draft-ietf-bfd-multipoint-19.txt   rfc8562.txt 
Internet Engineering Task Force D. Katz Internet Engineering Task Force (IETF) D. Katz
Internet-Draft Juniper Networks Request for Comments: 8562 Juniper Networks
Updates: 5880 (if approved) D. Ward Updates: 5880 D. Ward
Intended status: Standards Track Cisco Systems Category: Standards Track Cisco Systems
Expires: June 16, 2019 S. Pallagatti, Ed. ISSN: 2070-1721 S. Pallagatti, Ed.
Rtbrick VMware
G. Mirsky, Ed. G. Mirsky, Ed.
ZTE Corp. ZTE Corp.
December 13, 2018 April 2019
BFD for Multipoint Networks Bidirectional Forwarding Detection (BFD) for Multipoint Networks
draft-ietf-bfd-multipoint-19
Abstract Abstract
This document describes extensions to the Bidirectional Forwarding This document describes extensions to the Bidirectional Forwarding
Detection (BFD) protocol for its use in multipoint and multicast Detection (BFD) protocol for its use in multipoint and multicast
networks. networks.
This document updates RFC 5880. This document updates RFC 5880.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on June 16, 2019. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8562.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 5 5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Multipoint BFD Control Packets . . . . . . . . . . . . . 5 5.1. Multipoint BFD Control Packets . . . . . . . . . . . . . 6
5.2. Session Model . . . . . . . . . . . . . . . . . . . . . . 5 5.2. Session Model . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Session Failure Semantics . . . . . . . . . . . . . . . . 5 5.3. Session-Failure Semantics . . . . . . . . . . . . . . . . 6
5.4. State Variables . . . . . . . . . . . . . . . . . . . . . 5 5.4. State Variables . . . . . . . . . . . . . . . . . . . . . 6
5.4.1. New State Variable Values . . . . . . . . . . . . . . 6 5.4.1. New State Variable Values . . . . . . . . . . . . . . 6
5.4.2. State Variable Initialization and Maintenance . . . . 6 5.4.2. State Variable Initialization and Maintenance . . . . 7
5.5. State Machine . . . . . . . . . . . . . . . . . . . . . . 6 5.5. State Machine . . . . . . . . . . . . . . . . . . . . . . 7
5.6. Session Establishment . . . . . . . . . . . . . . . . . . 7 5.6. Session Establishment . . . . . . . . . . . . . . . . . . 8
5.7. Discriminators and Packet Demultiplexing . . . . . . . . 7 5.7. Discriminators and Packet Demultiplexing . . . . . . . . 8
5.8. Packet consumption on tails . . . . . . . . . . . . . . . 8 5.8. Packet Consumption on Tails . . . . . . . . . . . . . . . 9
5.9. Bringing Up and Shutting Down Multipoint BFD Service . . 8 5.9. Bringing Up and Shutting Down Multipoint BFD Service . . 9
5.10. Timer Manipulation . . . . . . . . . . . . . . . . . . . 9 5.10. Timer Manipulation . . . . . . . . . . . . . . . . . . . 10
5.11. Detection Times . . . . . . . . . . . . . . . . . . . . . 10 5.11. Detection Times . . . . . . . . . . . . . . . . . . . . . 10
5.12. State Maintenance for Down/AdminDown Sessions . . . . . . 10 5.12. State Maintenance for Down/AdminDown Sessions . . . . . . 11
5.12.1. MultipointHead Sessions . . . . . . . . . . . . . . 10 5.12.1. MultipointHead Sessions . . . . . . . . . . . . . . 11
5.12.2. MultipointTail Sessions . . . . . . . . . . . . . . 10 5.12.2. MultipointTail Sessions . . . . . . . . . . . . . . 11
5.13. Base Specification Text Replacement . . . . . . . . . . . 10 5.13. Base Specification Text Replacement . . . . . . . . . . . 11
5.13.1. Reception of BFD Control Packets . . . . . . . . . . 11 5.13.1. Reception of BFD Control Packets . . . . . . . . . . 12
5.13.2. Demultiplexing BFD Control Packets . . . . . . . . . 13 5.13.2. Demultiplexing BFD Control Packets . . . . . . . . . 15
5.13.3. Transmitting BFD Control Packets . . . . . . . . . . 15 5.13.3. Transmitting BFD Control Packets . . . . . . . . . . 16
6. Congestion Considerations . . . . . . . . . . . . . . . . . . 18 6. Congestion Considerations . . . . . . . . . . . . . . . . . . 19
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19 8. Security Considerations . . . . . . . . . . . . . . . . . . . 20
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 20 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 9.1. Normative References . . . . . . . . . . . . . . . . . . 21
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 9.2. Informative References . . . . . . . . . . . . . . . . . 22
11.1. Normative References . . . . . . . . . . . . . . . . . . 20 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 22
11.2. Informational References . . . . . . . . . . . . . . . . 20 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
The Bidirectional Forwarding Detection protocol [RFC5880] specifies a The Bidirectional Forwarding Detection (BFD) protocol [RFC5880]
method for verifying unicast connectivity between a pair of systems. specifies a method for verifying unicast connectivity between a pair
This document updates [RFC5880] by defining a new method for using of systems. This document updates [RFC5880] by defining a new method
BFD. This new method provides verification of multipoint or for using BFD. This new method provides verification of multipoint
multicast connectivity between a multipoint sender (the "head") and a or multicast connectivity between a multipoint sender (the "head")
set of one or more multipoint receivers (the "tails"). and a set of one or more multipoint receivers (the "tails").
As multipoint transmissions are inherently unidirectional, this As multipoint transmissions are inherently unidirectional, this
mechanism purports only to verify this unidirectional connectivity. mechanism purports only to verify this unidirectional connectivity.
Although this seems in conflict with the "Bidirectional" in BFD, the Although this seems in conflict with the "Bidirectional" in BFD, the
protocol is capable of supporting this use case. Use of BFD in protocol is capable of supporting this use case. Use of BFD in
Demand mode allows a tail to monitor the availability of a multipoint Demand mode allows a tail to monitor the availability of a multipoint
path even without the existence of some kind of a return path to the path even without the existence of some kind of a return path to the
head. As an option, if a return path from a tail to the head exists, head. As an option, if a return path from a tail to the head exists,
the tail may notify the head of the lack of multipoint connectivity. the tail may notify the head of the lack of multipoint connectivity.
Details of tail notification to the head are outside the scope of Details of tail notification to the head are outside the scope of
this document and are discussed in this document and are discussed in [RFC8563].
[I-D.ietf-bfd-multipoint-active-tail].
This application of BFD allows for the tails to detect a lack of This application of BFD allows for the tails to detect a lack of
connectivity from the head. For some applications such detection of connectivity from the head. For some applications, such detection of
the failure at the tail is useful. For example, use of multipoint the failure at the tail is useful, for example, the use of multipoint
BFD to enable fast failure detection and faster failover in multicast BFD to enable fast failure detection and faster failover in multicast
VPN described in [I-D.ietf-bess-mvpn-fast-failover]. Due to VPN as described in [MVPN-FAILOVER]. Due to its unidirectional
unidirectional nature, virtually all options and timing parameters nature, virtually all options and timing parameters are controlled by
are controlled by the head. the head.
Throughout this document, the term "multipoint" is defined as a Throughout this document, the term "multipoint" is defined as a
mechanism by which one or more systems receive packets sent by a mechanism by which one or more systems receive packets sent by a
single sender. This specifically includes such things as IP single sender. This specifically includes such things as IP
multicast and point-to-multipoint MPLS. multicast and point-to-multipoint MPLS.
