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Versions: (draft-song-ioam-ipv6-support) 00

IPPM                                                             H. Song
Internet-Draft                                                 Futurewei
Intended status: Standards Track                                   Z. Li
Expires: September 4, 2020                                       S. Peng
                                                     Huawei Technologies
                                                           March 3, 2020


                 Approaches on Supporting IOAM in IPv6
                  draft-song-ippm-ioam-ipv6-support-00

Abstract

   It has been proposed to encapsulate IOAM tracing option data fields
   in IPv6 HbH options header.  However, due to size of the trace data
   and its location in the IPv6 header packets, this arrangement creates
   practical challenges for implementation, especially when other
   extension headers, such as routing header, also exist and require in-
   network processing.  We propose several alternative approaches to
   address this challenge, including separating the IOAM trace data to a
   different extension header, using the postcard-based telemetry (e.g.,
   IOAM DEX) instead, and applying the segment IOAM trace export scheme,
   based on the network scenario and application requirements.  We
   discuss the pros and cons of each approach and foster standard
   convergence and industry adoption.

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 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 September 4, 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  IOAM Data Separate and Postpose . . . . . . . . . . . . . . .   3
     2.1.  IOAM Trace Data Encapsulation . . . . . . . . . . . . . .   5
   3.  Segment IOAM Data Export  . . . . . . . . . . . . . . . . . .   5
     3.1.  Independent of SRv6 . . . . . . . . . . . . . . . . . . .   5
     3.2.  Export at SRv6 node . . . . . . . . . . . . . . . . . . .   6
   4.  Direct Export Option  . . . . . . . . . . . . . . . . . . . .   7
   5.  Comparison  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   In-situ OAM (IOAM) [I-D.ietf-ippm-ioam-data] defines two options,
   pre-allocated tracing option and incremental tracing option, which
   record hop-by-hop data along a packet's forwarding path.  The draft
   [I-D.ietf-ippm-ioam-ipv6-options] proposes the method to encapsulate
   IOAM trace option data fields in IPv6.  Because the tracing options
   requires per hop processing, such options can only be encapsulated in
   IPv6 Hop-by-Hop (HbH) options header.  The draft
   [I-D.ioametal-ippm-6man-ioam-ipv6-deployment] further describes some
   deployment approaches.

   [RFC8200] mandates that the HbH options header, if exists, must be
   the first extension header following the IPv6 header.  However, the
   IOAM trace data can be large, which easily amount to tens to hundreds
   of bytes, making accessing other headers after it difficult.  There
   are practical limitations on how far the hardware can reach into a
   packet in forwarding hardware.  Even if the other headers can be
   reached, the deeper they are, the higher the cost to access and



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   process them, and the lower the forwarding performance.  A
   potentially more detrimental issue is that the incremental tracing
   option will expand the HbH header at each hop and push back all other
   headers, which keeps shifting the locations of the other extension
   headers, further complicating the hardware implementation and
   impeding the forwarding.

   The issue becomes severe when SRv6 and IOAM coexist.  The Segment
   Routing Extension Header (SRH) [I-D.ietf-6man-segment-routing-header]
   is encapsulated in a routing header which is after the HbH options
   header.  SRH itself can be large.  It requires read and write
   operations at each SRv6 node.  If it is deeply embedded in a packet
   and its location keeps shifting, either it is beyond the reach of
   hardware or the forwarding performance suffers.

   We can shun the problem by simply avoiding using both at the same
   time, but apparently this is not ideal, because IOAM is an important
   OAM tool and it is even more wanted when SRv6 brings more operational
   complexity into IPv6 networks.

   Our second recourse is to limit the IOAM to SRv6 nodes only.  That
   is, consider SRv6 as an overlay tunnel over IPv6 and apply the IOAM
   pipe mode as discussed in [I-D.song-ippm-ioam-tunnel-mode], which
   only collects data at each SRv6 nodes.  To realize this,
   [I-D.ali-spring-ioam-srv6] describes an approach that encapsulates
   the IOAM option data fields in an SRH TLV.  [I-D.song-6man-srv6-pbt]
   describes another approach to enable postcard-based telemetry for
   SRv6 without needing IOAM option encapsulation.  In either case, the
   SRH is close to the packet front and its location is fixed.  While
   these approaches are useful for use cases that only need to monitor
   the segment performance, it fails to cover all the IPv6 nodes in a
   network.

