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rfc:rfc9326



Internet Engineering Task Force (IETF) H. Song Request for Comments: 9326 Futurewei Category: Standards Track B. Gafni ISSN: 2070-1721 Nvidia

                                                          F. Brockners
                                                                 Cisco
                                                           S. Bhandari
                                                           Thoughtspot
                                                            T. Mizrahi
                                                                Huawei
                                                         November 2022
 In Situ Operations, Administration, and Maintenance (IOAM) Direct
                             Exporting

Abstract

 In situ Operations, Administration, and Maintenance (IOAM) is used
 for recording and collecting operational and telemetry information.
 Specifically, IOAM allows telemetry data to be pushed into data
 packets while they traverse the network.  This document introduces a
 new IOAM option type (denoted IOAM-Option-Type) called the "IOAM
 Direct Export (DEX) Option-Type".  This Option-Type is used as a
 trigger for IOAM data to be directly exported or locally aggregated
 without being pushed into in-flight data packets.  The exporting
 method and format are outside the scope of this document.

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/rfc9326.

Copyright Notice

 Copyright (c) 2022 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
 2.  Conventions
   2.1.  Requirements Language
   2.2.  Terminology
 3.  The Direct Exporting (DEX) IOAM-Option-Type
   3.1.  Overview
     3.1.1.  DEX Packet Selection
     3.1.2.  Responding to the DEX Trigger
   3.2.  The DEX Option-Type Format
 4.  IANA Considerations
   4.1.  IOAM Type
   4.2.  IOAM DEX Flags
   4.3.  IOAM DEX Extension-Flags
 5.  Performance Considerations
 6.  Security Considerations
 7.  References
   7.1.  Normative References
   7.2.  Informative References
 Appendix A.  Notes about the History of This Document
 Acknowledgments
 Contributors
 Authors' Addresses

1. Introduction

 IOAM [RFC9197] is used for monitoring traffic in the network and for
 incorporating IOAM data fields (denoted IOAM-Data-Fields) into in-
 flight data packets.
 IOAM makes use of four possible IOAM-Option-Types, defined in
 [RFC9197]: Pre-allocated Trace, Incremental Trace, Proof of Transit
 (POT), and Edge-to-Edge.
 This document defines a new IOAM-Option-Type called the "IOAM Direct
 Export (DEX) Option-Type".  This Option-Type is used as a trigger for
 IOAM nodes to locally aggregate and process IOAM data and/or to
 export it to a receiving entity (or entities).  Throughout the
 document, this functionality is referred to as "collection" and/or
 "exporting".  In this context, a "receiving entity" is an entity that
 resides within the IOAM domain such as a collector, analyzer,
 controller, decapsulating node, or software module in one of the IOAM
 nodes.
 Note that even though the IOAM-Option-Type is called "Direct Export",
 it depends on the deployment whether the receipt of a packet with a
 DEX Option-Type leads to the creation of another packet.  Some
 deployments might simply use the packet with the DEX Option-Type to
 trigger local processing of Operations, Administration, and
 Maintenance (OAM) data.  The functionality of this local processing
 is not within the scope of this document.

2. Conventions

2.1. Requirements Language

 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.

2.2. Terminology

 Abbreviations used in this document:
 IOAM:   In situ Operations, Administration, and Maintenance
 OAM:    Operations, Administration, and Maintenance [RFC6291]
 DEX:    Direct Exporting

