< draft-ietf-bfd-multipoint-active-tail-06.txt   draft-ietf-bfd-multipoint-active-tail-07.txt >
Internet Engineering Task Force D. Katz Internet Engineering Task Force D. Katz
Internet-Draft Juniper Networks Internet-Draft Juniper Networks
Intended status: Standards Track D. Ward Intended status: Standards Track D. Ward
Expires: June 22, 2018 Cisco Systems Expires: August 3, 2018 Cisco Systems
S. Pallagatti, Ed. S. Pallagatti, Ed.
Individual Contributor Individual Contributor
G. Mirsky, Ed. G. Mirsky, Ed.
ZTE Corp. ZTE Corp.
December 19, 2017 January 30, 2018
BFD Multipoint Active Tails. BFD Multipoint Active Tails.
draft-ietf-bfd-multipoint-active-tail-06 draft-ietf-bfd-multipoint-active-tail-07
Abstract Abstract
This document describes active tail extensions to the Bidirectional This document describes active tail extensions to the Bidirectional
Forwarding Detection (BFD) protocol for multipoint and multicast Forwarding Detection (BFD) protocol for 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 June 22, 2018. This Internet-Draft will expire on August 3, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 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.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 4 3. Operational Scenarios . . . . . . . . . . . . . . . . . . . . 4
3.1. Multipoint Client Session . . . . . . . . . . . . . . . . 4 3.1. No Head Notification . . . . . . . . . . . . . . . . . . 4
3.2. Multipoint Client Session Failure . . . . . . . . . . . . 5 3.2. Unreliable Head Notification . . . . . . . . . . . . . . 5
3.3. State Variables . . . . . . . . . . . . . . . . . . . . . 5 3.3. Semi-reliable Head Notification and Tail Solicitation . . 5
3.3.1. New State Variables . . . . . . . . . . . . . . . . . 5 3.4. Reliable Head Notification . . . . . . . . . . . . . . . 5
3.3.2. State Variable Initialization and Maintenance . . . . 6 4. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Controlling Multipoint BFD Options . . . . . . . . . . . 7 4.1. Multipoint Client Session . . . . . . . . . . . . . . . . 7
3.5. State Machine . . . . . . . . . . . . . . . . . . . . . . 8 4.2. Multipoint Client Session Failure . . . . . . . . . . . . 7
3.6. Session Establishment . . . . . . . . . . . . . . . . . . 8 4.3. State Variables . . . . . . . . . . . . . . . . . . . . . 7
3.7. Discriminators and Packet Demultiplexing . . . . . . . . 8 4.3.1. New State Variables . . . . . . . . . . . . . . . . . 7
3.8. Controlling Tail Packet Transmission . . . . . . . . . . 8 4.3.2. New State Variable Value . . . . . . . . . . . . . . 8
3.9. Soliciting the Tails . . . . . . . . . . . . . . . . . . 9 4.3.3. State Variable Initialization and Maintenance . . . . 8
3.10. Verifying Connectivity to Specific Tails . . . . . . . . 9 4.4. Controlling Multipoint BFD Options . . . . . . . . . . . 9
3.11. Detection Times . . . . . . . . . . . . . . . . . . . . . 10 4.5. State Machine . . . . . . . . . . . . . . . . . . . . . . 10
3.12. MultipointClient Down/AdminDown Sessions . . . . . . . . 11 4.6. Session Establishment . . . . . . . . . . . . . . . . . . 10
3.13. Base BFD Specification Text Replacement . . . . . . . . . 11 4.7. Discriminators and Packet Demultiplexing . . . . . . . . 10
3.13.1. Reception of BFD Control Packets . . . . . . . . . . 11 4.8. Controlling Tail Packet Transmission . . . . . . . . . . 11
3.13.2. Demultiplexing BFD Control Packets . . . . . . . . . 12 4.9. Soliciting the Tails . . . . . . . . . . . . . . . . . . 11
3.13.3. Transmitting BFD Control Packets . . . . . . . . . . 12 4.10. Verifying Connectivity to Specific Tails . . . . . . . . 12
4. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.11. Detection Times . . . . . . . . . . . . . . . . . . . . . 13
5. Operational Scenarios . . . . . . . . . . . . . . . . . . . . 13 4.12. MultipointClient Down/AdminDown Sessions . . . . . . . . 13
5.1. No Head Notification . . . . . . . . . . . . . . . . . . 14 4.13. Base BFD Specification Text Replacement . . . . . . . . . 13
5.2. Unreliable Head Notification . . . . . . . . . . . . . . 14 4.13.1. Reception of BFD Control Packets . . . . . . . . . . 14
5.3. Semi-reliable Head Notification and Tail Solicitation . . 14 4.13.2. Demultiplexing BFD Control Packets . . . . . . . . . 14
5.4. Reliable Head Notification . . . . . . . . . . . . . . . 15 4.13.3. Transmitting BFD Control Packets . . . . . . . . . . 15
5. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
10. Normative References . . . . . . . . . . . . . . . . . . . . 16 10. Normative References . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
This application of BFD is an extension to Multipoint BFD This application of BFD is an extension to Multipoint BFD
[I-D.ietf-bfd-multipoint], which allows tail to unreliably notify the [I-D.ietf-bfd-multipoint], which allows tails to unreliably notify
head of the lack of multipoint connectivity. As a further option, the head of the lack of multipoint connectivity. As a further
this notification can be made reliable. Notification to the head can option, this notification can be made reliable. Notification to the
be enabled for all tails, or for only a subset of the tails. head can be enabled for all tails, or for only a subset of the tails.
Multipoint BFD base document [I-D.ietf-bfd-multipoint] describes Multipoint BFD base document [I-D.ietf-bfd-multipoint] describes
procedures to verify only the head-to-tail connectivity over the procedures to verify only the head-to-tail connectivity over the
multipoint path. Although it may use unicast paths in both multipoint path. Although it may use unicast paths in both
directions, Multipoint BFD does not verify those paths (and in fact directions, Multipoint BFD does not verify those paths (and in fact
it is preferable if unicast paths share as little fate with the it is preferable if unicast paths share as little fate with the
multipoint path as is feasible.) multipoint path as is feasible, so to increase probability of
delivering the notification from the tail to the head).
