Guidelines for Characterizing "OAM"
draft-ietf-opsawg-oam-characterization-13

OPS Area Working Group                                      C. Pignataro
Internet-Draft                                      Blue Fern Consulting
Updates: 6291 (if approved)                                    A. Farrel
Intended status: Best Current Practice                Old Dog Consulting
Expires: 23 April 2026                                        T. Mizrahi
                                                                  Huawei
                                                         20 October 2025

                  Guidelines for Characterizing "OAM"
               draft-ietf-opsawg-oam-characterization-13

Abstract

   As the IETF continues to produce and standardize different
   Operations, Administration, and Maintenance (OAM) protocols and
   technologies, various qualifiers and modifiers are prepended to the
   OAM abbreviation.  While, at first glance, the most used appear to be
   well understood, the same qualifier may be interpreted differently in
   different contexts.  A case in point is the qualifiers "in-band" and
   "out-of-band" which have their origins in the radio lexicon, and
   which have been extrapolated into other communication networks.  This
   document recommends not to use these two terms when referring to OAM.

   This document considers some common qualifiers and modifiers that are
   prepended, within the context of packet networks, to the OAM
   abbreviation and lays out guidelines for their use in future IETF
   work.

   This document updates [RFC6291] by adding to the guidelines for the
   use of the term "OAM".  It does not modify any other part of
   [RFC6291].

Status of This Memo

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

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   This Internet-Draft will expire on 23 April 2026.

Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  In-Band and Out-of-Band OAM . . . . . . . . . . . . . . . . .   3
   3.  Terminology and Guidance  . . . . . . . . . . . . . . . . . .   3
     3.1.  Active, Passive, and Hybrid OAM . . . . . . . . . . . . .   4
     3.2.  Path Followed OAM . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Packet Forwarding Treatment OAM . . . . . . . . . . . . .   6
     3.4.  Using Multiple Criteria . . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Examples of the Use of the Term In-Band  . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   It is not uncommon for historical and popular terms to have nuances
   in how they are interpreted or understood.  This was, for example,
   the case with the abbreviation for Operations, Administration, and
   Maintenance, "OAM", and [RFC6291] provided guidelines for its use as
   well as definitions of its constituent parts.

   Characterizations or qualifiers for "OAM" within packet networks
   often encounter similar problems of interpretation, such as with the
   adjective phrases "in-band" and "out-of-band".  This document
   considers some common qualifiers and modifiers that are prepended to
   the OAM abbreviation, and lays out guidelines for their use in future
   IETF work to achieve consistent and unambiguous characterization.

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2.  In-Band and Out-of-Band OAM

   Historically, the terms "in-band" and "out-of-band" were used
   extensively in radio communications as well as in telephony signaling
   [RFC4733].  In both these cases, there is an actual "Band" (i.e., a
   "Channel" or "Frequency") to be within or outside.

   While those terms, useful in their simplicity, continued to be
   broadly used to mean "within something" and "outside something", a
   challenge is presented for IP communications and packet-switched
   networks (PSNs) which do not have a "band" per se, and, in fact, have
   multiple "somethings" that OAM traffic can be carried within or
   outside.  A frequently encountered case is the use of "in-band" to
   mean either In-Data-Packet or on-path.

   Within the IETF, the terms "in-band" and "out-of-band" cannot be
   reliably understood consistently and unambiguously.  Context-specific
   definitions of these terms are inconsistent and therefore cannot be
   generalized.  More importantly, the terms are not self-defining to
   any further extent and cannot be understood by someone exposed to
   them for the first time, since there is no "band" in IP.

   There are many examples of "in-band OAM" and "out-of-band OAM" in
   published RFCs.  For instance, the term "in-band" appears in both
   Virtual Circuit Connectivity Verification (VCCV) [RFC5085] and OAM
   for Deterministic Networking (DetNet) [RFC9551].  While the context
   in each of these documents is clear, the term carries different
   meanings in each case.  These two examples, as well as other examples
   of uses of the term "in-band" in other documents are described in
   Appendix A.

