wdiff rfc9940.original rfc9940.txt

Network Working Group

Internet Engineering Task Force (IETF) N. Davis, Ed.
Internet-Draft
Request for Comments: 9940 Ciena
Intended status:
Category: Informational A. Farrel, Ed.
Expires: 19 February 2026
ISSN: 2070-1721 Old Dog Consulting
T. Graf
Swisscom
Q. Wu
Huawei
C. Yu
Huawei Technologies
18 August 2025
February 2026

Some Key Terms for Network Fault and Problem Management
draft-ietf-nmop-terminology-23

Abstract

This document sets out some terms that are fundamental to a common
understanding of network fault and problem management within the
IETF.

The purpose of this document is to bring clarity to discussions and
other work related to network fault and problem management, management -- in
particular
particular, to YANG data models and management protocols that report,
make visible, or manage network faults and problems.

Status of This Memo

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

Internet-Drafts are working documents not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Engineering Task Force
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approved by the IESG are candidates for a maximum any level of Internet
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This Internet-Draft will expire on 19 February 2026.
https://www.rfc-editor.org/info/rfc9940.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Usage of Terms . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Context Terminology . . . . . . . . . . . . . . . . . . . 4
3.2. Core Terms . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Other Terms . . . . . . . . . . . . . . . . . . . . . . . 9
4. Workflow Explanations . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Informative References . . . . . . . . . . . . . . . . . . . . . 15
Acknowledgments
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16

1. Introduction

Successful operation of large networks depends on effective network
management. This requires a virtuous circle of network control,
network observability, network analytics, network assurance, and back
to network control. Network fault and problem management [RFC6632]
is an important aspect of network management and control solutions.
It deals with the detection, reporting, inspection, isolation,
correlation, and management of events within the network. The
intention of this document is to focus on those events that have a
negative effect on the network's ability to forward traffic according
to expected behavior and so deliver services, the ability to control
and operate the network, and other faults that reduce the quality or
reliability of the delivered service. The concept of fault and
problem management extends to include actions taken to determine the
causes of problems and to work toward recovery of expected network
behavior.

A number of work efforts within the IETF seek to provide components
of a fault management system, such as YANG data models or management
protocols. It is important that a common terminology is be used so that
there is a clear understanding of how the elements of the management
and control solutions fit together, together and how faults and problems will
be handled.

This document sets out some terms that are fundamental to a common
understanding of network fault and problem management. While
"faults" and "problems" are concepts that apply at all levels of
technology in the Internet, the scope of this document is restricted
to the network layer and below, hence below; hence, this document is specifically
about "network fault and problem management." management". The concept of
"incidents" is also touched on in this document, where an incident
results from one or more problems and is the disruption of a network
service.

Note that some useful terms are defined in [RFC3877] and [RFC8632].
The definitions in this document are informed by those documents, but
they are not dependent on that prior work.

2. Usage of Terms

The terms defined in this document are intended for consistent use
within the IETF in the scope of network fault and problem management.
Where similar concepts are described in other bodies, an attempt has
been made to harmonize with those other descriptions, but there is care is
needed where terms are not used consistently between bodies or where
terms are applied outside the network layer. If other bodies find
the terminology defined in this document useful, they are free to use
it.

The purpose of this document is to define the following terms for use
in other documents. Other terms are defined to enable those
definitions and may also be used by other documents, although that is
not the principal purpose of their definitions here.

* Event
* State
* Fault
* Problem
* Symptom
* Cause
* Alert
* Alarm

When other documents make use of the terms as defined in this
document, it is suggested here that such uses should use
capitalization of the terms as done in this document to help
distinguish them from colloquial uses, uses and should include an early
section listing the terms inherited from this document with a
citation.

3. Terminology

This section contains key terms. It is split into three subsections.

* Section 3.1 contains terms that help to set the context for network
fault and problem management systems.

* Section 3.2 includes specific and detailed core terms that will be
used in other documents that describe elements of the network
fault and problem management systems.

