[Docs] [txt|pdf] [Tracker] [WG] [Email] [Nits]



MPLS Working Group                                        R. Gandhi, Ed.
Internet-Draft                                               C. Filsfils
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: January 27, 2020                                       D. Voyer
                                                             Bell Canada
                                                              S. Salsano
                                        Universita di Roma "Tor Vergata"
                                                                 M. Chen
                                                                  Huawei
                                                           July 26, 2020


Performance Measurement Using RFC 6374 for Segment Routing Networks with
                            MPLS Data Plane
                    draft-ietf-mpls-rfc6374-sr-00

Abstract

   Segment Routing (SR) leverages the source routing paradigm.  RFC 6374
   specifies protocol mechanisms to enable the efficient and accurate
   measurement of packet loss, one-way and two-way delay, as well as
   related metrics such as delay variation in MPLS networks using probe
   messages.  This document utilizes these mechanisms for Performance
   Delay and Loss Measurements in Segment Routing networks with MPLS
   data plane (SR-MPLS), for both SR-MPLS Links and end-to-end Paths
   including SR-MPLS Policies.  In addition, this document defines
   Return Path TLV for two-way performance measurement and Block Number
   TLV for loss measurement.

Status of This Memo

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 27, 2020.






Gandhi, et al.          Expires December 27, 2020               [Page 1]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Reference Topology  . . . . . . . . . . . . . . . . . . .   5
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Probe Query and Response Messages . . . . . . . . . . . . . .   6
     4.1.  Probe Message for SR-MPLS Links . . . . . . . . . . . . .   6
     4.2.  Probe Message for SR-MPLS Policies  . . . . . . . . . . .   6
     4.3.  Probe Response Message for SR-MPLS Links and Policies . .   7
       4.3.1.  One-way Measurement Mode  . . . . . . . . . . . . . .   7
       4.3.2.  Two-way Measurement Mode  . . . . . . . . . . . . . .   8
       4.3.3.  Loopback Measurement Mode . . . . . . . . . . . . . .   8
     4.4.  Return Path TLV Extensions  . . . . . . . . . . . . . . .   8
   5.  Delay Measurement . . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  Delay Measurement Message Format  . . . . . . . . . . . .  10
     5.2.  Timestamps  . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Loss Measurement  . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Loss Measurement Message Format . . . . . . . . . . . . .  11
     6.2.  Block Number TLV Extensions . . . . . . . . . . . . . . .  11
     6.3.  Combined Loss/Delay Measurement Message Format  . . . . .  12
   7.  Performance Measurement for P2MP SR-MPLS Policies . . . . . .  12
   8.  ECMP for SR-MPLS Policies . . . . . . . . . . . . . . . . . .  13
   9.  SR-MPLS Link Extended TE Metrics Advertisements . . . . . . .  14
   10. Backwards Compatibility . . . . . . . . . . . . . . . . . . .  14
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  14
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     13.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  19



Gandhi, et al.          Expires December 27, 2020               [Page 2]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   Service provider's ability to satisfy Service Level Agreements (SLAs)
   depend on the ability to measure and monitor performance metrics for
   packet loss and one-way and two-way delay, as well as related metrics
   such as delay variation.  The ability to monitor these performance
   metrics also provides operators with greater visibility into the
   performance characteristics of their networks, thereby facilitating
   planning, troubleshooting, and network performance evaluation.

   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 in MPLS networks using
   probe messages.  The One-Way Active Measurement Protocol (OWAMP)
   defined in [RFC4656] and Two-Way Active Measurement Protocol (TWAMP)
   defined in [RFC5357] provide capabilities for the measurement of
   various performance metrics in IP networks.  However, mechanisms
   defined in [RFC6374] are more suitable for Segment Routing when using
   MPLS data plane (SR-MPLS).  [RFC6374] also supports "direct mode"
   Loss Measurement (LM), which is required in SR networks.

   [RFC7876] specifies the procedures to be used when sending and
   processing out-of-band performance measurement probe responses over
   an UDP return path when receiving RFC 6374 based probe queries.
   These procedures can be used to send out-of-band probe responses for
   both SR-MPLS Links and Policies for one-way measurement.

