IPPM                                                             H. Song
Internet-Draft                                                 Futurewei
Intended status: Standards Track                                   Z. Li
Expires: 5 September 2024                                        S. Peng
                                                     Huawei Technologies
                                                             J. Guichard
                                                               Futurewei
                                                            4 March 2024


             Scalable Approaches on Supporting IOAM in IPv6
                  draft-song-ippm-ioam-ipv6-support-03

Abstract

   IOAM pre-allocated trace option data fields can be encapsulated in
   IPv6 HbH options header as described in RFC9486.  However, due to the
   potential large size of the trace data and the HbH extension header
   location in the IPv6 packets, the scheme creates practical challenges
   for implementation, especially when other extension headers, such as
   a routing header, also exist and require on-path processing.  We
   propose two alternative approaches to address this challenge in
   addition to IOAM DEX: separating the IOAM incremental trace data from
   the IOAM instruction header, and applying the segment IOAM trace data
   export scheme, based on the network scenario and application
   requirements.  We discuss the pros and cons of each approach in this
   document.

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."



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   This Internet-Draft will expire on 5 September 2024.

Copyright Notice

   Copyright (c) 2024 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 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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  IOAM Trace Data Separate and Postpose . . . . . . . . . . . .   4
     2.1.  IOAM Incremental 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.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   In-situ OAM (IOAM) [RFC9197] defines two trace options, pre-allocated
   trace option and incremental trace option, which record hop-by-hop
   data along a packet's forwarding path.  [RFC9486] describes the
   method to encapsulate IOAM pre-allocated trace option data fields in
   IPv6.  Because the trace options requires per hop processing, such
   options can only be encapsulated in IPv6 Hop-by-Hop (HbH) options
   header.

   [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 can amount to tens to hundreds of
   bytes, making accessing other headers after it difficult or even
   impossible in some routers.  There are practical limitations on how
   far the hardware can reach into a packet in forwarding hardware.  The



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   IOAM trace option cannot be applied if it makes other extension
   headers inaccessible.  Even if the other headers can be reached, the
   deeper they are, the higher the cost to access and process them, and
   the lower the forwarding performance.  Note that [RFC9486] does not
   support the incremental trace option because it would expand the HbH
   header at each hop and push back all other headers after it.  The
   changing location of the later extension headers could further
   complicate the hardware implementation and affect the forwarding
   performance.

   The issue becomes more severe when SRv6 and IOAM coexist.  The
   Segment Routing Extension Header (SRH) [RFC8754] 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 segment
   endpoint 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 degrades.

   We can avoid the problem by not using both at the same time, but 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.

   The 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 segment endpoint nodes.  To realize
   this, [I-D.ali-spring-ioam-srv6] describes an approach that
   encapsulates the IOAM option data fields in an SRH TLV.  [RFC9259]
   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 endpoints, it fails to cover all the IPv6 nodes on the
   packet forwarding path in an IOAM domain.

   So the proposition of this draft is, if we need to apply IOAM on all
   nodes in an SRv6 network, how we can amend the approach in [RFC9486]
   or use alternative approaches to circumvent the aforementioned
   issues.  In this draft, we propose two viable approaches: (1)
   separating the IOAM trace data from the instruction header to a
   different extension header option after the routing header if it
   exists, and (2) applying the segment IOAM trace export scheme.  We
   discuss the pros and cons of each approach.







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2.  IOAM Trace 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
   follows the instruction part, there is not fundamental reason why
   these two parts must stick together.  This observation provides us an
   optimization opportunity to amend the original proposal in [RFC9486].

   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 extension header option after all the IPv6 extension headers
   that need to be examined and processed on the packet forwarding path
   (e.g., a routing header).  This arrangement allows us to use the
   incremental trace option efficiently.  Even if the data trace
   increases its size at each node, all IPv6 extension headers before it
   remain a fixed size, and new data is guaranteed to be inserted at a
   fixed location.

   Figure 1 shows the HbH option format for IOAM incremental trace type
   instruction.  The field specification is identical to that in
   [RFC8200] and [RFC9197].


  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<Inst.

      Figure 1: HbH Option Format for IOAM Incremental Trace Type
                              Instruction

   Figure 2 shows the TLV option format for IOAM trace type data.  The
   IOAM trace type data format is compliant with [RFC9197].












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

        Figure 2: Option Format for IOAM Incremental Trace Type Data

2.1.  IOAM Incremental Trace Data Encapsulation

   We have basically two methods to encapsulate the IOAM incremental
   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 Option Header (DOH).  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 to standardize a
   new extension header type; the second method is simpler but it needs
   to overcome the access constraints exerted by [RFC8200].

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 described in [RFC9486].  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



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   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.


 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 segment
   endpoint 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 segment endpoint node, after the
   trace data export, 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.






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   The incremental trace type is more proper in this approach than the
   pre-allocated trace type, due to the uncertainty of the number of
   hops between two segment endpoints.  In an extreme case when every
   node is also an SRv6 node, this approach regresses to a per-hop
   postcard-based telemetry approach such as IOAM DEX as described in
   [RFC9326].

