Internet DRAFT - draft-ietf-bess-multicast-damping
draft-ietf-bess-multicast-damping
Network Working Group T. Morin, Ed.
Internet-Draft S. Litkowski
Updates: 6514 (if approved) Orange
Intended status: Standards Track K. Patel
Expires: November 10, 2016 Cisco Systems
Z. Zhang
R. Kebler
J. Haas
Juniper Networks
May 09, 2016
Multicast VPN state damping
draft-ietf-bess-multicast-damping-06
Abstract
This document describes procedures to damp multicast VPN routing
state changes and control the effect of the churn due to the
multicast dynamicity in customer sites. The procedures described in
this document are applicable to BGP-based multicast VPN and help
avoid uncontrolled control plane load increase in the core routing
infrastructure. New procedures are proposed inspired from BGP
unicast route damping principles, but adapted to multicast.
Requirements Language
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 RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 10, 2016.
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Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Existing mechanisms . . . . . . . . . . . . . . . . . . . . . 5
4.1. Rate-limiting of multicast control traffic . . . . . . . 5
4.2. Existing PIM, IGMP and MLD timers . . . . . . . . . . . . 5
4.3. BGP Route Damping . . . . . . . . . . . . . . . . . . . . 6
5. Procedures for multicast state damping . . . . . . . . . . . 7
5.1. PIM procedures . . . . . . . . . . . . . . . . . . . . . 7
5.2. Procedures for multicast VPN state damping . . . . . . . 10
6. Procedures for P-tunnel state damping . . . . . . . . . . . . 11
6.1. Damping mVPN P-tunnel change events . . . . . . . . . . . 11
6.2. Procedures for Ethernet VPNs . . . . . . . . . . . . . . 12
7. Operational considerations . . . . . . . . . . . . . . . . . 12
7.1. Enabling multicast damping . . . . . . . . . . . . . . . 12
7.2. Troubleshooting and monitoring . . . . . . . . . . . . . 12
7.3. Default and maximum values . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
11.1. Normative References . . . . . . . . . . . . . . . . . . 15
11.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
In a multicast VPN [RFC6513] deployed with BGP-based procedures
[RFC6514], when receivers in VPN sites join and leave a given
multicast group or channel through multicast membership control
protocols (IGMP [RFC3376], MLD[RFC3810]), multicast routing protocols
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accordingly adjust multicast routing states and P-multicast tree
states, to forward or prune multicast traffic to these receivers.
Similar challenges arise in the context of multicast specification
for VPLS [RFC7117].
In VPN contexts, providing isolation between customers of a shared
infrastructure is a core requirement resulting in stringent
expectations with regards to risks of denial of service attacks.
By nature multicast memberships change based on the behavior of
multicast applications running on end hosts, hence the frequency of
membership changes can legitimately be much higher than the typical
churn of unicast routing states.
Hence, mechanisms need to be put in place to ensure that the load put
on the BGP control plane, and on the P-tunnel setup control plane,
remains under control regardless of the frequency at which multicast
memberships changes are made by end hosts.
This document describes procedures, inspired from existing BGP route
damping [RFC2439], aimed at offering means to set an upper bound to
the amount of processing for the mVPN control plane protocols, more
precisely the BGP control plane in [RFC6514], and the P-tunnel
control plane protocol in the contexts of [RFC6514] and multicast
specification for VPLS [RFC7117]. This aims to be achieved while at
the same time preserving the service provided (delivering the
multicast stream as requested by Customer Edge devices), although at
the expense of a minimal increase of average bandwidth use in the
provider network. The upper bound to the control plane load due to
the processing of a given multicast state, is controlled indirectly
via configurable parameters.
Section 16 of [RFC6514] specifically spells out the need for damping
the activity of C-multicast and Leaf Auto-discovery routes, and
outlines how to do it by "delaying the advertisement of withdrawals
of C-multicast routes". This specification provides appropriate
detail on how to implement this approach and how to provide control
to the operator, and for this reason, is an update to [RFC6514].
The base principle of this specification is described in Section 3.
Existing mechanisms that could be relied upon are discussed in
Section 4. Section 5 details the procedures introduced by this
specification.
Section 6 provides specific details related to the damping of
multicast VPNs P-tunnel state.