   So the proposition of this draft is, suppose we need to apply IOAM on
   all nodes in an SRv6 network, how we can amend the approach in
   [I-D.ietf-ippm-ioam-ipv6-options] or use alternative approaches to
   circumvent the aforementioned issues.  In this draft, we propose
   three such approaches: separating the IOAM trace data to a different
   extension header, using the postcard-based telemetry (e.g., IOAM DEX)
   instead, and applying the segment IOAM trace export scheme.  We
   discuss the pros and cons of each approach and hope to foster
   standard convergence and industry adoption.

2.  IOAM Data Separate and Postpose

   An IOAM trace type data fields contain two parts: instruction and
   trace data.  Although by convention the trace data part immediately
   follow the instruction part, there is not fundamental reason why



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   these two parts must stick together.  This observation provides us an
   optimization opportunity to amend the original proposal in
   [I-D.ietf-ippm-ioam-ipv6-options].

   We separate the IOAM trace type data fields into the instruction part
   and the trace data part.  We encapsulate only the instruction part in
   the HbH options header, and encapsulate the trace data part in
   another metadata extension header after all the IPv6 extension
   headers and before upper layer protocol headers.  This arrangement
   allows high performance hardware implementation.  When using the
   incremental data trace, even if the data trace size increases at each
   node, all IPv6 extension headers remain intact and new data is
   inserted at a fixed location.

   Figure 1 shows the HbH option format for IOAM trace type instruction.
   The field specification is identical to that in [RFC8200] and
   [I-D.ietf-ippm-ioam-data].

  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 |   Reserved    |   IOAM Type   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<------+
 |        Namespace-ID           |NodeLen  | Flags | RemainingLen| IOAM
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Trace
 |               IOAM-Trace-Type                 |  Reserved     | Type
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<Instr.+

        Figure 1: HbH Option Format for IOAM Trace Type Instruction

   Figure 2 shows the TLV option format for IOAM trace type data.  The
   IOAM trace type data format is compliant with
   [I-D.ietf-ippm-ioam-data].

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   IOAM Type   |     Length    |            Reserved           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                      IOAM Trace Type Data                     ~
    ~                                                               ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 2: Option Format for IOAM Trace Type Data





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2.1.  IOAM Trace Data Encapsulation

   We have basically two methods to encapsulate the IOAM trace data.
   First, we can define a new IPv6 extension header which is dedicated
   to metadata.  Once standardized, this extension header can also be
   used to host potential metadata from other applications such as NSH
   for SFC [RFC8300].  Second, this option can be carried as a TLV
   option in another existing extension header such as the destination
   header.  The only requirement is that this extension header should be
   the last one in the extension header chain.  The first method is
   cleaner but it requires extra standard effort; the second method is
   simpler but it needs to overcome the access constraints exerted by
   [RFC8300].

3.  Segment IOAM Data Export

   If the overhead of the IOAM trace type data fields is under control,
   we may still manage to encapsulate both instruction and data in HbH
   options header as in [I-D.ietf-ippm-ioam-ipv6-options].  To this end,
   we introduce two sub-approaches.

3.1.  Independent of SRv6

   [I-D.song-ippm-segment-ioam] proposes an enhancement to IOAM trace
   type which can configure the allowable overhead of the IOAM trace
   type data fields.  Once the trace data size is up to the limit at a
   network node (i.e., a segment or a fixed number of network nodes are
   traversed), the trace data will be stripped and exported so room is
   made to accommodate new trace data from nodes in the next segment of
   the forwarding path.

   This approach requires some moderate updates to the IOAM trace type
   data fields, as described in [I-D.song-ippm-segment-ioam].  Figure 3
   shows the format of the HbH Option Header containing Segment IOAM
   trace type data fields.  A flag bit (#23) in the Flags field is used
   to indicate the current header is a segment IOAM header.  In this
   context, the last octet in the IOAM header is partitioned into two
   4-bit nibbles.  The first nibble (SSize) is used to save the segment
   size and the second nibble (RHop) is used to save the remaining hops.
   This limits the maximum segment size to 15.