Goal of this application is for the head to reasonably rapidly have The goal of this application is for the head to reasonably rapidly
knowledge of tails that have lost connectivity from the head. have knowledge of tails that have lost connectivity from the head.
Since scaling is a primary concern (particularly state implosion Since scaling is a primary concern (particularly state implosion
toward the head), it is required that the head be in control of all toward the head), it is required that the head be in control of all
timing aspects of the mechanism, and that BFD packets from the tails timing aspects of the mechanism, and that BFD packets from the tails
to the head not be synchronized. to the head not be synchronized.
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.
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connectivity verification in transport network but as an alternative connectivity verification in transport network but as an alternative
to "continuity", i.e. existence of a path between the sender and the to "continuity", i.e. existence of a path between the sender and the
receiver. receiver.
This document effectively modifies and adds to the base BFD This document effectively modifies and adds to the base BFD
specification [RFC5880] and base BFD multipoint document specification [RFC5880] and base BFD multipoint document
[I-D.ietf-bfd-multipoint]. [I-D.ietf-bfd-multipoint].
2. Overview 2. Overview
Head may wish to be alerted to the tails' connectivity (or lack A head may wish to be alerted to the tails' connectivity (or lack
thereof), there are a number of options. First, if all that is thereof), there are a number of options. First, if all that is
needed is an unreliable failure notification, the head can direct the needed is an unreliable failure notification, as discussed in
tails to transmit unicast BFD Control packets back to the head when Section 3.2, the head can request the tails to transmit unicast BFD
the path fails. Control packets back to the head when the path fails, as described in
Section 4.4.
If the head wishes to know the identity of the tails on the If the head wishes to know the identity of the tails on the
multipoint path, it may solicit membership by sending a multipoint multipoint path, it may solicit membership by sending a multipoint
BFD Control packet with the Poll (P) bit set, which will induce the BFD Control packet with the Poll (P) bit set, which will induce the
tails to return a unicast BFD Control packet with the Final (F) bit tails to return a unicast BFD Control packet with the Final (F) bit
set. The head can then create BFD session state for each of the set. The head can then create BFD session state for each of the
tails that have multipoint connectivity. If the head sends such a tails that have multipoint connectivity. If the head sends such a
packet on occasion, it can keep track of which tails answer, thus packet on occasion, it can keep track of which tails answer, thus
providing a somewhat reliable mechanism for detecting which tails providing a somewhat reliable mechanism for detecting which tails
fail to respond (implying a loss of multipoint connectivity.) fail to respond (implying a loss of multipoint connectivity).
If the head wishes a reliable indication of the tails' connectivity, If the head wishes a reliable indication of the tails' connectivity,
it may do all of the above, but if it detects that a tail did not it may do all of the above, but if it detects that a tail did not
answer the previous multipoint poll, it may initiate a Demand mode answer the previous multipoint poll, it may initiate a Demand mode
Poll Sequence as a unicast to the tail. This covers the case where Poll Sequence as a unicast to that tail. This covers the case where
either the multipoint poll or the single reply thereto is lost in either the multipoint poll or the single reply also is lost in
transit. If desired, the head may Poll one or more tails proactively transit. If desired, the head may Poll one or more tails proactively
to track the tails' connectivity. to track the tails' connectivity.
If some tails are more equal than others, in the sense that the head If the awareness of the state of some nodes is more important for the
needs to detect the lack of multipoint connectivity to a subset of head, in the sense that the head needs to detect the lack of
tails at a different rate, the head may transmit unicast BFD Polls to multipoint connectivity to a subset of tails at a different rate, the
that subset of tails. In this case, the timing may be independent on head may transmit unicast BFD Polls to that subset of tails. In this
a tail-by-tail basis. case, the timing may be independent on a tail-by-tail basis.
Individual tails may be configured so that they never send BFD Individual tails may be configured so that they never send BFD
control packets to the head, even when the head wishes notification control packets to the head, even when the head wishes notification
of path failure from the tail. Such tails will never be known to the of path failure from the tail. Such tails will never be known to the
head, but will still be able to detect multipoint path failures from head, but will still be able to detect multipoint path failures from
the head. the head.
3. Protocol Details 3. Operational Scenarios
It is worth analyzing how this protocol reacts to various scenarios.
There are three path components present, namely, the multipoint path,
the forward unicast path (from head to a particular tail), and the
reverse unicast path (from a tail to the head). There are also four
options as to how the head is notified about failures from the tail.
3.1. No Head Notification
Since the only path used in this scenario is the multipoint path,
none of the others matter. A failure in the multipoint path will
result in the tail noticing the failure within a detection time, and
the head will remain ignorant of the tail state.
3.2. Unreliable Head Notification
In this scenario, the tail sends back unsolicited BFD packets in
response to the detection of a multipoint path failure. It uses the
reverse unicast path, but not the forward unicast path.
If the multipoint path fails but the reverse unicast path stays up,
the tail will detect the failure within a detection time, and the
head will know about it within one reverse packet time (since the
notification is delayed).
If both the multipoint path and the reverse unicast paths fail, the
tail will detect the failure but the head will remain unaware of it.
3.3. Semi-reliable Head Notification and Tail Solicitation
In this scenario, the head sends occasional multipoint Polls in
addition to (or in lieu of) non-Poll multipoint BFD Control packets,
expecting the tails to reply with Final. This also uses the reverse
unicast path, but not the forward unicast path.
If the multipoint path fails but the reverse unicast path stays up,
the tail will detect the failure within a detection time, and the
head will know about it within one reverse packet time (the
notification is delayed to avoid synchronization of the tails).
