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Simple TWAMP (STAMP) Extensions for Segment Routing Networks
draft-ietf-ippm-stamp-srpm-13

The information below is for an old version of the document.
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This is an older version of an Internet-Draft that was ultimately published as RFC 9503.
Authors Rakesh Gandhi , Clarence Filsfils , Daniel Voyer , Mach Chen , Bart Janssens , Richard "Footer" Foote
Last updated 2023-06-20 (Latest revision 2023-06-19)
Replaces draft-gandhi-ippm-stamp-srpm
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draft-ietf-ippm-stamp-srpm-13
IPPM Working Group                                        R. Gandhi, Ed.
Internet-Draft                                               C. Filsfils
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: 21 December 2023                                       D. Voyer
                                                             Bell Canada
                                                                 M. Chen
                                                                  Huawei
                                                             B. Janssens
                                                                    Colt
                                                                R. Foote
                                                                   Nokia
                                                            19 June 2023

      Simple TWAMP (STAMP) Extensions for Segment Routing Networks
                     draft-ietf-ippm-stamp-srpm-13

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 21 December 2023.

Copyright Notice

   Copyright (c) 2023 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.  Destination Node Address TLV  . . . . . . . . . . . . . . . .   4
   4.  Return Path TLV . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Return Path Sub-TLVs  . . . . . . . . . . . . . . . . . .   8
       4.1.1.  Return Path Control Code Sub-TLV  . . . . . . . . . .   8
       4.1.2.  Return Address Sub-TLV  . . . . . . . . . . . . . . .   9
       4.1.3.  Return Segment List Sub-TLVs  . . . . . . . . . . . .  10
   5.  Interoperability with TWAMP Light . . . . . . . . . . . . . .  12
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

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", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.2.  Abbreviations

   MPLS: Multiprotocol Label Switching.

   PM: Performance Measurement.

   SID: Segment Identifier.

   SR: Segment Routing.

   SR-MPLS: Segment Routing with MPLS forwarding plane.

   SRH: Segment Routing Header.

   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 T1 is a
   transmit timestamp and T4 is a receive timestamp added by node S1 in
   the STAMP test packet.  The T2 is a receive timestamp and T3 is a
   transmit timestamp added by node R1 in the STAMP test packet.

   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.  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 of the Session-Reflector e.g. when the STAMP test packet
   is encapsulated by a tunneling protocol e.g., encapsulated with an
   SR-MPLS Segment List and IPv4 header containing destination IPv4
   address from 127/8 range or encapsulated with outer IPv6 header and
   Segment Routing Header (SRH) with inner IPv6 header containing IPv6
   destination IPv6 address ::1/128.

   In an ECMP environment, the hashing function in forwarding may decide
   the outgoing path using the source address, destination address, UDP
   ports, IPv6 flow-label, etc. from the packet.  Hence for IPv4, for
   example, different values of IPv4 destination address from 127/8
   range may be used in the IPv4 header to measure different ECMP paths.

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   For IPv6, for example, different values of flow-label may be used in
   the IPv6 header to measure different ECMP paths.  In those cases, the
   STAMP test packet may reach the node that is not the Session-
   Reflector for this STAMP session in an error condition, and an un-
   intended node may transmit reply test packet that can result in
   reporting of invalid measurement metrics.

   [RFC8972] defines STAMP Session-Sender and Session-Reflector test
   packets that can include one or more optional TLVs.  In this
   document, the TLV type (value 9 for IPv4 and IPv6) is defined for the
   Destination Node Address TLV for the STAMP test packet [RFC8972].
   The formats of the Destination Node Address TLVs are 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=4              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         IPv4  Address                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    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=16             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                         IPv6 Address                          |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 1: Destination Node Address TLV Format

   TLV fields are defined as follows:

   STAMP TLV Flags : The STAMP TLV Flags follow the procedures described
   in [RFC8972] and this document.

   Type : Type (value 9) for IPv4 Destination Node Address TLV or IPv6
   Destination Node Address TLV.

   Length : A two-octet field equal to the length of the Address field
   in octets.  The length is 4 octet for IPv4 address and 16 octet for
   IPv6 address.

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   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.  The Destination Node Address is also used
   to uniquely identify the STAMP session on the Session-Reflector when
   the optional SSID is not sent.  For security reasons (e.g., to avoid
   node discovery), the Session-Reflector SHOULD use the received
   Destination Node Address as the Source Address in the IP header of
   the reply test packet only if the Destination Node Address is one of
   the addresses on the node, instead of using its Node Address.  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-Reflector that recognizes this TLV, MUST set the U flag
   [RFC8972] 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.  In this case, the Session-
   Reflector does not use the received Destination Node Address as the
   Source Address in the IP header of the reply test packet.  Otherwise,
   the Session-Reflector MUST set the U flag in the Destination Node
   Address TLV in the reply test packet to 0.

