Performance Measurement Using RFC 6374 with UDP Path for Segment Routing Networks
draft-gandhi-spring-rfc6374-srpm-udp-05

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Last updated 2020-08-06
Replaces draft-gandhi-spring-udp-pm
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SPRING Working Group                                      R. Gandhi, Ed.
Internet-Draft                                               C. Filsfils
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: February 7, 2021                                       D. Voyer
                                                             Bell Canada
                                                              S. Salsano
                                        Universita di Roma "Tor Vergata"
                                                                 M. Chen
                                                                  Huawei
                                                          August 6, 2020

Performance Measurement Using RFC 6374 with UDP Path for Segment Routing
                                Networks
                draft-gandhi-spring-rfc6374-srpm-udp-05

Abstract

   Segment Routing (SR) leverages the source routing paradigm.  Segment
   Routing (SR) is applicable to both Multiprotocol Label Switching (SR-
   MPLS) and IPv6 (SRv6) data planes.  This document specifies
   procedures for using UDP path for sending and processing probe query
   and response messages for Performance Measurement (PM).  The
   procedure uses the mechanisms defined in RFC 6374 for Performance
   Delay and Loss Measurement.  The procedure specified is applicable to
   SR-MPLS and SRv6 data planes for both Links and end-to-end SR Paths
   including SR Policies measurements.

Status of This Memo

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on February 7, 2021.

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Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Reference Topology  . . . . . . . . . . . . . . . . . . .   5
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Example Provisioning Model  . . . . . . . . . . . . . . .   6
   4.  Probe Query Message . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Delay Measurement Probe Query Message . . . . . . . . . .   7
     4.2.  Loss Measurement Probe Query Message  . . . . . . . . . .   7
     4.3.  Combined Loss/Delay Measurement Probe Query Message . . .   8
     4.4.  Probe Query Message for Links . . . . . . . . . . . . . .   9
     4.5.  Probe Query Message for SR Policies . . . . . . . . . . .   9
       4.5.1.  Probe Query Message for SR-MPLS Policy  . . . . . . .   9
       4.5.2.  Probe Query Message for SRv6 Policy . . . . . . . . .  10
   5.  Probe Response Message  . . . . . . . . . . . . . . . . . . .  11
     5.1.  One-way Measurement Mode  . . . . . . . . . . . . . . . .  13
       5.1.1.  Links and SR Policies . . . . . . . . . . . . . . . .  13
       5.1.2.  Probe Response Message to Controller  . . . . . . . .  13
     5.2.  Two-way Measurement Mode  . . . . . . . . . . . . . . . .  13
       5.2.1.  Links . . . . . . . . . . . . . . . . . . . . . . . .  13
       5.2.2.  SR Policies . . . . . . . . . . . . . . . . . . . . .  13
       5.2.3.  Return Path TLV Extensions  . . . . . . . . . . . . .  14
       5.2.4.  Probe Response Message for SR-MPLS Policy . . . . . .  14
       5.2.5.  Probe Response Message for SRv6 Policy  . . . . . . .  15
     5.3.  Loopback Measurement Mode . . . . . . . . . . . . . . . .  15
   6.  Performance Measurement for P2MP SR Policies  . . . . . . . .  16
   7.  ECMP Support for SR Policies  . . . . . . . . . . . . . . . .  16
   8.  Additional Probe Message Processing Rules . . . . . . . . . .  16
   9.  Sequence Numbers  . . . . . . . . . . . . . . . . . . . . . .  16
     9.1.  Sequence Number TLV Extension in Unauthenticated Mode . .  16

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     9.2.  Sequence Number TLV Extension in Authenticated Mode . . .  17
   10. Performance Delay and Liveness Monitoring . . . . . . . . . .  18
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  19
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  20
     13.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  22
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   Segment Routing (SR) leverages the source routing paradigm and
   greatly simplifies network operations for Software Defined Networks
   (SDNs).  SR is applicable to both Multiprotocol Label Switching (SR-
   MPLS) and IPv6 (SRv6) data planes.  SR takes advantage of the Equal-
   Cost Multipaths (ECMPs) between source and transit nodes, between
   transit nodes and between transit and destination nodes.  SR Policies
   as defined in [I-D.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).

