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Versions: 00

IPPM Working Group                                        R. Gandhi, Ed.
Internet-Draft                                               C. Filsfils
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: August 16, 2021                                        D. Voyer
                                                             Bell Canada
                                                                 M. Chen
                                                                  Huawei
                                                             B. Janssens
                                                                    Colt
                                                              S. Salsano
                                        Universita di Roma "Tor Vergata"
                                                       February 12, 2021


            Simple Two-Way Direct Loss Measurement Procedure
                draft-gandhi-ippm-simple-direct-loss-00

Abstract

   This document defines Simple Two-Way Direct Loss Measurement (DLM)
   procedure that can be used for Alternate-Marking Method for detecting
   accurate data packet loss in a network.  Specifically, DLM probe
   packets are defined for both unauthenticated and authenticated modes
   and they are efficient for hardware-based implementation.

Status of This Memo

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

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

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

   This Internet-Draft will expire on August 16, 2021.

Copyright Notice

   Copyright (c) 2021 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Reference Topology  . . . . . . . . . . . . . . . . . . .   4
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Session-Sender Direct Loss Measurement Probe Packet . . . . .   6
   5.  Session-Reflector Direct Loss Measurement Probe Packet  . . .   8
   6.  Data Loss Calculation . . . . . . . . . . . . . . . . . . . .  11
   7.  Optional Extensions . . . . . . . . . . . . . . . . . . . . .  12
   8.  Integrity Protection and Confidentiality Protection . . . . .  12
   9.  Operational Considerations  . . . . . . . . . . . . . . . . .  12
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  12
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     12.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Many Service Provider Service Level Agreements (SLAs) depend on the
   ability to measure performance loss metric experienced by the
   Customer data traffic flow.  The accurate Customer data packet loss
   can be measured by using the Direct Loss Measurement (DLM)
   procedures.  Currently there is no efficient active measurement
   procedure available for accurate data packet loss detection in IP
   networks.  Note that an approach for conducting packet loss
   measurement in IP networks is documented in [RFC7680].  This approach
   requires clock synchronization between the measurement points and
   lacks support for accurate data packet loss measurement.

   [ITU-Y1731] defines procedures for performance loss monitoring for
   Ethernet-based networks.  Specifically, the Loss Measurement Message
   (LMM) defined in Section 9.12 of [ITU-Y1731] can be used for accurate



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   frame loss measurement as described in Appendix II of that document.
   The procedure is specific to the Ethernet-based networks and does not
   apply to the IP networks.

   The Simple Two-Way Active Measurement Protocol (STAMP) [RFC8762]
   provides capabilities for the measurement of various performance
   metrics in IP networks using test packets.  It eliminates the need
   for control protocol by using configuration data model to provision
   test sessions.  The STAMP can be used for (synthetic or inferred)
   packet loss measurement based on the Sequence Number in the test
   packets, however, this method does not provide accurate data packet
   loss metrics.

   [RFC8972] defines optional extensions for STAMP.  The STAMP test
   packet with the "Direct Measurement" TLV (Type 5) [RFC8972] can be
   used for combined timestamp and data packet counter collection.  This
   method, however, has the following limitations when used for
   detecting data packet loss:

   o  For only direct measurement, the STAMP "Direct Measurement" TLV in
      the test packet requires the hardware to support timestamps, in
      addition to data packet counters.  One-way delay measurement also
      requires clock synchronization.

   o  The location of the transmit counter is not at the fixed location
      in the STAMP test packet with the "Direct Measurement" TLV.  Also,
      the location of the transmit counter on the STAMP Session-
      Reflector reply test packet is not at the same location as the
      STAMP Session-Sender test packet using the "Direct Measurement"
      TLV.  This makes it difficult to implement in hardware.

   o  Furthermore, for hardware-based implementation, the optional
      "Direct Measurement" TLV adds unnecessary processing overhead on
      the Session-Reflector as not all STAMP Session-Sender test packets
      carry the "Direct Measurement" TLV.  The Session-Reflector needs
      to search for the presence of this TLV, as there can be multiple
      TLVs present.

   o  The STAMP "Direct Measurement" TLV does not support 64-bit
      counters.

   o  The STAMP "Direct Measurement" TLV does not support counters for
      bytes.

   o  The STAMP "Direct Measurement" TLV does not support counters per
      traffic class.





