Internet Engineering Task Force (IETF) B. Claise

Internet Engineering Task Force (IETF) B. Claise
Request for Comments: 9418 J. Quilbeuf
Category: Standards Track Huawei
ISSN: 2070-1721 P. Lucente
NTT
P. Fasano
TIM S.p.A
T. Arumugam
Consultant
July 2023

A YANG Data Model for Service Assurance

Abstract

This document specifies YANG modules for representing assurance
graphs. These graphs represent the assurance of a given service by
decomposing it into atomic assurance elements called subservices.
The companion document, "Service Assurance for Intent-Based
Networking Architecture" (RFC 9417), presents an architecture for
implementing the assurance of such services.

The YANG data models in this document conform to the Network
Management Datastore Architecture (NMDA) defined in RFC 8342.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9418.

Copyright Notice

Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(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 Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.

Table of Contents

1. Introduction
1.1. Terminology
2. YANG Modules Overview
3. Base IETF Service Assurance YANG Module
3.1. Concepts
3.2. Tree View
3.3. YANG Module
3.4. Rejecting Circular Dependencies
4. Guidelines for Defining New Subservice Types
5. Subservice Augmentation: "ietf-service-assurance-device" YANG
Module
5.1. Tree View
5.2. Concepts
5.3. YANG Module
6. Subservice Augmentation: "ietf-service-assurance-interface"
YANG Module
6.1. Tree View
6.2. Concepts
6.3. YANG Module
7. Security Considerations
8. IANA Considerations
8.1. The IETF XML Registry
8.2. The YANG Module Names Registry
9. References
9.1. Normative References
9.2. Informative References
Appendix A. Vendor-Specific Subservice Augmentation:
"example-service-assurance-device-acme" YANG Module
A.1. Tree View
A.2. Concepts
A.3. YANG Module
Appendix B. Further Augmentations: IP Connectivity and IS-IS
Subservices
B.1. IP Connectivity Module Tree View
B.2. IS-IS Module Tree View
B.3. Global Tree View
B.4. IP Connectivity YANG Module
B.5. IS-IS YANG Module
Appendix C. Example of a YANG Instance
Appendix D. YANG Library for Service Assurance
Acknowledgements
Authors' Addresses

1. Introduction

[RFC9417] describes an architecture and a set of involved components
for service assurance, called Service Assurance for Intent-based
Networking (SAIN). This document complements the architecture by
specifying a data model for the interfaces between components. More
specifically, the document provides YANG modules for the purpose of
service assurance in a format that is:

* machine readable,

* vendor independent, and

* augmentable such that SAIN agents from Figure 1 of [RFC9417] can
support and expose new subservices to SAIN orchestrators and
collectors.

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 used in this document are defined in [RFC9417].

The meanings of the symbols in the tree diagrams are defined in
[RFC8340].

2. YANG Modules Overview

The main YANG module, "ietf-service-assurance" (Section 3), defines
objects for assuring network services based on their decomposition
into so-called subservices. The subservices are hierarchically
organized by dependencies. The subservices, along with the
dependencies, constitute an assurance graph. This module should be
supported by an agent that is able to interact with the devices in
order to produce the health statuses and symptoms for each subservice
in an assurance graph. This module is intended for the following use
cases:

* Assurance graph configuration:

- Subservices: Configure a set of subservices to assure by
specifying their types and parameters.

- Dependencies: Configure the dependencies between the
subservices, along with their types.

* Assurance telemetry: Export the assurance graph with health
statuses and symptoms for each node.

The module is also intended to be exported by the SAIN collector that
aggregates the output of several SAIN agents to provide the global
assurance graph. In that case, only the telemetry export use case is
considered.

The modules presented in this document conform to the Network
Management Datastore Architecture (NMDA) defined in [RFC8342].

The second YANG module, "ietf-service-assurance-device" (Section 5),
augments the "ietf-service-assurance" module by adding support for
the device subservice. Additional subservice types might be added
following a similar approach.

The third YANG module, "ietf-service-assurance-interface"
(Section 6), augments the "ietf-service-assurance" module as well by
adding support for the interface subservice.

We provide additional examples in the appendix. The module "example-
service-assurance-device-acme" (Appendix A) augments the "ietf-
service-assurance-device" module to customize it for devices of the
fictional Acme Corporation. Additional vendor-specific parameters
might be added following a similar approach. We also provide the
modules "example-service-assurance-ip-connectivity" and "example-
service-assurance-is-is" (Appendix B) to model the example in
Figure 2 from Section 3.1 of [RFC9417].

3. Base IETF Service Assurance YANG Module

3.1. Concepts

The "ietf-service-assurance" YANG module assumes a set of subservices
to be assured independently. A subservice is a feature or a subpart
of the network system that a given service instance depends on.
Examples of subservice types include the following:

* device: Whether a device is healthy, and if not, what are the
symptoms? Such a subservice might monitor the device resources,
such as CPU, RAM, or Ternary Content-Addressable Memory (TCAM).
Potential symptoms are "CPU overloaded", "Out of RAM", or "Out of
TCAM".

* ip-connectivity: Given two IP addresses bound to two devices, what
is the quality of the IP connectivity between them? Potential
symptoms are "No route available" or "Equal-Cost Multipaths
(ECMPs) imbalance".

An instance of the device subservice is representing a subpart of the
network system, namely a specific device. An instance of the ip-
connectivity subservice is representing a feature of the network,
namely the connectivity between two specific IP addresses on two
devices. In both cases, these subservices might depend on other
subservices, for instance, the connectivity might depend on a
subservice representing the routing system and on a subservice
representing ECMPs.

The two example subservices presented above need different sets of
parameters to fully characterize one of their instances. An instance
of the device subservice is fully characterized by a single parameter
allowing to identify the device to monitor. For the ip-connectivity
subservice, at least the device and IP address for both ends of the
link are needed to fully characterize an instance.

The base model presented in this section specifies a single type of
subservice, which represents service instances. Such nodes play a
particular role in the assurance graph because they represent the
starting point, or root, for the assurance graph of the corresponding
service instance. The parameters required to fully identify a
service instance are the name of the service and the name of the
service instance. To support other types of subservices, such as
device or ip-connectivity, the "ietf-service-assurance" module is
intended to be augmented.

The dependencies are modeled as a list, i.e., each subservice
contains a list of references to its dependencies. That list can be
empty if the subservice instance does not have any dependencies.

