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Versions: 00 01 02 03

SPRING Working Group                                      R. Gandhi, Ed.
Internet-Draft                                               C. Filsfils
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: April 24, 2021                                         D. Voyer
                                                             Bell Canada
                                                                 M. Chen
                                                                  Huawei
                                                             B. Janssens
                                                                    Colt
                                                        October 21, 2020


 Performance Measurement Using Simple TWAMP (STAMP) for Segment Routing
                                Networks
                   draft-gandhi-spring-stamp-srpm-03

Abstract

   Segment Routing (SR) leverages the source routing paradigm.  SR is
   applicable to both Multiprotocol Label Switching (SR-MPLS) and IPv6
   (SRv6) data planes.  This document specifies procedure for sending
   and processing probe query and response messages for Performance
   Measurement (PM) in Segment Routing networks.  The procedure uses the
   mechanisms defined in RFC 8762 (Simple Two-Way Active Measurement
   Protocol (STAMP)) and its TLV extensions for Performance Measurement.
   The procedure specified is applicable to SR-MPLS and SRv6 data planes
   and is used for both Links and end-to-end SR Paths including SR
   Policies.

Status of This Memo

   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 April 24, 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
   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 . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   3
     2.3.  Reference Topology  . . . . . . . . . . . . . . . . . . .   4
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Example Provisioning Model  . . . . . . . . . . . . . . .   6
   4.  Probe Messages  . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Probe Query Message . . . . . . . . . . . . . . . . . . .   7
       4.1.1.  Delay Measurement Query Message . . . . . . . . . . .   7
       4.1.2.  Loss Measurement Query Message  . . . . . . . . . . .   8
       4.1.3.  Probe Query for Links . . . . . . . . . . . . . . . .   8
       4.1.4.  Probe Query for SR Policy . . . . . . . . . . . . . .   9
     4.2.  Probe Response Message  . . . . . . . . . . . . . . . . .  11
       4.2.1.  One-way Measurement Mode  . . . . . . . . . . . . . .  11
       4.2.2.  Two-way Measurement Mode  . . . . . . . . . . . . . .  11
       4.2.3.  Loopback Measurement Mode . . . . . . . . . . . . . .  13
     4.3.  Additional Probe Message Processing Rules . . . . . . . .  14
       4.3.1.  TTL and Hop Limit . . . . . . . . . . . . . . . . . .  14
       4.3.2.  Router Alert Option . . . . . . . . . . . . . . . . .  14
       4.3.3.  UDP Checksum  . . . . . . . . . . . . . . . . . . . .  14
   5.  Performance Measurement for P2MP SR Policies  . . . . . . . .  15
   6.  ECMP Support for SR Policies  . . . . . . . . . . . . . . . .  16
   7.  Performance Delay and Liveness Monitoring . . . . . . . . . .  16
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     10.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20



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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).

   The Simple Two-way Active Measurement Protocol (STAMP) provides
   capabilities for the measurement of various performance metrics in IP
   networks using probe messages [RFC8762].  It eliminates the need for
   control-channel signaling by using configuration data model to
   provision a test-channel (e.g.  UDP paths).
   [I-D.ietf-ippm-stamp-option-tlv] defines TLV extensions for STAMP
   messages.

   This document specifies procedures for sending and processing probe
   query and response messages for Performance Measurement in SR
   networks.  The procedure uses the mechanisms defined in [RFC8762]
   (STAMP) and its TLV extensions [I-D.ietf-ippm-stamp-option-tlv] for
   Performance Measurement.  The procedure specified is applicable to
   SR-MPLS and SRv6 data planes and is used for both Links and end-to-
   end SR Paths including SR Policies and Flex-Algo IGP Paths.  Unless
   otherwise specified, the mechanisms defined in [RFC8762] and
   [I-D.ietf-ippm-stamp-option-tlv] are not modified by this document.

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.




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   HMAC: Hashed Message Authentication Code.

   LM: Loss Measurement.

   MPLS: Multiprotocol Label Switching.

   NTP: Network Time Protocol.

   OWAMP: One-Way Active Measurement Protocol.

   PM: Performance Measurement.

   PSID: Path Segment Identifier.

   PTP: Precision Time Protocol.

   SID: Segment ID.

   SL: Segment List.

   SR: Segment Routing.

   SRH: Segment Routing Header.

   SR-MPLS: Segment Routing with MPLS data plane.

   SRv6: Segment Routing with IPv6 data plane.

   SSID: STAMP Session Identifier.

   STAMP: Simple Two-way Active Measurement Protocol.

   TC: Traffic Class.

