SPRING Working Group                                      R. Gandhi, Ed.
Internet-Draft                                               C. Filsfils
Intended status: Standards Track Informational                       Cisco Systems, Inc.
Expires: January 7, 2022                                        D. Voyer
                                                             Bell Canada
                                                                 M. Chen
                                                                  Huawei
                                                             B. Janssens
                                                                    Colt
                                                                R. Foote
                                                                   Nokia
                                                           July 06, 2021

 Performance Measurement Using Simple TWAMP (STAMP) for Segment Routing
                                Networks
                    draft-ietf-spring-stamp-srpm-00
                    draft-ietf-spring-stamp-srpm-01

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 describes procedures for
   Performance Measurement in SR networks using the mechanisms defined
   in RFC 8762 (Simple Two-Way Active Measurement Protocol (STAMP)) and
   its optional extensions defined in RFC 8972 and further augmented in
   draft-ietf-ippm-stamp-srpm.  The procedure described is applicable to
   SR-MPLS and SRv6 data planes and is used for both links and end-to-
   end SR paths including SR Policies.

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   3
     2.3.  Reference Topology  . . . . . . . . . . . . . . . . . . .   4
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Example STAMP Reference Model . . . . . . . . . . . . . .   6
   4.  Delay Measurement for Links and SR Paths  . . . . . . . . . .   7
     4.1.  Session-Sender Test Packet  . . . . . . . . . . . . . . .   7
       4.1.1.  Session-Sender Test Packet for Links  . . . . . . . .   8
       4.1.2.  Session-Sender Test Packet for SR Paths . . . . . . .   8
     4.2.  Session-Reflector Test Packet . . . . . . . . . . . . . .  10
       4.2.1.  One-way Measurement Mode  . . . . . . . . . . . . . .  11
       4.2.2.  Two-way Measurement Mode  . . . . . . . . . . . . . .  11
       4.2.3.  Loopback Measurement Mode . . . . . . . . . . . . . .  13
     4.3.  Delay Measurement for P2MP SR Policies  . . . . . . . . .  14
     4.4.  Additional STAMP Test Packet Processing Rules . . . . . .  15
       4.4.1.  TTL . . . . . . . . . . . . . . . . . . . . . . . . .  16
       4.4.2.  IPv6 Hop Limit  . . . . . . . . . . . . . . . . . . .  16
       4.4.3.  Router Alert Option . . . . . . . . . . . . . . . . .  16
       4.4.4.  UDP Checksum  . . . . . . . . . . . . . . . . . . . .  16
   5.  Packet Loss Measurement for Links and SR Paths  . . . . . . .  16
   6.  Direct Measurement for Links and SR Paths . . . . . . . . . .  16
   7.  Session State for Links and SR Paths  . . . . . . . . . . . .  17
   8.  ECMP Support for SR Policies  . . . . . . . . . . . . . . . .  17
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     11.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

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 [RFC8402].  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.ietf-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 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 for STAMP.
   [I-D.ietf-ippm-stamp-srpm] augments that framework to define STAMP
   extensions for SR networks.

   This document describes procedures for Performance Measurement in SR
   networks using the mechanisms defined in STAMP [RFC8762] and its
   optional extensions defined in [RFC8972] and further augmented in
   [I-D.ietf-ippm-stamp-srpm].  The procedure described is applicable to
   SR-MPLS and SRv6 data planes and is used for both links and end-to-
   end SR paths including SR Policies [RFC8402].

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.

   HL: Hop Limit.

   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.

   SHA: Secure Hash Algorithm.

   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.

   SSID: STAMP Session Identifier.

   STAMP: Simple Two-way Active Measurement Protocol.

   TC: Traffic Class.

   TTL: Time To Live.

2.3.  Reference Topology

   In the Reference Topology shown below, the STAMP Session-Sender R1
   initiates a STAMP test packet and the STAMP Session-Reflector R3
   transmits a reply test packet.  The reply test packet may be
   transmitted to the STAMP Session-Sender R1 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.

