One document matched: draft-ietf-bfd-multipoint-07.xml
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<rfc category="std" docName="draft-ietf-bfd-multipoint-07" ipr="trust200902">
<!-- category values: std, bcp, info, exp, and historic
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<!-- ***** FRONT MATTER ***** -->
<front>
<title abbrev="BFD for Multipoint Networks">
BFD for Multipoint Networks
</title>
<!-- add 'role="editor"' below for the editors if appropriate -->
<!-- Another author who claims to be an editor -->
<author fullname="Dave Katz" initials="D."
surname="Katz">
<organization>Juniper Networks</organization>
<address>
<postal>
<street> 1194 N. Mathilda Ave.</street>
<city>Sunnyvale</city>
<region>California</region>
<code> 94089-1206</code>
<country>USA</country>
</postal>
<email>dkatz@juniper.net</email>
</address>
</author>
<author fullname="Dave Ward" initials="D."
surname="Ward">
<organization>Cisco Systems</organization>
<address>
<postal>
<street> 170 West Tasman Dr.</street>
<city>San Jose</city>
<region>California</region>
<code>95134</code>
<country>USA</country>
</postal>
<email>wardd@cisco.com</email>
</address>
</author>
<author fullname="Santosh Pallagatti" initials="S." role="editor"
surname="Pallagatti">
<organization>Juniper Networks</organization>
<address>
<postal>
<street>Embassy Business Park</street>
<city>Bangalore</city>
<region>KA</region>
<code>560093</code>
<country>India</country>
</postal>
<email>santoshpk@juniper.net</email>
</address>
</author>
<date year="2015" />
<area>BFD Working Group</area>
<workgroup>Internet Engineering Task Force</workgroup>
<!-- WG name at the upperleft corner of the doc,
IETF is fine for individual submissions.
If this element is not present, the default is "Network Working Group",
which is used by the RFC Editor as a nod to the history of the IETF. -->
<keyword>BFD</keyword>
<keyword>Multipoint BFD</keyword>
<!-- Keywords will be incorporated into HTML output
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<abstract>
<t>This document describes extensions to the Bidirectional Forwarding Detection (BFD) protocol for its use in multipoint and multicast networks. Comments on this draft should be directed to rtg-bfd@ietf.org.</t>
</abstract>
<note title="Requirements Language">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in <xref target="RFC2119">RFC 2119</xref>.</t>
</note>
</front>
<middle>
<section title="Introduction" anchor="Intro">
<t>The Bidirectional Forwarding Detection protocol <xref target="RFC5880" /> specifies a method for verifying unicast connectivity between a pair of systems. This document defines a method for using BFD to provide verification of multipoint or multicast connectivity between a multipoint sender (the "head") and a set of one or more multipoint receivers (the "tails").</t>
<t>As multipoint transmissions are inherently unidirectional, this mechanism purports only to verify this unidirectional connectivity. Although this seems in conflict with the "Bidirectional" in BFD, it is a natural fit for that protocol. </t>
<t>This application of BFD allows for the tails to detect a lack of connectivity from the head. Due to unidirectional nature, virtually all options and timing parameters are controlled by the head.</t>
<t>As an option, the tail may notify the head of the lack of multipoint connectivity. Details of tail notification to head are outside the scope of this document.</t>
<t>Throughout this document, the term "multipoint" is defined as a mechanism by which one or more systems receive packets sent by a single sender. This specifically includes such things as IP multicast and point-to-multipoint MPLS.</t>
<t>This document effectively modifies and adds to the base BFD specification. It is the intention of the authors to fold these extensions into the base specification at the appropriate time.</t>
</section>
<section title="Goals">
<t>The primary goal of this mechanism is to allow tails to rapidly detect the fact that multipoint connectivity from the head has failed.</t>
<t>Another goal is for the mechanism to work on any multicast or multipoint medium.</t>
<t>A further goal is to support multiple, overlapping multipoint paths, as well as multipoint paths with multiple heads, and to allow point-to-point BFD sessions to operate simultaneously among the systems participating in Multipoint BFD.</t>
<t>A final goal is to integrate multipoint operation into the base specification in such a way as to make it relatively easy to support both multipoint and point-to-point operation in a single implementation.</t>