   [RFC6374] specifies protocol mechanisms to enable the efficient and
   accurate measurement of performance metrics and can be used in SR
   networks with MPLS data plane [I-D.ietf-mpls-rfc6374-sr].  [RFC6374]
   addresses the limitations of the IP based performance measurement
   protocols as specified in Section 1 of [RFC6374].  [RFC6374] requires
   data plane to support MPLS Generic Associated Channel Label (GAL) and
   Generic Associated Channel (G-ACh), which may not be supported on all
   nodes in the segment routing network.

   [RFC7876] specifies the procedures to be used when sending and
   processing out-of-band performance measurement probe response
   messages over an UDP return path for RFC 6374 based probe queries.
   [RFC7876] can be used to send out-of-band probe response messages in
   both SR-MPLS and SRv6 networks for one-way performance measurement.

   For SR Policies, there are ECMPs between the source and transit
   nodes, between transit nodes and between transit and destination
   nodes.  RFC 6374 does not define handling for ECMP forwarding paths
   when used in SR networks.

   For two-way measurements for SR Policies, there is a requirement to
   specify a return path in the form of a Segment List in probe query
   messages that does not require on any SR Policy state information on
   the destination node.

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   This document specifies a procedure for sending and processing probe
   query and response messages using UDP paths for Performance
   Measurement in SR networks.  The procedure uses RFC 6374 defined
   mechanisms for Performance Delay and Loss Measurement and unless
   otherwise specified, the procedures from RFC 6374 are not modified.
   The procedure specified is applicable to both SR-MPLS and SRv6 data
   planes.  The procedure can be used for both Links and end-to-end SR
   Paths including SR Policies and Flex-Algo IGP Paths.

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.

   G-ACh: Generic Associated Channel (G-ACh).

   GAL: Generic Associated Channel (G-ACh) Label.

   LM: Loss Measurement.

   MPLS: Multiprotocol Label Switching.

   NTP: Network Time Protocol.

   PM: Performance Measurement.

   PSID: Path Segment Identifier.

   PTP: Precision Time Protocol.

   SID: Segment ID.

   SL: Segment List.

   SR: Segment Routing.

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   SRH: Segment Routing Header.

   SR-MPLS: Segment Routing with MPLS data plane.

   SRv6: Segment Routing with IPv6 data plane.

   TC: Traffic Class.

   URO: UDP Return Object.

2.3.  Reference Topology

   In the reference topology shown below, the querier node R1 initiates
   a probe query for performance measurement and the responder node R5
   sends a probe response message for the probe query message received.
   The probe response message may be sent to the querier node R1 or to a
   controller node R100.

   SR is enabled on nodes R1 and R5.  The nodes R1 and R5 may be
   directly connected via a Link enabled with Segment Routing or there
   exists a Point-to-Point (P2P) SR Path e.g.  SR Policy
   [I-D.ietf-spring-segment-routing-policy] on node R1 (called head-end)
   with destination to node R5 (called head-end).

                                             ------
                                             |R100|
                                             ------
                                               ^
                                               | Response
                                               |
                       t1                t2    |
                      /                   \    |
             +-------+       Query         +-------+
             |       | - - - - - - - - - ->|       |
             |   R1  |=====================|   R5  |
             |       |<- - - - - - - - - - |       |
             +-------+       Response      +-------+
                      \                   /
                       t4                t3
              Querier                      Responder

                       Reference Topology

3.  Overview

   For one-way, two-way and round-trip delay measurements in Segment
   Routing networks, the procedures defined in Section 2.4 and
   Section 2.6 of [RFC6374] are used.  For transmit and receive packet

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   loss measurements, the procedures defined in Section 2.2 and
   Section 2.6 of [RFC6374] are used.  The procedures use probe messages
   with IP/UDP path and do not use MPLS GAL.  For both Links and end-to-
   end SR Paths including SR Policies and Flex-Algo IGP Paths, no PM
   state for delay or loss measurement is created on the responder node
   R5 [RFC6374].

   Separate UDP destination port numbers are user-configured for delay
   and loss measurements from the range specified in [RFC8762].  The
   querier and responder nodes use the destination UDP port number
   following the guidelines specified in Section 6 in [RFC6335].  The
   same destination UDP port is used for Links and SR Paths and the
   responder is unaware if the query is for the Links or SR Paths.  The
   number of UDP ports with PM functionality needs to be minimized due
   to limited hardware resoucres.

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

   o  For delay measurement, the probe messages are sent on the
      congruent path of the data traffic by the querier node, and are
      used to measure the delay experienced by the actual data traffic
      flowing on the Links and SR Policies.