   While interpreting existing documents, it is important to understand
   the semantics of what the term "band" refers to, and to be more
   explicit if those documents are updated.  This document does not
   change the meaning of any terms in any prior RFCs.

3.  Terminology and Guidance

   This document recommends avoiding the terms "in-band" and "out-of-
   band" when referring to OAM.  Instead, it encourages the use of more
   fine-grained and descriptive terminology.  The document also presents
   alternative terms and definitions for use in future IETF documents
   referencing OAM, without precluding the use of other precise,
   descriptive terms that do not rely on the "-band" convention.

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   The terminology presented in this section classifies OAM according to
   three criteria: whether it operates in an active, passive, or hybrid
   mode; whether it follows the same path as data traffic; and whether
   it receives the same treatment as data traffic.

3.1.  Active, Passive, and Hybrid OAM

   [RFC7799] provides clear definitions for active and passive
   performance assessment, enabling the construction of metrics and
   methods to be described as either "Active" or "Passive".  Even though
   [RFC7799] does not explicitly use these terms as modifiers of "OAM",
   they are widely used in practice and are included here for clarity.
   The terms "Active", "Passive" and "Hybrid", as described below, are
   consistent with [RFC7799].  This document does not update or change
   the terms of [RFC7799].

   Active OAM:
      Uses dedicated OAM packets.

   Passive OAM:
      Relies on the observation of one or more existing data packet
      streams and does not use dedicated OAM packets and does not modify
      data packets.

   Hybrid OAM:
      Uses a combination of Active Methods and Passive Methods, which
      may include augmentation or modification of the stream of
      interest.  [RFC7799] makes a distinction between Hybrid Type I,
      referring to a single stream of interest, and Hybrid Type II,
      referring to two or more streams of interest.

   This document defines the term In-Data-Packet OAM as a more specific
   and narrowly scoped instance within the broader category of Hybrid
   OAM.  This new term allows for a more fine-grained classification of
   OAM mechanisms, as the broad category of Hybrid OAM includes a
   diverse set of possible OAM methods.

   In-Data-Packet OAM:
      OAM-related information is carried in the packets that also carry
      the data traffic.  This is a specific case of Hybrid OAM.  It was
      sometimes referred to as "in-band".

   Note that In-Data-Packet OAM is a specific case of Hybrid Type I, as
   it is applied to a single stream of interest.

   The following examples illustrate the terms Active, Passive, Hybrid,
   and In-Data-Packet OAM:

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   *  The MPLS echo request/reply messages [RFC8029] are an example of
      "Active OAM", since they are described as "An MPLS echo request/
      reply is a (possibly MPLS-labeled) IPv4 or IPv6 UDP packet".

   *  Monitoring a packet stream by maintaining counters for the packets
      within the stream is an example of "Passive OAM".

   *  An example of "Hybrid Type I OAM" that is also "In-Data-Packet
      OAM", is an IOAM (In Situ OAM) [RFC9197] trace option that is
      incorporated into data packets of a single stream of interest.
      According to [RFC9197], IOAM '...records OAM information within
      the packet while the packet traverses a particular network domain.
      The term "in situ" refers to the fact that the OAM data is added
      to the data packets rather than being sent within packets
      specifically dedicated to OAM.'

   *  Another example of "Hybrid Type I OAM" that is also "In-Data-
      Packet OAM" is Alternate Marking [RFC9341], when applied to data
      packets of a single stream.  In this case a small number of bits
      in the packet header is used for marking a subset of packets in a
      flow.

   *  An example of "Hybrid Type I OAM" which is not classified as "In-
      Data-Packet OAM" is Direct Loss Measurement [RFC6374], in which
      user packets are not modified by the protocol.  Instead, OAM
      packets are used for carrying information about observed network
      characteristics, namely user packet counter values, allowing for
      packet loss computation.

   *  Another example of "Hybrid Type I OAM" which is not "In-Data-
      Packet OAM" is the case where a packet stream is (actively)
      generated while an existing stream of interest is (passively)
      observed.  This example was introduced in [RFC7799] as a Hybrid
      Type I method.  Extending this example, if the packets of the
      active stream include an IOAM trace option, the method is
      characterized by the more general term, Hybrid Type I.