* Section 3.3 provides three further terms that may be helpful.

3.1. Context Terminology

This section includes some terminology that helps describe the
context for the rest of this work. The terms may be viewed as a
cascaded sequence of processes, starting with Network Telemetry and
building to Network Observability. The definitions are deliberately
kept relatively terse. Further documents may expand on these terms
without loss of specificity. Such contextualization (if any) should
be highlighted clearly in those documents.

Network Telemetry: This is defined in [RFC9232] and describes the
process of collecting operational network data categorized
according to the network plane (e.g., layer Layer 3, layer Layer 2, and layer Layer
1) from which it was derived. Data collected through the Network
Telemetry process does not contain any data related to service
definitions (i.e., "intent" per Section 3.1 of [RFC9315]).

Network Monitoring: This is the process of keeping a continuous
record of functions related to a network topology. It involves
tracking various aspects such as traffic patterns, device health,
performance metrics, and overall network behaviour. behavior. This approach
differentiates network monitoring from resource or device
monitoring, which focuses on individual components or resources or components
(Section 3.2).

Network Analytics: This is the process of deriving analytical
insights from operational network data. A process could be
executed by a piece of software, a system, or a human that
analyzes operational data and outputs new analytical data related
to the operational data, data -- for example, a symptom.

Network Observability: This is the process of enabling network
behavioral assessment through analysis of observed operational
network data (logs, alarms, traces, etc.) with the aim of
detecting symptoms of network behavior, and to identify anomalies
and their causes. Network Observability begins with information
gathered using Network Monitoring tools and that may be further
enriched with other operational data. The expected outcome of the
observability processes is identification and analysis of
deviations in observed state versus the expected state of a
network.

Thus, there is a cascaded sequence where the following relationships
apply:

* Network Telemetry is the process of collecting operational data
from a network.

* Network Monitoring is the process of creating/keeping a record of
data gathered in Network Telemetry.

* Network Analytics is the process of deriving insight through the
data recorded in Network Monitoring.

* Network Observability is the process of enabling behavioral
assessment of a network through Network Analytics.

3.2. Core Terms

The terms in this section are presented below in an order that is intended
to flow such that it is possible to gain understanding reading top to
bottom. The figures and explanations in Section 4 may aid
understanding the terms set out here.

Resource: An element of a network system.

* Resource is a recursive concept so that a Resource may be a
collection of other Resources (for example, a network node
comprises a collection of network interfaces).

Characteristic: Observable or measurable aspect or behavior
associated with a Resource.

* A Characteristic may be considered to be built on facts (see
'Value', below) and the contexts and descriptors that identify
and give meaning to the facts.

* The term "Metric" [RFC9417] is another word for a measurable
Characteristic which may also be thought of as analogous to a
'variable'.

Value: A Value is a measure of a Characteristic associated with a Resource. It
may be in the form of a categorization (e.g., high or low), an
integer (e.g., a count or gauge), or a reading of a continuous
variable (e.g., an analog measurement), etc.

Change: In the context of Network Monitoring, a Change is the variation in the
Value of a Characteristic associated with a
Resource and Resource. A Change
may arise over a period of time.

* Not all Changes are noteworthy (i.e., they do not have
Relevance).

* Perception of Change depends upon Detection, the sampling
rate/accuracy/detail, and perspective.

* It may be helpful to qualify this as "Value Change" because the
English word "change" is often heavily used.

Event: The variation in Value of a Characteristic of a Resource at a
distinct moment in time (i.e., the period is negligible).

* Compared with a Change, which may be over a period of time, an
Event happens at a distinct moment in time. Thus, an Event may
be the observation of a Change.

Condition: A Condition is an An interpretation of the Values of a set of one or more
Characteristics of a Resource (with respect to working order or
some other aspect relevant to the Resource
purpose/application), purpose/application) --
for example example, "low available memory". Thus, it is the output of a
function applied to a set of one or more variables.

