.

Authors' Addresses

   Wes Hardaker
   Google, Inc.
   Email: ietf@hardakers.net


   Warren Kumari
   Google, Inc.
   Email: warren@kumari.net


   Jim Reid
   RTFM llp
   St Andrews House
   382 Hillington Road, Glasgow Scotland
   G51 4BL
   United Kingdom
   Email: jim@rfc1035.com


   Geoff Huston
   APNIC
   6 Cordelia St
   South Brisbane  QLD 4101
   Australia
   Email: gih@apnic.net


















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