draft-ietf-bfd-multipoint-16.txt   draft-ietf-bfd-multipoint-17.txt 
Internet Engineering Task Force D. Katz Internet Engineering Task Force D. Katz
Internet-Draft Juniper Networks Internet-Draft Juniper Networks
Updates: 5880 (if approved) D. Ward Updates: 5880 (if approved) D. Ward
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: October 20, 2018 S. Pallagatti, Ed. Expires: December 6, 2018 S. Pallagatti, Ed.
Individual contributor Individual contributor
G. Mirsky, Ed. G. Mirsky, Ed.
ZTE Corp. ZTE Corp.
April 18, 2018 June 4, 2018
BFD for Multipoint Networks BFD for Multipoint Networks
draft-ietf-bfd-multipoint-16 draft-ietf-bfd-multipoint-17
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
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 October 20, 2018. This Internet-Draft will expire on December 6, 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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 4 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Multipoint BFD Control Packets . . . . . . . . . . . . . 4 5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Session Model . . . . . . . . . . . . . . . . . . . . . . 4 5.1. Multipoint BFD Control Packets . . . . . . . . . . . . . 5
4.3. Session Failure Semantics . . . . . . . . . . . . . . . . 5 5.2. Session Model . . . . . . . . . . . . . . . . . . . . . . 5
4.4. State Variables . . . . . . . . . . . . . . . . . . . . . 5 5.3. Session Failure Semantics . . . . . . . . . . . . . . . . 5
4.4.1. New State Variable Values . . . . . . . . . . . . . . 5 5.4. State Variables . . . . . . . . . . . . . . . . . . . . . 5
4.4.2. State Variable Initialization and Maintenance . . . . 6 5.4.1. New State Variable Values . . . . . . . . . . . . . . 6
4.5. State Machine . . . . . . . . . . . . . . . . . . . . . . 6 5.4.2. State Variable Initialization and Maintenance . . . . 6
4.6. Session Establishment . . . . . . . . . . . . . . . . . . 6 5.5. State Machine . . . . . . . . . . . . . . . . . . . . . . 6
4.7. Discriminators and Packet Demultiplexing . . . . . . . . 7 5.6. Session Establishment . . . . . . . . . . . . . . . . . . 7
4.8. Packet consumption on tails . . . . . . . . . . . . . . . 7 5.7. Discriminators and Packet Demultiplexing . . . . . . . . 7
4.9. Bringing Up and Shutting Down Multipoint BFD Service . . 8 5.8. Packet consumption on tails . . . . . . . . . . . . . . . 8
4.10. Timer Manipulation . . . . . . . . . . . . . . . . . . . 8 5.9. Bringing Up and Shutting Down Multipoint BFD Service . . 8
4.11. Detection Times . . . . . . . . . . . . . . . . . . . . . 9 5.10. Timer Manipulation . . . . . . . . . . . . . . . . . . . 9
4.12. State Maintenance for Down/AdminDown Sessions . . . . . . 9 5.11. Detection Times . . . . . . . . . . . . . . . . . . . . . 9
4.12.1. MultipointHead Sessions . . . . . . . . . . . . . . 9 5.12. State Maintenance for Down/AdminDown Sessions . . . . . . 10
4.12.2. MultipointTail Sessions . . . . . . . . . . . . . . 10 5.12.1. MultipointHead Sessions . . . . . . . . . . . . . . 10
4.13. Base Specification Text Replacement . . . . . . . . . . . 10 5.12.2. MultipointTail Sessions . . . . . . . . . . . . . . 10
4.13.1. Reception of BFD Control Packets . . . . . . . . . . 10 5.13. Base Specification Text Replacement . . . . . . . . . . . 10
4.13.2. Demultiplexing BFD Control Packets . . . . . . . . . 13 5.13.1. Reception of BFD Control Packets . . . . . . . . . . 11
4.13.3. Transmitting BFD Control Packets . . . . . . . . . . 14 5.13.2. Demultiplexing BFD Control Packets . . . . . . . . . 13
5. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.13.3. Transmitting BFD Control Packets . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 6. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17 8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18
10. Normative References . . . . . . . . . . . . . . . . . . . . 17 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 18
11.2. Informational References . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
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
"tails"). "tails").
