BFD for P2MP LSPs: Bidirectional Forwarding Detection (BFD) for Multipoint Networks over Point-to-Multipoint MPLS Label Switched Paths (LSPs)

Internet Engineering Task Force (IETF)                         G. Mirsky
Request for Comments: 9780                                      Ericsson
Updates: 8562                                                  G. Mishra
Category: Standards Track                                   Verizon Inc.
ISSN: 2070-1721                                          D. Eastlake 3rd
                                                             Independent
                                                                May 2025


 Bidirectional Forwarding Detection (BFD) for Multipoint Networks over
          Point-to-Multipoint MPLS Label Switched Paths (LSPs)

Abstract

   This document describes procedures for using Bidirectional Forwarding
   Detection (BFD) for multipoint networks to detect data plane failures
   in point-to-multipoint MPLS Label Switched Paths (LSPs) and Segment
   Routing (SR) point-to-multipoint policies with an SR over MPLS (SR-
   MPLS) data plane.

   Furthermore, this document updates RFC 8562 by recommending the use
   of an IPv6 address from the Dummy IPv6 Prefix address block
   100:0:0:1::/64 and discouraging the use of an IPv4 loopback address
   mapped to IPv6.

   In addition, this document describes the applicability of LSP Ping
   (as an in-band solution) and the control plane (as an out-of-band
   solution) to bootstrap a BFD session.  The document also describes
   the behavior of the active tail for head notification.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9780.

Copyright Notice

   Copyright (c) 2025 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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   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Conventions Used in This Document
     2.1.  Terminology
     2.2.  Requirements Language
   3.  Multipoint BFD Encapsulation
     3.1.  IP Encapsulation of Multipoint BFD
     3.2.  Non-IP Encapsulation of Multipoint BFD
   4.  Bootstrapping Multipoint BFD
     4.1.  LSP Ping
     4.2.  Control Plane
   5.  Operation of Multipoint BFD with Active Tail over P2MP MPLS LSP
   6.  Security Considerations
   7.  IANA Considerations
     7.1.  IPv6 Special-Purpose Address
     7.2.  MPLS Generalized Associated Channel (G-ACh) Type
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   [RFC8562] defines a method of using Bidirectional Forwarding
   Detection (BFD) [RFC5880] to monitor and detect failures between the
   sender (head) and one or more receivers (tails) in multipoint or
   multicast networks.

   [RFC8562] added two BFD session types: MultipointHead and
   MultipointTail.  Throughout this document, MultipointHead and
   MultipointTail refer to the value to which the bfd.SessionType is set
   on a BFD endpoint.

   This document describes procedures for using such modes of the BFD
   protocol to detect data plane failures in point-to-multipoint (P2MP)
   MPLS Label Switched Paths (LSPs) and Segment Routing (SR) point-to-
   multipoint policies with an SR over MPLS (SR-MPLS) data plane.

   The document also describes the applicability of LSP Ping (an in-band
   solution) and out-of-band solutions to bootstrap a BFD session in
   this environment.

   Historically, an address in the IPv6-mapped IPv4 loopback address
   block ::ffff:127.0.0.1/128 was mandated, although functionally, an
   IPv6 address from that address block is not analogous to its IPv4
   counterpart.  Furthermore, using the loopback address as the
   destination address, even for an inner IP encapsulation of a tunneled
   packet, violates Section 2.5.3 of [RFC4291].  Hence, IANA has
   allocated 100:0:0:1::/64 as a new Dummy IPv6 Prefix (Section 7.1) for
   destination IPv6 addresses used for IP/UDP encapsulation of
   management, control, and OAM (Operations, Administration, and
   Maintenance) packets.  A source-only IPv6 dummy address is used as
   the destination to generate an exception and a reply message to the
   request message received.  This document starts the transition to
   using the IPv6 addresses from the Dummy IPv6 Prefix address block
   100:0:0:1::/64 as the IPv6 destination address in the IP/UDP
   encapsulation of active OAM over the MPLS data plane.  Thus, this
   document updates [RFC8562] by recommending the use of an IPv6 address
   from the Dummy IPv6 Prefix address block 100:0:0:1::/64 (Section 7.1)
   while acknowledging that an address from the ::ffff:127.0.0.1/128
   address block might be used by existing implementations.  This
   document discourages the use of an address in the IPv6-mapped IPv4
   loopback address block.