<t>It is a non-goal for this protocol to verify point-to-point connectivity between the head and any tails. This can be done independently (and with no penalty in protocol overhead) by using point-to-point BFD.</t>
</section>
<section title="Overview">
<t>The heart of this protocol is the periodic transmission of BFD 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 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 tail declares the path to have failed. For some applications this is the only mechanism necessary; the head can remain ignorant of the tails.</t>
<t>Head may wish to be alerted to the tails' connectivity (or lack thereof). Details of how head keeps track of tails and how tails alert it's connectivity to head are outside scope of this document.</t>
<t>Although this document describes a single head and a set of tails spanned by a single multipoint path, the protocol is capable of supporting (and discriminating between) more than one multipoint path at both heads and tails. Furthermore, the same head and tail may share multiple multipoint paths, and a multipoint path may have multiple heads.</t>
</section>
<section title="Protocol Details">
<t>This section describes the operation of Multipoint BFD in detail.</t>
<section title="Multipoint BFD Control Packets">
<t>Multipoint BFD Control packets (packets sent by the head over a multipoint path) are explicitly marked as such, via the setting of the M bit. This means that Multipoint BFD does not depend 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 information may not be available to the recipient.</t>
</section>
<section title="Session Model">
<t>Multipoint BFD is modeled as a set of sessions of different types. The elements of procedure differ slightly for each type.</t>
<t>Point-to-point sessions, as described in [BFD], are of type PointToPoint.</t>
<t>The head has a session of type MultipointHead that is bound to a multipoint path. Multipoint BFD Control packets are sent by this session over the multipoint path, and no BFD Control packets are received by it.</t>
<t>Each tail has a session of type MultipointTail associated with a multipoint path. These sessions receive BFD Control packets from the head over multipoint path.</t>
</section>
<section title="Session Failure Semantics">
<t>The semantics of session failure are subtle enough to warrant further explanation.</t>
<t>MultipointHead sessions cannot fail (since they are controlled administratively.)</t>
<t>If a MultipointTail session fails, it means that the tail definitely has lost contact with the head (or the head has been administratively disabled) and the tail should take appropriate action.</t>
</section>
<section title="State Variables">
<t>Multipoint BFD introduces some new state variables, and modifies the usage of a few existing ones.</t>
<section title="New State Variables">
<t>A number of state variables are added to the base specification in support of Multipoint BFD.
<list style="empty">
<t>bfd.SessionType
<list style="empty">
<t>The type of this session. Allowable values are:
<list style="empty">
<t>PointToPoint: Classic point-to-point BFD.</t>
<t>MultipointHead: A session on the head responsible for the periodic transmission of multipoint BFD Control packets along the multipoint path.</t>
<t>MultipointTail: A multipoint session on a tail.</t>
</list>
</t>
<t>This variable MUST be initialized to the appropriate type when the session is created, according to the rules in <xref target="RFC5880_REPLACE"/></t>
</list>
</t>
<t>bfd.SilentTail
<list style="empty">
<t>Always set to 1, a tail will never transmit any BFD Control packets to the head under any circumstances. Setting to 0 is outside the scope of this document.</t>
<t>This variable is only pertinent when bfd.SessionType is MultipointTail.</t>
</list>
</t>
</list>
</t>
</section>
<section title="State Variable Initialization and Maintenance">
<t>Some state variables defined in section 6.8.1 of the <xref target="RFC5880" /> needs to be initialized or manipulated differently depending on the session type.
<list style="empty">
<t>bfd.RequiredMinRxInterval
<list style="empty">
<t>This variable MUST be set to 0 for session type MultipointHead.</t>
</list>
</t>
<t>bfd.DemandMode
<list style="empty">
<t>This variable MUST be initialized to 1 for session type
MultipointHead and MUST be initialized to
0 for session type MultipointTail.
