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Hybrid Two-Step Performance Measurement Method
draft-ietf-ippm-hybrid-two-step-02

Document Type Active Internet-Draft (ippm WG)
Authors Greg Mirsky , Wang Lingqiang , Guo Zhui , Haoyu Song , Pascal Thubert
Last updated 2024-09-04
Replaces draft-mirsky-ippm-hybrid-two-step
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draft-ietf-ippm-hybrid-two-step-02
IPPM Working Group                                             G. Mirsky
Internet-Draft                                                  Ericsson
Intended status: Standards Track                            W. Lingqiang
Expires: 8 March 2025                                            G. Zhui
                                                         ZTE Corporation
                                                                 H. Song
                                                  Futurewei Technologies
                                                              P. Thubert
                                                             Independent
                                                        4 September 2024

             Hybrid Two-Step Performance Measurement Method
                   draft-ietf-ippm-hybrid-two-step-02

Abstract

   The development and advancements in network operation automation have
   brought new measurement methodology requirements.  mong them is the
   ability to collect instant network state as the packet being
   processed by the networking elements along its path through the
   domain.  That task can be solved using on-path telemetry, also called
   hybrid measurement.  An on-path telemetry method allows the
   collection of essential information that reflects the operational
   state and network performance experienced by the packet.  This
   document introduces a method complementary to on-path telemetry that
   causes the generation of telemetry information.  This method,
   referred to as Hybrid Two-Step (HTS), separates the act of measuring
   and/or calculating the performance metric from collecting and
   transporting network state.  The HTS packet traverses the same set of
   nodes and links as the trigger packet, thus simplifying the
   correlation of informational elements originating on nodes traversed
   by the trigger packet.

Status of This Memo

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

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   This Internet-Draft will expire on 8 March 2025.

Copyright Notice

   Copyright (c) 2024 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions used in this document . . . . . . . . . . . . . .   4
     2.1.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  Problem Overview  . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Theory of Operation . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Operation of the HTS Ingress Node . . . . . . . . . . . .   7
     4.2.  Operation of the HTS Intermediate Node  . . . . . . . . .  10
     4.3.  Operation of the HTS Egress Node  . . . . . . . . . . . .  11
   5.  Operationaal Considerations . . . . . . . . . . . . . . . . .  11
     5.1.  Deploying HTS in a Multicast Network  . . . . . . . . . .  12
   6.  Authentication in HTS . . . . . . . . . . . . . . . . . . . .  12
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     7.1.  IOAM Option-Type for HTS  . . . . . . . . . . . . . . . .  14
     7.2.  HTS TLV Registry  . . . . . . . . . . . . . . . . . . . .  14
     7.3.  HTS Sub-TLV Type Sub-registry . . . . . . . . . . . . . .  15
     7.4.  HMAC Type Sub-registry  . . . . . . . . . . . . . . . . .  15
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  17
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     10.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

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1.  Introduction

   Successful resolution of challenges of automated network operation,
   as part of, for example, overall service orchestration or data center
   operation, relies on a timely collection of accurate information that
   reflects the state of network elements on an unprecedented scale.
   Because performing the analysis and act upon the collected
   information requires considerable computing and storage resources,
   the network state information is unlikely to be processed by the
   network elements themselves but will be relayed into the data storage
   facilities, e.g., data lakes.  The process of producing, collecting
   network state information also referred to in this document as
   network telemetry, and transporting it for post-processing should
   work equally well with data flows or injected in the network test
   packets.  [RFC7799] describes a combination of elements of passive
   and active measurement as a hybrid measurement.