   This document also describes the behavior of the active tail for head
   notification.

2.  Conventions Used in This Document

2.1.  Terminology

   ACH:  Associated Channel Header

   BFD:  Bidirectional Forwarding Detection

   GAL:  G-ACh Label

   G-ACh:  Generic Associated Channel

   LSP:  Label Switched Path

   LSR:  Label Switching Router

   MPLS:  Multiprotocol Label Switching

   P2MP:  Point-to-Multipoint

   PW:  Pseudowire (PW)

   SR:  Segment Routing

   SR-MPLS:  SR over MPLS

2.2.  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.

3.  Multipoint BFD Encapsulation

   [RFC8562] uses BFD in Demand mode from the very start of a point-to-
   multipoint (P2MP) BFD session.  Because the head doesn't receive any
   BFD Control packets from a tail, the head of the P2MP BFD session
   transmits all BFD Control packets with the value of the Your
   Discriminator field set to zero.  As a result, a tail cannot
   demultiplex BFD sessions using Your Discriminator, as defined in
   [RFC5880].  To demultiplex BFD sessions, [RFC8562] requires that the
   tail use the source IP address, My Discriminator, and the identity of
   the multipoint tree from which the BFD Control packet was received.
   If the BFD Control packet is encapsulated in IP/UDP, then the source
   IP address MUST be used to demultiplex the received BFD Control
   packet as described in Section 5.7 of [RFC8562].  The non-IP
   encapsulation case is described in Section 3.2.

3.1.  IP Encapsulation of Multipoint BFD

   [RFC8562] defines IP/UDP encapsulation for multipoint BFD over P2MP
   MPLS LSP.  This document updates Section 5.8 of [RFC8562] regarding
   the selection of the IPv6 destination address as follows:

   *  The sender of an MPLS echo request SHOULD use an address from the
      Dummy IPv6 Prefix address block 100:0:0:1::/64 (see Section 7.1).

   *  The sender of an MPLS echo request MAY select the IPv6 destination
      address from the ::ffff:7f00/104 address block.

   Section 1.2 of [RFC6790] lists several advantages of generating the
   entropy value by an ingress Label Switching Router (LSR) compared to
   when a transit LSR infers entropy using the information in the MPLS
   label stack or payload.  This specification further clarifies the
   following if multiple alternative paths for the given P2MP LSP
   Forwarding Equivalence Class (FEC) exist:

   *  The MultipointHead SHOULD use the Entropy Label [RFC6790] used for
      LSP Ping [RFC8029] to exercise those particular alternative paths;
      or

   *  The MultipointHead MAY use the UDP port number to possibly
      exercise those particular alternate paths.

3.2.  Non-IP Encapsulation of Multipoint BFD

   In some environments, the overhead of extra IP/UDP encapsulations may
   be considered burdensome, which makes the use of more compact Generic
   Associated Channel (G-ACh) [RFC5586] encapsulation attractive.  Also,
   the validation of the IP/UDP encapsulation of a BFD Control packet in
   a P2MP BFD session may fail because of a problem related to neither
   the MPLS label stack nor BFD.  Avoiding unnecessary encapsulation of
   P2MP BFD over an MPLS LSP improves the accuracy of the correlation of
   the detected failure and defect in MPLS LSP.

   Non-IP encapsulation for multipoint BFD over P2MP MPLS LSP (shown in
   Figure 1) MUST use the G-ACh Label (GAL) [RFC5586] at the bottom of
   the label stack followed by an Associated Channel Header (ACH).  If a
   BFD Control packet in PW-ACH encapsulation (without IP/UDP Headers)
   is to be used in ACH, an implementation would not be able to verify
   the identity of the MultipointHead and, as a result, will not
   properly demultiplex BFD packets.  Hence, a new channel type value is
   needed.  The Channel Type field in ACH MUST be set to Multipoint BFD
   Session (0x0013) (see Section 7.2).  To provide the identity of the
   MultipointHead for the particular multipoint BFD session, a Source
   Address TLV, as defined in Section 4.1 of [RFC7212], MUST immediately
   follow a BFD Control packet.  The use of other TLVs is outside the
   scope of this document.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               LSP Label               |  TC |S|       TTL     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  GAL                  |  TC |1|       TTL     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0 0 0 1|Version|     Flags     |      Channel Type = 0x0013    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                        BFD Control Packet                     ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type=0    |    Reserved   |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Reserved            |         Address Family        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                            Address                            ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 1: Non-IP Encapsulation for Multipoint BFD over a
                             Multicast MPLS LSP

   The fields in Figure 1 are interpreted as follows:

   *  The top three four-octet words are defined in [RFC5586].

