<?xml version="1.0" encoding="utf-8"?>

<!DOCTYPE rfc [
<!ENTITY nbsp "&#160;">
<!ENTITY zwsp "&#8203;">
<!ENTITY nbhy "&#8209;">
<!ENTITY wj "&#8288;">
]>
<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
<?rfc symrefs="yes"?>
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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std" docName="draft-ietf-mpls-p2mp-bfd-11" number="9780" consensus="true" ipr="trust200902" obsoletes="" updates="8562" submissionType="IETF" xml:lang="en" tocInclude="true" tocDepth="3" symRefs="true" sortRefs="true" version="3">

<!-- xml2rfc v2v3 conversion 3.12.0 -->
  <?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?> [rfced] We made the following changes to the document title: 1) updated
"Multi-Point" to "Multipoint" and 2) updated "Label Switched Path (LSP)"
to "Label Switched Paths (LSPs)" (plural). Let us know any concerns.

Original:
  Bidirectional Forwarding Detection (BFD) for Multipoint Networks over
  Point-to-Multi-Point MPLS Label Switched Path (LSP)

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

<!-- [rfced] Please review the following sentences in the abstract and
introduction to ensure that they align with the document title and the
rest of the document. These similar sentences mention SR P2MP policies
with an SR-MPLS data plane, which are not mentioned in the document
title. In addition, we only see SR and SR-MPLS mentioned in one sentence
in Section 4.1 (and in the Terminology section). Are any updates needed?

Document Title:
  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 MPLS point-to-multipoint Label Switched Paths (LSPs) and Segment
   Routing (SR) point-to-multipoint policies with an SR over MPLS (SR-
   MPLS) data plane.

Introduction:
   This document describes procedures for using such modes of the 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 an
   SR over MPLS (SR-MPLS) data plane.
-->

  <front>
    <title abbrev="Multi-Point abbrev="Multipoint BFD over P2MP MPLS LSP">Bidirectional
    Forwarding Detection (BFD) for Multipoint Networks over Point-to-Multi-Point
    Point-to-Multipoint MPLS Label Switched Path (LSP)</title> Paths (LSPs)</title>
    <seriesInfo name="Internet-Draft" value="draft-ietf-mpls-p2mp-bfd-11"/> name="RFC" value="9780"/>
    <author fullname="Greg Mirsky" initials="G." surname="Mirsky">
      <organization>Ericsson</organization>
      <address>
        <postal>
          <street/>
          <city/>
          <code/>
          <country/>
        </postal>
        <email>gregimirsky@gmail.com</email>
      </address>
    </author>
    <author fullname="Gyan Mishra" initials="G. " initials="G." surname="Mishra">
      <organization>Verizon Inc.</organization>
      <address>
        <email>gyan.s.mishra@verizon.com</email>
      </address>
    </author>
    <author fullname="Donald Eastlake, Eastlake 3rd" initials="D. " surname="Eastlake"> initials="D." surname="Eastlake 3rd">
      <organization>Independent</organization>
      <address>
        <postal>
          <street>2386 Panoramic Circle</street>
          <city>Apopka</city>
          <code>FL 32703</code>
          <country>USA</country>
          <region>FL</region><code>32703</code>
          <country>United States of America</country>
        </postal>
        <email>d3e3e3@gmail.com</email>
      </address>
    </author>

    <date year="2025"/>
    <area>Routing</area>
    <workgroup>MPLS Working Group</workgroup>
    <keyword>Internet-Draft</keyword> year="2025" month="May"/>

    <area>RTG</area>
    <workgroup>mpls</workgroup>

    <keyword>BFD</keyword>
    <keyword>Multipoint LSP</keyword>

<!-- [rfced] FYI - We updated "and recommends...and discourages" to "by
recommending...and discouraging" (we also made similar change in the
introduction). Please review and let us know any concerns.

Original:
   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.

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

    <abstract>
      <t>
   This document describes procedures for using Bidirectional Forwarding
   Detection (BFD) for multipoint networks to detect data plane failures
   in Multiprotocol Label Switching (MPLS) MPLS point-to-multipoint
   Label Switched Paths (LSPs) and Segment Routing (SR) point-to-multipoint policies
   with an SR over MPLS (SR-MPLS) data plane.
      </t>
      <t>
   Furthermore, this document also updates RFC 8562 and
   recommends by
   recommending the use of an IPv6 address from the Dummy IPv6 Prefix range TBA2/64 (<xref target="iana-ipv6-addr-alloc-sec"/>) 100:0:0:1::/64
   and discourages discouraging the use of an IPv4 loopback address mapped
   to IPv6.
   </t>
      <t>

<!-- [rfced] How may we update this sentence to improve readability?