   The nodes R1 and R3 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 link.  The
   SR path may be an SR Policy [I-D.ietf-spring-segment-routing-policy]
   on node R1 (called head-end) with destination to node R3 (called
   tail-end).

                          T1                T2
                         /                   \
                +-------+     Test Packet     +-------+
                |       | - - - - - - - - - ->|       |
                |   R1  |=====================|   R3  |
                |       |<- - - - - - - - - - |       |
                +-------+  Reply Test Packet  +-------+
                         \                   /
                          T4                T3

            STAMP Session-Sender        STAMP Session-Reflector

                          Reference Topology

3.  Overview

   For performance measurement in SR networks, the STAMP Session-Sender
   and Session-Reflector test packets defined in [RFC8762] are used.
   The STAMP test packets require to be encapsulated to be transmitted
   on a desired path under measurement.  The base STAMP test packets can
   be encapsulated using IP/UDP header and may use Destination UDP port
   862 [RFC8762].  In this document, the STAMP packets using IP/UDP
   header are considered for SR networks.

   The STAMP test packets are used in one-way, two-way (i.e. round-trip)
   and loopback measurement modes.  Note that one-way and round-trip are
   referred to in [RFC8762] and are further described in this document
   because of the introduction of loopback measurement mode in SR
   networks.  The procedures defined in this document are also used to
   infer packet loss in SR networks.

   The STAMP test packets are transmitted on the same path as the data
   traffic flow under measurement to measure the delay and packet loss
   experienced by the data traffic flow.

   Typically, the STAMP test packets are transmitted along an IP path
   between a Session-Sender and a Session-Reflector to measure delay and
   packet loss along that IP path.  Matching the forward and reverse
   direction paths for STAMP test packets, even for directly connected
   nodes is not guaranteed.

   It may be desired in SR networks that the same path (same set of
   links and nodes) between the Session-Sender and Session-Reflector be
   used for the STAMP test packets in both directions.  This is achieved
   by using the optional STAMP extensions for SR-MPLS and SRv6 networks
   specified in [I-D.ietf-ippm-stamp-srpm].  The STAMP Session-Reflector
   uses the return path parameters for the reply test packet from the
   received STAMP test packet, as described in
   [I-D.ietf-ippm-stamp-srpm].  This way signaling and maintaining
   dynamic SR network state for the STAMP sessions on the Session-
   Reflector are avoided.

   The optional STAMP extensions defined in [RFC8972] are used for
   direct measurement packet loss in SR networks.

3.1.  Example STAMP Reference Model

   An example of a STAMP reference model with some of the typical
   measurement parameters including the Destination UDP port for STAMP
   test session is shown in the following Figure 1:

                               +------------+
                               | Controller |
                               +------------+
                                   /    \
     Destination UDP Port         /      \      Destination UDP Port
     Authentication Mode         /        \     Authentication Mode
         Key-chain              /          \        Key-chain
     Timestamp Format          /            \   Timestamp Format
     Packet Loss Type         /              \  Session-Reflector Mode
     Delay Measurement Mode  /                \
                            v                  v
                        +-------+          +-------+
                        |       |          |       |
                        |   R1  |==========|   R3  |
                        |       |          |       |
                        +-------+          +-------+

                 STAMP Session-Sender  STAMP Session-Reflector

                  Figure 1: Example STAMP Reference Model

   A Destination UDP port number is selected as described in [RFC8762].
   The same Destination UDP port can be used for STAMP test sessions for
   link and end-to-end SR paths.  In this case, the Destination UDP port
   does not distinguish between link or end-to-end SR path measurements.

   Example of the Timestamp Format is Precision Time Protocol 64-bit
   truncated (PTPv2) [IEEE1588] and Network Time Protocol (NTP).  By
   default, the Session-Reflector replies in kind to the timestamp
   format received in the received Session-Sender test packet, as
   indicated by the "Z" field in the Error Estimate field as described
   in [RFC8762].

   The Session-Reflector mode can be Stateful or Stateless as defined in
   [RFC8762].

