wdiff rfc9196.original rfc9196.txt

NETCONF

Internet Engineering Task Force (IETF) B. Lengyel
Internet-Draft
Request for Comments: 9196 Ericsson
Intended status:
Category: Standards Track A. Clemm
Expires: 18 April 2022
ISSN: 2070-1721 Futurewei
B. Claise
Huawei
15 October 2021
February 2022

YANG Modules describing Describing Capabilities for Systems and Datastore Update
Notifications
draft-ietf-netconf-notification-capabilities-21

Abstract

This document defines two YANG modules,"ietf-system-capabilities" modules, "ietf-system-capabilities"
and "ietf-notification-capabilities".

The module "ietf-system-capabilities" provides a placeholder
structure that can be used to discover YANG related YANG-related system
capabilities for servers. The module can be used to report
capability information from the server at run time runtime or at
implementation time, time by making use of the YANG Instance Data File
Format. instance data file
format.

The module "ietf-notification-capabilities" augments "ietf-system-
capabilities" to specify capabilities related to Subscription "Subscription to
YANG Notifications for Datastore Updates. Updates" (RFC 8641).

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of six months RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on 18 April 2022.
https://www.rfc-editor.org/info/rfc9196.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info)
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Simplified Revised BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Providing System Capability Information . . . . . . . . . . . 4
3. Providing YANG-Push Notification Capabilities Information . . 5
4. System Capabilities Model . . . . . . . . . . . . . . . . . . 6
4.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 7
4.2. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 7
5. Notification Capabilities Model . . . . . . . . . . . . . . . 11
5.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 11
5.2. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 18
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7.1. The IETF XML Registry . . . . . . . . . . . . . . . . . . 19
7.2. The YANG Module Names Registry . . . . . . . . . . . . . 19
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1.
8.1. Normative References . . . . . . . . . . . . . . . . . . 20
9.2.
8.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Instance data example Data Example #1 . . . . . . . . . . . . . . 22
Appendix B. Instance data example Data Example #2 . . . . . . . . . . . . . . 24
Appendix C. Changes between revisions . . . . . . . . . . . . . 25
Acknowledgments
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29

1. Introduction

Servers and/or publishers often have capabilities, which can be
represented by values describing that designate operational behavior, that need
to be conveyed to clients, which is
enabled by the clients. The YANG modules described that are defined in this document.
document facilitate this.

There is a need to publish this capability information as it is part
of the API contract between the server and client. Examples include
the maximum size of data that can be stored or transferred,
information about counters (whether a node supports "on-change"
telemetry), etc. Such capabilities are often dependent on a vendor's
implementation or the available resources at deployment. Many such
capabilities are specific to the complete system, individual YANG
datastores [RFC8342], specific parts of the YANG schema, or even
individual data nodes. It is a goal of this document to provide a
common way of
representing to represent such capabilities in a format that is:

* vendor independent independent,

* machine-readable machine readable, and

* available in an identical format both at implementation time and
at run time. runtime.

Implementation-time information is needed by Network Management
System (NMS) implementers. An NMS implementation that supports
notifications needs the information about a system's capability so it can
send "on-change" notifications. If the information is not documented
in a way that is readily available to the NMS designer, but only as
instance data from the network node once it is deployed, the NMS
implementation will be delayed, delayed because it has to wait for the network
node to be ready. In addition, the assumption that all NMS
implementers will have a correctly configured network node available
from which to retrieve data from is an expensive proposition and may not
always hold. (An NMS may need to be able to handle many dozens of
network node types.) Often Often, a fully functional NMS is a requirement
for introducing a new network node type into a network, so delaying
NMS readiness effectively also delays the time at which a new network
node type can be introduced into the network.

Implementation-time information is needed by system integrators.
When introducing a network node type into their network, operators
often need to integrate the node type into their own management
system. The NMS may have management functions that depend on "on-
change" notifications. The network operators need to plan their
management practices and NMS implementation before they decide to buy
the specific network node type. Moreover, the decision to buy the
node type sometimes depends on these management possibilities.

Run-time

Runtime capability information is needed:

* for any "purely model driven" model-driven" application, e.g., a NETCONF- NETCONF
browser. Such applications depend on reading models and
capabilities at run time runtime to support all the publisher's available
functionality.

* in case the capability might change during run time runtime, e.g., due to
licensing, HW constraints hardware constraints, etc.

* to check that that capability information provided earlier, at
implementation time, is what the publisher has implemented.

1.1. Terminology

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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

The terms "YANG-Push", "on-change subscription" subscription", and "periodic
subscription" are used as defined in [RFC8641].

The terms "subscriber", "publisher" "publisher", and "receiver" are used as
defined in [RFC8639].

The term "server" is used as defined in [RFC8342].

The terms "YANG instance data file format", "instance data", and
"instance data set" are used as defined in
[I-D.ietf-netmod-yang-instance-file-format]. [RFC9195].