The term "connectivity" in this document is not being used in the The term "connectivity" in this document is not being used in the
context of connectivity verification in transport network but as an context of connectivity verification in a transport network but as an
alternative to "continuity", i.e., the existence of a forwarding path alternative to "continuity", i.e., the existence of a forwarding path
between the sender and the receiver. between the sender and the receiver.
This document effectively updates and extends the base BFD This document effectively updates and extends the base BFD
specification [RFC5880]. specification [RFC5880].
2. Keywords 2. Keywords
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Goals 3. Goals
The primary goal of this mechanism is to allow tails to rapidly The primary goal of this mechanism is to allow tails to rapidly
detect the fact that multipoint connectivity from the head has detect the fact that multipoint connectivity from the head has
failed. failed.
Another goal is for the mechanism to work on any multicast Another goal is for the mechanism to work on any multicast
technology. technology.
A further goal is to support multiple, overlapping point-to- A further goal is to support multiple, overlapping point-to-
multipoint paths, as well as multipoint-to-multipoint paths, and to multipoint paths, as well as multipoint-to-multipoint paths, and to
allow point-to-point BFD sessions to operate simultaneously among the allow point-to-point BFD sessions to operate simultaneously among the
systems participating in Multipoint BFD. systems participating in multipoint BFD.
It is not a goal for this protocol to verify point-to-point bi- It is not a goal for this protocol to verify point-to-point
directional connectivity between the head and any tail. This can be bidirectional connectivity between the head and any tail. This can
done independently (and with no penalty in protocol overhead) by be done independently (and with no penalty in protocol overhead) by
using point-to-point BFD. using point-to-point BFD.
4. Overview 4. Overview
The heart of this protocol is the periodic transmission of BFD The heart of this protocol is the periodic transmission of BFD
Control packets along a multipoint path, from the head to all tails Control packets along a multipoint path, from the head to all tails
on the path. The contents of the BFD packets provide the means for on the path. The contents of the BFD packets provide the means for
the tails to calculate the detection time for path failure. If no the tails to calculate the Detection Time for path failure. If no
BFD Control packets are received by a tail for a detection time, the BFD Control packets are received by a tail for a Detection Time, the
tail declares that the path has failed. For some applications this tail declares that the path has failed. For some applications, this
is the only mechanism necessary; the head can remain ignorant of the is the only mechanism necessary; the head can remain ignorant of the
status of connectivity to the tails. status of connectivity to the tails.
The head of a multipoint BFD session may wish to be alerted to the The head of a multipoint BFD session may wish to be alerted to the
tails' connectivity (or lack thereof). Details of how the head keeps tails' connectivity (or lack thereof). Details of how the head keeps
track of tails and how tails alert their connectivity to the head are track of tails and how tails alert their connectivity to the head are
outside the scope of this document and are discussed in outside the scope of this document and are discussed in [RFC8563].
[I-D.ietf-bfd-multipoint-active-tail].
Although this document describes a single head and a set of tails Although this document describes a single head and a set of tails
spanned by a single multipoint path, the protocol is capable of spanned by a single multipoint path, the protocol is capable of
supporting (and discriminating between) more than one multipoint path supporting (and discriminating between) more than one multipoint path
at both heads and tails, as described in Section 5.7 and at both heads and tails, as described in Sections 5.7 and 5.13.2.
Section 5.13.2. Furthermore, the same head and tail may share Furthermore, the same head and tail may share multiple multipoint
multiple multipoint paths, and a multipoint path may have multiple paths, and a multipoint path may have multiple heads.
heads.
5. Protocol Details 5. Protocol Details
This section describes the operation of Multipoint BFD in detail. This section describes the operation of Multipoint BFD in detail.
5.1. Multipoint BFD Control Packets 5.1. Multipoint BFD Control Packets
Multipoint BFD Control packets (packets sent by the head over a Multipoint BFD Control packets (packets sent by the head over a
multipoint path) are explicitly marked as such, via the setting of multipoint path) are explicitly marked as such, via the setting of
the M bit [RFC5880]. This means that Multipoint BFD does not depend the Multipoint (M) bit [RFC5880]. This means that multipoint BFD
on the recipient of a packet to know whether the packet was received does not depend on the recipient of a packet to know whether the
over a multipoint path. This can be useful in scenarios where this packet was received over a multipoint path. This can be useful in
information may not be available to the recipient. scenarios where this information may not be available to the
recipient.
5.2. Session Model 5.2. Session Model
Multipoint BFD is modeled as a set of sessions of different types. Multipoint BFD is modeled as a set of sessions of different types.
The elements of procedure differ slightly for each type. The elements of procedure differ slightly for each type.
The head has a session of type MultipointHead, as defined in The head has a session of type MultipointHead, as defined in
Section 5.4.1, that is bound to a multipoint path. Multipoint BFD Section 5.4.1, that is bound to a multipoint path. Multipoint BFD
Control packets are sent by this session over the multipoint path, Control packets are sent by this session over the multipoint path,
and no BFD Control packets are received by it. and no BFD Control packets are received by it.
Each tail has a session of type MultipointTail, as defined in Each tail has a session of type MultipointTail, as defined in
Section 5.4.1, associated with a multipoint path. These sessions Section 5.4.1, associated with a multipoint path. These sessions
receive BFD Control packets from the head over the multipoint path. receive BFD Control packets from the head over the multipoint path.
5.3. Session Failure Semantics 5.3. Session-Failure Semantics
The semantics of session failure is subtle enough to warrant further The semantics of session failure is subtle enough to warrant further
explanation. explanation.
MultipointHead sessions cannot fail (since they are controlled MultipointHead sessions cannot fail (since they are controlled
administratively). administratively).
If a MultipointTail session fails, it means that the tail definitely If a MultipointTail session fails, it means that the tail definitely
has lost contact with the head (or the head has been administratively has lost contact with the head (or the head has been administratively
disabled) and the tail may use mechanisms other than BFD, e.g., disabled), and the tail may use mechanisms other than BFD, e.g.,
logging or NETCONF [RFC6241], to send a notification to the user. logging or NETCONF [RFC6241], to send a notification to the user.
5.4. State Variables 5.4. State Variables
Multipoint BFD introduces some new state variables and modifies the Multipoint BFD introduces some new state variables and modifies the
usage of a few existing ones. usage of a few existing ones.
5.4.1. New State Variable Values 5.4.1. New State Variable Values
A number of new values of the state variable bfd.SessionType are A number of new values of the state variable bfd.SessionType are
added to the base BFD [RFC5880] and base S-BFD [RFC7880] added to the base BFD [RFC5880] and base Seamless Bidirectional
specifications in support of Multipoint BFD. Forwarding Detection (S-BFD) [RFC7880] specifications in support of
multipoint BFD.
bfd.SessionType bfd.SessionType
The type of this session as defined in [RFC7880]. Newly added The type of this session as defined in [RFC7880]. Newly added
values are: values are:
PointToPoint: Classic point-to-point BFD, as described in PointToPoint: Classic point-to-point BFD, as described in
[RFC5880]. [RFC5880].
MultipointHead: A session on the head responsible for the MultipointHead: A session on the head responsible for the
periodic transmission of multipoint BFD Control packets periodic transmission of multipoint BFD Control packets
along the multipoint path. along the multipoint path.
MultipointTail: A multipoint session on a tail. MultipointTail: A multipoint session on a tail.
This variable MUST be initialized to the appropriate type when This variable MUST be initialized to the appropriate type when
the session is created. the session is created.