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   o  The STAMP "Direct Measurement" TLV also does not identify the
      Block Number of the Direct Measurement, which is required for
      Alternate-Marking Method [RFC8321] for data packet loss
      measurement.  The AMM also handles the case of the out-of-order
      data packets.

   This document defines Simple Two-Way Direct Loss Measurement (DLM)
   procedure that can be used for Alternate-Marking Method [RFC8321] for
   detecting accurate data packet loss in a network.  Specifically, DLM
   probe packets are defined for both unauthenticated and authenticated
   modes and they are efficient for hardware-based implementation.

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

   AMM: Alternate-Marking Method.

   DLM: Direct Loss Measurement.

   HMAC: Hashed Message Authentication Code.

   MBZ: Must be Zero.

   PM: Performance Measurement.

   SHA: Secure Hash Algorithm.

   SSID: Sender Session Identifier.

   STAMP: Simple Two-Way Active Measurement Protocol.

   TTL: Time To Live.

2.3.  Reference Topology

   As shown in the reference topology, the Session-Sender R1 initiates a
   Direct Loss Measurement (DLM) probe packet over UDP transport.  The
   Session-Reflector R3 receives the Session-Sender's DLM probe packet
   and acts according to the local configuration.  The Session-Reflector
   R3 transmits a DLM reply probe packet to the Session-Sender R1.



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                        C1                    C2
                       /                       \
              +-------+     DLM Probe Packet    +-------+
              |       | - - - - - - - - - - - ->|       |
              |   R1  |=========================|   R3  |
              |       |<- - - - - - - - - - - - |       |
              +-------+  DLM Reply Probe Packet +-------+
                       \                       /
                        C4                    C3

            Session-Sender                  Session-Reflector

                         Reference Topology

3.  Overview

   For accurate data packet loss detection, the DLM probe packets are
   transmitted by the Session-Sender over UDP transport, and are used to
   collect the transmit and receive counters for the data traffic flow
   under measurement.  The DLM reply probe packets are transmitted by
   the Session-Reflector to collect the transmit and receive counters
   for the data traffic flow under measurement in the reverse direction.

   The DLM probe packets carry user-configured destination UDP port.
   The destination UDP port 862 is not used for the DLM probe packets.
   The user-configured destination UDP port follows the guidelines
   described in Section 4.1 of [RFC8762].  Different destination UDP
   port is used for DLM probe packets than the STAMP test packets
   defined in [RFC8762].  Hence, the Session-Sender and the Session-
   Reflector do not require backwards compatibility and support for
   STAMP.

   A DLM session is identified by the 4-tuple (source and destination IP
   addresses, source and destination UDP port numbers).  A DLM Session-
   Sender MAY generate a locally unique Sender Session Identifier
   (SSID).  The SSID is a two-octet, non-zero unsigned integer.  The
   SSID generation policy is implementation specific.  An implementation
   MUST NOT assign the same identifier to different DLM sessions.  A
   Session-Sender MAY use the SSID to identify a DLM session.  If the
   SSID is used, it MUST be present in each probe packet of the given
   DLM session.

   The DLM Session-Reflector operates in the Stateless mode.  The DLM
   Session-Reflector does not maintain session state and will use the
   value in the Sequence Number field in the received probe packet as
   the value for the Sequence Number field in the reply probe packet.
   As a result, values in the Sequence Number and Session-Sender
   Sequence Number fields are the same in this mode.



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4.  Session-Sender Direct Loss Measurement Probe Packet

   In this document, base Session-Sender DLM probe packet formats are
   defined as shown in Figure 1 and Figure 2 for unauthenticated and
   authenticated modes, respectively.  They are stand-alone DLM probe
   packet formats to carry the counters for the data traffic flow under
   measurement.  The DLM probe packet formats are similar to the base
   STAMP test packet formats (for example the locations of the Counters
   and Timestamps).

