rfc9780v1.txt   rfc9780.txt 
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Independent Independent
May 2025 May 2025
Bidirectional Forwarding Detection (BFD) for Multipoint Networks over Bidirectional Forwarding Detection (BFD) for Multipoint Networks over
Point-to-Multipoint MPLS Label Switched Paths (LSPs) Point-to-Multipoint MPLS Label Switched Paths (LSPs)
Abstract Abstract
This document describes procedures for using Bidirectional Forwarding This document describes procedures for using Bidirectional Forwarding
Detection (BFD) for multipoint networks to detect data plane failures Detection (BFD) for multipoint networks to detect data plane failures
in MPLS point-to-multipoint Label Switched Paths (LSPs) and Segment in point-to-multipoint MPLS Label Switched Paths (LSPs) and Segment
Routing (SR) point-to-multipoint policies with an SR over MPLS (SR- Routing (SR) point-to-multipoint policies with an SR over MPLS (SR-
MPLS) data plane. MPLS) data plane.
Furthermore, this document updates RFC 8562 by recommending the use 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 of an IPv6 address from the Dummy IPv6 Prefix address block
and discouraging the use of an IPv4 loopback address mapped to IPv6. 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, In addition, this document describes the applicability of LSP Ping
as in-band, and the control plane, as out-of-band, solutions to (as an in-band solution) and the control plane (as an out-of-band
bootstrap a BFD session. The document also describes the behavior of solution) to bootstrap a BFD session. The document also describes
the active tail for head notification. the behavior of the active tail for head notification.
Status of This Memo Status of This Memo
This is an Internet Standards Track document. This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has (IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841. Internet Standards is available in Section 2 of RFC 7841.
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Detection (BFD) [RFC5880] to monitor and detect failures between the Detection (BFD) [RFC5880] to monitor and detect failures between the
sender (head) and one or more receivers (tails) in multipoint or sender (head) and one or more receivers (tails) in multipoint or
multicast networks. multicast networks.
[RFC8562] added two BFD session types: MultipointHead and [RFC8562] added two BFD session types: MultipointHead and
MultipointTail. Throughout this document, MultipointHead and MultipointTail. Throughout this document, MultipointHead and
MultipointTail refer to the value to which the bfd.SessionType is set MultipointTail refer to the value to which the bfd.SessionType is set
on a BFD endpoint. on a BFD endpoint.
This document describes procedures for using such modes of the BFD This document describes procedures for using such modes of the BFD
protocol to detect data plane failures in MPLS point-to-multipoint protocol to detect data plane failures in point-to-multipoint (P2MP)
(P2MP) Label Switched Paths (LSPs) and Segment Routing (SR) point-to- MPLS Label Switched Paths (LSPs) and Segment Routing (SR) point-to-
multipoint policies with an SR over MPLS (SR-MPLS) data plane. multipoint policies with an SR over MPLS (SR-MPLS) data plane.
The document also describes the applicability of out-of-band The document also describes the applicability of LSP Ping (an in-band
solutions to bootstrap a BFD session in this environment. solution) and out-of-band solutions to bootstrap a BFD session in
this environment.