   This document utilizes the probe-based mechanisms defined in
   [RFC6374] for Performance Delay and Loss Measurements in SR networks
   with MPLS data plane, for both SR-MPLS Links and end-to-end Paths
   including SR-MPLS Policies.  In addition, this document defines
   Return Path TLV for two-way performance measurement and Block Number
   TLV for loss measurement.  The Performance Measurements (PM) for SR-
   MPLS Links are used to compute extended Traffic Engineering (TE)
   metrics for delay and loss and can be advertised in the network using



Gandhi, et al.          Expires December 27, 2020               [Page 3]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   the routing protocol extensions defined in [RFC7471], [RFC8570], and
   [RFC8571].

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

   ACH: Associated Channel Header.

   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.

   SR-MPLS: Segment Routing with MPLS data plane.

   TC: Traffic Class.

   TE: Traffic Engineering.




Gandhi, et al.          Expires December 27, 2020               [Page 4]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   URO: UDP Return Object.

2.3.  Reference Topology

   In the reference topology shown in Figure 1, the querier node R1
   initiates a performance measurement probe query and the responder
   node R5 sends a probe response message for the query message
   received.  The probe response message is typically sent back to the
   querier node R1.

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


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

                       Figure 1: Reference Topology

3.  Overview

   For one-way, two-way and round-trip delay measurements, the
   procedures defined in Section 2.4 and Section 2.6 of [RFC6374] are
   used.  For transmit and receive packet loss measurements, the
   procedures defined in Section 2.2 and Section 2.6 of [RFC6374] are
   used.  For both SR-MPLS Links and end-to-end Policies, no PM session
   for delay or loss measurement is created on the responder node R5
   [RFC6374].

   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 SR-MPLS Links and Policies.




Gandhi, et al.          Expires December 27, 2020               [Page 5]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   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 session state present).

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

4.  Probe Query and Response Messages

4.1.  Probe Message for SR-MPLS Links

   As described in Section 2.9.1 of [RFC6374], probe query and response
   messages flow over the MPLS Generic Associated Channel (G-ACh).  A
   probe message for SR-MPLS Links contains G-ACh Label (GAL) (with
   S=1).  The GAL is followed by an Associated Channel Header (ACH),
   which identifies the message type, and the message payload following
   the ACH as shown in Figure 2.  The probe messages are routed over the
   Links for both delay and loss measurement using the same procedure
   described in [RFC6374].  For SR-MPLS Links, the TTL value is set to 1
   in the SR-MPLS header for one-way and two-way measurement modes.


    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             GAL (value 13)            | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version| Reserved      | GAL Channel Type              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 2: Probe Message Header for an SR-MPLS Link

4.2.  Probe Message for SR-MPLS Policies

   As described in Section 2.9.1 of [RFC6374], probe query and response
   messages flow over the MPLS Generic Associated Channel (G-ACh).  A
   probe message for an end-to-end SR-MPLS Policy measurement contains
   SR-MPLS label stack [I-D.ietf-spring-segment-routing-policy], with
   the G-ACh Label (GAL) at the bottom of the stack (with S=1).  The GAL
   is followed by an Associated Channel Header (ACH), which identifies
   the message type, and the message payload following the ACH as shown
   in Figure 3.  For SR-MPLS Policies, the TTL value is set to 255 in
   the SR-MPLS header.



Gandhi, et al.          Expires December 27, 2020               [Page 6]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Label(1)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Label(n)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  GAL (value 13)       | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version| Reserved      | GAL Channel Type              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 3: Example Probe Message Header for an End-to-end SR-MPLS
                                  Policy

   The SR-MPLS label stack can be empty (as shown in Figure 2) to
   indicate Implicit NULL label case.

   For SR-MPLS Policy performance measurement, in order to ensure that
   the probe query message is processed by the intended responder node,
   Destination Address TLV (Type 129) [RFC6374] MAY be sent in the probe
   query message.  The responder node only returns Success in Control
   Code if it is the intended destination for the probe query.
   Otherwise, it MUST return 0x15: Error - Invalid Destination Node
   Identifier [RFC6374].

4.3.  Probe Response Message for SR-MPLS Links and Policies

4.3.1.  One-way Measurement Mode

   In one-way performance measurement mode [RFC7679], the querier node
   can receive "out-of-band" probe responses by properly setting the UDP
   Return Object (URO) TLV in the probe query message.  The URO TLV
   (Type=131) is defined in [RFC7876] and includes the UDP-Destination-
   Port and IP Address.  In particular, if the querier node sets its own
   IP address in the URO TLV, the probe response is sent back by the
   responder node to the querier node.  In addition, the "control code"
   in the probe query message is set to "out-of-band response
   requested".  In this delay measurement mode, as per Reference
   Topology, timestamps t1 and t2 are collected by the probes to measure
   one-way delay.  The one-way mode is applicable to both SR-MPLS Links
   and Policies.