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter (C1)                  |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|T| DSCP      | Block Number| SSID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                                                               |
    |                        MBZ (28 octets)                        |
    |                                                               |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 1: Session-Sender Direct Loss Measurement Probe Packet -
                           Unauthenticated Mode




















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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter (C1)                  |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|T| DSCP      | Block Number| SSID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                        MBZ (68 octets)                        |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                        HMAC (16 octets)                       |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 2: Session-Sender Direct Loss Measurement Probe Packet -
                            Authenticated Mode

   Fields are defined as the following:

   Sequence Number (32-bit): For each new DLM session, its value starts
   at zero and is incremented by one with each transmitted DLM probe
   packet.  The Sequence Number helps to check the DLM session status as
   active or not active.

   Transmit Counter (64-bit): The number of packets or octets
   transmitted by the Session-Sender in the DLM probe packet.  The
   counter is always written at the well-known fixed location in the DLM
   probe packet.  This is an important property for hardware-based
   implementation.  Counter is for the data traffic flow under
   measurement.

   XBT Flags (3-bit): 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 a DLM probe packet.  Set to 0 when
      the DLM probe packet is transmitted or received over an interface
      that writes 32-bit counter values.



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      B: Octet (byte) count.  When set to 1, indicates that the Counter
      fields represent octet counts.  The octet count applies to all
      packets within the DLM scope, and the octet count of a packet
      transmitted or received 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.

      T: Traffic-class-specific measurement indicator.  Set to 1 when
      the DLM session is scoped to data packets of a particular traffic
      class (DSCP value), and 0 otherwise.  When set to 1, the DSCP
      field of the DLM probe packet indicates the measured traffic
      class.

   DSCP (6-bit): DSCP of the data traffic flow being measured when T
   flag is set.

   Block Number (7-bit): The Direct Loss Measurement using Alternate-
   Marking Method [RFC8321] requires to collect Block Number of the
   counters for the data traffic flow under measurement.  To be able to
   correlate the transmit and receive counters of the matching Block
   Number, the Block Number of the counters carried in the DLM probe
   packets.

   SSID (16-bit): DLM Sender Session Identifier.

   HMAC: The use of the HMAC field is described in Section 4.4 of
   [RFC8762].  HMAC uses its own key and the mechanism to distribute the
   HMAC key is outside the scope of this document.

   MBZ: Must be Zero.  It MUST be all zeroed on the transmission and
   MUST be ignored on receipt.

5.  Session-Reflector Direct Loss Measurement Probe Packet

   The Session-Reflector receives the DLM Session-Sender probe packet
   and verifies it.  If the DLM probe packet is validated, the Session-
   Reflector that supports this specification prepares and transmits the
   DLM reply probe packet.  In this document, Session-Reflector DLM
   reply probe packet formats are defined as shown in Figure 3 and
   Figure 4, for unauthenticated and authenticated modes, respectively.










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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter (C3)                  |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|T| DSCP      | Block Number| SSID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Receive Counter (C2)                   |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Session-Sender Sequence Number         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Session-Sender Counter (C1)            |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |FLAGS| Ses-DSCP  |Ses-Block Num| MBZ (2 octets)                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Ses-Sender TTL |        MBZ                                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 3: Session-Reflector Direct Loss Measurement Probe Packet -
                           Unauthenticated Mode

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Transmit Counter (C3)                  |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |X|B|T| DSCP      | Block Number| SSID                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (4 octets)                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Receive Counter (C2)                   |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (8 octets)                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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    |                        Session-Sender Sequence Number         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Session-Sender Counter (C1)            |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |FLAGS| Ses-DSCP  |Ses-Block Num| MBZ (2 octets)                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (4 octets)                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Ses-Sender TTL |                                               |
    +-+-+-+-+-+-+-+-+                                               |
    |                        MBZ (15 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                        HMAC (16 octets)                       |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 4: Session-Reflector Direct Loss Measurement Probe Packet -
                            Authenticated Mode

   Fields are defined as the following:

   Sequence Number (32-bit): This is the exact copy of the Sequence
   Number from the received Session-Sender DLM probe packet that allows
   Stateless mode of Session-Reflector.