State: A particular Condition that a Resource has (i.e., it is in a
State) at a specific time. For example, a router may report the
total amount of memory it has, has and how much is free. These are the
Values of two Characteristics of a Resource. These Values can be
interpreted to determine the Condition of the Resource, and that
may determine the State of the router, such as shortage of memory.

* While a State may be observed at a specific moment in time, it
is actually determined by summarizing measurement over time in
a process sometimes called State compression.

* It may be helpful to qualify this as "Resource State" to make
clear the distinction between this and other uses of "state"
such as "protocol state".

* This term may be contrasted with "Operational State" as used in
[RFC8342]. For example, the state of a link might be up/down/
degraded, but the operational state of the link would include a
collection of Values of Characteristics of the link.

Detect (hence Detected, Detection): To notice the presence of
something (State, Change, Event, activity, etc.).

* Hence etc.) and hence also to
notice a Change (from the perspective of an observer such as a
monitoring system).

Relevance: Consideration of an Event, State, or Value (through the
application of policy, relative to a specific perspective, intent,
and in relation to other Events, States, and Values) to determine
whether it is of note to the system that controls or manages the
network. Note, for example, that not all Changes are Relevant.

* This term may also be used as "Relevant Event", "Relevant
State", or "Relevant Value".

Occurrence: A Relevant Event or a particular Relevant Change.

* An Occurrence may be an aggregation or abstraction of multiple
fine-grain
fine-grained Events or Changes.

* An Occurrence may occur at any macro or micro scale because
Resources are a recursive concept, and may be perceived perceived,
depending on the scope of observation (i.e., according to the
level of Resource recursion that is examined). That is,
Occurrences, themselves themselves, are a recursive concept.

Fault: An Occurrence (i.e., an Event or a Change) that is not
desired/required (as it may be indicative of a current or future
undesired State). Thus, a Fault happens at a moment in time. A
Fault can potentially be associated with a Cause. See [RFC8632]
for a more detailed discussion of network faults.

* Note that there is a distinction between a Fault and a Problem
that depends on context. For example, in a connectivity
service where redundancy is present, a link down is a Problem,
but from the perspective of managing the network resources, a
link down is a Fault. Likewise, for example, in a router with
two power supplies, if the backup power supply fails leaving
the primary unprotected, this is a Problem.

Problem: A State that is undesirable and that may require remedial
action. A Problem cannot necessarily be associated with a Cause.
The resolution of a Problem does not necessarily act on the thing
that has the Problem.

* Note that there is a historic aspect to the concept of a
Problem. The current State may be operational, but there could
have been a Fault that is unexplained, and the fact of that
unexplained recent Fault is a Problem.

* Note that while a Problem is unresolved it may continue to
require attention. A record of resolved Problems may be
maintained in a log.

* Note that there may be a State which that is considered to be a
Problem from several perspectives. For example, consider a
"loss of light" State that may cause multiple services to fail.
In this example, a new State (the light recovers) may cause the
Problem to be resolved from one perspective (the services are
operational once more), more) but may leave the Problem as unresolved
(because the loss of light has not been explained). Further,
in this example, there could be another development (the reason
for the temporary loss of light is traced to a microbend in the
fiber that is repaired) resulting in that unresolved Problem
now being resolved. But, in this example, this still leaves a
further Problem unresolved (a microbend occurred, and that
Problem is not resolved until it is understood how it occurred
and a remedy is put in place to prevent recurrence).

Cause: The Events (Detected or otherwise) that gave rise to a Fault/
Problem.

Incident: A (Network) Also referred to as "(Network) Incident". An Incident is
an undesired Occurrence such as an unexpected interruption of a
network service, degradation of the quality of a network service,
or the below-target performance of a network service. An Incident
results from one or more Problems, and a Problem may give rise to
or contribute to one or more Incidents. Greater discussion of
Network Incident relationships, including Customer Incidents and
Incident management, can be found in [I-D.ietf-nmop-network-incident-yang]. [Net-Incident-Mgmt-YANG].

