| Internet-Draft | CoRE ALPN | August 2024 |
| Lenders, et al. | Expires 28 February 2025 | [Page] |
This document specifies an Application-Layer Protocol Negotiation (ALPN) ID for transport-layer-secured CoAP services.¶
This note is to be removed before publishing as an RFC.¶
The latest revision of this draft can be found at https://anr-bmbf-pivot.github.io/draft-lenders-core-coap-dtls-svcb/draft-lenders-core-coap-dtls-svcb.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-lenders-core-coap-dtls-svcb/.¶
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Source for this draft and an issue tracker can be found at https://github.com/anr-bmbf-pivot/draft-lenders-core-coap-dtls-svcb.¶
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Application-Layer Protocol Negotiation (ALPN) enable communicating parties to agree on an application-layer protocol during a Transport Layer Security (TLS) handshake using an ALPN ID. 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. As an example, this information can be obtained as part of the discovery of DNS over CoAP (DoC) servers (see [I-D.ietf-core-dns-over-coap]) that deploy TLS or DTLS to secure their messages. This document specifies an ALPN ID for CoAP services that are secured by transport security using DTLS. An ALPN ID for CoAP service secured by TLS has already been specified in [RFC8323].¶
For CoAP over TLS an ALPN ID was defined as "coaps" 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.¶
ALPN ID values have variable length. Here, a short value ("co") is allocated for CoAP over DTLS, 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 "coaps" 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.¶
Any security considerations on ALPN (see [RFC7301]) and SVCB resource records (see [RFC9460]), also apply to this document.¶
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" group.¶
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].¶
## Since draft-lenders-core-coap-dtls-svcb-00 - Give rationale for short value - Fix presentation to focus on ALPN ID rather than SVCB records¶
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.¶