rfc9952.original.md   rfc9952.md 
--- ---
title: "ALPN ID Specification for CoAP over DTLS " title: "The Application-Layer Protocol Negotiation (ALPN) ID Specification for the Co nstrained Application Protocol (CoAP) over DTLS"
abbrev: "CoRE ALPN" abbrev: "CoRE ALPN"
category: info category: info
docname: draft-ietf-core-coap-dtls-alpn-05 docname: draft-ietf-core-coap-dtls-alpn-05
submissiontype: IETF # also: "independent", "editorial", "IAB", or "IRTF" submissiontype: IETF
number: number: 9952
date: updates:
obsoletes:
consensus: true consensus: true
ipr: trust200902
pi: [toc, symrefs, sortrefs]
date: 2026-03
v: 3 v: 3
area: "Web and Internet Transport" area: WIT
workgroup: "Constrained RESTful Environments" workgroup: core
keyword: keyword:
- CoRE - CoRE
- CoAP - CoAP
- SVCB - SVCB
- DTLS - DTLS
- ALPN - ALPN
venue:
group: "Constrained RESTful Environments"
type: "Working Group"
mail: "core@ietf.org"
arch: "https://mailarchive.ietf.org/arch/browse/core/"
github: "core-wg/coap-dtls-alpn"
latest: "https://core-wg.github.io/coap-dtls-alpn/draft-ietf-core-coap-dtls-alpn.
html"
author: author:
- fullname: Martine Sophie Lenders - fullname: Martine Sophie Lenders
org: TUD Dresden University of Technology org: TUD Dresden University of Technology
abbrev: TU Dresden abbrev: TU Dresden
street: Helmholtzstr. 10 street: Helmholtzstr. 10
city: Dresden city: Dresden
code: D-01069 code: D-01069
country: Germany country: Germany
email: martine.lenders@tu-dresden.de email: martine.lenders@tu-dresden.de
skipping to change at line 65 skipping to change at line 62
normative: normative:
RFC6347: dtls12 RFC6347: dtls12
RFC7252: coap RFC7252: coap
RFC7301: alpn RFC7301: alpn
RFC9147: dtls13 RFC9147: dtls13
RFC9460: svcb RFC9460: svcb
informative: informative:
RFC8323: coap-tcp RFC8323: coap-tcp
RFC8446: tls13 RFC8446: tls13
I-D.ietf-core-dns-over-coap: doc # I-D.ietf-core-dns-over-coap: doc
PRE-RFC9953:
-: doc
title: >
DNS over the Constrained Application Protocol (DoC)
target: https://www.rfc-editor.org/info/rfc9953
seriesinfo:
RFC: PRE-9953
DOI: 10.17487/PRE-RFC9953
date: March 2026
author:
-
fullname: Martine Sophie Lenders
-
fullname: Christian Amsüss
-
fullname: Cenk Gündoğan
-
fullname: Thomas C. Schmidt
-
fullname: Matthias Wählisch
RFC4944: 6lo RFC4944: 6lo
--- abstract --- abstract
<!-- [rfced] FYI - We updated [I-D.ietf-core-dns-over-coap] to [PRE-RFC9953]
for now. We will make the final updates in RFCXML (i.e., remove "PRE-").
-->
<!--[rfced] Author Names
a) Thomas, we note "T. C. Schmidt" in the document header; however, the
majority of past RFCs have used "T. Schmidt". Which form do you prefer?
b) Martine, please confirm if you prefer "M. S. Lenders" or "M. Lenders"
in the document header.
-->
<!-- [I-D.ietf-core-dns-over-coap] - RFC 9953
draft-ietf-core-dns-over-coap-20
Companion document (C554)
-->
<!--[rfced] Document Title
a) Please note that the document title has been updated as follows.
Abbreviations have been expanded per Section 3.6 of RFC 7322 ("RFC Style
Guide").
In addition, is "Specification" essential to the title or may it be removed
for conciseness?
Original (document title):
ALPN ID Specification for CoAP over DTLS
Current:
The Application-Layer Protocol Negotiation (ALPN) ID Specification for
the Constrained Application Protocol (CoAP) over DTLS
Perhaps:
Application-Layer Protocol Negotiation (ALPN) ID for
the Constrained Application Protocol (CoAP) over DTLS
b) For the short title that spans the header of the PDF file, should "CoRE
ALPN" be updated to "ALPN ID for CoAP over DTLS" to more closely match the
document title?