As multipoint transmissions are inherently unidirectional, this As multipoint transmissions are inherently unidirectional, this
mechanism purports only to verify this unidirectional connectivity. mechanism purports only to verify this unidirectional connectivity.
Although this seems in conflict with the "Bidirectional" in BFD, the Although this seems in conflict with the "Bidirectional" in BFD, the
protocol is capable supporting this use case. protocol is capable of supporting this use case. Use of BFD in
Demand mode enables a tail monitor availability of a multipoint path
even without the existence of some kind of a return path to the head.
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. For some applications such detection of
all options and timing parameters are controlled by the head. the failure at the tail is useful. For example, use of multipoint
BFD to enable fast failure detection and faster failover in multicast
VPN described in [I-D.ietf-bess-mvpn-fast-failover]. Due to
unidirectional nature, virtually 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 the head are outside connectivity. Details of tail notification to the head are outside
the scope of this document. the scope of this document and are discussed in
[I-D.ietf-bfd-multipoint-active-tail].
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 forwarding path alternative to "continuity", i.e., the existence of a forwarding path
between the sender and the receiver. between the sender and the receiver.
This document effectively modifies and adds to the base BFD This document effectively updates and extends the base BFD
specification [RFC5880]. specification [RFC5880].
2. Goals 2. Keywords
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Goals
The primary goal of this mechanism is to allow tails to rapidly The primary goal of this mechanism is to allow tails to rapidly
detect the fact that multipoint connectivity from the head has detect the fact that multipoint connectivity from the head has
failed. failed.
Another goal is for the mechanism to work on any multicast Another goal is for the mechanism to work on any multicast
technology. technology.
A further goal is to support multiple, overlapping point-to- A further goal is to support multiple, overlapping point-to-
multipoint paths, as well as multipoint-to-multipoint paths, and to multipoint paths, as well as multipoint-to-multipoint paths, and to
allow point-to-point BFD sessions to operate simultaneously among the allow point-to-point BFD sessions to operate simultaneously among the
systems participating in Multipoint BFD. systems participating in Multipoint BFD.
It is not a goal for this protocol to verify point-to-point bi- It is not a goal for this protocol to verify point-to-point bi-
directional connectivity between the head and any tail. This can be directional connectivity between the head and any tail. This can be
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 4. Overview
The heart of this protocol is the periodic transmission of BFD The heart of this protocol is the periodic transmission of BFD
Control packets along a multipoint path, from the head to all tails Control packets along a multipoint path, from the head to all tails
on the tree. The contents of the BFD packets provide the means for on the path. The contents of the BFD packets provide the means for
the tails to calculate the detection time for path failure. If no the tails to calculate the detection time for path failure. If no
BFD Control packets are received by a tail for a detection time, the BFD Control packets are received by a tail for a detection time, the
tail declares the path to having failed. For some applications this tail declares the path to having failed. For some applications this
is the only mechanism necessary; the head can remain ignorant of the is the only mechanism necessary; the head can remain ignorant of the
tails. tails.
The head of a multipoint BFD session may wish to be alerted to the The head of a multipoint BFD session may wish to be alerted to the
tails' connectivity (or lack thereof). Details of how the head keeps tails' connectivity (or lack thereof). Details of how the head keeps
track of tails and how tails alert their connectivity to the head are track of tails and how tails alert their connectivity to the head are
outside scope of this document. outside scope of this document and are discussed in
[I-D.ietf-bfd-multipoint-active-tail].
Although this document describes a single head and a set of tails Although this document describes a single head and a set of tails
spanned by a single multipoint path, the protocol is capable of spanned by a single multipoint path, the protocol is capable of
supporting (and discriminating between) more than one multipoint path supporting (and discriminating between) more than one multipoint path
at both heads and tails, as described in Section 4.7 and at both heads and tails, as described in Section 5.7 and
Section 4.13.2. Furthermore, the same head and tail may share Section 5.13.2. Furthermore, the same head and tail may share
multiple multipoint paths, and a multipoint path may have multiple multiple multipoint paths, and a multipoint path may have multiple
heads. heads.
4. Protocol Details 5. Protocol Details
This section describes the operation of Multipoint BFD in detail. This section describes the operation of Multipoint BFD in detail.
