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Versions: (draft-gandhi-spring-udp-pm) 00 01 02

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
                                                              S. Salsano
                                        Universita di Roma "Tor Vergata"
                                                            P. L. Ventre
                                                                    CNIT
                                                                 M. Chen
                                                                  Huawei
                                                            May 15, 2019


                Performance Measurement Using UDP Path
                     for Segment Routing Networks
               draft-gandhi-spring-rfc6374-srpm-udp-01

Abstract

   Segment Routing (SR) is applicable to both Multiprotocol Label
   Switching (SR-MPLS) and IPv6 (SRv6) data planes.  This document
   specifies procedures for using UDP path for sending and processing
   synthetic probe query and response messages for Performance
   Measurement (PM).  The procedure uses the RFC 6374 defined mechanisms
   for Performance Delay and Loss Measurement.  The procedure specified
   is applicable to SR-MPLS and SRv6 data planes for both links and
   end-to-end measurement for SR Policies.  In addition, this document
   defines Return Path TLV for two-way performance measurement and Block
   Number TLV for loss measurement.


Status of This Memo

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

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





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Copyright Notice

   Copyright (c) 2019 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
   (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
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  4
     2.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
     2.2.  Abbreviations  . . . . . . . . . . . . . . . . . . . . . .  4
     2.3.  Reference Topology . . . . . . . . . . . . . . . . . . . .  5
   3.  Probe Messages . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  Probe Query Message  . . . . . . . . . . . . . . . . . . .  7
       3.1.1.  Delay Measurement Probe Query Message  . . . . . . . .  7
       3.1.2.  Loss Measurement Probe Query Message . . . . . . . . .  7
         3.1.2.1.  Block Number TLV . . . . . . . . . . . . . . . . .  8
       3.1.3.  Probe Query for SR Links . . . . . . . . . . . . . . .  9
       3.1.4.  Probe Query for End-to-end Measurement for SR Policy .  9
         3.1.4.1.  Probe Query Message for SR-MPLS Policy . . . . . .  9
         3.1.4.2.  Probe Query Message for SRv6 Policy  . . . . . . . 10
     3.2.  Probe Response Message . . . . . . . . . . . . . . . . . . 10
       3.2.1.  One-way Measurement Mode . . . . . . . . . . . . . . . 11
         3.2.1.1.  SR Links and End-to-end Measurement for SR
                   Policy . . . . . . . . . . . . . . . . . . . . . . 11
         3.2.1.2.  Probe Response Message to Controller . . . . . . . 12
       3.2.2.  Two-way Measurement Mode . . . . . . . . . . . . . . . 12
         3.2.2.1.  SR Links . . . . . . . . . . . . . . . . . . . . . 12
         3.2.2.2.  End-to-end Measurement for SR Policy . . . . . . . 12
         3.2.2.3.  Return Path TLV  . . . . . . . . . . . . . . . . . 12
         3.2.2.4.  Probe Response Message for SR-MPLS Policy  . . . . 14
         3.2.2.5.  Probe Response Message for SRv6 Policy . . . . . . 14
       3.2.3.  Loopback Measurement Mode  . . . . . . . . . . . . . . 15
     3.3.  Checksum Complement  . . . . . . . . . . . . . . . . . . . 15
   4.  Performance Measurement for P2MP SR Policies . . . . . . . . . 15
   5.  ECMP Support for SR Policies . . . . . . . . . . . . . . . . . 16
   6.  Sequence Numbers . . . . . . . . . . . . . . . . . . . . . . . 16



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     6.1.  Sequence Number TLV in Unauthenticated Mode  . . . . . . . 17
     6.2.  Sequence Number TLV in Authenticated Mode  . . . . . . . . 17
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 20
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 20
   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . . . 23
   Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23



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.  These protocols rely on control channel
   signaling to establish a test channel over an UDP path.  These
   protocols lack support for IEEE 1588 timestamp [IEEE1588] format and
   direct-mode Loss Measurement (LM), which are required in SR networks
   [RFC6374].  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.  In addition,
   the STAMP supports IEEE 1588 timestamp format for Delay Measurement
   (DM).  The TWAMP Light from broadband forum [BBF.TR-390] provides
   simplified mechanisms for active performance measurement in Customer
   Edge IP networks.  [Y1731] specifies the mechanisms to carry OAM
   messages specifically for Ethernet networks that include Ethernet
   Frame Delay and Loss measurements.

