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Multicast On-path Telemetry using IOAM

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Authors Haoyu Song , Mike McBride , Greg Mirsky , Gyan Mishra , Hitoshi Asaeda , Tianran Zhou
Last updated 2023-03-10
Replaces draft-song-multicast-telemetry
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MBONED                                                           H. Song
Internet-Draft                                                M. McBride
Intended status: Standards Track                  Futurewei Technologies
Expires: 11 September 2023                                     G. Mirsky
                                                               ZTE Corp.
                                                               G. Mishra
                                                            Verizon Inc.
                                                               H. Asaeda
                                                                 T. Zhou
                                                     Huawei Technologies
                                                           10 March 2023

                 Multicast On-path Telemetry using IOAM


   This document specifies the requirements of on-path telemetry for
   multicast traffic using In-situ OAM.  While In-situ OAM is
   advantageous for multicast traffic telemetry, applying it presents
   some unique challenges.  This document provides the solutions based
   on the In-situ OAM trace option and direct export option to support
   the telemetry data correlation and the multicast tree reconstruction
   without incurring data redundancy.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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

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   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 11 September 2023.

Copyright Notice

   Copyright (c) 2023 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 (
   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements for Multicast Traffic Telemetry  . . . . . . . .   4
   3.  Issues of Existing Techniques . . . . . . . . . . . . . . . .   4
   4.  Modifications to Existing Solutions . . . . . . . . . . . . .   5
     4.1.  Per-hop postcard using IOAM DEX . . . . . . . . . . . . .   5
     4.2.  Per-section postcard for IOAM Trace . . . . . . . . . . .   7
   5.  Application Considerations for Multicast Protocols  . . . . .   8
     5.1.  Mtrace verson 2 . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Application in PIM  . . . . . . . . . . . . . . . . . . .   9
     5.3.  Application of MVPN X-PMSI Tunnel Encapsulation
           Attribute . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.4.  Application in BIER . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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1.  Introduction

   Multicast is used by residential broadband customers across operator
   networks, private MPLS customers, and internal customers within
   corporate intranet.  Multicast provides real time interactive online
   meetings or podcasts, IPTV and financial markets real-time data,
   which all have a reliance on UDP's unreliable transport.  End-to-end
   QOS, therefore, should be a critical component of multicast
   deployment in order to provide a good end user experience.  In
   multicast video streaming, if a packet is dropped, and that packet
   happens to be a reference frame (I-Frame) in the video feed, the
   client receiver of the multicast feed goes into buffering mode
   resulting in a frozen window.  Multicast packet drops and delay can
   severely affect the application performance and user experience.

   It is important to monitor the performance of the multicast traffic.
   New on-path telemetry techniques such as In-situ OAM (IOAM)
   [RFC9197], IOAM Direct Export (DEX) [RFC9326] IOAM Marking-based
   Postcard (PBT-M) [], and Hybrid
   Two-Step (HTS) [I-D.mirsky-ippm-hybrid-two-step] are useful and
   complementary to the existing active OAM performance monitoring
   methods, provide promising means to directly monitor the network
   experience of multicast traffic.  However, multicast traffic has some
   unique characteristics which pose some challenges on applying such
   techniques in an efficient way.

   The IP Multicast packet data for a particular (S, G) state is
   identical from one branch to another on its way to multiple
   receivers.  When adding IOAM trace data to multicast packets, each
   replicated packet would keep the telemetry data for its entire
   forwarding path.  Since the replicated packets all share some common
   path segments, redundant data will be collected for the same original
   multicast packet.  Such redundancy consumes extra network bandwidth
   unnecessarily.  Alternatively, it could be more efficient to collect
   the telemetry data using solutions such as IOAM DEX to eliminate the
   data redundancy.  However, IOAM DEX is lack of a branch identifier,
   making telemetry data correlation and multicast-tree reconstruction

   This draft provides two solutions to the IOAM data redundancy problem
   based on the IOAM standards.  The requirements for multicast traffic
   telemetry are discussed along with the issues of the existing on-path
   telemetry techniques.  We propose modifications to make these
   techniques adapt to multicast in order for the original multicast
   tree to be correctly reconstructed while eliminating redundant data.

