Performance Measurement Using TWAMP for Segment Routing Networks
draft-gandhi-spring-twamp-srpm-01

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SPRING Working Group                                      R. Gandhi, Ed.
Internet-Draft                                               C. Filsfils
Intended Status: Standards Track                     Cisco Systems, Inc.
Expires: November 16, 2019                                      D. Voyer
                                                             Bell Canada
                                                                 M. Chen
                                                                  Huawei
                                                            May 15, 2019

                   Performance Measurement Using TWAMP
                       for Segment Routing Networks 
                    draft-gandhi-spring-twamp-srpm-01

Abstract

   Segment Routing (SR) is applicable to both Multiprotocol Label
   Switching (SR-MPLS) and IPv6 (SRv6) data planes.  This document
   specifies procedures for sending and processing synthetic probe query
   and response messages for Performance Measurement (PM).  The
   procedure uses the mechanisms defined in RFC 5357 (Two-Way Active
   Measurement Protocol (TWAMP)) for Delay Measurement, and also uses
   the mechanisms specified in this document for direct-mode Loss
   Measurement.  The procedure specified is applicable to SR-MPLS and
   SRv6 data planes for both links and end-to-end measurement for 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
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Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

 

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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
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   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  . . . . . . . . . . . . . . . . . . . . . .  4
     2.3.  Reference Topology . . . . . . . . . . . . . . . . . . . .  4
   3.  Probe Messages . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Probe Query Message  . . . . . . . . . . . . . . . . . . .  5
       3.1.1.  Delay Measurement Probe Query Message  . . . . . . . .  6
         3.1.1.1.  Delay Measurement Message Checksum Complement  . .  6
         3.1.1.2.  Delay Measurement Authentication Mode  . . . . . .  7
       3.1.2.  Loss Measurement Probe Query Message . . . . . . . . .  7
         3.1.2.1.  Loss Measurement Message Checksum Complement . . . 10
         3.1.2.2.  Loss Measurement Authentication Mode . . . . . . . 10
       3.1.3.  Probe Query for SR Links . . . . . . . . . . . . . . . 10
       3.1.4.  Probe Query for End-to-end Measurement for SR Policy . 10
         3.1.4.1.  Probe Query Message for SR-MPLS Policy . . . . . . 10
         3.1.4.2.  Probe Query Message for SRv6 Policy  . . . . . . . 11
     3.2.  Probe Response Message . . . . . . . . . . . . . . . . . . 12
       3.2.1.  One-way Measurement Mode . . . . . . . . . . . . . . . 14
       3.2.2.  Two-way Measurement Mode . . . . . . . . . . . . . . . 15
         3.2.2.1.  Return Path TLV  . . . . . . . . . . . . . . . . . 15
         3.2.2.2.  Probe Response Message for SR-MPLS Policy  . . . . 16
         3.2.2.3.  Probe Response Message for SRv6 Policy . . . . . . 17
       3.2.3.  Loopback Measurement Mode  . . . . . . . . . . . . . . 17
   4.  Packet Loss Calculation  . . . . . . . . . . . . . . . . . . . 17
   5.  Performance Measurement for P2MP SR Policies . . . . . . . . . 18
   6.  ECMP Support for SR Policies . . . . . . . . . . . . . . . . . 18
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 19
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 20
   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . . . 22
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
 

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1.  Introduction

   Segment Routing (SR) technology 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, transit and destination nodes.  SR Policies as defined in
   [I-D.spring-segment-routing-policy] are used to steer traffic through
   a specific, user-defined path using a stack of Segments.  Built-in SR
   Performance Measurement (PM) is one of the essential requirements to
   provide Service Level Agreements (SLAs).

   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 using synthetic probe messages.  These
   protocols rely on control channel signaling to establish a test
   channel over an UDP path.  These protocols lack support for
   direct-mode Loss Measurement (LM) to detect actual data traffic loss
   which is required in SR networks.  The Simple Two-way Active
   Measurement Protocol (STAMP) [I-D.ippm-stamp] alleviates the control
   channel signaling by using configuration data model to provision test
   channels and UDP ports.  The TWAMP Light from broadband forum
   [BBF.TR-390] provides simplified mechanisms for active performance
   measurement in Customer Edge IP networks.

