IPPM Working Group                                        R. Gandhi, Ed.
Internet-Draft                                               C. Filsfils
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: 12 February 2023                                       D. Voyer
                                                             Bell Canada
                                                                 M. Chen
                                                                  Huawei
                                                             B. Janssens
                                                                    Colt
                                                                R. Foote
                                                                   Nokia
                                                          11 August 2022


      Simple TWAMP (STAMP) Extensions for Segment Routing Networks
                     draft-ietf-ippm-stamp-srpm-05

Abstract

   Segment Routing (SR) leverages the source routing paradigm.  SR is
   applicable to both Multiprotocol Label Switching (SR-MPLS) and IPv6
   (SRv6) forwarding planes.  This document specifies RFC 8762 (Simple
   Two-Way Active Measurement Protocol (STAMP)) extensions for SR
   networks, for both SR-MPLS and SRv6 forwarding planes by augmenting
   the optional extensions defined in RFC 8972.

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."

   This Internet-Draft will expire on 12 February 2023.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   3
     2.3.  Reference Topology  . . . . . . . . . . . . . . . . . . .   4
   3.  Verification Check Flag in TLV  . . . . . . . . . . . . . . .   4
   4.  Destination Node Address TLV  . . . . . . . . . . . . . . . .   5
   5.  Return Path TLV . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Return Path Sub-TLVs  . . . . . . . . . . . . . . . . . .   8
       5.1.1.  Return Path Control Code Sub-TLV  . . . . . . . . . .   8
       5.1.2.  Return Address Sub-TLV  . . . . . . . . . . . . . . .   9
       5.1.3.  Return Segment List Sub-TLVs  . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   Segment Routing (SR) leverages the source routing paradigm for
   Software Defined Networks (SDNs).  SR is applicable to both
   Multiprotocol Label Switching (SR-MPLS) and IPv6 (SRv6) forwarding
   planes [RFC8402].  SR Policies as defined in [RFC9256] are used to
   steer traffic through a specific, user-defined paths using a stack of
   Segments.  A comprehensive SR Performance Measurement (PM) toolset is
   one of the essential requirements to measure network performance to
   provide Service Level Agreements (SLAs).










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   The Simple Two-Way Active Measurement Protocol (STAMP) provides
   capabilities for the measurement of various performance metrics in IP
   networks [RFC8762] without the use of a control channel to pre-signal
   session parameters.  [RFC8972] defines optional extensions, in the
   form of TLVs, for STAMP.  Note that the YANG data model defined in
   [I-D.ietf-ippm-stamp-yang] can be used to provision the STAMP
   Session-Sender and STAMP Session-Reflector.

   The STAMP test packets are transmitted along an IP path between a
   Session-Sender and a Session-Reflector to measure performance delay
   and packet loss along that IP path.  It may be desired in SR networks
   that the same path (same set of links and nodes) between the Session-
   Sender and Session-Reflector is used for the STAMP test packets in
   both directions.  This is achieved by using the STAMP [RFC8762]
   extensions for SR-MPLS and SRv6 networks specified in this document
   by augmenting the optional extensions defined in [RFC8972].

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

   MPLS: Multiprotocol Label Switching.

   PM: Performance Measurement.

   SID: Segment ID.

   SL: Segment List.

   SR: Segment Routing.

   SR-MPLS: Segment Routing with MPLS forwarding plane.

   SRv6: Segment Routing with IPv6 forwarding plane.

   SSID: STAMP Session Identifier.

   STAMP: Simple Two-Way Active Measurement Protocol.






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2.3.  Reference Topology

   In the reference topology shown below, the STAMP Session-Sender S1
   initiates a STAMP test packet and the STAMP Session-Reflector R1
   transmits a reply STAMP test packet.  The reply test packet may be
   transmitted to the Session-Sender S1 on the same path (same set of
   links and nodes) or a different path in the reverse direction from
   the path taken towards the Session-Reflector R1.

   The nodes S1 and R1 may be connected via a link or an SR path
   [RFC8402].  The link may be a physical interface, virtual link, or
   Link Aggregation Group (LAG) [IEEE802.1AX], or LAG member.  The SR
   path may be an SR Policy [RFC9256] on node S1 (called head-end) with
   destination to node R1 (called tail-end).

