The DNS XFR URI Schemes
draft-hardaker-dnsop-dns-xfr-scheme-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Wes Hardaker | ||
| Last updated | 2025-11-25 | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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draft-hardaker-dnsop-dns-xfr-scheme-00
Domain Name System Operations W. Hardaker
Internet-Draft Google, Inc.
Intended status: Standards Track 25 November 2025
Expires: 29 May 2026
The DNS XFR URI Schemes
draft-hardaker-dnsop-dns-xfr-scheme-00
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.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on 29 May 2026.
Copyright Notice
Copyright (c) 2025 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Syntax of a DNS Transfer Protocol URI . . . . . . . . . . . . 3
4. URI Scheme Semantics . . . . . . . . . . . . . . . . . . . . 3
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
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 7
Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
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.
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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.
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.
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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].
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
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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
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.
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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>.
[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
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[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/.
* ixfr:ns.example.com/example.com.
* xot:ns.zone.example:8853/zone.example.
Author's Address
Wes Hardaker
Google, Inc.
Email: ietf@hardakers.net
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