   This document specifies procedures for sending and processing
   synthetic probe query and response messages for Performance
   Measurement.  The procedure uses the mechanisms defined in RFC 5357
   (Two-Way Active Measurement Protocol (TWAMP)) for Delay Measurement
   (DM), and also uses the mechanisms specified in this document for
   direct-mode Loss Measurement (LM).  The procedure specified is
   applicable to SR-MPLS and SRv6 data planes for both links and
   end-to-end measurement for SR Policies.  For SR Policies, there are
   Equal Cost Multi-Paths (ECMP) between the source and transit nodes,
   between transit nodes and between transit and destination nodes. 
   This document also defines mechanisms for handling ECMPs of SR
   Policies for performance delay measurement. 

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.
 

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2.2.  Abbreviations

   BSID: Binding Segment ID.

   DM: Delay Measurement.

   ECMP: Equal Cost Multi-Path.

   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.

   SR-MPLS: Segment Routing with MPLS data plane.

   SRv6: Segment Routing with IPv6 data plane.

   STAMP: Simple Two-way Active Measurement Protocol.

   TC: Traffic Class.

   TWAMP: Two-Way Active Measurement Protocol.

2.3.  Reference Topology

   In the reference topology, the querier node R1 initiates a probe
   query for performance measurement and the responder node R5 sends a
   probe response for the query message received.  The probe response
   may be sent to the querier node R1.  The nodes R1 and R5 may be
   directly connected via a link enabled with Segment Routing or there
   exists a Point-to-Point (P2P) SR Policy
   [I-D.spring-segment-routing-policy] on node R1 with destination to
 

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   node R5.  In case of Point-to-Multipoint (P2MP), SR Policy
   originating from source node R1 may terminate on multiple destination
   leaf nodes [I-D.spring-sr-p2mp-policy].

             +-------+        Query        +-------+
             |       | - - - - - - - - - ->|       |
             |   R1  |---------------------|   R5  |
             |       |<- - - - - - - - - - |       |
             +-------+       Response      +-------+

                        Reference Topology

   For delay and loss measurements, for both links and end-to-end SR
   Policies, no PM session is created on the responder node R5.  One-way
   delay and two-way delay measurements are defined in [RFC4656] and
   [RFC5357], respectively.  One-way loss measurement provides receive
   packet loss whereas two-way loss measurement provides both transmit
   and receive packet loss.

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

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

   o  For Loss Measurement, the probe messages are sent on the congruent
      path of the data traffic by the querier node, and are used to
      collect the receive traffic counters for the incoming link or
      incoming SID where the probe query messages are received at the
      responder node (incoming link or incoming SID used as the
      responder node has no PM session state present).

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

3.  Probe Messages

3.1.  Probe Query Message

   In this document, the probe messages defined in [RFC5357] are used
 

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   for Delay and Loss measurements for SR links and end-to-end SR
   Policies.  The user-configured UDP ports (separate UDP port for each
   message format) are used for identifying the PM probe packets and to
   avoid signaling to bootstrap PM sessions.  This approach is similar
   to the one defined in STAMP protocol [I-D.ippm-stamp].  The IPv4 TTL
   or IPv6 Hop Limit field of the IP header MUST be set to 255.

3.1.1.  Delay Measurement Probe Query Message

   The message content for Delay Measurement probe query message using
   UDP header [RFC768] is shown in Figure 1.  The DM probe query message
   is sent with user-configured Destination UDP port number for DM.  The
   Destination UDP port cannot be used as Source port, since the message
   does not have any indication to distinguish between query and
   response.  The DM probe query message contains the payload for delay
   measurement defined in Section 4.1.2 of OWAMP [RFC4656].  As an
   alternative, the DM probe query message contains the payload defined
   in Section 4.2.1 of TWAMP [RFC5357].

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Querier IPv4 or IPv6 Address             .
    .  Destination IP Address = Responder IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .  Router Alert Option Not Set                                  .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Querier                           .
    .  Destination Port = User-configured Port for Delay Measurement.
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = Message as specified in Section 4.2.1 of RFC 5357   |
    | | Payload = Message as specified in Section 4.1.2 of RFC 4656 |
    .                                                               .
    +---------------------------------------------------------------+

                   Figure 1: DM Probe Query Message

   Timestamp field is eight bytes.  It is recommended to use the IEEE
   1588v2 Precision Time Protocol (PTP) truncated 64-bit timestamp
   format [IEEE1588] using the procedure defined in [RFC8186].

3.1.1.1.  Delay Measurement Message Checksum Complement

   The Checksum Complement shown in Figure 3 for OWAMP in [RFC7820] and
   Figure 4 for TWAMP in [RFC7820] for delay measurement message format
   follows the procedure defined in [RFC7820] and can be used optionally
 

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   with the procedures defined in this document. 