2.3.  Reference Topology

   In the reference topology shown below, the sender node R1 initiates a
   performance measurement probe query message and the reflector node R5
   sends a probe response message for the query message received.  The
   probe response message is typically sent to the sender node R1.

   SR is enabled on nodes R1 and R5.  The nodes R1 and R5 may be
   directly connected via a Link 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 tail-
   end).





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

                         Reference Topology

3.  Overview

   For one-way and two-way delay measurements in Segment Routing
   networks, the probe messages defined in [RFC8762] are used.  For
   direct-mode and inferred-mode loss measurements, the probe messages
   defined in [I-D.gandhi-ippm-stamp-srpm] are used.  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 need to be created on the
   reflector node R5.

   Separate UDP destination port numbers are user-configured for delay
   and loss measurements from the range specified in [RFC8762].  As
   specified in [RFC8762], the reflector supports the destination UDP
   port 862 for delay measurement probe messages by default.  This UDP
   port however, is not used for loss measurement probe messages.  The
   sender uses the 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 reflector 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 resources.

   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 sender node, and are
      used to measure the delay experienced by the actual data traffic
      flowing on the Links and SR Paths.

   o  For loss measurement, the probe messages are sent on the congruent
      path of the data traffic by the sender 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
      reflector node (incoming link or incoming SID needed since the
      reflector node does not have PM state present).



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   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 of a provisioning model and typical measurement parameters
   for each user-configured destination UDP port for performance delay
   and loss measurements is shown in the following Figure 1:


                             +------------+
                             | Controller |
                             +------------+
   Destination UDP Port           /  \         Destination UDP port
   Measurement Protocol          /    \        Measurement Protocol
   Measurement Type             /      \       Measurement Type
     Delay/Loss                /        \        Delay/Loss
   Authentication Mode & Key  /          \     Authentication Mode & Key
   Timestamp Format          /            \    Loss Measurement Mode
   Delay Measurement Mode   /              \   SSID (Wildcard)
   Loss Measurement Mode   /                \
                          v                  v
                     +-------+            +-------+
                     |       |            |       |
                     |   R1  |============|   R5  |
                     |       |  SR Path   |       |
                     +-------+  Or Link   +-------+
                      Sender              Reflector

                   Figure 1: Example Provisioning Model

   Example of Measurement Protocol is STAMP, example of the Timestamp
   Format is PTPv2 [IEEE1588] or NTP and example of the Loss Measurement
   mode is inferred-mode or direct-mode.

   The mechanisms to provision the sender and reflector nodes are
   outside the scope of this document.  The provisioning model is not
   used for signaling the PM parameters between the reflector and sender
   nodes in SR networks.

   The reflector node R5 uses the parameters for the timestamp format
   and delay measurement mode (i.e. one-way or two-way mode) from the
   received probe query message.





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4.  Probe Messages

4.1.  Probe Query Message

   The probe messages defined in [RFC8762] are used for delay
   measurement for Links and end-to-end SR Paths including SR Policies.
   For loss measurement, the probe messages defined in [I-D.gandhi-ippm-
   stamp-srpm] are used.

4.1.1.  Delay Measurement Query Message

   The message content for delay measurement probe query message using
   UDP header [RFC0768] is shown in Figure 2.  The DM probe query
   message is sent with user-configured Destination UDP port number for
   DM.  The Destination UDP port cannot be used as Source port, since
   the message does not have any indication to distinguish between the
   query and response message.  The payload of the DM probe query
   message contains the delay measurement message defined in [RFC8762].

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Sender IPv4 or IPv6 Address              .
    .  Destination IP Address = Reflector IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Sender                            .
    .  Destination Port = User-configured Port for Delay Measurement.
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = DM Message as specified in Section 4.2 of RFC 8762  |
    .                                                               .
    +---------------------------------------------------------------+

                     Figure 2: DM Probe Query Message

   Timestamp field is eight bytes and use the format defined in
   Section 4.2.1 of [RFC8762].  It is recommended to use the IEEE 1588v2
   Precision Time Protocol (PTP) truncated 64-bit timestamp format
   [IEEE1588] as specified in [RFC8186], with hardware support in
   Segment Routing networks.

4.1.1.1.  Delay Measurement Authentication Mode

   When using the authenticated mode for delay measurement, the matching
   authentication type (e.g.  HMAC-SHA-256) and key are user-configured
   on both the sender and reflector nodes.  A separate user-configured



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   destination UDP port is used for the delay measurement in
   authentication mode due to the different probe message format.

