Subscription to Notifications in a Distributed Architecture

The mechanism to support a subscription of a continuous and customized stream of updates from a YANG datastore is defined in and . Requirements for Subscription to YANG Datastores are defined in . By streaming YANG-Push notifications from publishers to receivers, much better performance and fine-grained sampling can be achieved than with a polling-based mechanism. In a distributed forwarding system on a network node, the packet forwarding is delegated to multiple processors on line cards. In order not to overwhelm the route processor resources, it is not uncommon that data records are published directly from processors on line cards to target receivers to further increase efficiency on the routing system. This document complements the general subscription requirements defined in by the paragraph: A Subscription Service MAY support the ability to export from multiple software processes on a single routing system and expose the information which software process produced which message.

The following terms are defined in and are not redefined here: Subscriber Publisher Receiver Subscription The following terms are used with "ietf-notification-capabilities" in and are not redefined here: Notification Capabilities In addition, this document defines the below terms. Some of these terms are distinguished between global versus component and parent versus agent to distinguish their role within the distributed system. Global and Component is used to distinguish wherever the system component is reachable outside the distributed system or not. Parent and agent is used to distinguish wherever it manages or is being managed within the distributed system. Component: Refers to a network device component, such as a processor on a line card within a distributed routing system. Global Subscription: The Subscription requested by the Subscriber as described in Sections 2.4 and 2.5 of . It may be decomposed into multiple Component Subscriptions. Component Subscription: The Subscription that defines a data source which is managed and controlled by a single Publisher. Global Notification Capabilities: The overall notification capabilities that the group of Publishers can expose to the Subscriber as defined in for the distributed system. This includes which YANG nodes can be subscribed at which minimum-update-period for periodical subscriptions respectively which minimum-dampening-period for on-change subscriptions. Component Notification Capabilities: The notification capabilities that each Publisher exposes to the Publisher Parent. This includes which YANG nodes with which minimum-update-period for periodical subscriptions respectively which minimum-dampening-period for on-change subscriptions can be subscribed on which Component. Publisher Parent: The component of a Publisher that interacts with the Subscriber to deal with the Global Subscription. It decomposes the Global Subscription to multiple Component Subscriptions and interacts with the Publisher Agents. Publisher Agent: The component of a Publisher that interacts with the Publisher Parent to deal with the Component Subscription and pushing the data to the Receiver. Network Node: Is the network node of a distributed system which contains one or more Publishers that obtains the data from the YANG datastore and pushes it to the Receiver. Message Publisher: The Publisher that pushes the message to the Receiver. Message Publisher ID: A 32-bit identifier of the publishing process that is locally unique to the Network Node. With this identifier the publishing process from where the message was published from can be uniquely identified. Receivers SHOULD use the transport session and the Publisher ID field to separate different publisher streams originating from the same network Node.

In distributed forwarding systems of Network Nodes much YANG data is subscribed to many Components, processors on line cards, but published from a single route processor instead. This creates an unnecessary overhead at the route processor and a potential bottleneck. Publishing the YANG data directly from the Components avoids this inefficiency. This document proposes that subscribed YANG data can be published from Components. The route processor is only involved in maintaining and decomposing the Subscription, which includes notifying the Receiver which Subscription is being published from which Component with subscription state change notifications. To enable Receivers to map notification messages to a particular Publisher, the Message Publisher ID in the transport message header of the YANG notification message is introduced. In case of UDP transport, this is described in . With unique sequence-numbers per publishing process described in , each message can uniquely be identified, loss recognized and related to a transport session and publishing process.

below shows the distributed data export framework. A collector usually includes two components, the Subscriber generates the subscription instructions to express what and how the Receiver wants to receive the data; the Receiver is the target for the data publication. For one subscription, there can be one or more Receivers. And the Subscriber does not necessarily share the same IP address as the Receivers. In this framework, the Publisher pushes messages to the Receiver according to the subscription. The Publisher is either in the Parent or Agent role. The Publisher Parent knows all the capabilities that his Agents can provide and exposes the Global Notification Capabilities to the collector. The Subscriber maintains the Global Subscription at the Publisher Parent and disassembles the Global Subscription to multiple Component Subscriptions, depending upon which source data is needed. The Component Subscriptions are then distributed to the corresponding Publisher Agents on route and processors on line cards. Publisher Agents collects metrics according to the Component Subscription, add its metadata, encapsulates, and pushes messages. Messages may require segmentation depending on the amount of YANG data subscribed and maximum transmission unit of the interface where the message is published from. Implementations MUST NOT rely on IP fragmentation to carry large messages. The Receiver then decapsulates packets and reassembles notifications accordingly.