4.  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.

   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, measurement 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.

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   [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

   TLV fields are defined as follows:

   STAMP TLV Flags : The STAMP TLV Flags follow the procedures described
   in [RFC8972] and this document.

   Type : Type (value 10) for Return Path TLV.

   Length : A two-octet field equal to the length of the Return Path
   Sub-TLVs field in octets.

   Return Path Sub-TLVs : As defined in Section 5.1.

   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.

   A Session-Reflector that recognizes this TLV, MUST set the U flag
   [RFC8972] 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 U flag in the reply test packet to 0.

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

   A Return Path TLV MUST NOT contain more than one Control Code Sub-TLV
   or more than one Return Address Sub-TLV or more than one Segment List
   Sub-TLV in Session-Sender test packet.

   A Return Path TLV MUST NOT contain both Control Code Sub-TLV as well
   as Return Address or Return Segment List Sub-TLV in Session-Sender
   test packet.

   A Return Path TLV MAY contain both Return Address as well as Return
   Segment List Sub-TLV in Session-Sender test packet.

   Any extra Return Path Sub-TLV not procesed by the Session-Reflector
   is returned to the Session-Sender in reply test packet with U flag
   set to 1.

4.1.1.  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:

    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=4              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                   Control Code Flags                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   TLV fields are defined as follows:

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   *  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 Flags field.

   STAMP TLV Flags : The STAMP TLV Flags follow the procedures described
   in [RFC8972] and this document.

   Length : A two-octet field equal to the length of the Control Code
   flags which is 4 octets.

   Control Code Flags (32-bit): Reply Request Flag at bit 31 (least
   significant bit) is defined as follows.

       0x0 : No Reply Requested.

       0x1 : Reply Requested on the Same Link.

   All other bits are reserved and must be transmitted as 0 and ignored
   by the receiver.

   When Control Code flag for Reply Request 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 for Reply Request 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.  The
   link may be a physical interface, virtual link, or Link Aggregation
   Group (LAG) [IEEE802.1AX], or LAG member.  All other Return Path Sub-
   TLVs MUST be ignored in this case.  When using LAG member links,
   STAMP extension for Micro-Session ID TLV defined in
   [I-D.ietf-ippm-stamp-on-lag] can be used to identify the link.

4.1.2.  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.  This address is different than the Source Address in the
   Session-Sender test packet where normally the reply test packet is
   sent by the Session Reflector.  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-

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   Sender MUST follow the procedure defined in Section 4.3 of [RFC8762].

   The formats of the IPv4 and IPv6 Return Address Sub-TLVs are 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|     Type=2    |         Length=4              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Return IPv4 Address                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    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=16             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                    Return IPv6 Address                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   The TLV fields are defined as follows:

   *  Type : Type (value 2) for IPv4 Return Address or IPv6 Return
      Address.

   The Return Address is the Destination Address of the Session-
   Reflector reply test packet and is different than the Source Address
   in the Session-Sender test packet.

   STAMP TLV Flags : The STAMP TLV Flags follow the procedures described
   in [RFC8972] and this document.

   Length : A two-octet field equal to the length of the Return Address
   field in octets.  The length is 4 octet for IPv4 address and 16 octet
   for IPv6 address.

4.1.3.  Return Segment List Sub-TLVs

   The format of the Segment List Sub-TLVs in the Return Path TLV is
   shown in Figures 5 and 6.  The Segments carried in Segment List Sub-
   TLVs are described in [RFC8402].  The segment entries MUST be in
   network order.

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   The Session-Sender MUST only insert one Segment List Return Path Sub-
   TLV in the test packet and Segment List MUST contain at least one
   Segment.  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.

   TLV fields are defined as follows:

   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

   STAMP TLV Flags : The STAMP TLV Flags follow the procedures described
   in [RFC8972] and this document.

   Length : A two-octet field equal to the length of the Segment List
   field in octets.  Length MUST NOT be 0.

4.1.3.1.  Return Path SR-MPLS Segment-List Sub-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=3    |         Length                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Segment(1)                       | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Segment(n) (bottom of stack)     | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   The SR-MPLS Label Stack contains a list of 32-bit Label Stack Entry
   (LSE) that includes a 20-bit label value, 8-bit Time-To-Live (TTL)
   value, 3-bit Traffic Class (TC) value and 1-bit End-Of-Stack (S)
   field.

   An SR-MPLS Label Stack Sub-TLV may carry only the Binding SID Label
   [I-D.ietf-pce-binding-label-sid] of the Return SR-MPLS Policy.  The
   Binding SID Label of the Return SR-MPLS Policy is known at the
   Session-Reflector.  The mechanism to signal the Binding SID Label to
   the Session-Sender is outside the scope of this document.

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   An SR-MPLS Label Stack Sub-TLV may also include the Path Segment
   Identifier Label of the Return SR-MPLS Policy in the Segment List of
   the SR-MPLS Policy.