Historically, an IPv6-mapped IPv4 loopback range Historically, an address in the IPv6-mapped IPv4 loopback address
address::ffff:127.0.0.1/128 was mandated, although functionally, an block ::ffff:127.0.0.1/128 was mandated, although functionally, an
IPv6 address from that range is not analogous to its IPv4 IPv6 address from that address block is not analogous to its IPv4
counterpart. Furthermore, using the loopback address as the counterpart. Furthermore, using the loopback address as the
destination address, even for an inner IP encapsulation of a tunneled destination address, even for an inner IP encapsulation of a tunneled
packet, violates Section 2.5.3 of [RFC4291]. Hence, IANA has packet, violates Section 2.5.3 of [RFC4291]. Hence, IANA has
allocated 100:0:0:1::/64 as a new Dummy IPv6 Prefix (Section 7.1) to allocated 100:0:0:1::/64 as a new Dummy IPv6 Prefix (Section 7.1) for
select destination IPv6 addresses for IP/UDP encapsulation of destination IPv6 addresses used for IP/UDP encapsulation of
management, control, and Operations, Administration, and Maintenance management, control, and OAM (Operations, Administration, and
(OAM) packets. A source-only IPv6 dummy address is used as the Maintenance) packets. A source-only IPv6 dummy address is used as
destination to generate an exception and a reply message to the the destination to generate an exception and a reply message to the
request message received. This document starts the transition to request message received. This document starts the transition to
using the IPv6 addresses from the Dummy IPv6 Prefix range 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 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 encapsulation of active OAM over the MPLS data plane. Thus, this
document updates [RFC8562] by recommending the use of an IPv6 address 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 from the Dummy IPv6 Prefix address block 100:0:0:1::/64 (Section 7.1)
acknowledging that an address from the ::ffff:127.0.0.1/128 range while acknowledging that an address from the ::ffff:127.0.0.1/128
might be used by existing implementations. This document discourages address block might be used by existing implementations. This
the use of an address in the IPv6-mapped IPv4 loopback range. 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 This document also describes the behavior of the active tail for head
notification. notification.
2. Conventions Used in This Document 2. Conventions Used in This Document
2.1. Terminology 2.1. Terminology
ACH: Associated Channel Header ACH: Associated Channel Header
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multipoint (P2MP) BFD session. Because the head doesn't receive any multipoint (P2MP) BFD session. Because the head doesn't receive any
BFD Control packets from a tail, the head of the P2MP BFD session BFD Control packets from a tail, the head of the P2MP BFD session
transmits all BFD Control packets with the value of the Your transmits all BFD Control packets with the value of the Your
Discriminator field set to zero. As a result, a tail cannot Discriminator field set to zero. As a result, a tail cannot
demultiplex BFD sessions using Your Discriminator, as defined in demultiplex BFD sessions using Your Discriminator, as defined in
[RFC5880]. To demultiplex BFD sessions, [RFC8562] requires that the [RFC5880]. To demultiplex BFD sessions, [RFC8562] requires that the
tail use the source IP address, My Discriminator, and the identity of tail use the source IP address, My Discriminator, and the identity of
the multipoint tree from which the BFD Control packet was received. the multipoint tree from which the BFD Control packet was received.
If the BFD Control packet is encapsulated in IP/UDP, then the source If the BFD Control packet is encapsulated in IP/UDP, then the source
IP address MUST be used to demultiplex the received BFD Control IP address MUST be used to demultiplex the received BFD Control
packet as described in Section 3.1. The non-IP encapsulation case is packet as described in Section 5.7 of [RFC8562]. The non-IP
described in Section 3.2. encapsulation case is described in Section 3.2.
3.1. IP Encapsulation of Multipoint BFD 3.1. IP Encapsulation of Multipoint BFD
[RFC8562] defines IP/UDP encapsulation for multipoint BFD over P2MP [RFC8562] defines IP/UDP encapsulation for multipoint BFD over P2MP
MPLS LSP. This document updates Section 5.8 of [RFC8562] regarding MPLS LSP. This document updates Section 5.8 of [RFC8562] regarding
the selection of the IPv6 destination address as follows: the selection of the IPv6 destination address as follows:
* The sender of an MPLS echo request SHOULD use an address from the * The sender of an MPLS echo request SHOULD use an address from the
Dummy IPv6 Prefix range 100:0:0:1::/64 (see Section 7.1). Dummy IPv6 Prefix address block 100:0:0:1::/64 (see Section 7.1).
* The sender of an MPLS echo request MAY select the IPv6 destination * The sender of an MPLS echo request MAY select the IPv6 destination
address from the ::ffff:7f00/104 range. address from the ::ffff:7f00/104 address block.
