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SPRING Working Group                                      R. Gandhi, Ed.
Internet-Draft                                               C. Filsfils
Intended Status: Standards Track                     Cisco Systems, Inc.
Expires: May 7, 2020                                            D. Voyer
                                                             Bell Canada
                                                                 M. Chen
                                                                  Huawei
                                                             B. Janssens
                                                                    Colt
                                                        November 4, 2019

                Performance Measurement Using TWAMP Light
                      for Segment Routing Networks
                    draft-gandhi-spring-twamp-srpm-04

Abstract

   Segment Routing (SR) leverages the source routing paradigm.  SR is
   applicable to both Multiprotocol Label Switching (SR-MPLS) and IPv6
   (SRv6) data planes.  This document specifies procedure for sending
   and processing probe query and response messages for Performance
   Measurement (PM) in Segment Routing networks.  The procedure uses the
   mechanisms defined in RFC 5357 (Two-Way Active Measurement Protocol
   (TWAMP) Light) and Simple Two-Way Active Measurement Protocol (STAMP)
   for Delay Measurement, and also uses the mechanisms defined in this
   document for Loss Measurement.  The procedure specified is applicable
   to SR-MPLS and SRv6 data planes and are used for both links and
   end-to-end SR Policies.


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
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   Drafts is at http://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."


Copyright Notice




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   Copyright (c) 2019 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
   (http://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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  4
     2.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
     2.2.  Abbreviations  . . . . . . . . . . . . . . . . . . . . . .  4
     2.3.  Reference Topology . . . . . . . . . . . . . . . . . . . .  5
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Example Provisioning Model . . . . . . . . . . . . . . . .  6
     3.2.  STAMP Applicability  . . . . . . . . . . . . . . . . . . .  7
   4.  Probe Messages . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.1.  Probe Query Message  . . . . . . . . . . . . . . . . . . .  7
       4.1.1.  Delay Measurement Probe Query Message  . . . . . . . .  7
         4.1.1.1.  Delay Measurement Authentication Mode  . . . . . .  8
       4.1.2.  Loss Measurement Probe Query Message . . . . . . . . .  8
         4.1.2.1.  Loss Measurement Authentication Mode . . . . . . . 12
       4.1.3.  Probe Query for SR Links . . . . . . . . . . . . . . . 13
       4.1.4.  Probe Query for End-to-end Measurement for SR Policy . 13
         4.1.4.1.  Probe Query Message for SR-MPLS Policy . . . . . . 13
         4.1.4.2.  Probe Query Message for SRv6 Policy  . . . . . . . 13
     4.2.  Probe Response Message . . . . . . . . . . . . . . . . . . 14
       4.2.1.  One-way Measurement Mode . . . . . . . . . . . . . . . 18
       4.2.2.  Two-way Measurement Mode . . . . . . . . . . . . . . . 18
         4.2.2.1.  Return Path TLV  . . . . . . . . . . . . . . . . . 18
         4.2.2.2.  Probe Response Message for SR-MPLS Policy  . . . . 20
         4.2.2.3.  Probe Response Message for SRv6 Policy . . . . . . 20
       4.2.3.  Loopback Measurement Mode  . . . . . . . . . . . . . . 21
   5.  Performance Measurement for P2MP SR Policies . . . . . . . . . 21
   6.  ECMP Support for SR Policies . . . . . . . . . . . . . . . . . 22
   7.  Additional Message Processing Rules  . . . . . . . . . . . . . 22
     7.1.  TTL Value  . . . . . . . . . . . . . . . . . . . . . . . . 22
     7.2.  Router Alert Option  . . . . . . . . . . . . . . . . . . . 22
     7.3.  UDP Checksum . . . . . . . . . . . . . . . . . . . . . . . 23



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   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23
   10.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 24
     10.1.  Normative References  . . . . . . . . . . . . . . . . . . 24
     10.2.  Informative References  . . . . . . . . . . . . . . . . . 25
   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27



1.  Introduction

   Segment Routing (SR) leverages the source routing paradigm and
   greatly simplifies network operations for Software Defined Networks
   (SDNs).  SR is applicable to both Multiprotocol Label Switching
   (SR-MPLS) and IPv6 (SRv6) data planes.  SR takes advantage of the
   Equal-Cost Multipaths (ECMPs) between source and transit nodes,
   between transit nodes and between transit and destination nodes.  SR
   Policies as defined in [I-D.spring-segment-routing-policy] are used
   to steer traffic through a specific, user-defined paths using a stack
   of Segments.  Built-in SR Performance Measurement (PM) is one of the
   essential requirements to provide Service Level Agreements (SLAs).