By specifying service instances and their dependencies in terms of
subservices, one defines a global assurance graph. That assurance
graph is the result of merging all the individual assurance graphs
for the assured service instances. Each subservice instance is
expected to appear only once in the global assurance graph even if
several service instances depend on it. For example, an instance of
the device subservice is a dependency of every service instance that
relies on the corresponding device. The assurance graph of a
specific service instance is the subgraph obtained by traversing the
global assurance graph through the dependencies, starting from the
specific service instance.

An assurance agent configured with such a graph is expected to
produce, for each configured subservice, a health status that
indicates how healthy the subservice is. If the subservice is not
healthy, the agent is expected to produce a list of symptoms
explaining why the subservice is not healthy.

3.2. Tree View

The following tree diagram [RFC8340] provides an overview of the
"ietf-service-assurance" module.

module: ietf-service-assurance
+--ro assurance-graph-last-change yang:date-and-time
+--rw subservices
| +--rw subservice* [type id]
| +--rw type identityref
| +--rw id string
| +--ro last-change? yang:date-and-time
| +--ro label? string
| +--rw under-maintenance!
| | +--rw contact string
| +--rw (parameter)
| | +--:(service-instance-parameter)
| | +--rw service-instance-parameter
| | +--rw service string
| | +--rw instance-name string
| +--ro health-score int8
| +--ro symptoms-history-start? yang:date-and-time
| +--ro symptoms
| | +--ro symptom* [start-date-time agent-id symptom-id]
| | +--ro symptom-id leafref
| | +--ro agent-id -> /agents/agent/id
| | +--ro health-score-weight? uint8
| | +--ro start-date-time yang:date-and-time
| | +--ro stop-date-time? yang:date-and-time
| +--rw dependencies
| +--rw dependency* [type id]
| +--rw type
| | -> /subservices/subservice/type
| +--rw id leafref
| +--rw dependency-type? identityref
+--ro agents
| +--ro agent* [id]
| +--ro id string
| +--ro symptoms* [id]
| +--ro id string
| +--ro description string
+--ro assured-services
+--ro assured-service* [service]
+--ro service leafref
+--ro instances* [name]
+--ro name leafref
+--ro subservices* [type id]
+--ro type -> /subservices/subservice/type
+--ro id leafref

The date of the last change in "assurance-graph-last-change" is read
only. It must be updated each time the graph structure is changed by
addition or deletion of subservices and dependencies or modifications
of their configurable attributes, including their maintenance
statuses. Such modifications correspond to a structural change in
the graph. The date of the last change is useful for a client to
quickly check if there is a need to update the graph structure. A
change in the health score or symptoms associated to a service or
subservice does not change the structure of the graph, and thus has
no effect on the date of the last change.

The "subservices" list contains all the subservice instances
currently known by the server (i.e., SAIN agent or SAIN collector).
A subservice declaration MUST provide the following:

* a subservice type ("type"): a reference to an identity that
inherits from "subservice-base", which is the base identity for
any subservice type

* an id ("id"): a string uniquely identifying the subservice among
those with the same type

The type and id uniquely identify a given subservice.

The "last-change" indicates when the dependencies or maintenance
status of this particular subservice were last modified.

The "label" is a human-readable description of the subservice.

The presence of the "under-maintenance" container inhibits the
emission of symptoms for the subservice and subservices that depend
on them. In that case, a "contact" MUST be provided to indicate who
or which software is responsible for the maintenance. See
Section 3.6 of [RFC9417] for a more detailed discussion.

The "parameter" choice is intended to be augmented in order to
describe parameters that are specific to the current subservice type.
This base module defines only the subservice type representing
service instances. Service instances MUST be modeled as a particular
type of subservice with two parameters: "service" and "instance-
name". The "service" parameter is the name of the service defined in
the network orchestrator, for instance, "point-to-point-l2vpn". The
"instance-name" parameter is the name assigned to the particular
instance to be assured, for instance, the name of the customer using
that instance.

The "health-score" contains a value normally between 0 and 100,
indicating how healthy the subservice is. As mentioned in the health
score definition, the special value -1 can be used to specify that no
value could be computed for that health score, for instance, if some
metric needed for that computation could not be collected.

The "symptoms-history-start" is the cutoff date for reporting
symptoms. Symptoms that were terminated before that date are not
reported anymore in the model.

The status of each subservice contains a list of symptoms. Each
symptom is specified by:

* an identifier "symptom-id", which identifies the symptom locally
to an agent,

* an agent identifier "agent-id", which identifies the agent raising
the symptom,

* a "health-score-weight" specifying the impact to the health score
incurred by this symptom,

* a "start-date-time" indicating when the symptom became active, and

* a "stop-date-time" indicating when the symptom stopped being
active (this field is not present if the symptom is still active).

In order for the pair "agent-id" and "symptom-id" to uniquely
identify a symptom, the following is necessary:

* "agent-id" MUST be unique among all agents of the system.

* "symptom-id" MUST be unique among all symptoms raised by the
agent.

Note that "agent-id" and "symptom-id" are leafrefs pointing to the
objects defined later in the document. While the combination of
"symptom-id" and "agent-id" is sufficient as a unique key list, the
"start-date-time" second key helps to sort and retrieve relevant
symptoms.

The "dependency" list contains the dependencies for the current
subservice. Each of them is specified by a leafref to both "type"
and "id" of the target dependencies. A dependency has a type
indicated in the "dependency-type" field. Two types are specified in
the model:

* Impacting: Such a dependency indicates an impact on the health of
the dependent.

* Informational: Such a dependency might explain why the dependent
has issues but does not impact its health.

To illustrate the difference between "impacting" and "informational",
consider the interface subservice representing a network interface.
If the device to which the network interface belongs goes down, the
network interface will transition to a "down" state as well.
Therefore, the dependency of the interface subservice towards the
device subservice is "impacting". On the other hand, a dependency
towards the ecmp-load subservice, which checks that the load between
ECMPs remains stable throughout time, is only "informational".
Indeed, services might be perfectly healthy even if the load
distribution between ECMPs changed. However, such an instability
might be a relevant symptom for diagnosing the root cause of a
problem.

Within the container "agents", the list "agent" contains the list of
symptoms per agent. The key of the list is the "id", which MUST be
unique among agents of a given assurance system. For each agent, the
list "symptoms-description" maps an "id" to its "description". The
"id" MUST be unique among the symptoms raised by the agent.