3. The Direct Exporting (DEX) IOAM-Option-Type

3.1. Overview

 The DEX Option-Type is used as a trigger for collecting IOAM data
 locally or exporting it to a receiving entity (or entities).
 Specifically, the DEX Option-Type can be used as a trigger for
 collecting IOAM data by an IOAM node and locally aggregating it;
 thus, this aggregated data can be periodically pushed to a receiving
 entity or pulled by a receiving entity on-demand.
 This Option-Type is incorporated into data packets by an IOAM
 encapsulating node and removed by an IOAM decapsulating node, as
 illustrated in Figure 1.  The Option-Type can be read, but not
 modified, by transit nodes.  Note that the terms "IOAM encapsulating
 node", "IOAM decapsulating node", and "IOAM transit node" are as
 defined in [RFC9197].
                                    ^
                                    |Exported IOAM data
                                    |
                                    |
                                    |
              +--------------+------+-------+--------------+
              |              |              |              |
              |              |              |              |
User      +---+----+     +---+----+     +---+----+     +---+----+
packets   |Encapsu-|     | Transit|     | Transit|     |Decapsu-|
--------->|lating  |====>| Node   |====>| Node   |====>|lating  |---->
          |Node    |     | A      |     | B      |     |Node    |
          +--------+     +--------+     +--------+     +--------+
          Insert DEX       Export         Export       Remove DEX
          option and      IOAM data      IOAM data     option and
          export data                                  export data
                      Figure 1: DEX Architecture
 The DEX Option-Type is used as a trigger to collect and/or export
 IOAM data.  The trigger applies to transit nodes, the decapsulating
 node, and the encapsulating node:
  • An IOAM encapsulating node configured to incorporate the DEX

Option-Type encapsulates the packets (or possibly a subset of the

    packets) it forwards with the DEX Option-Type and MAY export and/
    or collect the requested IOAM data immediately.  Only IOAM
    encapsulating nodes are allowed to add the DEX Option-Type to a
    packet.  An IOAM encapsulating node can generate probe packets
    that incorporate the DEX Option-Type.  These probe packets can be
    generated periodically or on-demand (for example, triggered by the
    management plane).  The specification of such probe packets is
    outside the scope of this document.
  • A transit node that processes a packet with the DEX Option-Type

MAY export and/or collect the requested IOAM data.

  • An IOAM decapsulating node that processes a packet with the DEX

Option-Type MAY export and/or collect the requested IOAM data and

    MUST decapsulate the IOAM header.
 As in [RFC9197], the DEX Option-Type can be incorporated into all or
 a subset of the traffic that is forwarded by the encapsulating node,
 as further discussed in Section 3.1.1.  Moreover, IOAM nodes respond
 to the DEX trigger by exporting and/or collecting IOAM data either
 for all traversing packets that carry the DEX Option-Type or
 selectively only for a subset of these packets, as further discussed
 in Section 3.1.2.

3.1.1. DEX Packet Selection

 If an IOAM encapsulating node incorporates the DEX Option-Type into
 all the traffic it forwards, it may lead to an excessive amount of
 exported data, which may overload the network and the receiving
 entity.  Therefore, an IOAM encapsulating node that supports the DEX
 Option-Type MUST support the ability to incorporate the DEX Option-
 Type selectively into a subset of the packets that are forwarded by
 the IOAM encapsulating node.
 Various methods of packet selection and sampling have been previously
 defined, such as [RFC7014] and [RFC5475].  Similar techniques can be
 applied by an IOAM encapsulating node to apply DEX to a subset of the
 forwarded traffic.
 The subset of traffic that is forwarded or transmitted with a DEX
 Option-Type SHOULD NOT exceed 1/N of the interface capacity on any of
 the IOAM encapsulating node's interfaces.  It is noted that this
 requirement applies to the total traffic that incorporates a DEX
 Option-Type, including traffic that is forwarded by the IOAM
 encapsulating node and probe packets that are generated by the IOAM
 encapsulating node.  In this context, N is a parameter that can be
 configurable by network operators.  If there is an upper bound, M, on
 the number of IOAM transit nodes in any path in the network, then it
 is RECOMMENDED to use an N such that N >> M (i.e., N is much greater
 than M).  The rationale is that a packet that includes a DEX Option-
 Type may trigger an exported packet from each IOAM transit node along
 the path for a total of M exported packets.  Thus, if N >> M, then
 the number of exported packets is significantly lower than the number
 of data packets forwarded by the IOAM encapsulating node.  If there
 is no prior knowledge about the network topology or size, it is
 RECOMMENDED to use N>100.