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

Perhaps:
   This document also 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.
-->
<!-- [rfced] Please review the following sentences. The first sentence (from
the abstract) mentions both in-band and out-of-band solutions, but the
sentence (from the introduction) only mentions out-of-band
solutions. Should these be aligned?

Original:
   It also describes the applicability of LSP Ping, as in-band, and the
   control plane, as out-band, solutions to bootstrap a BFD session.
   ...
   The document also describes the applicability of out-band solutions
   to bootstrap a BFD session in this environment.
-->

   <t>
   In addition, this document describes the applicability of LSP Ping, as
   in-band, and the control plane, as out-of-band, solutions to bootstrap a
   BFD session.  The document also describes the behavior of the active tail for head
   notification.
      </t>
    </abstract>
  </front>

  <middle>
    <section anchor="intro-section" numbered="true" toc="default">
      <name>Introduction</name>
      <t>
      <xref target="RFC8562"/> defines a method of using Bidirectional Forwarding Detection (BFD) <xref target="RFC5880"/>
      to monitor and detect failures between the sender
   (head) and one or more receivers (tails) in multipoint or multicast
   networks.
      </t>
      <t>
   <xref target="RFC8562"/> added two BFD session types - 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.
      </t>

      <t>
      This document describes procedures for using such
   modes of the BFD protocol to detect data plane failures in Multiprotocol
   Label Switching (MPLS) MPLS point-to-multipoint (p2mp) (P2MP) Label Switched
   Paths (LSPs) and Segment Routing (SR) point-to-multipoint policies
   with an SR over MPLS (SR-MPLS) data plane plane.
      </t>
      <t>
   The document also describes the applicability of out-band out-of-band
   solutions to bootstrap a BFD session in this environment.
      </t>

<!-- [rfced] Please reivew "to select destination IPv6 addresses for"
here. Would updating as follows make this text more clear?

Original:
   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.

Perhaps:
   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 Operations, Administration, and Maintenance
   (OAM) packets.
-->

<!-- [rfced] We see both of the following in Section 1:

address::ffff:127.0.0.1/128
::ffff:127.0.0.1/128

Should "address::ffff:127.0.0.1/128" be updated as follows?

Current:
   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.

Perhaps:
   Historically, an address in the IPv6-mapped IPv4 loopback range
   ::ffff:127.0.0.1/128 was mandated, although functionally, an
   IPv6 address from that range is not analogous to its IPv4
   counterpart.
-->

<!-- [rfced] To improve readabilty, we split this long sentence into two
sentences. Would it be helpful to further update to use
"::ffff:127.0.0.1/128 range" instead of "IPv6-mapped IPv4 loopback range
address" in the second sentence?

Original:
   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.

Current:
   Thus, this
   document updates [RFC8562] by recommending the use of an IPv6 address
   from the Dummy IPv6 Prefix range 100:0:0:1::/64 (Section 7.1) while
   acknowledging that an address from the ::ffff:127.0.0.1/128 range
   might be used by existing implementations.  This document discourages
   the use of an address in the IPv6-mapped IPv4 loopback range.

Perhaps:
   Thus, this
   document updates [RFC8562] by recommending the use of an IPv6 address
   from the Dummy IPv6 Prefix range 100:0:0:1::/64 (Section 7.1) while
   acknowledging that an address from the ::ffff:127.0.0.1/128 range
   might be used by existing implementations.  This document discourages
   the use of an address from the ::ffff:127.0.0.1/128 range.
-->