   Transmit Counter (64-bit): The number of packets or octets
   transmitted by the Session-Reflector in the DLM reply probe packet.
   Counter is for the reverse direction data traffic flow under
   measurement.  The Session-Reflector writes the Transmit Counter at
   the same location in the DLM reply probe packet as the Session-Sender
   DLM probe packet.  This is an important property for hardware-based
   implementation.

   FLAGS (3-bit): The XBT Flags for the reverse direction data traffic
   flow under measurement set using the same procedure defined for the
   Session-Sender DLM probe packet.






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   DSCP (6-bit): Set for the reverse direction data traffic flow under
   measurement using the same procedure defined for the Session-Sender
   DLM probe packet.

   Block Number (7-bit): Set for the reverse direction data traffic flow
   under measurement using the same procedure defined for the Session-
   Sender DLM probe packet.

   SSID: SSID is the exact copy of the SSID in the received Session-
   Sender DLM probe packet.

   Receive Counter (64-bit): The number of packets or octets received at
   the Session-Reflector.  It is written by the Session-Reflector in the
   DLM reply probe packet.  Counter is for the data traffic flow under
   measurement.

   Session-Sender Counter (64-bit): This is the exact copy of the
   Transmit Counter from the received Session-Sender DLM probe packet.

   Session-Sender Sequence Number (32-bit): This is the exact copy of
   the Sequence Number from the received Session-Sender DLM probe
   packet.

   Session-Sender Block Number: This is the exact copy of the Block
   Number from the received Session-Sender DLM probe packet.

   Session-Sender FLAGS: This is the exact copy of the XBT Flags from
   the received Session-Sender DLM probe packet.

   Session-Sender DSCP: This is the exact copy of the DSCP from the
   received Session-Sender DLM probe packet.

   Session-Sender TTL: The Session-Sender TTL field is one octet long,
   and its value is the copy of the TTL field in IPv4 (or Hop Limit in
   IPv6) from the received Session-Sender DLM probe packet.

6.  Data Loss Calculation

   Using the Counters C1, C2, C3 and C4 as per reference topology, from
   the nth and (n-1)th DLM probe packets, packet loss and byte loss for
   the data traffic flow can be calculated as follows:

   Transmit Loss TxL[ n-1, n] = (C1[ n] - C1[ n-1]) - (C2[ n] - C2[
   n-1])

   Receive Loss RxL[ n-1, n] = (C3[ n] - C3[ n-1]) - (C4[ n] - C4[ n-1])

   The Total Transmit and Receive Loss are calculated as follows:



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   Total Transmit Loss = TxL[ 1, 2] + TxL[ 2, 3] + ...

   Total Receive Loss = RxL[ 1, 2] + RxL[ 2, 3] + ...

   These values are updated each time a DLM reply probe packet is
   received and processed at the Session-Sender, and they represent the
   Total Transmit and Total Receive Loss since the DLM session was
   initiated.  When computing the values TxL[n-1,n] and RxL[n-1,n], the
   possibility of counter wrap must be taken into account.

   When using Alternate-Marking Method, all Counters used for loss
   calculation belongs to the same Block Number, as described in
   Section 3.1 of [RFC8321].

7.  Optional Extensions

   There are currently no optional (TLV) extensions defined for the DLM
   probe packets.

8.  Integrity Protection and Confidentiality Protection

   The integrity protection and confidentiality protection specified in
   [RFC8762] also apply to the procedures defined in this document.

9.  Operational Considerations

   The operational considerations specified in [RFC8762] also apply to
   the procedures defined in this document.

10.  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 Session-
   Reflector.