   Example of Delay Measurement Mode is one-way, two-way (i.e. round-
   trip) and loopback mode as described in this document.

   Example of Packet Loss Type can be round-trip, near-end (forward) and
   far-end (backward) packet loss as defined in [RFC8762].

   When using the authenticated mode for the STAMP test sessions, the
   matching Authentication Type (e.g.  HMAC-SHA-256) and Key-chain are
   user-configured on STAMP Session-Sender and STAMP Session-Reflector
   [RFC8762].

   The controller shown in the example reference model is not intended
   for the dynamic signaling of the SR parameters for STAMP test
   sessions between the STAMP Session-Sender and STAMP Session-
   Reflector.

   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.

4.  Delay Measurement for Links and SR Paths

4.1.  Session-Sender Test Packet

   The content of an example STAMP Session-Sender test packet using an
   UDP header [RFC0768] is shown in Figure 2.  The payload contains the
   STAMP Session-Sender test packet defined in [RFC8762].

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Session-Sender IPv4 or IPv6 Address      .
    .  Destination IP Address=Session-Reflector IPv4 or IPv6 Address.
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Session-Sender                    .
    .  Destination Port = User-configured Destination Port | 862    .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = Test Packet as specified in Section 3 of RFC 8972   |
    .           in Figure 1 and Figure 3                            .
    .                                                               .
    +---------------------------------------------------------------+

               Figure 2: Example Session-Sender Test Packet

4.1.1.  Session-Sender Test Packet for Links

   The STAMP Session-Sender test packet as shown in Figure 2 is
   transmitted over the link under delay measurement.  The local and
   remote IP addresses of the link are used as Source and Destination
   Addresses, respectively.  For IPv6 links, the link local addresses
   [RFC7404] can be used in the IPv6 header.  The Session-Sender may use
   the local Address Resolution Protocol (ARP) table, Neighbor
   Solicitation or other bootstrap method to find the IP address for the
   links and refresh.  SR encapsulation (e.g. adjacency SID of the link)
   can be added for transmitting the STAMP test packets for links.

4.1.2.  Session-Sender Test Packet for SR Paths

   The delay measurement for end-to-end SR path in an SR network is
   applicable to both end-to-end SR-MPLS and SRv6 paths including SR
   Policies.

   The STAMP Session-Sender (the head-end of the SR Policy) IPv4 or IPv6
   address MUST be used as the Source Address in the IP header of the
   test packet.  The STAMP Session-Reflector (the SR Policy endpoint)
   IPv4 or IPv6 address MUST be used as the Destination Address in the
   IP header of the test packet.

   In the case of Color-Only Destination Steering, with IPv4 endpoint of
   0.0.0.0 or IPv6 endpoint of ::0
   [I-D.ietf-spring-segment-routing-policy], the loopback address from
   the range 127/8 for IPv4, or the loopback address ::1/128 for IPv6
   [RFC4291] is used as the Session-Reflector Address, respectively.

4.1.2.1.  Session-Sender Test Packet for SR-MPLS Policies

   An SR-MPLS Policy may contain a number of Segment Lists (SLs).  A
   STAMP Session-Sender test packet MUST be transmitted for each Segment
   List of the SR-MPLS Policy.  The content of an example STAMP Session-
   Sender test packet for an end-to-end SR-MPLS Policy is shown in
   Figure 3.

    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(1)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment(n)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                PSID                   | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Test Packet as shown in Figure 2               |
    .                                                               .
    +---------------------------------------------------------------+

      Figure 3: Example Session-Sender Test Packet for SR-MPLS Policy

   The Segment List can be empty in case of a single-hop SR-MPLS Policy
   with Implicit NULL label.

   The Path Segment Identifier (PSID)
   [I-D.ietf-spring-mpls-path-segment] of an SR-MPLS Policy can be
   carried in the MPLS header as shown in Figure 3, and can be used for
   direct measurement as described in Section 6, titled "Direct
   Measurement for Links and SR Paths".

