6MAN Working Group                                           G. Fioccola
Internet-Draft                                                   T. Zhou
Intended status: Standards Track                                  Huawei
Expires: November 5, 2020                                    M. Cociglio
                                                          Telecom Italia
                                                                  F. Qin
                                                            China Mobile
                                                             May 4, 2020

            IPv6 Application of the Alternate Marking Method


   This document describes how the Alternate Marking Method can be used
   as the passive performance measurement tool in an IPv6 domain and
   reports implementation considerations.  It proposes how to define a
   new Extension Header Option to encode alternate marking technique and
   both Hop-by-Hop Options Header and Destination Options Header are

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

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 November 5, 2020.

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Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Alternate Marking application to IPv6 . . . . . . . . . . . .   3
   3.  Definition of the AltMark Option  . . . . . . . . . . . . . .   4
     3.1.  Data Fields Format  . . . . . . . . . . . . . . . . . . .   4
   4.  Use of the AltMark Option . . . . . . . . . . . . . . . . . .   5
   5.  Alternate Marking Method Operation  . . . . . . . . . . . . .   7
     5.1.  Packet Loss Measurement . . . . . . . . . . . . . . . . .   7
     5.2.  Packet Delay Measurement  . . . . . . . . . . . . . . . .   8
     5.3.  Flow Monitoring Identification  . . . . . . . . . . . . .   9
     5.4.  Multipoint and Clustered Alternate Marking  . . . . . . .  10
     5.5.  Data Collection and Calculation . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   [RFC8321] and [I-D.ietf-ippm-multipoint-alt-mark] describe a passive
   performance measurement method, which can be used to measure packet
   loss, latency and jitter on live traffic.  Since this method is based
   on marking consecutive batches of packets, the method is often
   referred as Alternate Marking Method.

   The Alternate Marking Method has become mature to be implemented and
   encoded in the IPv6 protocol and this document defines how it can be
   used to measure packet loss and delay metrics in IPv6.

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   The format of the IPv6 addresses is defined in [RFC4291] while
   [RFC8200] defines the IPv6 Header, including a 20-bit Flow Label and
   the IPv6 Extension Headers.  The Segment Routing Header (SRH) is
   defined in [RFC8754].

   [I-D.fioccola-v6ops-ipv6-alt-mark] reported a summary on the possible
   implementation options for the application of the Alternate Marking
   Method in an IPv6 domain.  This document, starting from the outcome
   of [I-D.fioccola-v6ops-ipv6-alt-mark], introduces a new TLV that can
   be encoded in the Options Headers (both Hop-by-Hop or Destination)
   for the purpose of the Alternate Marking Method application in an
   IPv6 domain.  The case of SRH ([RFC8754]) is also discussed.

2.  Alternate Marking application to IPv6

   The Alternate Marking Method requires a marking field.  As mentioned,
   several alternatives have been analysed in
   [I-D.fioccola-v6ops-ipv6-alt-mark] such as IPv6 Extension Headers,
   IPv6 Address and Flow Label.

   The only correct and robust choice that can actually be standardized
   would be the use of a new TLV to be encoded in the Options Header
   (Hop-by-Hop or Destination Option).

   This approach is compliant with [RFC8200] indeed the Alternate
   Marking application to IPv6 involves the following operations:

   o  The source node is the only one that writes the Option Header to
      mark alternately the flow (for both Hop-by-Hop and Destination

   o  In case of Hop-by-Hop Option Header carrying Alternate Marking
      bits, it is not inserted or deleted, but can be read by any node
      along the path.  The intermediate nodes may be configured to
      support this Option or not.  Anyway this does not impact the
      traffic since the measurement can be done only for the nodes
      configured to read the Option.

   o  In case of Destination Option Header carrying Alternate Marking
      bits, it is not processed, inserted, or deleted by any node along
      the path until the packet reaches the destination node.

   Hop-by-Hop Option Header is also useful to signal to routers on the
   path to process the Alternate Marking, anyway it is to be expected
   that some routers cannot process it unless explicitly configured.

   The optimization of both implementation and scaling of the Alternate
   Marking Method is also considered and a way to identify flows is

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   required.  The Flow Monitoring Identification field (FlowMonID), as
   introduced in the next sections, goes in this direction and it is
   used to identify a monitored flow.

   Note that the FlowMonID is different from the Flow Label field of the
   IPv6 Header ([RFC8200]).  Flow Label is used for application service,
   like load-balancing/equal cost multi-path (LB/ECMP) and QoS.
   Instead, FlowMonID is only used to identify the monitored flow.  The
   reuse of flow label field for identifying monitored flows is not
   considered since it may change the application intent and forwarding
   behaviour.  Furthermore the flow label may be changed en route and
   this may also violate the measurement task.  Those reasons make the
   definition of the FlowMonID necessary for IPv6.  Flow Label and
   FlowMonID within the same packet have different scope, identify
   different flows, and associate different uses.