4.1. Multipoint BFD Control Packets 5.1. Multipoint BFD Control Packets
Multipoint BFD Control packets (packets sent by the head over a Multipoint BFD Control packets (packets sent by the head over a
multipoint path) are explicitly marked as such, via the setting of multipoint path) are explicitly marked as such, via the setting of
the M bit [RFC5880]. This means that Multipoint BFD does not depend the 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 5.2. Session Model
Multipoint BFD is modeled as a set of sessions of different types. Multipoint BFD is modeled as a set of sessions of different types.
The elements of procedure differ slightly for each type. The elements of procedure differ slightly for each type.
The head has a session of type MultipointHead, as defined in The head has a session of type MultipointHead, as defined in
Section 4.4.1, that is bound to a multipoint path. Multipoint BFD Section 5.4.1, that is bound to a multipoint path. Multipoint BFD
Control packets are sent by this session over the multipoint path, Control packets are sent by this session over the multipoint path,
and no BFD Control packets are received by it. and no BFD Control packets are received by it.
Each tail has a session of type MultipointTail, as defined in Each tail has a session of type MultipointTail, as defined in
Section 4.4.1, associated with a multipoint path. These sessions Section 5.4.1, associated with a multipoint path. These sessions
receive BFD Control packets from the head over the multipoint path. receive BFD Control packets from the head over the multipoint path.
4.3. Session Failure Semantics 5.3. Session Failure Semantics
The semantics of session failure is subtle enough to warrant further The semantics of session failure is subtle enough to warrant further
explanation. explanation.
MultipointHead sessions cannot fail (since they are controlled MultipointHead sessions cannot fail (since they are controlled
administratively). administratively).
If a MultipointTail session fails, it means that the tail definitely If a MultipointTail session fails, it means that the tail definitely
has lost contact with the head (or the head has been administratively has lost contact with the head (or the head has been administratively
disabled) and the tail should take appropriate action. disabled) and the tail should take appropriate action.
4.4. State Variables 5.4. State Variables
Multipoint BFD introduces some new state variables and modifies the Multipoint BFD introduces some new state variables and modifies the
usage of a few existing ones. usage of a few existing ones.
4.4.1. New State Variable Values 5.4.1. New State Variable Values
A number of new values of the state variable bfd.SessionType are A number of new values of the state variable bfd.SessionType are
added to the base BFD [RFC5880] and base S-BFD [RFC7880] added to the base BFD [RFC5880] and base 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:
skipping to change at page 6, line 5 skipping to change at page 6, line 28
MultipointHead: A session on the head responsible for the MultipointHead: A session on the head responsible for the
periodic transmission of multipoint BFD Control packets periodic transmission of multipoint BFD Control packets
along the multipoint path. along the multipoint path.
MultipointTail: A multipoint session on a tail. MultipointTail: A multipoint session on a tail.
This variable MUST be initialized to the appropriate type when This variable MUST be initialized to the appropriate type when
the session is created. the session is created.
4.4.2. State Variable Initialization and Maintenance 5.4.2. State Variable Initialization and Maintenance
Some state variables defined in section 6.8.1 of [RFC5880] need to be Some state variables defined in section 6.8.1 of [RFC5880] need to be
initialized or manipulated differently depending on the session type. initialized or manipulated differently depending on the session type.
bfd.RequiredMinRxInterval bfd.RequiredMinRxInterval
This variable MUST be initialized to 0 for session type This variable MUST be initialized to 0 for session type
MultipointHead. MultipointHead.
bfd.DemandMode bfd.DemandMode
This variable MUST be initialized to 1 for session type This variable MUST be initialized to 1 for session type
MultipointHead and MUST be initialized to 0 for session type MultipointHead and MUST be initialized to 0 for session type
MultipointTail. MultipointTail.
4.5. State Machine 5.5. 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 those packets MUST be with the State field being set to INIT, and those packets MUST be
ignored on 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
skipping to change at page 6, line 47 skipping to change at page 7, line 21
+------+ 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 5.6. Session Establishment
Unlike point-to-point BFD, Multipoint BFD provides a form of the Unlike point-to-point BFD, Multipoint BFD provides a form of the
discovery mechanism for tails to discover the head. The minimum discovery mechanism 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
binding to the multipoint path over which BFD is running. The head the binding to the multipoint path over which BFD is running. The
transmits Multipoint BFD packets on that tree, and the tails listen head transmits Multipoint BFD packets on that path, and the tails
for BFD packets on that tree. All other information MAY be listen for BFD packets on that path. 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 5.7. Discriminators and Packet Demultiplexing
The use of Discriminators is somewhat different in Multipoint BFD The use of Discriminators is somewhat different in Multipoint BFD
than in Point-to-point BFD. than in Point-to-point BFD.
