Ericsson

gregimirsky@gmail.com

Verizon Inc.

gyan.s.mishra@verizon.com

Independent

2386 Panoramic Circle Apopka FL 32703 United States of America d3e3e3@gmail.com

RTG mpls BFD Multipoint LSP 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 .

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 () in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.

Table of Contents

• .  Introduction
• .  Conventions Used in This Document
  • .  Terminology
  • .  Requirements Language
• .  Multipoint BFD Encapsulation
  • .  IP Encapsulation of Multipoint BFD
  • .  Non-IP Encapsulation of Multipoint BFD
• .  Bootstrapping Multipoint BFD
  • .  LSP Ping
  • .  Control Plane
• .  Operation of Multipoint BFD with Active Tail over P2MP MPLS LSP
• .  Security Considerations
• .  IANA Considerations
  • .  IPv6 Special-Purpose Address
  • .  MPLS Generalized Associated Channel (G-ACh) Type
• .  References
  • .  Normative References
  • .  Informative References
• Acknowledgements
• Authors' Addresses

Introduction defines a method of using Bidirectional Forwarding Detection (BFD) to monitor and detect failures between the sender (head) and one or more receivers (tails) in multipoint or multicast networks. 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 . Hence, IANA has allocated 100:0:0:1::/64 as a new Dummy IPv6 Prefix () 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 by recommending the use of an IPv6 address from the Dummy IPv6 Prefix address block 100:0:0:1::/64 () 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.

Conventions Used in This Document

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

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 when, and only when, they appear in all capitals, as shown here.

Multipoint BFD Encapsulation 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 . To demultiplex BFD sessions, 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 . The non-IP encapsulation case is described in .

IP Encapsulation of Multipoint BFD defines IP/UDP encapsulation for multipoint BFD over P2MP MPLS LSP. This document updates 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 ).
• The sender of an MPLS echo request MAY select the IPv6 destination address from the ::ffff:7f00/104 address block.

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 used for LSP Ping to exercise those particular alternative paths; or
• The MultipointHead MAY use the UDP port number to possibly exercise those particular alternate paths.

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) 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 ) MUST use the G-ACh Label (GAL) 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 ). To provide the identity of the MultipointHead for the particular multipoint BFD session, a Source Address TLV, as defined in , MUST immediately follow a BFD Control packet. The use of other TLVs is outside the scope of this document.

Non-IP Encapsulation for Multipoint BFD over a Multicast MPLS LSP 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 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The fields in are interpreted as follows:

• The top three four-octet words are defined in .
• The BFD Control Packet field is defined in .
• All the remaining fields are defined in .

Bootstrapping Multipoint BFD

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 , MAY be used to bootstrap MultipointTail. If LSP Ping is used, it MUST include the Target FEC Stack TLV and the BFD Discriminator TLV . For the case of P2MP MPLS LSP, the Target FEC Stack TLV MUST use sub-TLVs defined in . For the case of P2MP SR policy with an SR-MPLS data plane, an implementation of this specification MUST follow the procedures defined in . Setting the value of the Reply Mode field to "Do not reply" 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 . 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 ; 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.

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 .

Operation of Multipoint BFD with Active Tail over P2MP MPLS LSP defines how BFD Demand mode can be used in multipoint networks. When applied in MPLS, the procedures specified in 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. , using mechanisms defined in , 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 ) and is the simplest of the methods described in . 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 , 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.

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 . 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 . 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.

Security Considerations This document does not introduce new security considerations but inherits all security considerations from , , , , , and . Also, BFD for P2MP MPLS LSPs MUST follow the requirements listed in 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.

IANA Considerations

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

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

MPLS Generalized Associated Channel (G-ACh) Type IANA has allocated the following value in the "MPLS Generalized Associated Channel (G-ACh) Types" registry . Multipoint BFD Session G-ACh Type