Gandhi, et al.          Expires December 27, 2020               [Page 7]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


4.3.2.  Two-way Measurement Mode

   In two-way performance measurement mode [RFC6374], when using a
   bidirectional SR path [I-D.ietf-pce-sr-bidir-path], the probe
   response message is sent back to the querier node on the congruent
   path of the data traffic on the reverse direction SR-MPLS Link or
   associated SR-MPLS Policy [I-D.ietf-pce-sr-bidir-path] using a
   message with format similar to their probe query message.  In this
   case, the "control code" in the probe query message is set to "in-
   band response requested".  In this delay measurement mode, as per
   Reference Topology, all timestamps t1, t2, t3, and t4 are collected
   by the probes.  All four timestamps are used to measure two-way
   delay.  The two-way mode is applicable to both SR-MPLS Links and
   Policies.

   Specifically, the probe response message is sent back on the incoming
   physical interface where the probe query message is received.  This
   is useful for example, in case of two-way measurement mode for Link
   delay.

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

4.3.3.  Loopback Measurement Mode

   The Loopback measurement mode defined in Section 2.8 of [RFC6374] can
   be used to measure round-trip delay for a bidirectional SR-MPLS Path
   [I-D.ietf-pce-sr-bidir-path].  The probe query messages in this case
   carries the reverse Path label stack as part of the MPLS header.  The
   GAL is still carried at the bottom of the label stack (with S=1).
   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, the timestamps t1 and t4 are collected by the probes.  Both
   these timestamps are used to measure round-trip delay.

4.4.  Return Path TLV Extensions

   For two-way performance measurement, the responder node needs to send
   the probe response message on a specific reverse path.  The querier
   node can request in the probe query message to the responder node to
   send a response message back on a given reverse path (e.g. co-routed
   path for two-way measurement).  This way the destination node does
   not require any additional SR-MPLS Policy state.



Gandhi, et al.          Expires December 27, 2020               [Page 8]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   For one-way performance measurement, the querier node address may not
   be reachable via IP route from the responder node.  The querier node
   in this case needs to send its reachability path information to the
   responder node.

   [RFC6374] defines DM and LM probe query messages that can include one
   or more optional TLVs.  New TLV Type (TBA1) is defined in this
   document for Return Path to carry reverse path information in the
   probe query messages (in the payload).  The format of the Return Path
   TLV is shown in Figure 4 and Figure 5:


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Type = TBA1  |    Length     |      Reserved                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Return Path Sub-TLVs                       |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 4: Return Path TLV


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Type      |    Length     |      Reserved                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Label(1)                                   |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Label(n)                                   |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

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

   o  Type (value 1): SR-MPLS Label Stack of the Reverse Path





Gandhi, et al.          Expires December 27, 2020               [Page 9]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   o  Type (value 2): SR-MPLS Binding SID
      [I-D.ietf-pce-binding-label-sid] of the Reverse SR Policy

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

5.  Delay Measurement

5.1.  Delay Measurement Message Format

   As defined in [RFC6374], MPLS DM probe query and response messages
   use Associated Channel Header (ACH) (value 0x000C for delay
   measurement) [RFC6374], which identifies the message type, and the
   message payload following the ACH.  For both SR-MPLS Links and end-
   to-end Policies measurements, the same MPLS DM ACH value is used.

   The DM message payload as defined in Section 3.2 of [RFC6374] is used
   for SR-MPLS delay measurement, for both SR-MPLS Links and end-to-end
   Policies.

5.2.  Timestamps

   The Section 3.4 of [RFC6374] defines timestamp format that can be
   used for delay measurement.  The IEEE 1588 Precision Time Protocol
   (PTP) timestamp format [IEEE1588] is used by default as described in
   Appendix A of [RFC6374], with hardware support in Segment Routing
   networks.