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2.  Requirements for Multicast Traffic Telemetry

   Multicast traffic is forwarded through a multicast tree.  With PIM
   and P2MP (MLDP, RSVP-TE) the forwarding tree is established and
   maintained by the multicast routing protocol.  With BIER, no state is
   created in the network to establish a forwarding tree; instead, a
   bier header provides the necessary information for each packet to
   know the egress points.  Multicast packets are only replicated at
   each tree branch fork node for efficiency.

   There are several requirements for multicast traffic telemetry, a few
   of which are:

   *  Reconstruct and visualize the multicast tree through data plane

   *  Gather the multicast packet delay and jitter performance.

   *  Find the multicast packet drop location and reason.

   *  Gather the VPN state and tunnel information in case of P2MP

   In order to meet these requirements, we need the ability to directly
   monitor the multicast traffic and derive data from the multicast
   packets.  The conventional OAM mechanisms, such as multicast ping and
   trace, are not sufficient to meet these requirements.

3.  Issues of Existing Techniques

   On-path Telemetry techniques that directly retrieve data from
   multicast traffic's live network experience are ideal for addressing
   the aforementioned requirements.  The representative techniques
   include In-situ OAM (IOAM) Trace option [RFC9197], IOAM Direct Export
   (DEX) option [RFC9326], and PBT-M
   [].  However, unlike unicast,
   multicast poses some unique challenges to applying these techniques.

   Multicast packets are replicated at each branch fork node in the
   corresponding multicast tree.  Therefore, there are multiple copies
   of the original multicast packet in the network.

   If the IOAM trace option is used for on-path data collection, the
   partial trace data will also be replicated into the copy for each
   branch.  The end result is that, at the multicast tree leaves, each
   copy of the multicast packet has a complete trace.  Most of the data
   (except data from the last leaf branch), however, has redundant
   copies.  Data redundancy introduces unnecessary header overhead,

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   wastes network bandwidth, and complicates the data processing.  The
   larger the multicast tree is or the longer the multicast path is, the
   more severe the redundancy problem becomes.

   The postcard-based solutions, including the IOAM DEX and PBT-M, can
   be used to eliminate such data redundancy, because each node on the
   tree only sends a postcard covering local data.  However, they cannot
   track and correlate the tree branches properly due to the lack of
   branching information, so they can bring confusion about the
   multicast tree topology.  For example, in a multicast tree, Node A
   has two branches, one to Node B and the other to node C; further,
   Node B leads to Node D and Node C leads to Node E.  When applying
   postcard-based methods, one cannot tell whether or not Node D(E) is
   the next hop of Node B(C) from the received postcards.

   The fundamental reason for this problem is that there is not an
   identifier (either implicit or explicit) to correlate the data on
   each branch.

4.  Modifications to Existing Solutions

   We provide two solutions to address the above issues.  One is based
   on IOAM DEX and requires an extension to the instruction header of
   the IOAM DEX Option.  The second solution combines the IOAM trace
   option and postcards for redundancy removal.

4.1.  Per-hop postcard using IOAM DEX

   One way to mitigate the postcard-based telemetry's tree tracking
   weakness is to augment it with a branch identifier field.  Note that
   this works for the IOAM DEX option but not for PBT-M because the IOAM
   DEX option has an instruction header which can be used to hold the
   branch identifier.  To make the branch identifier globally unique,
   the branch fork node ID plus an index is used.  For example, Node A
   has two branches: one to Node B and the other to Node C.  Node A will
   use [A, 0] as the branch identifier for the branch to B, and [A, 1]
   for the branch to C.  The identifier is carried with the multicast
   packet until the next branch fork node.  Each node MUST export the
   branch identifier in the received IOAM DEX header in the postcards it
   sends.  The branch identifier, along with the other fields such as
   flow ID and sequence number, is sufficient for the data collector to
   reconstruct the topology of the multicast tree.

   Figure 1 shows an example of this solution.  "P" stands for the
   postcard packet.  The square brackets contains the branch identifier.
   The curly brace contains the telemetry data about a specific node.