In addition, this document defines the following terms:

"Implementation-time information":

Implementation-time information: Information about the server's
behavior that is made available during the implementation of the
server, available from a source other than a running server.

"Run-time information":

Runtime information: Information about the server's behavior that is
available from the running server via management protocols such as
NETCONF [RFC6241] or RESTCONF [RFC8040].

2. Providing System Capability Information

Capability information is represented by instance-data instance data based on one
or more "capability defining "capability-defining YANG modules". This allows a user to
discover capabilities both at implementation time and at run time.

* runtime.

For the implementation-time use case: Capabilities SHOULD be
provided by the implementer as YANG instance data files complying
to [I-D.ietf-netmod-yang-instance-file-format].
with [RFC9195]. When provided, the file MUST already be available already
at implementation time, time and retrievable in a way that does not
depend on a live network node.
E.g., download node, e.g., downloading from a product
website.

For the run-time runtime use case: Capabilities SHOULD be available via
NETCONF [RFC6241] or RESTCONF [RFC8040] from the live server
(implementing the publisher) during run time. runtime. Implementations that
support changing these capabilities at run time runtime SHOULD support "on-change" "on-
change" notifications about the system-capabilities container.

The module "ietf-system-capabilities" provides a placeholder
structure to be used to specify any YANG related YANG-related system capability.

The module "ietf-notification-capabilities" is defined to allow a
publisher to specify capabilities related to "Subscription to YANG
Notifications for Datastore Updates" [RFC8641], also known as YANG-
Push, augmenting "ietf-system-capabilities".

The YANG data models in this document conform to the Network
Management Datastore Architecture (NMDA) defined in [RFC8342].

3. Providing YANG-Push Notification Capabilities Information

A specific case is the need to specify capabilities in the YANG-Push
functionality. As defined in [RFC8641] [RFC8641], a publisher may allow
subscribers to subscribe to updates from a datastore and will
subsequently push such update notifications to the receiver.
Notifications may be sent periodically or "on-change" "on change" (more or less
immediately after each change).

A publisher supporting YANG-Push has a number of capabilities defined
in [RFC8641] that are often determined during the implementation of
the publisher. These include:

* Supported supported (reporting) periods for "periodic" subscriptions subscriptions.

* Maximum the maximum number of objects that can be sent in an update update.

* The the set of datastores or data nodes for which "periodic"
notification is supported.

Additional capabilities if the optional "on-change" feature is
supported include:

* Supported supported dampening periods for "on-change" subscriptions subscriptions.

* The the set of datastores or data nodes for which "on-change"
notification is supported supported.

Publishers might have some capabilities (or limitations) to document.
For document
-- for example, how many update notifications and how many datastore
node updates they can send out in a certain time-period. time period. Other
publishers might not support "periodic" subscriptions to all
datastores. In some cases, a publisher supporting "on-change"
notifications will not be able to push updates for some object types
"on-change".
"on change". Reasons for this might be that the value of the
datastore node changes frequently (e.g., in-octets in-octet counter), that
small object changes are frequent and irrelevant to the receiver
(e.g., a temperature gauge changing 0.1 degrees within a
predetermined and acceptable range), or that the implementation is
not capable of on-change notification for a particular object. In
all those cases, it will be important for subscriber applications to
have a way to identify which the objects for which "on-change"
notifications are supported and the objects for which ones they are not.

Faced with the reality that support

Support for "on-change" notification notifications does not mean that such
notifications will be sent for any specific data node, as the ability
to do so may not be supported for every data node. Therefore,
subscriber/management applications can not cannot rely on the "on-
change" "on-change"
functionality unless the subscriber has some means to identify which the
objects for which "on-change" notifications are supported for. in fact supported.
YANG data models are meant to be used as an interface contract.
Without identification of the data nodes actually supporting "on-change", "on-
change" notifications, this contract would be incomplete.

Clients of a server (and subscribers to a publisher, as subscribers
are also clients) need a method to gather capability information.

4. System Capabilities Model

The module "ietf-system-capabilities" is defined to provide a
structure that can be used to discover (as a read-only operational
state) any YANG related YANG-related system capability.

This module itself does not contain any capabilities; it provides
augmentation points for capabilities to be defined in subsequent YANG
modules. The ietf-system-capabilies "ietf-system-capabilities" is used by other modules to
augment in specific capability information. Every set of such
capabilities MUST be wrapped in a container under the augment
statement to cleanly separate different groups of capabilities.
These "wrapper containers" SHALL be augmented in at /sysc:system-
capabilities and /sysc:system-capabilities/sysc:datastore-
capabilities/sysc:per-node-capabilities.

Capability values can be specified on at the system level, at the
datastore level (by selecting all nodes in the datastore) datastore), or for
specific data nodes of a specific datastore (and their contained sub-trees).
subtrees). Capability values specified for a specific datastore or
node-set override values specified on at the system level.

Note: The solution is usable for both NMDA and non-NMDA systems.
For non-NMDA servers servers, "config false" data is considered as if it
were part of the running datastore.