   *  The BFD Control Packet field is defined in [RFC5880].

   *  All the remaining fields are defined in Section 4.1 of [RFC7212].

4.  Bootstrapping Multipoint BFD

4.1.  LSP Ping

   LSP Ping is the part of the on-demand OAM toolset used to detect and
   localize defects in the data plane and verify the control plane
   against the data plane by ensuring that the LSP is mapped to the same
   FEC at both egress and ingress endpoints.

   LSP Ping, as defined in [RFC6425], MAY be used to bootstrap
   MultipointTail.  If LSP Ping is used, it MUST include the Target FEC
   Stack TLV [RFC8029] and the BFD Discriminator TLV [RFC5884].  For the
   case of P2MP MPLS LSP, the Target FEC Stack TLV MUST use sub-TLVs
   defined in Section 3.1 of [RFC6425].  For the case of P2MP SR policy
   with an SR-MPLS data plane, an implementation of this specification
   MUST follow the procedures defined in [RFC8287].  Setting the value
   of the Reply Mode field to "Do not reply" [RFC8029] for the LSP Ping
   to bootstrap the MultipointTail of the P2MP BFD session is
   RECOMMENDED.  Indeed, because BFD over a multipoint network uses BFD
   Demand mode, the MPLS echo reply from a tail has no useful
   information to convey to the head, unlike in the case of BFD over a
   P2P MPLS LSP [RFC5884].  A MultipointTail that receives an LSP Ping
   that includes the BFD Discriminator TLV MUST do the following:

   *  validate the LSP Ping;

   *  associate the received BFD Discriminator value with the P2MP LSP;

   *  create a P2MP BFD session and set bfd.SessionType = MultipointTail
      as described in [RFC8562]; and

   *  use the source IP address of the LSP Ping, the value of BFD
      Discriminator from the BFD Discriminator TLV, and the identity of
      the P2MP LSP to properly demultiplex BFD sessions.

   Besides bootstrapping a BFD session over a P2MP LSP, LSP Ping SHOULD
   be used to verify the control plane against the data plane
   periodically by checking that the P2MP LSP is mapped to the same FEC
   at the MultipointHead and all active MultipointTails.  The rate of
   generation of these LSP Ping echo request messages SHOULD be
   significantly less than the rate of generation of the BFD Control
   packets because LSP Ping requires more processing to validate the
   consistency between the data plane and the control plane.  An
   implementation MAY provide configuration options to control the rate
   of generation of the periodic LSP Ping echo request messages.

4.2.  Control Plane

   The BFD Discriminator attribute MAY be used to bootstrap a multipoint
   BFD session on a tail, following the format and procedures given in
   Section 3.1.6 of [RFC9026].

5.  Operation of Multipoint BFD with Active Tail over P2MP MPLS LSP

   [RFC8562] defines how BFD Demand mode can be used in multipoint
   networks.  When applied in MPLS, the procedures specified in
   [RFC8562] allow an egress LSR to detect a failure in the part of the
   P2MP MPLS LSP from the ingress LSR to that egress LSR.  The ingress
   LSR is not aware of the state of the P2MP LSP.  [RFC8563], using
   mechanisms defined in [RFC8562], defines the behavior of an active
   tail.  An active tail might notify the head of the detected failure
   and respond to a poll sequence initiated by the head.  The first
   method, referred to as "Head Notification without Polling", is
   mentioned in Section 5.2.1 of [RFC8563]) and is the simplest of the
   methods described in [RFC8563].  The use of this method in BFD over
   P2MP MPLS LSP is discussed in this document.  Analysis of other
   methods for a head to learn of the state of the P2MP MPLS LSP is
   outside the scope of this document.

   As specified in [RFC8563], BFD variables MUST be as follows for the
   active tail mode:

   *  On an ingress LSR:

      -  bfd.SessionType is MultipointHead.

      -  bfd.RequiredMinRxInterval is nonzero, allowing egress LSRs to
         send BFD Control packets.

   *  On an egress LSR:

      -  bfd.SessionType is MultipointTail.

