Bidirectional Forwarding Detection (BFD) for Multipoint Networks over Point-to-Multi-Point MPLS Label Switched Path (LSP)
draft-ietf-mpls-p2mp-bfd-11

MPLS Working Group                                             G. Mirsky
Internet-Draft                                                  Ericsson
Updates: 8562 (if approved)                                    G. Mishra
Intended status: Standards Track                            Verizon Inc.
Expires: 23 August 2025                                      D. Eastlake
                                                             Independent
                                                        19 February 2025

 Bidirectional Forwarding Detection (BFD) for Multipoint Networks over
          Point-to-Multi-Point MPLS Label Switched Path (LSP)
                      draft-ietf-mpls-p2mp-bfd-11

Abstract

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

   Furthermore, this document also updates RFC 8562 and recommends the
   use of an IPv6 address from the Dummy IPv6 range TBA2/64
   (Section 7.1) and discourages the use of an IPv4 loopback address
   mapped to IPv6.

   It also describes the applicability of LSP Ping, as in-band, and the
   control plane, as out-band, solutions to bootstrap a BFD session.

   It also describes the behavior of the active tail for head
   notification.

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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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 23 August 2025.

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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
   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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  Multipoint BFD Encapsulation  . . . . . . . . . . . . . . . .   4
     3.1.  IP Encapsulation of Multipoint BFD  . . . . . . . . . . .   4
     3.2.  Non-IP Encapsulation of Multipoint BFD  . . . . . . . . .   5
   4.  Bootstrapping Multipoint BFD  . . . . . . . . . . . . . . . .   6
     4.1.  LSP Ping  . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Control Plane . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Operation of Multipoint BFD with Active Tail over P2MP MPLS
           LSP . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  IPv6 Address Allocation . . . . . . . . . . . . . . . . .  10
     7.2.  Multipoint BFD over MPLS LSP Associated Channel Type  . .  10
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

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

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   [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 BFD
   protocol to detect data plane failures in Multiprotocol Label
   Switching (MPLS) point-to-multipoint (p2mp) Label Switched Paths
   (LSPs) and Segment Routing (SR) point-to-multipoint policies with SR
   over MPLS (SR-MPLS) data plane

   The document also describes the applicability of out-band solutions
   to bootstrap a BFD session in this environment.

   Historically, an IPv6-mapped IPv4 loopback range
   address::ffff:127.0.0.1/128 was mandated, although functionally, an
   IPv6 address from that range 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 is requested
   to allocate TBA2/64 as a new Dummy IPv6 Prefix (Section 7.1) to
   select destination IPv6 addresses for IP/UDP encapsulation of
   management, control, and OAM 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 draft starts the
   transition to using the IPv6 addresses from the Dummy IPv6 Prefix
   range TBA2/64 as the IPv6 destination address in the IP/UDP
   encapsulation of active OAM over the MPLS data plane.  Thus, this
   document also updates [RFC8562] and recommends the use of an IPv6
   address from the Dummy IPv6 Prefix range TBA2/64 (Section 7.1) while
   acknowledging that an address from ::ffff:127.0.0.1/128 range might
   be used by existing implementations, discourages the use of the
   IPv6-mapped IPv4 loopback range address.

   It 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

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   LSP:  Label Switched Path

   LSR:  Label Switching Router

   MPLS:  Multiprotocol Label Switching

   p2mp:  Point-to-Multipoint

   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 the Demand mode from the very start of a point-
   to-multipoint (p2mp) BFD session.  Because the head doesn't receive
   any BFD Control packet from a tail, the head of the p2mp BFD session
   transmits all BFD Control packets with the value of Your
   Discriminator field set to zero.  As a result, a tail cannot
   demultiplex BFD sessions using Your Discriminator, as defined in
   [RFC5880].  [RFC8562] requires that to demultiplex BFD sessions, the
   tail uses 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 3.1.  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:

   *  The sender of an MPLS echo request SHOULD use an address from the
      Dummy IPv6 Prefix range TBA2/64 Section 7.1.

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

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   The Motivation section [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.  Thus, this
   specification further clarifies that:

      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, making 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 to 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.

   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.

   Non-IP encapsulation for multipoint BFD over p2mp MPLS LSP (shown in
   Figure 1) MUST use G-ACh Label (GAL) (see [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 (TBA1) value (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 message.  The use of other TLVs is outside the
   scope of this document.