4.1.2.2.  Session-Sender Test Packet for SRv6 Policies

   An SRv6 Policy may contain a number of Segment Lists.  A STAMP
   Session-Sender test packet MUST be transmitted for each Segment List
   of the SRv6 Policy.  An SRv6 Policy can contain an SRv6 Segment
   Routing Header (SRH) carrying a Segment List as described in
   [RFC8754].  The content of an example STAMP Session-Sender test
   packet for an end-to-end SRv6 Policy is shown in Figure 4.

   The SRv6 network programming is described in [RFC8986].  The
   procedure defined for Upper-Layer Header processing for SRv6 End SIDs
   in Section 4.1.1 in [RFC8986] is used to process the IPv6/UDP header
   in the received test packets on the Session-Reflector.

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Session-Sender IPv6 Address              .
    .  Destination IP Address = Destination IPv6 Address            .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | SRH as specified in RFC 8754                                  |
    .  <PSID, Segment List>                                         .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Session-Sender                    .
    .  Destination Port = User-configured Destination Port | 862    .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = Test Packet as specified in Section 3 of RFC 8972   |
    .           in Figure 1 and Figure 3                            .
    .                                                               .
    +---------------------------------------------------------------+

       Figure 4: Example Session-Sender Test Packet for SRv6 Policy

   The Segment List (SL) may be empty and no SRH may be carried.

   The Path Segment Identifier (PSID)
   [I-D.ietf-spring-srv6-path-segment] of the SRV6 Policy can be carried
   in the SRH as shown in Figure 4 and can be used for direct
   measurement as described in Section 6, titled "Direct Measurement for
   Links and SR Paths".

4.2.  Session-Reflector Test Packet

   The STAMP Session-Reflector reply test packet uses the IP/UDP
   information from the received test packet as shown in Figure 5.

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Session-Reflector IPv4 or IPv6 Address   .
    .  Destination IP Address                                       .
    .              = Source IP Address from Received Test Packet    .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Session-Reflector                 .
    .  Destination Port = Source Port from Received Test Packet     .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = Test Packet as specified in Section 3 of RFC 8972   |
    .           in Figure 2 and Figure 4                            .
    .                                                               .
    +---------------------------------------------------------------+

              Figure 5: Example Session-Reflector Test Packet

4.2.1.  One-way Measurement Mode

   In one-way delay measurement mode, a reply test packet as shown in
   Figure 5 is transmitted by the STAMP Session-Reflector, for both
   links and end-to-end SR Policies.  The reply test packet may be
   transmitted on the same path or a different path in the reverse
   direction.

   The STAMP Session-Sender address may not be reachable via IP route
   from the STAMP Session-Reflector.  The STAMP Session-Sender in this
   case MUST send its reachability path information to the STAMP
   Session-Reflector using the Return Path TLV defined in
   [I-D.ietf-ippm-stamp-srpm].

   In this mode, as per Reference Topology, all timestamps T1, T2, T3,
   and T4 are collected by the test packets.  However, only timestamps
   T1 and T2 are used to measure one-way delay as (T2 - T1).  The one-
   way delay measurement mode requires the clock on the Session-Sender
   and Session-Reflector to be synchronized.

4.2.2.  Two-way Measurement Mode

   In two-way (i.e. round-trip) delay measurement mode, a reply test
   packet as shown in Figure 5 is transmitted by the STAMP Session-
   Reflector on the same path in the reverse direction, e.g. on the
   reverse direction link or associated reverse SR path
   [I-D.ietf-pce-sr-bidir-path].

   For two-way delay measurement mode for links, the STAMP Session-
   Reflector transmits the reply test packet on the same link where the
   test packet is received.  The STAMP Session-Sender can request in the
   test packet to the STAMP Session-Reflector to transmit the reply test
   packet back on the same link using the Control Code Sub-TLV in the
   Return Path TLV defined in [I-D.ietf-ippm-stamp-srpm].