   The One-Way Active Measurement Protocol (OWAMP) defined in [RFC4656]
   and Two-Way Active Measurement Protocol (TWAMP) defined in [RFC5357]
   provide capabilities for the measurement of various performance
   metrics in IP networks using probe messages.  These protocols rely on
   control-channel signaling to establish a test-channel over an UDP
   path.  These protocols lack support for direct-mode Loss Measurement
   (LM) to detect actual data traffic loss which is required in SR
   networks.  The Simple Two-way Active Measurement Protocol (STAMP)
   [I-D.ippm-stamp] alleviates the control-channel signaling by using
   configuration data model to provision a test-channel.  The TWAMP
   Light [Appendix I in RFC5357] [BBF.TR-390] provides simplified
   mechanisms for active performance measurement in Customer IP networks
   by provisioning UDP paths and eliminates the control-channel
   signaling.

   This document specifies procedures for sending and processing probe
   query and response messages for Performance Measurement in SR
   networks.  The procedure uses the mechanisms defined in [RFC5357]
   (TWAMP Light) and STAMP for Delay Measurement (DM), and also uses the
   mechanisms defined in this document for Loss Measurement.  The
   procedure specified is applicable to SR-MPLS and SRv6 data planes and
   are used for both links and end-to-end SR Policies.  This document
   also defines mechanisms for handling ECMPs of SR Policies for
   performance delay measurements.




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2.  Conventions Used in This Document

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119] [RFC8174]
   when, and only when, they appear in all capitals, as shown here.

2.2.  Abbreviations

   BSID: Binding Segment ID.

   DM: Delay Measurement.

   ECMP: Equal Cost Multi-Path.

   HMAC: Hashed Message Authentication Code.

   LM: Loss Measurement.

   MPLS: Multiprotocol Label Switching.

   NTP: Network Time Protocol.

   OWAMP: One-Way Active Measurement Protocol.

   PM: Performance Measurement.

   PSID: Path Segment Identifier.

   PTP: Precision Time Protocol.

   SID: Segment ID.

   SL: Segment List.

   SR: Segment Routing.

   SRH: Segment Routing Header.

   SR-MPLS: Segment Routing with MPLS data plane.

   SRv6: Segment Routing with IPv6 data plane.

   STAMP: Simple Two-way Active Measurement Protocol.

   TC: Traffic Class.



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   TWAMP: Two-Way Active Measurement Protocol.


2.3.  Reference Topology

   In the reference topology shown below, the sender node R1 initiates a
   probe query for performance measurement and the responder node R5
   sends a probe response for the query message received.  The probe
   response is sent to the sender node R1.  The nodes R1 and R5 may be
   directly connected via a link enabled with Segment Routing or there
   exists a Point-to-Point (P2P) SR Policy
   [I-D.spring-segment-routing-policy] on node R1 with destination to
   node R5.  In case of Point-to-Multipoint (P2MP), SR Policy
   originating from source node R1 may terminate on multiple destination
   leaf nodes [I-D.spring-sr-p2mp-policy].


               +-------+        Query        +-------+
               |       | - - - - - - - - - ->|       |
               |   R1  |---------------------|   R5  |
               |       |<- - - - - - - - - - |       |
               +-------+       Response      +-------+
                Sender                       Responder

                          Reference Topology


3.  Overview

   For one-way, two-way and round-trip delay measurements in Segment
   Routing networks, the TWAMP Light procedures defined in Appendix I of
   [RFC5357] are used.  For one-way and two-way direct-mode and
   inferred-mode loss measurements in Segment Routing networks, the
   procedures defined in this document are used.  One-way loss
   measurement provides receive packet loss whereas two-way loss
   measurement provides both transmit and receive packet loss.  Separate
   UDP destination port numbers are user-configured for delay and loss
   measurements from the range specified in [I-D.ippm-stamp].  The
   sender uses the UDP port number following the guidelines specified in
   Section 6 in [RFC6335].  For both links and end-to-end SR Policies,
   no PM session for delay or loss measurement is created on the
   responder node R5 [RFC5357].

   For Performance Measurement, probe query and response messages are
   sent as following:

   o  For Delay Measurement, the probe messages are sent on the
      congruent path of the data traffic by the sender node, and are



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      used to measure the delay experienced by the actual data traffic
      flowing on the links and SR Policies.

   o  For Loss Measurement, the probe messages are sent on the congruent
      path of the data traffic by the sender node, and are used to
      collect the receive traffic counters for the incoming link or
      incoming SID where the probe query messages are received at the
      responder node (incoming link or incoming SID needed since the
      responder node does not have PM session state present).

   The In-Situ Operations, Administration, and Maintenance (IOAM)
   mechanisms for SR-MPLS defined in [I-D.spring-ioam-sr-mpls] and for
   SRv6 defined in [I-D.spring-ioam-srv6] are used to carry PM
   information such as timestamp in-band as part of the data packets,
   and are outside the scope of this document.

