1. Introduction

1. Introduction

Application-Layer Protocol Negotiation (ALPN) lets communicating parties agree on an application-layer protocol during a Transport Layer Security (TLS) handshake by using an ALPN ID [RFC7301].

ALPN IDs can also be discovered for services through DNS Service Bindings (SVCBs), using SVCB resource records with the "alpn" Service Parameter Key [RFC9460].

Applications that use Constrained Application Protocol (CoAP) [RFC7252] can obtain this information while discovering DNS over CoAP (DoC) servers [RFC9953]. Those servers can use TLS 1.3 [RFC8446] and DTLS 1.2 or 1.3 [RFC6347] [RFC9147] to secure their messages.

This document specifies an ALPN ID for CoAP services secured by DTLS. CoAP services secured by TLS already have an ALPN ID in [RFC8323].