      -  bfd.SilentTail is set to zero.

   Section 5.2.1 of [RFC8563] notes that "the tail sends unsolicited BFD
   packets in response to the detection of a multipoint path failure"
   but does not provide specifics about the information in the packets
   or the frequency of transmissions.  The procedure for an active tail
   with unsolicited notifications for P2MP MPLS LSP is defined below.

   Upon detecting the failure of the P2MP MPLS LSP, an egress LSR sends
   a BFD Control packet with the following settings:

   *  The Poll (P) bit is set.

   *  The Status (Sta) field is set to the Down value.

   *  The Diagnostic (Diag) field is set to the Control Detection Time
      Expired value.

   *  The value of the Your Discriminator field is set to the value the
      egress LSR has been using to demultiplex that BFD multipoint
      session.

   The BFD Control packet MAY be encapsulated in IP/UDP with the
   destination IP address of the ingress LSR and the UDP destination
   port number set to 4784 per [RFC5883].  If non-IP encapsulation is
   used, then a BFD Control packet is encapsulated using PW-ACH
   encapsulation (without IP/UDP Headers) with Channel Type 0x0007
   [RFC5885].

   The BFD Control packets are transmitted at the rate of one per second
   until either 1) the egress LSA receives a control packet from the
   ingress LSR that is valid for this BFD session and has the Final (F)
   bit set or 2) the defect condition clears.  However, to improve the
   likelihood of notifying the ingress LSR of the failure of the P2MP
   MPLS LSP, the egress LSR SHOULD initially transmit three BFD Control
   packets (as defined above) in short succession.  The actual
   transmission of the periodic BFD Control packet MUST be jittered by
   up to 25% within one-second intervals.  Thus, the interval MUST be
   reduced by a random value of 0 to 25%, to reduce the possibility of
   congestion on the ingress LSR's data and control planes.

   As described above, an ingress LSR that has received the BFD Control
   packet sends the unicast IP/UDP encapsulated BFD Control packet with
   the Final (F) bit set to the egress LSR.  In some scenarios (e.g.,
   when a P2MP LSP is broken close to its root and the number of egress
   LSRs is significantly large), the root might receive a large number
   of notifications.  The notifications from leaves to the root will not
   use resources allocated for the monitored multicast flow and, as a
   result, will not congest that particular flow, although they may
   negatively affect other flows.  However, the control plane of the
   ingress LSR might be congested by the BFD Control packets transmitted
   by egress LSRs and the process of generating unicast BFD Control
   packets, as noted above.  To mitigate that, a BFD implementation that
   supports this specification is RECOMMENDED to use a rate limiter of
   received BFD Control packets passed to the ingress LSR's control
   plane for processing.

6.  Security Considerations

   This document does not introduce new security considerations but
   inherits all security considerations from [RFC5880], [RFC5884],
   [RFC7726], [RFC8562], [RFC8029], and [RFC6425].

   Also, BFD for P2MP MPLS LSPs MUST follow the requirements listed in
   Section 4.1 of [RFC4687] to avoid congestion in the control plane or
   the data plane caused by the rate of generating BFD Control packets.
   An operator SHOULD consider the amount of extra traffic generated by
   P2MP BFD when selecting the interval at which the MultipointHead will
   transmit BFD Control packets.  The operator MAY consider the size of
   the packet the MultipointHead transmits periodically as using IP/UDP
   encapsulation, which adds up to 28 octets (more than 50% of the BFD
   Control packet length) compared to G-ACh encapsulation.

7.  IANA Considerations

7.1.  IPv6 Special-Purpose Address

   IANA has allocated the following in the "IANA IPv6 Special-Purpose
   Address Registry" [IANA-IPv6-REG]:

   Address Block:  100:0:0:1::/64
   Name:  Dummy IPv6 Prefix
   RFC:  RFC 9780
   Allocation Date:  2025-04
   Termination Date:  N/A
   Source:  True
   Destination:  False
   Forwardable:  False
   Globally Reachable:  False
   Reserved-by-Protocol:  False

7.2.  MPLS Generalized Associated Channel (G-ACh) Type

   IANA has allocated the following value in the "MPLS Generalized
   Associated Channel (G-ACh) Types" registry [IANA-G-ACh-TYPES].