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

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

3.1.  Example Provisioning Model

   An example provisioning model described in
   [I-D.gandhi-spring-stamp-srpm] is also applicable to the procedures
   defined in this document, albeit using the Measurrement Protocol as
   [RFC6374].  The querier node is the sender node and the responder
   node is the reflector node when using [RFC6374].  The provisioning
   model is not used for signaling PM parameters between the responder
   and querier nodes in SR networks.

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4.  Probe Query Message

   In this document, UDP path is used for delay and loss measurements
   for Links and end-to-end SR Policies for the probe messages defined
   in [RFC6374].  The user-configured destination UDP ports (separate
   UDP ports for different delay and loss message formats) are used for
   identifying the probe messages.

4.1.  Delay Measurement Probe Query Message

   The message content for delay measurement for probe query message
   using UDP header [RFC0768] is shown in Figure 1.  The DM probe query
   message is sent with user-configured Destination UDP port number for
   DM.  The Destination UDP port can also be used as Source port for
   two-way delay measurement, since the message has a flag to
   distinguish between query and response.  The DM probe query message
   contains the payload format for delay measurement defined in
   Section 3.2 of [RFC6374].

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Querier IPv4 or IPv6 Address             .
    .  Destination IP Address = Responder IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Querier                           .
    .  Destination Port = User-configured Port for Delay Measurement.
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = Message as specified in Section 3.2 of RFC 6374     |
    .                                                               .
    +---------------------------------------------------------------+

                     Figure 1: DM Probe Query Message

   It is recommended to use the IEEE 1588v2 Precision Time Protocol
   (PTP) truncated 64-bit timestamp format as a default format as
   specified in Appendix A of [RFC6374], with hardware support.  As an
   alternative, Network Time Protocol (NTP) timestamp format can also be
   used [RFC6374].

4.2.  Loss Measurement Probe Query Message

   The message content for loss measurement probe query message using
   UDP header [RFC0768] is shown in Figure 2.  As shown, the LM probe
   query message is sent with user-configured Destination UDP port

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   number for LM.  Separate Destination UDP ports are used for direct-
   mode and inferred-mode loss measurements.  The Destination UDP port
   can also be used as Source port for two-way loss measurement, since
   the message has a flag to distinguish between query and response.
   The LM probe query message contains the payload format for loss
   measurement defined in Section 3.1 of [RFC6374].

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Querier IPv4 or IPv6 Address             .
    .  Destination IP Address = Responder IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Querier                           .
    .  Destination Port = User-configured Port for Loss Measurement .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = Message as specified in Section 3.1 of RFC 6374     |
    .                                                               .
    +---------------------------------------------------------------+

                     Figure 2: LM Probe Query Message

4.3.  Combined Loss/Delay Measurement Probe Query Message

   The message content for combined Loss/Delay measurement probe query
   message using UDP header [RFC0768] is shown in Figure 3.  As shown,
   the probe query message is sent with user-configured Destination UDP
   port number for combined LM/DM message format.  Separate Destination
   UDP ports are used for direct-mode and inferred-mode loss
   measurements.  The Destination UDP port can also be used as Source
   port for two-way loss/delay measurement, since the message has a flag
   to distinguish between query and response.  The probe query message
   contains the payload format for combined loss/delay measurement
   defined in Section 3.3 of [RFC6374].

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    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Querier IPv4 or IPv6 Address             .
    .  Destination IP Address = Responder IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Querier                           .
    .  Destination Port = User-configured Port for                  .
    .                     Loss/Delay Measurement                    .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = Message as specified in Section 3.3 of RFC 6374     |
    .                                                               .
    +---------------------------------------------------------------+

                    Figure 3: LM/DM Probe Query Message

4.4.  Probe Query Message for Links

   The probe query message as defined in Figure 1 for delay measurement
   and Figure 2 for loss measurement are used for Links which may be
   physical, virtual or LAG (bundle), LAG (bundle) member, numbered/
   unnumbered Links.  The probe messages are pre-routed over the Link
   for both delay and loss measurement.