Within the container "assured-services", the list "assured-service"
contains the subservices indexed by assured service instances. For
each service type identified by the "service" leaf, all instances of
that service are listed in the "instances" list. For each instance
identified by the "name" leaf, the "subservices" list contains all
descendant subservices that are part of the assurance graph for that
specific instance. These imbricated lists provide a query
optimization to get the list of subservices in that assurance graph
in a single query instead of recursively querying the dependencies of
each subservice, starting from the node representing the service
instance.

The relation between the health score ("health-score") and the
"health-score-weight" of the currently active symptoms is not
explicitly defined in this document. The only requirement is that a
health score that is strictly smaller than 100 (the maximal value)
must be explained by at least one symptom. A way to enforce that
requirement is to first detect symptoms and then compute the health
score based on the "health-score-weight" of the detected symptoms.
As an example, such a computation could be to sum the "health-score-
weight" of the active symptoms, subtract that value from 100, and
change the value to 0 if the result is negative. The relation
between health score and "health-score-weight" is left to the
implementor (of an agent [RFC9417]).

Keeping the history of the graph structure is out of scope for this
YANG module. Only the current version of the assurance graph can be
fetched. In order to keep the history of the graph structure, some
time-series database (TSDB) or similar storage must be used.

3.3. YANG Module

This model contains references to [RFC6991].

<CODE BEGINS> file "[email protected]"
module ietf-service-assurance {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-service-assurance";
prefix sain;

import ietf-yang-types {
prefix yang;
reference
"RFC 6991: Common YANG Data Types";
}

organization
"IETF OPSAWG Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/opsawg/>
WG List: <mailto:[email protected]>
Author: Benoit Claise <mailto:[email protected]>
Author: Jean Quilbeuf <mailto:[email protected]>";
description
"This module defines objects for assuring services based on their
decomposition into so-called subservices, according to the
Service Assurance for Intent-based Networking (SAIN)
architecture.

The subservices hierarchically organized by dependencies
constitute an assurance graph. This module should be supported
by an assurance agent that is able to interact with the devices
in order to produce the health status and symptoms for each
subservice in the assurance graph.

This module is intended for the following use cases:
* Assurance graph configuration:
- Subservices: Configure a set of subservices to assure by
specifying their types and parameters.
- Dependencies: Configure the dependencies between the
subservices, along with their type.
* Assurance telemetry: Export the health statuses of the
subservices, along with the observed symptoms.

Copyright (c) 2023 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).

This version of this YANG module is part of RFC 9418; see the
RFC itself for full legal notices. ";

revision 2023-07-11 {
description
"Initial version.";
reference
"RFC 9418: YANG Modules for Service Assurance";
}

identity subservice-base {
description
"Base identity for subservice types.";
}

identity service-instance-type {
base subservice-base;
description
"Specific type of subservice that represents a service
instance. Instance of this type will depend on other
subservices to build the top of the assurance graph.";
}

identity dependency-type {
description
"Base identity for representing dependency types.";
}

identity informational {
base dependency-type;
description
"Indicates that symptoms of the dependency might be of interest
for the dependent, but the status of the dependency should not
have any impact on the dependent.";
}

identity impacting {
base dependency-type;
description
"Indicates that the status of the dependency directly impacts
the status of the dependent.";
}

grouping subservice-reference {
description
"Reference to a specific subservice identified by its type and
identifier. This grouping is only for internal use in this
module.";
leaf type {
type leafref {
path "/subservices/subservice/type";
}
description
"The type of the subservice to refer to (e.g., device).";
}
leaf id {
type leafref {
path "/subservices/subservice[type=current()/../type]/id";
}
description
"The identifier of the subservice to refer to.";
}
}

grouping subservice-dependency {
description
"Represents a dependency to another subservice. This grouping
is only for internal use in this module";
uses subservice-reference;
leaf dependency-type {
type identityref {
base dependency-type;
}
description
"Represents the type of dependency (e.g., informational or
impacting).";
}
}

leaf assurance-graph-last-change {
type yang:date-and-time;
config false;
mandatory true;
description
"Time and date at which the assurance graph last changed after
any structural changes (dependencies and/or maintenance
windows parameters) are applied to the subservice(s). The
time and date must be the same or more recent than the most
recent value of any changed subservices last-change time and
date.";
}
container subservices {
description
"Root container for the subservices.";
list subservice {
key "type id";
description
"List of configured subservices.";
leaf type {
type identityref {
base subservice-base;
}
description
"Type of the subservice identifying the type of the part
or functionality that is being assured by this list
entry, for instance, interface, device, or
ip-connectivity.";
}
leaf id {
type string;
description
"Identifier of the subservice instance. Must be unique
among subservices of the same type.";
}
leaf last-change {
type yang:date-and-time;
config false;
description
"Date and time at which the structure for this
subservice instance last changed, i.e., dependencies
and/or maintenance windows parameters.";
}
leaf label {
type string;
config false;
description
"Label of the subservice, i.e., text describing what the
subservice is to be displayed on a human interface.

It is not intended for random end users but for
network/system/software engineers that are able to
interpret it. Therefore, no mechanism for language
tagging is needed.";
}
container under-maintenance {
presence "true";
description
"The presence of this container indicates that the current
subservice is under maintenance.";
leaf contact {
type string;
mandatory true;
description
"A string used to model an administratively assigned name
of the resource that is performing maintenance.

It is suggested that this freeform field, which could be
a URI, contains one or more of the following: IP
address, management station name, network manager's
name, location, and/or phone number. It might even
contain the expected maintenance time.