4.1. Tree Diagram

The following tree diagram [RFC8340] provides an overview of the data
model.

module: ietf-system-capabilities
+--ro system-capabilities
+--ro datastore-capabilities* [datastore]
+--ro datastore -> /yanglib:yang-library/datastore/name
+--ro per-node-capabilities* []
+--ro (node-selection)?
+--:(node-selector)
+--ro node-selector? nacm:node-instance-identifier

4.2. YANG Module

This YANG module imports typedefs from [RFC8341] and a reference path
from [RFC8525].

<CODE BEGINS> file "ietf-system-capabilities@2021-10-12.yang" "ietf-system-capabilities@2022-01-21.yang"
module ietf-system-capabilities {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-system-capabilities";
prefix sysc;

import ietf-netconf-acm {
prefix nacm;
reference
"RFC 8341: Network Configuration Access Control Model";
}
import ietf-yang-library {
prefix yanglib;
description
"This module requires ietf-yang-library to be implemented.
Revision 2019-01-04 or a revision derived from it
is REQUIRED.";
reference
"RFC8525: YANG Library";
}

organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>

Editor: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>";
description
"This module specifies a structure to specify system
capabilities for a server or a publisher. System capabilities
may include capabilities of a NETCONF or RESTCONF server or a
notification publisher.

This module does not contain any specific capabilities, capabilities; it only
provides a structure where containers containing the actual
capabilities are augmented in.

Capability values can be specified on at the system level, at the
datastore level (by selecting all nodes in the datastore) datastore), or
for specific data nodes of a specific datastore (and their
contained sub-trees). subtrees).
Capability values specified for a specific datastore or
node-set override values specified on the system/publisher
level.

The same grouping MUST be used to define hierarchical
capabilities supported both at the system level and datastore/data node at the
datastore/data-node level.

To find a capability value for a specific data node in a
specific datastore datastore, the user SHALL:

1) search for a datastore-capabilities list entry for
the specific datastore. When stating a specific capability, the
relative path for any specific capability must be the same
under the system-capabilities container and under the
per-node-capabilities list.

2) If the datastore entry is found within that entry, process
all per-node-capabilities entries in the order they appear in
the list. The first entry that specifies the specific
capability and has a node-selector selecting the specific data
node defines the capability value.

3) If the capability value is not found above and the specific
capability is specified under the system-capabilities container
(outside the datastore-capabilities list), this value shall be
used.

4) If no values are found in the previous steps, the
system/publisher is not capable of providing a value. Possible
reasons are: are that it is unknown, the capability is changing for
some reason, there is no specified limit, etc. In this case case,
the system's behavior is unspecified.

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.

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 Simplified 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).

This version of this YANG module is part of RFC XXXX
(https://www.rfc-editor.org/info/rfcXXXX); 9196
(https://www.rfc-editor.org/info/rfc9196); see the RFC itself
for full legal notices.";

// RFC Ed.: replace XXXX with actual RFC number and remove this
// note.

revision 2021-10-12 2022-01-21 {
description
"Initial version
NOTE TO RFC EDITOR:
(1)Please replace the above revision date to
the date of RFC publication when published.
(2) Please replace the date in the file name
(ietf-system-capabilities@2021-10-12.yang)
to the date of RFC publication.
(3) Please replace the following reference
with RFC number when published
(i.e. RFC xxxx)."; version";
reference
"RFC XXXX: 9196: YANG Modules describing Describing Capabilities for Systems
and Datastore Update Notifications";
}

container system-capabilities {
config false;
description
"System capabilities.
Capability values specified here at the system level
are valid for all datastores and are used when the
capability is not specified on at the datastore level
or for specific data nodes.";
/*
* "Augmentation point for system level system-level capabilities."
*/
list datastore-capabilities {
key "datastore";
description
"Capabilities values per datastore.

For non-NMDA servers/publishers servers/publishers, 'config false' data is
considered as if it was were part of the running datastore.";
leaf datastore {
type leafref {
path
"/yanglib:yang-library/yanglib:datastore/yanglib:name";
}
description
"The datastore for which capabilities are defined.
Only one specific datastore can be specified specified,
e.g., ds:conventional, which ds:conventional must not be used, as it
represents a set of configuration datastores, must not be used."; datastores.";
}
list per-node-capabilities {
description
"Each list entry specifies capabilities for the selected
data nodes. The same capabilities apply for to the data nodes
in the subtree below the selected nodes.

The system SHALL order the entries according to their
precedence. The order of the entries MUST NOT change
unless the underlying capabilities also change.

Note that the longest patch matching can be achieved
by ordering more specific matches before less
specific ones.";
choice node-selection {
description
"A method to select some or all nodes within a
datastore.";
leaf node-selector {
type nacm:node-instance-identifier;
description
"Selects the data nodes for which capabilities are
specified. The special value '/' denotes all data
nodes in the datastore, consistent with the path
leaf node on page 41 of [RFC8341].";
reference
"RFC 8341: Network Configuration Access Control Model";
}
}
/*
* "Augmentation point for datastore datastore- or data node level data-node-level
* capabilities."
*/
}
}
}
}
<CODE ENDS>

5. Notification Capabilities Model

The YANG module "ietf-notification-capabilities" provides YANG-Push information
related capability information. to the YANG-Push capability.