3.2.  Path Followed OAM

   Path-Congruent OAM:
      The OAM information follows the exact same path as the observed
      data traffic.

   Non-Path-Congruent OAM:
      The OAM information is not guaranteed to follow the exact same
      path as the observed data traffic.  This can also be called Path-
      Incongruent OAM.

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   In this document, the term "path-congruent packets" describes packets
   that follow the exact same path (i.e., traverse the same nodes and
   links) within a network.  Note that this definition does not describe
   how the packets are treated in queues within the nodes on the path.

   An example of "Path-Congruent OAM" is the Virtual Circuit
   Connectivity Verification (VCCV) Type 1 [RFC5085], which was also
   referred to as In-Band VCCV.  The term "congruent" also appears in
   [RFC6669] in the context of path sharing.

3.3.  Packet Forwarding Treatment OAM

   Equal-Forwarding-Treatment OAM:
      The OAM packets receive the same forwarding (e.g., QoS) treatment
      as user data packets.

   Different-Forwarding-Treatment OAM:
      The OAM packets might receive different forwarding (e.g., QoS)
      treatment than user data packets.

   The motivation for Equal-Forwarding-Treatment OAM lies in the desire
   to ensure that OAM packets experience the same network conditions as
   the user data they are intended to monitor.  This includes not only
   traversing the same topological path but also receiving identical
   Quality of Service (QoS) treatment, such as queuing, scheduling, and
   traffic shaping.  When both topological and forwarding treatment
   equivalence are achieved, the OAM packets are said to exhibit fate-
   sharing [RFC7276] with the data traffic.  Fate-sharing ensures that
   any impairments or anomalies affecting the user traffic are also
   reflected in the behavior of the OAM packets, thereby making the
   results of the OAM observations more operationally meaningful and
   actionable.  Without such equivalence, discrepancies in treatment
   could lead to misleading measurements or diagnostics, and even
   inadequate corrective actions, reducing the utility of the OAM
   mechanism for performance monitoring and fault detection.

   An example of "Equal-Forwarding-Treatment OAM" is presented in
   [RFC9551] in the context of DetNet OAM: "it traverses the same set of
   links and interfaces receiving the same QoS and Packet Replication,
   Elimination, and Ordering Functions (PREOF) treatment as the
   monitored DetNet flow".

3.4.  Using Multiple Criteria

   OAM protocols and tools can be classified according to the three
   criteria that were described in the previous sections.  However, not
   all criteria are applicable to all OAM protocols, and not all
   combinations are necessarily possible.

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   When defining a new OAM mechanism or analyzing an existing one, it is
   recommended to explicitly consider which of these criteria are
   applicable and to describe the mechanism accordingly.  As a first
   step, all OAM mechanisms can be classified according to the first
   criterion, as Active, Passive, or Hybrid/In-Data-Packet.  Further
   classification according to the other two criteria should be
   considered on a case-by-case basis.

   In some cases, certain criteria are not relevant, or not all
   combinations are possible.  For example:

   *  Passive OAM relies solely on observing existing data traffic and
      does not generate dedicated OAM packets.  As such, the path
      congruence and forwarding treatment criteria are not relevant,
      since no dedicated OAM packets are exchanged between the
      measurement points.

   *  Non-Path-Congruent OAM, by nature, cannot be Equal-Forwarding-
      Treatment.

   A few examples of OAM classification according to the three criteria
   are presented below:

   *  IP Ping, which uses ICMP Echo messages, can be classified as
      Active OAM.  Since it is not guaranteed to follow the same path or
      receive the same treatment as user data packets, it is classified
      as Non-Path-Congruent and, consequently, as Different-Forwarding-
      Treatment.

   *  When an IOAM trace option [RFC9197] is incorporated in data
      packets it can be classified as In-Data-Packet, Path-Congruent and
      Equal-Forwarding-Treatment.