6.  Loss Measurement

   The LM protocol can perform two distinct kinds of loss measurement as
   described in Section 2.9.8 of [RFC6374].

   o  In inferred mode, LM will measure the loss of specially generated
      test messages in order to infer the approximate data plane loss
      level.  Inferred mode LM provides only approximate loss
      accounting.

   o  In direct mode, LM will directly measure data plane packet loss.
      Direct mode LM provides perfect loss accounting, but may require
      hardware support.





Gandhi, et al.          Expires December 27, 2020              [Page 10]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   For both of these modes of LM, Path Segment Identifier (PSID)
   [I-D.ietf-spring-mpls-path-segment] is used for accounting received
   traffic on the egress node of the SR-MPLS Policy as shown in
   Figure 6.  Different values of PSID can be used to measure packet
   loss per SR-MPLS Policy, per Candidate Path or per Segment List of
   the SR Policy.


    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  PSID                 | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  GAL (value 13)       | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version| Reserved      | GAL Channel Type              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 6: Example With Path Segment Identifier for SR-MPLS Policy

6.1.  Loss Measurement Message Format

   As defined in [RFC6374], MPLS LM probe query and response messages
   use Associated Channel Header (ACH) (value 0x000A for direct loss
   measurement or value 0x000B for inferred loss measurement), which
   identifies the message type, and the message payload following the
   ACH.  For both SR-MPLS Links and end-to-end Policies measurements,
   the same MPLS LM ACH value is used.

   The LM message payload as defined in Section 3.1 of [RFC6374] is used
   for SR-MPLS loss measurement, for both SR-MPLS Links and end-to-end
   Policies.

6.2.  Block Number TLV Extensions

   The loss measurement using Alternate-Marking method defined in
   [RFC8321] requires to color the data traffic.  To be able to
   correlate the transmit and receive traffic counters of the matching
   color, the Block Number (or color) of the traffic counters is carried
   by the probe query and response messages for loss measurement.  The
   probe query and response messages currently specified in [RFC6374]
   for loss measurement do not identify the Block Number of the
   counters.  The Block Number can also be used to aggregate performance
   metrics collected.

   [RFC6374] defines probe query and response messages that can include
   one or more optional TLVs.  New TLV Type (value TBA2) is defined in
   this document to carry the Block Number (8-bit) of the traffic



Gandhi, et al.          Expires December 27, 2020              [Page 11]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   counters in the probe query and response messages for loss
   measurement.  The format of the Block Number TLV is shown in
   Figure 7:


    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 TBA2   |    Length     | Reserved      | Block Number  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 7: Block Number TLV

   The Block Number TLV is a Mandatory TLV Type.  The querier node
   SHOULD only insert one Block Number TLV in the probe query message
   and the responder node in the probe response message SHOULD return
   the first Block Number TLV from the probe query messages and ignore
   other Block Number TLVs if present.  In probe messages, the counters
   MUST belong to the same Block Number.

6.3.  Combined Loss/Delay Measurement Message Format

   As defined in [RFC6374], Combined DM+LM probe query and response
   messages use Associated Channel Header (ACH) (value 0x000D for direct
   loss and delay measurement or value 0x000E for inferred loss and
   delay measurement), which identifies the message type, and the
   message payload following the ACH.  For both SR-MPLS Links and end-
   to-end Policies measurements, the same MPLS ACH value is used.

   The message payload as defined in Section 3.3 of [RFC6374] is used
   for SR-MPLS combined delay and loss measurement, for both SR-MPLS
   Links and end-to-end Policies.

7.  Performance Measurement for P2MP SR-MPLS Policies

   The Point-to-Multipoint (P2MP) SR-MPLS Path that originates from a
   root node terminates on multiple destinations called leaf nodes (e.g.
   P2MP SR-MPLS Policy [I-D.voyer-pim-sr-p2mp-policy] or P2MP Transport
   [I-D.shen-spring-p2mp-transport-chain]).

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

   o  The querier root node sends probe query messages using the Tree-
      SID defined in [I-D.voyer-pim-sr-p2mp-policy] for the P2MP SR-MPLS
      Policy as shown in Figure 8.



Gandhi, et al.          Expires December 27, 2020              [Page 12]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   o  The probe query messages can contain the replication SID as
      defined in [I-D.voyer-spring-sr-replication-segment].

   o  Each responder leaf node adds the "Source Address" TLV (Type 130)
      [RFC6374] with its IP address in the probe response messages.
      This TLV allows the querier root node to identify the responder
      leaf nodes of the P2MP SR-MPLS Policy.