The head sends Multipoint BFD Control packets over the multipoint The head sends Multipoint BFD Control packets over the multipoint
path via the MultipointHead session with My Discr set to a value path via the MultipointHead session with My Discr set to a value
bound to the multipoint path, and with Your Discr set to zero. bound to the multipoint path, and with Your Discr set to zero.
IP and MPLS multipoint tails MUST demultiplex BFD packets based on a IP and MPLS multipoint tails MUST demultiplex BFD packets based on a
combination of the source address, My Discriminator and the identity combination of the source address, My Discriminator and the identity
of the multipoint tree which the Multipoint BFD Control packet was of the multipoint path which the Multipoint BFD Control packet was
received from. Together they uniquely identify the head of the received from. Together they uniquely identify the head of the
multipoint path. Bootstrapping BFD session to multipoint MPLS LSP in multipoint path. Bootstrapping BFD session to multipoint MPLS LSP in
case of penultimate hop popping is outside the scope of this case of penultimate hop popping may use control plane, e.g., as
document. described in [I-D.ietf-bess-mvpn-fast-failover], and is outside the
scope of this document.
Note that, unlike point-to-point sessions, the My Discriminator value Note that, unlike point-to-point sessions, the My Discriminator value
on MultipointHead session MUST NOT be changed during the life of a on MultipointHead session MUST NOT be changed during the life of a
session. This is a side effect of the more complex demultiplexing session. This is a side effect of the more complex demultiplexing
scheme. scheme.
4.8. Packet consumption on tails 5.8. Packet consumption on tails
BFD packets received on tails for an IP multicast group MUST be BFD packets received on tails for an IP multicast group MUST be
consumed by tails and MUST NOT be forwarded to receivers. Node with consumed by tails and MUST NOT be forwarded to receivers. Nodes with
the BFD session of type MultipointTail MUST identify packet received the BFD session of type MultipointTail MUST identify packets received
on an IP multipoint path as BFD control packet if the destination UDP on an IP multipoint path as BFD control packet if the destination UDP
port value equals 3784. port value equals 3784.
For multipoint LSPs, when IP/UDP encapsulation of BFD control packets For multipoint LSPs, when IP/UDP encapsulation of BFD control packets
is used, MultipointTail MUST expect destination UDP port 3784. is used, MultipointTail MUST expect destination UDP port 3784.
Destination IP address of BFD control packet MUST be in 127.0.0.0/8 Destination IP address of BFD control packet MUST be in 127.0.0.0/8
range for IPv4 or in 0:0:0:0:0:FFFF:7F00:0/104 range for IPv6. The range for IPv4 or in 0:0:0:0:0:FFFF:7F00:0/104 range for IPv6. The
use of these destination addresses is consistent with the use of these destination addresses is consistent with the
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 demultiplexed as
described in Section 4.13.2. Use of other types of encapsulation of described in Section 5.13.2. Use of other types of encapsulation of
the BFD control message over multipoint LSP is outside the scope of the BFD control message over multipoint LSP is outside the scope of
this document. this document.
4.9. Bringing Up and Shutting Down Multipoint BFD Service 5.9. Bringing Up and Shutting Down Multipoint BFD Service
Because there is no three-way handshake in Multipoint BFD, a newly Because there is no three-way handshake in Multipoint BFD, a newly
started head (that does not have any previous state information started head (that does not have any previous state information
available) SHOULD start with bfd.SessionState set to Down and available) SHOULD start with bfd.SessionState set to Down and
bfd.RequiredMinRxInterval MUST be set to zero in the MultipointHead bfd.RequiredMinRxInterval MUST be set to zero in the MultipointHead
session. The session SHOULD remain in this state for a time equal to session. The session SHOULD remain in this state for a time equal to
(bfd.DesiredMinTxInterval * bfd.DetectMult). This will ensure that (bfd.DesiredMinTxInterval * bfd.DetectMult). This will ensure that
all MultipointTail sessions are reset (so long as the restarted head all MultipointTail sessions are reset (so long as the restarted head
is using the same or a larger value of bfd.DesiredMinTxInterval than is using the same or a larger value of bfd.DesiredMinTxInterval than
it did previously). it did previously).