Publisher Parent and Publisher Agents interact with each other in several ways: Publisher Agents need to register with the Parent at the beginning of their process life cycle. Contracts are created and maintained throughout the subscription lifecycle between the Publisher Parent and each Agent and on its Component Notification Capabilities, and the format for notification data structure. The Publisher Parent relays the component subscriptions to the Publisher Agents. The Publisher Agents announce the status of their Component Subscriptions to the Publisher Parent. The status of the overall subscription is maintained by the Publisher Parent. The Publisher Parent is responsible for notifying the subscriber in case of problems with the Component Subscriptions. The technical mechanisms or protocols used for the coordination of operational information between Publisher Parent and Agent is out of scope of this document.

The Collector can send subscription requests only to the Parent. This requires the Publisher Parent to: expose the Global Notification Capabilities that can be served by multiple Publisher Agents; disassemble the Global Subscription to multiple Component Subscriptions, and distribute them to the Publisher Agents of the corresponding metric sources from the YANG schema tree so that they do not overlap; How the subscription is being distributed is implementation specific and not part of this document. notify changes related to the existing subscriptions to the different Publisher Agents. And the Publisher Agent to: Inherit the Global Subscription properties from Publisher Parent for its Component Subscription; share the same life-cycle as the Global Subscription; share the same Subscription ID as the Global Subscription.

The Publisher Agent collects data and encapsulates the packets per Component Subscription. The format and structure of the data records are defined by the YANG schema, so that the decomposition at the Receiver can benefit from the structured and hierarchical data records. The Receiver can associate the YANG data records with Subscription ID to the subscribed subscription. Additionally, it can use the Message Publisher ID to determine the corresponding publisher process. For the dynamic subscription, the output of the "establish-subscription" RPC defined in MUST include a list of Message Publisher IDs to indicate how the Global Subscription is decomposed into several Component Subscriptions. The "subscription-started" and "subscription-modified" notification defined in and "push-update" and "push-change-update" notification defined in MUST also include a list of Message Publisher IDs to notify the current Publishers for the corresponding Global Subscription.

In addition to sending event records to Receivers, the Parent MUST also send subscription state change notifications when events related to subscription management have occurred. All the subscription state change notifications MUST be delivered by the Parent. When the subscription decomposition result changes, the "subscription-modified" notification MUST be sent to indicate the new list of Publisher Agents.

This document assumes that all Publisher Agents are preconfigured to push data. Publisher Agents that send data are selected based on the subscription decomposition result. From the Receivers perspective, all Publisher Agents share the same source IP address for data export. How connectivity is established within the distributed system architecture is out of scope of this document. For connectionless data transport such as UDP based transport the same Layer 4 source port for data export can be used. For connection based data transport such as HTTPS based transport, each Publisher Agent MUST be able to acknowledge packet retrieval from Receivers, and therefore requires a dedicated Layer 4 source port per software process. The specific configuration on transports is described in the respective documents.

This YANG module imports definitions from and . WG List: Authors: Guangying Zheng Tianran Zhou Thomas Graf Pierre Francois Eric Voit "; description "Defines augmentation for ietf-subscribed-notifications to enable the distributed publication with single subscription. Copyright (c) 2026 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 (https://trustee.ietf.org/license-info). All revisions of IETF and IANA published modules can be found at the YANG Parameters registry (https://www.iana.org/assignments/yang-parameters). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; revision 2026-02-21 { description "Initial version"; reference "RFC XXXX: Subscription to Notifications in a Distributed Architecture"; } grouping message-publisher-id { description "Provides a reusable leaf of the message-publisher-id."; leaf message-publisher-id { type uint32; config false; description "Identifies the Component software process which publishes notification messages (e.g., processor 1 on line card 1). This field is used to notify the receiver which publisher process published which message. The identifier is locally unique to the Network Node."; } } grouping message-publisher-ids { description "Provides a reusable leaf-list of message-publisher-id-list."; leaf-list message-publisher-id { type uint32; config false; description "Identifies the Component software process which publishes notification messages (e.g., processor 1 on line card 1). This field is used to notify the receiver which publisher processes are going to publish. The identifiers are locally unique to the Network Node."; } } augment "/sn:subscriptions/sn:subscription" { description "This augmentation allows the Message Publisher ID to be exposed for a subscription."; uses message-publisher-ids; } augment "/sn:subscription-started" { description "This augmentation adds the Message Publisher ID to the subscription-started subscription change notifications."; uses message-publisher-ids; } augment "/sn:subscription-modified" { description "This augmentation adds the Message Publisher ID to the subscription-modified subscription change notifications."; uses message-publisher-ids; } augment "/sn:establish-subscription/sn:output" { description "This augmentation adds the Message Publisher ID to the dynamic establish-subscription output."; uses message-publisher-ids; } augment "/yp:push-update" { description "This augmentation adds the Message Publisher ID in the push-update notification."; uses message-publisher-id; } augment "/yp:push-change-update" { description "This augmentation adds the Message Publisher ID in the push-change-update notification."; uses message-publisher-id; } } ]]>

This document registers the following namespace URI in the IETF XML Registry: URI: urn:ietf:params:xml:ns:yang:ietf-distributed-notif Maintained by IANA? N Registrant Contact: The IESG. XML: N/A; the requested URI is an XML namespace. This document registers the following YANG module in the YANG Module Names registry: Name: ietf-distributed-notif Maintained by IANA? N Namespace: urn:ietf:params:xml:ns:yang:ietf-distributed-notif Prefix: dn Reference: RFC XXXX

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

Huawei implemented the Subscription Decomposition described in this document for a YANG-Push publisher on UDP-based Transport for Configured Subscriptions in their VRP platform.