   For two-way delay measurement mode for end-to-end SR paths, the STAMP
   Session-Reflector transmits the reply test packet on a specific
   reverse path.  The STAMP Session-Sender can request in the test
   packet to the STAMP Session-Reflector to transmit the reply test
   packet back on a given reverse path using a Segment List sub-TLV in
   the Return Path TLV defined in [I-D.ietf-ippm-stamp-srpm].

   In this mode, as per Reference Topology, all timestamps T1, T2, T3,
   and T4 are collected by the test packets.  All four timestamps are
   used to measure two-way delay as ((T4 - T1) - (T3 - T2)).  When clock
   synchronization on the Session-Sender and Session-Reflector nodes is
   not possible, the one-way delay can be derived using two-way delay
   divided by two.

4.2.2.1.  Session-Reflector Test Packet for SR-MPLS Policies

   The content of an example STAMP Session-Reflector reply test packet
   transmitted on the same path as the data traffic flow under
   measurement for two-way delay measurement of an end-to-end SR-MPLS
   Policy is shown in Figure 6.

    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(1)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment(n)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Test Packet as shown in Figure 5               |
    .                                                               .
    +---------------------------------------------------------------+

    Figure 6: Example Session-Reflector Test Packet for SR-MPLS Policy

4.2.2.2.  Session-Reflector Test Packet for SRv6 Policies

   The content of an example STAMP Session-Reflector reply test packet
   transmitted on the same path as the data traffic flow under
   measurement for two-way delay measurement of an end-to-end SRv6
   Policy with SRH is shown in Figure 7.

   The procedure defined for Upper-Layer Header processing for SRv6 End
   SIDs in Section 4.1.1 in [RFC8986] is used to process the IPv6/UDP
   header in the received reply test packets on the Session-Sender.

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Session-Reflector IPv6 Address           .
    .  Destination IP Address = Destination IPv6 Address            .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | SRH as specified in RFC 8754                                  |
    .  <Segment List>                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Session-Reflector                 .
    .  Destination Port = Source Port from Received Test Packet     .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = Test Packet as specified in Section 3 of RFC 8972   |
    .           in Figure 2 and Figure 4                            .
    .                                                               .
    +---------------------------------------------------------------+

      Figure 7: Example Session-Reflector Test Packet for SRv6 Policy

4.2.3.  Loopback Measurement Mode

   The STAMP Session-Sender test packets are transmitted in loopback
   mode to measure loopback delay of a bidirectional circular path.  In
   this mode, the received Session-Sender test packets are not punted
   out of the fast path in forwarding (i.e. to slow path or control-
   plane) at the STAMP Session-Reflector.  In other words, the Session-
   Reflector does not process them and generate Session-Reflector test
   packets.  This is a new measurement mode, not defined by STAMP
   process [RFC8762].

   The STAMP Session-Sender MUST set the Destination UDP port to the UDP
   port it uses to receive the reply STAMP test packets.  Since the
   Session-Reflector does not support the STAMP process, the loopback
   function simply makes the necessary changes to the encapsulation
   including IP and UDP headers to return the test packet to the
   Session-Sender.  The typical Session-Reflector test packet is not
   used in this mode.  The loopback function simply returns the received
   Session-Sender test packet to the Session-Sender without STAMP
   modifications defined in [RFC8762].

   In case of SR-MPLS paths, the SR-MPLS header can contain the MPLS
   label stack of the forward path or both forward and the reverse
   paths.  The IP header of the STAMP Session-Sender test packets MUST
   set the Destination Address equal to the STAMP Session-Sender address
   and the Source Address equal to the STAMP Session-Reflector address.

   In case of SRv6 paths, the SRH can contain the Segment List of the
   forward path or both forward and the reverse paths.  In the former
   case, an inner IPv6 header (after SRH and before UDP header) MUST be
   added that contains the Destination Address equal to the STAMP
   Session-Sender address and the Source Address equal to the STAMP
   Session-Reflector address.