3.1.1.2.  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 querier and responder nodes.  A different user-configured
   destination UDP port is required for the delay measurement in
   authentication mode due to the different probe message format. 

3.1.2.  Loss Measurement Probe Query Message

   The message content for Loss Measurement probe query message using
   UDP header [RFC768] is shown in Figure 2.  The LM probe query message
   is sent with user-configured Destination UDP port number for LM. 
   Different 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 query and response.  The LM probe query
   message contains the payload for loss measurement as defined in
   Figure 2.  An alternative, the LM probe query message contains the
   payload defined in Figure 8. 

   Both of these LM message formats define fixed locations for the
   counters in the payload and are easy to implement in hardware.  In
   addition, new LM messages do not require any backwards compatibility
   or support for the existing DM message formats in [RFC5357].

    +---------------------------------------------------------------+
    | IP Header                                                     |  
    .  Source IP Address = Querier IPv4 or IPv6 Address             .
    .  Destination IP Address = Responder IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .  Router Alert Option Not Set                                  .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Querier                           .
    .  Destination Port = User-configured Port for Loss Measurement .
    .                                                               .
    +---------------------------------------------------------------+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Sender TTL   |X|B|0|0|0|0|0|0|         Block Number          |
 

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    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                         Packet Padding                        .
    .                                                               .
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |      Checksum Complement      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 2A: LM Probe Query Message for OWAMP

    +---------------------------------------------------------------+
    | IP Header                                                     |  
    .  Source IP Address = Querier IPv4 or IPv6 Address             .
    .  Destination IP Address = Responder IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .  Router Alert Option Not Set                                  .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Querier                           .
    .  Destination Port = User-configured Port for Loss Measurement .
    .                                                               .
    +---------------------------------------------------------------+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (8 octets)                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Sender TTL   |X|B|0|0|0|0|0|0|         Block Number          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        HMAC (16 octets)                       |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
 

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    .                         Packet Padding                        .
    .                                                               .
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |      Checksum Complement      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 2B: LM Probe Query Message for OWAMP - Authenticated Mode

   Sequence Number (32-bit): As defined in [RFC5357].

   Transmit Counter (64-bit): The number of packets sent by the querier
   node in the query message and by the responder node in the response
   message.  The counter is always written at the fixed location in the
   probe query and response messages.

   Receive Counter (64-bit): The number of packets received at the
   responder node.  It is written by the responder node in the probe
   response message.

   Sender Counter (64-bit): This is the exact copy of the transmit
   counter from the received query message.  It is written by the
   responder node in the probe response message.

   Sender Sequence Number (32-bit): As defined in [RFC5357].

   Sender TTL: As defined in [RFC5357].

   Flag: The meanings of the Flag bits are:

      X: Extended counter format indicator.  Indicates the use of
      extended (64-bit) counter values.  Initialized to 1 upon creation
      (and prior to transmission) of an LM Query and copied from an LM
      Query to an LM response.  Set to 0 when the LM message is
      transmitted or received over an interface that writes 32-bit
      counter values.

      B: Octet (byte) count.  When set to 1, indicates that the Counter
      1-4 fields represent octet counts.  The octet count applies to all
      packets within the LM scope, and the octet count of a packet sent
      or received over a channel includes the total length of that
      packet (but excludes headers, labels, or framing of the channel
      itself).  When set to 0, indicates that the Counter fields
      represent packet counts.

      0: Set to 0.

   Block Number (16-bit): The Loss Measurement using Alternate-Marking
 

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   method defined in [RFC8321] requires to identify the Block Number (or
   color) of the traffic counters.  The probe query and response
   messages carry Block Number for the traffic counters for loss
   measurement.  In both probe query and response messages, the counters
   MUST belong to the same Block Number.

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

   HMAC uses own key and the definition of the mechanism to distribute
   the HMAC key is outside the scope of this document.

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

3.1.2.1.  Loss Measurement Message Checksum Complement

   The Checksum Complement shown in Figure 2 for loss measurement
   message format follows the procedure defined in [RFC7820] and can be
   used optionally with the procedures defined in this document.

3.1.2.2.  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 querier and responder nodes.  A different user-configured
   destination UDP port is required for the loss measurement in
   authentication mode due to the different message format. 