                          T1                T2
                         /                   \
                +-------+     Test Packet     +-------+
                |       | - - - - - - - - - ->|       |
                |   S1  |=====================|   R1  |
                |       |<- - - - - - - - - - |       |
                +-------+  Reply Test Packet  +-------+
                         \                   /
                          T4                T3

            STAMP Session-Sender        STAMP Session-Reflector

                          Reference Topology

3.  Verification Check Flag in TLV

   The STAMP TLV option in [RFC8972] defines the use of the 8-bit flags
   field common to all STAMP TLVs.

   A one-bit flag called Verification Check (V) is defined at bit
   position (3) in the flags field of the STAMP TLV.  A Session-Sender
   MUST set the V flag to 0 before transmitting an extended STAMP test
   packet when reply test packet is required.  A Session-Reflector MUST
   set the V flag to 1 for any STAMP TLV that it supports that includes
   an instruction that cannot be met or conflicts with the Session-
   Reflector processing or capability.  The V flag MUST be set to 0 by
   the Session-Reflector when the instruction from the request is met.









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   A Session-Sender MUST set the V flag to 1 before transmitting an
   extended STAMP test packet when test packet reply is not required.  A
   Session-Reflector MUST NOT reply and MUST drop the test packet if the
   Session-Reflector determined for any STAMP TLV that is supports that
   includes an instruction that cannot be met or is in conflict with the
   Session-Reflector policy or capability.

   For the STAMP Session-Reflector that supports the STAMP TLV
   extensions defined in this document, the test packets may carry
   additional instructions in a TLV for the Session-Reflector to follow.
   In this case, the V flag provides feedback to the Session-Sender if
   the Session-Reflector was able to follow that instruction.  For
   example, Session-Reflector supports the TLV and it is well-formed,
   the STAMP test packet including all the TLVs was successfully
   processed but the additional instruction in one of the TLVs was not
   followed.  The Session-Reflector can either drop the packet or return
   the packet with the error back to the Session-Sender, based on the
   request in the test packet and local policy.

4.  Destination Node Address TLV

   The Session-Sender may need to transmit test packets to the Session-
   Reflector with a different destination address that is not matching
   an address on the Session-Reflector e.g. when the STAMP test packet
   is encapsulated by a tunneling protocol or an MPLS Segment List with
   destination IPv4 address from 127/8 range or Segment Routing Header
   (SRH) with destination IPv6 address ::1/128.  When using IPv4
   destination address from 127/8 range (e.g. for testing in an ECMP
   environment), the STAMP test packet may not reach the intended
   Session-Reflector in an error condition, and an un-intended node may
   transmit reply test packet resulting in reporting of invalid
   measurement metrics.

   [RFC8972] defines STAMP test packets that can include one or more
   optional TLVs.  In this document, the TLV type (value 9) is defined
   for the Destination Node Address TLV for the STAMP test packet
   [RFC8972].  The format of the Destination Node Address TLV is shown
   in Figure 1:

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|    Type=9     |         Length                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                           Address                             .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 1: Destination Node Address TLV Format



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   The Length field is used to decide the Address Family of the Address.

   The STAMP TLV Flags are set using the procedures described in
   [RFC8972].

   The Destination Node Address TLV is optional.  The Destination Node
   Address TLV indicates the address of the intended Session-Reflector
   node of the test packet that is also used to uniquely identify the
   STAMP session on the Session-Reflector when the optional SSID is not
   sent.  The Session-Reflector MUST add the received Destination Node
   Address TLV in the reply test packet to ensure the symmetric reply
   test packet size and to transmit the STAMP TLV Flags to the Session-
   Sender.

   A Session-Sender MUST set the V flag to 0 before transmitting an
   extended STAMP test packet when test packet reply is required.  A
   Session-Reflector that supports this TLV, MUST set the V flag in the
   reply test packet to 1 if the Session-Reflector determined that it is
   not the intended Destination as identified in the Destination Node
   Address TLV.  Otherwise, the Session-Reflector MUST set the V flag in
   the reply test packet to 0.

   A Session-Sender MUST set the V flag to 1 before transmitting an
   extended STAMP test packet when test packet reply is not required.  A
   Session-Reflector that supports this TLV, MUST NOT reply and MUST
   drop the test packet if the Session-Reflector determined that it is
   not the intended Destination as identified in the Destination Node
   Address TLV.