4.5.  Probe Query Message for SR Policies

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

4.5.1.  Probe Query Message for SR-MPLS Policy

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

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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment(1)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment(n)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                PSID                   | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Payload = DM Message as specified in Figure 1                 |
    . Payload = LM Message as specified in Figure 2                 .
    . Payload = LM/DM Message as specified in Figure 3              .
    .                                                               .
    +---------------------------------------------------------------+

         Figure 4: Example Probe Query Message for SR-MPLS Policy

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

   The Path Segment Identifier (PSID)
   [I-D.ietf-spring-mpls-path-segment] of the SR-MPLS Policy is used for
   accounting received traffic on the egress node for loss measurement.

4.5.2.  Probe Query Message for SRv6 Policy

   An SRv6 Policy setup using the SRv6 Segment Routing Header (SRH) and
   a Segment List is defined in [RFC8754].  The SRv6 network programming
   is defined in [I-D.ietf-spring-srv6-network-programming].  The probe
   query messages using UDP header for performance measurement of end-
   to-end SRv6 Policy is sent using its SRv6 Segment Routing Header
   (SRH) with Segment List as shown in Figure 5.  The procedure defined
   for upper-layer header processing for SRv6 SIDs in
   [I-D.ietf-spring-srv6-network-programming] is used to process the UDP
   header in the received probe query messages.

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    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Querier IPv6 Address                     .
    .  Destination IP Address = Destination IPv6 Address            .
    .                                                               .
    +---------------------------------------------------------------+
    | SRH as specified in RFC 8754                                  |
    .  <Segment List>                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | IP Header (as needed)                                         |
    .  Source IP Address = Querier IPv6 Address                     .
    .  Destination IP Address = Responder IPv6 Address              .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Querier                           .
    .  Destination Port = User-configured Port                      .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = DM Message as specified in Figure 1                 |
    . Payload = LM Message as specified in Figure 2                 .
    . Payload = LM/DM Message as specified in Figure 3              .
    .                                                               .
    +---------------------------------------------------------------+

           Figure 5: Example Probe Query Message for SRv6 Policy

5.  Probe Response Message

   When the received probe query message does not contain any UDP Return
   Object (URO) TLV [RFC7876], the probe response message is sent using
   the IP/UDP information from the received probe query message.  The
   content of the probe response message is shown in Figure 6.

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    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Responder IPv4 or IPv6 Address           .
    .  Destination IP Address = Source IP Address from Query        .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Responder                         .
    .  Destination Port = Source Port from Query                    .
    .                                                               .
    +---------------------------------------------------------------+
    | Message as specified in Section 3.2 of RFC 6374 for DM, or    |
    . Message as specified in Section 3.1 of RFC 6374 for LM, or    .
    . Message as specified in Section 3.3 of RFC 6374 for LM/DM     .
    .                                                               .
    +---------------------------------------------------------------+

                     Figure 6: Probe Response Message

   When the received probe query message contains UDP Return Object
   (URO) TLV [RFC7876], the probe response message uses the IP/UDP
   information from the URO in the probe query message.  The content of
   the probe response message is shown in Figure 7.

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Responder IPv4 or IPv6 Address           .
    .  Destination IP Address = URO.Address                         .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Responder                         .
    .  Destination Port = URO.UDP-Destination-Port                  .
    .                                                               .
    +---------------------------------------------------------------+
    | Message as specified in Section 3.2 of RFC 6374 for DM, or    |
    . Message as specified in Section 3.1 of RFC 6374 for LM, or    .
    . Message as specified in Section 3.3 of RFC 6374 for LM/DM     .
    .                                                               .
    +---------------------------------------------------------------+

        Figure 7: Probe Response Message Using URO from Probe Query

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5.1.  One-way Measurement Mode

5.1.1.  Links and SR Policies

   In one-way measurement mode, the probe response message as defined in
   Figure 6 or Figure 7 is sent out-of-band to the querier node, for
   both Links and SR Policies.

   The querier node can receive probe response message back by setting
   its own IP address as Source Address of the header or by adding URO
   TLV in the probe query message and setting its own IP address in the
   IP Address in the URO TLV (Type=131) [RFC7876].  The "control code"
   in the probe query message is set to "out-of-band response
   requested".  The "Source Address" TLV (Type 130), and "Return
   Address" TLV (Type 1), if present in the probe query message, are not
   used to send probe response message.  In this delay measurement mode,
   as per Reference Topology, timestamps t1 and t2 are collected by the
   probes to measure one-way delay as (t2 - t1).

5.1.2.  Probe Response Message to Controller

   As shown in the Reference Topology, if the querier node requires the
   probe response message to be sent to the controller R100, it adds URO
   TLV in the probe query message and sets the IP address of R100 in the
   IP Address field and user-configured UDP port for DM and for LM in
   the UDP-Destination-Port field of the URO TLV (Type=131) [RFC7876].