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     P:[A,0]{A}  P:[A,0]{B} P:[B,1]{D}  P:[B,0]{C}   P:[B,0]{E}
          ^            ^          ^        ^           ^
          :            :          :        :           :
          :            :          :        :           :
          :            :          :      +-:-+       +-:-+
          :            :          :      |   |       |   |
          :            :      +---:----->| C |------>| E |-...
        +-:-+        +-:-+    |   :      |   |       |   |
        |   |        |   |----+   :      +---+       +---+
        | A |------->| B |        :
        |   |        |   |--+   +-:-+
        +---+        +---+  |   |   |
                            +-->| D |--...
                                |   |

                         Figure 1: Per-hop Postcard

   Each branch fork node needs to generate a unique branch identifier
   (i.e., branch ID) for each branch in its multicast tree instance and
   include it in the IOAM DEX option header.  The branch ID remains
   unchanged until the next branch fork node.  The branch ID contains
   two parts: the branch fork node ID and an interface index.

   Conforming to the node ID specification in IOAM [RFC9197], the node
   ID is a 3-octet unsigned integer.  The interface index is a two-octet
   unsigned integer.  As shown in Figure 2, the branch ID consumes 8
   octets in total.  The three unused octets must be set to 0.

       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
      |                 node_id                       |     unused    |
      |       Interface Index         |           unused              |

                    Figure 2: Multicast Branch ID format

   Figure 3 shows that the branch ID is carried as an optional field
   after the flow ID and sequence number optional fields in the IOAM DEX
   option header.  Two bits "N" and "I" (i.e., the third and fourth bits
   in the Extension-Flags field) are reserved to indicate the presence
   of the optional branch ID field.  "N" stands for the Node ID and "I"
   stands for the interface index.  If "N" and "I" are both set to 1,
   the optional multicast branch ID field is present; otherwise it is

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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
       |        Namespace-ID           |     Flags     |F|S|N|I|E-Flags|
       |               IOAM-Trace-Type                 |   Reserved    |
       |                         Flow ID (optional)                    |
       |                     Sequence Number  (Optional)               |
       |                       Multicast Branch ID                     |
       |                            (optional)                         |

          Figure 3: Carry Branch ID in IOAM DEX option header

   Once a node gets the branch ID information from the upstream, it MUST
   carry this information in its telemetry data export postcards, so the
   original multicast tree can be correctly reconstructed based on the

4.2.  Per-section postcard for IOAM Trace

   The second solution is a combination of the IOAM trace option and the
   postcard-based telemetry.  To avoid data redundancy, at each branch
   fork node, the trace data accumulated up to this node is exported by
   a postcard before the packet is replicated.  In this solution, each
   branch also needs to maintain some identifier to help correlate the
   postcards for each tree section.  The natural way to accomplish this
   is to simply carry the branch fork node's data (including its ID) in
   the trace of each branch.  This is also necessary because each
   replicated multicast packet can have different telemetry data
   pertaining to this particular copy (e.g., node delay, egress
   timestamp, and egress interface).  As a consequence, the local data
   exported by each branch fork node can only contain partial data
   (e.g., ingress interface and ingress timestamp).

   Figure 4 shows an example in a segment of a multicast tree.  Node B
   and D are two branch fork nodes and they will export a postcard
   covering the trace data for the previous section.  The end node of
   each path will also need to export the data of the last section as a

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                P:{A,B'}            P:{B1,C,D'}
                   ^                     ^
                   :                     :
                   :                     :
                   :                     :    {D1}
                   :                     :    +--...
                   :        +---+      +---+  |
                   :   {B1} |   |{B1,C}|   |--+ {D2}
                   :    +-->| C |----->| D |-----...
       +---+     +---+  |   |   |      |   |--+
       |   | {A} |   |--+   +---+      +---+  |
       | A |---->| B |                        +--...
       |   |     |   |--+   +---+             {D3}
       +---+     +---+  |   |   |{B2,E}
                        +-->| E |--...
                       {B2} |   |

                       Figure 4: Per-section Postcard

   There is no need to modify the IOAM trace option header format as
   specified in [RFC9197].  We just need to configure the branch fork
   nodes to export the postcards and refresh the IOAM header and data
   (e.g., clear the node data list and reset the Remaining Length