   Several technical methods have been proposed to enable the collection
   of network state information instantaneous to the packet processing,
   among them [P4.INT] and [RFC9197].  The instantaneous, i.e., in the
   data packet itself, collection of telemetry information simplifies
   the process of attribution of telemetry information to the particular
   monitored flow.  On the other hand, this collection method impacts
   the data packets, potentially changing their treatment by the
   networking nodes.  Also, the amount of information the instantaneous
   method collects might be incomplete because of the limited space it
   can be allotted.  Other proposals defined methods to collect
   telemetry information in a separate packet from each node traversed
   by the monitored data flow.  Examples of this approach to collecting
   telemetry information are [RFC9326] and
   [I-D.song-ippm-postcard-based-telemetry].  These methods allow data
   collection from any arbitrary path and avoid directly impacting data
   packets.  On the other hand, the correlation of data and the
   monitored flow requires that each packet with telemetry information
   also includes characteristic information about the monitored flow.

   This document introduces Hybrid Two-Step (HTS) as a new method of
   telemetry collection that improvers accuracy of a measurement by
   separating the act of measuring or calculating the performance metric
   from the collecting and transporting this information while
   minimizing the overhead of the generated load in a network.  HTS
   method extends the two-step mode of Residence Time Measurement (RTM)
   defined in [RFC8169] to on-path network state collection and
   transport.  HTS allows the collection of telemetry information from
   any arbitrary path, does not change data packets of the monitored
   flow and makes the process of attribution of telemetry to the data
   flow simple.

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2.  Conventions used in this document

2.1.  Acronyms

   RTM Residence Time Measurement

   ECMP Equal Cost Multipath

   MTU Maximum Transmission Unit

   HTS Hybrid Two-Step

   HMAC Hashed Message Authentication Code

   TLV Type-Length-Value

   RTT Round-Trip Time

   Network telemetry - the process of collecting and reporting of
   network state

2.2.  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.

3.  Problem Overview

   Performance measurements are meant to provide data that characterize
   conditions experienced by traffic flows in the network and possibly
   trigger operational changes (e.g., re-route of flows, or changes in
   resource allocations).  Modifications to a network are determined
   based on the performance metric information available when a change
   is to be made.  The correctness of this determination is based on the
   quality of the collected metrics data.  The quality of collected
   measurement data is defined by:

   *  the resolution and accuracy of each measurement;

   *  predictability of both the time at which each measurement is made
      and the timeliness of measurement collection data delivery for
      use.

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   Consider the case of delay measurement that relies on collecting time
   of packet arrival at the ingress interface and time of the packet
   transmission at the egress interface.  The method includes recording
   a local clock value on receiving the first octet of an affected
   message at the device ingress, and again recording the clock value on
   transmitting the first byte of the same message at the device egress.
   In this ideal case, the difference between the two recorded clock
   times corresponds to the time that the message spent in traversing
   the device.  In practice, the time recorded can differ from the ideal
   case by any fixed amount.  A correction can be applied to compute the
   same time difference taking into account the known fixed time
   associated with the actual measurement.  In this way, the resulting
   time difference reflects any variable delay associated with queuing.

   Depending on the implementation, it may be a challenge to compute the
   difference between message arrival and departure times and - on the
   fly - add the necessary residence time information to the same
   message.  And that task may become even more challenging if the
   packet is encrypted.  Recording the departure of a packet time in the
   same packet may be decremental to the accuracy of the measurement
   because the departure time includes the variable time component (such
   as that associated with buffering and queuing of the packet).  A
   similar problem may lower the quality of, for example, information
   that characterizes utilization of the egress interface.  If unable to
   obtain the data consistently, without variable delays for additional
   processing, information may not accurately reflect the egress
   interface state.  To mitigate this problem [RFC8169] defined an RTM
   two-step mode.

   Another challenge associated with methods that collect network state
   information into the actual data packet is the risk to exceed the
   Maximum Transmission Unit (MTU) size on the path, especially if the
   packet traverses overlay domains or VPNs.  Since the fragmentation is
   not available at the transport network, operators may have to reduce
   MTU size advertised to the client layer or risk missing network state
   data for the part, most probably the latter part, of the path.

