Constrained RESTful Environments M. S. Lenders
Internet-Draft TU Dresden
Intended status: Informational C. Amsüss
Expires: 4 September 2025
T. C. Schmidt
HAW Hamburg
M. Wählisch
TU Dresden & Barkhausen Institut
3 March 2025
ALPN ID Specification for CoAP over DTLS
draft-ietf-core-coap-dtls-alpn-02
Abstract
This document specifies an Application-Layer Protocol Negotiation
(ALPN) ID for transport-layer-secured Constrained Application
Protocol (CoAP) services.
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://core-
wg.github.io/coap-dtls-alpn/draft-ietf-core-coap-dtls-alpn.html.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-core-coap-dtls-alpn/.
Discussion of this document takes place on the Constrained RESTful
Environments Working Group mailing list (mailto:core@ietf.org), which
is archived at https://mailarchive.ietf.org/arch/browse/core/.
Subscribe at https://www.ietf.org/mailman/listinfo/core/.
Source for this draft and an issue tracker can be found at
https://github.com/core-wg/coap-dtls-alpn.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Application-Layer Protocol Negotiation (ALPN) IDs . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
4.1. TLS ALPN for CoAP . . . . . . . . . . . . . . . . . . . . 3
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Normative References . . . . . . . . . . . . . . . . . . 4
5.2. Informative References . . . . . . . . . . . . . . . . . 4
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 4
A.1. Since draft-ietf-core-coap-dtls-alpn-01 . . . . . . . . . 5
A.2. Since draft-ietf-core-coap-dtls-alpn-00 . . . . . . . . . 5
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Application-Layer Protocol Negotiation (ALPN) enables communicating
parties to agree on an application-layer protocol during a Transport
Layer Security (TLS) handshake using an ALPN ID [RFC7301]. This ALPN
ID can be discovered for services as part of Service Bindings (SVCB)
via the DNS, using SVCB resource records with the "alpn" Service
Parameter Keys [RFC9460]. As an example, this information can be
obtained as part of the discovery of DNS over CoAP (DoC) servers (see
Section 3.2 of [I-D.ietf-core-dns-over-coap]) that deploy TLS or
Datagram Transport Layer Security (DTLS) to secure their messages.
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This document specifies an ALPN ID for CoAP services that are secured
by transport security using DTLS. An ALPN ID for CoAP services
secured by TLS has already been specified in [RFC8323].
2. Application-Layer Protocol Negotiation (ALPN) IDs
For CoAP over TLS, an ALPN ID was defined as "coap" in [RFC8323]. As
it is not advisable to re-use the same ALPN ID for a different
transport layer, an ALPN for CoAP over DTLS is registered in
Section 4.1.
ALPN ID values have variable length. For CoAP over DTLS, a short
value ("co") is allocated, as this can avoid fragmentation of Client
Hello and Server Hello messages in constrained networks with link-
layer fragmentation, such as 6LoWPAN [RFC4944].
To discover CoAP services that secure their messages with TLS or
DTLS, ALPN IDs "coap" and "co" can be used, respectively, in the same
manner as for any other service secured with transport layer
security, as described in [RFC9460]. Other authentication mechanisms
are currently out of scope.
3. Security Considerations
Any security considerations on ALPN (see [RFC7301]) and SVCB resource
records (see [RFC9460]), also apply to this document.
4. IANA Considerations
// RFC Ed.: throughout this section, please replace RFC-XXXX with the
// RFC number of this specification and remove this note.
This document has the following actions for IANA.
4.1. TLS ALPN for CoAP
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)
* Identification sequence: 0x63 0x6f ("co")
* Reference: [RFC7252] and [RFC-XXXX]
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Note that [RFC7252] 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 like those in
Section 8.2 of [RFC8323].
5. References
5.1. Normative References
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/rfc/rfc7252>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/rfc/rfc7301>.
[RFC9460] Schwartz, B., Bishop, M., and E. Nygren, "Service Binding
and Parameter Specification via the DNS (SVCB and HTTPS
Resource Records)", RFC 9460, DOI 10.17487/RFC9460,
November 2023, <https://www.rfc-editor.org/rfc/rfc9460>.
5.2. Informative References
[I-D.ietf-core-dns-over-coap]
Lenders, M. S., Amsüss, C., Gündoğan, C., Schmidt, T. C.,
and M. Wählisch, "DNS over CoAP (DoC)", Work in Progress,
Internet-Draft, draft-ietf-core-dns-over-coap-12, 14
February 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-core-dns-over-coap-12>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<https://www.rfc-editor.org/rfc/rfc4944>.
[RFC8323] Bormann, C., Lemay, S., Tschofenig, H., Hartke, K.,
Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained
Application Protocol) over TCP, TLS, and WebSockets",
RFC 8323, DOI 10.17487/RFC8323, February 2018,
<https://www.rfc-editor.org/rfc/rfc8323>.
Appendix A. Change Log
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A.1. Since draft-ietf-core-coap-dtls-alpn-01
(https://datatracker.ietf.org/doc/draft-ietf-core-coap-dtls-
alpn/01/)
* Address review by Esko Dijk
* Address review by Marco Tiloca
A.2. Since draft-ietf-core-coap-dtls-alpn-00
(https://datatracker.ietf.org/doc/draft-ietf-core-coap-dtls-
alpn/00/)
* Fix ALPN ID for CoAP over TLS
* Change intended status to Informational
Acknowledgments
We like to thank Rich Salz for the expert review on the "co" ALPN ID
allocation. We also like to thank Mohamed Boucadair and Ben Schwartz
for their early review before WG adoption of this draft and Esko
Dijk, Thomas Fossati, and Marco Tiloca for their feedback and
comments.
Authors' Addresses
Martine Sophie Lenders
TUD Dresden University of Technology
Helmholtzstr. 10
D-01069 Dresden
Germany
Email: martine.lenders@tu-dresden.de
Christian Amsüss
Email: christian@amsuess.com
Thomas C. Schmidt
HAW Hamburg
Berliner Tor 7
D-20099 Hamburg
Germany
Email: t.schmidt@haw-hamburg.de
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Matthias Wählisch
TUD Dresden University of Technology & Barkhausen Institut
Helmholtzstr. 10
D-01069 Dresden
Germany
Email: m.waehlisch@tu-dresden.de
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