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


    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      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              GAL (value 13)           | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version| Reserved      | GAL Channel Type              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 8: Example Probe Query with Tree-SID for SR-MPLS Policy

   The probe query messages can also be sent using the scheme defined
   for P2MP Transport using Chain Replication that may contain Bud SID
   as defined in [I-D.shen-spring-p2mp-transport-chain].

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

8.  ECMP for SR-MPLS Policies

   An SR-MPLS 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-MPLS Policy can
   result in ECMP paths via transit nodes part of that Anycast group.
   The probe messages need to be sent to traverse different ECMP paths
   to measure performance delay of each of the ECMP path of an SR-MPLS
   Policy.

   Forwarding plane has various hashing functions available to forward
   packets on specific ECMP paths.  For SR-MPLS Policy, sweeping of



Gandhi, et al.          Expires December 27, 2020              [Page 13]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   entropy label [RFC6790] values can be used in probe messages to take
   advantage of the hashing function in forwarding plane to influence
   the ECMP path taken by them.

   The considerations for performance loss measurement for different
   ECMP paths of an SR-MPLS Policy are outside the scope of this
   document.

9.  SR-MPLS Link Extended TE Metrics Advertisements

   The extended TE metrics for SR-MPLS Link delay and loss computed
   using the performance measurement procedures described in this
   document can be advertised in the routing domain as follows:

   o  For OSPF, ISIS, and BGP-LS, protocol extensions defined in
      [RFC7471], [RFC8570], and [RFC8571] are used, respectively for
      advertising the extended TE link metrics in the network.

   o  The advertised delay-variance metric is computed as specified in
      Section 4.2 of [RFC5481].

   o  The extended TE link one-way delay metrics can also be computed
      using two-way delay measurement or round-trip delay measurement
      from loopback mode by dividing the measured delay values by 2.

   o  The extended TE link delay and loss metrics are advertised for
      Layer 2 bundle members in OSPF [I-D.ketant-lsr-ospf-l2bundles] and
      ISIS [RFC8668] using the same mechanisms defined in [RFC7471] and
      [RFC8570], respectively.

10.  Backwards Compatibility

   The procedures defined in this document are backwards compatible with
   the procedures defined in [RFC6374] at both querier and responder
   nodes.  If the responder does not support the new Mandatory TLV Types
   defined in this document, it MUST return Error 0x17: Unsupported
   Mandatory TLV Object as per [RFC6374].

11.  Security Considerations

   This document describes the procedures for performance delay and loss
   measurement for SR-MPLS networks, for both SR-MPLS Links and end-to-
   end Policies using the mechanisms defined in [RFC6374] and [RFC7876].
   This document does not introduce any additional security
   considerations other than those covered in [RFC6374], [RFC7471],
   [RFC8570], [RFC8571], and [RFC7876].





Gandhi, et al.          Expires December 27, 2020              [Page 14]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


12.  IANA Considerations

   IANA is requested to allocate a value for the following Mandatory
   Return Path TLV Type for [RFC6374] to be carried in probe query
   message from the "MPLS Loss/Delay Measurement TLV Object" registry
   contained within the "Generic Associated Channel (G-ACh) Parameters"
   registry set:

   o  Type TBA1: Return Path TLV

   IANA is requested to create a sub-registry for "Return Path Sub-TLV
   Type" for the Return Path TLV.  All code points in the range 1
   through 32759 in this registry shall be allocated according to the
   "IETF Review" procedure as specified in [RFC8126].  Code points in
   the range 32760 through 65279 in this registry shall be allocated
   according to the "First Come First Served" procedure as specified in
   [RFC8126].  Remaining code points are allocated according to Table 1:

   +---------------+-------------------------+-------------------------+
   | Value         |       Description       | Reference               |
   +---------------+-------------------------+-------------------------+
   | 0- 32767      |      Mandatory TLV,     | IETF Review             |
   |               |        unassigned       |                         |
   | 32768 - 65279 |      Optional TLV,      | First Come First Served |
   |               |        unassigned       |                         |
   | 65280 - 65519 |       Experimental      | This document           |
   | 65520 - 65534 |       Private Use       | This document           |
   | 65535         |         Reserved        | This document           |
   +---------------+-------------------------+-------------------------+

                Table 1: Return Path Sub-TLV Type Registry

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

   o  Type (value 1): SR-MPLS Label Stack of the Reverse Path

   o  Type (value 2): SR-MPLS Binding SID
      [I-D.ietf-pce-binding-label-sid] of the Reverse SR Policy

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

   o  Type TBA2: Block Number TLV




Gandhi, et al.          Expires December 27, 2020              [Page 15]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


13.  References

13.1.  Normative References

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

   [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>.