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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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |  Option Type  |  Opt Data Len |   Reserved    |   IOAM Type   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<------+
  |       Namespace-ID            |NodeLen|Flags|1| SSize | RHop  | IOAM
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Segment
  |               IOAM-Trace-Type                 |  Reserved     | Trace
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type
  |                                                               | Data
  |                  Node Data List []                            | Fields
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<------+

    Figure 3: HbH Option Format for Segment IOAM Trace Type Data Fields

   At the beginning of each segment, the segment size (SSize) and the
   remaining hops (RHop) are initialized: RHop is set to equal to SSize.
   At each hop, if RHop is not zero, the node data is added to the node
   data list and then RHop is decremented by 1.  If RHop is equal to 0
   when receiving the packet, the node needs to remove (in incremental
   trace option) or clear (in pre-allocated trace option) the IOAM node
   data list and reset RHop to SSize.

   In this case, if we use the IOAM pre-allocated trace type, the size
   and location of each IPv6 extension header is fixed and predictable,
   and the hardware capability and performance can be guaranteed.

3.2.  Export at SRv6 node

   Whenever a packet with the IOAM option reaches a SRv6 node which
   needs to access the SRH, we can configure the node to export
   immediately the IOAM trace data accumulated so far.  In this case,
   basically at each SRv6 node, the HbH header size is fixed and the
   header contains an IOAM option with only the instruction part.  After
   the SRH processing, this node can add local IOAM trace data in the
   HbH option header before forwarding the packet.

   The incremental trace type can be used in this approach.  In an
   extreme case when every node is also an SRv6 node, this approach
   regresses to a per-hop postcard-based telemetry approach as described
   in [I-D.song-ippm-postcard-based-telemetry].  In this case, the HbH
   option for IOAM can even be avoided altogether if we can find a way
   to simply mark the packet for postcard export.







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4.  Direct Export Option

   As an embodiment of the PBT-I approach introduced in
   [I-D.song-ippm-postcard-based-telemetry], IOAM Direct Export (DEX)
   Option Type discussed in [I-D.ioamteam-ippm-ioam-direct-export] can
   be used to replace the IOAM trace type.  IOAM DEX only needs to
   encapsulate a fix-size instruction header in the HbH option header.

   Figure 4 shows the HbH option format for IOAM DEX type fields.  The
   field specification is identical to that in [RFC8200] and
   [I-D.ioamteam-ippm-ioam-direct-export].

    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 |   Reserved    |   IOAM Type   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<------+
   |        Namespace-ID           |           Flags               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IOAM
   |               IOAM-Trace-Type                 |  Reserved     | DEX
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type
   |                         Flow ID (optional)                    | Fields
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Sequence Number  (Optional)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<------+

           Figure 4: HbH Option Format for IOAM DEX Type Fields

5.  Comparison

   The following table compares the existing approach and the four other
   alternative approaches proposed in this draft.



















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   +--------------+-------------------------+--------------------------+
   |  Approach    |   Pros                  |   Cons                   |
   |              |                         |                          |
   +--------------+-------------------------+--------------------------+
   |IOAM Trace    |Comply w/ IOAM Data Spec |Variable and long HbH     |
   |in HbH        |                         |header impeding access of |
   |              |                         |later extension headers   |
   +--------------+-------------------------+--------------------------+
   |IOAM Trace    |Fix-size and short HbH   |Need extra extension      |
   |Data Separate |header, good for later   |header to hold trace data |
   |and Postpose  |extension header access  |                          |
   |(Sec. 2)      |                         |                          |
   +--------------+-------------------------+--------------------------+
   |Segment IOAM  |Fix-size and controllable|Need to enhance IOAM trace|
   |Data Export   |HbH header size          |type data field spec.     |
   |(Sec. 3.1)    |                         |                          |
   +--------------+-------------------------+--------------------------+
   |Trace Export  |Can be done through      |Specific to SRv6;         |
   |at SRv6 nodes |configuration            |No better than PB & IOAM  |
   |(Sec. 3.2)    |                         |DEX in the worst case     |
   +--------------+-------------------------+--------------------------+
   |IOAM Direct   |Comply w/ IOAM DEX Spec; |Need export data          |
   |Export in HbH |Fix-size and short HbH   |correlation               |
   |(Sec. 4)      |                         |                          |
   +--------------+-------------------------+--------------------------+

               Figure 5: Comparison of Different Approaches

6.  Security Considerations

   TBD.