   In some networks, for example, wireless that are in the scope of
   [RFC9450], it is beneficial to collect the telemetry, including the
   calculated performance metrics, that reflects conditions experienced
   by the monitored flow at a node, other than the egress.  For example,
   a head-end can optimize path selection based on the compounded
   information that reflects network conditions, resource utilization.
   This mode is referred to as the upstream collection and the other -
   downstream collection to differentiate between two modes of telemetry
   collection.

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4.  Theory of Operation

   The HTS method consists of two phases:

   *  performing a measurement and/or obtaining network state
      information on a node;

   *  collecting and transporting the measurement and/or the telemetry
      information.

   HTS may use an HTS Trigger carried in a data packet or a specially
   constructed test packet.  For example, an HTS Trigger could be a
   packet that has IOAM Option-Type set to the "IOAM Hybrid Two-Step
   Option-Type" value (TBA1) allocated by IANA (see Section 7.1).  The
   HTS Trigger also includes IOAM Namespace-ID and IOAM-Trace-Type
   information s defined in Section 5.3 and Section 5.4.1 [RFC9197]
   respectively (shown in Figure 1).  A packet in the flow to which the
   Alternate-Marking method, defined in [RFC9341] and [RFC9342], is
   applied can be used as an HTS Trigger.  The nature of the HTS Trigger
   is a transport network layer-specific, and its description is outside
   the scope of this document.  The packet that includes the HTS Trigger
   in this document is also referred to as the trigger packet.

        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           |            Reserved           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               IOAM-Trace-Type                 |   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 1: Hybrid Two-Step Trace IOAM Header

   The HTS method uses the HTS Follow-up packet, referred to as the
   follow-up packet, to collect measurement and network state data from
   the nodes.  The node that creates the HTS Trigger also generates the
   HTS Follow-up packet.  In some use cases, e.g., when HTS is used to
   collect the telemetry, including performance metrics, calculated
   based on a series of measurements, an HTS follow-up packet can be
   originated without using the HTS Trigger.  The follow-up packet
   contains characteristic information sufficient for participating HTS
   nodes to associate it with the monitored data flow.  The
   characteristic information can be obtained using the information of
   the trigger packet or constructed by a node that originates the
   follow-up packet.  As the follow-up packet is expected to traverse
   the same sequence of nodes, one element of the characteristic
   information is the information that determines the path in the data

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   plane.  For example, in a segment routing domain [RFC8402], a list of
   segment identifiers of the trigger packet is applied to the follow-up
   packet.  And in the case of the service function chain based on the
   Network Service Header [RFC8300], the Base Header and Service Path
   Header of the trigger packet will be applied to the follow-up packet.
   Also, when HTS is used to collect the telemetry information in an
   IOAM domain, the IOAM trace option header [RFC9197] of the trigger
   packet is applied in the follow-up packet.  The follow-up packet also
   uses the same network information used to load-balance flows in
   equal-cost multipath (ECMP) as the trigger packet, e.g., IPv6 Flow
   Label [RFC6437] or an entropy label [RFC6790].  The exact composition
   of the characteristic information is specific for each transport
   network, and its definition is outside the scope of this document.

   Only one outstanding follow-up packet MUST be on the node for the
   given path.  That means that if the node receives an HTS Trigger for
   the flow on which it still waits for the follow-up packet to the
   previous HTS Trigger, the node will originate the follow-up packet to
   transport the former set of the network state data and transmit it
   before it sends the follow-up packet with the latest collection of
   network state information.

   The following sections describe the operation of HTS nodes in the
   downstream mode of collecting the telemetry information.  In the
   upstream mode, the bahavior of HTS nodes, in general, identical with
   the exception that the HTS Trigger packet does not precede the HTS
   Follow-up packet.

4.1.  Operation of the HTS Ingress Node

   A node that originates the HTS Trigger is referred to as the HTS
   ingress node.  As stated, the ingress node originates the follow-up
   packet.  The follow-up packet has the transport network encapsulation
   identical with the trigger packet followed by the HTS shim and one or
   more telemetry information elements encoded as Type-Length-Value
   (TLV).  Figure 2 displays an example of the follow-up packet format.