4.1.3.2.  Return Path SRv6 Segment-List Sub-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=4    |         Length                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |      Segment(1) (128-bit IPv6 address)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |      Segment(n) (128-bit IPv6 address) (bottom of stack)      |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 6: SRv6 Segment List Sub-TLV in Return Path TLV

   The SRv6 Segment List contains a list of 128-bit IPv6 addresses
   representing the SRv6 SIDs.

   An SRv6 Segment List Sub-TLV may carry only the SRv6 Binding SID
   [I-D.ietf-pce-binding-label-sid] of the Return SRv6 Policy.  The SRv6
   Binding SID of the Return SRv6 Policy is known at the Session-
   Reflector.  The mechanism to signal the SRv6 Binding SID to the
   Session-Sender is outside the scope of this document.

   An SRv6 Segment List Sub-TLV may also include the SRv6 Path Segment
   Identifier of the Return SRv6 Policy in the Segment List of the SRv6
   Policy.

5.  Interoperability with TWAMP Light

   This document does not introduce any additional considerations for
   interoperability with TWAMP Light than those described in Section 4.6
   of [RFC8762].

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   As desctibed in [RFC8762], there are two possible combinations for
   such a interoperability use case:

   - STAMP Session-Sender with TWAMP Light Session-Reflector

   - TWAMP Light Session-Sender with STAMP Session-Reflector

   If any of STAMP extensions defined in this document are used by STAMP
   Session-Sender, the TWAMP Light Session-Reflector will view them as
   the Packet Padding field.

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.

   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
   authenticated mode and 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.

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   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   | This      |
        |                      | IPv4 or IPv6 Address | document  |
        +----------------------+----------------------+-----------+
        | 10 (Early            |     Return Path      | This      |
        | Allocation)          |                      | document  |
        +----------------------+----------------------+-----------+

                          Table 1: STAMP TLV Types

   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:

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          +===========+=========================+===============+
          | 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 IPv4 or IPv6 Address       | This document |
     +------+----------------------------------------+---------------+
     | 3    | SR-MPLS Label Stack of the Return Path | This document |
     +------+----------------------------------------+---------------+
     | 4    |  SRv6 Segment List of the Return Path  | This document |
     +------+----------------------------------------+---------------+
     | 255  |                Reserved                | This document |
     +------+----------------------------------------+---------------+

                     Table 3: Return Path Sub-TLV Types

   IANA is requested to create a sub-registry for "Return Path Control
   Code Flags" for the Return Path Control Code Sub-TLV.  All code
   points in the bit position 31 (counting from bit 31 as the least
   significant bit) through 12 in this registry shall be allocated
   according to the "IETF Review" procedure as specified in [RFC8126].
   Code points in the bit position 11 through 8 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 4:

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           +=========+=========================+===============+
           | Bit     |       Description       | Reference     |
           +=========+=========================+===============+
           | 31 - 12 |       IETF Review       | This document |
           +---------+-------------------------+---------------+
           | 11 - 8  | First Come First Served | This document |
           +---------+-------------------------+---------------+
           | 7 - 4   |     Experimental Use    | This document |
           +---------+-------------------------+---------------+
           | 3 - 0   |       Private Use       | This document |
           +---------+-------------------------+---------------+

              Table 4: Return Path Control Code Flags Registry

   IANA is requested to allocate the value for the following Return Path
   Control Code Flag from this registry.

                  +=====+===============+===============+
                  | Bit |  Description  | Reference     |
                  +=====+===============+===============+
                  | 31  | Reply Request | This document |
                  +-----+---------------+---------------+

                  Table 5: Return Path Control Code 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>.

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8.2.  Informative References

   [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-16, 27
              March 2023, <https://www.ietf.org/archive/id/draft-ietf-
              pce-binding-label-sid-16.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-11,
              13 March 2023, <https://www.ietf.org/archive/id/draft-
              ietf-ippm-stamp-yang-11.txt>.

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   [I-D.ietf-ippm-stamp-on-lag]
              Li, Z., Zhou, T., Guo, J., Mirsky, G., and R. Gandhi,
              "Simple Two-Way Active Measurement Protocol Extensions for
              Performance Measurement on LAG", Work in Progress,
              Internet-Draft, draft-ietf-ippm-stamp-on-lag-01, 3 March
              2023, <https://www.ietf.org/archive/id/draft-ietf-ippm-
              stamp-on-lag-01.txt>.

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

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, Henrik Nydell, and Cheng Li for providing comments and
   suggestions.  Thank you Joel Halpern for Gen-ART review, Martin Duke
   for AD review, and Kathleen Moriarty for Security review.  The
   authors would like to thank Robert Wilton, √Čric Vyncke, Paul Wouters,
   and Jim Guichard for IESG review.

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

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

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

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