5.2.  Two-way Measurement Mode

5.2.1.  Links

   In two-way measurement mode, when using a bidirectional link, the
   probe response message as defined in Figure 6 or Figure 7 is sent
   back on the congruent path of the data traffic to the querier node
   for Links.  In this case, the "control code" in the probe query
   message is set to "in-band response requested" [RFC6374].  In this
   delay measurement mode, as per Reference Topology, timestamps t1, t2,
   t3 and t4 are collected by the probes to measure two-way delay as
   ((t4 - t1) - (t3 - t2)).

5.2.2.  SR Policies

   In two-way measurement mode, when using a bidirectional path, the
   probe response message is sent back on the congruent path of the data
   traffic to the querier node for end-to-end SR Policies measurements.
   In this case, the "control code" in the probe query message is set to
   "in-band response requested" [RFC6374].

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5.2.3.  Return Path TLV Extensions

   For two-way measurement, the querier node can request the responder
   node to send a response message back on a given reverse path (e.g.
   co-routed path for two-way measurement).  Return Path TLV defined in
   [I-D.ietf-mpls-rfc6374-sr] is used to carry reverse SR path
   information as part of the payload of the probe query message.  This
   way the responder node does not require any additional SR state for
   PM (recall that in SR networks, the state is in the probe packet and
   signaling of the parameters is avoided).

   Additional Sub-TLVs are defined in this document for the Return Path
   TLV for the following Types:

   o  Type (value TBA1): SRv6 Segment List of the Reverse Path

   o  Type (value TBA2): SRv6 Binding SID
      [I-D.ietf-pce-binding-label-sid] of the Reverse SR Policy

5.2.4.  Probe Response Message for SR-MPLS Policy

   The message content for sending probe response message on the
   congruent path of the data traffic for two-way end-to-end SR-MPLS
   Policy performance measurement is shown in Figure 8.  The SR-MPLS
   label stack in the probe packet header is built using the Segment
   List received in the Return Path TLV in the probe query message.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment(1)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment(n)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Message as shown in Figure 6 or Figure 7       |
    .                                                               .
    +---------------------------------------------------------------+

        Figure 8: Example Probe Response Message for SR-MPLS Policy

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

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5.2.5.  Probe Response Message for SRv6 Policy

   The message content for sending probe response message on the
   congruent path of the data traffic for two-way end-to-end SRv6 Policy
   performance measurement is shown in Figure 9.  For SRv6 Policy using
   SRH, the SRv6 SID list in the SRH of the probe response message is
   built using the SRv6 Segment List received in the Return Path TLV in
   the probe query message.  The procedure defined for upper-layer
   header processing for SRv6 SIDs in
   [I-D.ietf-spring-srv6-network-programming] is used to process the UDP
   header in the received probe response messages.

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Responder IPv6 Address                   .
    .  Destination IP Address = Destination IPv6 Address            .
    .                                                               .
    +---------------------------------------------------------------+
    | SRH as specified in RFC 8754                                  |
    .  <Segment List>                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | IP Header (as needed)                                         |
    .  Source IP Address = Responder IPv6 Address                   .
    .  Destination IP Address = Querier IPv6 Address                .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Responder                         .
    .  Destination Port = Source Port from Query                    .
    .                                                               .
    +---------------------------------------------------------------+
    | Message as specified in Section 3.2 of RFC 6374 for DM, or    |
    . Message as specified in Section 3.1 of RFC 6374 for LM, or    .
    . Message as specified in Section 3.3 of RFC 6374 for LM/DM     .
    .                                                               .
    +---------------------------------------------------------------+

         Figure 9: Example Probe Response Message for SRv6 Policy

5.3.  Loopback Measurement Mode

   The Loopback measurement mode defined in Section 2.8 of [RFC6374] can
   be used to measure round-trip delay of a bidirectional SR Path.  The
   IP header of the probe query message contains the destination address
   equals to the querier node address and the source address equals to
   the responder address.  Optionally, the probe query message can carry
   the reverse path information (e.g. reverse path label stack for SR-

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   MPLS) as part of the SR header.  The responder node does not process
   the probe messages and generate response messages, and hence Loopback
   Request object (Type 3) is not required for SR.  In this delay
   measurement mode, as per Reference Topology, timestamps t1 and t4 are
   collected by the probes to measure round-trip delay.