If both the multipoint path and the reverse unicast paths fail, the
tail will detect the failure but the head will remain unaware of this
fact.
If the reverse unicast path fails but the multipoint path stays up,
the head will see the BFD session fail, but the state of the
multipoint path will be unknown to the head. The tail will continue
to receive multipoint data traffic.
If either the multipoint Poll or the unicast reply is lost in
transit, the head will see the BFD session fail, but the state of the
multipoint path will be unknown to the head. The tail will continue
to receive multipoint data traffic.
3.4. Reliable Head Notification
In this scenario, the head sends occasional multipoint Polls in
addition to (or in lieu of) non-Poll multipoint BFD control packets,
expecting the tails to reply with Final. If a tail that had
previously replied to a multipoint Poll fails to reply (or if the
head simply wishes to verify tail connectivity), the head issues a
unicast Poll Sequence to the tail. This scenario makes use of all
three paths.
If the multipoint path fails but the two unicast paths stay up, the
tail will detect the failure within a detection time, and the head
will know about it within one reverse packet time (since the
notification is delayed). Note that the reverse packet time may be
smaller in this case if the head has previously issued a unicast Poll
(since the tail will not delay transmission of the notification in
this case).
If both the multipoint path and the reverse unicast paths fail
(regardless of the state of the forward unicast path), the tail will
detect the failure but the head will remain unaware of this fact.
The head will detect a BFD session failure to the tail but cannot
make a determination about the state of the tail's multipoint
connectivity.
If the forward unicast path fails but the reverse unicast path stays
up, the head will detect a BFD session failure to the tail if it
happens to send a unicast Poll sequence, but cannot make a
determination about the state of the tail's multipoint connectivity.
If the multipoint path to the tail fails prior to any unicast Poll
being sent, the tail will detect the failure within a detection time,
and the head will know about it within one reverse packet time (since
the notification is delayed).
If the multipoint path stays up but the reverse unicast path fails,
the head will see the BFD session fail if it happens to send a Poll
Sequence, but the state of the multipoint path will be unknown to the
head. The tail will continue to receive multipoint data traffic.
If the multipoint path and the reverse unicast path both stay up but
the forward unicast path fails, neither side will notice so long as a
unicast Poll Sequence is never sent by the head. If the head sends a
unicast Poll Sequence, the head will see the BFD session fail, but
the state of the multipoint path will be unknown to the head. The
tail will continue to receive multipoint data traffic.
4. Protocol Details
This section describes the operation of BFD Multipoint active tail in This section describes the operation of BFD Multipoint active tail in
detail. This section is update to section 4 of detail. This section is an update to section 4 of
[I-D.ietf-bfd-multipoint]. [I-D.ietf-bfd-multipoint].
3.1. Multipoint Client Session 4.1. Multipoint Client Session
If the head is keeping track of some or all of the tails, it has a If the head is keeping track of some or all of the tails, it has a
session of type MultipointClient per tail that it cares about. All session of type MultipointClient per tail that it cares about. All
of the MultipointClient sessions for tails on a particular multipoint of the MultipointClient sessions for tails on a particular multipoint
path are grouped with the MultipointHead session to which the clients path are grouped with the MultipointHead session to which the clients
are listening. A BFD Poll Sequence may be sent over such a session are listening. A BFD Poll Sequence may be sent over such a session
to a tail if the head wishes to verify connectivity. These sessions to a tail if the head wishes to verify connectivity. These sessions
receive any BFD Control packets sent by the tails, and never transmit receive any BFD Control packets sent by the tails, and never transmit
periodic BFD Control packets other than Poll Sequences (since periodic BFD Control packets other than Poll Sequences (since
periodic transmission is always done by the MultipointHead session.) periodic transmission is always done by the MultipointHead session).
3.2. Multipoint Client Session Failure 4.2. Multipoint Client Session Failure
If a MultipointClient session receives a BFD Control packet from the If a MultipointClient session receives a BFD Control packet from the
tail with state Down or AdminDown, the head reliably knows that the tail with state Down or AdminDown, the head reliably knows that the
tail has lost multipoint connectivity. If the Detection Time expires tail has lost multipoint connectivity. If the Detection Time expires
on a MultipointClient session, it is ambiguous as to whether the on a MultipointClient session, it is ambiguous as to whether the
multipoint connectivity failed or whether there was a unicast path multipoint connectivity failed or whether there was a unicast path
problem in one direction or the other, so the head does not reliably problem in one direction or the other, so the head does not reliably
know the tail state. know the tail's state.
3.3. State Variables 4.3. State Variables
BFD Multipoint active tail introduces new state variables and BFD Multipoint active tail introduces new state variables and
modifies the usage of a few existing ones defined in section 4.4 of modifies the usage of a few existing ones defined in section 4.4 of
[I-D.ietf-bfd-multipoint]. [I-D.ietf-bfd-multipoint].
3.3.1. New State Variables 4.3.1. New State Variables
Few state variables are added and modified support of Multipoint BFD
active tail.
bfd.SessionType
The type of this session as defined in [RFC7880]. A new value
introduced is:
MultipointClient: A session on the head that tracks the
state of an individual tail, when desirable.
This variable MUST be initialized to the appropriate type when Few state variables are added in support of Multipoint BFD active
the session is created, according to the rules in section 4.13 tail.
of [I-D.ietf-bfd-multipoint].
bfd.SilentTail bfd.SilentTail
If 0, a tail may send packets to the head according to other If 0, a tail may send packets to the head according to other
parts of this specification. Setting this to 1 allows tails to parts of this specification. Setting this to 1 allows tails to
be provisioned to always be silent, even when the head is be provisioned to always be silent, even when the head is
soliciting traffic from the tails. This can be useful, for soliciting traffic from the tails. This can be useful, for
example, in deployments of a large number of tails when the example, in deployments of a large number of tails when the
head wishes to track the state of a subset of them. This head wishes to track the state of a subset of them. This
variable MUST be initialized based on configuration. variable MUST be initialized based on configuration.