3.1.3.  Probe Query for SR Links

   The probe query message as defined in Figure 1 is sent on the
   congruent path of the data traffic for Delay measurement.  The probe
   query message as defined in Figure 2 is sent on the congruent path of
   the data traffic for Loss measurement. 

3.1.4.  Probe Query for End-to-end Measurement for SR Policy

3.1.4.1.  Probe Query Message for SR-MPLS Policy

   The message content for the probe query message using UDP header for
 

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   end-to-end performance measurement of SR-MPLS Policy is shown in
   Figure 3.

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

             Figure 3: Probe Query Message for SR-MPLS Policy

   The Segment List (SL) can be empty to indicate Implicit NULL label
   case.

   The Path Segment Identifier (PSID) [I-D.spring-mpls-path-segment] of
   the SR-MPLS Policy is used for accounting received traffic on the
   egress node for loss measurement.  The PSID is not required for
   end-to-end SR Policy delay measurement.

3.1.4.2.  Probe Query Message for SRv6 Policy

   An SRv6 Policy setup using the SRv6 Segment Routing Header (SRH) and
   a Segment List as defined in [I-D.6man-segment-routing-header].  The
   probe query messages using UDP header for end-to-end performance
   measurement of an SRv6 Policy is sent using its SRv6 Segment Routing
   Header (SRH) and 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           SRH                                 |
    .   END.OTP (DM) or END.OP (LM) with Target SRv6 SID            .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Message as shown in Figure 1 for DM or Figure 2 for LM      |
    .   (Using IPv6 Addresses)                                      .
    .                                                               .
 

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    +---------------------------------------------------------------+

              Figure 4: Probe Query Message for SRv6 Policy

   For delay measurement of SRv6 Policy using SRH, END function END.OTP
   [I-D.spring-srv6-oam] is used with the target SRv6 SID to punt probe
   messages on the target node, as shown in Figure 4.  Similarly, for
   loss measurement of SRv6 Policy, END function END.OP
   [I-D.spring-srv6-oam] is used with target SRv6 SID to punt probe
   messages on the target node.

3.2.  Probe Response Message

   The probe response message is sent using the IP/UDP information from
   the probe query message.  The content of the probe response message
   is shown in Figure 5.

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Responder IPv4 or IPv6 Address           .
    .  Destination IP Address = Source IP Address from Query        .
    .  Protocol = UDP                                               .
    .  Router Alert Option Not Set                                  .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Responder                         .
    .  Destination Port = Source Port from Query                    .
    .                                                               .
    +---------------------------------------------------------------+
    | DM Payload as specified in Section 4.2.1 of RFC 5357, or      |
    . LM Payload as specified in Figure 8 in this document          .
    .                                                               .
    +---------------------------------------------------------------+

                    Figure 5: Probe Response Message

    +---------------------------------------------------------------+
    | IP Header                                                     |  
    .  Source IP Address = Querier IPv4 or IPv6 Address             .
    .  Destination IP Address = Responder IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .  Router Alert Option Not Set                                  .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Querier                           .
 

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    .  Destination Port = User-configured Port for Loss Measurement .
    .                                                               .
    +---------------------------------------------------------------+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Receive Counter                        |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Sequence Number                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Counter                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Sender TTL   |X|B|0|0|0|0|0|0|         Block Number          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                                                               .
    .                         Packet Padding                        .
    .                                                               .
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |     Checksum Complement       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 8A: LM Probe Response Message for TWAMP

    +---------------------------------------------------------------+
    | IP Header                                                     |  
    .  Source IP Address = Querier IPv4 or IPv6 Address             .
    .  Destination IP Address = Responder IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .  Router Alert Option Not Set                                  .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Querier                           .
    .  Destination Port = User-configured Port for Loss Measurement .
    .                                                               .
    +---------------------------------------------------------------+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 

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    |                        Transmit Counter                       |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (8 octets)                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Receive Counter                        |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (8 octets)                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Sequence Number                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Counter                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (8 octets)                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Sender TTL   |X|B|0|0|0|0|0|0|         Block Number          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        HMAC (16 octets)                       |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                                                               .
    .                         Packet Padding                        .
    .                                                               .
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |     Checksum Complement       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 8B: LM Probe Response Message for TWAMP - Authenticated Mode

3.2.1.  One-way Measurement Mode

 

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   In one-way performance measurement mode, the probe response message
   as defined in Figure 5 is sent for both SR links and SR Policies.

3.2.2.  Two-way Measurement Mode

   In two-way performance measurement mode, when using a bidirectional
   path, the probe response message as defined in Figure 5 is sent back
   on the congruent path of the data traffic to the querier node.