Original (short title):
CoRE ALPN
Perhaps:
ALPN ID for CoAP over DTLS
-->
<!-- [rfced] Abstract: Should the abstract mention DTLS?
Original:
This document specifies an Application-Layer Protocol Negotiation
(ALPN) ID for transport-layer-secured Constrained Application
Protocol (CoAP) services.
Perhaps (similar to text in the Introduction):
This document specifies an Application-Layer Protocol Negotiation
(ALPN) ID for Constrained Application
Protocol (CoAP) services that are secured by DTLS.
-->
<!-- [rfced] Introduction: We updated "by transport layer security using DTLS"
to "by TLS using DTLS" here. Would further updating as shown below improve
this sentence?
Original:
This document
specifies an ALPN ID for CoAP services that are secured by transport
layer security using DTLS.
Current:
This document
specifies an ALPN ID for CoAP services that are secured by TLS
using DTLS.
Perhaps:
This document
specifies an ALPN ID for CoAP services that are secured
by DTLS.
-->
This document specifies an Application-Layer Protocol Negotiation (ALPN) ID for This document specifies an Application-Layer Protocol Negotiation (ALPN) ID for
transport-layer-secured Constrained Application Protocol (CoAP) services. transport-layer-secured Constrained Application Protocol (CoAP) services.
--- middle --- middle
# Introduction # Introduction
Application-Layer Protocol Negotiation (ALPN) enables communicating parties to agree on an application-layer protocol during a Transport Layer Security (TLS) handshake us ing an ALPN ID {{-alpn}}. Application-Layer Protocol Negotiation (ALPN) enables communicating parties to agree on an application-layer protocol during a Transport Layer Security (TLS) handshake us ing an ALPN ID {{-alpn}}.
This ALPN ID can be discovered for services as part of Service Bindings (SVCB) via th e DNS, using SVCB resource records with the "alpn" Service Parameter Keys {{-svcb}}. This ALPN ID can be discovered for services as part of Service Bindings (SVCBs) via t he DNS, using SVCB resource records with the "alpn" Service Parameter Keys {{-svcb}}.
As an example, applications that use the Constrained Application Protocol (CoAP) {{-c oap}} can obtain this information as part of the discovery of DNS over CoAP (DoC) ser vers (see {{Section 3.2 of -doc}}) that deploy TLS 1.3 {{-tls13}} as well as Datagram Transport Layer Security (DTLS) 1.2 or 1.3 {{-dtls12}} {{-dtls13}} to secure their m essages. As an example, applications that use the Constrained Application Protocol (CoAP) {{-c oap}} can obtain this information as part of the discovery of DNS over CoAP (DoC) ser vers (see {{Section 3.2 of -doc}}) that deploy TLS 1.3 {{-tls13}} as well as Datagram Transport Layer Security (DTLS) 1.2 or 1.3 {{-dtls12}} {{-dtls13}} to secure their m essages.
This document specifies an ALPN ID for CoAP services that are secured by transport la yer security using DTLS. This document specifies an ALPN ID for CoAP services that are secured by TLS using DT LS.
An ALPN ID for CoAP services secured by TLS has already been specified in {{-coap-tcp }}. An ALPN ID for CoAP services secured by TLS has already been specified in {{-coap-tcp }}.
# Application-Layer Protocol Negotiation (ALPN) IDs # Application-Layer Protocol Negotiation (ALPN) IDs
For CoAP over TLS, an ALPN ID was defined as "coap" in {{-coap-tcp}}. For CoAP over TLS, an ALPN ID is defined as "coap" in {{-coap-tcp}}.
As it is not advisable to re-use the same ALPN ID for a different transport layer, an As it is not advisable to reuse the same ALPN ID for a different transport layer, an
ALPN for ALPN for
CoAP over DTLS is registered in {{iana-coap-alpn}}. CoAP over DTLS is registered in {{iana}}.
ALPN ID values have variable length. ALPN ID values have variable length.
For CoAP over DTLS, a short value ("co") is allocated, as this can avoid fragmentatio n of Client Hello and Server Hello messages in constrained networks with link-layer f ragmentation, such as 6LoWPAN {{-6lo}}. For CoAP over DTLS, a short value ("co") is allocated, as this can avoid fragmentatio n of Client Hello and Server Hello messages in constrained networks with link-layer f ragmentation, such as 6LoWPAN {{-6lo}}.
