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6man                                                        H. Song, Ed.
Internet-Draft                                    Futurewei Technologies
Intended status: Standards Track                            July 1, 2019
Expires: January 2, 2020


             Support Postcard-Based Telemetry for SRv6 OAM
                      draft-song-6man-srv6-pbt-00

Abstract

   This document describes a method based on Postcard-based Telemetry
   with Marking for SRv6 on-path OAM, which avoids the extra overhead
   for encapsulating telemetry-related instruction and metadata in SRv6
   packets.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119][RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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 January 2, 2020.

Copyright Notice

   Copyright (c) 2019 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



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   (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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  PBT Triggered by Marking for SRv6 . . . . . . . . . . . . . .   3
     2.1.  Data Template . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Postcard Correlation  . . . . . . . . . . . . . . . . . .   3
     2.3.  Operational Considerations  . . . . . . . . . . . . . . .   4
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The ability to collect the on-path data about SRv6 packets at each
   segment is important for SRv6 OAM, especially for monitoring the
   application-aware services.  The In-situ OAM (IOAM)
   [I-D.brockners-inband-oam-data] trace option can be used for such
   purpose.  However, SRv6's SRH can be large due to the long segment
   list.  The IOAM trace option introduces significant additional
   overhead to the SRv6 packets with its instruction and data trace.
   The large header overhead complicates the packet processing and may
   exceed the forwarding hardware's header processing capability.

   The extra IOAM trace option header also brings some encapsulation
   challenges as documented in [I-D.li-6man-ipv6-sfc-ifit].  Here we
   restate a subtle issue about the IOAM scope: if IOAM header is
   encapsulated as another IPv6 extension header, the juxtaposition of
   IOAM and SRH makes it ambiguous to determine the coverage of IOAM:
   should it be applied to the entire forwarding path or just to the
   segment nodes?

   The PBT-I scheme introduced in
   [I-D.song-ippm-postcard-based-telemetry] partially relieves the
   packet overhead pressure but the encapsulation issues remain.  In




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   this draft, we propose to apply the PBT-M scheme from the same
   document for on-path SRv6 telemetry.

2.  PBT Triggered by Marking for SRv6

   PBT-M requires marking a packet as a trigger to collect on-path data
   about the packet.  The collected data are exported by an independent
   "postcard" packet.  Therefore, there is no new header encapsulation
   requirement.

   Eight flag bits are currently reserved in SRH.  One of those bits can
   be used as the marking flag, as shown in the following figure.  If
   the "T"-bit is set to 1, the segment node which process the SRH needs
   to export the on-path data about this packet as configured.



        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Next Header   |  Hdr Ext Len  | Routing Type  | Segments Left |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Last Entry   |T|   Flags     |              Tag              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                                                               |
       ~            Segment List[] & TLV                               ~
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                     Figure 1: SRH with PBT Mark Flag

2.1.  Data Template

   Although it is possible to configure the segment nodes about the data
   set to collect, different flows may require different data collection
   profiles.  It would be more flexible to have multiple different data
   templates supported by the segment nodes and each packet can
   designate one template that best suits its interests to use.  The
   template ID can be carried as a TLV in SRH.

2.2.  Postcard Correlation

   As discussed in [I-D.song-ippm-postcard-based-telemetry], PBT-M has
   some issues to correlate the postcards from the different segment
   nodes for the same user packet.  While several solutions are given to



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   mitigate the problem, it is ideal to be able to correlate the
   postcards without any constraint and precondition.

   A flow ID and a sequence number can be included as TLVs in SRH.  The
   specification and usage of the flow ID and the sequence number are
   the same as those in PBT-I in
   [I-D.song-ippm-postcard-based-telemetry].  Further, the exported
   postcard may include the SRH or the current SID which provides a
   trace to order the postcards.

2.3.  Operational Considerations

   The SR source node is responsible to determine the policy for setting
   or resetting the "T"-bit.

   The segment node can decide independently whether or not to react on
   the "T"-bit.

3.  Security Considerations

   Since PBT incurs some extra packet processing and transport cost, "T"
   flag is usually selectively set on a subset of packets by the source
   node.  A potential DoS attack may set the "T" flag for all the packet
   with the intention to overwhelm the segment nodes.  Therefore, the
   postcards should be generated on the basis of the best effort.

4.  IANA Considerations

   [I-D.ietf-6man-segment-routing-header] defines a new registry named
   "Segment Routing Header Flags".  This document requests the
   allocation of a new flag bit "T" for the telemetry trigger mark.

5.  Contributors

   TBD.

6.  Acknowledgments

   TBD.

7.  References

7.1.  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>.



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   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

7.2.  Informative References

   [I-D.brockners-inband-oam-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-brockners-inband-oam-data-07 (work
              in progress), July 2017.

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
              Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment
              Routing Header (SRH)", draft-ietf-6man-segment-routing-
              header-21 (work in progress), June 2019.

   [I-D.li-6man-ipv6-sfc-ifit]
              Li, Z. and S. Peng, "Consideration of IPv6 Encapsulation
              for SFC and IFIT", draft-li-6man-ipv6-sfc-ifit-00 (work in
              progress), March 2019.

   [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-04 (work in progress), June
              2019.

Author's Address

   Haoyu Song (editor)
   Futurewei Technologies
   2330 Central Expressway
   Santa Clara
   USA

   Email: hsong@futurewei.com







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