3.2.2.1.  Return Path TLV

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

   [I-D.ippm-stamp-option-tlv] defines STAMP 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 SR path for
   probe response messages (in the payload of the message).  The format
   of the Return Path TLV is shown in Figure 8A and 8B:

    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 8A: 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                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Segment List(1)                            |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 

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    |                    Segment List(n)                            |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 8B: Segment List Sub-TLV in Return Path TLV

   The 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 SR Policy

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

   o  Type (value 3): SRv6 Segment List of the Reverse SR Policy

   o  Type (value 4): SRv6 Binding SID [I-D.pce-binding-label-sid] of
      the Reverse SR Policy

   With sub-TLV Type 1, the Segment List(1) can be used by the responder
   node to compute the next-hop IP address and outgoing interface to
   send the probe response messages.

   The Return Path TLV is optional.  The PM 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.

3.2.2.2.  Probe Response Message for SR-MPLS Policy

   The message content for sending probe response message using the UDP
   header for two-way end-to-end performance measurement of an SR-MPLS
   Policy is shown in Figure 6.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment List(1)        | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Segment List(n)        | TC  |S|      TTL      |
 

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    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Message as shown in Figure 5                   |
    .                                                               .
    +---------------------------------------------------------------+

           Figure 6: Probe Response Message for SR-MPLS Policy

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

3.2.2.3.  Probe Response Message for SRv6 Policy

   The message content for sending probe response message on the
   congruent path of the data traffic using UDP header for two-way
   end-to-end performance measurement of an SRv6 Policy with SRH 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          SRH                                  |
    .   END.OTP (DM) or END.OP (LM) with Target SRv6 SID            .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Message as shown in Figure 5 (with IPv6 Addresses)          |
    .                                                               .
    +---------------------------------------------------------------+

            Figure 7: Probe Response Message for SRv6 Policy

3.2.3.  Loopback Measurement Mode

   The Loopback measurement mode can be used to measure round-trip delay
   for a bidirectional Path.  The probe query messages in this case
   either carry the reverse Path information as part of the SR header or
   set the querier address as the destination address in the IP header. 
   The responder node does not process the PM probe messages and
   generate response messages.

4.  Packet Loss Calculation

   The formula for calculating the one-way packet loss using packet
   counters for a given block number is as following:

     One-way Packet_Loss[n-1, n]
 

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                 = (Sender_Counter[n] - Sender_Counter[n-1]) 
                   - (Receive_Counter[n] - Receive_Counter[n-1])

5.  Performance Measurement for P2MP SR Policies

   The procedures for delay and loss measurement described in this
   document for Point-to-Point (P2P) SR Policies
   [I-D.spring-segment-routing-policy] are also equally applicable to
   the Point-to-Multipoint (P2MP) SR Policies
   [I-D.spring-sr-p2mp-policy] as following:

   o  The querier root node sends probe query messages using the either
      Spray P2MP segment or TreeSID P2MP segment defined in
      [I-D.spring-sr-p2mp-policy] over the P2MP SR Policy.

   o  Each responder leaf node sends its IP address in the Source
      Address of the probe response messages.  This allows the querier
      root node to identify the responder leaf nodes of the P2MP SR
      Policy.

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

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 PM 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.  Following mechanisms can be used in
   PM probe messages to take advantage of the hashing function in
   forwarding plane to influence the path taken by them.

   o  The mechanisms described in [RFC8029] and [RFC5884] for handling
      ECMPs are also applicable to the performance measurement.  In the
      IP/UDP header of the PM probe messages, Destination Addresses in
      127/8 range for IPv4 or 0:0:0:0:0:FFFF:7F00/104 range for IPv6 can
      be used to exercise a particular ECMP path.  As specified in
      [RFC6437], 3-tuple of Flow Label, Source Address and Destination
      Address fields in the IPv6 header can also be used.

   o  For SR-MPLS Policy, entropy label [RFC6790] can be used in the PM
 

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      probe messages.

   o  For SRv6 Policy using SRH, Flow Label in the SRH
      [I-D.6man-segment-routing-header] of the PM probe messages can be
      used.

7.  Security Considerations

   The performance measurement is intended for deployment in
   well-managed private and service provider networks.  As such, it
   assumes that a node involved in a measurement operation has
   previously verified the integrity of the path and the identity of the
   far end responder node.