3.1.  Example Provisioning Model

   An example of a provisioning model and typical measurement parameters
   for performance delay and loss measurements using TWAMP Light is
   shown in the following Figure:


                             +------------+
                             | Controller |
                             +------------+
   Measurement Protocol           /  \         Measurement Protocol
   Destination UDP Port          /    \        Destination UDP port
   Measurement Type             /      \       Measurement Type
     Delay/Loss                /        \        Delay/Loss
   Authentication Mode & Key  /          \     Authentication Mode & Key
   Timestamp Format          /            \
   Delay Measurement Mode   /              \
   Padding/MBZ Bytes       /                \
   Loss Measurement Mode  /                  \
                         v                    v
                     +-------+            +-------+
                     |       |            |       |
                     |   R1  |------------|   R5  |
                     |       |            |       |
                     +-------+            +-------+
                      Sender              Responder

                            Provisioning Model

   The responder node R5 uses the parameters for the timestamp format,
   delay measurement mode, padding size and loss measurement mode from
   the received probe query message.



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   The mechanisms to provision the sender and responder nodes are
   outside the scope of this document.

3.2.  STAMP Applicability

   The Simple Two-way Active Measurement Protocol (STAMP)
   [I-D.ippm-stamp] and the STAMP TLVs [I-D.ippm-stamp-option-tlv] are
   both equally applicable to the procedures specified in this document.
    This is because the delay measurement message formats defined for
   STAMP and STAMP TLVs are backwards compatible with the delay
   measurement message formats defined in [RFC5357].  Hence, the same
   user-configured destination UDP port for delay measurement can be
   used for STAMP and TWAMP Light messages.  The STAMP with a TLV for
   "direct measurement" can be used for combined delay + loss
   measurement using a separate user-configured UDP destination port.

   The loss measurement probe and query messages defined in this
   document are also equally applicable to STAMP and STAMP TLVs, and use
   the message formats defined in [I-D.ippm-stamp].


4.  Probe Messages

4.1.  Probe Query Message

   In this document, the probe messages defined in [RFC5357] are used
   for Delay and Loss measurements for SR links and end-to-end SR
   Policies.  The user-configured destination UDP ports (separate UDP
   ports for different delay and loss message formats) are used for
   identifying the PM probe packets as described in Appendix I of
   [RFC5357].

4.1.1.  Delay Measurement Probe Query Message

   The message content for Delay Measurement probe query message using
   UDP header [RFC768] is shown in Figure 1.  The DM probe query message
   is sent with user-configured Destination UDP port number for DM.  The
   Destination UDP port cannot be used as Source port, since the message
   does not have any indication to distinguish between query and
   response.  The DM probe query message contains the payload for delay
   measurement defined in Section 4.1.2 of [RFC5357].  For symmetrical
   size query and response messages [RFC6038], the DM probe query
   message contains the payload format defined in Section 4.2.1 of
   [RFC5357].

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Sender IPv4 or IPv6 Address              .



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    .  Destination IP Address = Responder IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Sender                            .
    .  Destination Port = User-configured Port for Delay Measurement.
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = Message as specified in Section 4.2.1 of RFC 5357 | |
    . Payload = Message as specified in Section 4.1.2 of RFC 5357 | .
    . Payload = Message specified in Section 4.2 of [I-D.ippm-stamp].
    .                                                               .
    +---------------------------------------------------------------+

                    Figure 1: DM Probe Query Message

   Timestamp field is eight bytes and use the format defined in Section
   4.2.1 of [RFC5357] .  It is recommended to use the IEEE 1588v2
   Precision Time Protocol (PTP) truncated 64-bit timestamp format
   [IEEE1588] as specified in [RFC8186].

4.1.1.1.  Delay Measurement Authentication Mode

   When using the authenticated mode for delay measurement, the matching
   authentication type (e.g. HMAC-SHA-256) and key are user-configured
   on both the sender and responder nodes.  A separate user-configured
   destination UDP port is used for the delay measurement in
   authentication mode due to the different probe message format.

4.1.2.  Loss Measurement Probe Query Message

   In this document, new probe query message formats are defined for
   loss measurement as shown in Figure 3A and Figure 3B.  The message
   formats are hardware efficient due to the small size payload and
   well-known locations of counters.  They are similar to the delay
   measurement message formats and do not require any backwards
   compatibility and support for the existing DM message formats from
   [RFC5357].

   The message content for Loss Measurement probe query message using
   UDP header [RFC768] is shown in Figure 2.  The LM probe query message
   is sent with user-configured Destination UDP port number for LM.
   Separate Destination UDP ports are used for direct-mode and
   inferred-mode loss measurements.  The Destination UDP port cannot be
   used as Source port, since the message does not have any indication
   to distinguish between query and response.  The LM probe query
   message contains the payload for loss measurement as defined in



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   Figure 3A and Figure 3B.  For symmetrical size query and response
   messages [RFC6038], the LM probe query message contains the payload
   format defined in Figure 7A and Figure 7B for loss measurement.