4.1.2.  Loss Measurement Query Message

   The message content for loss measurement probe query message using
   UDP header [RFC0768] is shown in Figure 3.  The LM probe query
   message is sent with user-configured Destination UDP port number for
   LM, which is a different Destination UDP port number than DM.
   Separate Destination UDP ports are used for direct-mode and inferred-
   mode loss measurements.  The Destination UDP port cannot be used as
   Source port, since the message does not have any indication to
   distinguish between the query and response message.  The LM probe
   query message contains the payload for loss measurement as defined in
   [I-D.gandhi-ippm-stamp-srpm].

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Sender IPv4 or IPv6 Address              .
    .  Destination IP Address = Reflector IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Sender                            .
    .  Destination Port = User-configured Port for Loss Measurement .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = LM Message specified in [I-D.gandhi-ippm-stamp-srpm]|
    .                                                               .
    +---------------------------------------------------------------+

                     Figure 3: LM Probe Query Message

4.1.2.1.  Loss Measurement Authentication Mode

   When using the authenticated mode for loss measurement, the matching
   authentication type (e.g.  HMAC-SHA-256) and key are user-configured
   on both the sender and reflector nodes.  A separate user-configured
   destination UDP port is used for the loss measurement in
   authentication mode due to the different message format.

4.1.3.  Probe Query for Links

   The probe query message as defined in Figure 2 for delay measurement
   and Figure 3 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



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   for both delay and loss measurement.  The local and remote IP
   addresses of the link are used as Source and Destination Addresses.
   They can also be IPv6 link local address as probe messages are pre-
   routed.

4.1.4.  Probe Query for SR Policy

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

   The sender IPv4 or IPv6 address is used as the source address.  The
   endpoint IPv4 or IPv6 address is used as the destination address.  In
   the case of SR Policy with IPv4 endpoint of 0.0.0.0 or IPv6 endpoint
   of ::0 [I-D.ietf-spring-segment-routing-policy], the loopback address
   from range 127/8 for IPv4, or the loopback address ::1/128 for IPv6
   is used as the destination address, respectively.  In this case, Node
   Address TLV [I-D.gandhi-ippm-stamp-srpm] can be sent in the probe
   query message to identify the intended destination node.  The
   reflector node MUST NOT send response message if it is not the
   intended destination node in the Node Address TLV [I-D.gandhi-ippm-
   stamp-srpm].

4.1.4.1.  Probe Query Message for SR-MPLS Policy

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

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

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





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   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.

4.1.4.2.  Probe Query Message for SRv6 Policy

   An SRv6 Policy setup using the SRv6 Segment Routing Header (SRH) and
   a Segment List as defined in [RFC8754].  The SRv6 network programming
   is defined in [I-D.ietf-spring-srv6-network-programming].  The probe
   query messages for performance measurement of an end-to-end SRv6
   Policy is sent using its 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.

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Sender IPv6 Address                      .
    .  Destination IP Address = Destination IPv6 Address            .
    .                                                               .
    +---------------------------------------------------------------+
    | SRH as specified in RFC 8754                                  |
    .  <Segment List>                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | IP Header (as needed)                                         |
    .  Source IP Address = Sender IPv6 Address                      .
    .  Destination IP Address = Reflector IPv6 Address              .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Sender                            .
    .  Destination Port = User-configured Port                      .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = DM Message as specified in Section 4.2 of RFC 8762  |
    . Payload = LM Message specified in [I-D.gandhi-ippm-stamp-srpm].
    .                                                               .
    +---------------------------------------------------------------+

           Figure 5: Example Probe Query Message for SRv6 Policy







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4.2.  Probe Response Message

   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.

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Reflector IPv4 or IPv6 Address           .
    .  Destination IP Address = Source IP Address from Query        .
    .  Protocol = UDP                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Reflector                         .
    .  Destination Port = Source Port from Query                    .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = DM Message as specified in Section 4.3 of RFC 8762  |
    . Payload = LM Message specified in [I-D.gandhi-ippm-stamp-srpm].
    .                                                               .
    +---------------------------------------------------------------+

                     Figure 6: Probe Response Message

4.2.1.  One-way Measurement Mode

   In one-way measurement mode, the probe response message as defined in
   Figure 6 is sent back out-of-band to the sender node, for both Links
   and SR Policies.  The Sender Control Code is set to "Out-of-band
   Response Requested".  In this delay measurement mode, as per
   Reference Topology, all timestamps t1, t2, t3, and t4 are collected
   by the probes.  However, only timestamps t1 and t2 are used to
   measure one-way delay as (t2 - t1).

   For one-way performance measurement, the sender node address may not
   be reachable via IP route from the reflector node.  The sender node
   in this case needs to send its reachability path information to the
   reflector node using Return Path TLV defined in [I-D.gandhi-ippm-
   stamp-srpm].