3.1.2. Responding to the DEX Trigger

 The DEX Option-Type specifies which IOAM-Data-Fields should be
 exported and/or collected, as specified in Section 3.2.  As mentioned
 above, the data can be locally collected, aggregated, and/or exported
 to a receiving entity proactively or on-demand.  If IOAM data is
 exported, the format and encapsulation of the packet that contains
 the exported data is not within the scope of the current document.
 For example, the export format can be based on [IOAM-RAWEXPORT].
 An IOAM node that performs DEX-triggered exporting MUST support the
 ability to limit the rate of the exported packets.  The rate of
 exported packets SHOULD be limited so that the number of exported
 packets is significantly lower than the number of packets that are
 forwarded by the device.  The exported data rate SHOULD NOT exceed 1/
 N of the interface capacity on any of the IOAM node's interfaces.  It
 is RECOMMENDED to use N>100.  Depending on the IOAM node's
 architecture considerations, the export rate may be limited to a
 lower number in order to avoid loading the IOAM node.  An IOAM node
 MAY maintain a counter or a set of counters that count the events in
 which the IOAM node receives a packet with the DEX Option-Type and
 does not collect and/or export data due to the rate limits.
 IOAM nodes SHOULD NOT be configured to export packets over a path or
 a tunnel that is subject to IOAM direct exporting.  Furthermore, IOAM
 encapsulating nodes that can identify a packet as an IOAM exported
 packet MUST NOT push a DEX Option-Type into such a packet.  This
 requirement is intended to prevent nested exporting and/or exporting
 loops.
 A transit or decapsulating IOAM node that receives an unknown IOAM-
 Option-Type ignores it (as defined in [RFC9197]); specifically, nodes
 that do not support the DEX Option-Type ignore it.  As per [RFC9197],
 note that a decapsulating node removes the IOAM encapsulation and all
 its IOAM-Option-Types.  Specifically, this applies to the case where
 one of these options is a (possibly unknown) DEX Option-Type.  The
 ability to skip over a (possibly unknown) DEX Option-Type in the
 parsing or in the decapsulation procedure is dependent on the
 specific encapsulation, which is outside the scope of this document.
 For example, when IOAM is encapsulated in IPv6 [IOAM-IPV6-OPTIONS],
 the DEX Option-Type is incorporated either in a Hop-by-Hop options
 header or in a Destination options header; thus, it can be skipped
 using the length field in the options header.

3.2. The DEX Option-Type Format

 The format of the DEX Option-Type is depicted in Figure 2.  The
 length of the DEX Option-Type is at least 8 octets.  The DEX Option-
 Type MAY include one or more optional fields.  The existence of the
 optional fields is indicated by the corresponding flags in the
 Extension-Flags field.  Two optional fields are defined in this
 document: the Flow ID and Sequence Number fields.  Every optional
 field MUST be exactly 4 octets long.  Thus, the Extension-Flags field
 explicitly indicates the length of the DEX Option-Type.  Defining a
 new optional field requires an allocation of a corresponding flag in
 the Extension-Flags field, as specified in Section 4.2.
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Namespace-ID           |     Flags     |Extension-Flags|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               IOAM-Trace-Type                 |   Reserved    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Flow ID (Optional)                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Sequence Number  (Optional)               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    Figure 2: DEX Option-Type Format
 Namespace-ID:
    A 16-bit identifier of the IOAM namespace, as defined in
    [RFC9197].
 Flags:
    An 8-bit field, comprised of 8 1-bit subfields.  Flags are
    allocated by IANA, as defined in Section 4.2.
 Extension-Flags:
    An 8-bit field, comprised of 8 1-bit subfields.  Extension-Flags
    are allocated by IANA, as defined in Section 4.3.  Every bit in
    the Extension-Flag field that is set to 1 indicates the existence
    of a corresponding optional 4-octet field.  An IOAM node that
    receives a DEX Option-Type with an unknown flag set to 1 MUST
    ignore the corresponding optional field.
 IOAM-Trace-Type:
    A 24-bit identifier that specifies which IOAM-Data-Fields should
    be exported.  The format of this field is as defined in [RFC9197].
    Specifically, the bit that corresponds to the Checksum Complement
    IOAM-Data-Field SHOULD be assigned to be zero by the IOAM
    encapsulating node and ignored by transit and decapsulating nodes.
    The reason for this is that the Checksum Complement is intended
    for in-flight packet modifications and is not relevant for direct
    exporting.
 Reserved:
    This field MUST be ignored by the receiver.
 Optional fields:
    The optional fields, if present, reside after the Reserved field.
    The order of the optional fields is according to the order of the
    respective bits, starting from the most significant bit, that are
    enabled in the Extension-Flags field.  Each optional field is 4
    octets long.
    Flow ID:
       An optional 32-bit field representing the flow identifier.  If
       the actual Flow ID is shorter than 32 bits, it is zero padded
       in its most significant bits.  The field is set at the
       encapsulating node.  The Flow ID can be used to correlate the
       exported data of the same flow from multiple nodes and from
       multiple packets.  Flow ID values are expected to be allocated
       in a way that avoids collisions.  For example, random
       assignment of Flow ID values can be subject to collisions,
       while centralized allocation can avoid this problem.  The
       specification of the Flow ID allocation method is not within
       the scope of this document.
    Sequence Number:
       An optional 32-bit sequence number starting from 0 and
       incremented by 1 for each packet from the same flow at the
       encapsulating node that includes the DEX option.  The Sequence
       Number, when combined with the Flow ID, provides a convenient
       approach to correlate the exported data from the same user
       packet.