</t>
</list>
</t>
</list>
</t>
</section>
</section>
<section title="State Machine">
<t>The BFD state machine works slightly differently in the multipoint application. In particular, since there is a many-to-one mapping, three-way handshakes for session establishment and teardown are neither possible nor appropriate. As such there is no Init state.
Session of type MultipointHead MUST NOT send BFD control packets with the State field being set to INIT, and must be ignored on receipt.</t>
<t>The following diagram provides an overview of the state machine for session type MultipointTail. The notation on each arc represents the state of the remote system (as received in the State field in the BFD Control packet) or indicates the expiration of the Detection Timer.
<figure align="left"><preamble></preamble><artwork align="left"><![CDATA[ DOWN, ADMIN DOWN,
+------+ TIMER +------+
+----| |<---------------------| |----+
DOWN,| | DOWN | | UP | |UP
ADMIN DOWN,+--->| |--------------------->| |<---+
TIMER +------+ UP +------+
]]></artwork></figure>
Sessions of type MultipointHead never receive packets and have no Detection Timer, and as such all state transitions are administratively driven.</t>
</section>
<section title="Session Establishment">
<t>Unlike Point-to-point BFD, Multipoint BFD provides a form of discovery mechanism for tails to discover the head. The minimum amount of a priori information required both on the head and tails is the binding to the multipoint path over which BFD is running. The head transmits Multipoint BFD packets on that tree, and the tails listen for BFD packets on that tree. All other information MAY be determined dynamically.</t>
<t>A session of type MultipointHead is created for each multipoint path over which the head wishes to run BFD. This session runs in the Active role. Except when terminating BFD service, this session is always in state Up and always operates in Demand mode. No received packets are ever demultiplexed to the MultipointHead session. In this sense it is a degenerate form of a session.</t>
<t>Sessions on the tail MAY be established dynamically, based on the receipt of a Multipoint BFD Control packet from the head, and are of type MultipointTail. Tail sessions always take the Passive role.</t>
</section>
<section title="Discriminators and Packet Demultiplexing">
<t>The use of Discriminators is somewhat different in Multipoint BFD than in Point-to-point BFD.</t>
<t>The head sends Multipoint BFD Control packets over the MultipointHead session with My Discr set to a value bound to the multipoint path, and with Your Discr set to zero.</t>
<t>IP and MPLS multipoint tails MUST demultiplex BFD packets based on a combination of the source address, My Discriminator and the identity of the multipoint tree which the Multipoint BFD Control packet was received from. Together they uniquely identify the head of the multipoint path. Bootstrapping BFD session to a multipoint LSP in case of penultimate hop popping is outside the scope of this document.</t>
<t>Note that, unlike PointToPoint sessions, the discriminator values on all multipoint session types MUST NOT be changed during the life of a session. This is a side effect of the more complex demultiplexing scheme.</t>
</section>
<section title="Packet consumption on tails">
<t>BFD packets received on tails for a multicast group MUST be consumed by tails and MUST not be forwarded to receivers.
Session of type MultipointTail MUST identify the packet as BFD with the help of destination UDP port number "3784" on IP multipoint path.