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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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               LSP Label               |  TC |S|       TTL     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  GAL                  |  TC |1|       TTL     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0 0 0 1|Version|     Flags     |      Channel Type = TBA1      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                        BFD Control Message                    ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type=0    |    Reserved   |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Reserved            |         Address Family        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                            Address                            ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   Fields in Figure 1 are interpreted as follows:

   *  the top three four-octet words as defined in [RFC5586];

   *  the BFD Control Message field is as defined in [RFC5880];

   *  all the remaining fields are as 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
   TLV and the BFD Discriminator TLV defined in [RFC5884].  For the case
   of p2mp MPLS LSP, the Target FEC TLV MUST use sub-TLVs defined in
   Section 3.1 [RFC6425].  For the case of p2mp SR policy with SR-MPLS
   data plane, an implementation of this specification MUST follow
   procedures defined in [RFC8287].  Setting the value of Reply Mode
   field to "Do not reply" [RFC8029] for the LSP Ping to bootstrap
   MultipointTail of the p2mp BFD session is RECOMMENDED.  Indeed,

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   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 the BFD over a p2p MPLS LSP [RFC5884].  A
   MultipointTail that receives an LSP Ping that includes the BFD
   Discriminator TLV:

   *  MUST validate the LSP Ping;

   *  MUST associate the received BFD Discriminator value with the p2mp
      LSP;

   *  MUST create a p2mp BFD session and set bfd.SessionType =
      MultipointTail as described in [RFC8562];

   *  MUST use the source IP address of 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] defined how the BFD Demand mode can be used in multipoint
   networks.  When applied in MPLS, procedures specified in [RFC8562]
   allow an egress LSR to detect a failure of the part of the MPLS p2mp
   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], defined an "active tail" behavior.  An active
   tail might notify the head of the detected failure and responds 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
   [RFC8563], is the simplest of all described in [RFC8563].  The use of
   this method in BFD over MPLS p2mp LSP is discussed in this document.

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   Analysis of other methods of a head learning of the state of an MPLS
   p2mp LSP is outside the scope of this document.

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

   On an ingress LSR:

   *  bfd.SessionType is MultipointHead;

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

   On an egress LSR:

   *  bfd.SessionType is MultipointTail;

   *  bfd.SilentTail is set to zero.

   In Section 5.2.1 [RFC8563] is noted that "the tail sends unsolicited
   BFD packets in response to the detection of a multipoint path
   failure" but without the specifics on the information in the packet
   and frequency of transmissions.  This document defines below the
   procedure of an active tail with unsolicited notifications for p2mp
   MPLS LSP.

   Upon detecting the failure of the p2mp MPLS LSP, an egress LSR sends
   BFD Control packet with the following settings:

   *  the Poll (P) bit is set;

   *  the Status (Sta) field set to Down value;

   *  the Diagnostic (Diag) field set to 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;

   *  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];

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   *  these BFD Control packets are transmitted at the rate of one per
      second until either it receives a control packet valid for this
      BFD session with the Final (F) bit set from the ingress LSR or 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
      defined above in short succession.  The actual transmission of the
      periodic BFD Control message 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 LSP MUST follow the requirements listed in
   section 4.1 [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, comparing to G-ACh encapsulation.

7.  IANA Considerations

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7.1.  IPv6 Address Allocation

   IANA is requested to allocate an IPv6 TBA2/64 prefix as Dummy IPv6
   Prefix in the "IANA IPv6 Special Purpose Address Registry"
   [IANA-IPv6-Special-Purpose-Address-Registry] as in Table 1.

   +=======+======+=============+==========+===========+======+===========+===========+=========+=========+
   |Address|Name  |RFC          |Allocation|Termination|Source|Destination|Forwardable|Globally |Reserved-|
   |Block  |      |             |Date      |Date       |      |           |           |Reachable|by-      |
   |       |      |             |          |           |      |           |           |         |Protocol |
   +=======+======+=============+==========+===========+======+===========+===========+=========+=========+
   |TBA2   |Dummy |This document|The date  |N/A        |True  |False      |False      |False    |False    |
   |       |IPv6  |             |of        |           |      |           |           |         |         |
   |       |Prefix|             |allocation|           |      |           |           |         |         |
   +-------+------+-------------+----------+-----------+------+-----------+-----------+---------+---------+

                     Table 1: Dummy IPv6 Address Prefix

7.2.  Multipoint BFD over MPLS LSP Associated Channel Type

   IANA is requested to allocate value (TBA1) from its MPLS Generalized
   Associated Channel (G-ACh) Types registry.

            +=======+========================+===============+
            | Value |      Description       | Reference     |
            +=======+========================+===============+
            | TBA1  | Multipoint BFD Session | This document |
            +-------+------------------------+---------------+

                Table 2: Multipoint BFD Session G-ACh Type

8.  Acknowledgements

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

9.  References

9.1.  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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   [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>.

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   [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>.

9.2.  Informative References

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

   [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>.

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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

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