5.  Return Path TLV

   For end-to-end SR paths, the Session-Reflector may need to transmit
   the reply test packet on a specific return path.  The Session-Sender
   can request this in the test packet to the Session-Reflector using a
   Return Path TLV.  With this TLV carried in the Session-Sender test
   packet, signaling and maintaining dynamic SR network state for the
   STAMP sessions on the Session-Reflector are avoided.














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   There are two modes defined for the behaviors on the Session-
   Reflector in Section 4 of [RFC8762].  A Stateful Session-Reflector
   that requires configuration that must match all Session-Sender
   parameters, including Source Address, Destination Address, Source UDP
   Port, Destination UDP Port, and possibly SSID (assuming the SSID is
   configurable and not auto-generated).  In this case, a local policy
   can be used to direct the test packet by creating additional states
   for the STAMP sessions on the Session-Reflector.  In the case of
   promiscuous operation, the Stateless Session-Reflector will require
   an indication of how to return the test packet on a specific path,
   for example, in an ECMP environment.

   For links, the Session-Reflector may need to transmit the reply test
   packet on the same incoming link in the reverse direction.  The
   Session-Sender can request this in the test packet to the Session-
   Reflector using a Return Path TLV.

   [RFC8972] defines STAMP test packets that can include one or more
   optional TLVs.  In this document, the TLV Type (value 10) is defined
   for the Return Path TLV that carries the return path for the Session-
   Sender test packet.  The format of the Return Path TLV is shown in
   Figure 2:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|    Type=10    |         Length                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                   Return Path Sub-TLVs                        |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 2: Return Path TLV

   The STAMP TLV Flags are set using the procedures described in
   [RFC8972].

   The Return Path TLV is optional.  The Session-Sender MUST only insert
   one Return Path TLV in the STAMP test packet.  The Session-Reflector
   that supports this TLV, MUST only process the first Return Path TLV
   in the test packet and ignore other Return Path TLVs if present, and
   it MUST add the received Return Path TLV (including all Sub-TLVs) in
   the reply test packet to ensure the symmetric reply test packet size
   and to transmit the STAMP TLV Flags to the Session-Sender.  The
   Session-Reflector that supports this TLV MUST reply using the Return
   Path received in the Session-Sender test packet.  In the case where
   the Session-Reflector does not support this TLV, the procedure
   defined in [RFC8762] is followed by the Session-Reflector.



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   A Session-Sender MUST set the V flag to 0 before transmitting an
   extended STAMP test packet when test packet reply is required.  A
   Session-Reflector that supports this TLV, MUST set the V flag in the
   reply test packet to 1 if the Session-Reflector determined that it
   cannot use the return path in the test packet to transmit the reply
   test packet.  Otherwise, the Session-Reflector MUST set the V flag in
   the reply test packet to 0.

   A Session-Sender MUST set the V flag to 1 before transmitting an
   extended STAMP test packet when test packet reply is not required.  A
   Session-Reflector that supports this TLV, MUST NOT reply and MUST
   drop the test packet if the Session-Reflector determined that it
   cannot use the return path in the test packet to transmit the reply
   test packet.

5.1.  Return Path Sub-TLVs

   The Return Path TLV contains one or more Sub-TLVs to carry the
   information for the requested return path.  A Return Path Sub-TLV can
   carry Return Path Control Code, Return Path IP Address or Return Path
   Segment List.

   The STAMP Sub-TLV Flags are set using the procedures described in
   [RFC8972].

   When Return Path Sub-TLV is present in the Session-Sender test
   packet, the Session-Reflector that supports this TLV, MUST transmit
   reply test packet using the return path information specified in the
   Return Path Sub-TLV.

   A Return Path TLV MUST NOT contain both Control Code Sub-TLV as well
   as Return Address or Return Segment List Sub-TLV.

5.1.1.  Return Path Control Code Sub-TLV

   The format of the Return Path Control Code Sub-TLV is shown in
   Figure 3.  The Type of the Return Path Control Code Sub-TLV is
   defined as following:

   *  Type (value 1): Return Path Control Code.  The Session-Sender can
      request the Session-Reflector to transmit the reply test packet
      based on the flags defined in the Control Code field.