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        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~                      Transport Network                        ~
       |                        Encapsulation                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Ver|HTS Shim L |     Flags     |Sequence Number|   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        HTS Max Length                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    Telemetry Data Profile                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~                     Telemetry Data TLVs                       ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 2: Follow-up Packet Format

   Fields of the HTS shim are as follows:

    Version (Ver) is the two-bits long field.  It specifies the
    version of the HTS shim format.  This document defines the format
    for the 0b00 value of the field.

    HTS Shim Length is the six bits-long field.  It defines the length
    of the HTS shim in octets.  The minimal value of the field is
    eight octets.

         0
         0 1 2 3 4 5 6 7
        +-+-+-+-+-+-+-+-+
        |F|  Reserved   |
        +-+-+-+-+-+-+-+-+

                       Figure 3: Flags Field Format

    Flags is eight-bits long.  The format of the Flags field displayed
    in Figure 3.

    -  Full (F) flag MUST be set to zero by the node originating the
       HTS follow-up packet and MUST be set to one by the node that
       does not add its telemetry data to avoid exceeding MTU size.

    -  The node originating the follow-up packet MUST zero the
       Reserved field and ignore it on the receipt.

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    Sequence Number is one octet-long field.  The zero-based value of
    the field reflects the place of the HTS follow-up packet in the
    sequence of the HTS follow-up packets that originated in response
    to the same HTS trigger.  The ingress node MUST set the value of
    the field to zero.

    Reserved is one octet-long field.  It MUST be zeroed on
    transmission and ignored on recepit.

    HTS Max Length is four octet-long field.  The value of th HTS Max
    Length field indicates the maximum length of the HTS Follow-up
    packet in octets.  An operator MUST be able to configure the HTS
    Max Length field's value.  The value SHOULD be set equal to the
    path MTU.

    Telemetry Data Profile is the optional variable-length field of
    bit-size flags.  Each flag indicates the requested type of
    telemetry data to be collected at each HTS node.  The increment of
    the field is four bytes with a minimum length of zero.  For
    example, IOAM-Trace-Type information defined in [RFC9197] can be
    used in the Telemetry Data Profile field.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Type     |    Reserved   |           Length              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                            Value                              ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 4: Telemetry Data TLV Format

    Telemetry Data TLV is a variable-length field.  Multiple TLVs MAY
    be placed in an HTS packet.  Additional TLVs may be enclosed
    within a given TLV, subject to the semantics of the (outer) TLV in
    question.  Figure 4 presents the format of a Telemetry Data TLV,
    where fields are defined as the following:

    -  Type - a one-octet-long field that characterizes the
       interpretation of the Value field.

    -  Reserved - one-octet-long field.

    -  Length - two-octet-long field equal to the length of the Value
       field in octets.

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    -  Value - a variable-length field.  The value of the Type field
       determines its interpretation and encoding.  IOAM data fields,
       defined in [RFC9197], MAY be carried in the Value field.

   All multibyte fields defined in this specification are in network
   byte order.

4.2.  Operation of the HTS Intermediate Node

   Upon receiving the trigger packet, the HTS intermediate node MUST:

   *  copy the transport information;

   *  start the HTS Follow-up Timer for the obtained flow;

   *  transmit the trigger packet.