      <t>
   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 packet,
   violates Section 2.5.3 of <xref target="RFC4291"/>. target="RFC4291" sectionFormat="of" section="2.5.3"/>. Hence, IANA is requested to allocate
   TBA2/64 has allocated
   100:0:0:1::/64 as a new Dummy IPv6 Prefix (<xref target="iana-ipv6-addr-alloc-sec"/>)
   to select destination IPv6 addresses for IP/UDP encapsulation of management, control, and OAM Operations, Administration, and Maintenance (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 document starts the transition to using the IPv6 addresses from the Dummy IPv6 Prefix range TBA2/64 100:0:0:1::/64 as the IPv6 destination address
   in the IP/UDP encapsulation of active OAM over the MPLS data plane.
   Thus, this document also updates <xref target="RFC8562"/> and recommends by recommending the use of an IPv6 address from the
   Dummy IPv6 Prefix range TBA2/64 100:0:0:1::/64 (<xref target="iana-ipv6-addr-alloc-sec"/>) while
   acknowledging that an address from ::ffff:127.0.0.1/128 range the ::ffff:127.0.0.1/128&nbsp;range might be used by existing implementations, implementations. This document
   discourages the use of an address in the IPv6-mapped IPv4 loopback range address. range.
   </t>
      <t>
   It
   This document also describes the behavior of the active tail for head notification.
      </t>
    </section>
    <section numbered="true" toc="default">
      <name>Conventions used Used in this document</name> This Document</name>
      <section numbered="true" toc="default">
        <name>Terminology</name>
        <dl>
        <dt>ACH:</dt><dd>Associated Channel Header</dd>
        <dt>BFD:</dt><dd>Bidirectional Forwarding Detection</dd>
        <dt>GAL:</dt><dd>G-ACh Label</dd>
        <dt>G-ACh:</dt><dd>Generic Associated Channel</dd>
        <dt>LSP:</dt><dd>Label Switched Path</dd>
        <dt>LSR:</dt><dd>Label Switching Router</dd>
        <dt>MPLS:</dt><dd>Multiprotocol Label Switching</dd>
        <dt>p2mp:</dt><dd>Point-to-Multipoint</dd>
        <dt>P2MP:</dt><dd>Point-to-Multipoint</dd>
	<dt>PW:</dt><dd>Pseudowire (PW)</dd>
        <dt>SR:</dt><dd>Segment Routing</dd>
        <dt>SR-MPLS:</dt><dd>SR over MPLS</dd>
      </dl>
      </section>
      <section numbered="true" toc="default">
        <name>Requirements Language</name>
        <t>
    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
   "MAY", "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
    "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
    NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
    "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and "OPTIONAL" "<bcp14>OPTIONAL</bcp14>" in this document are
    to be interpreted as described in BCP 14 BCP&nbsp;14 <xref target="RFC2119" format="default"/> target="RFC2119"/>
    <xref target="RFC8174" format="default"/> target="RFC8174"/> when, and only when, they appear in all capitals,
    as shown here.
        </t>
      </section>
    </section>
    <section anchor="encaps-section" numbered="true" toc="default">
      <name>Multipoint BFD Encapsulation</name>

<!-- [rfced] We do not see "demultiplex" in Section 3.1. Please review and let
us know if any updates are needed.

Original:
   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.
-->

      <t>
      <xref target="RFC8562" format="default"/> uses BFD in the Demand mode
      from the very start of a point-to-multipoint (p2mp) (P2MP) BFD session. Because the
      head doesn't receive any BFD Control packet packets from a tail, the head of the p2mp 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 <xref target="RFC5880" format="default"/>.
      To demultiplex BFD sessions, <xref target="RFC8562" format="default"/> requires that to demultiplex BFD sessions,
      the tail uses 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
      <bcp14>MUST</bcp14> be used to demultiplex the received BFD Control packet as described in <xref target="ip-encaps-section" format="default"/>.
      The non-IP encapsulation case is described in <xref target="non-ip-encaps-section" format="default"/>.
      </t>
      <section anchor="ip-encaps-section" numbered="true" toc="default">
        <name>IP Encapsulation of Multipoint BFD</name>
        <t>
        <xref target="RFC8562" format="default"/> defines IP/UDP encapsulation for multipoint BFD
        over p2mp P2MP MPLS LSP. This document updates Section 5.8 of <xref target="RFC8562"/> target="RFC8562" sectionFormat="of" section="5.8"/> regarding the selection of
        the IPv6 destination address: address as follows:
        </t>

      <ul spacing="normal">
      <li>The sender of an MPLS echo request SHOULD <bcp14>SHOULD</bcp14> use an address from
      the Dummy IPv6 Prefix range TBA2/64 100:0:0:1::/64 (see <xref target="iana-ipv6-addr-alloc-sec"/>.</li> target="iana-ipv6-addr-alloc-sec"/>).</li>
      <li>The sender of an MPLS echo request MAY <bcp14>MAY</bcp14> select the IPv6 destination  address from the ::ffff:7f00/104 range.</li>
      </ul>

        <t>

<!-- [rfced] Should the introductory text include the first part of the
indented text here?