5.1. Tree Diagram

The following tree diagram [RFC8340] provides an overview of the data
model.

module: ietf-notification-capabilities
augment /sysc:system-capabilities:
+--ro subscription-capabilities
+--ro max-nodes-per-update? uint32
+--ro periodic-notifications-supported? notification-support
+--ro (update-period)?
| +--:(minimum-update-period)
| | +--ro minimum-update-period? uint32
| +--:(supported-update-period)
| +--ro supported-update-period* uint32
+--ro on-change-supported? notification-support
| {yp:on-change}?
+--ro minimum-dampening-period? uint32
| {yp:on-change}?
+--ro supported-excluded-change-type* union
{yp:on-change}?
augment /sysc:system-capabilities/sysc:datastore-capabilities
/sysc:per-node-capabilities:
+--ro subscription-capabilities
+--ro max-nodes-per-update? uint32
+--ro periodic-notifications-supported? notification-support
+--ro (update-period)?
| +--:(minimum-update-period)
| | +--ro minimum-update-period? uint32
| +--:(supported-update-period)
| +--ro supported-update-period* uint32
+--ro on-change-supported? notification-support
| {yp:on-change}?
+--ro minimum-dampening-period? uint32
| {yp:on-change}?
+--ro supported-excluded-change-type* union
{yp:on-change}?

5.2. YANG Module

This YANG module imports a feature and typedefs from [RFC8641] and
also imports the "ietf-system-capabilities" specified in this
document.

<CODE BEGINS> file "ietf-notification-capabilities@2021-10-12.yang" "ietf-notification-capabilities@2022-01-21.yang"
module ietf-notification-capabilities {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-notification-capabilities";
prefix notc;

import ietf-yang-push {
prefix yp;
description
"This module requires ietf-yang-push to be implemented.";
reference
"RFC 8641: Subscription to YANG Notifications for
Datastore Updates";
}
import ietf-system-capabilities {
prefix sysc;
description
"This module requires ietf-system-capabilities to be
implemented.";
reference
"RFC XXXX: 9196: YANG Modules describing Describing Capabilities for Systems
and Datastore Update Notifications";
}

// RFC Ed.: replace the above XXXX with actual RFC number
// and remove this note.

organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>

Editor: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>";
description
"This module specifies YANG-Push [RFC 8641] related publisher
capabilities. capabilities related to
YANG-Push (RFC 8641).

The module contains:

- a specification of which the data nodes that support 'on-change' or
'periodic' notifications.

- capabilities related to the throughput of notification data
that the publisher can support. (Note that for a specific
subscription, the publisher MAY allow only longer periods
or smaller updates depending on, e.g., actual load conditions.)

Capability values can be specified on at the system/publisher
level, at the datastore level level, or for specific data nodes of
a specific datastore (and their contained sub-trees), subtrees), as defined
in the ietf-system-capabilities module.

If different data nodes covered by a single subscription
have different values for a specific capability, then using
values that are only acceptable for some of these data nodes,
but not for others, may result in the rejection of the
subscription.

This version of this YANG module is part of RFC XXXX
(https://www.rfc-editor.org/info/rfcXXXX); 9196
(https://www.rfc-editor.org/info/rfc9196); see the RFC itself
for full legal notices.";

// RFC Ed.: replace XXXX with actual RFC number and remove this
// note.

revision 2021-10-12 2022-01-21 {
description
"Initial version";
reference
"RFC XXXX: 9196: YANG Modules describing Describing Capabilities for Systems
and Datastore Update Notifications";
}

// RFC Ed.: replace XXXX with actual RFC number and remove this
// note.

grouping subscription-capabilities {
description
"Capabilities related to YANG-Push subscriptions
and notifications";
container subscription-capabilities {
description
"Capabilities related to YANG-Push subscriptions
and notifications";
typedef notification-support {
type bits {
bit config-changes {
description
"The publisher is capable of sending
notifications for 'config true' nodes for the
relevant scope and subscription type.";
}
bit state-changes {
description
"The publisher is capable of sending
notifications for 'config false' nodes for the
relevant scope and subscription type.";
}
}
description
"Type for defining whether 'on-change' or
'periodic' notifications are supported for all data nodes,
'config false' data nodes, 'config true' data nodes, or
no data nodes.

If the bit

The bits config-changes or state-changes is have no effect
when they are set for a datastore, datastore or for a set of nodes
that does not contain nodes with the indicated config value, this has no
effect,
value. In those cases, the effect is the same as if no
support was declared. E.g. One example of this is indicating
support for state-changes for a candidate datastore that
has no effect.";
}

leaf max-nodes-per-update {
type uint32 {
range "1..max";
}
description
"Maximum number of data nodes that can be sent
in an update. The publisher MAY support more data nodes, nodes
but SHOULD support at least this number.