5.4.2. State Variable Initialization and Maintenance 5.4.2. State Variable Initialization and Maintenance
Some state variables defined in section 6.8.1 of [RFC5880] need to be Some state variables defined in Section 6.8.1 of [RFC5880] need to be
initialized or manipulated differently depending on the session type. initialized or manipulated differently depending on the session type.
bfd.RequiredMinRxInterval bfd.RequiredMinRxInterval
This variable MUST be initialized to 0 for session type This variable MUST be initialized to zero for session type
MultipointHead. MultipointHead.
bfd.DemandMode bfd.DemandMode
This variable MUST be initialized to 1 for session type This variable MUST be initialized to 1 for session type
MultipointHead and MUST be initialized to 0 for session type MultipointHead and MUST be initialized to zero for session type
MultipointTail. MultipointTail.
5.5. State Machine 5.5. State Machine
The BFD state machine works slightly differently in the multipoint There are slight differences in how the BFD state machine works in
application. In particular, since there is a many-to-one mapping, the multipoint application. In particular, since there is a many-to-
three-way handshakes for session establishment and teardown are one mapping, three-way handshakes for session establishment and
neither possible nor appropriate. As such, there is no Init state. teardown are neither possible nor appropriate. As such, there is no
Sessions of type MultipointHead MUST NOT send BFD control packets Init state. Sessions of type MultipointHead MUST NOT send BFD
with the State field being set to INIT, and those packets MUST be Control packets with the State field being set to INIT, and those
ignored on receipt. packets MUST be ignored on receipt.
The following diagram provides an overview of the state machine for The following diagram provides an overview of the state machine for
session type MultipointTail. The notation on each arc represents the session type MultipointTail. The notation on each arc represents the
state of the remote system (as received in the State field in the BFD state of the remote system (as received in the State field in the BFD
Control packet) or indicates the expiration of the Detection Timer. Control packet) or indicates the expiration of the Detection Timer.
DOWN, ADMIN DOWN, DOWN, ADMIN DOWN,
+------+ TIMER +------+ +------+ TIMER +------+
+----| |<---------------------| |----+ +----| |<---------------------| |----+
DOWN,| | DOWN | | UP | |UP DOWN,| | DOWN | | UP | |UP
ADMIN DOWN,+--->| |--------------------->| |<---+ ADMIN DOWN,+--->| |--------------------->| |<---+
TIMER +------+ UP +------+ TIMER +------+ UP +------+
Sessions of type MultipointHead never receive packets and have no Sessions of type MultipointHead never receive packets and have no
Detection Timer, and as such all state transitions are Detection Timer; as such, all state transitions are administratively
administratively driven. driven.
5.6. Session Establishment 5.6. Session Establishment
Unlike point-to-point BFD, Multipoint BFD provides a form of the Unlike point-to-point BFD, multipoint BFD provides a form of the
discovery mechanism for tails to discover the head. The minimum discovery mechanism that enables tails to discover the head. The
amount of a priori information required both on the head and tails is minimum amount of a priori information required both on the head and
the binding to the multipoint path over which BFD is running. The tails is the binding to the multipoint path over which BFD is
head transmits Multipoint BFD packets on that path, and the tails running. The head transmits multipoint BFD packets on that path, and
listen for BFD packets on that path. All other information can be the tails listen for BFD packets on that path. All other information
determined dynamically. can be determined dynamically.
A session of type MultipointHead is created for each multipoint path A session of type MultipointHead is created for each multipoint path
over which the head wishes to run BFD. This session runs in the over which the head wishes to run BFD. This session runs in the
Active role, per section 6.1 [RFC5880]. Except when administratively Active role, per Section 6.1 of [RFC5880]. Except when
terminating BFD service, this session is always in state Up and administratively terminating BFD service, this session is always in
always operates in Demand mode. No received packets are ever state Up and always operates in Demand mode. No received packets are
demultiplexed to the MultipointHead session. In this sense, it is a ever demultiplexed to the MultipointHead session. In this sense, it
degenerate form of a session. is a degenerate form of a session.
Sessions on the tail MAY be established dynamically, based on the Sessions on the tail MAY be established dynamically, based on the
receipt of a Multipoint BFD Control packet from the head, and are of receipt of a multipoint BFD Control packet from the head, and are of
type MultipointTail. Tail sessions always take the Passive role, per type MultipointTail. Tail sessions always take the Passive role, per
section 6.1 [RFC5880]. Section 6.1 of [RFC5880].
5.7. Discriminators and Packet Demultiplexing 5.7. Discriminators and Packet Demultiplexing
The use of Discriminators is somewhat different in Multipoint BFD The use of discriminators is somewhat different in multipoint BFD
than in Point-to-point BFD. than in point-to-point BFD.
The head sends Multipoint BFD Control packets over the multipoint The head sends multipoint BFD Control packets over the multipoint
path via the MultipointHead session with My Discriminator set to a path via the MultipointHead session with My Discriminator set to a
value bound to the multipoint path, and with Your Discriminator set value bound to the multipoint path and with Your Discriminator set to
to zero. zero.
IP and MPLS multipoint tails MUST demultiplex BFD packets based on a IP and MPLS multipoint tails MUST demultiplex BFD packets based on a
combination of the source address, My Discriminator and the identity combination of the source address, My Discriminator, and the identity
of the multipoint path which the Multipoint BFD Control packet was of the multipoint path that the multipoint BFD Control packet was
received from. Together they uniquely identify the head of the received from. Together they uniquely identify the head of the
multipoint path. Bootstrapping a BFD session to multipoint MPLS LSP multipoint path. Bootstrapping a BFD session to multipoint MPLS
may use the control plane, e.g., as described in Label Switched Path (LSP) may use the control plane, e.g., as
[I-D.ietf-bess-mvpn-fast-failover], and is outside the scope of this described in [MVPN-FAILOVER], and is outside the scope of this
document. document.
Note that, unlike point-to-point sessions, the My Discriminator value Note that, unlike point-to-point sessions, the My Discriminator value
on MultipointHead session MUST NOT be changed during the life of a on the MultipointHead session MUST NOT be changed during the life of
session. This is a side effect of the more complex demultiplexing a session. This is a side effect of the more complex demultiplexing
scheme. scheme.
5.8. Packet consumption on tails 5.8. Packet Consumption on Tails
BFD packets received on tails for an IP multicast group MUST be BFD packets received on tails for an IP multicast group MUST be
consumed by tails and MUST NOT be forwarded to receivers. Nodes with consumed by tails and MUST NOT be forwarded to receivers. Nodes with
the BFD session of type MultipointTail MUST identify packets received the BFD session of type MultipointTail MUST identify packets received
on an IP multipoint path as BFD control packet if the destination UDP on an IP multipoint path as a BFD Control packet if the destination
port value equals 3784. UDP port value equals 3784.
For multipoint LSPs, when IP/UDP encapsulation of BFD control packets For multipoint LSPs, when IP/UDP encapsulation of BFD Control packets
is used, MultipointTail MUST expect destination UDP port 3784. is used, MultipointTail MUST expect destination UDP port 3784. The
Destination IP address of BFD control packet MUST be in 127.0.0.0/8 destination IP address of a BFD Control packet MUST be in the
range for IPv4 or in 0:0:0:0:0:FFFF:7F00:0/104 range for IPv6. The 127.0.0.0/8 range for IPv4 or in the 0:0:0:0:0:FFFF:7F00:0/104 range
use of these destination addresses is consistent with the for IPv6. The use of these destination addresses is consistent with
explanations and usage in [RFC8029]. Packets identified as BFD the explanations and usage in [RFC8029]. Packets identified as BFD
packets MUST be consumed by MultipointTail and demultiplexed as packets MUST be consumed by MultipointTail and demultiplexed as
described in Section 5.13.2. Use of other types of encapsulation of described in Section 5.13.2. Use of other types of encapsulation of
the BFD control message over multipoint LSP is outside the scope of the BFD control message over multipoint LSP is outside the scope of
this document. this document.