   Upon receiving the follow-up packet, the HTS intermediate node MUST:

   1.  verify that the matching transport information exists and the
       Full flag is cleared, then stop the associated HTS Follow-up
       Timer;

   2.  otherwise, transmit the received packet.  Proceed to Step 8;

   3.  collect telemetry data requested in the Telemetry Data Profile
       field or defined by the local HTS policy;

   4.  if adding the collected telemetry would not exceed HTS Max Length
       field's value, then append data as a new Telemetry Data TLV and
       transmit the follow-up packet.  Proceed to Step 8;

   5.  otherwise, set the value of the Full flag to one, copy the
       transport information from the received follow-up packet and
       transmit it accordingly.  Proceed to Step 8;

   6.  originate the new follow-up packet using the transport
       information copied from the received follow-up packet.  The value
       of the Sequence Number field in the HTS shim MUST be set to the
       value of the field in the received follow-up packet incremented
       by one;

   7.  copy collected telemetry data into the first Telemetry Data TLV's
       Value field and then transmit the packet;

   8.  processing completed.

   If the HTS Follow-up Timer expires, the intermediate node MUST:

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   *  originate the follow-up packet using transport information
      associated with the expired timer;

   *  initialize the HTS shim by setting the Version field's value to
      0b00 and Sequence Number field to 0.  Values of HTS Shim Length
      and Telemetry Data Profile fields MAY be set according to the
      local policy.

   *  copy telemetry information into Telemetry Data TLV's Value field
      and transmit the packet.

   If the intermediate node receives a "late" follow-up packet, i.e., a
   packet to which the node has no associated HTS Follow-up timer, the
   node MUST forward the "late" packet.

4.3.  Operation of the HTS Egress Node

   Upon receiving the trigger packet, the HTS egress node MUST:

   *  copy the transport information;

   *  start the HTS Collection timer for the obtained flow.

   When the egress node receives the follow-up packet for the known
   flow, i.e., the flow to which the Collection timer is running, the
   node for each of Telemetry Data TLVs MUST:

   *  if HTS is used in the authenticated mode, verify the
      authentication of the Telemetry Data TLV using the Authentication
      sub-TLV (see Section 6);

   *  copy telemetry information from the Value field;

   *  restart the corresponding Collection timer.

   When the Collection timer expires, the egress relays the collected
   telemetry information for processing and analysis to a local or
   remote agent.

5.  Operationaal Considerations

   Correctly attributing information originated by the particular
   trigger packet to the proper HTS Follow-up packet is essential for
   the HTS protocol.  That can be achieved using characteristic
   information that uniquely idetifies the trigger packet within a given
   HTS domain.  For example, a combination of the flow identifier and
   packet's sequence number within that flow, as Flow ID and Sequence
   Number in IOAM Direct Export [RFC9326], can be used to correlate

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   between stored telemetry information and the appropriate HTS Follow-
   up packet.  In case the trigger packet doesn't include data that
   distinguish it from other trigger packets in the HTS domain, then for
   the particular flow, there MUST be no more than one HTS Trigger,
   values of HTS timers bounded by the rate of the trigger generation
   for that flow.  In practice, the minimal interval between HTS Trigger
   packets SHOULD be selected from the range determined by the round-
   trip time (RTT) between HTS Ingress and HTS Egress nodes as [RTT/2,
   RTT].

5.1.  Deploying HTS in a Multicast Network

   Previous sections discussed the operation of HTS in a unicast
   network.  Multicast services are important, and the ability to
   collect telemetry information is invaluable in delivering a high
   quality of experience.  While the replication of data packets is
   necessary, replication of HTS follow-up packets is not.  Replication
   of multicast data packets down a multicast tree may be set based on
   multicast routing information or explicit information included in the
   special header, as, for example, in Bit-Indexed Explicit Replication
   [RFC8296].  A replicating node processes the HTS packet as defined
   below:

   *  the first transmitted multicast packet MUST be followed by the
      received corresponding HTS packet as described in Section 4.2;

   *  each consecutively transmitted copy of the original multicast
      packet MUST be followed by the new HTS packet originated by the
      replicating node that acts as an intermediate HTS node when the
      HTS Follow-up timer expired.

   As a result, there are no duplicate copies of Telemetry Data TLV for
   the same pair of ingress and egress interfaces.  At the same time,
   all ingress/egress pairs traversed by the given multicast packet
   reflected in their respective Telemetry Data TLV.  Consequently, a
   centralized controller would reconstruct and analyze the state of the
   particular multicast distribution tree based on HTS packets collected
   from egress nodes.