May be used to avoid the 'update-too-big' error
during subscription.";
reference
"RFC 8641: Subscription to YANG Notifications for
Datastore Updates, the 'update-too-big' error/identity";
}
leaf periodic-notifications-supported {
type notification-support;
description
"Specifies whether the publisher is capable of
sending 'periodic' notifications for the selected
data nodes nodes, including any subtrees that may exist
below them.";
reference
"RFC 8641: Subscription to YANG Notifications for
Datastore Updates, 'periodic' subscription concept";
}
choice update-period {
description
"Supported update period value or values for
'periodic' subscriptions.";
leaf minimum-update-period {
type uint32;
units "centiseconds";
description
"Indicates the minimal update period that is
supported for a 'periodic' subscription.

A subscription request to the selected data nodes with
a smaller period than what this leaf specifies is
likely to result in a 'period-unsupported' error.";
reference
"RFC 8641: Subscription to YANG Notifications for
Datastore Updates, the period leaf in the ietf-yang-push
YANG module";
}
leaf-list supported-update-period {
type uint32;
units "centiseconds";
description
"Supported update period values for a 'periodic'
subscription.

A subscription request to the selected data nodes with a
period not included in the leaf-list will result in a
'period-unsupported' error.";
reference
"RFC 8641: Subscription to YANG Notifications for
Datastore Updates, the period leaf in the ietf-yang-push
YANG module";
}
}
leaf on-change-supported {
if-feature "yp:on-change";
type notification-support;
description
"Specifies whether the publisher is capable of
sending 'on-change' notifications for the selected
data nodes and the subtree below them.";
reference
"RFC 8641: Subscription to YANG Notifications for Datastore
Updates, on-change concept";
}
leaf minimum-dampening-period {
if-feature "yp:on-change";
type uint32;
units "centiseconds";
description
"The minimum dampening-period dampening period supported for 'on-change'
subscriptions for the selected data nodes.

If this value is present and greater than zero,
that implies dampening is mandatory.";
reference
"RFC 8641: Subscription to YANG Notifications for
Datastore Updates, the dampening-period leaf in the
ietf-yang-push YANG module";
}
leaf-list supported-excluded-change-type {
if-feature "yp:on-change";
type union {
type enumeration {
enum none {
value -2;
description
"None of the change types can be excluded.";
}
enum all {
value -1;
description
"Any combination of change types can be excluded.";
}
}
type yp:change-type;
}
description
"The change types that can be excluded in
YANG-Push subscriptions for the selected data nodes.";
reference
"RFC 8641: Subscription to YANG Notifications for Datastore
Updates, the change-type typedef in the ietf-yang-push
YANG module";
}
}
}

augment "/sysc:system-capabilities" {
description
"Add system level capabilities";
uses subscription-capabilities {
refine
"subscription-capabilities/supported-excluded-change-type" {
default "none";
}
}
}

augment "/sysc:system-capabilities/sysc:datastore-capabilities"
+ "/sysc:per-node-capabilities" {
description
"Add datastore and node level node-level capabilities";
uses subscription-capabilities {
refine
"subscription-capabilities/supported-excluded-change-type" {
default "none";
}
}
}
}
<CODE ENDS>

6. Security Considerations

The YANG modules specified in this document define a schema for data
that is designed to be accessed via network management protocols such
as NETCONF [RFC6241] or RESTCONF [RFC8040] or as YANG instance data.
The lowest NETCONF layer is the secure transport layer, and the
mandatory-to-implement secure transport is Secure Shell (SSH)
[RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-
implement secure transport is TLS [RFC8446].

The Network Configuration Access Control Model (NACM) [RFC8341]
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.

This document outlines a framework for conveying system capability
information that is inherently flexible and extensible. While the
full set of use cases is not known now, they may range as wide as
conveying the minimum update period for periodic subscription updates
and what protocols might be used for such notifications. Knowledge
of this type of value might, for example, allow an attacker to gain
insight into how long unauthorized configuration changes might be
active prior to detection, detection and what communications channels might be
disrupted to extend the period of non-detection. Documents adding
additional capabilities via augmenting this module are encouraged to
document the security considerations of the new YANG nodes, according
to the guidance in BCP 216. 216 [RFC8407].

All protocol-accessible data nodes in augmented modules are read-only
and cannot be modified. The data in these modules is not security
sensitive. Access control may be configured, configured to avoid
exposing the any read-only data. data that is defined by the augmenting module
documentation as being security sensitive.

When that data is in file format, the data should be protected
against modification or unauthorized access using normal file file-
handling mechanisms. The data in file format also inherits all the
security considerations of [I-D.ietf-netmod-yang-instance-file-format] [RFC9195], which
has includes additional
considerations about read protections; protections and distinguishes between data
at rest and in motion.