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Set to 1 if a tail receives a unicast BFD Control packet from Set to 1 if a tail receives a unicast BFD Control packet from
the head. This variable MUST be set to zero if the session the head. This variable MUST be set to zero if the session
transitions from Up state to some other state. transitions from Up state to some other state.
This variable MUST be initialized to zero. This variable MUST be initialized to zero.
This variable is only pertinent when Bfd.SessionType is This variable is only pertinent when Bfd.SessionType is
MultipointTail. MultipointTail.
3.3.2. State Variable Initialization and Maintenance 4.3.2. New State Variable Value
A new state variable value being added to:
bfd.SessionType
The type of this session as defined in [RFC7880]. A new value
introduced is:
MultipointClient: A session on the head that tracks the state
of an individual tail, when desirable.
This variable MUST be initialized to the appropriate type when the
session is created, according to the rules in section 4.13 of
[I-D.ietf-bfd-multipoint].
4.3.3. State Variable Initialization and Maintenance
Some state variables defined in section 6.8.1 of the [RFC5880] needs Some state variables defined in section 6.8.1 of the [RFC5880] needs
to be initialized or manipulated differently depending on the session to be initialized or manipulated differently depending on the session
type (see section 4.4.2 of [I-D.ietf-bfd-multipoint]). type (see section 4.4.2 of [I-D.ietf-bfd-multipoint]).
bfd.LocalDiscr bfd.LocalDiscr
For session type MultipointClient, this variable MUST always For session type MultipointClient, this variable MUST always
match the value of bfd.LocalDiscr in the associated match the value of bfd.LocalDiscr in the associated
MultipointHead session. MultipointHead session.
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MultipointHead session. MultipointHead session.
bfd.RequiredMinRxInterval bfd.RequiredMinRxInterval
It should be noted that for sessions of type MultipointTail, It should be noted that for sessions of type MultipointTail,
this variable only affects the rate of unicast Polls sent by this variable only affects the rate of unicast Polls sent by
the head; the rate of multipoint packets is necessarily the head; the rate of multipoint packets is necessarily
unaffected by it. unaffected by it.
bfd.DemandMode bfd.DemandMode
This variable MUST be initialized to 1 for session types This variable MUST be initialized to 1 for session types
MultipointClient. MultipointClient.
bfd.DetectMult bfd.DetectMult
For session type MultipointClient, this variable MUST always For session type MultipointClient, this variable MUST always
match the value of bfd.DetectMult in the associated match the value of bfd.DetectMult in the associated
MultipointHead session. MultipointHead session.
3.4. Controlling Multipoint BFD Options 4.4. Controlling Multipoint BFD Options
The state variables defined above are used to choose which The state variables defined above are used to choose which
operational options are active. operational options are active.
The most basic form of operation as explained in The most basic form of operation, as explained in
[I-D.ietf-bfd-multipoint], in which BFD Control packets flow only [I-D.ietf-bfd-multipoint], in which BFD Control packets flow only
from the head and no tracking is desired of tail state at the head, from the head and no tracking is desired of tail state at the head,
is accomplished by setting bfd.ReportTailDown to 0 in the is accomplished by setting bfd.ReportTailDown to 0 in the
MultipointHead session. MultipointHead session (Section 3.1).
If the head wishes to know the identity of the tails, it sends If the head wishes to know the identity of the tails, it sends
multipoint Polls as needed. Previously known tails that don't multipoint Polls as needed. Previously known tails that don't
respond to the Polls will be detected. respond to the Polls will be detected (as per Section 3.3).
If the head wishes to be notified by the tails when they lose If the head wishes to be notified by the tails when they lose
connectivity, it sets bfd.ReportTailDown to 1 in either the connectivity, it sets bfd.ReportTailDown to 1 in either the
MultipointHead session (if such notification is desired from all MultipointHead session (if such notification is desired from all
tails) or in the MultipointClient session (if notification is desired tails) or in the MultipointClient session (if notification is desired
from a particular tail.) Note that the setting of this variable in a from a particular tail). Note that the setting of this variable in a
MultipointClient session for a particular tail overrides the setting MultipointClient session for a particular tail overrides the setting
in the MultipointHead session. in the MultipointHead session.
If the head wishes to verify the state of a tail on an ongoing basis, If the head wishes to verify the state of a tail on an ongoing basis,
it sends a Poll Sequence from the MultipointClient session associated it sends a Poll Sequence from the MultipointClient session associated
with that tail as needed. with that tail as needed.
If the head wants to more quickly be alerted to a session failure If the head wants to more quickly be alerted to a session failure
from a particular tail, it sends a BFD Control packet from the from a particular tail, it sends a BFD Control packet from the
MultipointClient session associated with that tail. This has the MultipointClient session associated with that tail. This has the
effect of eliminating the initial delay that the tail would otherwise effect of eliminating the initial delay, described in Section 4.13.3,
insert prior to transmission of the packet. that the tail would otherwise insert prior to transmission of the
packet.
If a tail wishes to operate silently (sending no BFD Control packets If a tail wishes to operate silently (sending no BFD Control packets
to the head) it sets bfd.SilentTail to 1 in the MultipointTail to the head) it sets bfd.SilentTail to 1 in the MultipointTail
session. This allows a tail to be silent independent of the settings session. This allows a tail to be silent independent of the settings
on the head. on the head.
3.5. State Machine 4.5. State Machine
State machine for session of type MultipointClient is same as defined The state machine for session of type MultipointClient is same as
in section 4.5 of [I-D.ietf-bfd-multipoint]. defined in section 4.5 of [I-D.ietf-bfd-multipoint].