In some cases, the agent itself will be the owner of an
entry. In these cases, this string shall be set to a
string starting with 'monitor'.";
}
}
choice parameter {
mandatory true;
description
"Specify the required parameters per subservice type. Each
module augmenting this module with a new subservice type
that is a new identity based on subservice-base should
augment this choice as well by adding a container
available only if the current subservice type is
the newly added identity.";
container service-instance-parameter {
when "derived-from-or-self(../type,
'sain:service-instance-type')";
description
"Specify the parameters of a service instance.";
leaf service {
type string;
mandatory true;
description
"Name of the service.";
}
leaf instance-name {
type string;
mandatory true;
description
"Name of the instance for that service.";
}
}
// Other modules can augment their own cases into here.
}
leaf health-score {
type int8 {
range "-1 .. 100";
}
config false;
mandatory true;
description
"Score value of the subservice health. A value of 100
means that the subservice is healthy. A value of 0 means
that the subservice is broken. A value between 0 and 100
means that the subservice is degraded. The special value
-1 means that the health score could not be computed.";
}
leaf symptoms-history-start {
type yang:date-and-time;
config false;
description
"Date and time at which the symptom's history starts for
this subservice instance, either because the subservice
instance started at that date and time or because the
symptoms before that were removed due to a garbage
collection process.";
}
container symptoms {
config false;
description
"Symptoms for the subservice.";
list symptom {
key "start-date-time agent-id symptom-id";
unique "agent-id symptom-id";
description
"List of symptoms of the subservice. While the
start-date-time key is not necessary per se, this would
get the entries sorted by start-date-time for easy
consumption.";
leaf symptom-id {
type leafref {
path "/agents/agent[id=current()/../agent-id]"
+ "/symptoms/id";
}
description
"Identifier of the symptom to be interpreted according
to the agent identified by the agent-id.";
}
leaf agent-id {
type leafref {
path "/agents/agent/id";
}
description
"Identifier of the agent raising the current symptom.";
}
leaf health-score-weight {
type uint8 {
range "0 .. 100";
}
description
"The weight to the health score incurred by this
symptom. The higher the value, the more of an impact
this symptom has. If a subservice health score is not
100, there must be at least one symptom with a
health-score-weight larger than 0.";
}
leaf start-date-time {
type yang:date-and-time;
description
"Date and time at which the symptom was detected.";
}
leaf stop-date-time {
type yang:date-and-time;
description
"Date and time at which the symptom stopped being
detected. Must be after the start-date-time. If the
symptom is ongoing, this field should not be
populated.";
}
}
}
container dependencies {
description
"Indicates the set of dependencies of the current
subservice, along with their types.";
list dependency {
key "type id";
description
"List of dependencies of the subservice.";
uses subservice-dependency;
}
}
}
}
container agents {
config false;
description
"Container for the list of agents' symptoms.";
list agent {
key "id";
description
"Contains symptoms of each agent involved in computing the
health status of the current graph. This list acts as a
glossary for understanding the symptom ids returned by each
agent.";
leaf id {
type string;
description
"Id of the agent for which we are defining the symptoms.
This identifier must be unique among all agents.";
}
list symptoms {
key "id";
description
"List of symptoms raised by the current agent that is
identified by the symptom-id.";
leaf id {
type string;
description
"Id of the symptom for the current agent. The agent must
guarantee the unicity of this identifier.";
}
leaf description {
type string;
mandatory true;
description
"Description of the symptom, i.e., text describing what
the symptom is, is to be computer consumable and
displayed on a human interface.

It is not intended for random end users but for
network/system/software engineers that are able to
interpret it. Therefore, no mechanism for language
tagging is needed.";
}
}
}
}
container assured-services {
config false;
description
"Container for the index of assured services.";
list assured-service {
key "service";
description
"Service instances that are currently part of the assurance
graph. The list must contain an entry for every service
that is currently present in the assurance graph. This list
presents an alternate access to the graph stored in
subservices that optimizes querying the assurance graph of
a specific service instance.";
leaf service {
type leafref {
path "/subservices/subservice/service-instance-parameter/"
+ "service";
}
description
"Name of the service.";
}
list instances {
key "name";
description
"Instances of the service. The list must contain
an entry for every instance of the parent service.";
leaf name {
type leafref {
path "/subservices/subservice/service-instance-parameter"
+ "/instance-name";
}
description
"Name of the service instance. The leafref must point to
a service-instance-parameter whose service leaf matches
the parent service.";
}
list subservices {
key "type id";
description
"Subservices that appear in the assurance graph of the
current service instance.

The list must contain the subservice corresponding to
the service instance, i.e., the subservice that
matches the service and instance-name keys.

For every subservice in the list, all subservices listed
as dependencies must also appear in the list.";
uses subservice-reference;
}
}
}
}
}
<CODE ENDS>

3.4. Rejecting Circular Dependencies

The statuses of services and subservices depend on the statuses of
their dependencies, and thus circular dependencies between them
prevent the computation of statuses. Section 3.1.1 of the SAIN
architecture document [RFC9417] discusses how such dependencies
appear and how they could be removed. The responsibility of avoiding
such dependencies falls to the SAIN orchestrator. However, we
specify in this section the expected behavior when a server
supporting the "ietf-service-assurance" module receives a data
instance containing circular dependencies.

Enforcing the absence of circular dependencies as a YANG constraint
falls back to implementing a graph traversal algorithm with XPath and
checking that the current node is not reachable from its
dependencies. Even with such a constraint, there is no guarantee
that merging two graphs without dependency loops will result in a
graph without dependency loops. Indeed, Section 3.1.1 of [RFC9417]
presents an example where merging two graphs without dependency loops
results in a graph with a dependency loop.

Therefore, a server implementing the "ietf-service-assurance" module
MUST check that there is no dependency loop whenever the graph is
modified. A modification creating a dependency loop MUST be
rejected.

4. Guidelines for Defining New Subservice Types

The base YANG module defined in Section 3.3 only defines a single
type of subservice that represent service instances. As explained
above, this model is meant to be augmented so that a variety of
subservices can be used in the assurance graph. In this section, we
propose some guidelines for specifying such extensions at IETF.

The mechanism to add a new subservice type is to define a new module
for that subservice. The module name should start with "ietf-
service-assurance-". The namespace of the module should start with
"urn:ietf:params:xml:ns:yang:ietf-service-assurance-". The prefix of
the module should start with "sain-". For instance, the subservice
type representing the assurance of a device should have:

* the name "ietf-service-assurance-device",

* the namespace "urn:ietf:params:xml:ns:yang:ietf-service-assurance-
device", and

* the prefix "sain-device".

The new module should define:

* a new identity to represent the new type and

* the parameters fully specifying an instance of the new subservice
type.

The new identity should be based on the "subservice-base" identity.
The name of the identity should end with "-type", for instance,
"device-type".

The parameters should be defined in a container named "parameters"
that augments the choice "/subservices/subservice/parameter" from the
main module. The augmentation should be restricted to cases where
the type of the subservice matches the identity representing the new
service type.

We define two subservice types in the next sections: the "device"
subservice type is defined in Section 5 and the "interface"
subservice type is defined is Section 6. These subservices can be
taken as examples of the rules defined in this section.