7. IANA Considerations

7.1. The IETF XML Registry

This document registers two the following URIs in the IETF "IETF XML registry [RFC3688].
Following the format in [RFC3688], the following registrations are
requested: Registry"
[RFC3688]:

URI: urn:ietf:params:xml:ns:yang:ietf-system-capabilities
Registrant Contact: The NETCONF WG of the IETF. IESG.
XML: N/A, the requested URI is an XML namespace.

URI: urn:ietf:params:xml:ns:yang:ietf-notification-capabilities
Registrant Contact: The NETCONF WG of the IETF. IESG.
XML: N/A, the requested URI is an XML namespace.

7.2. The YANG Module Names Registry

This document registers two the following YANG modules in the YANG "YANG
Module Names Names" registry [RFC6020]. Following the format in [RFC6020], the following
registrations are requested: [RFC6020]:

name: ietf-system-capabilities
namespace: urn:ietf:params:xml:ns:yang:ietf-system-capabilities
prefix: sysc
reference: RFC XXXX 9196

name: ietf-notification-capabilities
namespace:
urn:ietf:params:xml:ns:yang:ietf-notification-capabilities urn:ietf:params:xml:ns:yang:ietf-notification-
capabilities
prefix: notc
reference: RFC XXXX 9196

8. Acknowledgments

For their valuable comments, discussions, and feedback, we wish to
acknowledge Andy Bierman, Juergen Schoenwaelder, Rob Wilton, Kent
Watsen, Eric Voit, Joe Clarke, Martin Bjorklund, Ladislav Lhotka, Qin
Wu, Mahesh Jethanandani, Ran Tao, Reshad Rahman and other members of
the Netmod WG.

9. References

9.1.

8.1. Normative References

[I-D.ietf-netmod-yang-instance-file-format]
Lengyel, B. and B. Claise, "YANG Instance Data File
Format", Work in Progress, Internet-Draft, draft-ietf-
netmod-yang-instance-file-format-19, 16 September 2021,
<https://www.ietf.org/archive/id/draft-ietf-netmod-yang-
instance-file-format-19.txt>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.

[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.

[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.

[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/info/rfc6242>.

[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/info/rfc8341>.

[RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "Network Management Datastore Architecture
(NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
<https://www.rfc-editor.org/info/rfc8342>.

[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.

[RFC8525] Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
and R. Wilton, "YANG Library", RFC 8525,
DOI 10.17487/RFC8525, March 2019,
<https://www.rfc-editor.org/info/rfc8525>.

[RFC8639] Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
E., and A. Tripathy, "Subscription to YANG Notifications",
RFC 8639, DOI 10.17487/RFC8639, September 2019,
<https://www.rfc-editor.org/info/rfc8639>.

[RFC8641] Clemm, A. and E. Voit, "Subscription to YANG Notifications
for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
September 2019, <https://www.rfc-editor.org/info/rfc8641>.

9.2. Informative References

[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/info/rfc6242>.

[RFC8040] Bierman, A., Bjorklund, M.,

[RFC9195] Lengyel, B. and K. Watsen, "RESTCONF
Protocol", B. Claise, "A File Format for YANG
Instance Data", RFC 8040, 9195, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>. 10.17487/RFC9195, February
2022, <https://www.rfc-editor.org/info/rfc9195>.

8.2. Informative References

[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.

[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3",

[RFC8407] Bierman, A., "Guidelines for Authors and Reviewers of
Documents Containing YANG Data Models", BCP 216, RFC 8446, 8407,
DOI 10.17487/RFC8446, August 10.17487/RFC8407, October 2018,
<https://www.rfc-editor.org/info/rfc8446>.
<https://www.rfc-editor.org/info/rfc8407>.

[RFC8792] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
<https://www.rfc-editor.org/info/rfc8792>.

Appendix A. Instance data example Data Example #1

The following examples use artwork folding [RFC8792] for better
formatting.

The following instance data example describes the notification
capabilities of a hypothetical "acme-router". The router implements
the running and operational datastores. Every change can be reported
"on-change" from the running datastore, but only "config false" nodes
and some "config false" data can be reported on-change from the
operational datastore. Interface statistics are not reported "on-change", "on-
change"; only two important
counters. counters are. Datastore subscription
capabilities are not reported "on-
change", "on-change", as they never change on
the acme-router during run time. runtime.