   The Session-Sender may use the SSID field in the received reply test
   packet or local configuration to identify its test session using the
   loopback mode.  In the received Session-Sender test packet at the
   Session-Sender, the 'Session-Sender Sequence Number', 'Session-Sender
   Timestamp', 'Session-Sender Error Estimate', and 'Session-Sender TTL'
   fields are not present in this mode.

   In this mode, as per Reference Topology, the test packet received
   back at the Session-Sender retrieves the timestamp T1 from the test
   packet and adds the received timestamp T4 locally.  Both these
   timestamps are used to measure the loopback delay as (T4 - T1).  The
   one-way delay can be derived using the loopback delay divided by two.
   In loopback mode, the loopback delay includes the processing delay on
   the Session-Reflector.  The Session-Reflector processing delay
   component includes only the time required to loop the test packet
   from the incoming interface to the outgoing interface in forwarding
   plane.

4.3.  Delay Measurement for P2MP SR Policies

   The Point-to-Multipoint (P2MP) SR path that originates from a root
   node terminates on multiple destinations called leaf nodes (e.g.
   P2MP SR Policy [I-D.ietf-pim-sr-p2mp-policy]).

   The procedures for delay and loss measurement described in this
   document for end-to-end P2P SR Policies are also equally applicable
   to the P2MP SR Policies.  The procedure for one-way measurement is
   defined as following:

   o  The STAMP Session-Sender root node transmits test packets using
      the Tree-SID defined in [I-D.ietf-pim-sr-p2mp-policy] for the P2MP
      SR-MPLS Policy as shown in Figure 8.  The STAMP Session-Sender
      test packets may contain the replication SID as defined in
      [I-D.ietf-spring-sr-replication-segment].

   o  The Destination Address MUST be set to the loopback address from
      the range 127/8 for IPv4, or the loopback address ::1/128 for
      IPv6.

   o  Each STAMP Session-Reflector leaf node MUST transmit its node
      address in the Source Address of the reply test packets shown in
      Figure 5.  This allows the STAMP Session-Sender root node to
      identify the STAMP Session-Reflector leaf nodes of the P2MP SR
      Policy.

   o  The P2MP root node measures the delay for each P2MP leaf node
      individually.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              Tree-SID                 | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Test Packet as shown in Figure 2                            |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 8: Example Session-Sender Test Packet with Tree-SID for SR-
                                MPLS Policy

   The considerations for two-way mode for P2MP SR Policy (e.g.  for co-
   routed bidirectional SR-MPLS path) are outside the scope of this
   document.

4.4.  Additional STAMP Test Packet Processing Rules

   The processing rules described in this section are applicable to the
   STAMP test packets for links and end-to-end SR paths including SR
   Policies.

4.4.1.  TTL

   The TTL field in the IPv4 and MPLS headers of the STAMP Session-
   Sender and STAMP Session-Reflector test packet is set to 255 as per
   Generalized TTL Security Mechanism (GTSM) [RFC5082].

4.4.2.  IPv6 Hop Limit

   The Hop Limit (HL) field in the IPv6 and SRH headers of the STAMP
   Session-Sender and STAMP Session-Reflector test packet is set to 255
   as per Generalized TTL Security Mechanism (GTSM) [RFC5082].

4.4.3.  Router Alert Option

   The Router Alert IP option (RAO) [RFC2113] is not set in the STAMP
   test packets for links and end-to-end SR paths.

4.4.4.  UDP Checksum

   For IPv4 test packets, where the hardware is not capable of re-
   computing the UDP checksum or adding checksum complement [RFC7820],
   the Session-Sender may set the UDP checksum value to 0 [RFC8085].

   For IPv6 test packets, where the hardware is not capable of re-
   computing the UDP checksum or adding checksum complement [RFC7820],
   the Session-Sender and Session-Reflector may use the procedure
   defined in [RFC6936] for the UDP checksum.