For multipoint LSP, MultipointTail MUST use destination UDP port "3784" and IP "127.0.0.0/8" range. Packet identified as BFD packet MUST
be consumed by MultipointTail and demultiplex as described in <xref target="DEMUX"/></t>
</section>
<section title="Bringing Up and Shutting Down Multipoint BFD Service">
<t>Because there is no three-way handshake in Multipoint BFD, a newly started head (that does not have any previous state information available) SHOULD start with bfd.SessionState set to Down and with bfd.RequiredMinRxInterval set to zero in the MultipointHead session. The session SHOULD remain in this state for a time equal to (bfd.DesiredMinTxInterval * bfd.DetectMult). This will ensure that all MultipointTail sessions are reset (so long as the restarted head is using the same or larger value of bfd.DesiredMinTxInterval than it did previously.)</t>
<t>Multipoint BFD service is brought up by administratively setting bfd.SessionState to Up in the MultipointHead session. </t>
<t>A head may wish to shut down its BFD service in a controlled fashion. This is desirable because the tails need not wait a detection time prior to declaring the multipoint session to be down (and taking whatever action is necessary in that case.) </t>
<t>To shut down a multipoint session a head MUST administratively set bfd.SessionState in the MultipointHead session to either Down or AdminDown and SHOULD set bfd.RequiredMinRxInterval to zero. The session SHOULD send BFD Control packets in this state for a period equal to (bfd.DesiredMinTxInterval * bfd.DetectMult).</t>
<t>The semantic difference between Down and AdminDown state is for further discussion. </t>
</section>
<section title="Timer Manipulation">
<t> Because of the one-to-many mapping, a session of type MultipointHead SHOULD NOT initiate a Poll Sequence in conjunction with timer value changes. However to indicate change in packet MultipointHead session MUST send packet with P bit set. MultipointTail session MUST NOT reply if packet has M, P bit set and bfd.RequiredMinRxInterval set to 0.</t>
<t>The MultipointHead MUST send bfd.DetectMult packets with P bit set at the old transmit interval before using the higher value in order to avoid false detection timeouts at the tails. MultipointHead May also wait some amount of time before making the changes to the transmit interval (through configuration).</t>
<t>Change in the value of bfd.RequiredMinRxInterval is outside the scope of this document.</t>
</section>
<section title="Detection Times" anchor="DETECT">
<t>Multipoint BFD is inherently asymmetric. As such, each session type has a different approach to detection times.</t>
<t>Since the MultipointHead session never receives packets, it does not calculate a detection time.</t>
<t>MultipointTail sessions cannot influence the transmission rate of the MultipointHead session using the Required Min Rx Interval field because of its one-to-many nature. As such, the Detection Time calculation for a MultipointTail session does not use bfd.RequiredMinRxInterval in the calculation. The detection time is calculated as the product of the last received values of Desired Min TX Interval and Detect Mult.</t>
<t>The value of bfd.DetectMult may be changed at any time on any session type.</t>
</section>
<section title="State Maintenance for Down/AdminDown Sessions">
<t>The length of time session state is kept after the session goes down determines how long the session will continue to send BFD Control packets (since no packets can be sent after the session is destroyed.)</t>
<section title="MultipointHead Sessions">
<t>When a MultipointHead session transitions to states Down or AdminDown, the state SHOULD be maintained for a period equal to (bfd.DesiredMinTxInterval * bfd.DetectMult) to ensure that the tails more quickly detect the session going down (by continuing to transmit BFD Control packets with the new state.) </t>
</section>
<section title="MultipointTail Sessions">
<t> MultipointTail sessions MAY be destroyed immediately upon leaving Up state, since tail will transmit no packets.</t>
<t>Otherwise, MultipointTail sessions SHOULD be maintained as long as BFD Control packets are being received by it (which by definition will indicate that the head is not Up.)</t>
</section>
</section>
<section title="Base Specification Text Replacement" anchor="RFC5880_REPLACE">
<t>The following sections are meant to replace the corresponding sections in the base specification.</t>
<section title="Reception of BFD Control Packets">
<t>The following procedure replaces section 6.8.6 of <xref target="RFC5880" />.</t>
<t>When a BFD Control packet is received, the following procedure MUST be followed, in the order specified. If the packet is discarded according to these rules, processing of the packet MUST cease at that point.
<list style="empty">
<t>If the version number is not correct (1), the packet MUST be discarded.</t>
<t> If the Length field is less than the minimum correct value (24 if
the A bit is clear, or 26 if the A bit is set), the packet MUST be
discarded.
</t>
<t>If the Length field is greater than the payload of the
encapsulating protocol, the packet MUST be discarded.
</t>
<t>If the Detect Mult field is zero, the packet MUST be discarded.</t>
<t>If the My Discriminator field is zero, the packet MUST be discarded.</t>
<t>Demultiplex the packet to a session according to <xref target="DEMUX"/>
below. The result is either a session of the proper type, or the
packet is discarded (and packet processing MUST cease.)
</t>
<t>If the A bit is set and no authentication is in use (bfd.AuthType
is zero), the packet MUST be discarded.