    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Sender IPv4 or IPv6 Address              .
    .  Destination IP Address = Responder IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Sender                            .
    .  Destination Port = User-configured Port for Loss Measurement .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = Message as specified in Figure 3A or 3B |           |
    . Payload = Message as specified in Figure 3C or 3D             .
    .                                                               .
    +---------------------------------------------------------------+

                    Figure 2: LM Probe Query Message


    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|I|  Reserved               |         Block Number          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                        Packet Padding                         .
    .                                                               .
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |      Checksum Complement      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 3A: LM Probe Query Message Format


    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|I|   Reserved              |         Block Number          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (4 octets)                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        HMAC (16 octets)                       |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                        Packet Padding                         .
    .                                                               .
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |      Checksum Complement      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 3B: LM Probe Query Message Format - Authenticated Mode


    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|I|  Reserved               |         Block Number          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                        MBZ (28 octets)                        |
    |                                                               |
    |                                                               |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 3C: STAMP LM Probe Query Message 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|I|   Reserved              |         Block Number          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                                                               ~
    |                        MBZ (68 octets)                        |
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        HMAC (16 octets)                       |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 3D: STAMP LM Probe Query Message Format - Authenticated Mode



   Sequence Number (32-bit): As defined in [RFC5357].

   Transmit Counter (64-bit): The number of packets sent by the sender
   node in the query message and by the responder node in the response
   message.  The counter is always written at the fixed location in the
   probe query and response messages.

   Receive Counter (64-bit): The number of packets received at the
   responder node.  It is written by the responder node in the probe
   response message.

   Sender Counter (64-bit): This is the exact copy of the transmit
   counter from the received query message.  It is written by the
   responder node in the probe response message.

   Sender Sequence Number (32-bit): As defined in [RFC5357].

   Sender TTL: As defined in [RFC5357].

   Flag: The meanings of the Flag bits are:



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      X: Extended counter format indicator.  Indicates the use of
      extended (64-bit) counter values.  Initialized to 1 upon creation
      (and prior to transmission) of an LM Query and copied from an LM
      Query to an LM response.  Set to 0 when the LM message is
      transmitted or received over an interface that writes 32-bit
      counter values.

      B: Octet (byte) count.  When set to 1, indicates that the Counter
      1-4 fields represent octet counts.  The octet count applies to all
      packets within the LM scope, and the octet count of a packet sent
      or received includes the total length of that packet (but excludes
      headers, labels, or framing of the channel itself).  When set to
      0, indicates that the Counter fields represent packet counts.

      I: Inferred Mode Loss Measurement:  When set to 1, indicates that
      inferred-mode of loss measurement is used.  When set to 0, it
      indicates direct-mode of loss measurement is used.


   Block Number (16-bit): The Loss Measurement using Alternate-Marking
   method defined in [RFC8321] requires to identify the Block Number (or
   color) of the traffic counters.  The probe query and response
   messages carry Block Number for the traffic counters for loss
   measurement.  In both probe query and response messages, the counters
   MUST belong to the same Block Number.

   HMAC: The PM probe packet in authenticated mode includes a key Hashed
   Message Authentication Code (HMAC) ([RFC2104]) hash.  Each probe
   query and response messages are authenticated by adding Sequence
   Number with Hashed Message Authentication Code (HMAC) TLV.  It can
   use HMAC-SHA-256 truncated to 128 bits (similarly to the use of it in
   IPSec defined in [RFC4868]); hence the length of the HMAC field is 16
   octets.

   HMAC uses its own key and the mechanism to distribute the HMAC key is
   outside the scope of this document.

   In authenticated mode, only the sequence number is encrypted, and the
   other payload fields are sent in clear text.  The probe packet MAY
   include Comp.MBZ (Must Be Zero) variable length field to align the
   packet on 16 octets boundary.

4.1.2.1.  Loss Measurement Authentication Mode

   When using the authenticated mode for loss measurement, the matching
   authentication type (e.g. HMAC-SHA-256) and key are user-configured
   on both the sender and responder nodes.  A separate user-configured
   destination UDP port is used for the loss measurement in



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   authentication mode due to the different message format.

4.1.3.  Probe Query for SR Links

   The probe query message as defined in Figure 1 is sent on the
   congruent path of the data traffic for Delay measurement.  The probe
   query message as defined in Figure 2 is sent on the congruent path of
   the data traffic for Loss measurement.

4.1.4.  Probe Query for End-to-end Measurement for SR Policy

   The performance delay and loss measurement for segment routing is
   applicable to both SR-MPLS and SRv6 Policies.

4.1.4.1.  Probe Query Message for SR-MPLS Policy

   The probe query messages for end-to-end performance measurement of an
   SR-MPLS Policy is sent using its SR-MPLS header containing the MPLS
   segment list as shown in Figure 4.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment List(1)        | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment List(n)        | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                PSID                   | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Message as shown in Figure 1 for DM or Figure 2 for LM      |
    .                                                               .
    +---------------------------------------------------------------+

             Figure 4: Probe Query Message for SR-MPLS Policy

   The Segment List (SL) can be empty to indicate Implicit NULL label
   case for a single-hop SR Policy.