3.  Definition of the AltMark Option

   The desired choice is to define a new TLV for the Options Extension
   Headers, carrying the data fields dedicated to the alternate marking

3.1.  Data Fields Format

   The following figure shows the data fields format for enhanced
   alternate marking TLV.  This AltMark data is expected to be
   encapsulated in the IPv6 Options Headers (Hop-by-Hop or Destination

    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
                                   |  Option Type  |  Opt Data Len |
   |              FlowMonID                |L|D|     Reserved      |


   o  Option Type: 8 bit identifier of the type of Option that needs to
      be allocated.  Unrecognised Types MUST be ignored on receipt.  For
      Hop-by-Hop Options Header or Destination Options Header, [RFC8200]
      defines how to encode the three high-order bits of the Option Type
      field.  The two high-order bits specify the action that must be
      taken if the processing IPv6 node does not recognize the Option
      Type; for AltMark these two bits MUST be set to 00 (skip over this
      Option and continue processing the header).  The third-highest-
      order bit specifies whether or not the Option Data can change en

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      route to the packet's final destination; for AltMark the value of
      this bit MUST be set to 0 (Option Data does not change en route).

   o  Opt Data Len: The length of the Option Data Fields of this Option
      in bytes.

   o  FlowMonID: 20 bits unsigned integer.  The FlowMon identifier is
      described hereinafter.

   o  L: Loss flag for Packet Loss Measurement as described hereinafter;

   o  D: Delay flag for Single Packet Delay Measurement as described

   o  Reserved: is reserved for future use.  These bits MUST be set to
      zero on transmission and ignored on receipt.

4.  Use of the AltMark Option

   The AltMark Option is the best way to implement the Alternate Marking
   method and can be carried by the Hop-by-Hop Options header and the
   Destination Options header.  In case of Destination Option, it is
   processed only by the source and destination nodes: the source node
   inserts and the destination node removes it.  While, in case of Hop-
   by-Hop Option, it may be examined by any node along the path, if
   explicitly configured to do so.  In this way an unrecognized Hop-by-
   Hop Option may be just ignored without impacting the traffic.

   So it is important to highlight that the Option Layout can be used
   both as Destination Option and as Hop-by-Hop Option depending on the
   Use Cases and it is based on the chosen type of performance
   measurement.  In general, it is needed to perform both end to end and
   hop by hop measurements, and the alternate marking methodology
   allows, by definition, both performance measurements.  Anyway, in
   many cases the end-to-end measurement is not enough and it is
   required also the hop-by-hop measurement, so the most complete choice
   is the Hop-by-Hop Options Header.

   IPv6, as specified in [RFC8200], allows nodes to optionally process
   Hop-by-Hop headers.  Specifically the Hop-by-Hop Options header is
   not inserted or deleted, but may be examined or processed by any node
   along a packet's delivery path, until the packet reaches the node (or
   each of the set of nodes, in the case of multicast) identified in the
   Destination Address field of the IPv6 header.  Also, it is expected
   that nodes along a packet's delivery path only examine and process
   the Hop-by-Hop Options header if explicitly configured to do so.

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   The Hop-by-Hop Option defined in this document is designed to take
   advantage of the property of how Hop-by-Hop options are processed.
   Nodes that do not support this Option SHOULD ignore them.  This can
   mean that, in this case, the performance measurement does not account
   for all links and nodes along a path.

   Another application that can be mentioned is SRv6.  SRv6 leverages
   the Segment Routing header which consists of a new type of routing
   header.  Like any other use case of IPv6, Hop-by-Hop and Destination
   Options are useable when SRv6 header is present.  Because SRv6 is a
   routing header, Destination Options before the routing header are
   processed by each destination in the route list.

   In summary, it is possible to list the alternative possibilities:

   o  Destination Option => measurement only by node in Destination

   o  Hop-by-Hop Option => every router on the path with feature

   o  Destination Option + SRH => every node that is an identity in the
      SR path.

   In general, Hop-by-Hop and Destination Options are the most suitable
   ways to implement Alternate Marking.

   It is worth mentioning that new Hop-by-Hop Options are not strongly
   recommended in [RFC7045] and [RFC8200], unless there is a clear
   justification to standardize it, because nodes may be configured to
   ignore the Options Header, drop or assign packets containing an
   Options Header to a slow processing path.  In case of the AltMark
   data fields described in this document, the motivation to standardize
   a new Hop-by-Hop Option is that it is needed for OAM.  An
   intermediate node can read it or not but this does not affect the
   packet behavior.  The source node is the only one that writes the
   Hop-by-Hop Option to mark alternately the flow, so, the performance
   measurement can be done for those nodes configured to read this
   Option, while the others are simply not considered for the metrics.