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Finally, Section 7 discusses operational considerations related to
the proposed mechanism.
2. Terminology
This document reuses terminology from [RFC7761] and [RFC6514].
In this specification, damping of a multicast state will be said to
be "active" or "inactive". Note that in [RFC2439], the term used for
a unicast route which is dampened is "suppressed", but we will avoid
this term in this specification given that the proposed solution
consist in holding active a damped multicast state.
3. Overview
The procedures described in this document allow the network operator
to configure multicast VPN PEs (Provider Edge routers) so that they
can delay the propagation of multicast state prune messages between
PEs, when faced with a rate of multicast state dynamicity exceeding a
certain configurable threshold. Assuming that the number of
multicast states that can be created by a receiver is bounded,
delaying the propagation of multicast state pruning results in
setting up an upper bound to the average frequency at which the
router will send state updates to an upstream router.
From the point of view of a downstream router, such as a CE (Customer
Edge router), this approach has no impact: the multicast routing
states changes that it solicits to its PE will be honored without any
additional delay. Indeed the propagation of joins is not impacted by
the procedures specified here, and having the upstream router delay
state prune propagation to its own upstream router does not affect
what traffic is sent to the downstream router. In particular, the
amount of bandwidth used on the PE-CE link downstream to a PE
applying this damping technique is not increased.
This approach increases the average bandwidth utilization on a link
upstream to a PE applying this technique, such as a PE-PE link:
indeed, a given multicast flow will be forwarded for a longer time
than if no damping was applied. That said, it is expected that this
technique will meet the goals of protecting the multicast routing
infrastructure control plane without a significant average increase
of bandwidth; for instance, damping events happening at a frequency
higher than one event per X second, can be done without increasing by
more than X second the time during which a multicast flow is present
on a link.
That said, simulation of the exponential decay algorithm show that
the multicast state churn can be drastically reduced without
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significantly increasing the duration for which multicast traffic is
forwarded. Hence, using this technique will efficiently protect the
multicast routing infrastructure control plane against the issues
described here, without a significant average increase of bandwidth.
The exception will be a scenario with strict constraints on multicast
bandwidth, where extending the time a multicast flow is forwarded
would result in congestion.
To be practical, such a mechanism requires configurability. In
particular, means are required to control when damping is triggered,
and to allow delaying the pruning of a multicast state for a time
increasing with the churn of this multicast state. This will let the
operator control the tradeoff made between minimizing the dynamicity
and reducing bandwidth consumption.
4. Existing mechanisms
This section describes mechanisms that could be considered to address
the issue, but that end up appearing as not suitable or not efficient
enough.
4.1. Rate-limiting of multicast control traffic
PIM-SM specification [RFC7761] examine multicast security threats and
among other things the risk of denial of service attacks described in
Section 1. A mechanism relying on rate-limiting PIM messages is
proposed in section 5.3.3 of [RFC4609], but has the identified
drawbacks of impacting the service delivered and having side-effects
on legitimate users.
4.2. Existing PIM, IGMP and MLD timers
In the context of PIM multicast routing protocols [RFC7761], a
mechanism exists that may offer a form of de-facto damping of
multicast states, under some conditions. Indeed, when active, the
prune override mechanism consists in having a PIM upstream router
introduce a delay ("prune override interval") before taking into
account a PIM Prune message sent by a downstream neighbor.
This mechanism has not been designed specifically for the purpose of
damping multicast state, but as a means to allow PIM to operate on
multi-access networks. See [RFC7761] section 4.3.3. However, when
active, this mechanism will prevent a downstream router to produce
multicast routing protocol messages that would cause, for a given
multicast state, the upstream router to send to its own upstream
router, multicast routing protocol messages at a rate higher than
1/[JP_Override_Interval]. This provides de-facto a form of damping.
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Similarly, the IGMP and MLD multicast membership control protocols
can provide a similar behavior, under the right conditions.