5.9. Bringing Up and Shutting Down Multipoint BFD Service 5.9. Bringing Up and Shutting Down Multipoint BFD Service
Because there is no three-way handshake in Multipoint BFD, a newly Because there is no three-way handshake in multipoint BFD, a newly
started head (that does not have any previous state information started head (that does not have any previous state information
available) SHOULD start with bfd.SessionState set to Down and available) SHOULD start with bfd.SessionState set to Down, and
bfd.RequiredMinRxInterval MUST be set to zero in the MultipointHead bfd.RequiredMinRxInterval MUST be set to zero in the MultipointHead
session. The session SHOULD remain in this state for a time equal to session. The session SHOULD remain in this state for a time equal to
(bfd.DesiredMinTxInterval * bfd.DetectMult). This will ensure that (bfd.DesiredMinTxInterval * bfd.DetectMult). This will ensure that
all MultipointTail sessions are reset (so long as the restarted head all MultipointTail sessions are reset (so long as the restarted head
is using the same or a larger value of bfd.DesiredMinTxInterval than is using the same or a larger value of bfd.DesiredMinTxInterval than
it did previously). it did previously).
Multipoint BFD service is brought up by administratively setting Multipoint BFD service is brought up by administratively setting
bfd.SessionState to Up in the MultipointHead session. bfd.SessionState to Up in the MultipointHead session.
The head of a multipoint BFD session may wish to shut down its BFD The head of a multipoint BFD session may wish to shut down its BFD
service in a controlled fashion. This is desirable because the tails service in a controlled fashion. This is desirable because the tails
need not wait a detection time prior to declaring the multipoint need not wait for a Detection Time prior to declaring the multipoint
session to be down (and taking whatever action is necessary in that session to be down (and taking whatever action is necessary in that
case). case).
To shut down a multipoint session in a controlled fashion the head To shut down a multipoint session in a controlled fashion, the head
MUST administratively set bfd.SessionState in the MultipointHead MUST administratively set bfd.SessionState in the MultipointHead
session to either Down or AdminDown and SHOULD set session to either Down or AdminDown and SHOULD set
bfd.RequiredMinRxInterval to zero. The session SHOULD send BFD bfd.RequiredMinRxInterval to zero. The session SHOULD send BFD
Control packets in this state for a period equal to Control packets in this state for a period equal to
(bfd.DesiredMinTxInterval * bfd.DetectMult). Alternatively, the head (bfd.DesiredMinTxInterval * bfd.DetectMult). Alternatively, the head
MAY stop transmitting BFD Control packets and not send any more BFD MAY stop transmitting BFD Control packets and not send any more BFD
Control packets with the new state (Down or AdminDown). Tails will Control packets with the new state (Down or AdminDown). Tails will
declare the multipoint session down only after the detection time declare the multipoint session down only after the Detection Time
interval runs out. interval runs out.
5.10. Timer Manipulation 5.10. Timer Manipulation
Because of the one-to-many mapping, a session of type MultipointHead Because of the one-to-many mapping, a session of type MultipointHead
SHOULD NOT initiate a Poll Sequence in conjunction with timer value SHOULD NOT initiate a Poll Sequence in conjunction with timer value
changes. However, to indicate a change in the packets, changes. However, to indicate a change in the packets, a
MultipointHead session MUST send packets with the P bit set. MultipointHead session MUST send packets with the P bit set. A
MultipointTail session MUST NOT reply if the packet has M and P bits MultipointTail session MUST NOT reply if the packet has the M and P
set and bfd.RequiredMinRxInterval set to 0. Because the Poll bits set and bfd.RequiredMinRxInterval set to zero. Because the Poll
Sequence is not used, the tail cannot negotiate down MultpointHead's Sequence is not used, the tail cannot negotiate down MultpointHead's
transmit interval. If the value of Desired Min TX Interval in the transmit interval. If the value of Desired Min TX Interval in the
BFD Control packet received by MultipointTail is too high (that BFD Control packet received by MultipointTail is too high (that
determination may change in time based on the current environment) it determination may change in time based on the current environment),
must be handled by the implementation and may be controlled by local it must be handled by the implementation and may be controlled by
policy, e.g., close the MultipointTail session. local policy, e.g., close the MultipointTail session.
The MultipointHead, when changing the transmit interval to a higher The MultipointHead, when changing the transmit interval to a higher
value, MUST send BFD control packets with P bit set at the old value, MUST send BFD Control packets with the P bit set at the old
transmit interval before using the higher value in order to avoid transmit interval before using the higher value in order to avoid
false detection timeouts at the tails. MultipointHead session MAY false detection timeouts at the tails. A MultipointHead session MAY
also wait some amount of time before making the changes to the also wait some amount of time before making the changes to the
transmit interval (through configuration). transmit interval (through configuration).
Change in the value of bfd.RequiredMinRxInterval is outside the scope Change in the value of bfd.RequiredMinRxInterval is outside the scope
of this document and is discussed in of this document and is discussed in [RFC8563].
[I-D.ietf-bfd-multipoint-active-tail].
5.11. Detection Times 5.11. Detection Times
Multipoint BFD is inherently asymmetric. As such, each session type Multipoint BFD is inherently asymmetric. As such, each session type
has a different approach to detection times. has a different approach to Detection Times.
Since MultipointHead sessions never receive packets, they do not Since MultipointHead sessions never receive packets, they do not
calculate a detection time. calculate a Detection Time.
MultipointTail sessions cannot influence the transmission rate of the MultipointTail sessions cannot influence the transmission rate of the
MultipointHead session using the Required Min Rx Interval field MultipointHead session using the Required Min Rx Interval field
because of its one-to-many nature. As such, the detection time because of its one-to-many nature. As such, the Detection Time
calculation for a MultipointTail session does not use calculation for a MultipointTail session does not use
bfd.RequiredMinRxInterval. The detection time is calculated as the bfd.RequiredMinRxInterval. The Detection Time is calculated as the
product of the last received values of Desired Min TX Interval and product of the last received values of Desired Min TX Interval and
Detect Mult. Detect Mult.
The value of bfd.DetectMult may be changed at any time on any session The value of bfd.DetectMult may be changed at any time on any session
type. type.
5.12. State Maintenance for Down/AdminDown Sessions 5.12. State Maintenance for Down/AdminDown Sessions
The length of time session state is kept after the session goes down The length of time the session state is kept after the session goes
determines how long the session will continue to send BFD Control down determines how long the session will continue to send BFD
packets (since no packets can be sent after the session is Control packets (since no packets can be sent after the session is
destroyed). destroyed).
5.12.1. MultipointHead Sessions 5.12.1. MultipointHead Sessions
When a MultipointHead session transitions to states Down or When a MultipointHead session transitions to states Down or
AdminDown, the state SHOULD be maintained for a period equal to AdminDown, the state SHOULD be maintained for a period equal to
(bfd.DesiredMinTxInterval * bfd.DetectMult) to ensure that the tails (bfd.DesiredMinTxInterval * bfd.DetectMult) to ensure that the tails
more quickly detect the session going down (by continuing to transmit more quickly detect the session going down (by continuing to transmit
BFD Control packets with the new state). BFD Control packets with the new state).
5.12.2. MultipointTail Sessions 5.12.2. MultipointTail Sessions
MultipointTail sessions MAY be destroyed immediately upon leaving Up MultipointTail sessions MAY be destroyed immediately upon leaving Up
state, since tail will transmit no packets. state, since the tail will transmit no packets.