   In addition to the previous alternatives, for legacy network it is
   possible to mention a non-conventional application of the Destination
   Option for the hop by hop usage.  [RFC8200] defines that the nodes
   along a path examine and process the Hop-by-Hop Options header only
   if Hop-by-Hop processing is explicitly configured.  On the other
   hand, using the Destination Option for hop by hop action would cause
   worse performance than Hop-by-Hop.  The only motivation for the hop

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   by hop usage of Destination Options can be for compatibility reasons
   but in general it is not recommended.

5.  Alternate Marking Method Operation

   This section describes how the method operates.  [RFC8321] introduces
   several alternatives but in this section the most applicable methods
   are reported and a new fied is introduced to facilitate the
   deployment and improve the scalability.

5.1.  Packet Loss Measurement

   The measurement of the packet loss is really straightforward.  The
   packets of the flow are grouped into batches, and all the packets
   within a batch are marked by setting the L bit (Loss flag) to a same
   value.  The source node can switch the value of the L bit between 0
   and 1 after a fixed number of packets or according to a fixed timer,
   and this depends on the implementation.  By counting the number of
   packets in each batch and comparing the values measured by different
   network nodes along the path, it is possible to measure the packet
   loss occurred in any single batch between any two nodes.  Each batch
   represents a measurable entity unambiguously recognizable by all
   network nodes along the path.

   It is important to mention that for the application of this method
   there are two elements to consider: the clock error between network
   nodes and the network delay.  These can create offsets between the
   batches and out-of-order of the packets.  The consequence is that it
   is necessary to define a waiting interval where to get stable
   counters and to avoid these issues.  In addition this implies that
   the length of the batches MUST be chosen large enough so that it is
   not affected by those factors.

   L bit=1   ----------+           +-----------+           +----------
                       |           |           |           |
   L bit=0             +-----------+           +-----------+
              Batch n        ...      Batch 3     Batch 2     Batch 1
            <---------> <---------> <---------> <---------> <--------->

                                Traffic Flow
   L bit   ...1111111111 0000000000 11111111111 00000000000 111111111...

     Figure 1: Packet Loss Measurement and Single-Marking Methodology
                                using L bit

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5.2.  Packet Delay Measurement

   The same principle used to measure packet loss can be applied also to
   one-way delay measurement.  Delay metrics MAY be calculated using the
   two possibilities:

   1.  Single-Marking Methodology: This approach uses only the L bit to
       calculate both packet loss and delay.  In this case, the D flag
       MUST be set to zero on transmit and ignored by the monitoring
       points.  The alternation of the values of the L bit can be used
       as a time reference to calculate the delay.  Whenever the L bit
       changes and a new batch starts, a network node can store the
       timestamp of the first packet of the new batch, that timestamp
       can be compared with the timestamp of the first packet of the
       same batch on a second node to compute packet delay.  Anyway this
       measurement is accurate only if no packet loss occurs and if
       there is no packet reordering at the edges of the batches.  A
       different approach can also be considered and it is based on the
       concept of the mean delay.  The mean delay for each batch is
       calculated by considering the average arrival time of the packets
       for the relative batch.  There are limitations also in this case
       indeed, each node needs to collect all the timestamps and
       calculate the average timestamp for each batch.  In addition the
       information is limited to a mean value.

   2.  Double-Marking Methodology: This approach is more complete and
       uses the L bit only to calculate packet loss and the D bit (Delay
       flag) is fully dedicated to delay measurements.  The idea is to
       use the first marking with the L bit to create the alternate flow
       and, within the batches identified by the L bit, a second marking
       is used to select the packets for measuring delay.  The D bit
       creates a new set of marked packets that are fully identified
       over the network, so that a network node can store the timestamps
       of these packets; these timestamps can be compared with the
       timestamps of the same packets on a second node to compute packet
       delay values for each packet.  The most efficient and robust mode
       is to select a single double-marked packet for each batch, in
       this way there is no time gap to consider between the double-
       marked packets to avoid their reorder.  If a double-marked packet
       is lost, the delay measurement for the considered batch is simply
       discarded, but this is not a big problem because it is easy to
       recognize the problematic batch and skip the measurement just for
       that one.  So in order to have more information about the delay
       and to overcome out-of-order issues this method is preferred.

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   L bit=1   ----------+           +-----------+           +----------
                       |           |           |           |
   L bit=0             +-----------+           +-----------+

   D bit=1         +          +          +          +            +
                   |          |          |          |            |
   D bit=0   ------+----------+----------+----------+------------+-----

                                Traffic Flow
   L bit   ...1111111111 0000000000 11111111111 00000000000 111111111...

   D bit   ...0000010000 0000010000 00000100000 00001000000 000001000...