4. IANA Considerations

4.1. IOAM Type

 The "IOAM Option-Type" registry is defined in Section 7.1 of
 [RFC9197].  IANA has allocated the following code point from the
 "IOAM Option-Type" registry as follows:
 Code Point:  4
 Name  IOAM Direct Export (DEX) Option-Type
 Description:  Direct exporting
 Reference:  This document

4.2. IOAM DEX Flags

 IANA has created the "IOAM DEX Flags" registry.  This registry
 includes 8 flag bits.  Allocation is based on the "IETF Review"
 procedure defined in [RFC8126].
 New registration requests MUST use the following template:
 Bit:  Desired bit to be allocated in the 8-bit Flags field of the DEX
    Option-Type.
 Description:  Brief description of the newly registered bit.
 Reference:  Reference to the document that defines the new bit.

4.3. IOAM DEX Extension-Flags

 IANA has created the "IOAM DEX Extension-Flags" registry.  This
 registry includes 8 flag bits.  Bit 0 (the most significant bit) and
 bit 1 in the registry are allocated by this document and described in
 Section 3.2.  Allocation of the other bits should be performed based
 on the "IETF Review" procedure defined in [RFC8126].
 Bit 0:  "Flow ID [RFC9326]"
 Bit 1:  "Sequence Number [RFC9326]"
 New registration requests MUST use the following template:
 Bit:  Desired bit to be allocated in the 8-bit Extension-Flags field
    of the DEX Option-Type.
 Description:  Brief description of the newly registered bit.
 Reference:  Reference to the document that defines the new bit.

5. Performance Considerations

 The DEX Option-Type triggers IOAM data to be collected and/or
 exported packets to be exported to a receiving entity (or entities).
 In some cases, this may impact the receiving entity's performance or
 the performance along the paths leading to it.
 Therefore, the performance impact of these exported packets is
 limited by taking two measures: at the encapsulating nodes by
 selective DEX encapsulation (Section 3.1.1) and at the transit nodes
 by limiting exporting rate (Section 3.1.2).  These two measures
 ensure that direct exporting is used at a rate that does not
 significantly affect the network bandwidth and does not overload the
 receiving entity.  Moreover, it is possible to load balance the
 exported data among multiple receiving entities, although the
 exporting method is not within the scope of this document.
 It should be noted that, in some networks, DEX data may be exported
 over an out-of-band network in which a large volume of exported
 traffic does not compromise user traffic.  In this case, an operator
 may choose to disable the exporting rate limiting.

6. Security Considerations

 The security considerations of IOAM in general are discussed in
 [RFC9197].  Specifically, an attacker may try to use the
 functionality that is defined in this document to attack the network.
 An attacker may attempt to overload network devices by injecting
 synthetic packets that include the DEX Option-Type.  Similarly, an
 on-path attacker may maliciously incorporate the DEX Option-Type into
 transit packets or maliciously remove it from packets in which it is
 incorporated.
 Forcing DEX, either in synthetic packets or in transit packets, may
 overload the IOAM nodes and/or the receiving entity (or entities).
 Since this mechanism affects multiple devices along the network path,
 it potentially amplifies the effect on the network bandwidth, the
 storage of the devices that collect the data, and the receiving
 entity's load.
 The amplification effect of DEX may be worse in wide area networks in
 which there are multiple IOAM-Domains.  For example, if DEX is used
 in IOAM-Domain 1 for exporting IOAM data to a receiving entity, then
 the exported packets of IOAM-Domain 1 can be forwarded through IOAM-
 Domain 2, in which they are subject to DEX.  In turn, the exported
 packets of IOAM-Domain 2 may be forwarded through another IOAM domain
 (or through IOAM-Domain 1); theoretically, this recursive
 amplification may continue infinitely.
 In order to mitigate the attacks described above, the following
 requirements (Section 3) have been defined:
  • Selective DEX (Section 3.1.1) is applied by IOAM encapsulating

