draft-ietf-bfd-multipoint-14.txt   draft-ietf-bfd-multipoint-15.txt 
Internet Engineering Task Force D. Katz Internet Engineering Task Force D. Katz
Internet-Draft Juniper Networks Internet-Draft Juniper Networks
Updates: 5880, 7880 (if approved) D. Ward Updates: 5880 (if approved) D. Ward
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: August 25, 2018 S. Pallagatti, Ed. Expires: October 19, 2018 S. Pallagatti, Ed.
Individual contributor Individual contributor
G. Mirsky, Ed. G. Mirsky, Ed.
ZTE Corp. ZTE Corp.
February 21, 2018 April 17, 2018
BFD for Multipoint Networks BFD for Multipoint Networks
draft-ietf-bfd-multipoint-14 draft-ietf-bfd-multipoint-15
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.
Requirements Language Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
skipping to change at page 1, line 45 skipping to change at page 1, line 45
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 25, 2018. This Internet-Draft will expire on October 19, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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4.12.1. MultipointHead Sessions . . . . . . . . . . . . . . 9 4.12.1. MultipointHead Sessions . . . . . . . . . . . . . . 9
4.12.2. MultipointTail Sessions . . . . . . . . . . . . . . 10 4.12.2. MultipointTail Sessions . . . . . . . . . . . . . . 10
4.13. Base Specification Text Replacement . . . . . . . . . . . 10 4.13. Base Specification Text Replacement . . . . . . . . . . . 10
4.13.1. Reception of BFD Control Packets . . . . . . . . . . 10 4.13.1. Reception of BFD Control Packets . . . . . . . . . . 10
4.13.2. Demultiplexing BFD Control Packets . . . . . . . . . 13 4.13.2. Demultiplexing BFD Control Packets . . . . . . . . . 13
4.13.3. Transmitting BFD Control Packets . . . . . . . . . . 14 4.13.3. Transmitting BFD Control Packets . . . . . . . . . . 14
5. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 16 5. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
10. Normative References . . . . . . . . . . . . . . . . . . . . 17 10. Normative References . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
The Bidirectional Forwarding Detection protocol [RFC5880] specifies a The Bidirectional Forwarding Detection protocol [RFC5880] specifies a
method for verifying unicast connectivity between a pair of systems. method for verifying unicast connectivity between a pair of systems.
This document defines a method for using BFD to provide verification This document defines a method for using BFD to provide verification
of multipoint or multicast connectivity between a multipoint sender of multipoint or multicast connectivity between a multipoint sender
(the "head") and a set of one or more multipoint receivers (the (the "head") and a set of one or more multipoint receivers (the
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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 supporting this use case. protocol is capable supporting this use case.
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. Due to unidirectional nature, virtually connectivity from the head. Due to unidirectional nature, virtually
all options and timing parameters are controlled by the head. all options and timing parameters are controlled by the head.
As an option, the tail may notify the head of the lack of multipoint As an option, the tail may notify the head of the lack of multipoint
connectivity. Details of tail notification to head are outside the connectivity. Details of tail notification to the head are outside
scope of this document. the scope of this document.
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.
Term "connectivity" in this document is not being used in the context Term "connectivity" in this document is not being used in the context
of connectivity verification in transport network but as an of connectivity verification in transport network but as an
alternative to "continuity", i.e. existence of a path between the alternative to "continuity", i.e. existence of a forwarding path
sender and the receiver. between the sender and the receiver.
This document effectively modifies and adds to the base BFD This document effectively modifies and adds to the base BFD
specification [RFC5880]. specification [RFC5880].
2. Goals 2. 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.
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done independently (and with no penalty in protocol overhead) by done independently (and with no penalty in protocol overhead) by
using point-to-point BFD. using point-to-point BFD.
3. Overview 3. 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 tree. The contents of the BFD packets provide the means for on the tree. 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 the path to have failed. For some applications this is tail declares the path to having failed. For some applications this
the only mechanism necessary; the head can remain ignorant of the is the only mechanism necessary; the head can remain ignorant of the
tails. tails.
A head may wish to be alerted to the tails' connectivity (or lack The head of a multipoint BFD session may wish to be alerted to the
thereof). Details of how the head keeps track of tails and how tails tails' connectivity (or lack thereof). Details of how the head keeps
alert their connectivity to the head are outside scope of this track of tails and how tails alert their connectivity to the head are
document. outside scope of this document.
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. Furthermore, the same head and tail may at both heads and tails, as described in Section 4.7 and
share multiple multipoint paths, and a multipoint path may have Section 4.13.2. Furthermore, the same head and tail may share
multiple heads. multiple multipoint paths, and a multipoint path may have multiple
heads.
4. Protocol Details 4. Protocol Details
This section describes the operation of Multipoint BFD in detail. This section describes the operation of Multipoint BFD in detail.