Otherwise, MultipointTail sessions SHOULD be maintained as long as Otherwise, MultipointTail sessions SHOULD be maintained as long as
BFD Control packets are being received by it (which by definition BFD Control packets are being received by it (which by definition
will indicate that the head is not Up). will indicate that the head is not Up).
5.13. Base Specification Text Replacement 5.13. Base Specification Text Replacement
The following sections are meant to replace the corresponding The following sections are meant to replace the corresponding
sections in the base specification [RFC5880] in support of BFD for sections in the base specification [RFC5880] to support BFD for
multipoint networks while not changing processing for point-to-point multipoint networks while not changing processing for point-to-point
BFD. BFD.
5.13.1. Reception of BFD Control Packets 5.13.1. Reception of BFD Control Packets
The following procedure replaces the entire section 6.8.6 of The following procedure replaces Section 6.8.6 of [RFC5880] entirely.
[RFC5880].
When a BFD Control packet is received, the following procedure MUST When a BFD Control packet is received, the following procedure MUST
be followed, in the order specified. If the packet is discarded be followed, in the order specified. If the packet is discarded
according to these rules, processing of the packet MUST cease at that according to these rules, processing of the packet MUST cease at that
point. point.
If the version number is not correct (1), the packet MUST be If the version number is not correct (1), the packet MUST be
discarded. discarded.
If the Length field is less than the minimum correct value (24 if If the Length field is less than the minimum correct value (24 if
skipping to change at page 11, line 32 skipping to change at page 12, line 29
discarded. discarded.
If the Length field is greater than the payload of the If the Length field is greater than the payload of the
encapsulating protocol, the packet MUST be discarded. encapsulating protocol, the packet MUST be discarded.
If the Detect Mult field is zero, the packet MUST be discarded. If the Detect Mult field is zero, the packet MUST be discarded.
If the My Discriminator field is zero, the packet MUST be If the My Discriminator field is zero, the packet MUST be
discarded. discarded.
Demultiplex the packet to a session according to Section 5.13.2 Demultiplex the packet to a session according to Section 5.13.2.
below. The result is either a session of the proper type, or the The result is either a session of the proper type, or the packet
packet is discarded (and packet processing MUST cease). is discarded (and packet processing MUST cease).
If the A bit is set and no authentication is in use (bfd.AuthType If the A bit is set and no authentication is in use (bfd.AuthType
is zero), the packet MUST be discarded. is zero), the packet MUST be discarded.
If the A bit is clear and authentication is in use (bfd.AuthType If the A bit is clear and authentication is in use (bfd.AuthType
is nonzero), the packet MUST be discarded. is nonzero), the packet MUST be discarded.
If the A bit is set, the packet MUST be authenticated under the If the A bit is set, the packet MUST be authenticated under the
rules of [RFC5880] section 6.7, based on the authentication type rules of Section 6.7 of [RFC5880], based on the authentication
in use (bfd.AuthType). This may cause the packet to be discarded. type in use (bfd.AuthType). This may cause the packet to be
discarded.
Set bfd.RemoteDiscr to the value of My Discriminator. Set bfd.RemoteDiscr to the value of My Discriminator.
Set bfd.RemoteState to the value of the State (Sta) field. Set bfd.RemoteState to the value of the State (Sta) field.
Set bfd.RemoteDemandMode to the value of the Demand (D) bit. Set bfd.RemoteDemandMode to the value of the Demand (D) bit.
Set bfd.RemoteMinRxInterval to the value of Required Min RX Set bfd.RemoteMinRxInterval to the value of Required Min RX
Interval. Interval.
If the Required Min Echo RX Interval field is zero, the If the Required Min Echo RX Interval field is zero, the
transmission of Echo packets, if any, MUST cease. transmission of Echo packets, if any, MUST cease.
If a Poll Sequence is being transmitted by the local system and If a Poll Sequence is being transmitted by the local system and
the Final (F) bit in the received packet is set, the Poll Sequence the Final (F) bit in the received packet is set, the Poll Sequence
MUST be terminated. MUST be terminated.
If bfd.SessionType is PointToPoint, update the transmit interval If bfd.SessionType is PointToPoint, update the transmit interval
as described in [RFC5880] section 6.8.2. as described in Section 6.8.2 of [RFC5880].
If bfd.SessionType is PointToPoint, update the Detection Time as If bfd.SessionType is PointToPoint, update the Detection Time as
described in section 6.8.4 of [RFC5880]. described in Section 6.8.4 of [RFC5880].
Else Else
If bfd.SessionType is MultipointTail, then update the Detection If bfd.SessionType is MultipointTail, then update the Detection
Time as the product of the last received values of Desired Min Time as the product of the last received values of Desired Min
TX Interval and Detect Mult, as described in Section 5.11 of TX Interval and Detect Mult, as described in Section 5.11 of
this specification. this specification.
If bfd.SessionState is AdminDown If bfd.SessionState is AdminDown
Discard the packet Discard the packet
If the received state is AdminDown If the received State is AdminDown
If bfd.SessionState is not Down If bfd.SessionState is not Down
Set bfd.LocalDiag to 3 (Neighbor signaled session down) Set bfd.LocalDiag to 3 (Neighbor signaled session down)
Set bfd.SessionState to Down Set bfd.SessionState to Down
Else Else
If bfd.SessionState is Down If bfd.SessionState is Down
skipping to change at page 13, line 26 skipping to change at page 14, line 26
Else (bfd.SessionState is Up) Else (bfd.SessionState is Up)
If received State is Down If received State is Down
Set bfd.LocalDiag to 3 (Neighbor signaled session down) Set bfd.LocalDiag to 3 (Neighbor signaled session down)
Set bfd.SessionState to Down Set bfd.SessionState to Down
Check to see if Demand mode should become active or not (see Check to see if Demand mode should become active or not (see
[RFC5880] section 6.6). [RFC5880], Section 6.6).
If bfd.RemoteDemandMode is 1, bfd.SessionState is Up and If bfd.RemoteDemandMode is 1, bfd.SessionState is Up, and
bfd.RemoteSessionState is Up, Demand mode is active on the remote bfd.RemoteSessionState is Up, Demand mode is active on the remote
system and the local system MUST cease the periodic transmission system and the local system MUST cease the periodic transmission
of BFD Control packets (see Section 5.13.3). of BFD Control packets (see Section 5.13.3).
If bfd.RemoteDemandMode is 0, or bfd.SessionState is not Up, or If bfd.RemoteDemandMode is zero, bfd.SessionState is not Up, or
bfd.RemoteSessionState is not Up, Demand mode is not active on the bfd.RemoteSessionState is not Up, Demand mode is not active on the
remote system and the local system MUST send periodic BFD Control remote system and the local system MUST send periodic BFD Control
packets (see Section 5.13.3). packets (see Section 5.13.3).
If the Poll (P) bit is set, and bfd.SessionType is PointToPoint, If the Poll (P) bit is set, and bfd.SessionType is PointToPoint,
send a BFD Control packet to the remote system with the Poll (P) send a BFD Control packet to the remote system with the Poll (P)
bit clear, and the Final (F) bit set (see Section 5.13.3). bit clear, and the Final (F) bit set (see Section 5.13.3).
If the packet was not discarded, it has been received for purposes If the packet was not discarded, it has been received for purposes
of the Detection Time expiration rules in [RFC5880] section 6.8.4. of the Detection Time expiration rules in Section 6.8.4 of
[RFC5880].
5.13.2. Demultiplexing BFD Control Packets 5.13.2. Demultiplexing BFD Control Packets
This section is part of the replacement for [RFC5880] section 6.8.6, This section is part of the replacement for Section 6.8.6 of
separated for clarity. [RFC5880]; it is separated for clarity.