3.6. Session Establishment 4.6. Session Establishment
If BFD Control packets are received at the head, they are If BFD Control packets are received at the head, they are
demultiplexed to sessions of type MultipointClient, which represent demultiplexed to sessions of type MultipointClient, which represent
the set of tails that the head is interested in tracking. These the set of tails that the head is interested in tracking. These
sessions will typically also be established dynamically based on the sessions will typically also be established dynamically based on the
receipt of BFD Control packets. The head has broad latitude in receipt of BFD Control packets. The head has broad latitude in
choosing which tails to track, if any, without affecting the basic choosing which tails to track, if any, without affecting the basic
operation of the protocol. The head directly controls whether or not operation of the protocol. The head directly controls whether or not
tails are allowed to send BFD Control packets back to the head. tails are allowed to send BFD Control packets back to the head.
3.7. Discriminators and Packet Demultiplexing 4.7. Discriminators and Packet Demultiplexing
When the tails send BFD Control packets to the head from the When the tails send BFD Control packets to the head from the
MultipointTail session, the contents of Your Discr (the discriminator MultipointTail session, the contents of Your Discr (the discriminator
received from the head) will not be sufficient for the head to received from the head) will not be sufficient for the head to
demultiplex the packet, since the same value will be received from demultiplex the packet, since the same value will be received from
all tails on the multicast tree. In this case, the head MUST all tails on the multicast tree. In this case, the head MUST
demultiplex packets based on the source address and the value of Your demultiplex packets based on the source address and the value of Your
Discr, which together uniquely identify the tail and the multipoint Discr, which together uniquely identify the tail and the multipoint
path. path.
When the head sends unicast BFD Control packets to a tail from a When the head sends unicast BFD Control packets to a tail from a
MultipointClient session, the value of Your Discr will be valid, and MultipointClient session, the value of Your Discr will be valid, and
the tail MUST demultiplex the packet based solely on Your Discr. the tail MUST demultiplex the packet based solely on Your Discr.
3.8. Controlling Tail Packet Transmission 4.8. Controlling Tail Packet Transmission
As the fan-in from the tails to the head may be very large, it is As the fan-in from the tails to the head may be very large, it is
critical that the flow of BFD Control packets from the tails is critical that the flow of BFD Control packets from the tails is
controlled. controlled.
The head always operates in Demand mode. This means that no tail The head always operates in Demand mode. This means that no tail
will send an asynchronous BFD Control packet as long as the session will send an asynchronous BFD Control packet as long as the session
is Up. is Up.
The value of Required Min Rx Interval received by a tail in a unicast The value of Required Min Rx Interval received by a tail in a unicast
BFD Control packet, if any, always takes precedence over the value BFD Control packet, if any, always takes precedence over the value
received in Multipoint BFD Control packets. This allows the packet received in Multipoint BFD Control packets. This allows the packet
rate from individual tails to be controlled separately as desired by rate from individual tails to be controlled separately as desired by
sending a BFD Control packet from the corresponding MultipointClient sending a BFD Control packet from the corresponding MultipointClient
session. This also eliminates the random delay prior to transmission session. This also eliminates the random delay, as discussed in
from the tail that would otherwise be inserted, reducing the latency Section 4.13.3, prior to transmission from the tail that would
of reporting a failure to the head. otherwise be inserted, reducing the latency of reporting a failure to
the head.
If the head wishes to suppress traffic from the tails when they If the head wishes to suppress traffic from the tails when they
detect a session failure, it MAY set bfd.RequiredMinRxInterval to detect a session failure, it MAY set bfd.RequiredMinRxInterval to
zero, which is a reserved value that indicates that the sender wishes zero, which is a reserved value that indicates that the sender wishes
to receive no periodic traffic. This can be set in the to receive no periodic traffic. This can be set in the
MultipointHead session (suppressing traffic from all tails) or it can MultipointHead session (suppressing traffic from all tails) or it can
be set in a MultipointClient session (suppressing traffic from only a be set in a MultipointClient session (suppressing traffic from only a
single tail.) single tail).
Any tail may be provisioned to never send *any* BFD Control packets Any tail may be provisioned to never send *any* BFD Control packets
to the head by setting bfd.SilentTail to 1. This provides a to the head by setting bfd.SilentTail to 1. This provides a
mechanism by which only a subset of tails report their session status mechanism by which only a subset of tails report their session status
to the head. to the head.
3.9. Soliciting the Tails 4.9. Soliciting the Tails
If the head wishes to know the identities of the tails, the If the head wishes to know the identities of the tails, the
MultipointHead session MAY send a BFD Control packet as specified in MultipointHead session MAY send a BFD Control packet as specified in
Section 3.13.3, with the Poll (P) bit set to 1. This will cause all Section 4.13.3, with the Poll (P) bit set to 1. This will cause all
of the tails to reply with a unicast BFD Control Packet, randomized of the tails to reply with a unicast BFD Control Packet, randomized
across one packet interval. across one packet interval.
The decision as to when to send a multipoint Poll is outside the The decision as to when to send a multipoint Poll is outside the
scope of this specification. However, it must never be sent more scope of this specification. However, it must never be sent more
often than the regular multipoint BFD Control packet. Since the tail often than the regular multipoint BFD Control packet. Since the tail
will treat a multipoint Poll like any other multipoint BFD Control will treat a multipoint Poll like any other multipoint BFD Control
packet, Polls may be sent in lieu of non-Poll packets. packet, Polls may be sent in lieu of non-Poll packets.
Soliciting the tails also starts the Detection Timer for each Soliciting the tails also starts the Detection Timer for each
associated MultipointClient session, which will cause those sessions associated MultipointClient session, which will cause those sessions
to time out if the associated tails do not respond. to time out if the associated tails do not respond.
Note that for this mechanism to work properly, the Detection Time Note that for this mechanism to work properly, the Detection Time
(which is equal to bfd.DesiredMinTxInterval) MUST be greater than the (which is equal to bfd.DesiredMinTxInterval) MUST be greater than the
round trip time of BFD Control packets from the head to the tail (via round trip time of BFD Control packets from the head to the tail (via
the multipoint path) and back (via a unicast path.) See Section 3.11 the multipoint path) and back (via a unicast path). See Section 4.11
for more details. for more details.