13.2.  Informative References

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

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006,
              <https://www.rfc-editor.org/info/rfc4656>.

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, DOI 10.17487/RFC5357, October 2008,
              <https://www.rfc-editor.org/info/rfc5357>.

   [RFC5481]  Morton, A. and B. Claise, "Packet Delay Variation
              Applicability Statement", RFC 5481, DOI 10.17487/RFC5481,
              March 2009, <https://www.rfc-editor.org/info/rfc5481>.

   [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>.



Gandhi, et al.          Expires December 27, 2020              [Page 16]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   [RFC7679]  Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
              Ed., "A One-Way Delay Metric for IP Performance Metrics
              (IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January
              2016, <https://www.rfc-editor.org/info/rfc7679>.

   [RFC7471]  Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
              Previdi, "OSPF Traffic Engineering (TE) Metric
              Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
              <https://www.rfc-editor.org/info/rfc7471>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

   [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>.

   [RFC8570]  Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
              D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
              Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
              2019, <https://www.rfc-editor.org/info/rfc8570>.

   [RFC8571]  Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
              C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
              IGP Traffic Engineering Performance Metric Extensions",
              RFC 8571, DOI 10.17487/RFC8571, March 2019,
              <https://www.rfc-editor.org/info/rfc8571>.

   [RFC8668]  Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri,
              M., and E. Aries, "Advertising Layer 2 Bundle Member Link
              Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668,
              December 2019, <https://www.rfc-editor.org/info/rfc8668>.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-07 (work in progress),
              May 2020.




Gandhi, et al.          Expires December 27, 2020              [Page 17]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   [I-D.voyer-pim-sr-p2mp-policy]
              Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z.
              Zhang, "Segment Routing Point-to-Multipoint Policy",
              draft-voyer-pim-sr-p2mp-policy-01 (work in progress),
              April 2020.

   [I-D.voyer-spring-sr-replication-segment]
              Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z.
              Zhang, "SR Replication Segment for Multi-point Service
              Delivery", draft-voyer-spring-sr-replication-segment-03
              (work in progress), June 2020.

   [I-D.shen-spring-p2mp-transport-chain]
              Shen, Y., Zhang, Z., Parekh, R., Bidgoli, H., and Y.
              Kamite, "Point-to-Multipoint Transport Using Chain
              Replication in Segment Routing", draft-shen-spring-p2mp-
              transport-chain-02 (work in progress), April 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-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.ketant-lsr-ospf-l2bundles]
              Talaulikar, K. and P. Psenak, "Advertising L2 Bundle
              Member Link Attributes in OSPF", draft-ketant-lsr-ospf-
              l2bundles-01 (work in progress), January 2020.

   [I-D.ietf-pce-sr-bidir-path]
              Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
              "PCEP Extensions for Associated Bidirectional Segment
              Routing (SR) Paths", draft-ietf-pce-sr-bidir-path-02 (work
              in progress), March 2020.





Gandhi, et al.          Expires December 27, 2020              [Page 18]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


Acknowledgments

   The authors would like to thank Thierry Couture for the discussions
   on the use-cases for the performance measurement in segment routing
   networks.  Authors would like to thank Patrick Khordoc for
   implementing the mechanisms defined in this document.  The authors
   would like to thank Greg Mirsky for providing many useful comments
   and suggestions.  The authors would also like to thank Stewart
   Bryant, Sam Aldrin, Tarek Saad, and Rajiv Asati for their review
   comments.  Thanks to Huaimo Chen, Yimin Shen, and Xufeng Liu for
   MPLS-RT expert review.

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

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





Gandhi, et al.          Expires December 27, 2020              [Page 19]


Internet-Draft         Using RFC 6374 for SR-MPLS              June 2020


   Stefano Salsano
   Universita di Roma "Tor Vergata"
   Italy

   Email: stefano.salsano@uniroma2.it


   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com








































Gandhi, et al.          Expires December 27, 2020              [Page 20]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/