   If desired, attacks can be mitigated by performing basic validation
   and sanity checks, at the querier, 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 [I-D.6man-segment-routing-header]. 
   Hence, PM probe messages for SRv6 may not need authentication mode. 
   Cryptographic measures may be enhanced by the correct configuration
   of access-control lists and firewalls.

8.  IANA Considerations

   IANA is requested to allocate values for the following Return Path
   TLV Type for [I-D.ippm-stamp-option-tlv] to be carried in PM probe
   query messages:

      o  Type TBA1: Return Path TLV

9.  References

9.1.  Normative References

   [RFC768]   Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              August 1980.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
 

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              Requirement Levels", RFC 2119, March 1997.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, September 2006.

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, October 2008.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", RFC 8174, May 2017.

   [I-D.spring-srv6-oam]  Ali, Z., et al., "Operations, Administration,
              and Maintenance (OAM) in Segment Routing Networks with
              IPv6 Data plane (SRv6)", draft-ali-spring-srv6-oam, work
              in progress.

   [I-D.ippm-stamp-option-tlv]  Mirsky, G., et al., "Simple Two-way
              Active Measurement Protocol Optional Extensions",
              draft-mirsky-ippm-stamp-option-tlv, work in progress.

9.2.  Informative References

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

   [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.

   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437, November 2011.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, November 2012.

   [RFC7820]  Mizrahi, T., "UDP Checksum Complement in the One-Way
              Active Measurement Protocol (OWAMP) and Two-Way Active
              Measurement Protocol (TWAMP)", RFC 7820, March 2016.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Kumar, N.,
              Aldrin, S. and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029, March
              2017.
 

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   [RFC8186]  Mirsky, G., and I. Meilik, "Support of the IEEE 1588
              Timestamp Format in a Two-Way Active Measurement Protocol
              (TWAMP)", RFC 8186, June 2017.

   [RFC8321]  Fioccola, G. Ed., "Alternate-Marking Method for Passive
              and Hybrid Performance Monitoring", RFC 8321, January
              2018.

   [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>.

   [I-D.spring-segment-routing-policy]  Filsfils, C., et al., "Segment
              Routing Policy Architecture",
              draft-ietf-spring-segment-routing-policy, work in
              progress.

   [I-D.spring-sr-p2mp-policy]  Voyer, D. Ed., et al., "SR Replication
              Policy for P2MP Service Delivery",
              draft-voyer-spring-sr-p2mp-policy, work in progress.

   [I-D.spring-mpls-path-segment]  Cheng, W., et al., "Path Segment in
              MPLS Based Segment Routing Network",
              draft-ietf-spring-mpls-path-segment, work in progress.

   [I-D.6man-segment-routing-header]  Filsfils, C., et al., "IPv6
              Segment Routing Header (SRH)",
              draft-ietf-6man-segment-routing-header, work in progress.

   [I-D.ippm-stamp]  Mirsky, G. et al. "Simple Two-way Active
              Measurement Protocol", draft-ietf-ippm-stamp, work in
              progress.

   [I-D.pce-binding-label-sid]  Filsfils, C., et al., "Carrying Binding
              Label Segment-ID in PCE-based Networks",
              draft-sivabalan-pce-binding-label-sid, work in progress.

   [BBF.TR-390]  "Performance Measurement from IP Edge to Customer
              Equipment using TWAMP Light", BBF TR-390, May 2017.

   [I-D.spring-ioam-sr-mpls]  Gandhi, R. Ed., et al., "Segment Routing
              with MPLS Data Plane Encapsulation for In-situ OAM Data",
              draft-gandhi-spring-ioam-sr-mpls, work in progress.

   [RFC2104]  Krawczyk, H., Bell-are, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104, February
              1997.
 

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   [RFC4868]  Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
              384, and HMAC-SHA-512 with IPsec", RFC 4868, May 2007.

Acknowledgments

   The authors would like to thank Thierry Couture for various
   discussions on the use-cases for TWAMP in segment routing.  The
   authors would also like to thank Greg Mirsky for reviewing this
   document and providing useful comments and suggestions.

Authors' Addresses

   Rakesh Gandhi (editor)
   Cisco Systems, Inc.
   Canada
   Email: rgandhi@cisco.com

   Clarence Filsfils
   Cisco Systems, Inc.
   Email: cfilsfil@cisco.com

   Daniel Voyer
   Bell Canada
   Email: daniel.voyer@bell.ca

   Mach(Guoyi) Chen
   Huawei
   Email: mach.chen@huawei.com

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