Section 1.2 of [RFC6790] lists several advantages of generating the Section 1.2 of [RFC6790] lists several advantages of generating the
entropy value by an ingress Label Switching Router (LSR) compared to entropy value by an ingress Label Switching Router (LSR) compared to
when a transit LSR infers entropy using the information in the MPLS when a transit LSR infers entropy using the information in the MPLS
label stack or payload. This specification further clarifies that: label stack or payload. This specification further clarifies the
following if multiple alternative paths for the given P2MP LSP
Forwarding Equivalence Class (FEC) exist:
* if multiple alternative paths for the given P2MP LSP Forwarding * The MultipointHead SHOULD use the Entropy Label [RFC6790] used for
Equivalence Class (FEC) exist, the MultipointHead SHOULD use the LSP Ping [RFC8029] to exercise those particular alternative paths;
Entropy Label [RFC6790] used for LSP Ping [RFC8029] to exercise or
those particular alternative paths;
* or the MultipointHead MAY use the UDP port number to possibly * The MultipointHead MAY use the UDP port number to possibly
exercise those particular alternate paths. exercise those particular alternate paths.
3.2. Non-IP Encapsulation of Multipoint BFD 3.2. Non-IP Encapsulation of Multipoint BFD
In some environments, the overhead of extra IP/UDP encapsulations may In some environments, the overhead of extra IP/UDP encapsulations may
be considered burdensome, which makes the use of more compact Generic be considered burdensome, which makes the use of more compact Generic
Associated Channel (G-ACh) [RFC5586] encapsulation attractive. Also, Associated Channel (G-ACh) [RFC5586] encapsulation attractive. Also,
the validation of the IP/UDP encapsulation of a BFD Control packet in 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 a P2MP BFD session may fail because of a problem related to neither
the MPLS label stack nor BFD. Avoiding unnecessary encapsulation of the MPLS label stack nor BFD. Avoiding unnecessary encapsulation of
P2MP BFD over an MPLS LSP improves the accuracy of the correlation of P2MP BFD over an MPLS LSP improves the accuracy of the correlation of
the detected failure and defect in MPLS LSP. 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 Non-IP encapsulation for multipoint BFD over P2MP MPLS LSP (shown in
Figure 1) MUST use the G-ACh Label (GAL) [RFC5586] at the bottom of Figure 1) MUST use the G-ACh Label (GAL) [RFC5586] at the bottom of
the label stack followed by an Associated Channel Header (ACH). If a the label stack followed by an Associated Channel Header (ACH). If a
BFD Control packet in PW-ACH encapsulation (without IP/UDP Headers) 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 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 the identity of the MultipointHead and, as a result, will not
properly demultiplex BFD packets. Hence, a new channel type value is properly demultiplex BFD packets. Hence, a new channel type value is
needed. The Channel Type field in ACH MUST be set to Multipoint BFD needed. The Channel Type field in ACH MUST be set to Multipoint BFD
Session (0x0013) (see Section 7.2). To provide the identity of the Session (0x0013) (see Section 7.2). To provide the identity of the
MultipointHead for the particular multipoint BFD session, a Source MultipointHead for the particular multipoint BFD session, a Source
Address TLV, as defined in Section 4.1 of [RFC7212], MUST immediately 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 follow a BFD Control packet. The use of other TLVs is outside the
scope of this document. scope of this document.
0 1 2 3 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 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 | | LSP Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL | TC |1| TTL | | GAL | TC |1| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Flags | Channel Type = 0x0013 | |0 0 0 1|Version| Flags | Channel Type = 0x0013 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ BFD Control Message ~ ~ BFD Control Packet ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0 | Reserved | Length | | Type=0 | Reserved | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Address Family | | Reserved | Address Family |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Address ~ ~ Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Non-IP Encapsulation for Multipoint BFD over a Figure 1: Non-IP Encapsulation for Multipoint BFD over a
Multicast MPLS LSP Multicast MPLS LSP
The fields in Figure 1 are interpreted as follows: The fields in Figure 1 are interpreted as follows:
* The top three four-octet words are defined in [RFC5586]. * The top three four-octet words are defined in [RFC5586].
* The BFD Control Message field is defined in [RFC5880]. * The BFD Control Packet field is defined in [RFC5880].
* All the remaining fields are defined in Section 4.1 of [RFC7212]. * All the remaining fields are defined in Section 4.1 of [RFC7212].
4. Bootstrapping Multipoint BFD 4. Bootstrapping Multipoint BFD
4.1. LSP Ping 4.1. LSP Ping
LSP Ping is the part of the on-demand OAM toolset used to detect and 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 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 against the data plane by ensuring that the LSP is mapped to the same
FEC at both egress and ingress endpoints. FEC at both egress and ingress endpoints.