        Figure 2: Double-Marking Methodology using L bit and D bit

   Similar to packet delay measurement (both for Single Marking and
   Double Marking), the method can also be used to measure the inter-
   arrival jitter.

5.3.  Flow Monitoring Identification

   The Flow Monitoring Identification (FlowMonID) is required for some
   general reasons:

      First, it helps to reduce the per node configuration.  Otherwise,
      each node needs to configure an access-control list (ACL) for each
      of the monitored flows.  Moreover, using a flow identifier allows
      a flexible granularity for the flow definition.

      Second, it simplifies the counters handling.  Hardware processing
      of flow tuples (and ACL matching) is challenging and often incurs
      into performance issues, especially in tunnel interfaces.

      Third, it eases the data export encapsulation and correlation for
      the collectors.

   The FlowMon identifier field is to uniquely identify a monitored flow
   within the measurement domain.  The field is set at the source node.
   The FlowMonID can be uniformly assigned by the central controller or
   algorithmically generated by the source node.  The latter approach
   cannot guarantee the uniqueness of FlowMonID but it may be preferred
   for local or private network, where the conflict probability is small
   due to the large FlowMonID space.

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5.4.  Multipoint and Clustered Alternate Marking

   The Alternate Marking method can also be extended to any kind of
   multipoint to multipoint paths, and the network clustering approach
   allows a flexible and optimized performance measurement, as described
   in [I-D.ietf-ippm-multipoint-alt-mark].

   The Cluster is the smallest identifiable subnetwork of the entire
   Network graph that still satisfies the condition that the number of
   packets that goes in is the same that goes out.  With network
   clustering, it is possible to use the partition of the network into
   clusters at different levels in order to perform the needed degree of
   detail.  So, for Multipoint Alternate Marking, FlowMonID can identify
   in general a multipoint-to-multipoint flow and not only a point-to-
   point flow.

5.5.  Data Collection and Calculation

   The nodes enabled to perform performance monitoring collect the value
   of the packet counters and timestamps.  There are several
   alternatives to implement Data Collection and Calculation, but this
   is not specified in this document.

6.  Security Considerations

   This document aims to apply a method to perform measurements that
   does not directly affect Internet security nor applications that run
   on the Internet.  However, implementation of this method must be
   mindful of security and privacy concerns.There are two types of
   security concerns: potential harm caused by the measurements and
   potential harm to the measurements.

   Security concerns are limited since the method implies modifications
   to an Option of the data packets but this must be performed in a way
   that doesn't alter the quality of service experienced by packets
   subject to measurements and that preserves stability of nodes.  In
   addition, an attacker cannot gain information about network
   performance from a monitoring node; it must use synchronized
   monitoring nodes at multiple points on the path but this is very
   difficult since the alternate methodology is applied only in the
   context of a controlled domain.

   Privacy concerns are also limited because the method only relies on
   information contained in the Option Header without any release of
   user data.

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7.  IANA Considerations

   The Option Type should be assigned in IANA's "Destination Options and
   Hop-by-Hop Options" registry.

   This draft requests the following IPv6 Option Type assignments from
   the Destination Options and Hop-by-Hop Options sub-registry of
   Internet Protocol Version 6 (IPv6) Parameters

      Hex Value    Binary Value      Description           Reference
                   act chg rest
      TBD          00   0  tbd       AltMark               [This draft]

8.  Acknowledgements

   The authors would like to thank Bob Hinden, Ole Troan, Tom Herbert,
   Stefano Previdi, Brian Carpenter, Eric Vyncke, Ron Bonica for the
   precious comments and suggestions.

9.  References

9.1.  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,

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,

9.2.  Informative References

              Fioccola, G., Velde, G., Cociglio, M., and P. Muley, "IPv6
              Performance Measurement with Alternate Marking Method",
              draft-fioccola-v6ops-ipv6-alt-mark-01 (work in progress),
              June 2018.

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              Fioccola, G., Cociglio, M., Sapio, A., and R. Sisto,
              "Multipoint Alternate Marking method for passive and
              hybrid performance monitoring", draft-ietf-ippm-
              multipoint-alt-mark-09 (work in progress), March 2020.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers", RFC 7045,
              DOI 10.17487/RFC7045, December 2013,

   [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>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,

Authors' Addresses

   Giuseppe Fioccola
   Riesstrasse, 25
   Munich  80992

   Email: giuseppe.fioccola@huawei.com

   Tianran Zhou
   156 Beiqing Rd.
   Beijing  100095

   Email: zhoutianran@huawei.com

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   Mauro Cociglio
   Telecom Italia
   Via Reiss Romoli, 274
   Torino  10148

   Email: mauro.cociglio@telecomitalia.it

   Fengwei Qin
   China Mobile
   32 Xuanwumenxi Ave.
   Beijing  100032

   Email: qinfengwei@chinamobile.com

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