   [RFC6374] specifies protocol mechanisms to enable the efficient and
   accurate measurement of performance metrics and can be used in SR
   networks with MPLS data plane [I-D.spring-rfc6374-srpm-mpls].
   [RFC6374] addresses the limitations of the IP based performance
   measurement protocols as specified in Section 1 of [RFC6374].  The
   [RFC6374] requires data plane to support MPLS Generic Associated



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   Channel Label (GAL) and Generic Associated Channel (G-Ach), which may
   not be supported on all nodes in the network.

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

   For SR Policies, there are ECMPs between the source and transit
   nodes, between transit nodes and between transit and destination
   nodes.  Existing PM protocols (e.g. RFC 6374) do not define handling
   for ECMP forwarding paths in SR networks.

   For two-way measurements for SR Policies, there is a need to specify
   a return path in the form of a Segment List in PM probe query
   messages without requiring any SR Policy state on the destination
   node.  Existing protocols do not have such mechanisms to specify
   return path in the PM probe query messages.

   This document specifies a procedure for using UDP path for sending
   and processing synthetic probe query and response messages for
   Performance Measurement that does not require to bootstrap PM
   sessions.  The procedure uses RFC 6374 defined mechanisms for
   Performance Delay and Loss Measurement and unless otherwise
   specified, the procedures from RFC 6374 are not modified.  The
   procedure specified is applicable to both SR-MPLS and SRv6 data
   planes.  The procedure can be used for both SR links and end-to-end
   performance measurement for SR Policies.  This document also defines
   mechanisms for handling Equal Cost Multi-Paths (ECMPs) of SR Policies
   for performance delay measurement.  In addition, this document
   defines Return Path TLV for two-way performance measurement, Block
   Number TLV for loss measurement and Sequence Number TLV.


2.  Conventions Used in This Document

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119] [RFC8174]
   when, and only when, they appear in all capitals, as shown here.

2.2.  Abbreviations

   ACH: Associated Channel Header.




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   BSID: Binding Segment ID.

   DFLag: Data Format Flag.

   DM: Delay Measurement.

   ECMP: Equal Cost Multi-Path.

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

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

   LM: Loss Measurement.

   MPLS: Multiprotocol Label Switching.

   NTP: Network Time Protocol.

   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.

   URO: UDP Return Object.


2.3.  Reference Topology

   In the reference topology, the querier node R1 initiates a probe



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   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 or to a controller node R100.  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
   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].

                                             ------
                                             |R100|
                                             ------
                                               ^
                                               | Response
                                               |
             +-------+        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 Section 2.4 of
   [RFC6374].  Transmit and Receive packet loss measurements are defined
   in Section 2.2 and Section 2.6 of [RFC6374].  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)



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   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, UDP path is used for Delay and Loss measurements
   for SR links and end-to-end SR Policies.  The user-configured UDP
   ports are used for identifying 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 for 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 can also be used as Source port for
   two-way delay measurement, since the message has a flag to
   distinguish between query and response.  The DM probe query message
   contains the payload for delay measurement defined in Section 3.2 of
   [RFC6374].

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Querier IPv4 or IPv6 Address             .
    .  Destination IP Address = Responder IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .  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 3.2 of RFC 6374     |
    .                                                               .
    +---------------------------------------------------------------+

                   Figure 1: DM Probe Query Message

3.1.2.  Loss Measurement Probe Query Message



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   The message content for Loss measurement probe query message using
   UDP header [RFC768] is shown in Figure 2.  As shown, 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
   can also be used as Source port for two-way loss measurement, since
   the message has a flag to distinguish between query and response.
   The LM probe query message contains the payload for loss measurement
   defined in Section 3.1 of [RFC6374].


    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Querier IPv4 or IPv6 Address             .
    .  Destination IP Address = Responder IPv4 or IPv6 Address      .
    .  Protocol = UDP                                               .
    .  Router Alert Option Not Set                                  .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Querier                           .
    .  Destination Port = User-configured Port for Loss Measurement .
    .                                                               .
    +---------------------------------------------------------------+
    | Payload = Message as specified in Section 3.1 of RFC 6374     |
    .                                                               .
    +---------------------------------------------------------------+

                  Figure 2: LM Probe Query Message



3.1.2.1.  Block Number TLV

   The Loss Measurement using Alternate-Marking method defined in
   [RFC8321] requires to identify the Block Number (or color) of the
   traffic counters carried by the probe query and response messages.
   Probe query and response messages specified in [RFC6374] for Loss
   Measurement do not define any means to carry the Block Number.