Original:
   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.

Perhaps:
   This
   specification further clarifies the following if multiple alternative paths
   for the given P2MP LSP Forwarding Equivalence Class (FEC) exist:

   *  The Motivation section <xref 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.
-->

      <t><xref target="RFC6790" sectionFormat="of" section="1.2" format="default"/>
      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
      This specification further clarifies that:
        </t> that:</t>
        <ul empty="true" spacing="normal">
          <li>if multiple alternative paths for the given p2mp P2MP LSP Forwarding
          Equivalence Class (FEC) exist, the MultipointHead
        SHOULD
          <bcp14>SHOULD</bcp14> use the Entropy Label <xref target="RFC6790"
          format="default"/> used for LSP Ping <xref target="RFC8029"
          format="default"/> to exercise those particular alternative
          paths;</li>
        <li>

       or
          <li>or the MultipointHead MAY <bcp14>MAY</bcp14> use the UDP port
          number to possibly exercise those particular alternate paths.
        </li> paths.</li>
        </ul>

      </section>
      <section anchor="non-ip-encaps-section" numbered="true" toc="default">
        <name>Non-IP Encapsulation of Multipoint BFD</name>
        <t>
          In some environments, the overhead of extra IP/UDP encapsulations may be
   considered burdensome, making which makes the use of more compact Generic Associated Channel (G-ACh) (<xref target="RFC5586"/>) <xref target="RFC5586"/>
   encapsulation attractive. Also, the validation of the IP/UDP encapsulation of a BFD Control packet in a p2mp P2MP BFD session
   may fail because of a problem related to neither the MPLS label stack nor to BFD. Avoiding unnecessary encapsulation
   of p2mp P2MP BFD over an MPLS LSP improves the accuracy of the correlation of the detected failure and defect in MPLS LSP.
   </t>
<!-- [rfced] The following sentences appear twice in Section 3.2 (as the
second paragraph and in the third paragraph). Which should be removed?

Original:
   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.
-->

   <t>
      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.
   </t>
   <t>
     Non-IP encapsulation for multipoint BFD over p2mp P2MP MPLS LSP (shown in <xref target="non-ip-p2mp-bfd-pic" format="default"/>)
     MUST
     <bcp14>MUST</bcp14> use the G-ACh Label (GAL) (see <xref target="RFC5586" format="default"/>) format="default"/> 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 <bcp14>MUST</bcp14> be set to
        Multipoint BFD Session (TBA1) value (<xref (0x0013) (see <xref target="iana-ach-sec"/>). To provide the identity of the MultipointHead for the particular
        multipoint BFD session, a Source Address TLV, as defined in Section 4.1 of <xref target="RFC7212" format="default"/>,
        MUST sectionFormat="of" section="4.1"/>,
        <bcp14>MUST</bcp14> immediately follow a BFD Control message. The use of other TLVs is outside the scope of this document.
        </t>

      <figure anchor="non-ip-p2mp-bfd-pic">
          <name>Non-IP Encapsulation for Multipoint BFD Over over a Multicast MPLS LSP</name>
          <artwork name="" type="" align="left" alt=""><![CDATA[
 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 0x0013    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                        BFD Control Message                    ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type=0    |    Reserved   |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Reserved            |         Address Family        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                            Address                            ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
        </figure>
<t>Fields
<t>The fields in <xref target="non-ip-p2mp-bfd-pic"/> are interpreted as follows:</t>
<ul>
<li>the

<!-- [rfced] Would it be helpful to clarify "the top three four-octet words"
here? Will readers understand what is defined in RFC 5586?

Original:
  *  the top three four-octet words as defined in <xref target="RFC5586"/>;</li>
<li>the [RFC5586];
-->

<!-- [rfced] We do not see mention of "BFD Control Message" in [RFC5880].
Please review.

Original:
   *  the BFD Control Message field is as defined in [RFC5880];
-->
<ul>
<li>The top three four-octet words are defined in <xref target="RFC5586"/>.</li>
<li>The BFD Control Message field is defined in <xref target="RFC5880"/>;</li>
<li>all target="RFC5880"/>.</li>
<li>All the remaining fields are as defined in Section 4.1 of <xref target="RFC7212"/>.</li> target="RFC7212" sectionFormat="of" section="4.1"/>.</li>
</ul>
      </section>
    </section>
    <section anchor="bootstrapping-section" numbered="true" toc="default">
      <name>Bootstrapping Multipoint BFD</name>
      <section anchor="lsp-section" numbered="true" toc="default">
        <name>LSP Ping</name>
        <t>
        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.
        </t>
        <t>

<!-- [rfced] Should the two instances of "Target FEC TLV" here be "Target FEC
Stack TLV"? We see "Target FEC Stack TLV" in RFC 6425.