   The Path Segment Identifier (PSID) [I-D.spring-mpls-path-segment] of
   the SR-MPLS Policy is used for accounting received traffic on the
   egress node for loss measurement.  The PSID is not required for
   end-to-end SR Policy delay measurement.

4.1.4.2.  Probe Query Message for SRv6 Policy



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   An SRv6 Policy setup using the SRv6 Segment Routing Header (SRH) and
   a Segment List as defined in [I-D.6man-segment-routing-header].  The
   probe query messages for end-to-end performance measurement of an
   SRv6 Policy is sent using its SRH and Segment List as shown in Figure
   5.

    +---------------------------------------------------------------+
    |                           SRH                                 |
    .   END.OTP (DM) or END.OP (LM) with Target SRv6 SID            .
    .                                                               .
    +---------------------------------------------------------------+
    |   Message as shown in Figure 1 for DM or Figure 2 for LM      |
    .   (Using IPv6 Source and Destination Addresses)               .
    .                                                               .
    +---------------------------------------------------------------+

              Figure 5: Probe Query Message for SRv6 Policy

   For delay measurement of SRv6 Policy using SRH, END function END.OTP
   [I-D.6man-srv6-oam] is used with the target SRv6 SID to punt probe
   messages on the target node, as shown in Figure 5.  Similarly, for
   loss measurement of SRv6 Policy, END function END.OP
   [I-D.6man-srv6-oam] is used with target SRv6 SID to punt probe
   messages on the target node.

4.2.  Probe Response Message

   The probe response message is sent using the IP/UDP information from
   the received probe query message.  The content of the probe response
   message is shown in Figure 6.

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Responder IPv4 or IPv6 Address           .
    .  Destination IP Address = Source IP Address from Query        .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Responder                         .
    .  Destination Port = Source Port from Query                    .
    .                                                               .
    +---------------------------------------------------------------+
    | DM Payload as specified in Section 4.2.1 of RFC 5357, or      |
    . DM payload as specified in Section 4.3 of [I-D.ippm-stamp]    .
    . LM Payload as specified in Figure 7A or 7B in this document or.
    . LM Payload as specified in Figure 7C or 7D in this document   .
    .                                                               .



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    +---------------------------------------------------------------+

                     Figure 6: Probe Response Message


   In this document, new probe response message formats are defined for
   loss measurement as shown in Figure 7A and Figure 7B.  The message
   formats are hardware efficient due to the small size payload and well
   known locations of the counters.  They are also similar to the delay
   measurement message formats.


    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|I|   Reserved              |         Block Number          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Receive Counter                        |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Sequence Number                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Counter                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|I|   Reserved              |     Sender Block Number       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Sender TTL   |                                               |
    +-+-+-+-+-+-+-+-+                                               +
    |                        Packet Padding                         |
    .                                                               .
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |      Checksum Complement      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 7A: LM Probe Response Message Format


    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|I|   Reserved              |         Block Number          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (4 octets)                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Receive Counter                        |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (8 octets)                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Sequence Number                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Counter                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|I|   Reserved              |     Sender Block Number       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (4 octets)                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Sender TTL   |                                               |
    +-+-+-+-+-+-+-+-+                                               +
    |                        MBZ (15 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        HMAC (16 octets)                       |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                                                               .
    .                        Packet Padding                         .
    .                                                               .
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |     Checksum Complement       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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    Figure 7B: LM Probe Response Message Format - Authenticated Mode


    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|I|   Reserved              |         Block Number          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Receive Counter                        |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Sequence Number                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Counter                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|I|   Reserved              |     Sender Block Number       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Ses-Sender TTL| Reserved                                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 7C: STAMP LM Probe Response Message Format


    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|I|   Reserved              |         Block Number          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (4 octets)                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Receive Counter                        |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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    |                        MBZ (8 octets)                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Sequence Number                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Counter                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|I|   Reserved              |     Sender Block Number       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (4 octets)                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Ses-Sender TTL|                                               |
    +-+-+-+-+-+-+-+-+                                               +
    |                        MBZ (15 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        HMAC (16 octets)                       |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 7D: STAMP LM Probe Response Message Format - Authenticated


4.2.1.  One-way Measurement Mode

   In one-way performance measurement mode, the probe response message
   as defined in Figure 6 is sent back out of band to the sender node,
   for both SR links and SR Policies.

4.2.2.  Two-way Measurement Mode

   In two-way performance measurement mode, when using a bidirectional
   path, the probe response message as defined in Figure 6 is sent back
   on the congruent path of the data traffic to the sender node, for
   both SR links and SR Policies.

4.2.2.1.  Return Path TLV

   For two-way performance measurement, the responder node needs to send
   the probe response message on a specific reverse path.  This way the



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   destination node does not require any additional state.  The sender
   node can request in the probe query message to the responder node to
   send a response back on a given reverse path (e.g. co-routed path for
   two-way measurement).