5.  Packet Loss Measurement for Links and SR Paths

   The procedure described in Section 4 for delay measurement using
   STAMP test packets can be used to detect (test) packet loss for links
   and end-to-end SR paths.  The Sequence Number field in the STAMP test
   packet is used as described in Section 4 "Theory of Operation" where
   Stateful and Stateless Session-Reflector operations are defined
   [RFC8762], to detect round-trip, near-end (forward) and far-end
   (backward) packet loss.  In the case of the loopback mode introduced
   in this document, only the round-trip packet loss is applicable.

   This method can be used for inferred packet loss measurement,
   however, it provides only approximate view of the data packet loss.

6.  Direct Measurement for Links and SR Paths

   The STAMP "Direct Measurement" TLV (Type 5) defined in [RFC8972] can
   be used in SR networks for data packet loss measurement.  The STAMP
   test packets with this TLV are transmitted using the procedures
   described in Section 4 to collect the transmit and receive counters
   of the data flow for the links and end-to-end SR paths.

   The PSID carried in the received data packet for the traffic flow
   under measurement can be used to measure receive data packets (for
   receive traffic counter) for an end-to-end SR path on the STAMP
   Session-Reflector.  The PSID in the received Session-Sender test
   packet header can be used to associate the receive traffic counter on
   the Session-Reflector for the end-to-end SR path.

   The STAMP "Direct Measurement" TLV (Type 5) lacks the support to
   identify the Block Number of the Direct Measurement traffic counters,
   which is required for Alternate-Marking Method [RFC8321] for accurate
   data packet loss metric.

7.  Session State for Links and SR Paths

   The STAMP test session state allows to know if the performance
   measurement test is active.  The threshold-based notification may not
   be generated if the delay values do not change significantly.  For an
   unambiguous monitoring, the controller needs to distinguish the cases
   whether the performance measurement is active, or delay values are
   not changing to cross threshold.

   The STAMP test session state initially is declared active when one or
   more reply test packets are received at the STAMP Session-Sender.
   The STAMP test session state is declared idle (or failed) when
   consecutive N number of reply test packets are not received at the
   STAMP Session-Sender, where N is locally provisioned value.

8.  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 test packets
   SHOULD be transmitted to traverse different ECMP paths to measure
   end-to-end 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
   delay measurement.

   For SR-MPLS Policy, sweeping of MPLS entropy label [RFC6790] values
   can be used in Session-Sender test packets and Session-Reflector test
   packets to take advantage of the hashing function in forwarding plane
   to influence the ECMP path taken by them.

   In IPv4 header of the STAMP Session-Sender test packets, sweeping of
   Session-Reflector Address from the range 127/8 can be used to
   exercise ECMP paths.  In this case, both the forward and the return
   paths MUST be SR-MPLS paths when using the loopback mode.

   As specified in [RFC6437], Flow Label field in the outer IPv6 header
   can also be used for sweeping to exercise different IPv6 ECMP paths.

   The "Destination Node Address" TLV [I-D.ietf-ippm-stamp-srpm] MUST be
   carried in the STAMP Session-Sender test packet to identify the
   intended Session-Reflector, when using IPv4 Session-Reflector Address
   from 127/8 range for a P2P SR Policy, when the STAMP test packet is
   encapsulated by a tunneling protocol or an MPLS Segment List.

9.  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
   STAMP Session-Reflector.

   If desired, attacks can be mitigated by performing basic validation
   and sanity checks, at the STAMP Session-Sender, of the counter or
   timestamp fields in received measurement 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
   packet to a single test cycle.

   Use of HMAC-SHA-256 in the authenticated mode protects the data
   integrity of the test packets.  SRv6 has HMAC protection
   authentication defined for SRH [RFC8754].  Hence, test packets for
   SRv6 may not need authentication mode.  Cryptographic measures may be
   enhanced by the correct configuration of access-control lists and
   firewalls.

   The security considerations specified in [RFC8762] and [RFC8972] also
   apply to the procedures described in this document.

   The Security Considerations specified in [I-D.ietf-ippm-stamp-srpm]
   are also equally applicable to the procedures defined in this
   document.

   When using the procedures defined in [RFC6936], the security
   considerations specified in [RFC6936] also apply.