Vendors can specify their own subservices types by defining the
corresponding modules in their own namespace. An example of such a
vendor-specific module is specified in Appendix A. Vendors can also
augment existing IETF-specified subservices to add their own vendor-
specific information.

5. Subservice Augmentation: "ietf-service-assurance-device" YANG Module

5.1. Tree View

The following tree diagram [RFC8340] provides an overview of the
"ietf-service-assurance-device" module.

module: ietf-service-assurance-device

augment /sain:subservices/sain:subservice/sain:parameter:
+--rw parameters
+--rw device string

A complete tree view of the base module with all augmenting modules
presented in this document is available in Appendix B.3.

5.2. Concepts

As the number of subservices will grow over time, the YANG module is
designed to be extensible. A new subservice type requires the
precise specifications of its type and expected parameters. Let us
illustrate the example of the new device subservice type. As the
name implies, it monitors and reports the device health, along with
some symptoms in case of degradation.

For our device subservice definition, the new identity "device-type"
is specified as an inheritance from the base identity for
subservices. This indicates to the assurance agent that we are now
assuring the health of a device.

The typical parameter for the configuration of the device subservice
is the name of the device that we want to assure. By augmenting the
parameter choice from the "ietf-service-assurance" YANG module for
the case of the "device-type" subservice type, this new parameter is
specified.

5.3. YANG Module

<CODE BEGINS> file "[email protected]"
module ietf-service-assurance-device {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-service-assurance-device";
prefix sain-device;

import ietf-service-assurance {
prefix sain;
reference
"RFC 9418: YANG Modules for Service Assurance";
}

organization
"IETF OPSAWG Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/opsawg/>
WG List: <mailto:[email protected]>
Author: Benoit Claise <mailto:[email protected]>
Author: Jean Quilbeuf <mailto:[email protected]>";
description
"This module augments the ietf-service-assurance module with
support of the device subservice.

Copyright (c) 2023 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).

This version of this YANG module is part of RFC 9418; see the
RFC itself for full legal notices. ";

revision 2023-07-11 {
description
"Initial revision.";
reference
"RFC 9418: YANG Modules for Service Assurance";
}

identity device-type {
base sain:subservice-base;
description
"Identity of device subservice.";
}

augment "/sain:subservices/sain:subservice/sain:parameter" {
when "derived-from-or-self(sain:type, 'device-type')";
description
"Augments the parameter choice from the ietf-service-assurance
module with a case specific to the device subservice.";
container parameters {
description
"Parameters for the device subservice type.";
leaf device {
type string;
mandatory true;
description
"Identifier of the device to monitor. The
identifier (e.g., device id, hostname, or management IP)
depends on the context.";
}
}
}
}
<CODE ENDS>

6. Subservice Augmentation: "ietf-service-assurance-interface" YANG
Module

6.1. Tree View

The following tree diagram [RFC8340] provides an overview of the
"ietf-service-assurance-interface" data model.

module: ietf-service-assurance-interface

augment /sain:subservices/sain:subservice/sain:parameter:
+--rw parameters
+--rw device string
+--rw interface string

A complete tree view of the base module with all augmenting modules
presented in this document is available in Appendix B.3.

6.2. Concepts

For the interface subservice definition, the new interface-type is
specified as an inheritance from the base identity for subservices.
This indicates to the assurance agent that we are now assuring the
health of an interface.

The parameters for the configuration of the interface subservice are
the name of the device and, on that specific device, a specific
interface. These parameters are aligned with the "ietf-interfaces"
model described in [RFC8343], where the name of the interface is the
only key needed to identify an interface on a given device. By
augmenting the parameter choice from the "ietf-service-assurance"
YANG module for the case of the interface-type subservice type, those
two new parameters are specified.

6.3. YANG Module

<CODE BEGINS> file "[email protected]"
module ietf-service-assurance-interface {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-service-assurance-interface";
prefix sain-interface;

import ietf-service-assurance {
prefix sain;
reference
"RFC 9418: YANG Modules for Service Assurance";
}

organization
"IETF OPSAWG Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/opsawg/>
WG List: <mailto:[email protected]>
Author: Benoit Claise <mailto:[email protected]>
Author: Jean Quilbeuf <mailto:[email protected]>";
description
"This module extends the ietf-service-assurance module to add
support for the interface subservice.

It checks whether an interface is healthy.

Copyright (c) 2023 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).

This version of this YANG module is part of RFC 9418; see the
RFC itself for full legal notices. ";

revision 2023-07-11 {
description
"Initial revision.";
reference
"RFC 9418: YANG Modules for Service Assurance";
}

identity interface-type {
base sain:subservice-base;
description
"Checks whether an interface is healthy.";
}

augment "/sain:subservices/sain:subservice/sain:parameter" {
when "derived-from-or-self(sain:type, 'interface-type')";
description
"Augments the parameter choice from ietf-service-assurance
module with a case specific to the interface subservice.";
container parameters {
description
"Parameters for the interface subservice type.";
leaf device {
type string;
mandatory true;
description
"Device supporting the interface.";
}
leaf interface {
type string;
mandatory true;
description
"Name of the interface.";
}
}
}
}
<CODE ENDS>

7. Security Considerations

The YANG modules specified in this document define schema for data
that is designed to be accessed via network management protocols such
as NETCONF [RFC6241] or RESTCONF [RFC8040]. 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.

There are a number of data nodes defined in these YANG modules that
are writable/creatable/deletable (i.e., config true, which is the
default). These data nodes may be considered sensitive or vulnerable
in some network environments. Write operations (e.g., edit-config)
to these data nodes without proper protection can have a negative
effect on network operations. These are the subtrees and data nodes
and their sensitivity/vulnerability:

* /subservices/subservice : By modifying this subtree, one can
modify the structure of the assurance graph, which could alter the
status of the services reported by the assurance framework. On
one hand, modifications can cause the assurance system to report a
service as broken when it is actually healthy (false positive),
resulting in engineers or automation software losing time and
potentially causing real issues by doing unnecessary modifications
on the network. On the other hand, modifications could prevent
the assurance system from reporting actual issues (false
negative), resulting in failures that could have been avoided.
Depending on the service, the impact of these avoidable failures
could be Service-Level Agreement (SLA) violations fees or
disruption of emergency calls.