   [I-D.ippm-stamp-option-tlv] defines STAMP probe query messages that
   can include one or more optional TLVs.  New TLV Type (TBA1) is
   defined in this document for Return Path to carry reverse path for
   probe response messages (in the payload of the message).  The format
   of the Return Path TLV is shown in Figure 8A and Figure 8B:

    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 = TBA1  |    Length     |      Reserved                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Return Path Sub-TLVs                       |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 8A: Return Path TLV


    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      |    Length     |      Reserved                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Segment List(1)                            |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Segment List(n)                            |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 8B: Segment List Sub-TLV in Return Path TLV


   The Segment List Sub-TLV in the Return Path TLV can be one of the
   following Types:


   o  Type (value 1): Respond back on Incoming Interface (Layer-3 and
      Layer-2) (Segment List is Empty)



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   o  Type (value 2): SR-MPLS Segment List (Label Stack) of the Reverse
      SR Path

   o  Type (value 3): SR-MPLS Binding SID [I-D.pce-binding-label-sid] of
      the Reverse SR Policy

   o  Type (value 4): SRv6 Segment List of the Reverse SR Path

   o  Type (value 5): SRv6 Binding SID [I-D.pce-binding-label-sid] of
      the Reverse SR Policy


   The Return Path TLV is optional.  The PM sender node MUST only insert
   one Return Path TLV in the probe query message and the responder node
   MUST only process the first Return Path TLV in the probe query
   message and ignore other Return Path TLVs if present.  The responder
   node MUST send probe response message back on the reverse path
   specified in the Return Path TLV and MUST NOT add Return Path TLV in
   the probe response message.

4.2.2.2.  Probe Response Message for SR-MPLS Policy

   The message content for sending probe response message for two-way
   end-to-end performance measurement of an SR-MPLS Policy is shown in
   Figure 9.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment List(1)        | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment List(n)        | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Message as shown in Figure 6                   |
    .                                                               .
    +---------------------------------------------------------------+

           Figure 9: Probe Response Message for SR-MPLS Policy

   The Path Segment Identifier (PSID) [I-D.spring-mpls-path-segment] of
   the forward SR Policy can be used to find the reverse SR Policy to
   send the probe response message for two-way measurement of SR Policy.

4.2.2.3.  Probe Response Message for SRv6 Policy



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   The message content for sending probe response message on the
   congruent path of the data traffic for two-way end-to-end performance
   measurement of an SRv6 Policy with SRH is shown in Figure 10.

    +---------------------------------------------------------------+
    |                          SRH                                  |
    .   END.OTP (DM) or END.OP (LM) with Target SRv6 SID            .
    .                                                               .
    +---------------------------------------------------------------+
    |   Message as shown in Figure 6                                |
    .   (with IPv6 Source and Destination Addresses)                .
    .                                                               .
    +---------------------------------------------------------------+

            Figure 10: Probe Response Message for SRv6 Policy


4.2.3.  Loopback Measurement Mode

   The Loopback measurement mode can be used to measure round-trip delay
   for a bidirectional SR Path.  The IP header of the probe query
   message contains the destination address equals to the sender address
   and the source address equals to the responder address.  Optionally,
   the probe query message can carry the reverse path information (e.g.
   reverse path label stack for SR-MPLS) as part of the SR header.  The
   responder node does not process the PM probe messages and generate
   response messages.


5.  Performance Measurement for P2MP SR Policies

   The procedures for delay and loss measurement described in this
   document for Point-to-Point (P2P) SR Policies
   [I-D.spring-segment-routing-policy] are also equally applicable to
   the Point-to-Multipoint (P2MP) SR Policies
   [I-D.spring-sr-p2mp-policy] as following:

   o  The sender root node sends probe query messages using the
      Replication Segment defined in [I-D.spring-sr-p2mp-policy] for the
      P2MP SR Policy as shown in Figure 11.

   o  Each responder leaf node sends its IP address in the Source
      Address of the probe response messages.  This allows the sender
      root node to identify the responder leaf nodes of the P2MP SR
      Policy.

   o  The P2MP root node measures the end-to-end delay and loss
      performance for each P2MP leaf node of the P2MP SR Policy.



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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              Replication SID          | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Message as shown in Figure 1 for DM or Figure 2 for LM      |
    .                                                               .
    +---------------------------------------------------------------+

         Figure 11: With Replication Segment for SR-MPLS Policy


6.  ECMP Support for SR Policies

   An SR Policy can have ECMPs between the source and transit nodes,
   between transit nodes and between transit and destination nodes.
   Usage of Anycast SID [RFC8402] by an SR Policy can result in ECMP
   paths via transit nodes part of that Anycast group.  The PM probe
   messages need to be sent to traverse different ECMP paths to measure
   performance delay of an SR Policy.