If the Multipoint (M) bit is set If the Multipoint (M) bit is set
If the Your Discriminator field is nonzero, the packet MUST be If the Your Discriminator field is nonzero, the packet MUST be
discarded. discarded.
Select a session as based on source address, My Discriminator Select a session based on the source address, My Discriminator,
and the identity of the multipoint path which the Multipoint and the identity of the multipoint path on which the multipoint
BFD Control packet was received. BFD Control packet was received.
If a session is found, and bfd.SessionType is not If a session is found, and bfd.SessionType is not
MultipointTail, the packet MUST be discarded. MultipointTail, the packet MUST be discarded.
Else Else
If a session is not found, a new session of type If a session is not found, a new session of type
MultipointTail MAY be created, or the packet MAY be MultipointTail MAY be created, or the packet MAY be
discarded. This choice can be controlled by the local discarded. This choice can be controlled by the local
policy, e.g., by settinga maximum number of MultipointTail policy, e.g., by setting a maximum number of MultipointTail
sessions. Use of the local policy and the exact mechanism sessions. Use of the local policy and the exact mechanism
of it are outside the scope of this specification. of it are outside the scope of this specification.
Else (Multipoint bit is clear) Else (Multipoint (M) bit is clear)
If the Your Discriminator field is nonzero If the Your Discriminator field is nonzero
Select a session based on the value of Your Discriminator. Select a session based on the value of Your Discriminator.
If no session is found, the packet MUST be discarded. If no session is found, the packet MUST be discarded.
Else (Your Discriminator is zero) Else (Your Discriminator is zero)
If the State field is not Down or AdminDown, the packet MUST If the State field is not Down or AdminDown, the packet MUST
be discarded. be discarded.
Otherwise, the session MUST be selected based on some Otherwise, the session MUST be selected based on some
combination of other fields, possibly including source combination of other fields, possibly including source
addressing information, the My Discriminator field, and the addressing information, the My Discriminator field, and the
interface over which the packet was received. The exact interface over which the packet was received. The exact
method of selection is application-specific and is thus method of selection is application specific and is thus
outside the scope of this specification. outside the scope of this specification.
If a matching session is found, and bfd.SessionType is not If a matching session is found, and bfd.SessionType is not
PointToPoint, the packet MUST be discarded. PointToPoint, the packet MUST be discarded.
If a matching session is not found, a new session of type If a matching session is not found, a new session of type
PointToPoint MAY be created, or the packet MAY be discarded. PointToPoint MAY be created, or the packet MAY be discarded.
This choice MAY be controlled by a local policy and is This choice MAY be controlled by a local policy and is
outside the scope of this specification. outside the scope of this specification.
If the State field is Init and bfd.SessionType is not If the State field is Init and bfd.SessionType is not
PointToPoint, the packet MUST be discarded. PointToPoint, the packet MUST be discarded.
5.13.3. Transmitting BFD Control Packets 5.13.3. Transmitting BFD Control Packets
The following procedure replaces the entire section 6.8.7 of The following procedure replaces Section 6.8.7 of [RFC5880] entirely.
[RFC5880].
With the exceptions listed in the remainder of this section, a system With the exceptions listed in the remainder of this section, a system
MUST NOT transmit BFD Control packets at an interval less than the MUST NOT transmit BFD Control packets at an interval less than the
larger of bfd.DesiredMinTxInterval and bfd.RemoteMinRxInterval, less larger of bfd.DesiredMinTxInterval and bfd.RemoteMinRxInterval, less
applied jitter (see below). In other words, the system reporting the applied jitter (see below). In other words, the system reporting the
slower rate determines the transmission rate. slower rate determines the transmission rate.
The periodic transmission of BFD Control packets MUST be jittered on The periodic transmission of BFD Control packets MUST be jittered on
a per-packet basis by up to 25%, that is, the interval MUST be a per-packet basis by up to 25%; that is, the interval MUST be
reduced by a random value of 0 to 25%, in order to avoid self- reduced by a random value of 0 to 25%, in order to avoid self-
synchronization with other systems on the same subnetwork. Thus, the synchronization with other systems on the same subnetwork. Thus, the
average interval between packets will be roughly 12.5% less than that average interval between packets will be roughly 12.5% less than that
negotiated. negotiated.
If bfd.DetectMult is equal to 1, the interval between transmitted BFD If bfd.DetectMult is equal to 1, the interval between transmitted BFD
Control packets MUST be no more than 90% of the negotiated Control packets MUST be no more than 90% of the negotiated
transmission interval, and MUST be no less than 75% of the negotiated transmission interval and MUST be no less than 75% of the negotiated
transmission interval. This is to ensure that, on the remote system, transmission interval. This is to ensure that, on the remote system,
the calculated Detection Time does not pass prior to the receipt of the calculated Detection Time does not pass prior to the receipt of
the next BFD Control packet. the next BFD Control packet.
A system MUST NOT transmit any BFD Control packets if bfd.RemoteDiscr A system MUST NOT transmit any BFD Control packets if bfd.RemoteDiscr
is zero and the system is taking the Passive role. is zero and the system is taking the Passive role.
A system MUST NOT transmit any BFD Control packets if bfd.SessionType A system MUST NOT transmit any BFD Control packets if bfd.SessionType
is MultipointTail. is MultipointTail.
A system MUST NOT periodically transmit BFD Control packets if Demand A system MUST NOT periodically transmit BFD Control packets if Demand
mode is active on the remote system (bfd.RemoteDemandMode is 1, mode is active on the remote system (bfd.RemoteDemandMode is 1,
bfd.SessionState is Up, and bfd.RemoteSessionState is Up) and a Poll bfd.SessionState is Up, and bfd.RemoteSessionState is Up), and a Poll
Sequence is not being transmitted. Sequence is not being transmitted.
A system MUST NOT periodically transmit BFD Control packets if A system MUST NOT periodically transmit BFD Control packets if
bfd.RemoteMinRxInterval is zero. bfd.RemoteMinRxInterval is zero.
If bfd.SessionType is MultipointHead, the transmit interval MUST be If bfd.SessionType is MultipointHead, the transmit interval MUST be
set to bfd.DesiredMinTxInterval (this should happen automatically, as set to bfd.DesiredMinTxInterval (this should happen automatically, as
bfd.RemoteMinRxInterval will be zero). bfd.RemoteMinRxInterval will be zero).
If bfd.SessionType is not MultipointHead, the transmit interval MUST If bfd.SessionType is not MultipointHead, the transmit interval MUST
be recalculated whenever bfd.DesiredMinTxInterval changes, or be recalculated whenever bfd.DesiredMinTxInterval changes, or
whenever bfd.RemoteMinRxInterval changes, and is equal to the greater whenever bfd.RemoteMinRxInterval changes, and is equal to the greater
of those two values. See [RFC5880] sections 6.8.2 and 6.8.3 for of those two values. See Sections 6.8.2 and 6.8.3 of [RFC5880] for
details on transmit timers. details on transmit timers.
A system MUST NOT set the Demand (D) bit if bfd.SessionType is A system MUST NOT set the Demand (D) bit if bfd.SessionType is
MultipointTail. MultipointTail.
A system MUST NOT set the Demand (D) bit if bfd.SessionType A system MUST NOT set the Demand (D) bit if bfd.SessionType is
PointToPoint unless bfd.DemandMode is 1, bfd.SessionState is Up, and PointToPoint unless bfd.DemandMode is 1, bfd.SessionState is Up, and
bfd.RemoteSessionState is Up. bfd.RemoteSessionState is Up.