Symptom: An observable Value, Change, State, Event, or Condition
considered as an indication of a Problem or potential Problem.

Anomaly: A (Network) Also referred to as "(Network) Anomaly". An Anomaly is an
unusual or unexpected Event or pattern in network data in the
forwarding plane, control plane, or management plane that deviates
from the normal, expected behavior. See [I-D.ietf-nmop-network-anomaly-architecture] [Net-Anomaly-Arch] for
more details.

Alert: An indication of a Fault.

Alarm: As specified in [RFC8632], an Alarm signifies an undesirable State in
a Resource that requires corrective action. From a management
point of view, an Alarm can be seen as a State in its own right
and the transition to this State may result in an Alert being
issued. The receipt of this Alert may give rise to a continuous
indication (to a human operator) highlighting the potential or
actual presence of a Problem.

3.3. Other Terms

Three other terms may be helpful:

Intermittent: A State that is not continuous, continuous but that keeps
recurring in some time frame.

Transient: A State that is not continuous, continuous and that occurs once in
some time frame.

Recurrent: A Problem that is actively resolved, resolved but that returns.

4. Workflow Explanations

This section aims to add information about the relationship between
the terms defined in Section 3.2 in the context of network fault and
problem management. The text and figures here are for explanation
and are not normative for the definition of terms.

The relationship between Resources and Characteristics is shown in
Figure 1. Note that there is a 1:n relationship between a Network
system and Resources, Resources and between Resources and Characteristics: For
clarity, this is not shown on in the figure for clarity. figure.

Characteristics
^
|
Resources
^
|
Network system

Figure 1: Resources and Characteristics

The Value of a Characteristic of a Resource may change over time.
Specific Changes in Value may be noticed at a specific time (as
digital Changes), Detected, and treated as Events. This is shown on
the left left-hand side of Figure 2.

The center of Figure 2 shows how the Value of a Characteristic may
change over time. The Value may be Detected at specific times or
periodically and give rise to Conditions that are States (and
consequently State Changes).

In practice, the Characteristic may vary in an analog manner over
time as shown on the right-hand side of Figure 2. The Value can be
read or reported (i.e., Detected) periodically leading to analog
Values that may be deemed Relevant Values, or it may be evaluated
over time as shown in Figure 6.

Event State Value
Condition
^ ^ ^
Detect : Detect : Detect :
: : :

^ ^ ^ ^ ^ /\
: : : : : / \
: : : : : /\ / \
__ __ _____ / \/
| | | | /\/
__| |__ ____| |____ /

Change at a time Change over time Change over time

Figure 2: Characteristics and Changes

Figure 3 shows the workflow progress for Events. As noted above, an
Event is a Change in the Value of a Characteristic at a time. The
Event may be evaluated (considering policy, relative to a specific
perspective, with a view to intent, and in relation to other Events,
States, and Values) to determine if it is an Occurrence and possibly
to indicate a Change of State. An Occurrence may be undesirable (a
Fault) and that can cause an Alert to be generated, may be evidence
of a Problem and could directly indicate a Cause. In some cases, an
Alert may give rise to an Alarm highlighting the potential or actual
presence of a Problem.

Alert - - - > Alarm
^
|
| -----> Cause
| |
|----------> Problem
|
|
Fault
^
|
|
|
Occurrence
^
|
|----------> State
|
|
Event

Figure 3: Event and Dependent Terms

Parallel to the workflow for Events, Figure 4 shows the workflow
progress for States. As shown in Figure 2, Change noted at a
particular time gives rise to State. The State may be deemed to have
Relevance considering policy, relative to a specific perspective,
with a view to intent, and in relation to other Events, States, and
Values. A Relevant State may be deemed a Problem, or it may indicate
a Problem or potential Problem.