Original:
   LSP Ping, as defined in <xref target="RFC6425" format="default"/>, [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 <xref target="RFC5884" format="default"/>. [RFC5884].  For the case
   of p2mp MPLS LSP, the Target FEC TLV MUST use sub-TLVs defined in
   Section 3.1 [RFC6425].
-->

        <t>
      LSP Ping,  as defined in <xref target="RFC6425" format="default"/>, <bcp14>MAY</bcp14> be used to bootstrap MultipointTail. If LSP Ping is used,
        it <bcp14>MUST</bcp14> include the Target FEC TLV and the BFD Discriminator TLV defined in <xref target="RFC5884" format="default"/>. For the case of p2mp P2MP MPLS LSP, the Target FEC TLV
        <bcp14>MUST</bcp14> use sub-TLVs defined in <xref target="RFC6425" sectionFormat="of" section="3.1"/>. For the case of P2MP SR policy with an SR-MPLS data plane,
        an implementation of this specification MUST <bcp14>MUST</bcp14> follow the procedures defined in <xref target="RFC8287" format="default"/>. Setting the value
        of the Reply Mode field to "Do not reply" <xref target="RFC8029"/> for the  LSP Ping to bootstrap the MultipointTail of the p2mp P2MP BFD session is RECOMMENDED. <bcp14>RECOMMENDED</bcp14>.
        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 the BFD over a p2p P2P MPLS LSP <xref target="RFC5884" format="default"/>.
        A MultipointTail that receives an LSP Ping that includes the BFD Discriminator TLV:
        </t>

<!-- [rfced] May we update the introductory text to use "MUST" and remove
"MUST" from each bullet? Or do you prefer the current?

Original:
   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.

Perhaps:
   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.
-->

        <ul spacing="normal">
          <li>
        MUST
        <bcp14>MUST</bcp14> validate the LSP Ping;
        </li>
          <li>
        MUST
        <bcp14>MUST</bcp14> associate the received BFD Discriminator value with the p2mp P2MP LSP;
        </li>
          <li>
        MUST
        <bcp14>MUST</bcp14> create a p2mp P2MP BFD session and set bfd.SessionType =
      MultipointTail as described in <xref target="RFC8562" format="default"/>; and
      </li>
          <li>
      MUST
      <bcp14>MUST</bcp14> 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 P2MP LSP
       to properly demultiplex BFD sessions.</li>
        </ul>
        <t>
        Besides bootstrapping a BFD session over a p2mp P2MP LSP, LSP Ping SHOULD <bcp14>SHOULD</bcp14> be used to verify the control plane
        against the data plane periodically by checking that the p2mp 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 <bcp14>SHOULD</bcp14> 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 <bcp14>MAY</bcp14> provide configuration
   options to control the rate of generation of the periodic LSP Ping Echo request messages.
        </t>
      </section>
      <section anchor="control-plane-section" numbered="true" toc="default">
        <name>Control Plane</name>
        <t>
           The BFD Discriminator Attribute MAY attribute <bcp14>MAY</bcp14> be used to bootstrap a multipoint
   BFD session on a tail, following the format and procedures given in
   Section 3.1.6 of
   <xref target="RFC9026" format="default"/>. sectionFormat="of" section="3.1.6"/>.
   </t>
      </section>
    </section>
    <section anchor="operation-sec" numbered="true" toc="default">
      <name>Operation of Multipoint BFD with Active Tail over P2MP MPLS LSP</name>