</t>
<t>If the A bit is clear and authentication is in use (bfd.AuthType
is nonzero), the packet MUST be discarded.
</t>
<t>If the A bit is set, the packet MUST be authenticated under the
rules of section 6.7, based on the authentication type in use
(bfd.AuthType.) This may cause the packet to be discarded.
</t>
<t>Set bfd.RemoteDiscr to the value of My Discriminator.</t>
<t>Set bfd.RemoteState to the value of the State (Sta) field.</t>
<t>Set bfd.RemoteDemandMode to the value of the Demand (D) bit.</t>
<t>Set bfd.RemoteMinRxInterval to the value of Required Min RX Interval.</t>
<t>If the Required Min Echo RX Interval field is zero, the
transmission of Echo packets, if any, MUST cease.</t>
<t>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 MUST be terminated.</t>
<t>If bfd.SessionType is PointToPoint, update the
transmit interval as described in <xref target="RFC5880" /> section 6.8.2.
</t>
<t>If bfd.SessionType is PointToPoint, update the Detection Time as
described in <xref target="RFC5880" /> section 6.8.4. Otherwise, update the Detection
Time as described in <xref target="DETECT"/> above.
</t>
<t>If bfd.SessionState is AdminDown
<list style="empty">
<t>Discard the packet</t>
</list>
</t>
<t>If received state is AdminDown
<list style="empty">
<t>If bfd.SessionState is not Down
<list style="empty">
<t>Set bfd.LocalDiag to 3 (Neighbor signaled session down)</t>
<t>Set bfd.SessionState to Down</t>
</list>
</t>
</list>
</t>
<t>Else
<list style="empty">
<t>If bfd.SessionState is Down
<list style="empty">
<t>If bfd.SessionType is PointToPoint
<list style="empty">
<t>If received State is Down
<list style="empty">
<t>Set bfd.SessionState to Init</t>
</list>
</t>
<t>Else if received State is Init
<list style="empty">
<t>Set bfd.SessionState to Up</t>
</list>
</t>
</list>
</t>
<t>Else (bfd.SessionType is not PointToPoint)
<list style="empty">
<t>If received State is Up
<list style="empty">
<t>Set bfd.SessionState to Up</t>
</list>
</t>
</list>
</t>
</list>
</t>
<t>Else if bfd.SessionState is Init
<list style="empty">
<t>If received State is Init or Up
<list style="empty">
<t>Set bfd.SessionState to Up</t>
</list>
</t>
</list>
</t>
<t>Else (bfd.SessionState is Up)
<list style="empty">
<t>If received State is Down
<list style="empty">
<t>Set bfd.LocalDiag to 3 (Neighbor signaled session down)</t>
<t>Set bfd.SessionState to Down</t>
</list>
</t>
</list>
</t>
</list>
</t>
<t>Check to see if Demand mode should become active or not (see <xref target="RFC5880" /> section 6.6).</t>
<t>If bfd.RemoteDemandMode is 1, bfd.SessionState is Up, and
bfd.RemoteSessionState is Up, Demand mode is active on the remote
system and the local system MUST cease the periodic transmission
of BFD Control packets (see <xref target="TRANSMIT"/>.)
</t>
<t>If bfd.RemoteDemandMode is 0, or bfd.SessionState is not Up, or
bfd.RemoteSessionState is not Up, Demand mode is not active on the
remote system and the local system MUST send periodic BFD Control
packets (see see <xref target="TRANSMIT"/>.)
</t>
<t>If the packet was not discarded, it has been received for purposes
of the Detection Time expiration rules in <xref target="RFC5880" /> section 6.8.4.
</t>
</list>
</t>
</section>
<section title="Demultiplexing BFD Control Packets" anchor="DEMUX">
<t>This section is part of the replacement for <xref target="RFC5880" /> section 6.8.6, separated for clarity.
<list style="empty">
<t>If the Multipoint (M) bit is set
<list style="empty">
<t>If the Your Discriminator field is nonzero, the packet MUST be discarded.</t>
<t>Select a session as based on source address, My Discriminator and the identity
of the multipoint tree which the Multipoint BFD Control packet was received.