4.2.2.  Two-way Measurement Mode

   In two-way measurement mode, when using a bidirectional path, the
   probe response message as defined in Figure 6 is sent back to the
   sender node on the congruent path of the data traffic on the same
   reverse direction Link or associated reverse SR Policy
   [I-D.ietf-pce-sr-bidir-path].  The Sender Control Code is set to "In-



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   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
   as ((t4 - t1) - (t3 - t2)).

   For two-way measurement mode for Links, the probe response message is
   sent back on the incoming physical interface where the probe query
   message is received.

   For two-way measurement mode for SR Policy, the reflector node needs
   to send the probe response message on a specific reverse path.  The
   sender node can request in the probe query message to the reflector
   node to send a response message back on a given reverse path (e.g.
   co-routed bidirectional path) using Return Path TLV defined in [I-
   D.gandhi-ippm-stamp-srpm].  This way the reflector 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
   undesired).

4.2.2.1.  Probe Response Message for SR-MPLS Policy

   The message content for sending probe response message for two-way
   performance measurement of an end-to-end SR-MPLS Policy 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment(1)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment(n)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Message as shown in Figure 6                   |
    .                                                               .
    +---------------------------------------------------------------+

        Figure 7: Example Probe Response Message for SR-MPLS Policy

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



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4.2.2.2.  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 performance
   measurement of an end-to-end SRv6 Policy with SRH is shown in
   Figure 8.  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 = Reflector IPv6 Address                   .
    .  Destination IP Address = Destination IPv6 Address            .
    .                                                               .
    +---------------------------------------------------------------+
    | SRH as specified in RFC 8754                                  |
    .  <Segment List>                                               .
    .                                                               .
    +---------------------------------------------------------------+
    | IP Header (as needed)                                         |
    .  Source IP Address = Reflector IPv6 Address                   .
    .  Destination IP Address = Source IPv6 Address from Query      .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Sender                            .
    .  Destination Port = User-configured Port                      .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = DM Message as specified in Section 4.3 of RFC 8762  |
    . Payload = LM Message specified in [I-D.gandhi-ippm-stamp-srpm].
    .                                                               .
    +---------------------------------------------------------------+

         Figure 8: Example Probe Response Message for SRv6 Policy

4.2.3.  Loopback Measurement Mode

   The Loopback measurement mode can be used to measure round-trip delay
   for a bidirectional SR Path.  The IP header of the probe query
   message contains the destination address equals to the sender address
   and the source address equals to the reflector address.  Optionally,
   the probe query message can carry the reverse path information (e.g.
   reverse path label stack for SR-MPLS) as part of the SR header.  The
   probe messages are not punted at the reflector node and it does not
   process them and generate response messages.  The Sender Control Code
   is set to the default value of 0.  In this mode, as the probe packet
   is not punted on the reflector node for processing, the querier



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   copies the 'Sequence Number' in 'Session-Sender Sequence Number'
   directly.  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 as (t4 - t1).

4.3.  Additional Probe Message Processing Rules

   The processing rules defined in this section are applicable to the
   STAMP messages for delay and loss measurement for Links and end-to-
   end SR Paths including SR Policies.

4.3.1.  TTL and Hop Limit

   The TTL field in the IPv4 and MPLS headers of the probe query
   messages is set to 255 [RFC8762].  Similarly, the Hop Limit field in
   the IPv6 and SRH headers of the probe query messages is set to 255
   [RFC8762].

   When using the Destination IPv4 Address from range 127/8, the TTL
   field in the IPv4 header is set to 1 [RFC8029].  Similarly, when
   using the Destination IPv6 Address from the ::FFFF:127/104 range, the
   Hop Limit field in the IPv6 header is set to 1.

   For Link performance delay and loss measurements, the TTL or Hop
   Limit field in the probe message is set to 1 in both one-way and two-
   way measurement modes.

4.3.2.  Router Alert Option

   The Router Alert IP option (RAO) [RFC2113] is not set in the probe
   messages.

4.3.3.  UDP Checksum

   The UDP Checksum Complement for delay and loss measurement messages
   follows the procedure defined in [RFC7820] and can be optionally used
   with the procedures defined in this document.

   For IPv4 and IPv6 probe messages, where the hardware is not capable
   of re-computing the UDP checksum or adding checksum complement
   [RFC7820], the sender node sets the UDP checksum to 0 [RFC6936]
   [RFC8085].  The receiving node bypasses the checksum validation and
   accepts the packets with UDP checksum value 0 for the UDP port being
   used for delay and loss measurements.