7.  Normative References

   [I-D.ali-spring-ioam-srv6]
              Ali, Z., Gandhi, R., Filsfils, C., Brockners, F., Kumar,
              N., Pignataro, C., Li, C., Chen, M., and G. Dawra,
              "Segment Routing Header encapsulation for In-situ OAM
              Data", draft-ali-spring-ioam-srv6-02 (work in progress),
              November 2019.

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", draft-ietf-6man-segment-routing-header-26 (work in
              progress), October 2019.





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   [I-D.ietf-ippm-ioam-data]
              Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
              Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
              P., remy@barefootnetworks.com, r., daniel.bernier@bell.ca,
              d., and J. Lemon, "Data Fields for In-situ OAM", draft-
              ietf-ippm-ioam-data-08 (work in progress), October 2019.

   [I-D.ietf-ippm-ioam-ipv6-options]
              Bhandari, S., Brockners, F., Pignataro, C., Gredler, H.,
              Leddy, J., Youell, S., Mizrahi, T., Kfir, A., Gafni, B.,
              Lapukhov, P., Spiegel, M., Krishnan, S., and R. Asati,
              "In-situ OAM IPv6 Options", draft-ietf-ippm-ioam-
              ipv6-options-00 (work in progress), September 2019.

   [I-D.ioametal-ippm-6man-ioam-ipv6-deployment]
              Bhandari, S., Brockners, F., Mizrahi, T., Kfir, A., Gafni,
              B., Spiegel, M., Krishnan, S., and M. Smith, "Deployment
              Considerations for In-situ OAM with IPv6 Options", draft-
              ioametal-ippm-6man-ioam-ipv6-deployment-02 (work in
              progress), September 2019.

   [I-D.ioamteam-ippm-ioam-direct-export]
              Song, H., Gafni, B., Zhou, T., Li, Z., Brockners, F.,
              Bhandari, S., Sivakolundu, R., and T. Mizrahi, "In-situ
              OAM Direct Exporting", draft-ioamteam-ippm-ioam-direct-
              export-00 (work in progress), October 2019.

   [I-D.song-6man-srv6-pbt]
              Song, H., "Support Postcard-Based Telemetry for SRv6 OAM",
              draft-song-6man-srv6-pbt-01 (work in progress), October
              2019.

   [I-D.song-ippm-ioam-tunnel-mode]
              Song, H., Li, Z., Zhou, T., and Z. Wang, "In-situ OAM
              Processing in Tunnels", draft-song-ippm-ioam-tunnel-
              mode-00 (work in progress), June 2018.

   [I-D.song-ippm-postcard-based-telemetry]
              Song, H., Zhou, T., Li, Z., Shin, J., and K. Lee,
              "Postcard-based On-Path Flow Data Telemetry", draft-song-
              ippm-postcard-based-telemetry-06 (work in progress),
              October 2019.

   [I-D.song-ippm-segment-ioam]
              Song, H. and T. Zhou, "Control In-situ OAM Overhead with
              Segment IOAM", draft-song-ippm-segment-ioam-01 (work in
              progress), April 2018.




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   [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>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.

Authors' Addresses

   Haoyu Song
   Futurewei
   Santa Clara  95050
   USA

   Email: haoyu.song@futurewei.com


   Zhenbin Li
   Huawei Technologies
   Beijing  100095
   China

   Email: lizhenbin@huawei.com


   Shuping Peng
   Huawei Technologies
   Beijing  100095
   China

   Email: pengshuping@huawei.com












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