   [RFC6374] defines probe query and response messages that can include
   one or more optional TLVs.  New TLV Type (value TBA2) is defined in
   this document to carry Block Number (16-bit) for the traffic counters
   in the probe query and response messages for loss measurement.  The
   format of the Block Number TLV is shown in Figure 11:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1



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

                    Figure 11: Block Number TLV

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

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 performance Delay measurement.
    Similarly, the probe query message as defined in Figure 2 is sent on
   the congruent path of the data traffic for performance 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
   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      |
    .                                                               .
    +---------------------------------------------------------------+




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             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 delay
   measurement.

3.1.4.2.  Probe Query Message for SRv6 Policy

   An SRv6 Policy is 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)                                      .
    .                                                               .
    +---------------------------------------------------------------+

              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

   When the received probe query message does not contain any UDP Return
   Object (URO) TLV [RFC7876], the probe response message is sent using
   the IP/UDP information from the probe query message.  The content of
   the probe response message is shown in Figure 5.

    +---------------------------------------------------------------+
    | IP Header                                                     |



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    .  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                    .
    .                                                               .
    +---------------------------------------------------------------+
    | Message as specified in Section 3.2 of RFC 6374 for DM, or    |
    . Message as specified in Section 3.1 of RFC 6374 for LM        .
    .                                                               .
    +---------------------------------------------------------------+

                    Figure 5: Probe Response Message

   When the received probe query message contains UDP Return Object
   (URO) TLV [RFC7876], the probe response message uses the IP/UDP
   information from the URO in the probe query message.  The content of
   the probe response message is shown in Figure 6.

    +---------------------------------------------------------------+
    | IP Header                                                     |
    .  Source IP Address = Responder IPv4 or IPv6 Address           .
    .  Destination IP Address = URO.Address                         .
    .  Protocol = UDP                                               .
    .  Router Alert Option Not Set                                  .
    .                                                               .
    +---------------------------------------------------------------+
    | UDP Header                                                    |
    .  Source Port = As chosen by Responder                         .
    .  Destination Port = URO.UDP-Destination-Port                  .
    .                                                               .
    +---------------------------------------------------------------+
    | Message as specified in Section 3.2 of RFC 6374 for DM, or    |
    . Message as specified in Section 3.1 of RFC 6374 for LM        .
    .                                                               .
    +---------------------------------------------------------------+

      Figure 6: Probe Response Message Using URO from Probe Query

3.2.1.  One-way Measurement Mode

3.2.1.1.  SR Links and End-to-end Measurement for SR Policy

   In one-way performance measurement mode, the probe response message



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   as defined in Figure 5 or Figure 6 is sent out-of-band for both SR
   links and SR Policies.

   The PM querier node can receive probe response message back by
   setting its own IP address as Source Address of the header or by
   adding URO TLV in the probe query message and setting its own IP
   address in the IP Address in the URO TLV (Type=131) [RFC7876].  The
   "control code" in the probe query message is set to "out-of-band
   response requested".  The "Source Address" TLV (Type 130), and
   "Return Address" TLV (Type 1), if present in the probe query message,
   are not used to send probe response message.

3.2.1.2.  Probe Response Message to Controller

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

3.2.2.  Two-way Measurement Mode

3.2.2.1.  SR Links

   In two-way performance measurement mode, when using a bidirectional
   link, the probe response message as defined in Figure 5 or Figure 6
   is sent back on the congruent path of the data traffic to the querier
   node for SR links.  In this case, the "control code" in the probe
   query message is set to "in-band response requested" [RFC6374].

3.2.2.2.  End-to-end Measurement for SR Policy

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

3.2.2.3.  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).

   [RFC6374] defines DM and LM probe query messages that can include one



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   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 7A and 7B:

    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 7A: 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)                            |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Segment List(n)                            |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 7B: 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




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   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.

3.2.2.4.  Probe Response Message for SR-MPLS 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 SR-MPLS Policy is shown in
   Figure 8.  The SR-MPLS label stack in the packet header is built
   using the Segment List received in the Return Path TLV in the probe
   query message.

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

           Figure 8: Probe Response Message for SR-MPLS Policy

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

3.2.2.5.  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 is shown in



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   Figure 9.  For SRv6 Policy using SRH, the SRv6 SID list in the SRH of
   the probe response message is built using the SRv6 Segment List
   received in the Return Path TLV in the probe query message.

    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 or 6 (with IPv6 Addresses)     |
    .                                                               .
    +---------------------------------------------------------------+

            Figure 9: Probe Response Message for SRv6 Policy


3.2.3.  Loopback Measurement Mode

   The Loopback measurement mode defined in Section 2.8 of [RFC6374] can
   be used to measure round-trip delay of a bidirectional 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 in
   the destination address in the IP header.  The responder node does
   not process the PM probe messages and generate response messages.