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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|   Type=1      |         Length                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                   Control Code                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 3: Control Code Sub-TLV in Return Path TLV

   Control Code Flags (32-bit): Defined as follows.

       0x0: No Reply Requested.

       0x1: Reply Requested on the Same Link.

   When Control Code flag is set to 0x0 in the Session-Sender test
   packet, the Session-Reflector does not transmit reply test packet to
   the Session-Sender and terminates the STAMP test packet.  Only the
   one-way measurement is applicable in this case.  Optionally, the
   Session-Reflector may locally stream performance metrics via
   telemetry using the information from the received test packet.  All
   other Return Path Sub-TLVs MUST be ignored in this case.

   When Control Code flag is set to 0x1 in the Session-Sender test
   packet, the Session-Reflector transmits the reply test packet over
   the same incoming link where the test packet is received in the
   reverse direction towards the Session-Sender.  All other Return Path
   Sub-TLVs MUST be ignored in this case.

5.1.2.  Return Address Sub-TLV

   The STAMP reply test packet may be transmitted to the Session-Sender
   to a different destination address on the Session-Sender using Return
   Path TLV.  For this, the Session-Sender can specify in the test
   packet the receiving destination node address for the Session-
   Reflector reply test packet.  When transmitting the STAMP test packet
   to a different destination address, the Session-Sender MUST follow
   the procedure defined in Section 4.3 of [RFC8762].

   The format of the Return Address Sub-TLV is shown in Figure 4.  The
   Address Family field indicates the type of the address, and it SHALL
   be set to one of the assigned values in the "IANA Address Family
   Numbers" registry.  The Type of the Return Address Sub-TLV is defined
   as following:






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   *  Type (value 2): Return Address.  Destination node address of the
      Session-Reflector reply test packet different than the Source
      Address in the Session-Sender test 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|     Type=2    |         Length                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Reserved                      | Address Family                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                           Address                             .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 4: Return Address Sub-TLV in Return Path TLV

5.1.3.  Return Segment List Sub-TLVs

   The format of the Segment List Sub-TLVs in the Return Path TLV is
   shown in Figures 5, 6, and 7.  The segment entries MUST be in network
   order.  The Segment List Sub-TLV can be one of the following Types:

   *  Type (value 3): SR-MPLS Label Stack of the Return Path

   *  Type (value 4): SRv6 Segment List of the Return Path

   *  Type (value 5): Structured SRv6 Segment List of the Return Path

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|     Type=3    |         Length                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Segment(1)                                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Segment(n) (bottom of stack)               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 5: SR-MPLS Segment List Sub-TLV in Return Path TLV








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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|     Type=4    |         Length                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                    Segment(1)                                 |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                    Segment(n) (bottom of stack)               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 6: SRv6 Segment List Sub-TLV in 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|     Type=5    |         Length                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    LB Length  |  LN Length    | Fun. Length   |  Arg. Length  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                    Segment(1)                                 |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    LB Length  |  LN Length    | Fun. Length   |  Arg. Length  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                    Segment(n) (bottom of stack)               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 7: Structured SRv6 Segment List Sub-TLV in Return Path TLV




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   The SR-MPLS Label Stack contains a list of 32-bit Label Stack Entry
   (LSE) that includes a 20-bit label value, 8-bit TTL value, 3-bit TC
   value and 1-bit EOS field.  An SR-MPLS Label Stack Sub-TLV may carry
   only Binding SID Label [I-D.ietf-pce-binding-label-sid] of the Return
   SR-MPLS Policy.

   An SRv6 Segment List Sub-TLV and Structured SRv6 Segment List Sub-TLV
   may carry only Binding SID [I-D.ietf-pce-binding-label-sid] of the
   Return SRv6 Policy.

   A Structured SRv6 Segment List Sub-TLV is used carry the structure
   and behavior for SRv6 SIDs [RFC8986] used in the Return SRv6 path as
   shown in Figure 7.  The structure is intended for informational use
   by the control and management planes.  The fields in the structure of
   the Sub-TLV are defined as follows [RFC8986]:

   *  LB Length: 1 octet.  SRv6 SID Locator Block (LB) length in bits.

   *  LN Length: 1 octet.  SRv6 SID Locator Node (LN) length in bits.

   *  Fun. Length: 1 octet.  SRv6 SID Function length in bits.