========== NOTE: '\' line wrapping per RFC 8792) ===========

<?xml version="1.0" encoding="UTF-8"?>
<instance-data-set xmlns=\
"urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">
<name>acme-router-notification-capabilities</name>
<content-schema>
<module>ietf-system-capabilities@2021-10-12</module>
<module>ietf-notification-capabilities@2021-10-12</module>
<module>ietf-system-capabilities@2022-01-21</module>
<module>ietf-notification-capabilities@2022-01-21</module>
</content-schema>
<description>Defines the notification capabilities of an
acme-router. The router only has running and operational
datastores. Every change can be reported on-change from the
running datastore, but only "config false" nodes and some
"config false" data can be reported on-change from the
operational datastore. Statistics
are not reported on-change except for two important counters,
where a small dampening period is mandated.
</description>
<content-data>
<system-capabilities \
xmlns="urn:ietf:params:xml:ns:yang:ietf-system-capabilities" \
xmlns:notc=\
"urn:ietf:params:xml:ns:yang:ietf-notification-capabilities" \
xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
<notc:subscription-capabilities>
<notc:minimum-update-period>500</notc:minimum-update-period>
<notc:max-nodes-per-update>2000</notc:max-nodes-per-update>
<notc:minimum-dampening-period>100</notc:minimum-dampening-period>
<notc:minimum-dampening-period>\
100\
</notc:minimum-dampening-period>
<notc:periodic-notifications-supported>\
config-changes state-changes\
</notc:periodic-notifications-supported>
<notc:on-change-supported>\
config-changes state-changes\
</notc:on-change-supported>
<notc:supported-excluded-change-type>\
all\
</notc:supported-excluded-change-type>
</notc:subscription-capabilities>
<datastore-capabilities>
<datastore>ds:operational</datastore>
<per-node-capabilities>
<node-selector>\
/if:interfaces/if:interface[if:name='lo']\
</node-selector>
<notc:subscription-capabilities>
<notc:on-change-supported/>
<notc:periodic-notifications-supported/>
</notc:subscription-capabilities>
</per-node-capabilities>
<per-node-capabilities>
<node-selector>\
/if:interfaces/if:interface/if:statistics/if:in-octets\
</node-selector>
<notc:subscription-capabilities>
<notc:minimum-dampening-period>10
</notc:minimum-dampening-period>
<notc:on-change-supported>\
state-changes\
</notc:on-change-supported>
</notc:subscription-capabilities>
</per-node-capabilities>
<per-node-capabilities>
<node-selector>\
/if:interfaces/if:interface/if:statistics/if:out-octets\
</node-selector>
<notc:subscription-capabilities>
<notc:minimum-dampening-period>10
</notc:minimum-dampening-period>
<notc:on-change-supported>\
state-changes\
</notc:on-change-supported>
</notc:subscription-capabilities>
</per-node-capabilities>
<per-node-capabilities>
<node-selector>\
/if:interfaces/if:interface/if:statistics\
</node-selector>
<notc:subscription-capabilities>
<notc:on-change-supported/>
</notc:subscription-capabilities>
</per-node-capabilities>
</datastore-capabilities>
</system-capabilities>
</content-data>
</instance-data-set>

Figure 1: Notification Capabilities with data node specific settings Settings Specific to the
Data Node

Appendix B. Instance data example Data Example #2

The following examples use artwork folding [RFC8792] for better
formatting.

The following instance data example describes the notification
capabilities of a hypothetical "acme-switch". The switch implements
the running, candidate candidate, and operational datastores. Every change can
be reported "on-change" from the running datastore, nothing can be
reported on-change from the candidate datastore datastore, and all "config
false" data can be reported on-change from the operational datastore. "periodic"
"Periodic" subscriptions are supported for running and
operational, operational
but not for candidate datastores.

========== NOTE: '\' line wrapping per RFC 8792) ===========

<?xml version="1.0" encoding="UTF-8"?>
<instance-data-set xmlns=\
"urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">
<name>acme-switch-notification-capabilities</name>
<content-schema>
<module>ietf-system-capabilities@2021-10-12</module>
<module>ietf-notification-capabilities@2021-10-12</module>
<module>ietf-system-capabilities@2022-01-21</module>
<module>ietf-notification-capabilities@2022-01-21</module>
</content-schema>
<description>Notification capabilities of acme-switch.
Acme-switch implements the running, candidate candidate, and operational
datastores. Every change can be reported on-change from the
running datastore, nothing from the candidate datastore and
all "config false" data from the operational datastore. Periodic
subscriptions are supported for running and operational, but not
for candidate datastore.
</description>
<content-data>
<system-capabilities \
xmlns="urn:ietf:params:xml:ns:yang:ietf-system-capabilities" \
xmlns:notc=\
"urn:ietf:params:xml:ns:yang:ietf-notification-capabilities" \
xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
<notc:subscription-capabilities>
<notc:minimum-update-period>500</notc:minimum-update-period>
<notc:max-nodes-per-update>2000</notc:max-nodes-per-update>
<notc:minimum-dampening-period>100</notc:minimum-dampening-period>
<notc:minimum-dampening-period>\
100\
</notc:minimum-dampening-period>
<notc:periodic-notifications-supported>\
config-changes state-changes\
</notc:periodic-notifications-supported>
</notc:subscription-capabilities>
<datastore-capabilities>
<datastore>ds:operational</datastore>
<per-node-capabilities>
<node-selector>/</node-selector>
<notc:subscription-capabilities>
<notc:on-change-supported>\
state-changes\
</notc:on-change-supported>
</notc:subscription-capabilities>
</per-node-capabilities>
</datastore-capabilities>
<datastore-capabilities>
<datastore>ds:candidate</datastore>
<per-node-capabilities>
<node-selector>/</node-selector>
<notc:subscription-capabilities>
<notc:on-change-supported/>
<notc:periodic-notifications-supported/>
</notc:subscription-capabilities>
</per-node-capabilities>
</datastore-capabilities>
<datastore-capabilities>
<datastore>ds:running</datastore>
<per-node-capabilities>
<node-selector>/</node-selector>
<notc:subscription-capabilities>
<notc:on-change-supported>\
config-changes\
</notc:on-change-supported>
</notc:subscription-capabilities>
</per-node-capabilities>
</datastore-capabilities>
</system-capabilities>
</content-data>
</instance-data-set>