If bfd.SessionType is PointToPoint or MultipointHead, a BFD Control If bfd.SessionType is PointToPoint or MultipointHead, a BFD Control
packet SHOULD be transmitted during the interval between periodic packet SHOULD be transmitted during the interval between periodic
Control packet transmissions when the contents of that packet would Control packet transmissions when the contents of that packet would
differ from that in the previously transmitted packet (other than the differ from that in the previously transmitted packet (other than the
Poll and Final bits) in order to more rapidly communicate a change in Poll (P) and Final (F) bits) in order to more rapidly communicate a
state. change in state.
The contents of transmitted BFD Control packets MUST be set as The contents of transmitted BFD Control packets MUST be set as
follows: follows:
Version Version
Set to the current version number (1). Set to the current version number (1).
Diagnostic (Diag) Diagnostic (Diag)
Set to bfd.LocalDiag. Set to bfd.LocalDiag.
State (Sta) State (Sta)
Set to the value indicated by bfd.SessionState. Set to the value indicated by bfd.SessionState.
Poll (P) Poll (P)
Set to 1 if the local system is sending a Poll Sequence or is a Set to 1 if the local system is sending a Poll Sequence or is a
session of type MultipointHead soliciting the identities of the session of type MultipointHead soliciting the identities of the
tails, or 0 if not. tails, or zero if not.
Final (F) Final (F)
Set to 1 if the local system is responding to a Control packet Set to 1 if the local system is responding to a BFD Control
received with the Poll (P) bit set, or 0 if not. packet received with the Poll (P) bit set, or zero if not.
Control Plane Independent (C) Control Plane Independent (C)
Set to 1 if the local system's BFD implementation is Set to 1 if the local system's BFD implementation is
independent of the control plane (it can continue to function independent of the control plane (it can continue to function
through a disruption of the control plane). through a disruption of the control plane).
Authentication Present (A) Authentication Present (A)
Set to 1 if authentication is in use in this session Set to 1 if authentication is in use in this session
(bfd.AuthType is nonzero), or 0 if not. (bfd.AuthType is nonzero), or zero if not.
Demand (D) Demand (D)
Set to bfd.DemandMode if bfd.SessionState is Up and Set to bfd.DemandMode if bfd.SessionState is Up and
bfd.RemoteSessionState is Up. Set to 1 if bfd.SessionType is bfd.RemoteSessionState is Up. Set to 1 if bfd.SessionType is
MultipointHead. Otherwise it is set to 0. MultipointHead. Otherwise, it is set to zero.
Multipoint (M) Multipoint (M)
Set to 1 if bfd.SessionType is MultipointHead. Otherwise, it Set to 1 if bfd.SessionType is MultipointHead. Otherwise, it
is set to 0. is set to zero.
Detect Mult Detect Mult
Set to bfd.DetectMult. Set to bfd.DetectMult.
Length Length
Set to the appropriate length, based on the fixed header length Set to the appropriate length, based on the fixed header length
(24) plus any Authentication Section. (24) plus any Authentication Section.
skipping to change at page 17, line 45 skipping to change at page 19, line 11
Desired Min TX Interval Desired Min TX Interval
Set to bfd.DesiredMinTxInterval. Set to bfd.DesiredMinTxInterval.
Required Min RX Interval Required Min RX Interval
Set to bfd.RequiredMinRxInterval. Set to bfd.RequiredMinRxInterval.
Required Min Echo RX Interval Required Min Echo RX Interval
Set to 0 if bfd.SessionType is MultipointHead or Set to zero if bfd.SessionType is MultipointHead or
MultipointTail. Otherwise, set to the minimum required Echo MultipointTail. Otherwise, set to the minimum required Echo
packet receive interval for this session. If this field is set packet receive interval for this session. If this field is set
to zero, the local system is unwilling or unable to loop back to zero, the local system is unwilling or unable to loop back
BFD Echo packets to the remote system, and the remote system BFD Echo packets to the remote system, and the remote system
will not send Echo packets. will not send Echo packets.
Authentication Section Authentication Section
Included and set according to the rules in [RFC5880] section Included and set according to the rules in Section 6.7 of
6.7 if authentication is in use (bfd.AuthType is nonzero). [RFC5880] if authentication is in use (bfd.AuthType is
Otherwise, this section is not present. nonzero). Otherwise, this section is not present.
6. Congestion Considerations 6. Congestion Considerations
As a foreword, although congestion can occur because of a number of As a foreword, although congestion can occur because of a number of
factors, it should be noted that high transmission rates are by factors, it should be noted that high transmission rates are by
themselves subject to creating congestion either along the path or at themselves subject to creating congestion either along the path or at
the tail end(s). As such, as stated in [RFC5883]: the tail end(s). As such, as stated in [RFC5883]:
"it is required that the operator correctly provision the rates at it is required that the operator correctly provision the rates at
which BFD is transmitted to avoid congestion (e.g link, I/O, CPU) which BFD is transmitted to avoid congestion (e.g link, I/O, CPU)
and false failure detection." and false failure detection.
Use of BFD in multipoint networks, as specified in this document, Use of BFD in multipoint networks, as specified in this document,
over multiple hops requires consideration of the mechanisms to react over multiple hops requires consideration of the mechanisms to react
to network congestion. Requirements stated in Section 7 of the BFD to network congestion. Requirements stated in Section 7 of the BFD
base specification [RFC5880] equally apply to BFD in multipoint base specification [RFC5880] equally apply to BFD in multipoint
networks and are repeated here: networks and are repeated here:
"When BFD is used across multiple hops, a congestion control When BFD is used across multiple hops, a congestion control
mechanism MUST be implemented, and when congestion is detected, mechanism MUST be implemented, and when congestion is detected,
the BFD implementation MUST reduce the amount of traffic it the BFD implementation MUST reduce the amount of traffic it
generates." generates.
The mechanism to control the load of BFD traffic MAY use BFD's The mechanism to control the load of BFD traffic MAY use BFD's
configuration interface to control BFD state variable configuration interface to control BFD state variable
bfd.DesiredMinTxInterval. However, such a control loop do not form bfd.DesiredMinTxInterval. However, such a control loop does not form
part of the BFD protocol itself and its specification is thus outside part of the BFD protocol itself, and its specification is thus
the scope of this document. outside the scope of this document.
Additional considerations apply to BFD in multipoint networks, as Additional considerations apply to BFD in multipoint networks, as
specified in this document. Indeed, because a tail does not transmit specified in this document. Indeed, because a tail does not transmit
any BFD Control packets to the head of the BFD session, such head any BFD Control packets to the head of the BFD session, such a head
node has no BFD based mechanism to be aware of the state of the node has no BFD-based mechanism and thus is not aware of the state of
session at the tail. In the absence of any other mechanism, the head the session at the tail. In the absence of any other mechanism, the
of the session could thus continue to send packets towards the head of the session could thus continue to send packets towards the
tail(s) even though a link failure has happened. In such a scenario tail(s) even though a link failure has happened. In such a scenario,
when it is required for the head of the session to be aware of the when it is required for the head of the session to be aware of the
state of the tail of the session, it is RECOMMENDED to implement state of the tail of the session, it is RECOMMENDED to implement the
[I-D.ietf-bfd-multipoint-active-tail]. extension described in [RFC8563].
7. IANA Considerations 7. IANA Considerations
This document has no actions for IANA. This document has no IANA actions.