If a session is found, and bfd.SessionType is not MultipointTail, the packet MUST be
discarded. If a session is not found, a new session of type
MultipointTail MAY be created, or the packet MAY be discarded.
This choice is outside the scope of this specification.
</t>
</list>
</t>
<t>Else (Multipoint bit is clear)
<list style="empty">
<t>If the Your Discriminator field is nonzero
<list style="empty">
<t>Select a session based on the value of Your Discriminator. If no session is found, the packet MUST be discarded.</t>
</list>
</t>
<t>Else (Your Discriminator is zero)
<list style="empty">
<t>If the State field is not Down or AdminDown, the packet MUST be discarded.</t>
<t>Otherwise, the session MUST be selected based on some
combination of other fields, possibly including source
addressing information, the My Discriminator field, and the
interface over which the packet was received. The exact
method of selection is application-specific and is thus
outside the scope of this specification.
</t>
<t>If a matching session is found, and bfd.SessionType is not
PointToPoint, the packet MUST be discarded.
</t>
<t>If a matching session is not found, a new session of type
PointToPoint may be created, or the packet may be discarded.
This choice is outside the scope of this specification.
</t>
</list>
</t>
<t>If the State field is Init and bfd.SessionType is not PointToPoint, the packet MUST be discarded.</t>
</list>
</t>
</list>
</t>
</section>
<section title="Transmitting BFD Control Packets" anchor="TRANSMIT">
<t>The following procedure replaces section 6.8.7 of <xref target="RFC5880" />.</t>
<t> BFD Control packets MUST be transmitted periodically at the rate determined according to <xref target="RFC5880" /> section 6.8.2, except as specified in this section.</t>
<t>A system MUST NOT transmit any BFD Control packets if bfd.RemoteDiscr is zero and the system is taking the Passive role. </t>
<t>A system MUST NOT transmit any BFD Control packets if bfd.SilentTail is 1.</t>
<t>A system MUST NOT periodically transmit BFD Control packets if Demand mode is active on the remote system (bfd.RemoteDemandMode is 1, bfd.SessionState is Up, and bfd.RemoteSessionState is Up) and a Poll Sequence is not being transmitted.</t>
<t>A system MUST NOT periodically transmit BFD Control packets if bfd.RemoteMinRxInterval is zero.</t>
<t>If bfd.SessionType is MultipointHead, the transmit interval MUST be set to bfd.DesiredMinTxInterval (this should happen automatically, as bfd.RemoteMinRxInterval will be zero.) </t>
<t>If bfd.SessionType is not MultipointHead, the transmit interval MUST be recalculated whenever bfd.DesiredMinTxInterval changes, or whenever bfd.RemoteMinRxInterval changes, and is equal to the greater of those two values. See [BFD] sections 6.8.2 and 6.8.3 for details on transmit timers. </t>
<t>A system MUST NOT set the Demand (D) bit if bfd.SessionType is MultipointTail.</t>
<t>A system MUST NOT set the Demand (D) bit if bfd.SessionType PointToPoint unless bfd.DemandMode is 1, bfd.SessionState is Up, and bfd.RemoteSessionState is Up.</t>
<t>If bfd.SessionType is PointToPoint or MultipointHead, a BFD Control packet SHOULD be transmitted during the interval between periodic Control packet transmissions when the contents of that packet would differ from that in the previously transmitted packet (other than the Poll and Final bits) in order to more rapidly communicate a change in state.</t>
<t>The contents of transmitted BFD Control packets MUST be set as follows:
<list style="empty">
<t>Version
<list style="empty">
<t>Set to the current version number (1).</t>
</list>
</t>
<t>Diagnostic (Diag)
<list style="empty">
<t>Set to bfd.LocalDiag.</t>
</list>
</t>
<t>State (Sta)
<list style="empty">
<t>Set to the value indicated by bfd.SessionState.</t>
</list>
</t>
<t>Poll (P)
<list style="empty">
<t>Set to 1 if the local system is sending a Poll Sequence or is a
session of type MultipointHead soliciting the identities of the
tails, or 0 if not.