Some readable data nodes in these YANG modules 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. These are the subtrees and data
nodes and their sensitivity/vulnerability:

* /subservices/subservice

* /agents/agent

* /assured-services/assured-service

Each of these subtrees contains information about services,
subservices, or possible symptoms raised by the agents. The
information contained in this subtree might give information about
the underlying network as well as services deployed for the
customers. For instance, a customer might be given access to monitor
their services status (e.g., via model-driven telemetry). In that
example, the customer access should be restricted to nodes
representing their services so as not to divulge information about
the underlying network structure or others customers services.

8. IANA Considerations

8.1. The IETF XML Registry

IANA has registered the following three URIs in the "IETF XML
Registry" [RFC3688]:

URI: urn:ietf:params:xml:ns:yang:ietf-service-assurance
Registrant Contact: The OPSAWG WG of the IETF.
XML: N/A; the requested URI is an XML namespace.

URI: urn:ietf:params:xml:ns:yang:ietf-service-assurance-device
Registrant Contact: The OPSAWG WG of the IETF.
XML: N/A; the requested URI is an XML namespace.

URI: urn:ietf:params:xml:ns:yang:ietf-service-assurance-interface
Registrant Contact: The OPSAWG WG of the IETF.
XML: N/A; the requested URI is an XML namespace.

8.2. The YANG Module Names Registry

IANA has registered the following three YANG modules in the "YANG
Module Names" registry [RFC7950]:

name: ietf-service-assurance
namespace: urn:ietf:params:xml:ns:yang:ietf-service-assurance
prefix: sain
reference: RFC 9418

name: ietf-service-assurance-device
namespace: urn:ietf:params:xml:ns:yang:ietf-service-assurance-device
prefix: sain-device
reference: RFC 9418

name: ietf-service-assurance-interface
namespace: urn:ietf:params:xml:ns:yang:ietf-service-assurance-
interface
prefix: sain-interface
reference: RFC 9418

These modules are not maintained by IANA.

9. References

9.1. Normative References

[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>.

[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>.

[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<https://www.rfc-editor.org/info/rfc6991>.

[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.

[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>.

[RFC9417] Claise, B., Quilbeuf, J., Lopez, D., Voyer, D., and T.
Arumugam, "Service Assurance for Intent-Based Networking
Architecture", RFC 9417, DOI 10.17487/RFC9417, July 2023,
<https://www.rfc-editor.org/info/rfc9417>.

9.2. 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>.

[RFC8343] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
<https://www.rfc-editor.org/info/rfc8343>.

[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>.

Appendix A. Vendor-Specific Subservice Augmentation: "example-service-
assurance-device-acme" YANG Module

A.1. Tree View

The following tree diagram [RFC8340] provides an overview of the
"example-service-assurance-device-acme" module.

module: example-service-assurance-device-acme

augment /sain:subservices/sain:subservice/sain:parameter:
+--rw parameters
+--rw device string
+--rw acme-specific-parameter string

A complete tree view of the base module with all augmenting modules
presented in this document is available in Appendix B.3.

A.2. Concepts

Under some circumstances, vendor-specific subservice types might be
required. As an example of this vendor-specific implementation, this
section shows how to augment the "ietf-service-assurance-device"
module to add custom support for the device subservice specific to
the Acme Corporation. The specific version adds a new parameter
named "acme-specific-parameter". It's an implementation choice to
either derive a new specific identity from the "subservice-base"
identity defined in the "ietf-service-assurance" module or to augment
the parameters from the "ietf-service-assurance-device" module; here,
we choose to create a new identity.

A.3. YANG Module

module example-service-assurance-device-acme {
yang-version 1.1;
namespace "urn:example:example-service-assurance-device-acme";
prefix example-device-acme;

import ietf-service-assurance {
prefix sain;
reference
"RFC 9418: YANG Modules for Service Assurance";
}
import ietf-service-assurance-device {
prefix sain-device;
reference
"RFC 9418: YANG Modules for Service Assurance";
}

organization
"IETF OPSAWG Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/opsawg/>
WG List: <mailto:[email protected]>
Author: Benoit Claise <mailto:[email protected]>
Author: Jean Quilbeuf <mailto:[email protected]>";
description
"This example module extends the ietf-service-assurance-device
module to add specific support for devices of the Acme
Corporation. ";

revision 2023-07-11 {
description
"Initial revision.";
reference
"RFC 9418: YANG Modules for Service Assurance";
}

identity device-acme-type {
base sain-device:device-type;
description
"Network device is healthy.";
}

augment "/sain:subservices/sain:subservice/sain:parameter" {
when "derived-from-or-self(sain:type, 'device-acme-type')";
description
"Augments the parameter choice from the ietf-service-assurance
module with a case specific to the device-acme subservice.";
container parameters {
description
"Parameters for the device-acme subservice type.";
leaf device {
type string;
mandatory true;
description
"The device to monitor.";
}
leaf acme-specific-parameter {
type string;
mandatory true;
description
"The Acme-Corporation-specific parameter.";
}
}
}
}

Appendix B. Further Augmentations: IP Connectivity and IS-IS
Subservices

In this section, we provide two additional YANG modules to completely
cover the example in Figure 2 from Section 3.1 of [RFC9417]. The two
missing subservice types are IP connectivity and the Intermediate
System to Intermediate System (IS-IS) routing protocol. These
modules are presented as examples; some future work is needed to
propose a more complete version.

B.1. IP Connectivity Module Tree View

That subservice represents the unicast connectivity between two IP
addresses located on two different devices. Such a subservice could
report symptoms such as "No route found". The following tree diagram
[RFC8340] provides an overview of the "example-service-assurance-ip-
connectivity" module.

module: example-service-assurance-ip-connectivity

augment /sain:subservices/sain:subservice/sain:parameter:
+--rw parameters
+--rw device1 string
+--rw address1 inet:ip-address
+--rw device2 string
+--rw address2 inet:ip-address

To specify the connectivity that we are interested in, we specify two
IP addresses and two devices. The subservice assures that the
connectivity between IP address 1 on device 1 and IP address 2 on
device 2 is healthy.

B.2. IS-IS Module Tree View

The following tree diagram [RFC8340] provides an overview of the
"example-service-assurance-is-is" module.

module: example-service-assurance-is-is

augment /sain:subservices/sain:subservice/sain:parameter:
+--rw parameters
+--rw instance-name string

The parameter of this subservice is the name of the IS-IS instance to
assure.