              +========+========================+===========+
              | Value  |      Description       | Reference |
              +========+========================+===========+
              | 0x0013 | Multipoint BFD Session | RFC 9780  |
              +--------+------------------------+-----------+

                 Table 1: Multipoint BFD Session G-ACh Type

8.  References

8.1.  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>.

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586,
              DOI 10.17487/RFC5586, June 2009,
              <https://www.rfc-editor.org/info/rfc5586>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

   [RFC5883]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
              June 2010, <https://www.rfc-editor.org/info/rfc5883>.

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
              June 2010, <https://www.rfc-editor.org/info/rfc5884>.

   [RFC5885]  Nadeau, T., Ed. and C. Pignataro, Ed., "Bidirectional
              Forwarding Detection (BFD) for the Pseudowire Virtual
              Circuit Connectivity Verification (VCCV)", RFC 5885,
              DOI 10.17487/RFC5885, June 2010,
              <https://www.rfc-editor.org/info/rfc5885>.

   [RFC6425]  Saxena, S., Ed., Swallow, G., Ali, Z., Farrel, A.,
              Yasukawa, S., and T. Nadeau, "Detecting Data-Plane
              Failures in Point-to-Multipoint MPLS - Extensions to LSP
              Ping", RFC 6425, DOI 10.17487/RFC6425, November 2011,
              <https://www.rfc-editor.org/info/rfc6425>.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <https://www.rfc-editor.org/info/rfc6790>.

   [RFC7212]  Frost, D., Bryant, S., and M. Bocci, "MPLS Generic
              Associated Channel (G-ACh) Advertisement Protocol",
              RFC 7212, DOI 10.17487/RFC7212, June 2014,
              <https://www.rfc-editor.org/info/rfc7212>.

   [RFC7726]  Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S.
              Aldrin, "Clarifying Procedures for Establishing BFD
              Sessions for MPLS Label Switched Paths (LSPs)", RFC 7726,
              DOI 10.17487/RFC7726, January 2016,
              <https://www.rfc-editor.org/info/rfc7726>.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [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>.

   [RFC8287]  Kumar, N., Ed., Pignataro, C., Ed., Swallow, G., Akiya,
              N., Kini, S., and M. Chen, "Label Switched Path (LSP)
              Ping/Traceroute for Segment Routing (SR) IGP-Prefix and
              IGP-Adjacency Segment Identifiers (SIDs) with MPLS Data
              Planes", RFC 8287, DOI 10.17487/RFC8287, December 2017,
              <https://www.rfc-editor.org/info/rfc8287>.

   [RFC8562]  Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
              Ed., "Bidirectional Forwarding Detection (BFD) for
              Multipoint Networks", RFC 8562, DOI 10.17487/RFC8562,
              April 2019, <https://www.rfc-editor.org/info/rfc8562>.

   [RFC8563]  Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
              Ed., "Bidirectional Forwarding Detection (BFD) Multipoint
              Active Tails", RFC 8563, DOI 10.17487/RFC8563, April 2019,
              <https://www.rfc-editor.org/info/rfc8563>.

   [RFC9026]  Morin, T., Ed., Kebler, R., Ed., and G. Mirsky, Ed.,
              "Multicast VPN Fast Upstream Failover", RFC 9026,
              DOI 10.17487/RFC9026, April 2021,
              <https://www.rfc-editor.org/info/rfc9026>.

8.2.  Informative References

   [IANA-G-ACh-TYPES]
              IANA, "MPLS Generalized Associated Channel (G-ACh) Types",
              <https://www.iana.org/assignments/g-ach-parameters>.

   [IANA-IPv6-REG]
              IANA, "IANA IPv6 Special-Purpose Address Registry",
              <https://www.iana.org/assignments/iana-ipv6-special-
              registry>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [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,
              <https://www.rfc-editor.org/info/rfc4687>.

Acknowledgements

   The authors sincerely appreciate the comments received from Andrew
   Malis, Italo Busi, and Shraddha Hegde.  The authors also appreciate
   the thought-stimulating questions from Carlos Pignataro.

Authors' Addresses

   Greg Mirsky
   Ericsson
   Email: gregimirsky@gmail.com


   Gyan Mishra
   Verizon Inc.
   Email: gyan.s.mishra@verizon.com


   Donald Eastlake 3rd
   Independent
   2386 Panoramic Circle
   Apopka, FL 32703
   United States of America
   Email: d3e3e3@gmail.com