LSP Ping, as defined in [RFC6425], MAY be used to bootstrap LSP Ping, as defined in [RFC6425], MAY be used to bootstrap
MultipointTail. If LSP Ping is used, it MUST include the Target FEC MultipointTail. If LSP Ping is used, it MUST include the Target FEC
TLV and the BFD Discriminator TLV defined in [RFC5884]. For the case Stack TLV [RFC8029] and the BFD Discriminator TLV [RFC5884]. For the
of P2MP MPLS LSP, the Target FEC TLV MUST use sub-TLVs defined in case of P2MP MPLS LSP, the Target FEC Stack TLV MUST use sub-TLVs
Section 3.1 of [RFC6425]. For the case of P2MP SR policy with an SR- defined in Section 3.1 of [RFC6425]. For the case of P2MP SR policy
MPLS data plane, an implementation of this specification MUST follow with an SR-MPLS data plane, an implementation of this specification
the procedures defined in [RFC8287]. Setting the value of the Reply MUST follow the procedures defined in [RFC8287]. Setting the value
Mode field to "Do not reply" [RFC8029] for the LSP Ping to bootstrap of the Reply Mode field to "Do not reply" [RFC8029] for the LSP Ping
the MultipointTail of the P2MP BFD session is RECOMMENDED. Indeed, to bootstrap the MultipointTail of the P2MP BFD session is
because BFD over a multipoint network uses BFD Demand mode, the MPLS RECOMMENDED. Indeed, because BFD over a multipoint network uses BFD
echo reply from a tail has no useful information to convey to the Demand mode, the MPLS echo reply from a tail has no useful
head, unlike in the case of BFD over a P2P MPLS LSP [RFC5884]. A information to convey to the head, unlike in the case of BFD over a
MultipointTail that receives an LSP Ping that includes the BFD P2P MPLS LSP [RFC5884]. A MultipointTail that receives an LSP Ping
Discriminator TLV: that includes the BFD Discriminator TLV MUST do the following:
* MUST validate the LSP Ping; * validate the LSP Ping;
* MUST associate the received BFD Discriminator value with the P2MP * associate the received BFD Discriminator value with the P2MP LSP;
LSP;
* MUST create a P2MP BFD session and set bfd.SessionType = * create a P2MP BFD session and set bfd.SessionType = MultipointTail
MultipointTail as described in [RFC8562]; and as described in [RFC8562]; and
* MUST use the source IP address of the LSP Ping, the value of BFD * use the source IP address of the LSP Ping, the value of BFD
Discriminator from the BFD Discriminator TLV, and the identity of Discriminator from the BFD Discriminator TLV, and the identity of
the P2MP LSP to properly demultiplex BFD sessions. the P2MP LSP to properly demultiplex BFD sessions.
Besides bootstrapping a BFD session over a P2MP LSP, LSP Ping SHOULD Besides bootstrapping a BFD session over a P2MP LSP, LSP Ping SHOULD
be used to verify the control plane against the data plane be used to verify the control plane against the data plane
periodically by checking that the P2MP LSP is mapped to the same FEC periodically by checking that the P2MP LSP is mapped to the same FEC
at the MultipointHead and all active MultipointTails. The rate of at the MultipointHead and all active MultipointTails. The rate of
generation of these LSP Ping Echo request messages SHOULD be generation of these LSP Ping echo request messages SHOULD be
significantly less than the rate of generation of the BFD Control significantly less than the rate of generation of the BFD Control
packets because LSP Ping requires more processing to validate the packets because LSP Ping requires more processing to validate the
consistency between the data plane and the control plane. An consistency between the data plane and the control plane. An
implementation MAY provide configuration options to control the rate implementation MAY provide configuration options to control the rate
of generation of the periodic LSP Ping Echo request messages. of generation of the periodic LSP Ping echo request messages.
4.2. Control Plane 4.2. Control Plane
The BFD Discriminator attribute MAY be used to bootstrap a multipoint The BFD Discriminator attribute MAY be used to bootstrap a multipoint
BFD session on a tail, following the format and procedures given in BFD session on a tail, following the format and procedures given in
Section 3.1.6 of [RFC9026]. Section 3.1.6 of [RFC9026].