Problems may be considered based on Symptoms and may map directly or
indirectly to Causes. An Incident results from one or more Problems.
An Alarm may be raised as the result of a Problem, and the transition
to an Alarmed state may give rise to an Alert.

Alarm - - -> Alert
^
| ------> Incident
| |
| | ---> Cause
| | |
Problem---------> Symptom
^
|
| Relevance
|
|
State

Figure 4: State and Dependent Terms

Figure 5 shows how Faults and Problems may be consolidated to
determine the Causes. The arrows show how one item may give rise to
another.

A Cause can be indicated by or determined from Faults, Problems, and
Symptoms. It may be that one Cause points to another, and it can
also be considered as a Symptom. The determination of Causes can
consider multiple inputs. An Incident results from one or more
Problems.

---------
------------- | |
| ----------> | Symptom |
| | | |
| | ---------
v | ^
--------- |
------->| Cause |<--------- |
| --------- | |
| ^ | | |
| | | | |
| --- | |
| | |
--------- --------- ----------
| Fault |------------------->| Problem |------->| Incident |
--------- --------- ----------

Figure 5: Consolidation of Symptoms and Causes

Figure 6 shows how thresholds are important in the consideration of
analog Values and Events. The arrows in the figure show how one item
may give rise to or utilize another. The use of threshold-driven
Events and States (and the Alerts that they might give rise to) must
be treated with caution to dampen any "flapping" (so that consistent
States may be observed) and to avoid overwhelming management
processes or systems. Analog Values may be read or notified from the
Resource and could transition a threshold, be deemed Relevant Values,
or be evaluated over time. Events may be counted, and the Count may
cross a threshold or reach a Relevant Value.

The Threshold Process may be implementation-specific implementation specific and subject to
policies. When a threshold is crossed and any other conditions are
matched, an Event may be determined, determined and may be treated like any other
Event.

Occurrence
^
|
|---------------------> State
|
| ------- Relevance
|------>| Count |-----------------------------> Value
| ------- | ^
| | | |
| | | | Relevance
| | v |
| | ----------- ----------------
Event | | Evaluated | | |
^ | | over time |<--------| Analog Value |
| v ----------- | |
| ----------- | | |
| | Threshold | | | |
|<----| Process |<------ | |
| | |<----------------------| |
| ----------- ----------------
| ^
| |
| Detect Detect |
| |
Change at a Time Change over Time

Figure 6: Counts, Thresholds, and Values

5. Security Considerations

This document specifies terminology and has no direct effect on the
security of implementations or deployments. However, protocol
solutions and management models need to be aware of several aspects:

* The exposure of information pertaining to Faults and Problems may
make available knowledge of the internal workings of a network (in
particular
particular, its vulnerabilities) that may be of use to an
attacker.

* Systems that generate management information (messages,
notifications, etc.) when Faults occur, occur may be attacked by causing
them to generate so much information that the system that manages
the network is swamped and unable to properly manage the network.

* Reporting false information about Faults (or masking reports of
Faults) may cause the system that manages the network to function
incorrectly.

6. Privacy Considerations

Network fault and problem management should preserve user privacy by
not exposing user data or information about end-user activities.

Network Telemetry involves observing network traffic and collecting
operational data from the network, while Network Monitoring is the
process of keeping records of data gathered in Network Telemetry.
Therefore, it is possible that the data observed and collected
includes users' privacy information. Such information must be
protected and controlled to avoid exposure to unauthorised unauthorized parties.
Particular care may need to be exercised over stores of such
information which that might be accessed at any time (including far into
the future).

Additionally, a network operator will be concerned to keep about keeping
control of all information about Faults to protect their own privacy
and the details of how they operate their network.

7. IANA Considerations

This document makes has no requests for IANA action.

Acknowledgments

The authors would like to thank Med Boucadair, Wanting Du, Joe
Clarke, Javier Antich, Benoit Claise, Christopher Janz, Sherif
Mostafa, Kristian Larsson, Dirk Hugo, Carsten Bormann, Hilarie Orman,
Stewart Bryant, Bo Wu, Paul Kyzivat, Jouni Korhonen, Reshad Rahman,
Rob Wilton, Mahesh Jethanandani, Tim Bray, Paul Aitken, and Deb
Cooley for their helpful comments.