These mechanisms are not considered suitable to meet the goals
spelled out in Section 1, the main reasons being that:
o when enabled, these mechanisms require additional bandwidth on the
local link on which the effect of a prune is delayed (in our case
the PE-CE link)
o when enabled, these mechanisms require disabling explicit tracking
(see Section 4.3.3 of [RFC7761]), even though enabling this
feature may otherwise be desired
o on certain implementations, these mechanisms are incompatible with
behaviors that cannot be turned off (e.g. implementation applying
a fast-leave behavior on interfaces with only two neighbors)
o they do not provide a suitable level of configurability
o they do not provide a way to discriminate between multicast flows
based on estimation of their dynamicity
4.3. BGP Route Damping
The procedures defined in [RFC2439] and [RFC7196] for BGP route flap
damping are useful for operators who want to control the impact of
unicast route churn on the routing infrastructure, and offer a
standardized set of parameters to control damping.
These procedures are not directly relevant in a multicast context,
for the following reasons:
o they are not specified for multicast routing protocol in general
o even in contexts where BGP routes are used to carry multicast
routing states (e.g. [RFC6514]), these procedures do not allow to
implement the principle described in this document, the main
reason being that a damped route becomes suppressed, while the
target behavior would be to keep advertising when damping is
triggered on a multicast route
However, the set of parameters standardized to control the thresholds
of the exponential decay mechanism can be relevantly reused. This is
the approach proposed for the procedures described in this document
(Section 5). Motivations for doing so is to help the network
operator deploy this feature based on consistent configuration
parameter, and obtain predictable results, without the drawbacks of
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relying on rate-limiting of multicast control protocol exchanges (as
exposed in Section 4.1) or on the use of existing PIM/IGMP timers (as
exposed in Section 4.2).
5. Procedures for multicast state damping
5.1. PIM procedures
This section describes procedures for multicast state damping
satisfying the goals spelled out in Section 1. This section spells
out procedures for (S,G) states in the PIM-SM protocol [RFC7761];
they apply unchanged for such states created based on multicast group
management protocols (IGMP [RFC3376], MLD [RFC3810]) on downstream
interfaces. The same procedures are applied to (*,G) states in the
context of PIM-SM ASM groups (damping is not applied to (S,G,Rpt)
Prune state).
The following notions of [RFC2439] are reused in these procedures:
figure-of-merit: a number reflecting the current estimation of
recent past activity of an (S,G) multicast routing state, which
increases based on routing events related to this state, and
between these events decreases following an exponential decay
function (see below); the activation or inactivation of damping on
the state is based on this number; this number is associated to
the upstream state machine for (S,G) and is initialized to a value
of zero on state creation
exponential decay function: a mathematical function as defined
inSection 2.3 of [RFC2439] (ignoring the first paragraph of that
section that does not apply here)
decay-half-life: duration used to control how fast is the
exponential decay of the *figure-of-merit* ; this parameter of the
exponential decay function is the time duration during which the
*figure-of-merit* will be reduced by half, in the absence of a
routing event (configurable parameter)
cutoff-threshold: value of the *figure-of-merit* over which damping
is applied (configurable parameter)
reuse-threshold: value of the *figure-of-merit* under which damping
stops being applied (configurable parameter)
Additionally to these values, a configurable *increment-factor*
parameter is introduced, that controls by how much the *figure-of-
merit* is incremented on multicast state update events.
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Section 7.3 proposes default and maximum values for the configurable
parameters.
On reception of updated multicast membership or routing information
on a downstream interface I for a given (S,G) state, that results in
a change of the state of the PIM downstream state machine (see
section 4.5.3 of [RFC7761]), a router implementing these procedures
MUST:
o apply procedures of [RFC7761] unchanged, for everything relating
to what multicast traffic ends up being sent on downstream
interfaces, including interface I
o update the *figure-of-merit* following the exponential decay
algorithm
o increase the *figure-of-merit* for the (S,G) by the *increment-
factor*
o update the damping state for the (S,G) state: damping becomes
active on the state if the recomputed *figure-of-merit* is
strictly above the configured *cutoff-threshold*
* if damping remains inactive on (S,G) state, update the upstream
state machine as usual (as per section 4.5.7 of [RFC7761])
* if damping becomes active for the (S,G) state:
+ if the received message has caused the upstream state
machine to transition to Joined state, update the upstream
state machine for (S,G) (applying usual PIM procedures in
section 4.5.7 of [RFC7761], including sending a PIM Join to
the upstream neighbor)
+ if the received message has caused the upstream state
machine to transition to NotJoined state, do not update the
upstream state machine for (S,G)
+ hold the upstream state machine in Joined state until the
reuse threshold is reached : for the purpose of updating
this state machine, events that may result in updating the
state based on [RFC7761] SHOULD be ignored until the *reuse-
threshold* is reached. The effect is that in the meantime,
while PIM Join messages may be sent as refreshes to the
upstream neighbor, no PIM Prune message will be sent.