6WIND implemented the Subscription Decomposition described in this document for a YANG-Push publisher on UDP-based Transport for Configured Subscriptions in their VSR platform.

This section uses the template described in . The 'ietf-distributed-notif' YANG module defines a data model that is designed to be accessed via YANG-based management protocols, such as NETCONF and RESTCONF . These YANG-based management protocols (1) have to use a secure transport layer (e.g., SSH , TLS , and QUIC ) and (2) 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. There are no data nodes defined in this YANG module that are writable/creatable/deletable (i.e., "config true", which is the default). Some of the readable data nodes in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or Notification) to these data nodes. Specifically, the following subtrees and data nodes have particular sensitivities/vulnerabilities:

/sn:subscriptions/sn:subscription/dn:message-publisher-id
/sn:subscription-started/dn:message-publisher-id
/sn:subscription-modified/dn:message-publisher-id
/sn:establish-subscription/dn:message-publisher-id

The entries in the list above will show the identity of the originating Publisher process. Exposure of this information may assist an attacker in mapping the distributed system or in injecting spoofed Notifications. Implementations SHOULD ensure that access to this data is restricted and that Notifications are sent over secure and authenticated channels. Security Considerations defined in do also apply for this document.

We thank Kent Watsen, Mahesh Jethanandani, Martin Bjorklund, Tim Carey, Qin Wu, Robert Wilton, Benoit Claise, Alex Huang Feng, Camilo Cardona and Juergen Schoenwaelder for their constructive suggestions for improving this document.

This appendix is non-normative.

shows a typical dynamic subscription to the Network Node with distributed data export capability. The Subscriber is a NETCONF/RESTCONF client and the Publisher Parent is the NETCONF/RESTCONF server.

+ component | | | subscription | | +-------------->+ | | | | | Acknowledged | | RPC Reply: OK, id #22 |<--------------| | Message Publisher ID [#1,#2] | | +<------------------------------+ | | | | | notif-mesg, id #22 | | | Message Publisher ID #1 | | +<------------------------------+ | | | | | notif-mesg, id#22 | | | Message Publisher ID #2 | | +<----------------------------------------------+ | | | | modify-subscription (id#22) | | +------------------------------>+ component | | | subscription | | RPC Reply: OK, id #22 +-------------->+ | | | | | Acknowledged | | |<--------------| +<------------------------------+ | | | | | subscription-modified, id#22 | | | Message Publisher ID [#1] | | +<------------------------------+ | | | | | notif-mesg, id #22 | | | Message Publisher ID #1 | | +<------------------------------+ | | | | | | | + + + ]]> A "establish-subscription" RPC request as per is sent to the Parent with a successful response. An example of using NETCONF:

ds:operational

/ex:foo

500 ]]> As the Network Node is able to fully satisfy the request, the request is given a subscription ID of 22. The response as in indicates that the subscription is decomposed into two component subscriptions which will be published by two message Message Publisher ID: #1 and #2.

2 ]]> Then, both Publishers send notifications with the corresponding piece of data to the Receiver. The subscriber may invoke the "modify-subscription" RPC for a subscription it previously established. The RPC has no difference to the single publisher case as in [RFC8641]. provides an example where a subscriber attempts to modify the period and datastore XPath filter of a subscription using NETCONF.

22 ds:operational

/if:interfaces/if:interface

250 ]]> If the modification is successfully accepted, the "subscription-modified" subscription state notification is sent to the subscriber by the Parent. The notification, for example, indicates the modified subscription is decomposed into one component subscription which will be published by message Message Publisher ID #1.

2007-09-01T10:00:00Z 22 ds:operational

/ex:bar

250

]]>

shows a typical configured subscription to the Network Node with distributed data export capability. Subscripton request has been removed for brevity.

Before starting to push data, the "subscription-started" subscription state notification is sent to the Receiver. The following example assumes the NETCONF transport has already established. The notification indicates that the configured subscription is decomposed into two component subscriptions which will be published by two message Message Publisher IDs: #1 and #2.

2007-09-01T10:00:00Z 39 ds:operational

/ex:foo

250

]]> Then, both Publishers send notifications with the corresponding data record to the Receiver.