3.10. Verifying Connectivity to Specific Tails 4.10. Verifying Connectivity to Specific Tails
If the head wishes to verify connectivity to a specific tail, the If the head wishes to verify connectivity to a specific tail, the
corresponding MultipointClient session MAY send a BFD Poll Sequence corresponding MultipointClient session MAY send a BFD Poll Sequence
to said tail. This might be done in reaction to the expiration of to said tail. This might be done in reaction to the expiration of
the Detection Timer (the tail didn't respond to a multipoint Poll), the Detection Timer (the tail didn't respond to a multipoint Poll),
or it might be done on a proactive basis. or it might be done on a proactive basis.
The interval between transmitted packets in the Poll Sequence MUST be The interval between transmitted packets in the Poll Sequence MUST be
calculated as specified in the base BFD specification [RFC5880] (the calculated as specified in the base BFD specification [RFC5880] (the
greater of bfd.DesiredMinTxInterval and bfd.RemoteMinRxInterval.) greater of bfd.DesiredMinTxInterval and bfd.RemoteMinRxInterval).
The value transmitted in Required Min RX Interval will be used by the The value transmitted in Required Min RX Interval will be used by the
tail (rather than the value received in any multipoint packet) when tail (rather than the value received in any multipoint packet) when
it transmits BFD Control packets to the head notifying it of a it transmits BFD Control packets to the head notifying it of a
session failure, and the transmitted packets will not be delayed. session failure, and the transmitted packets will not be delayed.
This value can potentially be set much lower than in the multipoint This value can potentially be set much lower than in the multipoint
case, in order to speed up notification to the head, since the value case, in order to speed up notification to the head, since the value
will be used only by the single tail. This value (and the lack of will be used only by the single tail. This value (and the lack of
delay) are "sticky", in that once the tail receives it, it will delay) are "sticky", in that once the tail receives it, it will
continue to use it indefinitely. Therefore, if the head no longer continue to use it indefinitely. Therefore, if the head no longer
wishes to single out the tail, it SHOULD reset the timer to the wishes to single out the tail, it SHOULD reset the timer to the
default by sending a Poll Sequence with the same value of Required default by sending a Poll Sequence with the same value of Required
Min Rx Interval as is carried in the multipoint packets, or it MAY Min Rx Interval as is carried in the multipoint packets, or it MAY
reset the tail session by sending a Poll Sequence with state reset the tail session by sending a Poll Sequence with state
AdminDown (after the completion of which the session will come back AdminDown (after the completion of which the session will come back
up.) up).
Note that a failure of the head to receive a response to a Poll Note that a failure of the head to receive a response to a Poll
Sequence does not necessarily mean that the tail has lost multipoint Sequence does not necessarily mean that the tail has lost multipoint
connectivity, though a reply to a Poll Sequence does reliably connectivity, though a reply to a Poll Sequence does reliably
indicate connectivity or lack thereof (by virtue of the tail's state indicate connectivity or lack thereof (by virtue of the tail's state
not being Up in the BFD Control packet.) not being Up in the BFD Control packet).
3.11. Detection Times 4.11. Detection Times
MultipointClient sessions at the head are always in Demand mode, and MultipointClient sessions at the head are always in Demand mode, and
as such only care about detection time in two cases. First, if a as such only care about detection time in two cases. First, if a
Poll Sequence is being sent on a MultipointClient session, the Poll Sequence is being sent on a MultipointClient session, the
detection time on this session is calculated according to the base detection time on this session is calculated according to the base
BFD specification [RFC5880], that is, the transmission interval BFD specification [RFC5880], that is, the transmission interval
multiplied by bfd.DetectMult. Second, when a multipoint Poll is sent multiplied by bfd.DetectMult. Second, when a multipoint Poll is sent
to solicit tail replies, the detection time on all associated to solicit tail replies, the detection time on all associated
MultipointClient sessions that aren't currently sending Poll MultipointClient sessions that aren't currently sending Poll
Sequences is set to a value greater than or equal to Sequences is set to a value greater than or equal to
bfd.RequiredMinRxInterval (one packet time.) This value can be made bfd.RequiredMinRxInterval (one packet time). This value can be made
arbitrarily large in order to ensure that the detection time is arbitrarily large in order to ensure that the detection time is
greater than the round trip time of a BFD Control packet between the greater than the round trip time of a BFD Control packet between the
head and the tail with no ill effects, other than delaying the head and the tail with no ill effects, other than delaying the
detection of unresponsive tails. Note that a detection time detection of unresponsive tails. Note that a detection time
expiration on a MultipointClient session at the head, while expiration on a MultipointClient session at the head, while
indicating a BFD session failure, cannot be construed to mean that indicating a BFD session failure, cannot be construed to mean that
the tail is not hearing multipoint packets from the head. the tail is not hearing multipoint packets from the head.
3.12. MultipointClient Down/AdminDown Sessions 4.12. MultipointClient Down/AdminDown Sessions
If the MultipointHead session is going down (which only happens If the MultipointHead session is going down (which only happens
administratively), all associated MultipointClient sessions SHOULD be administratively), all associated MultipointClient sessions SHOULD be
destroyed as they are superfluous. destroyed as they are superfluous.
If a MultipointClient session goes down due to the receipt of an If a MultipointClient session goes down due to the receipt of an
unsolicited BFD Control packet from the tail with state Down or unsolicited BFD Control packet from the tail with state Down or
AdminDown (not in response to a Poll), and tail connectivity AdminDown (not in response to a Poll), and tail connectivity
verification is not being done, the session MAY be destroyed. If verification is not being done, the session MAY be destroyed. If
verification is desired, the session SHOULD send a Poll Sequence and verification is desired, the session SHOULD send a Poll Sequence and
the session SHOULD be maintained. the session SHOULD be maintained.