To discover CoAP services that secure their messages with TLS or DTLS, the ALPN IDs " coap" and "co" can be used, respectively, in To discover CoAP services that secure their messages with TLS or DTLS, the ALPN IDs " coap" and "co" can be used, respectively, in
the same manner as for any other service secured with transport layer security, as the same manner as for any other service secured with TLS, as
described in {{-svcb}}. described in {{-svcb}}.
The discovery of CoAP services that rely on other security mechanisms is out of the s cope of this document. The discovery of CoAP services that rely on other security mechanisms is out of the s cope of this document.
# Security Considerations # Security Considerations
Any security considerations on ALPN (see {{-alpn}}) and SVCB resource records (see {{ -svcb}}) also apply to this document. Any security considerations for ALPN (see {{-alpn}}) and SVCB resource records (see { {-svcb}}) also apply to this document.
# IANA Considerations {#iana} # IANA Considerations {#iana}
[^replace-xxxx] IANA has added the following entry to the "TLS Application-Layer Protocol Negotiation
(ALPN) Protocol IDs" registry in the "Transport Layer Security (TLS) Extensions" reg
[^replace-xxxx]: RFC Ed.: throughout this section, please replace istry group.
RFC-XXXX with the RFC number of this specification and remove this
note.
This document has the following actions for IANA.
## TLS ALPN for CoAP {#iana-coap-alpn}
The following entry has been added to the "TLS Application-Layer Protocol Negotiation
(ALPN) Protocol IDs" registry, which is part of the "Transport Layer Security (TLS)
Extensions" registry group.
* Protocol: CoAP (over DTLS) | Protocol | Identification Sequence | Reference |
* Identification sequence: 0x63 0x6f ("co") | CoAP (over DTLS) | 0x63 0x6f ("co") | {{-coap}}, RFC 9952 |
* Reference: {{-coap}} and \[RFC-XXXX\] {: title="TLS Application-Layer Protocol Negotiation (ALPN) Protocol IDs Registry" #t
able1}
Note that {{-coap}} does not define the use of the ALPN TLS extension during the DTLS connection handshake. Note that {{-coap}} does not define the use of the ALPN TLS extension during the DTLS connection handshake.
This document does not change this behavior, and thus does not establish any rules li ke those in {{Section 8.2 of -coap-tcp}}. This document does not change this behavior and thus does not establish any rules lik e those in {{Section 8.2 of -coap-tcp}}.
--- back --- back
# Change Log
## Since [draft-ietf-core-coap-dtls-alpn-04]
- Address Deb Cooley's IESG ballot COMMENT
## Since [draft-ietf-core-coap-dtls-alpn-03]
- Make DTLS references normative
## Since [draft-ietf-core-coap-dtls-alpn-02]
- Address shepherd review
## Since [draft-ietf-core-coap-dtls-alpn-01]
- Address review by Esko Dijk
- Address review by Marco Tiloca
## Since [draft-ietf-core-coap-dtls-alpn-00]
- Fix ALPN ID for CoAP over TLS
- Change intended status to Informational
[draft-ietf-core-coap-dtls-alpn-04]: https://datatracker.ietf.org/doc/draft-ietf-core
-coap-dtls-alpn/04/
[draft-ietf-core-coap-dtls-alpn-03]: https://datatracker.ietf.org/doc/draft-ietf-core
-coap-dtls-alpn/03/
[draft-ietf-core-coap-dtls-alpn-02]: https://datatracker.ietf.org/doc/draft-ietf-core
-coap-dtls-alpn/02/
[draft-ietf-core-coap-dtls-alpn-01]: https://datatracker.ietf.org/doc/draft-ietf-core
-coap-dtls-alpn/01/
[draft-ietf-core-coap-dtls-alpn-00]: https://datatracker.ietf.org/doc/draft-ietf-core
-coap-dtls-alpn/00/
# Acknowledgments # Acknowledgments
{:unnumbered} {:unnumbered}
We like to thank Rich Salz for the expert review on the "co" ALPN ID allocation. We would like to thank {{{Rich Salz}}} for the expert review on the "co" ALPN ID allo
We also like to thank Mohamed Boucadair and Ben Schwartz for their early review befor cation.
e WG adoption We would also like to thank {{{Mohamed Boucadair}}} and {{{Ben Schwartz}}} for their
of this draft and Esko Dijk, Thomas Fossati, and Marco Tiloca for their feedback and early reviews before WG adoption
comments. of this specification and {{{Esko Dijk}}}, {{{Thomas Fossati}}}, and {{{Marco Tiloca}
}} for their feedback and comments.
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let us know if any changes are needed. Updates of this nature typically
result in more precise language, which is helpful for readers.
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