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* if damping was already active: do not update the upstream state
machine for (S,G) (the upstream state machine was frozen after
processing the previous message)
Once the *figure-of-merit* for (S,G) damping state decays to a value
strictly below the configured *reuse-threshold*, the upstream state
machine for (S,G) is recomputed based on states of downstream state
machines, eventually leading to a PIM Join or Prune message to be
sent to the upstream neighbor.
Given the specificity of multicast applications, it is REQUIRED for
the implementation to let the operator configure the *decay-half-
life* in seconds, rather than in minutes.
This specification does not impose the use of a particular technique
to update the *figure-of-merit* following the exponential decay
controlled by the configured *decay-half-life*. For instance, the
same techniques as the ones described in [RFC2439] can be applied.
The only requirement is that the *figure-of-merit* has to be updated
prior to increasing it, and that its decay below the *reuse-
threshold* has to be timely reacted upon: in particular, if the
recomputation is done with a fixed time granularity, this granularity
should be low enough to not significantly delay the inactivation of
damping on a multicast state beyond what the operator wanted to
configure (e.g. for a *decay-half-life* of 10s, recomputing the
*figure-of-merit* each minute would result in a multicast state to
remained damped for a much longer time than specified).
PIM implementations typically follow [RFC7761] suggestion that
"implementations will only maintain state when it is relevant to
forwarding operations - for example, the 'NoInfo' state might be
assumed from the lack of other state information, rather than being
held explicitly" (Section 4.1 of [RFC7761]). To properly implement
damping procedures, an implementation MUST keep an explicit (S,G)
state as long as damping is active on an (S,G). Once an (S,G) state
expires, and damping becomes inactive on this state, its associated
*figure-of-merit* and damping state are removed as well.
Note that these procedures:
o do not impact PIM procedures related to refreshes or expiration of
multicast routing states: PIM Prune messages triggered by the
expiration of the (S,G) keep-alive timer, are not suppressed or
delayed, and the reception of Join messages not causing transition
of state on the downstream interface does not lead to incrementing
the *figure-of-merit*;
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o do not impact the PIM assert mechanism, in particular PIM Prune
messages triggered by a change of the PIM assert winner on the
upstream interface, are not suppressed or delayed;
o do not impact PIM Prune messages that are sent when the RPF
neighbor is updated for a given multicast flow;
o do not impact PIM Prune messages that are sent in the context of
switching between a Rendez-vous Point Tree and a Shortest Path
Tree.
Note also that no action is triggered based on the reception of PIM
Prune messages (or corresponding IGMP/MLD messages) that relate to
non-existing (S,G) state, in particular, no *figure-of-merit* or
damping state is created in this case.
5.2. Procedures for multicast VPN state damping
The procedures described in Section 5.1 can be applied in the VRF
PIM-SM implementation (in the "C-PIM instance"), with the
corresponding action to suppressing the emission of a Prune(S,G)
message being to not withdraw the C-multicast Source Tree Join
(C-S,C-G) BGP route. An implementation of [RFC6513] relying on the
use of PIM to carry C-multicast routing information MUST support this
technique, to be compliant with this specification.
In the context of [RFC6514] where BGP is used to distribute
C-multicast routing information, the following procedure is proposed
as an alternative to the procedures in Section 5.1 and consists in
applying damping in the BGP implementation, based on existing BGP
damping mechanism, applied to C-multicast Source Tree Join routes and
Shared Tree Join routes (and as well to Leaf A-D routes - see
Section 6), and modified to implement the behavior described in
Section 3 along the following guidelines:
o not withdrawing (instead of not advertising) damped routes
o providing means to configure the *decay-half-life* in seconds if
that option is not already available
o using parameters for the exponential decay that are specific to
multicast, based on default values and multicast specific
configuration
While these procedures would typically be implemented on PE routers,
in a context where BGP Route Reflectors (RRs, [RFC4456]) are used it
can be considered useful to also be able to apply damping on RRs as
well to provide additional protection against activity created behind
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multiple PEs. Additionally, for mVPN Inter-AS deployments, it can be
needed to protect one AS from the dynamicity of multicast VPN routing
events from other ASes.