4.1. Multipoint BFD Control Packets 4.1. 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 M bit [RFC5880]. This means that Multipoint BFD does not depend
on the recipient of a packet to know whether the packet was received on the recipient of a packet to know whether the packet was received
over a multipoint path. This can be useful in scenarios where this over a multipoint path. This can be useful in scenarios where this
information may not be available to the recipient. information may not be available to the recipient.
4.2. Session Model 4.2. 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.
Point-to-point sessions, as described in [RFC5880], are of type
PointToPoint.
The head has a session of type MultipointHead, as defined in The head has a session of type MultipointHead, as defined in
Section 4.4.1, that is bound to a multipoint path. Multipoint BFD Section 4.4.1, 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 4.4.1, associated with a multipoint path. These sessions Section 4.4.1, 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.
4.3. Session Failure Semantics 4.3. Session Failure Semantics
The semantics of session failure are 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 should take appropriate action. disabled) and the tail should take appropriate action.
4.4. State Variables 4.4. 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.
4.4.1. New State Variable Values 4.4.1. 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 S-BFD [RFC7880]
specifications in support of Multipoint BFD. 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. PointToPoint: Classic point-to-point BFD, as described in
[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, according to the rules in Section 4.13 the session is created, according to the rules in Section 4.13
4.4.2. State Variable Initialization and Maintenance 4.4.2. 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 set to 0 for session type MultipointHead. This variable MUST be initialized to 0 for session type
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 0 for session type
MultipointTail. MultipointTail.
4.5. State Machine 4.5. State Machine
The BFD state machine works slightly differently in the multipoint The BFD state machine works slightly differently in the multipoint
application. In particular, since there is a many-to-one mapping, application. In particular, since there is a many-to-one mapping,
three-way handshakes for session establishment and teardown are three-way handshakes for session establishment and teardown are
neither possible nor appropriate. As such there is no Init state. neither possible nor appropriate. As such, there is no Init state.
Sessions of type MultipointHead MUST NOT send BFD control packets Sessions of type MultipointHead MUST NOT send BFD control packets
with the State field being set to INIT, and MUST be ignored on with the State field being set to INIT, and those packets MUST be
receipt. 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, and as such all state transitions are
administratively driven. administratively driven.
4.6. Session Establishment 4.6. Session Establishment
Unlike point-to-point BFD, Multipoint BFD provides a form of Unlike point-to-point BFD, Multipoint BFD provides a form of the
discovery mechanism for tails to discover the head. The minimum discovery mechanism for tails to discover the head. The minimum
amount of a priori information required both on the head and tails is amount of a priori information required both on the head and tails is
the binding to the multipoint path over which BFD is running. The binding to the multipoint path over which BFD is running. The head
head transmits Multipoint BFD packets on that tree, and the tails transmits Multipoint BFD packets on that tree, and the tails listen
listen for BFD packets on that tree. All other information MAY be for BFD packets on that tree. All other information MAY be
determined dynamically. 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 Active role , per section 6.1 [RFC5880]. Except when
administratively terminating BFD service, this session is always in administratively terminating BFD service, this session is always in
state Up and always operates in Demand mode. No received packets are state Up and always operates in Demand mode. No received packets are
ever demultiplexed to the MultipointHead session. In this sense it ever demultiplexed to the MultipointHead session. In this sense, it
is a 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 [RFC5880].
4.7. Discriminators and Packet Demultiplexing 4.7. Discriminators and Packet Demultiplexing
The use of Discriminators is somewhat different in Multipoint BFD The use of Discriminators is somewhat different in Multipoint BFD
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explanations and usage in [RFC8029]. Packets identified as BFD explanations and usage in [RFC8029]. Packets identified as BFD
packets MUST be consumed by MultipointTail and demultiplex as packets MUST be consumed by MultipointTail and demultiplex as
described in Section 4.13.2. Use of other types of encapsulation of described in Section 4.13.2. 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.
4.9. Bringing Up and Shutting Down Multipoint BFD Service 4.9. 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 with available) SHOULD start with bfd.SessionState set to Down and
bfd.RequiredMinRxInterval set to zero in the MultipointHead session. bfd.RequiredMinRxInterval MUST be set to zero in the MultipointHead
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 larger value of bfd.DesiredMinTxInterval than it is using the same or a larger value of bfd.DesiredMinTxInterval than
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.
A head may wish to shut down its BFD service in a controlled fashion. The head of a multipoint BFD session may wish to shut down its BFD
This is desirable because the tails need not wait a detection time service in a controlled fashion. This is desirable because the tails
prior to declaring the multipoint session to be down (and taking need not wait a detection time prior to declaring the multipoint
whatever action is necessary in that case). session to be down (and taking whatever action is necessary in that
case).