10.  IANA Considerations

   This document does not require any IANA action.

11.  References

11.1.  Normative References

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <https://www.rfc-editor.org/info/rfc768>.

   [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>.

   [I-D.ietf-ippm-stamp-srpm]
              Gandhi, R., Filsfils, C., Voyer, D., Chen, M., Janssens,
              B., and R. Foote, "Simple TWAMP (STAMP) Extensions for
              Segment Routing Networks", draft-ietf-ippm-stamp-srpm-00
              (work in progress), June 2021.

11.2.  Informative References

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

   [RFC2113]  Katz, D., "IP Router Alert Option", RFC 2113,
              DOI 10.17487/RFC2113, February 1997,
              <https://www.rfc-editor.org/info/rfc2113>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC5082]  Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
              Pignataro, "The Generalized TTL Security Mechanism
              (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
              <https://www.rfc-editor.org/info/rfc5082>.

   [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, <https://www.rfc-editor.org/info/rfc5884>.

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

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

   [RFC6936]  Fairhurst, G. and M. Westerlund, "Applicability Statement
              for the Use of IPv6 UDP Datagrams with Zero Checksums",
              RFC 6936, DOI 10.17487/RFC6936, April 2013,
              <https://www.rfc-editor.org/info/rfc6936>.

   [RFC7404]  Behringer, M. and E. Vyncke, "Using Only Link-Local
              Addressing inside an IPv6 Network", RFC 7404,
              DOI 10.17487/RFC7404, November 2014,
              <https://www.rfc-editor.org/info/rfc7404>.

   [RFC7820]  Mizrahi, T., "UDP Checksum Complement in the One-Way
              Active Measurement Protocol (OWAMP) and Two-Way Active
              Measurement Protocol (TWAMP)", RFC 7820,
              DOI 10.17487/RFC7820, March 2016,
              <https://www.rfc-editor.org/info/rfc7820>.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [RFC8321]  Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli,
              L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
              "Alternate-Marking Method for Passive and Hybrid
              Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321,
              January 2018, <https://www.rfc-editor.org/info/rfc8321>.

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

   [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>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

   [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>.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-11 (work in progress),
              April 2021.

   [I-D.ietf-spring-sr-replication-segment]
              Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z.
              Zhang, "SR Replication Segment for Multi-point Service
              Delivery", draft-ietf-spring-sr-replication-segment-04
              (work in progress), February 2021.

   [I-D.ietf-pim-sr-p2mp-policy]
              Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z.
              Zhang, "Segment Routing Point-to-Multipoint Policy",
              draft-ietf-pim-sr-p2mp-policy-02 (work in progress),
              February 2021.

   [I-D.ietf-spring-mpls-path-segment]
              Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler,
              "Path Segment in MPLS Based Segment Routing Network",
              draft-ietf-spring-mpls-path-segment-04 (work in progress),
              April 2021.

   [I-D.ietf-spring-srv6-path-segment]
              Li, C., Cheng, W., Chen, M., Dhody, D., and R. Gandhi,
              "Path Segment for SRv6 (Segment Routing in IPv6)", draft-
              ietf-spring-srv6-path-segment-00 (work in progress),
              November 2020.

   [I-D.ietf-pce-sr-bidir-path]
              Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
              "Path Computation Element Communication Protocol (PCEP)
              Extensions for Associated Bidirectional Segment Routing
              (SR) Paths", draft-ietf-pce-sr-bidir-path-05 (work in
              progress), January 2021.

   [I-D.ietf-ippm-stamp-yang]
              Mirsky, G., Min, X., and W. S. Luo, "Simple Two-way Active
              Measurement Protocol (STAMP) Data Model", draft-ietf-ippm-
              stamp-yang-07 (work in progress), March 2021.

   [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, Gyan Mishra, Xie
   Jingrong, and Mike Koldychev for reviewing this document and
   providing useful comments and suggestions.  Patrick Khordoc and Radu
   Valceanu have helped improve the mechanisms described in this
   document.

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