   *  Arg. Length: 1 octet.  SRv6 SID Arguments length in bits.

   In Structured SRv6 Segment List Sub-TLV, the sum of all four sizes
   MUST be less than or equal to 128 bits.  If the sum of all four sizes
   is larger than 128 bits, the Sub-TLV MUST NOT be used by the Session-
   Reflector.

   The Session-Sender MUST only insert one Segment List Return Path Sub-
   TLV in the test packet.  The Session-Reflector MUST only process the
   first Segment List Return Path Sub-TLV in the test packet and ignore
   other Segment List Return Path Sub-TLVs if present.

   Note that in addition to P2P SR paths, the Return Segment List Sub-
   TLV is also applicable to P2MP SR paths.  For example, for P2MP SR
   paths, it may only carry the Node Segment Identifier of the Session-
   Sender in order for the reply test packet to follow an SR path to the
   Session-Sender.

6.  Security Considerations

   The usage of STAMP protocol is intended for deployment in limited
   domains [RFC8799].  As such, it assumes that a node involved in STAMP
   protocol operation has previously verified the integrity of the path
   and the identity of the far-end Session-Reflector.





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   If desired, attacks can be mitigated by performing basic validation
   and sanity checks, at the Session-Sender, of the timestamp fields in
   received reply test packets.  The minimal state associated with these
   protocols also limits the extent of measurement disruption that can
   be caused by a corrupt or invalid test packet to a single test cycle.

   The security considerations specified in [RFC8762] and [RFC8972] also
   apply to the extensions defined in this document.  Specifically, the
   message integrity protection using HMAC, as defined in [RFC8762]
   Section 4.4, also apply to the procedure described in this document.

   STAMP uses the well-known UDP port number that could become a target
   of denial of service (DoS) or could be used to aid man-in-the-middle
   (MITM) attacks.  Thus, the security considerations and measures to
   mitigate the risk of the attack documented in Section 6 of [RFC8545]
   equally apply to the STAMP extensions in this document.

   The STAMP extensions defined in this document may be used for
   potential "proxying" attacks.  For example, a Session-Sender may
   specify a return path that has a destination different from that of
   the Session-Sender.  But normally, such attacks will not happen in an
   SR domain where the Session-Senders and Session-Reflectors belong to
   the same domain.  In order to prevent using the extension defined in
   this document for proxying any possible attacks, the return path has
   destination to the same node where the forward path is from.  The
   Session-Reflector may drop the Session-Sender test packet when it
   cannot determine whether the Return Path has the destination to the
   Session-Sender.  That means, the Session-Sender should choose a
   proper source address according to the specified Return Path to help
   the Session-Reflector to make that decision.

7.  IANA Considerations

   IANA has created the "STAMP TLV Types" registry for [RFC8972].  IANA
   has early allocated a value for the Destination Address TLV Type and
   a value for the Return Path TLV Type from the IETF Review TLV range
   of the same registry.

   +=======================+==========================+===============+
   | Value                 |       Description        | Reference     |
   +=======================+==========================+===============+
   | 9 (Early Allocation)  | Destination Node Address | This document |
   +-----------------------+--------------------------+---------------+
   | 10 (Early Allocation) |       Return Path        | This document |
   +-----------------------+--------------------------+---------------+

                         Table 1: STAMP TLV Types




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   IANA is requested to create a sub-registry for "Return Path Sub-TLV
   Type".  All code points in the range 1 through 175 in this registry
   shall be allocated according to the "IETF Review" procedure as
   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 as specified in [RFC8126].  Remaining code points
   are allocated according to Table 2:

          +===========+=========================+===============+
          | Value     |       Description       | Reference     |
          +===========+=========================+===============+
          | 1 - 175   |       IETF Review       | This document |
          +-----------+-------------------------+---------------+
          | 176 - 239 | First Come First Served | This document |
          +-----------+-------------------------+---------------+
          | 240 - 251 |     Experimental Use    | This document |
          +-----------+-------------------------+---------------+
          | 252 - 254 |       Private Use       | This document |
          +-----------+-------------------------+---------------+

                 Table 2: Return Path Sub-TLV Type Registry

   IANA is requested to allocate the values for the following Sub-TLV
   Types from this registry.