6.  Authentication in HTS

   Telemetry information may be used to drive network operation, closing
   the control loop for self-driving, self-healing networks.  Thus it is
   critical to provide a mechanism to protect the telemetry information
   collected using the HTS method.  This document defines an optional
   authentication of a Telemetry Data TLV that protects the collected
   information's integrity.

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   The format of the Authentication sub-TLV is displayed in Figure 5.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Authentic. Type|   HMAC Type   |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                            Digest                             |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Figure 5: HMAC sub-TLV

   where fields are defined as follows:

   *  Authentication Type - is a one-octet-long field, value 1 is
      allocated by IANA Section 7.2.

   *  Length - two-octet-long field, set equal to the length of the
      Digest field in octets.

   *  HMAC Type - is a one-octet-long field that identifies the type of
      the HMAC and the length of the digest and the length of the digest
      according to the HTS HMAC Type sub-registry (see Section 7.4).

   *  Digest - is a variable-length field that carries HMAC digest of
      the text that includes the encompassing TLV.

   This specification defines the use of HMAC-SHA-256 truncated to 128
   bits ([RFC4868]) in HTS.  Future specifications may define the use in
   HTS of more advanced cryptographic algorithms or the use of digest of
   a different length.  HMAC is calculated as defined in [RFC2104] over
   text as the concatenation of the Sequence Number field of the follow-
   up packet (see Figure 2) and the preceding data collected in the
   Telemetry Data TLV.  The digest then MUST be truncated to 128 bits
   and written into the Digest field.  Distribution and management of
   shared keys are outside the scope of this document.  In the HTS
   authenticated mode, the Authentication sub-TLV MUST be present in
   each Telemetry Data TLV.  HMAC MUST be verified before using any data
   in the included Telemetry Data TLV.  If HMAC verification fails, the
   system MUST stop processing corresponding Telemetry Data TLV and
   notify an operator.  Specification of the notification mechanism is
   outside the scope of this document.

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7.  IANA Considerations

7.1.  IOAM Option-Type for HTS

   The IOAM Option-Type registry is requested in [RFC9197].  IANA is
   requested to allocate a new code point as listed in Table 1.

      +=======+======================+=============+===============+
      | Value | Name                 | Description | Reference     |
      +=======+======================+=============+===============+
      | TBA1  | IOAM Hybrid Two-Step | HTS         | This document |
      |       |  (HTS) Option-Type   | Exporting   |               |
      +-------+----------------------+-------------+---------------+

                    Table 1: IOAM Option-Type for HTS

7.2.  HTS TLV Registry

   IANA is requested to create "Hybrid Two-Step" registry group.  IANA
   is requested to create the HTS TLV Type registry in "Hybrid Two-Step"
   registry group.  All code points in the range 1 through 175 in this
   registry shall be allocated according to the "IETF Review" procedure
   specified in [RFC8126].  Code points in the range 176 through 239 in
   this registry shall be allocated according to the "First Come First
   Served" procedure specified in [RFC8126].  The remaining code points
   are allocated according to Table 2:

               +===========+==============+===============+
               | Value     | Description  | Reference     |
               +===========+==============+===============+
               | 0         |   Reserved   | This document |
               +-----------+--------------+---------------+
               | 1- 175    |  Unassigned  | This document |
               +-----------+--------------+---------------+
               | 176 - 239 |  Unassigned  | This document |
               +-----------+--------------+---------------+
               | 240 - 251 | Experimental | This document |
               +-----------+--------------+---------------+
               | 252 - 254 | Private Use  | This document |
               +-----------+--------------+---------------+
               | 255       |   Reserved   | This document |
               +-----------+--------------+---------------+

                      Table 2: HTS TLV Type Registry

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7.3.  HTS Sub-TLV Type Sub-registry