5. Operation of Multipoint BFD with Active Tail over P2MP MPLS LSP 5. Operation of Multipoint BFD with Active Tail over P2MP MPLS LSP
[RFC8562] defines how BFD Demand mode can be used in multipoint [RFC8562] defines how BFD Demand mode can be used in multipoint
networks. When applied in MPLS, the procedures specified in networks. When applied in MPLS, the procedures specified in
[RFC8562] allow an egress LSR to detect a failure in the part of the [RFC8562] allow an egress LSR to detect a failure in the part of the
MPLS P2MP LSP from the ingress LSR to that egress LSR. The ingress P2MP MPLS LSP from the ingress LSR to that egress LSR. The ingress
LSR is not aware of the state of the P2MP LSP. [RFC8563], using LSR is not aware of the state of the P2MP LSP. [RFC8563], using
mechanisms defined in [RFC8562], defines the behavior of an active mechanisms defined in [RFC8562], defines the behavior of an active
tail. An active tail might notify the head of the detected failure tail. An active tail might notify the head of the detected failure
and respond to a poll sequence initiated by the head. The first and respond to a poll sequence initiated by the head. The first
method, referred to as "Head Notification without Polling", is method, referred to as "Head Notification without Polling", is
mentioned in Section 5.2.1 of [RFC8563]) and is the simplest of the mentioned in Section 5.2.1 of [RFC8563]) and is the simplest of the
methods described in [RFC8563]. The use of this method in BFD over methods described in [RFC8563]. The use of this method in BFD over
MPLS P2MP LSP is discussed in this document. Analysis of other P2MP MPLS LSP is discussed in this document. Analysis of other
methods for a head to learn of the state of an MPLS P2MP LSP is methods for a head to learn of the state of an P2MP MPLS LSP is
outside the scope of this document. outside the scope of this document.
As specified in [RFC8563], BFD variables MUST be as follows for the As specified in [RFC8563], BFD variables MUST be as follows for the
active tail mode: active tail mode:
* On an ingress LSR: * On an ingress LSR:
- bfd.SessionType is MultipointHead. - bfd.SessionType is MultipointHead.
- bfd.RequiredMinRxInterval is nonzero, allowing egress LSRs to - bfd.RequiredMinRxInterval is nonzero, allowing egress LSRs to
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* The Status (Sta) field is set to the Down value. * The Status (Sta) field is set to the Down value.
* The Diagnostic (Diag) field is set to the Control Detection Time * The Diagnostic (Diag) field is set to the Control Detection Time
Expired value. Expired value.
* The value of the Your Discriminator field is set to the value the * The value of the Your Discriminator field is set to the value the
egress LSR has been using to demultiplex that BFD multipoint egress LSR has been using to demultiplex that BFD multipoint
session. session.
* The BFD Control packet MAY be encapsulated in IP/UDP with the The BFD Control packet MAY be encapsulated in IP/UDP with the
destination IP address of the ingress LSR and the UDP destination destination IP address of the ingress LSR and the UDP destination
port number set to 4784 per [RFC5883]. If non-IP encapsulation is port number set to 4784 per [RFC5883]. If non-IP encapsulation is
used, then a BFD Control packet is encapsulated using PW-ACH used, then a BFD Control packet is encapsulated using PW-ACH
encapsulation (without IP/UDP Headers) with Channel Type 0x0007 encapsulation (without IP/UDP Headers) with Channel Type 0x0007
[RFC5885]. [RFC5885].
