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, the packet forwarding is delegated to multiple processors on line cards. To 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 defined in and are not redefined here: Capability In addition, this document defines the following terms: Global Subscription: The Subscription requested by the subscriber. 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 Capability: The overall subscription capability 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 Capability: The subscription capability that each Publisher exposes to the Publisher Master. 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 Master: 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 Master to deal with the Component Subscription and pushing the data to the Receiver. Node: Is the network node 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 publisher 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 much YANG data is subscribed to processors on line cards and published from the route processor, creating an unnecessary overhead at the route processor and a potential bottleneck. This document proposes that subscribed YANG data can be published from processors on line cards while for such Subscriptions the route processor is only involved in maintaining and decomposing the Subscription, which includes notifying the Receiver which Subscription is being published from which line card processor with subscription state change notifications. To enable Receivers to detect notification message loss when publishers share a transport session, 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 Master or Agent role. The Publisher Master knows all the capabilities that his Agents can provide and exposes the Global Capability to the collector. The Subscriber maintains the Global Subscription at the Publisher Master and disassembles the Global Subscription to multiple Component Subscriptions, depending 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. The Receiver then reassembles packets and decapsulates notifications accordingly.

Publisher Master and Publisher Agents interact with each other in several ways: Publisher Agents need to register at the Master at the beginning of their process life cycle. Contracts are created and maintained throughout the subscription lifecycle between the Publisher Master and each Agent on the Component Capability, and the format for notification data structure. The Publisher Master relays the component subscriptions to the Publisher Agents. The Publisher Agents announce the status of their Component Subscriptions to the Publisher Master. The status of the overall subscription is maintained by the Publisher Master. The Publisher Master 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 Master and Agent is out of scope of this document.

The Collector can only subscribe to the Master. This requires the Publisher Master to: expose the Global Capability 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 Master 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 Master 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 Master. When the subscription decomposition result changed, 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. The actual working Publisher Agents are selected based on the subscription decomposition result. All Publisher Agents share the same source IP address for data export. 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 responsible documents.

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) 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 (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 2025-04-12 { description "Initial version"; reference "RFC XXXX: Subscription to Distributed Notifications"; } 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 software process which publishes the message (e.g., processor 1 on line card 1). This field is used to notify the receiver which publisher process published which message."; } } 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 software process which publishes the message (e.g., processor 1 on line card 1). This field is used to notify the receiver which publisher processes are going to publish."; } } 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 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 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.

The YANG module specified in this document defines a schema for data that is designed to be accessed via network management protocols such as NETCONF or RESTCONF. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH). The lowest layer is HTTPS, and the mandatory-to-implement secure transport is TLS. The NETCONF Access Control Model (NACM) provides the means to restrict access particulary for NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content. The new data nodes introduced 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-config or notification) to this data nodes. These are the subtrees and data nodes and their sensitivity/vulnerability: /subscriptions/subscription/message-publisher-ids The entries in the two lists above will show where subscribed resources might be located on the publishers. Access control MUST be set so that only someone with proper access permissions has the ability to access this resource. Other Security Considerations is the same as those discussed in .

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.

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

/ex:bar

250 ]]> If the modification is successfully accepted, the "subscription-modified" subscription state notification is sent to the subscriber by the Master. 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.

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.