   *  VCCV [RFC5085], as discussed above, is classified as Active, Path-
      Congruent and Different-Forwarding-Treatment.

   *  MPLS Inferred Loss Measurement [RFC6374] uses specially generated
      test messages, and therefore can be classified as Active.  It is
      also Path-Congruent, and can be deployed either as Equal- or
      Different-Forwarding-Treatment OAM.  MPLS Direct Loss Measurement
      [RFC6374] uses OAM messages that carry counters that count user
      data traffic.  Hence, it is classified as Hybrid Type I OAM, and
      as in the Inferred Loss Measurement, it is Path-Congruent, and can
      be either Equal- or Different-Forwarding-Treatment OAM.

   In measurement protocols, accurate results depend on path congruence
   and equal forwarding treatment.  In contrast, these properties are
   not always required in other OAM protocols.  For example,

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   Bidirectional Forwarding Detection (BFD) control packets are often
   sent with the highest priority, which means they do not adhere to the
   equal forwarding treatment property.

   This multi-dimensional classification enables a more precise and
   consistent understanding of OAM mechanisms.

4.  Security Considerations

   Security is improved when terms are used with precision, and their
   definitions are unambiguous.

5.  IANA Considerations

   This document has no IANA actions.

6.  Acknowledgements

   The creation of this document was triggered when observing one of
   many on-mailing-list discussions of what these terms mean, and how to
   abbreviate them.  Participants on that mailing thread include,
   alphabetically: Adrian Farrel, Alexander Vainshtein, Florian Kauer,
   Frank Brockners, Greg Mirsky, Italo Busi, Loa Andersson, Med
   Boucadair, Michael Richardson, Quan Xiong, Stewart Bryant, Tom Petch,
   Eduard Vasilenko, and Xiao Min.

   The authors wish to thank, chronologically, Hesham Elbakoury, Michael
   Richardson, Stewart Bryant, Greg Mirsky, Med Boucadair, Loa
   Andersson, Thomas Graf, Alex Huang Feng, Xiao Min, Dhruv Dhody, Henk
   Birkholz, Alex Huang Feng, Tom Petch, Roni Even, Tim Chown, Marcus
   Ihlar, Med Boucadair, Benoit Claise, and Chongfeng Xie for their
   thorough review and useful feedback comments that greatly improved
   this document.

7.  References

7.1.  Normative References

   [RFC6291]  Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
              D., and S. Mansfield, "Guidelines for the Use of the "OAM"
              Acronym in the IETF", BCP 161, RFC 6291,
              DOI 10.17487/RFC6291, June 2011,
              <https://www.rfc-editor.org/info/rfc6291>.

7.2.  Informative References

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   [I-D.ietf-raw-architecture]
              Thubert, P., "Reliable and Available Wireless
              Architecture", Work in Progress, Internet-Draft, draft-
              ietf-raw-architecture-30, 25 July 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-raw-
              architecture-30>.

   [I-D.kumar-ippm-ifa]
              Kumar, J., Anubolu, S., Lemon, J., Manur, R., Holbrook,
              H., Ghanwani, A., Cai, D., Ou, H., Li, Y., and X. Wang,
              "Inband Flow Analyzer", Work in Progress, Internet-Draft,
              draft-kumar-ippm-ifa-08, 26 April 2024,
              <https://datatracker.ietf.org/doc/html/draft-kumar-ippm-
              ifa-08>.

   [I-D.song-opsawg-ifit-framework]
              Song, H., Qin, F., Chen, H., Jin, J., and J. Shin,
              "Framework for In-situ Flow Information Telemetry", Work
              in Progress, Internet-Draft, draft-song-opsawg-ifit-
              framework-21, 23 October 2023,
              <https://datatracker.ietf.org/doc/html/draft-song-opsawg-
              ifit-framework-21>.

   [P4-INT-2.1]
              "In-band Network Telemetry (INT) Dataplane Specification,
              Version 2.1", 11 November 2020,
              <https://p4.org/p4-spec/docs/INT_v2_1.pdf>.