* The BFD Control packets are transmitted at the rate of one per The BFD Control packets are transmitted at the rate of one per second
second until either 1) it receives a control packet valid for this until either 1) the egress LSA receives a control packet from the
BFD session with the Final (F) bit set from the ingress LSR or 2) ingress LSR that is valid for this BFD session and has the Final (F)
the defect condition clears. However, to improve the likelihood bit set or 2) the defect condition clears. However, to improve the
of notifying the ingress LSR of the failure of the P2MP MPLS LSP, likelihood of notifying the ingress LSR of the failure of the P2MP
the egress LSR SHOULD initially transmit three BFD Control packets MPLS LSP, the egress LSR SHOULD initially transmit three BFD Control
defined above in short succession. The actual transmission of the packets (as defined above) in short succession. The actual
periodic BFD Control message MUST be jittered by up to 25% within transmission of the periodic BFD Control packet MUST be jittered by
one-second intervals. Thus, the interval MUST be reduced by a up to 25% within one-second intervals. Thus, the interval MUST be
random value of 0 to 25%, to reduce the possibility of congestion reduced by a random value of 0 to 25%, to reduce the possibility of
on the ingress LSR's data and control planes. congestion on the ingress LSR's data and control planes.
As described above, an ingress LSR that has received the BFD Control As described above, an ingress LSR that has received the BFD Control
packet sends the unicast IP/UDP encapsulated BFD Control packet with 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., 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 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 LSRs is significantly large), the root might receive a large number
of notifications. The notifications from leaves to the root will not of notifications. The notifications from leaves to the root will not
use resources allocated for the monitored multicast flow and, as a use resources allocated for the monitored multicast flow and, as a
result, will not congest that particular flow, although they may result, will not congest that particular flow, although they may
negatively affect other flows. However, the control plane of the negatively affect other flows. However, the control plane of the
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Termination Date: N/A Termination Date: N/A
Source: True Source: True
Destination: False Destination: False
Forwardable: False Forwardable: False
Globally Reachable: False Globally Reachable: False
Reserved-by-Protocol: False Reserved-by-Protocol: False
7.2. MPLS Generalized Associated Channel (G-ACh) Type 7.2. MPLS Generalized Associated Channel (G-ACh) Type
IANA has allocated the following value in the "MPLS Generalized IANA has allocated the following value in the "MPLS Generalized
Associated Channel (G-ACh) Types" registry. Associated Channel (G-ACh) Types" registry [IANA-G-ACh-TYPES].
+========+========================+===========+ +========+========================+===========+
| Value | Description | Reference | | Value | Description | Reference |
+========+========================+===========+ +========+========================+===========+
| 0x0013 | Multipoint BFD Session | RFC 9780 | | 0x0013 | Multipoint BFD Session | RFC 9780 |
+--------+------------------------+-----------+ +--------+------------------------+-----------+
Table 1: Multipoint BFD Session G-ACh Type Table 1: Multipoint BFD Session G-ACh Type
8. References 8. References
skipping to change at line 538 skipping to change at line 535
Active Tails", RFC 8563, DOI 10.17487/RFC8563, April 2019, Active Tails", RFC 8563, DOI 10.17487/RFC8563, April 2019,
<https://www.rfc-editor.org/info/rfc8563>. <https://www.rfc-editor.org/info/rfc8563>.
[RFC9026] Morin, T., Ed., Kebler, R., Ed., and G. Mirsky, Ed., [RFC9026] Morin, T., Ed., Kebler, R., Ed., and G. Mirsky, Ed.,
"Multicast VPN Fast Upstream Failover", RFC 9026, "Multicast VPN Fast Upstream Failover", RFC 9026,
DOI 10.17487/RFC9026, April 2021, DOI 10.17487/RFC9026, April 2021,
<https://www.rfc-editor.org/info/rfc9026>. <https://www.rfc-editor.org/info/rfc9026>.
8.2. Informative References 8.2. Informative References
[IANA-G-ACh-TYPES]
IANA, "MPLS Generalized Associated Channel (G-ACh) Types",
<https://www.iana.org/assignments/g-ach-parameters>.
[IANA-IPv6-REG] [IANA-IPv6-REG]
IANA, "IANA IPv6 Special-Purpose Address Registry", IANA, "IANA IPv6 Special-Purpose Address Registry",
<https://www.iana.org/assignments/iana-ipv6-special- <https://www.iana.org/assignments/iana-ipv6-special-
registry>. registry>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>. 2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4687] Yasukawa, S., Farrel, A., King, D., and T. Nadeau, [RFC4687] Yasukawa, S., Farrel, A., King, D., and T. Nadeau,
 End of changes. 32 change blocks. 
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