   IANA is requested to create the HTS sub-TLV Type sub-registry as part
   of the HTS TLV Type registry.  All code points in the range 1 through
   175 in this registry shall be allocated according to the "IETF
   Review" procedure specified in [RFC8126].  Code points in the range
   176 through 239 in this registry shall be allocated according to the
   "First Come First Served" procedure specified in [RFC8126].  The
   remaining code points are allocated according to Table 3:

          +===========+==============+==========+===============+
          | Value     | Description  | TLV Used | Reference     |
          +===========+==============+==========+===============+
          | 0         |   Reserved   |   None   | This document |
          +-----------+--------------+----------+---------------+
          | 1         |     HMAC     |   Any    | This document |
          +-----------+--------------+----------+---------------+
          | 2 - 175   |  Unassigned  |          | This document |
          +-----------+--------------+----------+---------------+
          | 176 - 239 |  Unassigned  |          | This document |
          +-----------+--------------+----------+---------------+
          | 240 - 251 | Experimental |          | This document |
          +-----------+--------------+----------+---------------+
          | 252 - 254 | Private Use  |          | This document |
          +-----------+--------------+----------+---------------+
          | 255       |   Reserved   |   None   | This document |
          +-----------+--------------+----------+---------------+

                   Table 3: HTS Sub-TLV Type Sub-registry

7.4.  HMAC Type Sub-registry

   IANA is requested to create the HMAC Type sub-registry as part of the
   HTS TLV Type registry.  All code points in the range 1 through 127 in
   this registry shall be allocated according to the "IETF Review"
   procedure specified in [RFC8126].  Code points in the range 128
   through 239 in this registry shall be allocated according to the
   "First Come First Served" procedure specified in [RFC8126].  The
   remaining code points are allocated according to Table 4:

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        +===========+=============================+===============+
        | Value     |         Description         | Reference     |
        +===========+=============================+===============+
        | 0         |           Reserved          | This document |
        +-----------+-----------------------------+---------------+
        | 1         | HMAC-SHA-256 16 octets long | This document |
        +-----------+-----------------------------+---------------+
        | 2 - 127   |          Unassigned         | This document |
        +-----------+-----------------------------+---------------+
        | 128 - 239 |          Unassigned         | This document |
        +-----------+-----------------------------+---------------+
        | 240 - 249 |         Experimental        | This document |
        +-----------+-----------------------------+---------------+
        | 250 - 254 |         Private Use         | This document |
        +-----------+-----------------------------+---------------+
        | 255       |           Reserved          | This document |
        +-----------+-----------------------------+---------------+

                      Table 4: HMAC Type Sub-registry

8.  Security Considerations

   Nodes that practice the HTS method are presumed to share a trust
   model that depends on the existence of a trusted relationship among
   nodes.  This is necessary as these nodes are expected to correctly
   modify the specific content of the data in the follow-up packet, and
   the degree to which HTS measurement is useful for network operation
   depends on this ability.  In practice, this means either
   confidentiality or integrity protection cannot cover those portions
   of messages that contain the network state data.  Though there are
   methods that make it possible in theory to provide either or both
   such protections and still allow for intermediate nodes to make
   detectable yet authenticated modifications, such methods do not seem
   practical at present, particularly for protocols that used to measure
   latency and/or jitter.

   This document defines the use of authentication (Section 6) to
   protect the integrity of the telemetry information collected using
   the HTS method.  Privacy protection can be achieved by, for example,
   sharing the IPsec tunnel with a data flow that generates information
   that is collected using HTS.

   While it is possible for a supposed compromised node to intercept and
   modify the network state information in the follow-up packet; this is
   an issue that exists for nodes in general - for all data that to be
   carried over the particular networking technology - and is therefore
   the basis for an additional presumed trust model associated with an
   existing network.