B.3. Global Tree View

The following tree diagram [RFC8340] provides an overview of the
"ietf-service-assurance", "ietf-service-assurance-device", "example-
service-assurance-device-acme", "example-service-assurance-ip-
connectivity", and "example-service-assurance-is-is" modules.

module: ietf-service-assurance
+--ro assurance-graph-last-change yang:date-and-time
+--rw subservices
| +--rw subservice* [type id]
| +--rw type identityref
| +--rw id string
| +--ro last-change?
| | yang:date-and-time
| +--ro label? string
| +--rw under-maintenance!
| | +--rw contact string
| +--rw (parameter)
| | +--:(service-instance-parameter)
| | | +--rw service-instance-parameter
| | | +--rw service string
| | | +--rw instance-name string
| | +--:(example-ip-connectivity:parameters)
| | | +--rw example-ip-connectivity:parameters
| | | +--rw example-ip-connectivity:device1 string
| | | +--rw example-ip-connectivity:address1
| | | | inet:ip-address
| | | +--rw example-ip-connectivity:device2 string
| | | +--rw example-ip-connectivity:address2
| | | inet:ip-address
| | +--:(example-is-is:parameters)
| | | +--rw example-is-is:parameters
| | | +--rw example-is-is:instance-name string
| | +--:(sain-device:parameters)
| | | +--rw sain-device:parameters
| | | +--rw sain-device:device string
| | +--:(example-device-acme:parameters)
| | | +--rw example-device-acme:parameters
| | | +--rw example-device-acme:device
| | | | string
| | | +--rw example-device-acme:acme-specific-parameter
| | | string
| | +--:(sain-interface:parameters)
| | +--rw sain-interface:parameters
| | +--rw sain-interface:device string
| | +--rw sain-interface:interface string
| +--ro health-score int8
| +--ro symptoms-history-start?
| | yang:date-and-time
| +--ro symptoms
| | +--ro symptom* [start-date-time agent-id symptom-id]
| | +--ro symptom-id leafref
| | +--ro agent-id -> /agents/agent/id
| | +--ro health-score-weight? uint8
| | +--ro start-date-time yang:date-and-time
| | +--ro stop-date-time? yang:date-and-time
| +--rw dependencies
| +--rw dependency* [type id]
| +--rw type
| | -> /subservices/subservice/type
| +--rw id leafref
| +--rw dependency-type? identityref
+--ro agents
| +--ro agent* [id]
| +--ro id string
| +--ro symptoms* [id]
| +--ro id string
| +--ro description string
+--ro assured-services
+--ro assured-service* [service]
+--ro service leafref
+--ro instances* [name]
+--ro name leafref
+--ro subservices* [type id]
+--ro type -> /subservices/subservice/type
+--ro id leafref

B.4. IP Connectivity YANG Module

module example-service-assurance-ip-connectivity {
yang-version 1.1;
namespace "urn:example:example-service-assurance-ip-connectivity";
prefix example-ip-connectivity;

import ietf-inet-types {
prefix inet;
reference
"RFC 6991: Common YANG Data Types";
}
import ietf-service-assurance {
prefix sain;
reference
"RFC 9418: YANG Modules for Service Assurance";
}

organization
"IETF OPSAWG Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/opsawg/>
WG List: <mailto:[email protected]>
Author: Benoit Claise <mailto:[email protected]>
Author: Jean Quilbeuf <mailto:[email protected]>";
description
"This example module augments the ietf-service-assurance module
to add support for the subservice ip-connectivity.

It checks whether the IP connectivity between two IP addresses
belonging to two network devices is healthy.";

revision 2023-07-11 {
description
"Initial version.";
reference
"RFC 9418: YANG Modules for Service Assurance";
}

identity ip-connectivity-type {
base sain:subservice-base;
description
"Checks connectivity between two IP addresses.";
}

augment "/sain:subservices/sain:subservice/sain:parameter" {
when "derived-from-or-self(sain:type, 'ip-connectivity-type')";
description
"Augments the parameter choice from the ietf-service-assurance
module with a case specific to the ip-connectivity
subservice.";
container parameters {
description
"Parameters for the ip-connectivity subservice type.";
leaf device1 {
type string;
mandatory true;
description
"Device at the first end of the connection.";
}
leaf address1 {
type inet:ip-address;
mandatory true;
description
"Address at the first end of the connection.";
}
leaf device2 {
type string;
mandatory true;
description
"Device at the second end of the connection.";
}
leaf address2 {
type inet:ip-address;
mandatory true;
description
"Address at the second end of the connection.";
}
}
}
}

B.5. IS-IS YANG Module

module example-service-assurance-is-is {
yang-version 1.1;
namespace "urn:example:example-service-assurance-is-is";
prefix example-is-is;

import ietf-service-assurance {
prefix sain;
reference
"RFC 9418: YANG Modules for Service Assurance";
}

organization
"IETF OPSAWG Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/opsawg/>
WG List: <mailto:[email protected]>
Author: Benoit Claise <mailto:[email protected]>
Author: Jean Quilbeuf <mailto:[email protected]>";
description
"This example module augments the ietf-service-assurance module
to add support for the subservice is-is.

It checks whether an IS-IS instance is healthy.";

revision 2023-07-11 {
description
"Initial version.";
reference
"RFC 9418: YANG Modules for Service Assurance";
}

identity is-is-type {
base sain:subservice-base;
description
"Health of IS-IS routing protocol.";
}

augment "/sain:subservices/sain:subservice/sain:parameter" {
when "derived-from-or-self(sain:type, 'is-is-type')";
description
"Augments the parameter choice from the ietf-service-assurance
module with a case specific to the is-is subservice.";
container parameters {
description
"Parameters for the is-is subservice type.";
leaf instance-name {
type string;
mandatory true;
description
"The instance to monitor.";
}
}
}
}

Appendix C. Example of a YANG Instance

This section contains an example of a YANG instance that conforms to
the YANG modules. The validity of this data instance has been
checked using yangson <https://yangson.labs.nic.cz/>. Yangson
requires a YANG library [RFC8525] to define the complete model
against which the data instance must be validated. In Appendix D, we
provide the JSON library file named "ietf-service-assurance-
library.json", which we used for validation.

Below, we provide the contents of the file
"example_configuration_instance.json", which contains the
configuration data that models Figure 2 from Section 3.1 of
[RFC9417]. The instance can be validated with yangson by using the
invocation "yangson -v example_configuration_instance.json ietf-
service-assurance-library.json", assuming all the files (YANG and
JSON) defined in this document reside in the current folder.