      <t>
<xref target="RFC8562" format="default"/> defined defines how the BFD Demand mode can be used in multipoint networks.
When applied in MPLS, the procedures specified in <xref target="RFC8562" format="default"/> allow an egress LSR to detect a failure of in the part of the MPLS p2mp P2MP LSP
from the ingress LSR to that egress LSR. The ingress LSR is not aware of the state of the p2mp P2MP LSP.  <xref target="RFC8563" format="default"/>, using mechanisms defined in <xref target="RFC8562" format="default"/>,
defined
defines the behavior of an "active tail" behavior. active tail. An active tail might notify the head of the detected failure and responds respond to a poll sequence initiated by the head.
The first method, referred to as Head "Head Notification without Polling, Polling", is mentioned in Section 5.2.1 <xref target="RFC8563" format="default"/>, sectionFormat="of" section="5.2.1"/>) and
is the simplest of all the methods described in <xref target="RFC8563" format="default"/>.
The use of this method in BFD over MPLS p2mp P2MP LSP is discussed in this document.
Analysis of other methods of for a head learning to learn of the state of an MPLS p2mp P2MP LSP is outside the scope of this document.
</t>
      <t>
As specified in <xref target="RFC8563" format="default"/> for the active tail mode, format="default"/>, BFD variables MUST <bcp14>MUST</bcp14> be as follows: follows for the active tail mode:
</t>
      <t>On

<ul spacing="normal">
      <li><t>On an ingress LSR:
</t> LSR:</t>

      <ul spacing="normal">
        <li>bfd.SessionType is MultipointHead;</li> MultipointHead.</li>
        <li>bfd.RequiredMinRxInterval is set to nonzero, allowing egress LSRs to send BFD Control packets.</li>
      </ul>
      <t>On
      </li>
      <li><t>On an egress LSR:
</t> LSR:</t>

      <ul spacing="normal">
        <li>bfd.SessionType is MultipointTail;</li> MultipointTail.</li>
        <li>bfd.SilentTail is set to zero.</li>
      </ul>
      </li>
</ul>
      <t>
In Section 5.2.1
	<xref target="RFC8563" format="default"/> is noted sectionFormat="of" section="5.2.1"/> notes that "the tail sends unsolicited BFD packets in response
to the detection of a multipoint path failure" but without the does not provide specifics on about the information in the packet and packets or the frequency of transmissions.
This document defines below the
The procedure of for an active tail with unsolicited notifications for p2mp P2MP MPLS LSP. LSP is defined below.
</t>
      <t>Upon detecting the failure of the p2mp P2MP MPLS LSP, an egress LSR sends a BFD Control packet with the following settings:
</t>
      <ul spacing="normal">
        <li>the
        <li>The Poll (P) bit is set;</li>
        <li>the set.</li>
        <li>The Status (Sta) field is set to the Down value;</li>
        <li>the value.</li>
        <li>The Diagnostic (Diag) field is set to the Control Detection Time Expired value;</li>
        <li>the value.</li>
        <li>The value of the Your Discriminator field is set to the value the egress LSR has been using to demultiplex that BFD multipoint session;</li> session.</li>
        <li>
The BFD Control packet MAY <bcp14>MAY</bcp14> be encapsulated in IP/UDP with the destination IP address of the ingress LSR
and the UDP destination port number set to 4784 per <xref target="RFC5883" format="default"/>. 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 <xref target="RFC5885" format="default"/>; format="default"/>.
	</li>
        <li>

<!-- [rfced] The second bulleted list in Section 5 is prefaced with the
following text. However, it looks like only the first four bullets detail
settings. Should the last two bullets be regular paragraphs rather than
part of the list? Or should this introductory text be updated?

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

<!-- [rfced] What does "it" refer to here?

Original:
   *  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.

Perhaps:
   *  These 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.
-->

<!-- [rfced] Please clarify "defined above" here. Is the intent "as defined
above" (with "as"), "with the settings described above", or something
else?

Original:
   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.

Perhaps:
   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.
-->

        <li>
The BFD Control packets are transmitted at the rate of one per second
  until either 1) it receives a control packet valid for this BFD session
  with the Final (F) bit set from the ingress LSR 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 <bcp14>SHOULD</bcp14> initially transmit three BFD Control packets defined above in short succession.
  The actual transmission of the periodic BFD Control message MUST <bcp14>MUST</bcp14> be jittered by up to 25% within one-second intervals.
  Thus, the interval MUST <bcp14>MUST</bcp14> 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.
  </li>
      </ul>
      <t>
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., scenarios (e.g., when a p2mp P2MP LSP is broken close to its root, root and the number of egress LSRs is significantly large, 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 <bcp14>RECOMMENDED</bcp14> to use a rate limiter
of received BFD Control packets passed to the ingress LSR’s LSR's control plane for processing.
</t>
    </section>
    <section anchor="Security" numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>
      This document does not introduce new security considerations but inherits all security considerations
      from <xref target="RFC5880" format="default"/>, <xref target="RFC5884" format="default"/>, <xref target="RFC7726" format="default"/>,
      <xref target="RFC8562" format="default"/>, <xref target="RFC8029" format="default"/>, and <xref target="RFC6425" format="default"/>.
      </t>