   [RFC4733]  Schulzrinne, H. and T. Taylor, "RTP Payload for DTMF
              Digits, Telephony Tones, and Telephony Signals", RFC 4733,
              DOI 10.17487/RFC4733, December 2006,
              <https://www.rfc-editor.org/info/rfc4733>.

   [RFC5085]  Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual
              Circuit Connectivity Verification (VCCV): A Control
              Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085,
              December 2007, <https://www.rfc-editor.org/info/rfc5085>.

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374,
              DOI 10.17487/RFC6374, September 2011,
              <https://www.rfc-editor.org/info/rfc6374>.

   [RFC6669]  Sprecher, N. and L. Fang, "An Overview of the Operations,
              Administration, and Maintenance (OAM) Toolset for MPLS-
              Based Transport Networks", RFC 6669, DOI 10.17487/RFC6669,
              July 2012, <https://www.rfc-editor.org/info/rfc6669>.

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   [RFC7276]  Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
              Weingarten, "An Overview of Operations, Administration,
              and Maintenance (OAM) Tools", RFC 7276,
              DOI 10.17487/RFC7276, June 2014,
              <https://www.rfc-editor.org/info/rfc7276>.

   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <https://www.rfc-editor.org/info/rfc7799>.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [RFC9197]  Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
              Ed., "Data Fields for In Situ Operations, Administration,
              and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
              May 2022, <https://www.rfc-editor.org/info/rfc9197>.

   [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>.

   [RFC9341]  Fioccola, G., Ed., Cociglio, M., Mirsky, G., Mizrahi, T.,
              and T. Zhou, "Alternate-Marking Method", RFC 9341,
              DOI 10.17487/RFC9341, December 2022,
              <https://www.rfc-editor.org/info/rfc9341>.

   [RFC9551]  Mirsky, G., Theoleyre, F., Papadopoulos, G., Bernardos,
              CJ., Varga, B., and J. Farkas, "Framework of Operations,
              Administration, and Maintenance (OAM) for Deterministic
              Networking (DetNet)", RFC 9551, DOI 10.17487/RFC9551,
              March 2024, <https://www.rfc-editor.org/info/rfc9551>.

Appendix A.  Examples of the Use of the Term In-Band

   This appendix provides a few examples of the use of the term "in-
   band".  These are intended to highlight the varying interpretations
   of the term across different contexts, which led to the guidelines in
   this document.

   In-Data-Packet OAM was in some cases referred to as "in-band".
   Initially, "In situ OAM" [RFC9197] was also referred to as "In-band
   OAM", but was renamed due to the overloaded meaning of "In-band OAM".
   Further, [RFC9232] also intertwines the terms "in-band" with "in

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   situ", though [I-D.song-opsawg-ifit-framework] settled on using "in
   Situ".  Other similar uses, including [P4-INT-2.1] and
   [I-D.kumar-ippm-ifa], still use variations of "in-band", "in band",
   or "inband".

   Path-Congruent OAM was sometimes referred to as "in-band".  As
   described in [RFC5085], "The VCCV message travels in-band with the
   Session and follows the exact same path as the user data for the
   session".  The term "in-band" is also used in Section 2 of [RFC6669]
   with the same meaning.  Non-Path-Congruent OAM was referred to in
   [RFC5085] as Out-of-Band.

   The property of "Equal-Forwarding-Treatment" is referred to in
   [RFC9551] as "In-band OAM".  Similarly, the property of "Different-
   Forwarding-Treatment OAM" can be found in the following definition in
   [RFC9551]: "Out-of-band OAM: an active OAM method whose path through
   the DetNet domain may not be topologically identical to the path of
   the monitored DetNet flow, its test packets may receive different QoS
   and/or PREOF treatment, or both."  [I-D.ietf-raw-architecture] uses
   similar text.

Authors' Addresses

   Carlos Pignataro
   Blue Fern Consulting
   United States of America
   Email: cpignata@gmail.com, carlos@bluefern.consulting

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

   Tal Mizrahi
   Huawei
   Matam
   Haifa 3190501
   Israel
   Email: tal.mizrahi.phd@gmail.com

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