Multipoint BFD service is brought up by administratively setting Multipoint BFD service is brought up by administratively setting
bfd.SessionState to Up in the MultipointHead session. bfd.SessionState to Up in the MultipointHead session.
The head of a multipoint BFD session may wish to shut down its BFD The head of a multipoint BFD session may wish to shut down its BFD
service in a controlled fashion. This is desirable because the tails service in a controlled fashion. This is desirable because the tails
need not wait a detection time prior to declaring the multipoint need not wait a detection time prior to declaring the multipoint
session to be down (and taking whatever action is necessary in that session to be down (and taking whatever action is necessary in that
case). case).
To shut down a multipoint session the head MUST administratively set To shut down a multipoint session in a controlled fashion the head
bfd.SessionState in the MultipointHead session to either Down or MUST administratively set bfd.SessionState in the MultipointHead
AdminDown and SHOULD set bfd.RequiredMinRxInterval to zero. The session to either Down or AdminDown and SHOULD set
session SHOULD send BFD Control packets in this state for a period bfd.RequiredMinRxInterval to zero. The session SHOULD send BFD
equal to (bfd.DesiredMinTxInterval * bfd.DetectMult). Control packets in this state for a period equal to
(bfd.DesiredMinTxInterval * bfd.DetectMult). Alternatively, the head
The semantic difference between Down and AdminDown state is for MAY stop transmitting BFD Control packets and not send any more BFD
further discussion. Control packets with the new state (Down or AdminDown). Tails will
declare the multipoint session down only after the detection time
interval runs out.
4.10. Timer Manipulation 5.10. Timer Manipulation
Because of the one-to-many mapping, a session of type MultipointHead Because of the one-to-many mapping, a session of type MultipointHead
SHOULD NOT initiate a Poll Sequence in conjunction with timer value SHOULD NOT initiate a Poll Sequence in conjunction with timer value
changes. However, to indicate a change in the packets, changes. However, to indicate a change in the packets,
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 the packet has M and P bits MultipointTail session MUST NOT reply if the packet has M and P bits
set and bfd.RequiredMinRxInterval set to 0. set and bfd.RequiredMinRxInterval set to 0. Because the Poll
Sequence is not used, the tail cannot negotiate down MultpointHead's
transmit interval. If the value Desired Min TX Interval in the
received by MultipointTail BFD Control packet is too high (that
determination may change in time based on the current environment) it
must be handled by the implementation and may be controlled by local
policy, e.g., close the MultipointTail session.
The MultipointHead, when changing the transmit interval to a higher The MultipointHead, when changing the transmit interval to a higher
value, MUST send BFD control packets with P bit set at the old value, MUST send BFD control packets with 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 and is discussed in
[I-D.ietf-bfd-multipoint-active-tail].
4.11. Detection Times 5.11. Detection Times
Multipoint BFD is inherently asymmetric. As such, each session type Multipoint BFD is inherently asymmetric. As such, each session type
has a different approach to detection times. has a different approach to detection times.
Since MultipointHead sessions never receive packets, they do not Since MultipointHead sessions never receive packets, they do not
calculate a detection time. calculate a detection time.
MultipointTail sessions cannot influence the transmission rate of the MultipointTail sessions cannot influence the transmission rate of the
MultipointHead session using the Required Min Rx Interval field MultipointHead session using the Required Min Rx Interval field
because of its one-to-many nature. As such, the detection time because of its one-to-many nature. As such, the detection time
calculation for a MultipointTail session does not use calculation for a MultipointTail session does not use
bfd.RequiredMinRxInterval in the calculation. The detection time is bfd.RequiredMinRxInterval. The detection time is calculated as the
calculated as the product of the last received values of Desired Min product of the last received values of Desired Min TX Interval and
TX Interval and Detect Mult. Detect Mult.
The value of bfd.DetectMult may be changed at any time on any session The value of bfd.DetectMult may be changed at any time on any session
type. type.