      <t>
      Also, BFD for p2mp P2MP MPLS LSP MUST LSPs <bcp14>MUST</bcp14> follow the requirements listed in section 4.1 <xref target="RFC4687" format="default"/> sectionFormat="of" section="4.1"/> to avoid congestion
      in the control plane or the data plane caused by the rate of generating BFD Control packets. An operator SHOULD <bcp14>SHOULD</bcp14>
      consider the amount of extra traffic generated by p2mp P2MP BFD when selecting the interval at which the
      MultipointHead will transmit BFD Control packets. The operator MAY <bcp14>MAY</bcp14> consider the size of the packet the MultipointHead transmits
      periodically as using IP/UDP encapsulation, which adds up to 28 octets, more octets (more than 50%
      of the BFD Control packet length, comparing length) compared to G-ACh encapsulation.
      </t>
    </section>

    <section anchor="iana-sec" numbered="true" toc="default">
      <name>IANA Considerations</name>
      <!--
      <section anchor="iana-ipv4-addr-alloc-sec" anchor="iana-ipv6-addr-alloc-sec" numbered="true" toc="default">
      <name>IPv4 Address Allocation</name>
      <name>IPv6 Special-Purpose Address</name>
      <t>
      IANA is requested to allocate an IPv4 TBA3/24 prefix as Associated Channel IPv4/UDP Prefix has allocated the following in the "Internet
   Protocol Version 4 "IANA
   IPv6 Special-Purpose Address Space" and add the prefix Registry" <xref target="IANA-IPv6-REG"/>:
      </t>
<!-- [rfced] FYI - We updated Table 2 to <dl> as the table was too wide for
the txt output. Note that <dl> was used in other RFCs that have made
allocations in the "IANA
   IPv4 Special Purpose IPv6 Special-Purpose Address Registry".
   </t>
      </section> Registry" (e.g.,
RFCs 9637, 9602, and 9374).
-->
      <section anchor="iana-ipv6-addr-alloc-sec" numbered="true" toc="default">
      <name>IPv6 Address Allocation</name>
      <t>
      IANA

<!-- [rfced] An informative reference is requested to allocate an IPv6 TBA2/64 prefix as Dummy IPv6 Prefix in listed for the "IANA IPv6 Special
Purpose Address Registry" <xref target="IANA-IPv6-Special-Purpose-Address-Registry"/>
    as in <xref target="dummy-ipv6-range-table"/>.
   </t>
       <table anchor="dummy-ipv6-range-table" align="center">
        <name>Dummy IPv6 Address Prefix</name>
        <thead>
          <tr>
            <th align="left">Address Block</th>
            <th align="left">Name</th>
            <th align="left">RFC</th>
            <th align="left">Allocation Date</th>
            <th align="left">Termination Date</th>
            <th align="left">Source</th>
            <th align="left">Destination</th>
            <th align="left">Forwardable</th>
            <th align="left">Globally Reachable</th>
            <th align="left">Reserved-by-Protocol</th>
          </tr>
        </thead>
        <tbody>
          <tr>
            <td align="left">TBA2</td>
            <td align="left">Dummy Section 7.1. Would you like to also add an
informative reference for the "MPLS Generalized Associated Channel
(G-ACh) Types" registry in Section 7.2?
-->

      <dl spacing="compact">
<dt>Address Block:</dt><dd>100:0:0:1::/64</dd>
<dt>Name:</dt><dd>Dummy IPv6 Prefix</td>
            <td align="left">This document</td>
            <td align="left">The date of allocation</td>
            <td align="left">N/A</td>
            <td align="left">True</td>
            <td align="left">False</td>
            <td align="left">False</td>
            <td align="left">False</td>
            <td align="left">False</td>
          </tr>
        </tbody>
      </table> Prefix</dd>
<dt>RFC:</dt><dd>RFC 9780</dd>
<dt>Allocation Date:</dt><dd>2025-04</dd>
<dt>Termination Date:</dt><dd>N/A</dd>
<dt>Source:</dt><dd>True</dd>
<dt>Destination:</dt><dd>False</dd>
<dt>Forwardable:</dt><dd>False</dd>
<dt>Globally Reachable:</dt><dd>False</dd>
<dt>Reserved-by-Protocol:</dt><dd>False</dd>
      </dl>
      </section>