5.  Application Considerations for Multicast Protocols

5.1.  Mtrace verson 2

   Mtrace version 2 (Mtrace2) [RFC8487] is a protocol that allows the
   tracing of an IP multicast routing path.  Mtrace2 provides additional
   information such as the packet rates and losses, as well as other
   diagnostic information.  Unlike unicast traceroute, Mtrace2 traces
   the path that a packet would take from a source to a receiver.  It is
   usually initiated from an Mtrace2 client by sending an Mtrace2 Query
   to a Last-Hop Router (LHR) or to a Rendezvous Point (RP).  The LHR/RP
   turns the Query packet into an Mtrace2 Request, appends a Standard
   Response Block containing its interface addresses and packet
   statistics to the Request packet, and forwards the packet towards the
   source/RP.  In a similar fashion, each router along the path to the
   source/RP appends a Standard Response Block to the end of the Request
   packet and forwards it to its upstream router.  When the First-Hop
   Router (FHR) receives the Request packet, it appends its own Standard
   Response Block, turns the Request packet into a Reply, and unicasts
   the Reply back to the Mtrace2 client.

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   New on-path telemetry techniques will enhance Mtrace2, and other
   existing OAM solutions, with more granular and realtime network
   status data through direct measurements.  There are various multicast
   protocols that are used to forward the multicast data.  Each will
   require their own unique on-path telemetry solution.

5.2.  Application in PIM

   PIM-SM [RFC7761] is the most widely used multicast routing protocol
   deployed today.  Of the various PIM modes (PIM-SM, PIM-DM, BIDIR-PIM,
   PIM-SSM), PIM-SSM is the preferred method due to its simplicity and
   removal of network source discovery complexity.  With all PIM modes,
   control plane state is established in the network in order to forward
   multicast UDP data packets.  All PIM modes utilize network based
   source discovery except for PIM-SSM, which utilizes application based
   source discovery.  IP Multicast packets fall within the range of through  The telemetry solution will need
   to work within this address range and provide telemetry data for this
   UDP traffic.

   A proposed solution for encapsulating the telemetry instruction
   header and metadata in IPv6 packets is described in

5.3.  Application of MVPN X-PMSI Tunnel Encapsulation Attribute

   Multipoint Label Distribution Protocol (mLDP), P2MP RSVP-TE, Ingress
   Replication (IR), PIM MDT SAFI with GRE Transport, are commonly used
   within a Multicast VPN (MVPN) environment utilizing MVPN procedures
   Multicast in MPLS/BGP IP VPNs [RFC6513] and BGP Encoding and
   Procedures for Multicast in MPLS/BGP IP VPNs [RFC6514].  MLDP LDP
   Extension for P2MP and MP2MP LSPs [RFC6388] provides extensions to
   LDP to establish point-to-multipoint (P2MP) and multipoint-to-
   multipoint (MP2MP) label switched paths (LSPs) in MPLS networks.
   P2MP RSVP-TE provides extensions to RSVP-TE RSVP-TE for P2MP LSPs
   [RFC4875] for establish traffic-engineered P2MP LSPs in MPLS
   networks.  Ingress Replication (IR) P2MP Trees Ingress Replication
   Tunnels in Multicast VPNs [RFC7988] using unicast replication from
   parent node to child node over MPLS Unicast Tunnel.  PIM MDT SAFI
   Multicast in BGP/MPLS IP VPNs [RFC6037]utilizes PIM modes PIM-SSM,
   PIM-SM, PIM-BIDIR control plane with GRE transport data plane in the
   core for X-PMSI P-Tree using MVPN procedures.  Replication SID SR
   Replication Segment for Multi-point Service Delivery
   [I-D.ietf-spring-sr-replication-segment] replication segments for
   P2MP multicast service delivery in Segment Routing SR-MPLS networks.
   The telemetry solution will need to be able to follow these P2MP and
   MP2MP paths.  The telemetry instruction header and data should be
   encapsulated into MPLS packets on P2MP and MP2MP paths.  A

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   corresponding proposal is described in

5.4.  Application in BIER

   BIER [RFC8279] adds a new header to multicast packets and allows the
   multicast packets to be forwarded according to the header only.  By
   eliminating the requirement of maintaining per multicast group state,
   BIER is more scalable than the traditional multicast solutions.

   OAM Requirements for BIER [I-D.ietf-bier-oam-requirements] lists many
   of the requirements for OAM at the BIER layer which will help in the
   forming of on-path telemetry requirements as well.