6.  Performance Measurement for P2MP SR Policies

   The procedure defined for P2MP SR Policies
   [I-D.ietf-pim-sr-p2mp-policy] in [I-D.gandhi-spring-stamp-srpm] is
   also applicable using the RFC 6374 defined messages in the payload.

7.  ECMP Support for SR Policies

   The procedure defined for handling ECMP for SR Policies in
   [I-D.gandhi-spring-stamp-srpm] is also applicable to the procedure
   defined in this document.

8.  Additional Probe Message Processing Rules

   The additional probe message processing rules defined in
   [I-D.gandhi-spring-stamp-srpm] are also applicable to the procedures
   defined in this document.

9.  Sequence Numbers

   The message formats for DM and LM [RFC6374] can carry either
   timestamp or sequence number but not both.  There are case where both
   timestamp and sequence number are desired for both DM and LM.
   Sequence numbers can be useful when some probe query messages are
   lost or they arrive out of order.  In addition, the sequence numbers
   can be useful for detecting denial-of-service (DoS) attacks on UDP
   ports.

9.1.  Sequence Number TLV Extension in Unauthenticated Mode

   [RFC6374] defines DM and LM probe query and response messages that
   can include one or more optional TLVs.  New TLV Type (value TBA3) is
   defined in this document to carry sequence number for probe query and
   response messages for delay and loss measurement.  The format of the
   Sequence Number TLV in unauthenticated mode is shown in Figure 10.

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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Type TBA3   |    Length     |      Reserved                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Sequence Number                            |
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 10: Sequence Number TLV - Unauthenticated Mode

   o  The sequence numbers start with 0 and are incremented by one for
      each subsequent probe query message.

   o  The sequence number are independent for DM and LM messages.

   o  The sequence number can be of any length determined by the querier
      node.

   o  The Sequence Number TLV is optional.

   o  The querier node SHOULD only insert one Sequence Number TLV in the
      probe query message and the responder node in the probe response
      message SHOULD return the first Sequence Number TLV from the probe
      query message and ignore the other Sequence Number TLVs if
      present.

   o  When Sequence Number TLV is added, the DM and LM messages SHOULD
      NOT carry sequence number in the timestamp field of the message.

9.2.  Sequence Number TLV Extension in Authenticated Mode

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

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

   The computation of HMAC field using HMAC-SHA1 can be used with the
   procedure defined in this document.  HMAC uses own key and the
   definition of the mechanism to distribute the HMAC key is outside the

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   scope of this document.  Both the authentication type and key can be
   user-configured on both the querier and responder nodes.

   The format of the Sequence Number TLV in authentication mode is shown
   in Figure 11.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Type TBA4   |    Length     |      Reserved                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Sequence Number                            |
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                    Comp.MBZ                                   ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    HMAC (16 octets)                           |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 11: Sequence Number TLV - Authenticated Mode

   o  This TLV is mandatory in the authenticated mode.

   o  The node MUST discard the probe message if HMAC is invalid.

   o  The Sequence Number follows the same processing rule as defined in
      the unauthenticated mode.

10.  Performance Delay and Liveness Monitoring

   Liveness monitoring is required for connectivity verification and
   continuity check in an SR network.  The procedure defined in this
   document for one-way, two-way and loopback mode for delay measurement
   can also be applied to liveness monitoring of Links and SR Paths.
   Liveness failure is notified when consecutive N number of probe
   response messages are not received back at the querier node, where N
   is locally provisioned value.  Note that for one-way and two-way
   modes, the failure detection interval and scale for number of probe
   messages need to account for the processing of the probe query
   messages which need to be punted from the forwarding fast path (to
   slow path or control plane), and response messages need to be
   injected on the responder node.  Hence, loopback mode is more
   suitbale for liveness monitoring.

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11.  Security Considerations

   The performance measurement is intended for deployment in well-
   managed private and service provider networks.  As such, it assumes
   that a node involved in a measurement operation has previously
   verified the integrity of the path and the identity of the far end
   responder node.  The security considerations described in Section 8
   of [RFC6374] are applicable to this specification, and particular
   attention should be paid to the last three paragraphs.