      <section anchor="iana-ach-sec" numbered="true" toc="default">
      <name>Multipoint BFD over MPLS LSP
      <name>MPLS Generalized Associated Channel (G-ACh) Type</name>
    <t>
    IANA is requested to allocate has allocated the following value (TBA1) from its MPLS in the "MPLS Generalized Associated Channel (G-ACh) Types Types" registry.
      </t>
      <table anchor="p2mp-ach-table" align="center">
        <name>Multipoint BFD Session G-ACh Type</name>
        <thead>
          <tr>
            <th align="left">Value</th>
            <th align="center">Description</th>
            <th align="left">Reference</th>
          </tr>
        </thead>
        <tbody>
          <tr>
            <td align="left">TBA1</td> align="left">0x0013</td>
            <td align="center">Multipoint BFD Session</td>
            <td align="left">This document</td> align="left">RFC 9780</td>
          </tr>
        </tbody>
      </table>
      </section>
    </section>

    <section anchor="Acknowledgements" numbered="true" toc="default">
      <name>Acknowledgements</name>
      <t>
      The authors sincerely appreciate the comments received from Andrew Malis, Italo Busi, Shraddha Hegde,
      and thought stimulating questions from Carlos Pignataro.
      </t>
    </section>

  </middle>

  <back>
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5880.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5880.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5884.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5884.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8029.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8029.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8287.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8287.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6790.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6790.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5586.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5586.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7212.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7212.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6425.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6425.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7726.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7726.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8562.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8562.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8563.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8563.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5883.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5883.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5885.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5885.xml"/>
	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.9026.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9026.xml"/>
      </references>
      <references>
        <name>Informative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4687.xml"/> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4687.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4291.xml"/>
         <!-- <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5952.xml"/> --> href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4291.xml"/>

<reference anchor="IANA-IPv6-Special-Purpose-Address-Registry" target="https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml"> anchor="IANA-IPv6-REG" target="https://www.iana.org/assignments/iana-ipv6-special-registry">
        <front>
            <title>IANA IPv6 Special-Purpose Address Registry</title>
            <author>
              <organization>IANA</organization>
            </author>
          </front>
        </reference>

      </references>
    </references>
    <section anchor="Acknowledgements" numbered="false" toc="default">
      <name>Acknowledgements</name>
      <t>The authors sincerely appreciate the comments received from <contact
      fullname="Andrew Malis"/>, <contact fullname="Italo Busi"/>, and
      <contact fullname="Shraddha Hegde"/>. The authors also appreciate the
      thought-stimulating questions from <contact fullname="Carlos
      Pignataro"/>.</t>
    </section>

  </back>

<!-- [rfced] Terminology

a) We see the following forms used in this document. Should "P2MP" or "MPLS"
come first in this phrase?

p2mp MPLS LSP
MPLS p2mp LSP
Point-to-Multipoint MPLS Label Switched Path (LSP)
MPLS point-to-multipoint Label Switched Paths (LSPs)

b) Please review the instances of "echo" in the document and let us know if
they should be capitalized or lowercased.

MPLS echo reply
MPLS echo request
LSP Ping Echo request message

c) We have updated "out-band" to "out-of-band" (two instances). Let us know any
objections.

d) Would either of the following read more clearly? Or is the current okay?

Current:
  the Dummy IPv6 Prefix range 100:0:0:1::/64

Perhaps ("address block" instead of "range"):
  the Dummy IPv6 Prefix address block 100:0:0:1::/64

Or ("address block" and parentheses):
  the Dummy IPv6 Prefix address block (100:0:0:1::/64)
-->

<!-- [rfced] Abbreviations

a) We updated "p2mp" (lowercase) to "P2MP" (caps). The capitalized form is much
more common in published RFCs, including in RFCs 9026 and 6425, which are
normatively referenced by this document.

b) FYI - We have added expansions for the following abbreviations
per Section 3.6 of RFC 7322 ("RFC Style Guide"). Please review each
expansion in the document carefully to ensure correctness.

Operations, Administration, and Maintenance (OAM)
Pseudowire (PW)
-->

<!-- [rfced] Please review the "Inclusive Language" portion of the online
Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language>
and let us know if any changes are needed.  Updates of this nature typically
result in more precise language, which is helpful for readers.

For example, please consider whether the following should be updated:

Dummy
-->

</rfc>