If the tail replies to a Poll Sequence with state Down or AdminDown, If the tail replies to a Poll Sequence with state Down or AdminDown,
it means that the tail session is definitely down. In this case, the it means that the tail session is definitely down. In this case, the
session MAY be destroyed. session MAY be destroyed.
If the Detection Time expires on a MultipointClient session (meaning If the Detection Time expires on a MultipointClient session (meaning
that the tail did not reply to a Poll Sequence) the session MAY be that the tail did not reply to a Poll Sequence) the session MAY be
destroyed. destroyed.
3.13. Base BFD Specification Text Replacement 4.13. Base BFD 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. sections in the base specifications [RFC5880] and
[I-D.ietf-bfd-multipoint].
3.13.1. Reception of BFD Control Packets 4.13.1. Reception of BFD Control Packets
The following procedure replaces section 6.8.6 of [RFC5880]. The following procedure replaces section 6.8.6 of [RFC5880].
When a BFD Control packet is received, procedure defined in section When a BFD Control packet is received, procedure defined in section
4.13.1 of [I-D.ietf-bfd-multipoint] MUST be followed, in the order 4.13.1 of [I-D.ietf-bfd-multipoint] MUST be followed, in the order
specified. If the packet is discarded according to these rules, specified. If the packet is discarded according to these rules,
processing of the packet MUST cease at that point. In addition to processing of the packet MUST cease at that point. In addition to
that if tail tracking is desired by head below procedure MUST be that, if tail tracking is desired by head, below procedure MUST be
applied. applied.
If bfd.SessionType is MultipointTail If bfd.SessionType is MultipointTail
If bfd.UnicastRcvd is 0 or the M bit is clear, set If bfd.UnicastRcvd is 0 or the M bit is clear, set
bfd.RemoteMinRxInterval to the value of Required Min RX bfd.RemoteMinRxInterval to the value of Required Min RX
Interval. Interval.
If the M bit is clear, set bfd.UnicastRcvd to 1. If the M bit is clear, set bfd.UnicastRcvd to 1.
skipping to change at page 12, line 4 skipping to change at page 14, line 25
If bfd.SessionType is MultipointTail If bfd.SessionType is MultipointTail
If bfd.UnicastRcvd is 0 or the M bit is clear, set If bfd.UnicastRcvd is 0 or the M bit is clear, set
bfd.RemoteMinRxInterval to the value of Required Min RX bfd.RemoteMinRxInterval to the value of Required Min RX
Interval. Interval.
If the M bit is clear, set bfd.UnicastRcvd to 1. If the M bit is clear, set bfd.UnicastRcvd to 1.
Else (not MultipointTail) Else (not MultipointTail)
Set bfd.RemoteMinRxInterval to the value of Required Min RX Set bfd.RemoteMinRxInterval to the value of Required Min RX
Interval. Interval.
If the Poll (P) bit is set, and bfd.SilentTail is zero, send a BFD If the Poll (P) bit is set, and bfd.SilentTail is zero, send a BFD
Control packet to the remote system with the Poll (P) bit clear, Control packet to the remote system with the Poll (P) bit clear,
and the Final (F) bit set (see Section 3.13.3.) and the Final (F) bit set (see Section 4.13.3).
3.13.2. 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
and addition to section 4.13.2 of [I-D.ietf-bfd-multipoint], and addition to section 4.13.2 of [I-D.ietf-bfd-multipoint],
separated for clarity. separated for clarity.
If Multipoint (M) bit is clear If 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.
skipping to change at page 12, line 38 skipping to change at page 15, line 11
the value of Your Discriminator. If a session is found the value of Your Discriminator. If a session is found
and is not MulticastClient, the packet MUST be discarded. and is not MulticastClient, the packet MUST be discarded.
If no session is found, a new session of type If no session is found, a new session of type
MultipointClient MAY be created, or the packet MAY be MultipointClient MAY be created, or the packet MAY be
discarded. This choice is outside the scope of this discarded. This choice is outside the scope of this
specification. specification.
If bfd.SessionType is not MulticastClient, the packet If bfd.SessionType is not MulticastClient, the packet
MUST be discarded. MUST be discarded.
3.13.3. Transmitting BFD Control Packets 4.13.3. Transmitting BFD Control Packets
The following procedure replaces section 6.8.7 of [RFC5880]. The following procedure replaces section 6.8.7 of [RFC5880].
A system MUST NOT periodically transmit BFD Control packets if A system MUST NOT periodically transmit BFD Control packets if
bfd.SessionType is MulticastClient and a Poll Sequence is not being bfd.SessionType is MulticastClient and a Poll Sequence is not being
transmitted. transmitted.
If bfd.SessionType is MulticastTail and periodic transmission of BFD If bfd.SessionType is MulticastTail and periodic transmission of BFD
Control packets is just starting (due to Demand mode not being active Control packets is just starting (due to Demand mode not being active
on the remote system), the first packet to be transmitted MUST be on the remote system), the first packet to be transmitted MUST be
skipping to change at page 13, line 26 skipping to change at page 15, line 46
amount of time between zero and (0.9 * bfd.RemoteMinRxInterval). amount of time between zero and (0.9 * bfd.RemoteMinRxInterval).
Otherwise, the packet MUST be transmitted as soon as practicable. Otherwise, the packet MUST be transmitted as soon as practicable.
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
MultipointClient unless bfd.DemandMode is 1, bfd.SessionState is Up, MultipointClient unless bfd.DemandMode is 1, bfd.SessionState is Up,
and bfd.RemoteSessionState is Up. and bfd.RemoteSessionState is Up.
Contents of transmitted packet MUST be as explained in section 4.13.3 Contents of transmitted packet MUST be as explained in section 4.13.3
of [I-D.ietf-bfd-multipoint]. of [I-D.ietf-bfd-multipoint].