4.12. State Maintenance for Down/AdminDown Sessions 5.12. State Maintenance for Down/AdminDown Sessions
The length of time session state is kept after the session goes down The length of time session state is kept after the session goes down
determines how long the session will continue to send BFD Control determines how long the session will continue to send BFD Control
packets (since no packets can be sent after the session is packets (since no packets can be sent after the session is
destroyed). destroyed).
4.12.1. MultipointHead Sessions 5.12.1. MultipointHead Sessions
When a MultipointHead session transitions to states Down or When a MultipointHead session transitions to states Down or
AdminDown, the state SHOULD be maintained for a period equal to AdminDown, the state SHOULD be maintained for a period equal to
(bfd.DesiredMinTxInterval * bfd.DetectMult) to ensure that the tails (bfd.DesiredMinTxInterval * bfd.DetectMult) to ensure that the tails
more quickly detect the session going down (by continuing to transmit more quickly detect the session going down (by continuing to transmit
BFD Control packets with the new state). BFD Control packets with the new state).
4.12.2. MultipointTail Sessions 5.12.2. MultipointTail Sessions
MultipointTail sessions MAY be destroyed immediately upon leaving Up MultipointTail sessions MAY be destroyed immediately upon leaving Up
state, since tail will transmit no packets. state, since tail will transmit no packets.
Otherwise, MultipointTail sessions SHOULD be maintained as long as Otherwise, MultipointTail sessions SHOULD be maintained as long as
BFD Control packets are being received by it (which by definition BFD Control packets are being received by it (which by definition
will indicate that the head is not Up). will indicate that the head is not Up).
4.13. Base Specification Text Replacement 5.13. Base Specification Text Replacement
The following sections are meant to replace the corresponding The following sections are meant to replace the corresponding
sections in the base specification [RFC5880] in support of BFD for sections in the base specification [RFC5880] in support of BFD for
multipoint networks while not changing processing for point-to-point multipoint networks while not changing processing for point-to-point
BFD. BFD.
4.13.1. Reception of BFD Control Packets 5.13.1. Reception of BFD Control Packets
The following procedure replaces section 6.8.6 of [RFC5880]. The following procedure replaces entire section 6.8.6 of [RFC5880].
When a BFD Control packet is received, the following procedure MUST When a BFD Control packet is received, the following procedure MUST
be followed, in the order specified. If the packet is discarded be followed, in the order specified. If the packet is discarded
according to these rules, processing of the packet MUST cease at that according to these rules, processing of the packet MUST cease at that
point. point.
If the version number is not correct (1), the packet MUST be If the version number is not correct (1), the packet MUST be
discarded. discarded.
If the Length field is less than the minimum correct value (24 if If the Length field is less than the minimum correct value (24 if
skipping to change at page 10, line 45 skipping to change at page 11, line 29
discarded. discarded.
If the Length field is greater than the payload of the If the Length field is greater than the payload of the
encapsulating protocol, the packet MUST be discarded. encapsulating protocol, the packet MUST be discarded.
If the Detect Mult field is zero, the packet MUST be discarded. If the Detect Mult field is zero, the packet MUST be discarded.
If the My Discriminator field is zero, the packet MUST be If the My Discriminator field is zero, the packet MUST be
discarded. discarded.
Demultiplex the packet to a session according to Section 4.13.2 Demultiplex the packet to a session according to Section 5.13.2
below. The result is either a session of the proper type, or the below. The result is either a session of the proper type, or the
packet is discarded (and packet processing MUST cease). packet is discarded (and packet processing MUST cease).
If the A bit is set and no authentication is in use (bfd.AuthType If the A bit is set and no authentication is in use (bfd.AuthType
is zero), the packet MUST be discarded. is zero), the packet MUST be discarded.
If the A bit is clear and authentication is in use (bfd.AuthType If the A bit is clear and authentication is in use (bfd.AuthType
is nonzero), the packet MUST be discarded. is nonzero), the packet MUST be discarded.
If the A bit is set, the packet MUST be authenticated under the If the A bit is set, the packet MUST be authenticated under the
skipping to change at page 11, line 32 skipping to change at page 12, line 16
transmission of Echo packets, if any, MUST cease. transmission of Echo packets, if any, MUST cease.