{
"ietf-service-assurance:subservices": {
"subservice": [
{
"type": "service-instance-type",
"id": "simple-tunnel/example",
"service-instance-parameter": {
"service": "simple-tunnel",
"instance-name": "example"
},
"dependencies": {
"dependency": [
{
"type":
"ietf-service-assurance-interface:interface-type",
"id": "interface/peer1/tunnel0",
"dependency-type": "impacting"
},
{
"type":
"ietf-service-assurance-interface:interface-type",
"id": "interface/peer2/tunnel9",
"dependency-type": "impacting"
},
{
"type":
"example-service-assurance-ip-connectivity:ip-connectivity-type",
"id":
"connectivity/peer1/2001:db8::1/peer2/2001:db8::2",
"dependency-type": "impacting"
}
]
}
},
{
"type":
"example-service-assurance-ip-connectivity:ip-connectivity-type",
"id": "connectivity/peer1/2001:db8::1/peer2/2001:db8::2",
"example-service-assurance-ip-connectivity:parameters": {
"device1": "Peer1",
"address1": "2001:db8::1",
"device2": "Peer2",
"address2": "2001:db8::2"
},
"dependencies": {
"dependency": [
{
"type":
"ietf-service-assurance-interface:interface-type",
"id": "interface/peer1/physical0",
"dependency-type": "impacting"
},
{
"type":
"ietf-service-assurance-interface:interface-type",
"id": "interface/peer2/physical5",
"dependency-type": "impacting"
},
{
"type": "example-service-assurance-is-is:is-is-type",
"id": "is-is/instance1",
"dependency-type": "impacting"
}
]
}
},
{
"type": "example-service-assurance-is-is:is-is-type",
"id": "is-is/instance1",
"example-service-assurance-is-is:parameters": {
"instance-name": "instance1"
}
},
{
"type": "ietf-service-assurance-interface:interface-type",
"id": "interface/peer1/tunnel0",
"ietf-service-assurance-interface:parameters": {
"device": "Peer1",
"interface": "tunnel0"
},
"dependencies": {
"dependency": [
{
"type":
"ietf-service-assurance-interface:interface-type",
"id": "interface/peer1/physical0",
"dependency-type": "impacting"
}
]
}
},
{
"type": "ietf-service-assurance-interface:interface-type",
"id": "interface/peer1/physical0",
"ietf-service-assurance-interface:parameters": {
"device": "Peer1",
"interface": "physical0"
},
"dependencies": {
"dependency": [
{
"type": "ietf-service-assurance-device:device-type",
"id": "interface/peer1",
"dependency-type": "impacting"
}
]
}
},
{
"type": "ietf-service-assurance-device:device-type",
"id": "interface/peer1",
"ietf-service-assurance-device:parameters": {
"device": "Peer1"
}
},
{
"type": "ietf-service-assurance-interface:interface-type",
"id": "interface/peer2/tunnel9",
"ietf-service-assurance-interface:parameters": {
"device": "Peer2",
"interface": "tunnel9"
},
"dependencies": {
"dependency": [
{
"type":
"ietf-service-assurance-interface:interface-type",
"id": "interface/peer2/physical5",
"dependency-type": "impacting"
}
]
}
},
{
"type": "ietf-service-assurance-interface:interface-type",
"id": "interface/peer2/physical5",
"ietf-service-assurance-interface:parameters": {
"device": "Peer2",
"interface": "physical5"
},
"dependencies": {
"dependency": [
{
"type": "ietf-service-assurance-device:device-type",
"id": "interface/peer2",
"dependency-type": "impacting"
}
]
}
},
{
"type": "ietf-service-assurance-device:device-type",
"id": "interface/peer2",
"ietf-service-assurance-device:parameters": {
"device": "Peer2"
}
}
]
}
}

Appendix D. YANG Library for Service Assurance

This section provides the JSON encoding of the YANG library [RFC8525]
that lists all modules defined in this document and their
dependencies. This library can be used to validate data instances
using yangson, as explained in the previous section.

{
"ietf-yang-library:modules-state": {
"module-set-id": "ietf-service-assurance@2023-07-11",
"module": [
{
"name": "ietf-service-assurance",
"namespace":
"urn:ietf:params:xml:ns:yang:ietf-service-assurance",
"revision": "2023-07-11",
"conformance-type": "implement"
},
{
"name": "ietf-service-assurance-device",
"namespace":
"urn:ietf:params:xml:ns:yang:ietf-service-assurance-device",
"revision": "2023-07-11",
"conformance-type": "implement"
},
{
"name": "ietf-service-assurance-interface",
"namespace":
"urn:ietf:params:xml:ns:yang:ietf-service-assurance-interface",
"revision": "2023-07-11",
"conformance-type": "implement"
},
{
"name": "example-service-assurance-device-acme",
"namespace":
"urn:example:example-service-assurance-device-acme",
"revision": "2023-07-11",
"conformance-type": "implement"
},
{
"name": "example-service-assurance-is-is",
"namespace": "urn:example:example-service-assurance-is-is",
"revision": "2023-07-11",
"conformance-type": "implement"
},
{
"name": "example-service-assurance-ip-connectivity",
"namespace":
"urn:example:example-service-assurance-ip-connectivity",
"revision": "2023-07-11",
"conformance-type": "implement"
},
{
"name": "ietf-yang-types",
"namespace": "urn:ietf:params:xml:ns:yang:ietf-yang-types",
"revision": "2013-07-05",
"conformance-type": "import"
},
{
"name": "ietf-inet-types",
"namespace": "urn:ietf:params:xml:ns:yang:ietf-inet-types",
"revision": "2013-07-05",
"conformance-type": "import"
}
]
}
}

Acknowledgements

The authors would like to thank Jan Lindblad for his help during the
design of these YANG modules. The authors would like to thank
Stephane Litkowski, Charles Eckel, Mohamed Boucadair, Tom Petch,
Dhruv Dhody, and Rob Wilton for their reviews.

Authors' Addresses

Benoit Claise
Huawei
Email: [email protected]

Jean Quilbeuf
Huawei
Email: [email protected]

Paolo Lucente
NTT
Siriusdreef 70-72
2132 Hoofddorp
Netherlands
Email: [email protected]

Paolo Fasano
TIM S.p.A
via G. Reiss Romoli, 274
10148 Torino
Italy
Email: [email protected]

Thangavelu Arumugam
Consultant
Milpitas, California
United States of America
Email: [email protected]