3.3.  Checksum Complement

   For both delay and loss measurement, when the probe packets are
   updated with timestamp or counter, UDP Checksum field also need
   updating since these packets are transported over UDP.  As an
   alternative, the Checksum Complement field (2 Bytes) can be
   optionally updated using the procedure defined in [RFC7820].  The
   Checksum Complement field can be any unused field in the probe
   message and is a local behavior.


4.  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



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      [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.


5.  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
      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.


6.  Sequence Numbers

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



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   can be useful for detecting denial-of-service (DoS) attacks on UDP
   ports.

6.1.  Sequence Number TLV in Unauthenticated Mode

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

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Type TBA3   |    Length     |      Reserved                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Sequence Number                            |
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 10: Sequence Number TLV - Unauthenticated Mode

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

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

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

   o  The Sequence Number TLV is optional.

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

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


6.2.  Sequence Number TLV in Authenticated Mode

   The PM probe query and response packet format in authenticated mode
   includes a key Hashed Message Authentication Code (HMAC) ([RFC2104])
   hash.  Each probe query and response messages are authenticated by
   adding Sequence Number with Hashed Message Authentication Code (HMAC)



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   TLV.  It can use HMAC-SHA-256 truncated to 128 bits (similarly to the
   use of it in IPSec defined in [RFC4868]); hence the length of the
   HMAC field is 16 octets.

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

   The OWAMP and TWAMP compute HMAC field using HMAC-SHA1 and can also
   be used with the procedure defined in this document.

   HMAC uses own key and the definition of the mechanism to distribute
   the HMAC key is outside the scope of this document.  Both the
   authentication type and key can be user-configured on both the
   querier and responder nodes.

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

           Figure 11: Sequence Number TLV - Authenticated Mode


   o  This TLV is mandatory in the authenticated mode.

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

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


7.  Security Considerations

   The performance measurement is intended for deployment in
   well-managed private and service provider networks.  As such, it



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   assumes that a node involved in a measurement operation has
   previously verified the integrity of the path and the identity of the
   far end responder node.  The security considerations described in
   Section 8 of [RFC6374] are applicable to this specification, and
   particular attention should be paid to the last three paragraphs.

   Use of HMAC-SHA-256 in the authenticated mode defined in this
   document protects the data integrity of the probe messages.  SRv6 has
   HMAC protection authentication defined for SRH
   [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 RFC 6374 to be carried in PM probe query messages:

      o  Type TBA1: Return Path TLV


   IANA is requested to allocate the values for the following Sub-TLV
   Types for the Return Path TLV.

      o  Type 1: SR-MPLS Label Stack of the Reverse SR Policy

      o  Type 2: SR-MPLS Binding SID of the Reverse SR Policy

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

      o  Type 4: SRv6 Binding SID of the Reverse SR Policy


   IANA is also requested to allocate a value for the following Block
   Number TLV Type for RFC 6374 to be carried in the PM probe query and
   response messages for loss measurement:

      o  Type TBA2: Block Number TLV


   IANA is also requested to allocate a value for the following Sequence
   Number TLV Types for RFC 6374 to be carried in the PM probe query and
   response messages for delay and loss measurement:

      o  Type TBA3: Sequence Number TLV in Unauthenticated Mode




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      o  Type TBA4: Sequence Number TLV in Authenticated Mode


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
              Requirement Levels", RFC 2119, March 1997.

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS networks', RFC 6374, September 2011.

   [RFC7876]  Bryant, S., Sivabalan, S., and Soni, S., "UDP Return Path
              for Packet Loss and Delay Measurement for MPLS Networks",
              RFC 7876, July 2016.

   [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.

9.2.  Informative References

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

   [Y1731]    ITU-T Recommendation Y.1731 (02/08), "OAM functions and
              mechanisms for Ethernet based networks", February 2008.

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

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

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



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              editor.org/info/rfc4868>.

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

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



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   [I-D.spring-rfc6374-srpm-mpls]  Filsfils, C., Gandhi, R. Ed., et al.
              "Performance Measurement in Segment Routing Networks with
              MPLS Data Plane", draft-gandhi-spring-rfc6374-srpm-mpls,
              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.

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




























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Acknowledgments

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



Contributors

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


   Patrick Khordoc
   Cisco Systems, Inc.
   Email: pkhordoc@cisco.com


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


Authors' Addresses

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


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


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


   Stefano Salsano



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   Universita di Roma "Tor Vergata"
   Italy
   Email: stefano.salsano@uniroma2.it


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


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





































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