If a Poll Sequence is being transmitted by the local system and If a Poll Sequence is being transmitted by the local system and
the Final (F) bit in the received packet is set, the Poll Sequence the Final (F) bit in the received packet is set, the Poll Sequence
MUST be terminated. MUST be terminated.
If bfd.SessionType is PointToPoint, update the transmit interval If bfd.SessionType is PointToPoint, update the transmit interval
as described in [RFC5880] section 6.8.2. as described in [RFC5880] section 6.8.2.
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].
MultipointTail, then update the Detection Time as the product of
the last received values of Desired Min TX Interval and Detect Else
Mult, as described in Section 4.11 of this specification.
If bfd.SessionType is MultipointTail, then update the Detection
Time as the product of the last received values of Desired Min
TX Interval and Detect Mult, as described in Section 5.11 of
this specification.
If bfd.SessionState is AdminDown If bfd.SessionState is AdminDown
Discard the packet Discard the packet
If the received state is AdminDown If the received state is AdminDown
If bfd.SessionState is not Down If bfd.SessionState is not Down
Set bfd.LocalDiag to 3 (Neighbor signaled session down) Set bfd.LocalDiag to 3 (Neighbor signaled session down)
skipping to change at page 12, line 40 skipping to change at page 13, line 28
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 5.13.3).
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 Section 4.13.3). packets (see Section 5.13.3).
If the packet was not discarded, it has been received for purposes If the packet was not discarded, it has been received for purposes
of the Detection Time expiration rules in [RFC5880] section 6.8.4. of the Detection Time expiration rules in [RFC5880] section 6.8.4.
4.13.2. Demultiplexing BFD Control Packets 5.13.2. Demultiplexing BFD Control Packets
This section is part of the replacement for [RFC5880] section 6.8.6, This section is part of the replacement for [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
If the Your Discriminator field is nonzero, the packet MUST be If the Your Discriminator field is nonzero, the packet MUST be
discarded. discarded.
Select a session as based on source address, My Discriminator Select a session as based on source address, My Discriminator
and the identity of the multipoint tree which the Multipoint and the identity of the multipoint path which the Multipoint
BFD Control packet was received. If a session is found, and BFD Control packet was received.
bfd.SessionType is not MultipointTail, the packet MUST be
discarded. If a session is not found, a new session of type If a session is found, and bfd.SessionType is not
MultipointTail MAY be created, or the packet MAY be discarded. MultipointTail, the packet MUST be discarded.
This choice is outside the scope of this specification.
Else
If a session is not found, a new session of type
MultipointTail MAY be created, or the packet MAY be
discarded. This choice MAY be controlled by the local
policy, e.g. a maximum number of MultipointTail sessions and
number of active MultipointTail sessions, and is outside the
scope of this specification.
Else (Multipoint bit is clear) Else (Multipoint bit is clear)
If the Your Discriminator field is nonzero If the Your Discriminator field is nonzero
Select a session based on the value of Your Discriminator. Select a session based on the value of Your Discriminator.
If no session is found, the packet MUST be discarded. If no session is found, the packet MUST be discarded.
Else (Your Discriminator is zero) Else (Your Discriminator is zero)
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addressing information, the My Discriminator field, and the addressing information, the My Discriminator field, and the
interface over which the packet was received. The exact interface over which the packet was received. The exact
method of selection is application-specific and is thus method of selection is application-specific and is thus
outside the scope of this specification. outside the scope of this specification.
If a matching session is found, and bfd.SessionType is not If a matching session is found, and bfd.SessionType is not
PointToPoint, the packet MUST be discarded. PointToPoint, the packet MUST be discarded.
If a matching session is not found, a new session of type If a matching session is not found, a new session of type
PointToPoint MAY be created, or the packet MAY be discarded. PointToPoint MAY be created, or the packet MAY be discarded.
This choice is outside the scope of this specification. This choice MAY be controlled by a local policy and is
outside the scope of this specification.
If the State field is Init and bfd.SessionType is not If the State field is Init and bfd.SessionType is not
PointToPoint, the packet MUST be discarded. PointToPoint, the packet MUST be discarded.
4.13.3. Transmitting BFD Control Packets 5.13.3. Transmitting BFD Control Packets
The following procedure replaces section 6.8.7 of [RFC5880]. The following procedure replaces entire section 6.8.7 of [RFC5880].