   Forwarding plane has various hashing functions available to forward
   packets on specific ECMP paths.  The mechanisms described in
   [RFC8029] and [RFC5884] for handling ECMPs are also applicable to the
   performance measurement.  In the IP header of the PM probe messages,
   Destination Addresses in 127/8 range for IPv4 or
   0:0:0:0:0:FFFF:7F00/104 range for IPv6 can be used to exercise a
   particular ECMP path.  As specified in [RFC6437], 3-tuple of Flow
   Label, Source Address and Destination Address fields in the IPv6
   header can also be used.


7.  Additional Message Processing Rules

7.1.  TTL Value

   The TTL or the Hop Limit field in the IP, MPLS and SRH headers of the
   probe query messages are set to 255 [RFC5357].

   When using the Destination IPv4 Address from the 127/8 range, the TTL
   in the IPv4 header is set to 1 [RFC8029].  Similarly, when using the
   Destination IPv6 Address from the 0:0:0:0:0:FFFF:7F00/104 range, the
   Hop Limit field in the inner IPv6 header is set to 1 whereas in the
   outer IPv6 header is set to 255.

7.2.  Router Alert Option

   The Router Alert IP option is not set when using the routable



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   Destination IP Address in the probe messages.

   When using the Destination IPv4 Address from the 127/8 range, to be
   able to punt probe packets on the responder node, the Router Alert IP
   Option of value 0x0 [RFC2113] for IPv4 MAY be added [RFC8029].
   Similarly, when using the Destination IPv6 Address from the
   0:0:0:0:0:FFFF:7F00/104 range, the Router Alert IP Option of value 69
   [RFC7506] for IPv6 MAY be added in the destination option.  For SRv6
   Policy, it is added in the inner IPv6 header.

7.3.  UDP Checksum

   The Checksum Complement for delay and loss measurement messages
   follows the procedure defined in [RFC7820] and can be optionally used
   with the procedures defined in this document.

   For IPv4 and IPv6 probe messages, where the hardware is not capable
   of re-computing the UDP checksum or adding checksum complement
   [RFC7820], the sender node sets the UDP checksum to 0 [RFC6936]
   [RFC8085].  The receiving node bypasses the checksum validation and
   accepts the packets with UDP checksum of 0 for the UDP port being
   used for PM.


8.  Security Considerations

   The performance measurement is intended for deployment in
   well-managed private and service provider networks.  As such, it
   assumes that a node involved in a measurement operation has
   previously verified the integrity of the path and the identity of the
   far-end responder node.

   If desired, attacks can be mitigated by performing basic validation
   and sanity checks, at the sender, of the counter or timestamp fields
   in received measurement response messages.  The minimal state
   associated with these protocols also limits the extent of measurement
   disruption that can be caused by a corrupt or invalid message to a
   single query/response cycle.

   Use of HMAC-SHA-256 in the authenticated mode protects the data
   integrity of the probe messages.  SRv6 has HMAC protection
   authentication defined for SRH [I-D.6man-segment-routing-header].
   Hence, PM probe messages for SRv6 may not need authentication mode.
   Cryptographic measures may be enhanced by the correct configuration
   of access-control lists and firewalls.


9.  IANA Considerations



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   IANA is requested to allocate value for the following Return Path TLV
   Type for [I-D.ippm-stamp-option-tlv] to be carried in PM probe query
   messages:

      o  Type TBA1: Return Path TLV

   IANA is also requested to allocate the values for the following
   Sub-TLV Types for the Return Path TLV.

      o  Type (value 1): Respond back on Incoming Interface (Layer-3 and
                         Layer-2) (Segment List is Empty)

      o  Type (value 2): SR-MPLS Segment List (Label Stack) of the
                         Reverse SR Path

      o  Type (value 3): SR-MPLS Binding SID [I-D.pce-binding-label-sid]
                         of the Reverse SR Policy

      o  Type (value 4): SRv6 Segment List of the Reverse SR Path

      o  Type (value 5): SRv6 Binding SID [I-D.pce-binding-label-sid] of
                         the Reverse SR Policy


10.  References

10.1.  Normative References

   [RFC768]   Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              August 1980.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, March 1997.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, September 2006.

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, October 2008.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", RFC 8174, May 2017.

   [I-D.6man-srv6-oam]  Ali, Z., et al., "Operations, Administration,
              and Maintenance (OAM) in Segment Routing Networks with
              IPv6 Data plane (SRv6)", draft-ietf-6man-spring-srv6-oam,



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              work in progress.

   [I-D.ippm-stamp]  Mirsky, G. et al. "Simple Two-way Active
              Measurement Protocol", draft-ietf-ippm-stamp, work in
              progress.

   [I-D.ippm-stamp-option-tlv]  Mirsky, G., et al., "Simple Two-way
              Active Measurement Protocol Optional Extensions",
              draft-ietf-ippm-stamp-option-tlv, work in progress.

