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ippm                                                        H. Song, Ed.
Internet-Draft                                                   T. Zhou
Intended status: Standards Track                                  Huawei
Expires: October 19, 2018                                 April 17, 2018


             Control In-situ OAM Overhead with Segment IOAM
                    draft-song-ippm-segment-ioam-01

Abstract

   This document describes a proposal which partitions an in-situ OAM
   (iOAM) domain into multiple segments in order to control the iOAM
   data overhead, adapt to the path MTU limitations, and enable new
   applications.  We discuss several use cases to motivate our proposal
   and base the necessary modifications on the current in-situ OAM
   header format specification.

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
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   This Internet-Draft will expire on October 19, 2018.

Copyright Notice

   Copyright (c) 2018 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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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e 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.  Segment In-situ OAM . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Segment and Hops  . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Considerations for Data Handling  . . . . . . . . . . . .   4
     2.3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   In-situ OAM (iOAM) [I-D.brockners-inband-oam-requirements] records
   OAM information within user packets while the packets traverse a
   network.  The data types and data formats for in-situ OAM data
   records have been defined in [I-D.ietf-ippm-ioam-data].

   iOAM may incur significant overhead on user packets.  The overhead
   includes the iOAM header and the node data list for each network
   element.

   The total size of data is limited by the MTU.  When the number of
   required data types is large and the forwarding path length is long,
   it is possible that there is not enough space in the user packets to
   hold the iOAM header and data.  The current proposal is to label the
   overflow status and stop adding new node data to the packet, leading
   to the loss of information.

   Even if the header has enough space to hold the iOAM data, the
   overhead may be too large and consumes too much bandwidth.  For
   example, if we assume moderate 20 bytes of data per node, a path with
   length of 10 will need 200 bytes to hold the data.  This will inflate
   small 64-byte packets by more than four times.  Even for the largest
   packet size (e.g., 1500 bytes), the overhead (>10%) is not
   negligible.  Therefore, we need to limit the iOAM data overhead
   without sacrificing the data collection capability.

   Here we have another interesting related issue.  Packets can be
   dropped anywhere in a network for various reasons.  If we can only
   collect iOAM data at the path end, we lose all data from the dropped




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   packets and have no idea where the packets are dropped.  This defies
   the purpose of iOAM and makes those iOAM-enabled nodes work in vain.

2.  Segment In-situ OAM

   Based on the observation in Section 1, we propose a method to limit
   the size of the node data list.

2.1.  Segment and Hops

   A hop is a node on a flow's forwarding path which is capable of
   processing iOAM data.  A segment is a fixed number hops on a flow's
   forwarding path.  While working in the "per hop" trace mode, the
   segment size (SSize) and the remaining hops (RHop), is added to the
   iOAM header at the edge.  Initially, RHop is equal to SSize.  At each
   hop, if RH is not zero, the node data is added to the node data list
   at the corresponding location and then RH is decremented by 1.  If RH
   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.  Then the node will
   add its data to the node data list as if it is the edge node.

   The stripped iOAM data at the segement edge can be immediately
   exported to a collector.

   Figure 1 shows the proposed in-situ OAM header format.  The 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.


       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Base OAM Trace Type        |NodeLen|Flags|1| SSize | RHop  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                  Node Data List []                            |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 1: Segment iOAM Header Format

   In the special case when SSize is set to 0, no data will be recorded
   in the node data list.  The requested data listed in the OAM Trace



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   Type will be immediately exported to the collector.  This way the
   iOAM overhead is minimized.

2.2.  Considerations for Data Handling

   At any hop when RHop is equal to 0, the node data list is copied from
   the iOAM header.  The data can be encapsulated and reported to the
   controller or the edge node as configured.  The encapsulation and
   report method is beyond the scope of this draft but should be comply
   with the method used by the iOAM edge node.

   The actual size of the last segment may not be equal to SSize but
   this is not a problem.

2.3.  Use Cases

   Segment iOAM is necessary in the following example scenarios:

   o  Segment iOAM can be used to detect at which segment the flow
      packet is dropped.  If the SSize is set to 1, then the exact drop
      node can be identified.  The iOAM data before the dropping point
      is also retained.

   o  The path MTU allows to add at most k node data in the list to
      avoid fragmentation.  Therefore SSize is set to k and at each hop
      where RHop is 0, the node data list is retrieved and sent in a
      standalone packet.

   o  A flow contains mainly short packets and travels a long path.  It
      would be inefficient to keep a large node data list in the packet
      so the network bandwidth utilization rate is low.  In this case,
      segment iOAM can be used to limit the ratio of the iOAM data to
      the flow packet payload.

   o  The network allows at most n bytes budget for the iOAM data.
      There is a tradeoff between the number of data types that can be
      collected and the number of hops for data collecting.  The segment
      size is therefore necessary to meet the application's data
      requirement (i.e., SSize * Node Data Size < n).

3.  Security Considerations

   There is no extra security considerations beyond those have been
   identified by in-situ OAM protocol.







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4.  IANA Considerations

   This memo includes no request to IANA.

5.  Acknowledgments

   We would like to thank Frank Brockners, Carlos Pignataro, and Shwetha
   Bhandari for helpful comments and suggestions.

6.  Contributors

   The document is inspired by numerous discussions with James N.
   Guichard.  He also provided significant comments and suggestions to
   help improve this document.

7.  Informative References

   [I-D.brockners-inband-oam-requirements]
              Brockners, F., Bhandari, S., Dara, S., Pignataro, C.,
              Gredler, H., Leddy, J., Youell, S., Mozes, D., Mizrahi,
              T., <>, P., and r. remy@barefootnetworks.com,
              "Requirements for In-situ OAM", draft-brockners-inband-
              oam-requirements-02 (work in progress), October 2016.

   [I-D.ietf-ippm-ioam-data]
              Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
              Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
              P., Chang, R., and d. daniel.bernier@bell.ca, "Data Fields
              for In-situ OAM", draft-ietf-ippm-ioam-data-00 (work in
              progress), September 2017.

Authors' Addresses

   Haoyu Song (editor)
   Huawei
   2330 Central Expressway
   Santa Clara, 95050
   USA

   Email: haoyu.song@huawei.com











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   Tianran Zhou
   Huawei
   156 Beiqing Road
   Beijing, 100095
   P.R. China

   Email: zhoutianran@huawei.com












































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