BFD Control packets MUST be transmitted periodically at the rate BFD Control packets MUST be transmitted periodically at the rate
determined according to [RFC5880] section 6.8.2, except as specified determined according to [RFC5880] section 6.8.2, except as specified
in this section. in this section.
A system MUST NOT transmit any BFD Control packets if bfd.RemoteDiscr A system MUST NOT transmit any BFD Control packets if bfd.RemoteDiscr
is zero and the system is taking the Passive role. is zero and the system is taking the Passive role.
A system MUST NOT transmit any BFD Control packets if bfd.SessionType A system MUST NOT transmit any BFD Control packets if bfd.SessionType
is MultipointTail. is MultipointTail.
skipping to change at page 16, line 37 skipping to change at page 17, line 34
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 6. Assumptions
If authentication is in use, all tails must be configured to have a Shared keys in multipoint scenarios allow any tail to spoof the head
common authentication key in order to receive the multipoint BFD from the viewpoint of any other tail. For this reason, using shared
Control packets. keys to authenticate BFD Control packets in multipoint scenarios is a
significant security exposure unless all tails can be trusted not to
spoof the head. Otherwise, asymmetric message authentication would
be needed, e.g., protocols that use Timed Efficient Stream Loss-
Tolerant Authentication (TESLA) as described in [RFC4082].
6. IANA Considerations If authentication is in use, the head and all tails may be configured
to have a common authentication key in order for the tails to
validate multipoint BFD Control packets.
7. IANA Considerations
This document has no actions for IANA. This document has no actions for IANA.
7. Security Considerations 8. Security Considerations
The same security considerations as those described in [RFC5880] The same security considerations as those described in [RFC5880]
apply to this document. Additionally, implementations that create apply to this document. Additionally, implementations that create
MultpointTail sessions dynamically upon receipt of Multipoint BFD MultpointTail sessions dynamically upon receipt of Multipoint BFD
Control packets MUST implement protective measures to prevent an Control packets MUST implement protective measures to prevent an
infinite number of MultipointTail sessions being created. Below are infinite number of MultipointTail sessions 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 the expected interface, with expected MPLS label, path (e.g., on the expected interface, with expected MPLS label,
etc), 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 9. 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. Acknowledgments 10. 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 11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>. <https://www.rfc-editor.org/info/rfc5880>.
skipping to change at page 18, line 15 skipping to change at page 19, line 29
[RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., [RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
Aldrin, S., and M. Chen, "Detecting Multiprotocol Label Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
Switched (MPLS) Data-Plane Failures", RFC 8029, Switched (MPLS) Data-Plane Failures", RFC 8029,
DOI 10.17487/RFC8029, March 2017, DOI 10.17487/RFC8029, March 2017,
<https://www.rfc-editor.org/info/rfc8029>. <https://www.rfc-editor.org/info/rfc8029>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Authors' Addresses 11.2. Informational References
[I-D.ietf-bess-mvpn-fast-failover]
Morin, T., Kebler, R., and G. Mirsky, "Multicast VPN fast
upstream failover", draft-ietf-bess-mvpn-fast-failover-03
(work in progress), May 2018.
[I-D.ietf-bfd-multipoint-active-tail]
Katz, D., Ward, D., Networks, J., and G. Mirsky, "BFD
Multipoint Active Tails.", draft-ietf-bfd-multipoint-
active-tail-08 (work in progress), June 2018.
[RFC4082] Perrig, A., Song, D., Canetti, R., Tygar, J., and B.
Briscoe, "Timed Efficient Stream Loss-Tolerant
Authentication (TESLA): Multicast Source Authentication
Transform Introduction", RFC 4082, DOI 10.17487/RFC4082,
June 2005, <https://www.rfc-editor.org/info/rfc4082>.
Authors' Addresses
Dave Katz Dave Katz
Juniper Networks Juniper Networks
1194 N. Mathilda Ave. 1194 N. Mathilda Ave.
Sunnyvale, California 94089-1206 Sunnyvale, California 94089-1206
USA USA
Email: dkatz@juniper.net Email: dkatz@juniper.net
Dave Ward Dave Ward
Cisco Systems Cisco Systems
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