</t>
</list>
</t>
<t>Final (F)
<list style="empty">
<t>Set to 1 if the local system is responding to a Control packet received with the Poll (P) bit set, or 0 if not.</t>
</list>
</t>
<t>Control Plane Independent (C)
<list style="empty">
<t>Set to 1 if the local system's BFD implementation is independent
of the control plane (it can continue to function through a
disruption of the control plane.)</t>
</list>
</t>
<t>Authentication Present (A)
<list style="empty">
<t>Set to 1 if authentication is in use on this session (bfd.AuthType is nonzero), or 0 if not.</t>
</list>
</t>
<t>Demand (D)
<list style="empty">
<t>Set to bfd.DemandMode if bfd.SessionState is Up and
bfd.RemoteSessionState is Up. Set to 1 if bfd.SessionType is
MultipointHead. Otherwise it is set to 0.
</t>
</list>
</t>
<t>Multipoint (M)
<list style="empty">
<t>Set to 1 if bfd.SessionType is MultipointHead. Otherwise it is set to 0.</t>
</list>
</t>
<t>Detect Mult
<list style="empty">
<t>Set to bfd.DetectMult.</t>
</list>
</t>
<t>Length
<list style="empty">
<t>Set to the appropriate length, based on the fixed header length
(24) plus any Authentication Section.
</t>
</list>
</t>
<t>My Discriminator
<list style="empty">
<t>Set to bfd.LocalDiscr.</t>
</list>
</t>
<t>Your Discriminator
<list style="empty">
<t>Set to bfd.RemoteDiscr.</t>
</list>
</t>
<t>Desired Min TX Interval
<list style="empty">
<t>Set to bfd.DesiredMinTxInterval.</t>
</list>
</t>
<t>Required Min RX Interval
<list style="empty">
<t>Set to bfd.RequiredMinRxInterval.</t>
</list>
</t>
<t>Required Min Echo RX Interval
<list style="empty">
<t>Set to 0 if bfd.SessionType is MultipointHead or MultipointTail.</t>
</list>
</t>
<t>Authentication Section
<list style="empty">
<t>Included and set according to the rules in section 6.7 if
authentication is in use (bfd.AuthType is nonzero.) Otherwise
this section is not present.
</t>
</list>
</t>
</list>
</t>
</section>
</section>
</section>
<section title="Assumptions">
<t>If authentication is in use, all tails must be configured to have a common authentication key in order to receive the multipoint BFD Control packets.</t>
</section>
<section title="IANA Considerations">
<t>This document has no actions for IANA.</t>
</section>
<section title="Security Considerations">
<t>Implementations that creates MultpointTail sessions dynamically upon receipt of Multipoint BFD Control packets MUST implement protective measures to prevent infinite number of MultipointTail session being created. Below lists some points to be considered in such implementations.
<list style="empty">
<t>If a Multipoint BFD Control packet did not arrive on a multicast tree (ex: on expected interface, with expected MPLS label, etc), then a MultipointTail session should not be created.</t>
<t>If redundant streams are expected for a given multicast stream, then the implementations should not create more MultipointTail sessions than the number of streams. Additionally, when the number of MultipointTail sessions exceeds the number of expected streams, then the implementation should generate an alarm to users to indicate the anomaly.</t>
<t>The implementation should have a reasonable upper bound on the number of MultipointTail sessions that can be created, with the upper bound potentially being computed based on the number of multicast streams that the system is expecting.</t>
</list>
</t>
</section>
<section title="Contributors">
<t>Rahul Aggarwal of Juniper Networks and George Swallow of Cisco Systems provided the initial idea for this specification and contributed to its development.</t>
</section>
<section title="Acknowledgements">
<t>Authors would also like to thank Nobo Akiya, Vengada Prasad Govindan, Jeff Haas, Wim Henderickx, Gregory Mirsky and Mingui Zhang who have greatly contributed to this document.</t>
</section>
</middle>
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<back>
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<references title="Normative References">
<?rfc include="reference.RFC.5880"?>
<?rfc include="reference.RFC.2119"?>
</references>
</back>
</rfc>
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