     +======+========================================+===============+
     | Type |              Description               | Reference     |
     +======+========================================+===============+
     | 0    |                Reserved                | This document |
     +------+----------------------------------------+---------------+
     | 1    |        Return Path Control Code        | This document |
     +------+----------------------------------------+---------------+
     | 2    |             Return Address             | This document |
     +------+----------------------------------------+---------------+
     | 3    | SR-MPLS Label Stack of the Return Path | This document |
     +------+----------------------------------------+---------------+
     | 4    |  SRv6 Segment List of the Return Path  | This document |
     +------+----------------------------------------+---------------+
     | 5    |  Structured SRv6 Segment List of the   | This document |
     |      |              Return Path               |               |
     +------+----------------------------------------+---------------+
     | 255  |                Reserved                | This document |
     +------+----------------------------------------+---------------+

                     Table 3: Return Path Sub-TLV Types






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   IANA has created the "STAMP TLV Flags" subregistry.  IANA has early
   allocated the following bit position in the "STAMP TLV Flags"
   subregistry.

    +======================+========+====================+===========+
    | Bit Position         | Symbol |    Description     | Reference |
    +======================+========+====================+===========+
    | 3 (Early Allocation) |   V    | Verification Check | This      |
    |                      |        |                    | document  |
    +----------------------+--------+--------------------+-----------+

                         Table 4: STAMP TLV Flags

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8762]  Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple
              Two-Way Active Measurement Protocol", RFC 8762,
              DOI 10.17487/RFC8762, March 2020,
              <https://www.rfc-editor.org/info/rfc8762>.

   [RFC8972]  Mirsky, G., Min, X., Nydell, H., Foote, R., Masputra, A.,
              and E. Ruffini, "Simple Two-Way Active Measurement
              Protocol Optional Extensions", RFC 8972,
              DOI 10.17487/RFC8972, January 2021,
              <https://www.rfc-editor.org/info/rfc8972>.

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/info/rfc8986>.

8.2.  Informative References







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   [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>.

   [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>.

   [RFC8545]  Morton, A., Ed. and G. Mirsky, Ed., "Well-Known Port
              Assignments for the One-Way Active Measurement Protocol
              (OWAMP) and the Two-Way Active Measurement Protocol
              (TWAMP)", RFC 8545, DOI 10.17487/RFC8545, March 2019,
              <https://www.rfc-editor.org/info/rfc8545>.

   [RFC8799]  Carpenter, B. and B. Liu, "Limited Domains and Internet
              Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
              <https://www.rfc-editor.org/info/rfc8799>.

   [RFC9256]  Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture",
              RFC 9256, DOI 10.17487/RFC9256, July 2022,
              <https://www.rfc-editor.org/info/rfc9256>.

   [I-D.ietf-pce-binding-label-sid]
              Sivabalan, S., Filsfils, C., Tantsura, J., Previdi, S.,
              and C. L. (editor), "Carrying Binding Label/Segment
              Identifier in PCE-based Networks.", Work in Progress,
              Internet-Draft, draft-ietf-pce-binding-label-sid-15, 20
              March 2022, <https://www.ietf.org/archive/id/draft-ietf-
              pce-binding-label-sid-15.txt>.

   [I-D.ietf-ippm-stamp-yang]
              Mirsky, G., Min, X., and W. S. Luo, "Simple Two-way Active
              Measurement Protocol (STAMP) Data Model", Work in
              Progress, Internet-Draft, draft-ietf-ippm-stamp-yang-10,
              10 July 2022, <https://www.ietf.org/archive/id/draft-ietf-
              ippm-stamp-yang-10.txt>.

   [IEEE802.1AX]
              IEEE Std. 802.1AX, "IEEE Standard for Local and
              metropolitan area networks - Link Aggregation", November
              2008.







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Acknowledgments

   The authors would like to thank Thierry Couture for the discussions
   on the use-cases for Performance Measurement in Segment Routing.  The
   authors would also like to thank Greg Mirsky, Mike Koldychev, Gyan
   Mishra, Tianran Zhou, Al Mortons, Reshad Rahman, Zhenqiang Li, Frank
   Brockners, and Cheng Li for providing comments and suggestions.

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
   Email: mach.chen@huawei.com


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


   Richard Foote
   Nokia
   Email: footer.foote@nokia.com












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