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9.  Acknowledgments

   Authors express their gratitude and appreciation to Joel Halpern for
   the most helpful and insightful discussion on the applicability of
   HTS in a Service Function Chaining domain.  Also, authors thank Bjørn
   Ivar Teigen for the discussion about ensuring proper correlation
   between generated telemetry information and an HTS Follow-up packet.

10.  References

10.1.  Normative References

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              DOI 10.17487/RFC2104, February 1997,
              <https://www.rfc-editor.org/info/rfc2104>.

   [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>.

   [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>.

   [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>.

10.2.  Informative References

   [I-D.song-ippm-postcard-based-telemetry]
              Song, H., Mirsky, G., Zhou, T., Li, Z., Graf, T., Mishra,
              G. S., Shin, J., and K. Lee, "On-Path Telemetry using
              Packet Marking to Trigger Dedicated OAM Packets", Work in
              Progress, Internet-Draft, draft-song-ippm-postcard-based-
              telemetry-16, 2 June 2023,
              <https://datatracker.ietf.org/doc/html/draft-song-ippm-
              postcard-based-telemetry-16>.

   [P4.INT]   "In-band Network Telemetry (INT)", P4.org Specification,
              October 2017.

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   [RFC4868]  Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
              384, and HMAC-SHA-512 with IPsec", RFC 4868,
              DOI 10.17487/RFC4868, May 2007,
              <https://www.rfc-editor.org/info/rfc4868>.

   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437,
              DOI 10.17487/RFC6437, November 2011,
              <https://www.rfc-editor.org/info/rfc6437>.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <https://www.rfc-editor.org/info/rfc6790>.

   [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>.

   [RFC8169]  Mirsky, G., Ruffini, S., Gray, E., Drake, J., Bryant, S.,
              and A. Vainshtein, "Residence Time Measurement in MPLS
              Networks", RFC 8169, DOI 10.17487/RFC8169, May 2017,
              <https://www.rfc-editor.org/info/rfc8169>.

   [RFC8296]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
              for Bit Index Explicit Replication (BIER) in MPLS and Non-
              MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
              2018, <https://www.rfc-editor.org/info/rfc8296>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [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>.

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   [RFC9326]  Song, H., Gafni, B., Brockners, F., Bhandari, S., and T.
              Mizrahi, "In Situ Operations, Administration, and
              Maintenance (IOAM) Direct Exporting", RFC 9326,
              DOI 10.17487/RFC9326, November 2022,
              <https://www.rfc-editor.org/info/rfc9326>.

   [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>.

   [RFC9342]  Fioccola, G., Ed., Cociglio, M., Sapio, A., Sisto, R., and
              T. Zhou, "Clustered Alternate-Marking Method", RFC 9342,
              DOI 10.17487/RFC9342, December 2022,
              <https://www.rfc-editor.org/info/rfc9342>.

   [RFC9450]  Bernardos, CJ., Ed., Papadopoulos, G., Thubert, P., and F.
              Theoleyre, "Reliable and Available Wireless (RAW) Use
              Cases", RFC 9450, DOI 10.17487/RFC9450, August 2023,
              <https://www.rfc-editor.org/info/rfc9450>.

Authors' Addresses

   Greg Mirsky
   Ericsson
   Email: gregimirsky@gmail.com

   Wang Lingqiang
   ZTE Corporation
   No 19 ,East Huayuan Road
   Beijing
   100191
   China
   Phone: +86 10 82963945
   Email: wang.lingqiang@zte.com.cn

   Guo Zhui
   ZTE Corporation
   No 19 ,East Huayuan Road
   Beijing
   100191
   China
   Phone: +86 10 82963945
   Email: guo.zhui@zte.com.cn

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   Haoyu Song
   Futurewei Technologies
   2330 Central Expressway
   Santa Clara,
   United States of America
   Email: hsong@futurewei.com

   Pascal Thubert
   Independent
   06330 Roquefort-les-Pins
   France
   Email: pascal.thubert@gmail.com

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