To shut down a multipoint session a head MUST administratively set To shut down a multipoint session the head MUST administratively set
bfd.SessionState in the MultipointHead session to either Down or bfd.SessionState in the MultipointHead session to either Down or
AdminDown and SHOULD set bfd.RequiredMinRxInterval to zero. The AdminDown and SHOULD set bfd.RequiredMinRxInterval to zero. The
session SHOULD send BFD Control packets in this state for a period session SHOULD send BFD Control packets in this state for a period
equal to (bfd.DesiredMinTxInterval * bfd.DetectMult). equal to (bfd.DesiredMinTxInterval * bfd.DetectMult).
The semantic difference between Down and AdminDown state is for The semantic difference between Down and AdminDown state is for
further discussion. further discussion.
4.10. Timer Manipulation 4.10. 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,
MultipointHead session MUST send packets with the P bit set. MultipointHead session MUST send packets with the P bit set.
MultipointTail session MUST NOT reply if packet has M, P bit set and
bfd.RequiredMinRxInterval set to 0.
The MultipointHead, when changing the transmit interval to higher MultipointTail session MUST NOT reply if the packet has M and P bits
set and bfd.RequiredMinRxInterval set to 0.
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 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. 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. of this document.
4.11. Detection Times 4.11. Detection Times
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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]. If bfd.SessionType is described in section 6.8.4 of [RFC5880]. If bfd.SessionType is
MultipointTail, then update the Detection Time as the product of MultipointTail, then update the Detection Time as the product of
the last received values of Desired Min TX Interval and Detect the last received values of Desired Min TX Interval and Detect
Mult, as described in Section 4.11 of this specification. Mult, as described in Section 4.11 of this specification.
If bfd.SessionState is AdminDown If bfd.SessionState is AdminDown
Discard the packet Discard the packet
If 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
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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 4.13.3). of BFD Control packets (see Section 4.13.3).
If bfd.RemoteDemandMode is 0, or bfd.SessionState is not Up, or If bfd.RemoteDemandMode is 0, or 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 see Section 4.13.3). packets (see Section 4.13.3).
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 [RFC5880] section 6.8.4.
4.13.2. Demultiplexing BFD Control Packets 4.13.2. 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 [RFC5880] section 6.8.6,
separated for clarity. separated for clarity.
If the Multipoint (M) bit is set If the Multipoint (M) bit is set
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received with the Poll (P) bit set, or 0 if not. received with the Poll (P) bit set, or 0 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 on 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 0 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 0.
Multipoint (M) Multipoint (M)
Set to 1 if bfd.SessionType is MultipointHead. Otherwise it is Set to 1 if bfd.SessionType is MultipointHead. Otherwise, it
set to 0. is set to 0.
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.
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Required Min Echo RX Interval Required Min Echo RX Interval
Set to 0 if bfd.SessionType is MultipointHead or Set to 0 if bfd.SessionType is MultipointHead or
MultipointTail. MultipointTail.
Authentication Section Authentication Section
Included and set according to the rules in [RFC5880] section Included and set according to the rules in [RFC5880] section
6.7 if authentication is in use (bfd.AuthType is nonzero). 6.7 if authentication is in use (bfd.AuthType is nonzero).
Otherwise this section is not present. Otherwise, this section is not present.
5. Assumptions 5. Assumptions
If authentication is in use, all tails must be configured to have a If authentication is in use, all tails must be configured to have a
common authentication key in order to receive the multipoint BFD common authentication key in order to receive the multipoint BFD
Control packets. Control packets.
6. IANA Considerations 6. IANA Considerations
This document has no actions for IANA. This document has no actions for IANA.
7. Security Considerations 7. 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 Control packets MUST implement protective measures to prevent an
infinite number of MultipointTail sessions being created. Below are infinite number of MultipointTail sessions being created. Below are
listed some points to be considered in such implementations. listed some points to be considered 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
tree (e.g. on expected interface, with expected MPLS label, etc), tree (e.g. on the expected interface, with expected MPLS label,
then a MultipointTail session should not be created. etc), then 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 then the implementations should not create more MultipointTail
sessions than the number of streams. Additionally, when the sessions than the number of streams. Additionally, when the
number of MultipointTail sessions exceeds the number of expected number of MultipointTail sessions exceeds the number of expected
streams, then the implementation should generate an alarm to users streams, then the implementation should generate an alarm to users
to indicate the anomaly. to indicate the anomaly.
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.
8. Contributors 8. Contributors
Rahul Aggarwal of Juniper Networks and George Swallow of Cisco Rahul Aggarwal of Juniper Networks and George Swallow of Cisco
Systems provided the initial idea for this specification and Systems provided the initial idea for this specification and
contributed to its development. contributed to its development.
9. Acknowledgements 9. Acknowledgments
Authors would also like to thank Nobo Akiya, Vengada Prasad Govindan, Authors would also like to thank Nobo Akiya, Vengada Prasad Govindan,
Jeff Haas, Wim Henderickx, Gregory Mirsky and Mingui Zhang who have Jeff Haas, Wim Henderickx, Gregory Mirsky and Mingui Zhang who have
greatly contributed to this document. greatly contributed to this document.
10. Normative References 10. 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,
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