   If desired, attacks can be mitigated by performing basic validation
   and sanity checks, at the Session-Sender, of the Counter fields in
   received DLM reply probe packets.  The minimal state associated with
   these protocols also limits the extent of measurement disruption that
   can be caused by a corrupt or invalid packet to a single measurement
   cycle.

   Use of HMAC-SHA-256 in the authenticated mode protects the data
   integrity of the probe packets.  Cryptographic measures may be
   enhanced by the correct configuration of access-control lists and
   firewalls.



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   The security considerations specified in [RFC8762] also apply to the
   procedure defined in this document.

11.  IANA Considerations

   This document has no IANA actions.

12.  References

12.1.  Normative References

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

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

   [RFC8321]  Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli,
              L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
              "Alternate-Marking Method for Passive and Hybrid
              Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321,
              January 2018, <https://www.rfc-editor.org/info/rfc8321>.

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

12.2.  Informative References

   [RFC7680]  Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
              Ed., "A One-Way Loss Metric for IP Performance Metrics
              (IPPM)", STD 82, RFC 7680, DOI 10.17487/RFC7680, January
              2016, <https://www.rfc-editor.org/info/rfc7680>.

   [RFC8972]  Mirsky, G., Min, X., Nydell, H., Foote, R., Masputra, A.,
              and E. Ruffini, "Simple Two-Way Active Measurement
              Protocol Optional Extensions", RFC 8972,
              DOI 10.17487/RFC8972, January 2021,
              <https://www.rfc-editor.org/info/rfc8972>.








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Internet-Draft  Simple Direct Loss Measurement Procedure   February 2021


   [ITU-Y1731]
              Recommendation ITU-TG.8013/Y.1731:
              https://www.itu.int/rec/T-REC-G.8013-201508-I/en, "G.8013/
              Y.1731 : Operations, administration and maintenance (OAM)
              functions and mechanisms for Ethernet-based networks",
              August 2015.

   [SRV6-PM-TNSM]
              Loreti, P., Mayer, A., Lungaroni, P., Lombardo, F.,
              Scarpitta, C., Sidoretti, G., Bracciale, L., Ferrari, M.,
              Salsano, S., Abdelsalam, A., Gandhi, R., and C. Filsfils,
              IEEE Transactions on Network and Service Management,
              "SRv6-PM: Performance Monitoring of SRv6 Networks with a
              Cloud-Native Architecture:
              https://arxiv.org/pdf/2007.08633.pdf", February 2021.

   [SRV6-PM-IEEE]
              Loreti, P., Mayer, A., Lungaroni, P., Salsano, S., Gandhi,
              R., and C. Filsfils, IEEE International Conference on High
              Performance Switching and Routing, "Implementation of
              Accurate Per-Flow Packet Loss Monitoring in Segment
              Routing over IPv6 Networks:
              https://arxiv.org/pdf/2004.11414.pdf", May 2020.

Acknowledgments

   The authors would like to thank Greg Mirsky, Tianran Zhou, Gyan
   Mishra, Zhenqiang Li, Reshad Rahman, Cheng Li, and Yali Wang for the
   comments on Direct Loss Measurement.  The authors would like to thank
   Pierpaolo Loreti and the team for the Open Source implementation of
   SRv6-PM Loss Monitoring and its publications in [SRV6-PM-TNSM] and
   [SRV6-PM-IEEE].  The authors would like to acknowledge the earlier
   work on the loss measurement using TWAMP described in draft-xiao-
   ippm-twamp-ext-direct-loss.

Authors' Addresses

   Rakesh Gandhi (editor)
   Cisco Systems, Inc.
   Canada

   Email: rgandhi@cisco.com


   Clarence Filsfils
   Cisco Systems, Inc.

   Email: cfilsfil@cisco.com



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Internet-Draft  Simple Direct Loss Measurement Procedure   February 2021


   Daniel Voyer
   Bell Canada

   Email: daniel.voyer@bell.ca


   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com


   Bart Janssens
   Colt

   Email: Bart.Janssens@colt.net


   Stefano Salsano
   Universita di Roma "Tor Vergata"
   Italy

   Email: stefano.salsano@uniroma2.it




























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