nodes in order to limit the potential impact of DEX attacks to a

    small fraction of the traffic.
  • Rate limiting of exported traffic (Section 3.1.2) is applied by

IOAM nodes in order to prevent overloading attacks and to

    significantly limit the scale of amplification attacks.
  • IOAM encapsulating nodes are required to avoid pushing the DEX

Option-Type into IOAM exported packets (Section 3.1.2), thus

    preventing some of the amplification and export loop scenarios.
 Although the exporting method is not within the scope of this
 document, any exporting method MUST secure the exported data from the
 IOAM node to the receiving entity in order to protect the
 confidentiality and guarantee the integrity of the exported data.
 Specifically, an IOAM node that performs DEX exporting MUST send the
 exported data to a pre-configured trusted receiving entity that is in
 the same IOAM-Domain as the exporting IOAM node.  Furthermore, an
 IOAM node MUST gain explicit consent to export data to a receiving
 entity before starting to send exported data.
 An attacker may keep track of the information sent in DEX headers as
 a means of reconnaissance.  This form of recon can be mitigated to
 some extent by careful allocation of the Flow ID and Sequence Number
 space in a way that does not compromise privacy aspects, such as
 customer identities.
 The integrity of the DEX Option-Type can be protected through a
 mechanism of the encapsulating protocol.  While [IOAM-DATA-INTEGRITY]
 introduces an integrity protection mechanism that protects the
 integrity of IOAM-Data-Fields, the DEX Option-Type does not include
 IOAM-Data-Fields; therefore, these integrity protection mechanisms
 are not applicable to the DEX Option-Type.  As discussed in the
 threat analysis of [IOAM-DATA-INTEGRITY], injection or modification
 of IOAM-Option-Type headers are threats that are not addressed in
 IOAM.
 IOAM is assumed to be deployed in a restricted administrative domain,
 thus limiting the scope of the threats above and their effect.  This
 is a fundamental assumption with respect to the security aspects of
 IOAM, as further discussed in [RFC9197].

7. References

7.1. 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>.
 [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>.
 [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>.

7.2. Informative References

 [IOAM-DATA-INTEGRITY]
            Brockners, F., Bhandari, S., Mizrahi, T., and J. Iurman,
            "Integrity of In-situ OAM Data Fields", Work in Progress,
            Internet-Draft, draft-ietf-ippm-ioam-data-integrity-02, 5
            July 2022, <https://datatracker.ietf.org/doc/html/draft-
            ietf-ippm-ioam-data-integrity-02>.
 [IOAM-IPV6-OPTIONS]
            Bhandari, S. and F. Brockners, "In-situ OAM IPv6 Options",
            Work in Progress, Internet-Draft, draft-ietf-ippm-ioam-
            ipv6-options-09, 11 October 2022,
            <https://datatracker.ietf.org/doc/html/draft-ietf-ippm-
            ioam-ipv6-options-09>.
 [IOAM-RAWEXPORT]
            Spiegel, M., Brockners, F., Bhandari, S., and R.
            Sivakolundu, "In-situ OAM raw data export with IPFIX",
            Work in Progress, Internet-Draft, draft-spiegel-ippm-ioam-
            rawexport-06, 21 February 2022,
            <https://datatracker.ietf.org/doc/html/draft-spiegel-ippm-
            ioam-rawexport-06>.
 [POSTCARD-BASED-TELEMETRY]
            Song, H., Mirsky, G., Filsfils, C., Abdelsalam, A., Zhou,
            T., Li, Z., Graf, T., Mishra, G. S., Shin, J., and K. Lee,
            "Marking-based Direct Export for On-path Telemetry", Work
            in Progress, Internet-Draft, draft-song-ippm-postcard-
            based-telemetry-14, 7 September 2022,
            <https://datatracker.ietf.org/doc/html/draft-song-ippm-
            postcard-based-telemetry-14>.
 [RFC5475]  Zseby, T., Molina, M., Duffield, N., Niccolini, S., and F.
            Raspall, "Sampling and Filtering Techniques for IP Packet
            Selection", RFC 5475, DOI 10.17487/RFC5475, March 2009,
            <https://www.rfc-editor.org/info/rfc5475>.
 [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>.
 [RFC7014]  D'Antonio, S., Zseby, T., Henke, C., and L. Peluso, "Flow
            Selection Techniques", RFC 7014, DOI 10.17487/RFC7014,
            September 2013, <https://www.rfc-editor.org/info/rfc7014>.
 [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
            Writing an IANA Considerations Section in RFCs", BCP 26,
            RFC 8126, DOI 10.17487/RFC8126, June 2017,
            <https://www.rfc-editor.org/info/rfc8126>.
 [RFC9322]  Mizrahi, T., Brockners, F., Bhandari, S., Gafni, B., and
            M. Spiegel, "In Situ Operations, Administration, and
            Maintanence (IOAM) Loopback and Active Flags", RFC 9322,
            DOI 10.17487/RFC9322, November 2022,
            <https://www.rfc-editor.org/info/rfc9322>.