   Depending on how the BIER header is encapsulated into packets with
   different transport protocols, the method to encapsulate the
   telemetry instruction header and metadata also varies.  It is also
   possible to make the instruction header and metadata a part of the
   BIER header itself, such as in a TLV.

6.  Security Considerations

   No new security issues are identified other than those discovered by
   the IOAM trace and DEX options.

7.  IANA Considerations

   The document requests two new extension flag registrations in the
   "IOAM DEX Extension-Flags" registry, as described in Section 4.1.

   Bit 2 "Multicast Branching Node ID [RFC XXXX] [RFC Editor: please
   replace with the RFC number of the current document]".

   Bit 3 "Multicast Branching Interface Index [RFC XXXX] [RFC Editor:
   please replace with the RFC number of the current document]".

8.  Acknowledgments

   The authors would like to thank Frank Brockners, Nils Warnke, Jake
   Holland, and Dino Farinacci for the comments and suggestions.

9.  References

9.1.  Normative References

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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,

   [RFC4687]  Yasukawa, S., Farrel, A., King, D., and T. Nadeau,
              "Operations and Management (OAM) Requirements for Point-
              to-Multipoint MPLS Networks", RFC 4687,
              DOI 10.17487/RFC4687, September 2006,

   [RFC4875]  Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
              Yasukawa, Ed., "Extensions to Resource Reservation
              Protocol - Traffic Engineering (RSVP-TE) for Point-to-
              Multipoint TE Label Switched Paths (LSPs)", RFC 4875,
              DOI 10.17487/RFC4875, May 2007,

   [RFC6037]  Rosen, E., Ed., Cai, Y., Ed., and IJ. Wijnands, "Cisco
              Systems' Solution for Multicast in BGP/MPLS IP VPNs",
              RFC 6037, DOI 10.17487/RFC6037, October 2010,

   [RFC6388]  Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
              Thomas, "Label Distribution Protocol Extensions for Point-
              to-Multipoint and Multipoint-to-Multipoint Label Switched
              Paths", RFC 6388, DOI 10.17487/RFC6388, November 2011,

   [RFC6513]  Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
              BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
              2012, <>.

   [RFC6514]  Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
              Encodings and Procedures for Multicast in MPLS/BGP IP
              VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,

   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <>.

   [RFC7988]  Rosen, E., Ed., Subramanian, K., and Z. Zhang, "Ingress
              Replication Tunnels in Multicast VPN", RFC 7988,
              DOI 10.17487/RFC7988, October 2016,

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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,

   [RFC8487]  Asaeda, H., Meyer, K., and W. Lee, Ed., "Mtrace Version 2:
              Traceroute Facility for IP Multicast", RFC 8487,
              DOI 10.17487/RFC8487, October 2018,

   [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, <>.

   [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,

9.2.  Informative References

              Mirsky, G., Nainar, N. K., Chen, M., and S. Pallagatti,
              "Operations, Administration and Maintenance (OAM)
              Requirements for Bit Index Explicit Replication (BIER)
              Layer", Work in Progress, Internet-Draft, draft-ietf-bier-
              oam-requirements-11, 15 November 2020,

              Bhandari, S. and F. Brockners, "In-situ OAM IPv6 Options",
              Work in Progress, Internet-Draft, draft-ietf-ippm-ioam-
              ipv6-options-10, 28 February 2023,

              Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z.
              J. Zhang, "SR Replication Segment for Multi-point Service
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              T., Li, Z., Graf, T., Mishra, G. S., Shin, J., and K. Lee,
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              Xie, J., Geng, L., McBride, M., Asati, R., Dhanaraj, S.,
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Authors' Addresses

   Haoyu Song
   Futurewei Technologies
   2330 Central Expressway
   Santa Clara,
   United States of America

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   Mike McBride
   Futurewei Technologies
   2330 Central Expressway
   Santa Clara,
   United States of America

   Greg Mirsky
   ZTE Corp.

   Gyan Mishra
   Verizon Inc.

   Hitoshi Asaeda
   National Institute of Information and Communications Technology
   4-2-1 Nukui-Kitamachi, Tokyo

   Tianran Zhou
   Huawei Technologies

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