Figure 2: Notification Capabilities with datastore level settings

Appendix C. Changes between revisions

Note to RFC Editor (To be removed by RFC Editor)

v20 - v21
* IESG review

v19 - v20

* IESG review

v18 - v19

* IESG review

v17 - v18

* IESG review

v16 - v17

* AD review comments addressed

v15 - v16

* Two editorial comments from document shepherd

v14 - v15

* Address the last comments from document shepherd

v13 - v14

* Updated according to sheperds review

* Added to import, which imported modules need to be implemented.

* Added notes to the RFC editor

* Re-arrange the sections, for a better reading flow

* Many editorial changes

* Replace YANG module prefix

v12 - v13

* Rearranged order of notification capability leafs into 3 groups:
generic, specific to periodic subscriptions, specific to on-
change.

* Introduced artwork folding in the examples
* Updated to follow draft-ietf-netmod-yang-instance-file-format-10

* Various editing changes

v11 - v12

* Updated max-nodes-per-update description

* Reformatted YANG models with pyang -f yang --keep-comments --yang-
line-length 69

v10 - v11

* Updated examples

* Updated typedef notification-support

v09 - v10

* Removed description text from imports about the need for
implementing the imported module.

* Changed notification-support to bits with shorter names

* Assigned enum values to supported-excluded-change-type

* Made node-selector a choice to allow for future alternative
selection methods.

* Changed precedence of per-node-capabilities entries. Precedence
is now according to the position of entries in the list.

v08 - v09

* Split the YANG module into two: ietf-system-capabilities and ietf-
notification-capabilities. Restructured/updated the draft
accordingly.

v07 - v08

* Prepared the YANG model to include other non-YANG-Push related
capabilities.

* Renamed the top level container to system-capabilities

* Added a container subscription-capabilities to the grouping
subscription-capabilities to contain all subscription related
capabilities
* Updated examples according to draft-ietf-netmod-yang-instance-
file-format-06.

v06 - v07

* Updated examples according to draft-ietf-netmod-yang-instance-
file-format-05.

v05 - v06

* Providing the capability data is only a "SHOULD" recommendation.
Some reviewers wanted MUST some wanted much less.

* The YANG module import statements now indicate the imported
modules that must be implemented not just available as import as
requested by the YangDoctors review.

v04 - v05

* Added new capabilities periodic-notifications-supported Datastore-Level Settings

Acknowledgments

For their valuable comments, discussions, and
supported-excluded-change-type.

* Restructured YANG module to make the node-selector's usage similar
to how NACM uses it: "/" means the whole datastore.

* Small corrections, spelling, rewording

* Replaced the term server with the term publisher except in cases
where feedback, we speak about datastores and functionality based on get,
getconfig operations. In this latter case it is really the server
functionality that is discussed.

v03 - v04

* Clarified recommended support for on-change notifications about
the datastore-subscription-capabilities.

v02 - v03

* Allow throughput related capabilities to be defined on top,
datastore or data node level. Described that specific capability
values always override generic ones.

* Indicate that non-NMDA servers can also use this model.

* Updated according wish to draft-ietf-netmod-yang-instance-file-
format-04
v01 - v02

* Added instance data examples

* On-change capability can be defined per datastore

* Added "if-feature yp:on-change" where relevant

* Unified units used

v00 - v01

* Add more capabilities: minimum period, supported period max-number
acknowledge Andy Bierman, Juergen Schoenwaelder, Rob Wilton, Kent
Watsen, Eric Voit, Joe Clarke, Martin Bjorklund, Ladislav Lhotka, Qin
Wu, Mahesh Jethanandani, Ran Tao, Reshad Rahman, and other members of objects, min dampening period, dampening supported
the Netmod Working Group.

Authors' Addresses

Balazs Lengyel
Ericsson
1117
Budapest
Magyar Tudosok korutja 11
1117
Hungary

Email: balazs.lengyel@ericsson.com

Alexander Clemm
Futurewei
2330 Central Expressway
Santa Clara, CA 95050, 95050
United States of America

Email: ludwig@clemm.org

Benoit Claise
Huawei
George's Court Townsend Street
Dublin 2
Ireland

Email: benoit.claise@huawei.com