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5.  Performance Measurement for P2MP SR Policies

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

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

   o  The sender root node sends probe query messages using the Tree-SID
      defined in [I-D.ietf-pim-sr-p2mp-policy] for the P2MP SR-MPLS
      Policy as shown in Figure 9.

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

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

   o  Each reflector leaf node sends its IP address in the Source
      Address of the probe response messages as shown in Figure 9.  This
      allows the sender root node to identify the reflector leaf nodes
      of the P2MP SR Policy.

   o  The P2MP root node measures the delay and loss performance for
      each P2MP leaf node of the end-to-end P2MP 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              Tree-SID                 | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Message as shown in Figure 2 for DM or Figure 3 for LM      |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 9: Example Probe Query with Tree-SID for SR-MPLS Policy






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   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 Policy (e.g. for bidirectional SR Path) are outside the scope
   of this document.

6.  ECMP Support for SR Policies

   An SR Policy can have ECMPs between the source and transit nodes,
   between transit nodes and between transit and destination nodes.
   Usage of Anycast SID [RFC8402] by an SR Policy can result in ECMP
   paths via transit nodes part of that Anycast group.  The probe
   messages need to be sent to traverse different ECMP paths to measure
   performance delay of an SR Policy.

   Forwarding plane has various hashing functions available to forward
   packets on specific ECMP paths.  The mechanisms described in
   [RFC8029] and [RFC5884] for handling ECMPs are also applicable to the
   performance measurement.  In IPv4 header of the probe messages,
   sweeping of Destination Address from range 127/8 can be used to
   exercise particular ECMP paths.  As specified in [RFC6437], Flow
   Label field in the outer IPv6 header can also be used for sweeping.

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

7.  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 delay measurement using the STAMP probe messages can
   also be applied to liveness monitoring of Links and SR Paths.  The
   one-way or two-way measurement mode can be used for liveness
   monitoring.  Liveness failure is notified when consecutive N number
   of probe response messages are not received back at the sender 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 reflector node.  This is improved by using the probes in
   loopback mode.







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8.  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
   reflector node.

   If desired, attacks can be mitigated by performing basic validation
   and sanity checks, at the sender, 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 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.

9.  IANA Considerations

   This document does not require any IANA action.

10.  References

10.1.  Normative References

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

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

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

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

   [I-D.gandhi-ippm-stamp-srpm]
              Gandhi, R., Filsfils, C., Voyer, D., Chen, M., and B.
              Janssens, "Simple TWAMP (STAMP) Extensions for Segment
              Routing", draft-gandhi-ippm-stamp-srpm-00 (work
              in progress), October 2020.


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   [I-D.ietf-ippm-stamp-option-tlv]
              Mirsky, G., Min, X., Nydell, H., Foote, R., Masputra, A.,
              and E. Ruffini, "Simple Two-way Active Measurement
              Protocol Optional Extensions", draft-ietf-ippm-stamp-
              option-tlv-09 (work in progress), August 2020.

10.2.  Informative References

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

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

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
              June 2010, <https://www.rfc-editor.org/info/rfc5884>.

   [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>.

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

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

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







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

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

   [RFC8186]  Mirsky, G. and I. Meilik, "Support of the IEEE 1588
              Timestamp Format in a Two-Way Active Measurement Protocol
              (TWAMP)", RFC 8186, DOI 10.17487/RFC8186, June 2017,
              <https://www.rfc-editor.org/info/rfc8186>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

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

   [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-spring-sr-replication-segment]
              Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z.
              Zhang, "SR Replication Segment for Multi-point Service
              Delivery", draft-ietf-spring-sr-replication-segment-00
              (work in progress), July 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-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.



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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-03 (work in progress),
              September 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-24 (work in
              progress), October 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-03 (work in
              progress), September 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.

   [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-03 (work
              in progress), September 2020.

Acknowledgments

   The authors would like to thank Thierry Couture for the discussions
   on the use-cases for Performance Measurement in Segment Routing.  The
   authors would also like to thank Greg Mirsky for reviewing this
   document and providing useful comments and suggestions.  Patrick
   Khordoc and Radu Valceanu, both from Cisco Systems have helped
   significantly improve the mechanisms defined in this document.  The
   authors would also like to thank Sam Aldrin for the discussions to
   check for broken path.

Authors' Addresses








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   Rakesh Gandhi (editor)
   Cisco Systems, Inc.
   Canada

   Email: rgandhi@cisco.com


   Clarence Filsfils
   Cisco Systems, Inc.

   Email: cfilsfil@cisco.com


   Daniel Voyer
   Bell Canada

   Email: daniel.voyer@bell.ca


   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com


   Bart Janssens
   Colt

   Email: Bart.Janssens@colt.net






















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