Value	Description	Reference
0x0013	Multipoint BFD Session	RFC 9780

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document generalizes the applicability of the pseudowire (PW) Associated Channel Header (ACH), enabling the realization of a control channel associated to MPLS Label Switched Paths (LSPs) and MPLS Sections in addition to MPLS pseudowires. In order to identify the presence of this Associated Channel Header in the label stack, this document also assigns one of the reserved MPLS label values to the Generic Associated Channel Label (GAL), to be used as a label based exception mechanism. This document describes a protocol intended to detect faults in the bidirectional path between two forwarding engines, including interfaces, data link(s), and to the extent possible the forwarding engines themselves, with potentially very low latency. It operates independently of media, data protocols, and routing protocols. [STANDARDS-TRACK] This document describes the use of the Bidirectional Forwarding Detection (BFD) protocol over multihop paths, including unidirectional links. [STANDARDS-TRACK] One desirable application of Bidirectional Forwarding Detection (BFD) is to detect a Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) data plane failure. LSP Ping is an existing mechanism for detecting MPLS data plane failures and for verifying the MPLS LSP data plane against the control plane. BFD can be used for the former, but not for the latter. However, the control plane processing required for BFD Control packets is relatively smaller than the processing required for LSP Ping messages. A combination of LSP Ping and BFD can be used to provide faster data plane failure detection and/or make it possible to provide such detection on a greater number of LSPs. This document describes the applicability of BFD in relation to LSP Ping for this application. It also describes procedures for using BFD in this environment. [STANDARDS-TRACK] This document describes Connectivity Verification (CV) Types using Bidirectional Forwarding Detection (BFD) with Virtual Circuit Connectivity Verification (VCCV). VCCV provides a control channel that is associated with a pseudowire (PW), as well as the corresponding operations and management functions such as connectivity verification to be used over that control channel. [STANDARDS-TRACK] Recent proposals have extended the scope of Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs) to encompass point-to-multipoint (P2MP) LSPs. The requirement for a simple and efficient mechanism that can be used to detect data-plane failures in point-to-point (P2P) MPLS LSPs has been recognized and has led to the development of techniques for fault detection and isolation commonly referred to as "LSP ping". The scope of this document is fault detection and isolation for P2MP MPLS LSPs. This documents does not replace any of the mechanisms of LSP ping, but clarifies their applicability to MPLS P2MP LSPs, and extends the techniques and mechanisms of LSP ping to the MPLS P2MP environment. This document updates RFC 4379. [STANDARDS-TRACK] Load balancing is a powerful tool for engineering traffic across a network. This memo suggests ways of improving load balancing across MPLS networks using the concept of "entropy labels". It defines the concept, describes why entropy labels are useful, enumerates properties of entropy labels that allow maximal benefit, and shows how they can be signaled and used for various applications. This document updates RFCs 3031, 3107, 3209, and 5036. [STANDARDS-TRACK] The MPLS Generic Associated Channel (G-ACh) provides an auxiliary logical data channel associated with a Label Switched Path (LSP), a pseudowire, or a section (link) over which a variety of protocols may flow. These protocols are commonly used to provide Operations, Administration, and Maintenance (OAM) mechanisms associated with the primary data channel. This document specifies simple procedures by which an endpoint of an LSP, pseudowire, or section may inform the other endpoints of its capabilities and configuration parameters, or other application-specific information. This information may then be used by the receiver to validate or adjust its local configuration, and by the network operator for diagnostic purposes. This document clarifies the procedures for establishing, maintaining, and removing multiple, concurrent BFD (Bidirectional Forwarding Detection) sessions for a given as described in RFC 5884. This document describes a simple and efficient mechanism to detect data-plane failures in Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs). It defines a probe message called an "MPLS echo request" and a response message called an "MPLS echo reply" for returning the result of the probe. The MPLS echo request is intended to contain sufficient information to check correct operation of the data plane and to verify the data plane against the control plane, thereby localizing faults. This document obsoletes RFCs 4379, 6424, 6829, and 7537, and updates RFC 1122. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. A Segment Routing (SR) architecture leverages source routing and tunneling paradigms and can be directly applied to the use of a Multiprotocol Label Switching (MPLS) data plane. A node steers a packet through a controlled set of instructions called "segments" by prepending the packet with an SR header. The segment assignment and forwarding semantic nature of SR raises additional considerations for connectivity verification and fault isolation for a Label Switched Path (LSP) within an SR architecture. This document illustrates the problem and defines extensions to perform LSP Ping and Traceroute for Segment Routing IGP-Prefix and IGP-Adjacency Segment Identifiers (SIDs) with an MPLS data plane. This document describes extensions to the Bidirectional Forwarding Detection (BFD) protocol for its use in multipoint and multicast networks. This document updates RFC 5880. This document describes active tail extensions to the Bidirectional Forwarding Detection (BFD) protocol for multipoint networks. This document defines Multicast Virtual Private Network (VPN) extensions and procedures that allow fast failover for upstream failures by allowing downstream Provider Edges (PEs) to consider the status of Provider-Tunnels (P-tunnels) when selecting the Upstream PE for a VPN multicast flow. The fast failover is enabled by using "Bidirectional Forwarding Detection (BFD) for Multipoint Networks" (RFC 8562) and the new BGP Attribute, BFD Discriminator. Also, this document introduces a new BGP Community, Standby PE, extending BGP Multicast VPN (MVPN) routing so that a C-multicast route can be advertised toward a Standby Upstream PE. Informative References IANA IANA This specification defines the addressing architecture of the IP Version 6 (IPv6) protocol. The document includes the IPv6 addressing model, text representations of IPv6 addresses, definition of IPv6 unicast addresses, anycast addresses, and multicast addresses, and an IPv6 node's required addresses. This document obsoletes RFC 3513, "IP Version 6 Addressing Architecture". [STANDARDS-TRACK] Multi-Protocol Label Switching (MPLS) has been extended to encompass point-to-multipoint (P2MP) Label Switched Paths (LSPs). As with point-to-point MPLS LSPs, the requirement to detect, handle, and diagnose control and data plane defects is critical. For operators deploying services based on P2MP MPLS LSPs, the detection and specification of how to handle those defects are important because such defects not only may affect the fundamentals of an MPLS network, but also may impact service level specification commitments for customers of their network. This document describes requirements for data plane operations and management for P2MP MPLS LSPs. These requirements apply to all forms of P2MP MPLS LSPs, and include P2MP Traffic Engineered (TE) LSPs and multicast LSPs. This memo provides information for the Internet community.

Acknowledgements The authors sincerely appreciate the comments received from , , and . The authors also appreciate the thought-stimulating questions from .

Authors' Addresses Ericsson

gregimirsky@gmail.com

Verizon Inc.

gyan.s.mishra@verizon.com

Independent

2386 Panoramic Circle Apopka FL 32703 United States of America d3e3e3@gmail.com