YANG Notification Transport Capabilities

The "ietf-system-capabilities" YANG module defined in allows a client to discover a set of capabilities supported by a server (including, basic system capabilities and YANG-Push related capabilities) both at implementation time and at runtime. These capabilities allow a client to adjust its behavior to take advantage of the features exposed by the server. However, clients and servers may still support various different transport specific parameters (e.g., transport protocol, encoding format or encryption). As described in . A simple negotiation (e.g., inserting hints into error responses to a failed RPC request) between subscribers and publishers for subscription parameters increases the likelihood of success for subsequent RPC requests, but not guaranteed and widely supported, which may cause unexpected failure or additional message exchange between client and server. This document defines a more deterministic solution that relies upon a YANG module for YANG notifications transport capabilities that is built on top of . The module can be used by a client to discover capability information from a server at runtime or at implementation time, by making use of the YANG instance data file format.

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 when, and only when, they appear in all capitals, as shown here. The terms "subscriber", "publisher", and "receiver" are used as defined in . The terms "client", and "server" are used as defined in .

lists the server capabilities related to YANG-Push that are supported in the YANG module "ietf-notification-capabilities". These server capabilities are transport independent, session level capabilities. They can be provided either at the implementation time or reported at runtime. This document provides additional transport related attributes associated with system capabilities: Specification of transport protocols that a client can request to establish an HTTPS-based or UDP-based configured transport connection. Specification of transport encoding, including JSON or XML as defined in or CBOR as defined in the client can request to encode YANG notifications; Specification of secure transport mechanisms that are needed by a client to communicate with a server including DTLS 1.2 , DTLS 1.3 , TLS 1.2 , TLS 1.3 . To that end, the model defined in this document augments the System Capabilities model.

The following tree diagram provides an overview of the data model.

WG List: Authors: Qin Wu Qiufang Ma Alex Huang Feng Thomas Graf "; description "This module defines an extension to YANG-Push Notification Capabilities model that provides additional transport specific capabilities for YANG notifications. 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 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here. Copyright (c) 2025 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Revised BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for full legal notices."; revision 2025-06-07 { description "Initial revision."; reference "RFC XXXX: YANG Notifications Transport Capabilities"; } identity security-protocol { description "Identity for security protocols."; } identity dtls12 { base security-protocol; description "Indicates DTLS Protocol Version 1.2. DTLS 1.2 is obsolete, and thus it is NOT RECOMMENDED to enable this feature."; reference "RFC 6347: The Datagram Transport Layer Security (DTLS) Protocol Version 1.2"; } identity dtls13 { base security-protocol; description "Indicates DTLS Protocol Version 1.3."; reference "RFC 9147: The Datagram Transport Layer Security (DTLS) Protocol Version 1.3"; } augment "/sysc:system-capabilities" + "/notc:subscription-capabilities" { description "Adds system level capabilities."; container transport-capabilities { description "Specifies capabilities related to YANG-Push transports."; list transport-capability { key "transport-protocol"; description "Indicates a list of capabilities related to notification transport."; leaf transport-protocol { type identityref { base sn:transport; } description "Indicates supported transport protocol for YANG-Push."; } leaf-list security-protocol { type union { type identityref { base security-protocol; } type identityref { base tlscmn:tls-version-base; } } description "Indicates transport security protocol."; } leaf-list encoding-format { type identityref { base sn:encoding; } description "Indicates supported encoding formats."; } } } } } ]]>

This document registers a URI in the "IETF XML Registry" . Following the format in , the following registration has been made:

This document registers one YANG module in the "YANG Module Names" registry . Following the format in , the following registration has been made:

Note to the RFC-Editor: Please remove this section before publishing.

Huawei implemented this document for a YANG Push publisher in their VRP platform.

Cisco implemented this document for a YANG Push publisher in their IOS XR platform.

This section is modeled after the template described in The "ietf-yp-transport-capabilities" YANG module defines a data model that is designed to be accessed via YANG-based management protocols, such as NETCONF and RESTCONF . These protocols have to use a secure transport layer (e.g., SSH , TLS , and QUIC ) and have to use mutual authentication. The Network Configuration Access Control Model (NACM) provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content. All protocol-accessible data nodes are read-only and cannot be modified. The data in the module is not security sensitive. It inherits all the security considerations of .

Ran Tao Huawei 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China Email: taoran20@huawei.com Liang Geng China Mobile 32 Xuanwumen West St, Xicheng District Beijing 10053 China Email: gengliang@chinamobile.com Peng Liu China Mobile Beiqijia Town, Changping District Beijing 10053 China Email: liupengyjy@chinamobile.com Wei Wang China Telecom 32 Xuanwumen West St, Xicheng District Beijing 102209 China Email: wangw36@chinatelecom.cn

The authors would like to thank Mohamed Boucadair, Kent Watson, Jan Lindblad, Reshad Rahman, Xiao Min, Per Andersson and Rob Wilton for their review and valuable comments.

The following instance-data example describes the notification transport capabilities of a hypothetical "acme-router". acme-router-notification-capabilities

ietf-system-capabilities@2020-03-23 ietf-notification-capabilities@2020-03-23 ietf-yp-transport-capabilities@2025-06-07

Server Capability Discovery

hnt:https

sn:encode-xml

sn:encode-json

tlscmn:tls12

tlscmn:tls13

unt:udp-notif

sn:encode-json

unt:encode-cbor

dtls12

dtls13

]]> In addition, the client could also query notification transport capabilities from the server. For example, the client sends <get> request message to the the server to query from the server.

]]> The server returns server data export capability using <rpc-reply> as follows:

hnt:https

sn:encode-xml

sn:encode-json

tlscmn:tls12

tlscmn:tls13

unt:udp-notif

sn:encode-json

unt:encode-cbor

dtls12

dtls13

]]>