4.  Direct Export Option

   It is worth noting that, instead of using the IOAM trace options,
   IOAM Direct Export (DEX) Option Type [RFC9326] can be used for fixed
   and small packet overhead since it only needs to encapsulate a fix-
   size instruction header in the HbH option header.  The scheme is
   covered in [RFC9486].

5.  Comparison

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

   +--------------+-------------------------+--------------------------+
   |  Approach    |   Pros                  |   Cons                   |
   |              |                         |                          |
   +--------------+-------------------------+--------------------------+
   |IOAM Trace    |Comply w/ IOAM Data Spec |Variable, long HbH        |
   |Option in     |                         |header impedes access of  |
   |HbH (RFC9486) |                         |other extension headers   |
   +--------------+-------------------------+--------------------------+
   |IOAM Trace    |Fix-size and short HbH   |Need extra extension      |
   |Data Separate |header, good for         |header option to hold     |
   |and Postpose  |accessing other extension|trace data                |
   |(Sec. 2)      |headers                  |                          |
   +--------------+-------------------------+--------------------------+
   |Segment IOAM  |Fix-size and controllable|Need to update 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 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, and other    |
   |(RFC9486)     |                         |issues of DEX (RFC9326)   |
   +--------------+-------------------------+--------------------------+

               Figure 4: Comparison of Different Approaches




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   IOAM trace option is easy to implement and extensible for data types.
   Complementary to [RFC9486], the scalable solutions for using it in
   IPv6 networks discussed in this document can fully carry out the
   benefits of IOAM trace option and meanwhile avoid potential issues
   associated with variable and high header overhead.

6.  Security Considerations

   No new security issue is identified other than those for IOAM trace
   option [RFC9197], IOAM DEX [RFC9326], and IPv6 extension headers
   [RFC8200].

7.  IANA Considerations

   This document requires no IANA actions.

8.  Acknowledgments


9.  Normative References

   [I-D.ali-spring-ioam-srv6]
              Ali, Z., Gandhi, R., Filsfils, C., Brockners, F., Nainar,
              N. K., Pignataro, C., Li, C., Chen, M., and G. Dawra,
              "Segment Routing Header encapsulation for In-situ OAM
              Data", Work in Progress, Internet-Draft, draft-ali-spring-
              ioam-srv6-06, 10 July 2022,
              <https://datatracker.ietf.org/doc/html/draft-ali-spring-
              ioam-srv6-06>.

   [I-D.song-ippm-ioam-tunnel-mode]
              Song, H., Li, Z., Zhou, T., and Z. Wang, "In-situ OAM
              Processing in Tunnels", Work in Progress, Internet-Draft,
              draft-song-ippm-ioam-tunnel-mode-00, 27 June 2018,
              <https://datatracker.ietf.org/doc/html/draft-song-ippm-
              ioam-tunnel-mode-00>.

   [I-D.song-ippm-segment-ioam]
              Song, H. and T. Zhou, "Control In-situ OAM Overhead with
              Segment IOAM", Work in Progress, Internet-Draft, draft-
              song-ippm-segment-ioam-01, 17 April 2018,
              <https://datatracker.ietf.org/doc/html/draft-song-ippm-
              segment-ioam-01>.

   [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>.



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   [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>.

   [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,
              <https://www.rfc-editor.org/info/rfc8754>.

   [RFC9197]  Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
              Ed., "Data Fields for In Situ Operations, Administration,
              and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
              May 2022, <https://www.rfc-editor.org/info/rfc9197>.

   [RFC9259]  Ali, Z., Filsfils, C., Matsushima, S., Voyer, D., and M.
              Chen, "Operations, Administration, and Maintenance (OAM)
              in Segment Routing over IPv6 (SRv6)", RFC 9259,
              DOI 10.17487/RFC9259, June 2022,
              <https://www.rfc-editor.org/info/rfc9259>.

   [RFC9326]  Song, H., Gafni, B., Brockners, F., Bhandari, S., and T.
              Mizrahi, "In Situ Operations, Administration, and
              Maintenance (IOAM) Direct Exporting", RFC 9326,
              DOI 10.17487/RFC9326, November 2022,
              <https://www.rfc-editor.org/info/rfc9326>.

   [RFC9486]  Bhandari, S., Ed. and F. Brockners, Ed., "IPv6 Options for
              In Situ Operations, Administration, and Maintenance
              (IOAM)", RFC 9486, DOI 10.17487/RFC9486, September 2023,
              <https://www.rfc-editor.org/info/rfc9486>.

Authors' Addresses

   Haoyu Song
   Futurewei
   United States of America
   Email: haoyu.song@futurewei.com


   Zhenbin Li
   Huawei Technologies
   China



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   Email: lizhenbin@huawei.com


   Shuping Peng
   Huawei Technologies
   China
   Email: pengshuping@huawei.com


   James Guichard
   Futurewei
   United States of America
   Email: james.n.guichard@futurewei.com






































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