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

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

12.  IANA Considerations

   IANA is requested to allocate the values for the following Sub-TLV
   Types for the Return Path TLV for RFC 6374 from the sub-registry
   "Return Path Sub-TLV Type" of the "MPLS Loss/Delay Measurement TLV
   Object" registry contained within the "Generic Associated Channel
   (G-ACh) Parameters" registry set:

   o  Type TBA1: SRv6 Segment List of the Reverse Path

   o  Type TBA2: SRv6 Binding SID of the Reverse SR Policy

   IANA is also requested to allocate the values for the following
   Sequence Number TLV Types for RFC 6374 to be carried in the probe
   query and response messages for delay and loss measurement from the
   "MPLS Loss/Delay Measurement TLV Object" registry contained within
   the "Generic Associated Channel (G-ACh) Parameters" registry set:

   o  Type TBA3: Sequence Number TLV in Unauthenticated Mode

   o  Type TBA4: Sequence Number TLV in Authenticated Mode

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13.  References

13.1.  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>.

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374,
              DOI 10.17487/RFC6374, September 2011,
              <https://www.rfc-editor.org/info/rfc6374>.

   [RFC7876]  Bryant, S., Sivabalan, S., and S. Soni, "UDP Return Path
              for Packet Loss and Delay Measurement for MPLS Networks",
              RFC 7876, DOI 10.17487/RFC7876, July 2016,
              <https://www.rfc-editor.org/info/rfc7876>.

   [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>.

   [I-D.ietf-mpls-rfc6374-sr]
              Gandhi, R., Filsfils, C., Voyer, D., Salsano, S., and M.
              Chen, "Performance Measurement Using RFC 6374 for Segment
              Routing Networks with MPLS Data Plane", draft-ietf-mpls-
              rfc6374-sr-00 (work in progress), July 2020.

   [I-D.gandhi-spring-stamp-srpm]
              Gandhi, R., Filsfils, C., Voyer, D., Chen, M., and B.
              Janssens, "Performance Measurement Using STAMP for Segment
              Routing Networks", draft-gandhi-spring-stamp-srpm-02 (work
              in progress), August 2020.

13.2.  Informative References

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

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

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165,
              RFC 6335, DOI 10.17487/RFC6335, August 2011,
              <https://www.rfc-editor.org/info/rfc6335>.

   [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>.

   [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>.

   [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-08 (work in progress),
              July 2020.

   [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-00 (work in progress), July
              2020.

   [I-D.ietf-pce-binding-label-sid]
              Filsfils, C., Sivabalan, S., Tantsura, J., Hardwick, J.,
              Previdi, S., and C. Li, "Carrying Binding Label/Segment-ID
              in PCE-based Networks.", draft-ietf-pce-binding-label-
              sid-03 (work in progress), June 2020.

   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-16 (work in
              progress), June 2020.

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   [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-02 (work in progress),
              February 2020.

   [I-D.gandhi-mpls-ioam-sr]
              Gandhi, R., Ali, Z., Filsfils, C., Brockners, F., Wen, B.,
              and V. Kozak, "MPLS Data Plane Encapsulation for In-situ
              OAM Data", draft-gandhi-mpls-ioam-sr-02 (work in
              progress), March 2020.

   [I-D.ali-spring-ioam-srv6]
              Ali, Z., Gandhi, R., Filsfils, C., Brockners, F., Kumar,
              N., Pignataro, C., Li, C., Chen, M., and G. Dawra,
              "Segment Routing Header encapsulation for In-situ OAM
              Data", draft-ali-spring-ioam-srv6-02 (work in progress),
              November 2019.

Acknowledgments

   The authors would like to thank Patrick Khordoc for the discussions
   on RFC 6374; Nagendra Kumar and Carlos Pignataro for the discussion
   on SRv6 Performance Measurement.  The authors would like to thank
   Thierry Couture for the discussions on the use-cases for the
   performance measurement in segment routing networks.  The authors
   would also like to thank Stewart Bryant for the discussion on UDP
   port allocation for Performance Measurement and Greg Mirsky for
   providing useful comments and suggestions.

Contributors

   Sagar Soni
   Cisco Systems, Inc.
   Email: sagsoni@cisco.com

   Zafar Ali
   Cisco Systems, Inc.
   Email: zali@cisco.com

   Pier Luigi Ventre
   CNIT
   Italy
   Email: pierluigi.ventre@cnit.it

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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

   Stefano Salsano
   Universita di Roma "Tor Vergata"
   Italy

   Email: stefano.salsano@uniroma2.it

   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com

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