8. Security Considerations 8. Security Considerations
The same security considerations as those described in [RFC5880] The same security considerations as those described in [RFC5880]
apply to this document. Additionally, implementations that create apply to this document. Additionally, implementations that create
MultpointTail sessions dynamically upon receipt of Multipoint BFD MultpointTail sessions dynamically upon receipt of multipoint BFD
Control packets MUST implement protective measures to prevent an Control packets MUST implement protective measures to prevent an
infinite number of MultipointTail sessions being created. Below are infinite number of MultipointTail sessions from being created. Below
listed some points to be considered in such implementations. are some points to consider in such implementations.
If a Multipoint BFD Control packet did not arrive on a multicast If a multipoint BFD Control packet did not arrive on a multicast
path (e.g., on the expected interface, with expected MPLS label, path (e.g., on the expected interface, with the expected MPLS
etc), then a MultipointTail session should not be created. label, etc.), a MultipointTail session should not be created.
If redundant streams are expected for a given multicast stream, If redundant streams are expected for a given multicast stream,
then the implementations should not create more MultipointTail the implementations should not create more MultipointTail sessions
sessions than the number of streams. Additionally, when the than the number of streams. Additionally, when the number of
number of MultipointTail sessions exceeds the number of expected MultipointTail sessions exceeds the number of expected streams,
streams, then the implementation should generate an alarm to users the implementation should generate an alarm to users to indicate
to indicate the anomaly. the anomaly.
The implementation should have a reasonable upper bound on the The implementation should have a reasonable upper bound on the
number of MultipointHead sessions that can be created, with the number of MultipointHead sessions that can be created, with the
upper bound potentially being computed based on the load these upper bound potentially being computed based on the load these
would generate. would generate.
The implementation should have a reasonable upper bound on the The implementation should have a reasonable upper bound on the
number of MultipointTail sessions that can be created, with the number of MultipointTail sessions that can be created, with the
upper bound potentially being computed based on the number of upper bound potentially being computed based on the number of
multicast streams that the system is expecting. multicast streams that the system is expecting.
skipping to change at page 19, line 50 skipping to change at page 21, line 12
to have a common authentication key in order for the tails to to have a common authentication key in order for the tails to
validate multipoint BFD Control packets. validate multipoint BFD Control packets.
Shared keys in multipoint scenarios allow any tail to spoof the head Shared keys in multipoint scenarios allow any tail to spoof the head
from the viewpoint of any other tail. For this reason, using shared from the viewpoint of any other tail. For this reason, using shared
keys to authenticate BFD Control packets in multipoint scenarios is a keys to authenticate BFD Control packets in multipoint scenarios is a
significant security exposure unless all tails can be trusted not to significant security exposure unless all tails can be trusted not to
spoof the head. Otherwise, asymmetric message authentication would spoof the head. Otherwise, asymmetric message authentication would
be needed, e.g., protocols that use Timed Efficient Stream Loss- be needed, e.g., protocols that use Timed Efficient Stream Loss-
Tolerant Authentication (TESLA) as described in [RFC4082]. Tolerant Authentication (TESLA) as described in [RFC4082].
Applicability of the assymetric message authentication to BFD for Applicability of the asymmetric message authentication to BFD for
multipoint networks is ouside the scope of this specification and is multipoint networks is outside the scope of this specification and is
for further study. for further study.
9. Contributors 9. References
Rahul Aggarwal of Juniper Networks and George Swallow of Cisco
Systems provided the initial idea for this specification and
contributed to its development.
10. Acknowledgments
Authors would also like to thank Nobo Akiya, Vengada Prasad Govindan,
Jeff Haas, Wim Henderickx, Gregory Mirsky and Mingui Zhang who have
greatly contributed to this document.
11. References
11.1. Normative References 9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>. <https://www.rfc-editor.org/info/rfc5880>.
[RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S. [RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and
Pallagatti, "Seamless Bidirectional Forwarding Detection S. Pallagatti, "Seamless Bidirectional Forwarding
(S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016, Detection (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July
<https://www.rfc-editor.org/info/rfc7880>. 2016, <https://www.rfc-editor.org/info/rfc7880>.
[RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., [RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
Aldrin, S., and M. Chen, "Detecting Multiprotocol Label Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
Switched (MPLS) Data-Plane Failures", RFC 8029, Switched (MPLS) Data-Plane Failures", RFC 8029,
DOI 10.17487/RFC8029, March 2017, DOI 10.17487/RFC8029, March 2017,
<https://www.rfc-editor.org/info/rfc8029>. <https://www.rfc-editor.org/info/rfc8029>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
11.2. Informational References 9.2. Informative References
[I-D.ietf-bess-mvpn-fast-failover]
Morin, T., Kebler, R., and G. Mirsky, "Multicast VPN fast
upstream failover", draft-ietf-bess-mvpn-fast-failover-04
(work in progress), November 2018.
[I-D.ietf-bfd-multipoint-active-tail] [MVPN-FAILOVER]
Katz, D., Ward, D., Networks, J., and G. Mirsky, "BFD Morin, T., Ed., Kebler, R., Ed., and G. Mirsky, Ed.,
Multipoint Active Tails.", draft-ietf-bfd-multipoint- "Multicast VPN fast upstream failover", Work in Progress,
active-tail-10 (work in progress), November 2018. draft-ietf-bess-mvpn-fast-failover-05, February 2019.
[RFC4082] Perrig, A., Song, D., Canetti, R., Tygar, J., and B. [RFC4082] Perrig, A., Song, D., Canetti, R., Tygar, J., and
Briscoe, "Timed Efficient Stream Loss-Tolerant B. Briscoe, "Timed Efficient Stream Loss-Tolerant
Authentication (TESLA): Multicast Source Authentication Authentication (TESLA): Multicast Source Authentication
Transform Introduction", RFC 4082, DOI 10.17487/RFC4082, Transform Introduction", RFC 4082, DOI 10.17487/RFC4082,
June 2005, <https://www.rfc-editor.org/info/rfc4082>. June 2005, <https://www.rfc-editor.org/info/rfc4082>.
[RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883, (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
June 2010, <https://www.rfc-editor.org/info/rfc5883>. June 2010, <https://www.rfc-editor.org/info/rfc5883>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>. <https://www.rfc-editor.org/info/rfc6241>.
[RFC8563] Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
Ed., "Bidirectional Forwarding Detection (BFD) Multipoint
Active Tails", RFC 8563, DOI 10.17487/RFC8563, April 2019,
<https://www.rfc-editor.org/info/rfc8563>.
Acknowledgments
The authors would like to thank Nobo Akiya, Vengada Prasad Govindan,
Jeff Haas, Wim Henderickx, Gregory Mirsky, and Mingui Zhang who have
greatly contributed to this document.
Contributors
Rahul Aggarwal of Juniper Networks and George Swallow of Cisco
Systems provided the initial idea for this specification and
contributed to its development.
Authors' Addresses Authors' Addresses
Dave Katz Dave Katz
Juniper Networks Juniper Networks
1194 N. Mathilda Ave. 1194 N. Mathilda Ave.
Sunnyvale, California 94089-1206 Sunnyvale, California 94089-1206
USA United States of America
Email: dkatz@juniper.net Email: dkatz@juniper.net
Dave Ward Dave Ward
Cisco Systems Cisco Systems
170 West Tasman Dr. 170 West Tasman Dr.
San Jose, California 95134 San Jose, California 95134
USA United States of America
Email: wardd@cisco.com Email: wardd@cisco.com
Santosh Pallagatti (editor) Santosh Pallagatti (editor)
Rtbrick VMware
Email: santosh.pallagatti@gmail.com Email: santosh.pallagatti@gmail.com
Greg Mirsky (editor) Greg Mirsky (editor)
ZTE Corp. ZTE Corp.
Email: gregimirsky@gmail.com Email: gregimirsky@gmail.com
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