Appendix A. Notes about the History of This Document

 This document evolved from combining some of the concepts of PBT-I
 from [POSTCARD-BASED-TELEMETRY] with immediate exporting from early
 versions of [RFC9322].
 In order to help correlate and order the exported packets, it is
 possible to include the Hop_Lim/Node_ID IOAM-Data-Field in exported
 packets.  If the IOAM-Trace-Type [RFC9197] has the Hop_Lim/Node_ID
 bit set, then exported packets include the Hop_Lim/Node_ID IOAM-Data-
 Field, which contains the TTL/Hop Limit value from a lower layer
 protocol.  An alternative approach was considered during the design
 of this document, according to which a 1-octet Hop Count field would
 be included in the DEX header (presumably by claiming some space from
 the Flags field).  The Hop Limit would start from 0 at the
 encapsulating node and be incremented by each IOAM transit node that
 supports the DEX Option-Type.  In this approach, the Hop Count field
 value would also be included in the exported packet.

Acknowledgments

 The authors thank Martin Duke, Tommy Pauly, Meral Shirazipour, Colin
 Perkins, Stephen Farrell, Linda Dunbar, Justin Iurman, Greg Mirsky,
 and other members of the IPPM working group for many helpful
 comments.

Contributors

 The Editors would like to recognize the contributions of the
 following individuals to this document.
 Tianran Zhou
 Huawei
 156 Beiqing Rd.
 Beijing
 100095
 China
 Email: zhoutianran@huawei.com
 Zhenbin Li
 Huawei
 156 Beiqing Rd.
 Beijing
 100095
 China
 Email: lizhenbin@huawei.com
 Ramesh Sivakolundu
 Cisco Systems, Inc.
 170 West Tasman Dr.
 San Jose, CA 95134
 United States of America
 Email: sramesh@cisco.com

Authors' Addresses

 Haoyu Song
 Futurewei
 2330 Central Expressway
 Santa Clara,  95050
 United States of America
 Email: haoyu.song@futurewei.com
 Barak Gafni
 Nvidia
 Suite 100
 350 Oakmead Parkway
 Sunnyvale, CA 94085
 United States of America
 Email: gbarak@nvidia.com
 Frank Brockners
 Cisco Systems, Inc.
 Hansaallee 249
 40549 Duesseldorf
 Germany
 Email: fbrockne@cisco.com
 Shwetha Bhandari
 Thoughtspot
 3rd Floor, Indiqube Orion, Garden Layout, HSR Layout
 24th Main Rd
 Bangalore 560 102
 Karnataka
 India
 Email: shwetha.bhandari@thoughtspot.com
 Tal Mizrahi
 Huawei
 8-2 Matam
 Haifa 3190501
 Israel
 Email: tal.mizrahi.phd@gmail.com
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