Special thanks to the team that met at a side meeting at IETF-120 to
discuss some of the thorny issues:

* Benoit Claise
* Watson Ladd
* Brad Peters
* Bo Wu
* Georgios Karagiannis
* Olga Havel
* Vincenzo Riccobene
* Yi Lin
* Jie Dong
* Aihua Guo
* Thomas Graf
* Qin Wu
* Chaode Yu
* Adrian Farrel actions.

8. Informative References

[I-D.ietf-nmop-network-anomaly-architecture]

[Net-Anomaly-Arch]
Graf, T., Du, W., Francois, P., and A. H. Huang Feng, "A
Framework for a Network Anomaly Detection Architecture",
Work in Progress, Internet-Draft, draft-ietf-nmop-network-
anomaly-architecture-04, 4 July
anomaly-architecture-06, 21 November 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-nmop-
network-anomaly-architecture-04>.

[I-D.ietf-nmop-network-incident-yang]
network-anomaly-architecture-06>.

[Net-Incident-Mgmt-YANG]
Hu, T., Contreras, L. M., Wu, Q., Davis, N., and C. Feng,
"A YANG Data Model for Network Incident Management", Work
in Progress, Internet-Draft, draft-ietf-nmop-network-
incident-yang-05, 6 July 2025,
incident-yang-08, 13 February 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-nmop-
network-incident-yang-05>.
network-incident-yang-08>.

[RFC3877] Chisholm, S. and D. Romascanu, "Alarm Management
Information Base (MIB)", RFC 3877, DOI 10.17487/RFC3877,
September 2004, <https://www.rfc-editor.org/info/rfc3877>.

[RFC6632] Ersue, M., Ed. and B. Claise, "An Overview of the IETF
Network Management Standards", RFC 6632,
DOI 10.17487/RFC6632, June 2012,
<https://www.rfc-editor.org/info/rfc6632>.

[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>.

[RFC8632] Vallin, S. and M. Bjorklund, "A YANG Data Model for Alarm
Management", RFC 8632, DOI 10.17487/RFC8632, September
2019, <https://www.rfc-editor.org/info/rfc8632>.

[RFC9232] Song, H., Qin, F., Martinez-Julia, P., Ciavaglia, L., and
A. Wang, "Network Telemetry Framework", RFC 9232,
DOI 10.17487/RFC9232, May 2022,
<https://www.rfc-editor.org/info/rfc9232>.

[RFC9315] Clemm, A., Ciavaglia, L., Granville, L. Z., and J.
Tantsura, "Intent-Based Networking - Concepts and
Definitions", RFC 9315, DOI 10.17487/RFC9315, October
2022, <https://www.rfc-editor.org/info/rfc9315>.

[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>.

Acknowledgments

Special thanks to the team that met at a side meeting at IETF 120 to
discuss some of the thorny issues:

* Benoit Claise
* Watson Ladd
* Brad Peters
* Bo Wu
* Georgios Karagiannis
* Olga Havel
* Vincenzo Riccobene
* Yi Lin
* Jie Dong
* Aihua Guo
* Thomas Graf
* Qin Wu
* Chaode Yu
* Adrian Farrel

Authors' Addresses

Nigel Davis (editor)
Ciena
United Kingdom
Email: ndavis@ciena.com

Adrian Farrel (editor)
Old Dog Consulting
United Kingdom
Email: adrian@olddog.co.uk

Thomas Graf
Swisscom
Binzring 17
CH-8045 Zurich
Switzerland
Email: thomas.graf@swisscom.com

Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing
Jiangsu, 210012
China
Email: bill.wu@huawei.com

Chaode Yu
Huawei Technologies
Email: yuchaode@huawei.com