10.2.  Informative References

   [IEEE1588] IEEE, "1588-2008 IEEE Standard for a Precision Clock
              Synchronization Protocol for Networked Measurement and
              Control Systems", March 2008.

   [RFC2104]  Krawczyk, H., Bell-are, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104, February
              1997.

   [RFC2113]  Katz, D., "IP Router Alert Option", RFC 2113, February
              1997.

   [RFC4868]  Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
              384, and HMAC-SHA-512 with IPsec", RFC 4868, May 2007.

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
              June 2010.

   [RFC6038]  Morton, A. and L. Ciavattone, "Two-Way Active Measurement
              Protocol (TWAMP) Reflect Octets and Symmetrical Size
              Features", RFC 6038, October, 2010

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165,RFC
              6335, August 2011.

   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437, November 2011.

   [RFC6936]  Fairhurst, G. and M. Westerlund, "Applicability Statement
              for the Use of IPv6 UDP Datagrams with Zero Checksums",
              RFC 6936, April 2013.




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Internet-Draft      TWAMP Light for Segment Routing     November 4, 2019


   [RFC7506]  Raza, K., Akiya, N., and C. Pignataro, "IPv6 Router Alert
              Option for MPLS Operations, Administration, and
              Maintenance (OAM)", RFC 7506, DOI 10.17487/RFC7506, April
              2015, <http://www.rfc-editor.org/info/rfc7506>.

   [RFC7820]  Mizrahi, T., "UDP Checksum Complement in the One-Way
              Active Measurement Protocol (OWAMP) and Two-Way Active
              Measurement Protocol (TWAMP)", RFC 7820, March 2016.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Kumar, N.,
              Aldrin, S. and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029, March
              2017.

   [RFC8085]  Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
              Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
              March 2017, <http://www.rfc-editor.org/info/rfc8085>.

   [RFC8186]  Mirsky, G., and I. Meilik, "Support of the IEEE 1588
              Timestamp Format in a Two-Way Active Measurement Protocol
              (TWAMP)", RFC 8186, June 2017.

   [RFC8321]  Fioccola, G. Ed., "Alternate-Marking Method for Passive
              and Hybrid Performance Monitoring", RFC 8321, January
              2018.

   [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>.

   [I-D.spring-segment-routing-policy]  Filsfils, C., et al., "Segment
              Routing Policy Architecture",
              draft-ietf-spring-segment-routing-policy, work in
              progress.

   [I-D.spring-sr-p2mp-policy]  Voyer, D. Ed., et al., "SR Replication
              Segment for Multi-point Service Delivery",
              draft-voyer-spring-sr-replication-segment, work in
              progress.

   [I-D.spring-mpls-path-segment]  Cheng, W., et al., "Path Segment in
              MPLS Based Segment Routing Network",
              draft-ietf-spring-mpls-path-segment, work in progress.

   [I-D.6man-segment-routing-header]  Filsfils, C., et al., "IPv6
              Segment Routing Header (SRH)",
              draft-ietf-6man-segment-routing-header, work in progress.



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   [I-D.pce-binding-label-sid]  Filsfils, C., et al., "Carrying Binding
              Label/ Segment-ID in PCE-based Networks",
              draft-ietf-pce-binding-label-sid, work in progress.

   [BBF.TR-390]  "Performance Measurement from IP Edge to Customer
              Equipment using TWAMP Light", BBF TR-390, May 2017.

   [I-D.spring-ioam-sr-mpls]  Gandhi, R. Ed., et al., "Segment Routing
              with MPLS Data Plane Encapsulation for In-situ OAM Data",
              draft-gandhi-spring-ioam-sr-mpls, work in progress.

   [I-D.spring-ioam-srv6]  Ali, Z., et al., "Segment Routing Header
              encapsulation for In-situ OAM Data",
              draft-ali-spring-ioam-srv6, work in progress.


Acknowledgments

   The authors would like to thank Thierry Couture for the discussions
   on the use-cases for TWAMP Light in Segment Routing.  The authors
   would also like to thank Greg Mirsky for reviewing this document and
   providing useful comments and suggestions.  Patrick Khordoc and Radu
   Valceanu, both from Cisco Systems have helped significantly improve
   the mechanisms defined in this document.  The authors would like to
   acknowledge the earlier work on the loss measurement using TWAMP
   described in draft-xiao-ippm-twamp-ext-direct-loss.


Authors' Addresses

   Rakesh Gandhi (editor)
   Cisco Systems, Inc.
   Canada
   Email: rgandhi@cisco.com


   Clarence Filsfils
   Cisco Systems, Inc.
   Email: cfilsfil@cisco.com


   Daniel Voyer
   Bell Canada
   Email: daniel.voyer@bell.ca


   Mach(Guoyi) Chen
   Huawei



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   Email: mach.chen@huawei.com


   Bart Janssens
   Colt
   Email: Bart.Janssens@colt.net













































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