4. Assumptions 5. Assumptions
If head notification is to be used, it is assumed that a multipoint If head notification is to be used, it is assumed that a multipoint
BFD packet encapsulation contains enough information so that a tail BFD packet encapsulation contains enough information so that a tail
can address a unicast BFD packet to the head. can address a unicast BFD packet to the head.
If head notification is to be used, it is assumed that is that there If head notification is to be used, it is assumed that is that there
is bidirectional unicast communication available (at the same is bidirectional unicast communication available (at the same
protocol layer within which BFD is being run) between the tail and protocol layer within which BFD is being run) between the tail and
head. head.
skipping to change at page 13, line 48 skipping to change at page 16, line 21
connectivity, the unicast paths in both directions between that tail connectivity, the unicast paths in both directions between that tail
and the head must remain operational when the multipoint path fails. and the head must remain operational when the multipoint path fails.
It is thus desirable that unicast paths not share fate with the It is thus desirable that unicast paths not share fate with the
multipoint path to the extent possible if the head wants reliable multipoint path to the extent possible if the head wants reliable
knowledge of tail state. knowledge of tail state.
Since the normal BFD three-way handshake is not used in this Since the normal BFD three-way handshake is not used in this
application, a tail transitioning from state Up to Down and back to application, a tail transitioning from state Up to Down and back to
Up again may not be reliably detected at the head. Up again may not be reliably detected at the head.
5. Operational Scenarios
It is worth analyzing how this protocol reacts to various scenarios.
There are three path components present, namely, the multipoint path,
the forward unicast path (from head to a particular tail), and the
reverse unicast path (from a tail to the head.) There are also four
options as to how the head is notified about failures from the tail.
5.1. No Head Notification
Since the only path used in this scenario is the multipoint path,
none of the others matter. A failure in the multipoint path will
result in the tail noticing the failure within a detection time, and
the head will remain ignorant of the tail state.
5.2. Unreliable Head Notification
In this scenario, the tail sends back unsolicited BFD packets in
response to the detection of a multipoint path failure. It uses the
reverse unicast path, but not the forward unicast path.
If the multipoint path fails but the reverse unicast path stays up,
the tail will detect the failure within a detection time, and the
head will know about it within one reverse packet time (since the
notification is delayed.)
If both the multipoint path and the reverse unicast paths fail, the
tail will detect the failure but the head will remain unaware of it.
5.3. Semi-reliable Head Notification and Tail Solicitation
In this scenario, the head sends occasional multipoint Polls in
addition to (or in lieu of) non-Poll multipoint BFD Control packets,
expecting the tails to reply with Final. This also uses the reverse
unicast path, but not the forward unicast path.
If the multipoint path fails but the reverse unicast path stays up,
the tail will detect the failure within a detection time, and the
head will know about it within one reverse packet time (the
notification is delayed to avoid synchronization of the tails.)
If both the multipoint path and the reverse unicast paths fail, the
tail will detect the failure but the head will remain unaware of this
fact.
If the reverse unicast path fails but the multipoint path stays up,
the head will see the BFD session fail, but the state of the
multipoint path will be unknown to the head. The tail will continue
to receive multipoint data traffic.
If either the multipoint Poll or the unicast reply is lost in
transit, the head will see the BFD session fail, but the state of the
multipoint path will be unknown to the head. The tail will continue
to receive multipoint data traffic.
5.4. Reliable Head Notification
In this scenario, the head sends occasional multipoint Polls in
addition to (or in lieu of) non-Poll multipoint BFD control packets,
expecting the tails to reply with Final. If a tail that had
previously replied to a multipoint Poll fails to reply (or if the
head simply wishes to verify tail connectivity,) the head issues a
unicast Poll Sequence to the tail. This scenario makes use of all
three paths.
If the multipoint path fails but the two unicast paths stay up, the
tail will detect the failure within a detection time, and the head
will know about it within one reverse packet time (since the
notification is delayed.) Note that the reverse packet time may be
smaller in this case if the head has previously issued a unicast Poll
(since the tail will not delay transmission of the notification in
this case.)
If both the multipoint path and the reverse unicast paths fail
(regardless of the state of the forward unicast path), the tail will
detect the failure but the head will remain unaware of this fact.
The head will detect a BFD session failure to the tail but cannot
make a determination about the state of the tail's multipoint
connectivity.
If the forward unicast path fails but the reverse unicast path stays
up, the head will detect a BFD session failure to the tail if it
happens to send a unicast Poll sequence, but cannot make a
determination about the state of the tail's multipoint connectivity.
If the multipoint path to the tail fails prior to any unicast Poll
being sent, the tail will detect the failure within a detection time,
and the head will know about it within one reverse packet time (since
the notification is delayed.)
If the multipoint path stays up but the reverse unicast path fails,
the head will see the BFD session fail if it happens to send a Poll
Sequence, but the state of the multipoint path will be unknown to the
head. The tail will continue to receive multipoint data traffic.
If the multipoint path and the reverse unicast path both stay up but
the forward unicast path fails, neither side will notice so long as a
unicast Poll Sequence is never sent by the head. If the head sends a
unicast Poll Sequence, the head will see the BFD session fail, but
the state of the multipoint path will be unknown to the head. The
tail will continue to receive multipoint data traffic.
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] and
[I-D.ietf-bfd-multipoint] apply to this document.
This specification does not raise any additional security issues This specification does not raise any additional security issues
beyond those of the specifications referred to in the list of beyond those of the specifications referred to in the list of
normative references. normative references.
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. Acknowledgements
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
[I-D.ietf-bfd-multipoint] [I-D.ietf-bfd-multipoint]
Katz, D., Ward, D., and J. Networks, "BFD for Multipoint Katz, D., Ward, D., Networks, J., and G. Mirsky, "BFD for
Networks", draft-ietf-bfd-multipoint-11 (work in Multipoint Networks", draft-ietf-bfd-multipoint-12 (work
progress), December 2017. in progress), December 2017.
[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>.
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