The choice to implement damping based on BGP routes or the procedures
described in Section 5.1, is up to the implementor, but at least one
of the two MUST be implemented. In the perspective of allowing
damping to be done on RRs and ASBRs, implementing the BGP approach is
recommended.
When not all routers in a deployment have the capability to drop
traffic coming from the wrong PE (as spelled out in section 9.1.1 of
[RFC6513]), then the withdrawal of a C-multicast route resulting from
a change in the Upstream Multicast Hop or Upstream Multicast PE
SHOULD NOT be damped. An implementation of this specification MUST
whether, not damp these withdrawals by default, or alternatively
provide a tuning knob to disable the damping of these withdrawals.
Additionally, in such a deployment context, it is RECOMMENDED to not
enable any multicast VPN route damping on RRs and ASBRs, since these
equipments cannot distinguish the event having caused a C-multicast
to be withdrawn.
Note well that it is out of scope of this section to consider the
application of these damping techniques on mVPN BGP routes other than
C-multicast routes.
6. Procedures for P-tunnel state damping
6.1. Damping mVPN P-tunnel change events
When selective P-tunnels are used (see section 7 of [RFC6513]), the
effect of updating the upstream state machine for a given (C-S,C-G)
state on a PE connected to multicast receivers, is not only to
generate activity to propagate C-multicast routing information to the
source connected PE, but also to possibly trigger changes related to
the P-tunnels carrying (C-S,C-G) traffic. Protecting the provider
network from an excessive amount of change in the state of P-tunnels
is required, and this section details how this can be done.
A PE implementing these procedures for mVPN MUST damp Leaf A-D
routes, in the same manner as it would for C-multicast routes (see
Section 5.2).
A PE implementing these procedures for mVPN MUST damp the activity
related to removing itself from a P-tunnel. Possible ways to do so
depend on the type of P-tunnel, and local implementation details are
left up to the implementor.
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The following is proposed as example of how the above can be
achieved:
o For P-tunnels implemented with the PIM protocol, this consists in
applying multicast state damping techniques described in
Section 5.1 to the P-PIM instance, at least for (S,G) states
corresponding to P-tunnels.
o For P-tunnels implemented with the mLDP protocol, this consists in
applying damping techniques completely similar to the one
described in Section 5, but generalized to apply to mLDP states
o For root-initiated P-tunnels (P-tunnels implemented with the P2MP
RSVP-TE, or relying on ingress replication), no particular action
needs to be implemented to damp P-tunnels membership, if the
activity of Leaf A-D route themselves is damped
o Another possibility is to base the decision to join or not join
the P-tunnel to which a given (C-S,C-G) is bound, and to advertise
or not advertise a Leaf A-D route related to (C-S,C-G), based on
whether or not a C-multicast Source Tree Join route is being
advertised for (C-S,C-G), rather than by relying on the state of
the C-PIM Upstream state machine for (C-S,C-G)
6.2. Procedures for Ethernet VPNs
Specifications exist to support or optimize multicast and broadcast
in the context of Ethernet VPNs [RFC7117], relying on the use of
S-PMSI and P-tunnels. For the same reasons as for IP multicast VPNs,
an implementation of [RFC7117] MUST follow the procedures described
in Section 6.1, to be compliant with this specification.
7. Operational considerations
7.1. Enabling multicast damping
In the context of multicast VPNs, these procedures would be enabled
on PE routers. Additionally in the case of C-multicast routing based
on BGP extensions ([RFC6514]) these procedures can be enabled on
ASBRs and Route Reflectors.
7.2. Troubleshooting and monitoring
Implementing the damping mechanisms described in this document should
be complemented by appropriate tools to observe and troubleshoot
damping activity.
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Complementing the existing interface providing information on
multicast states with information on eventual damping of
corresponding states (e.g. MRIB states) is RECOMMENDED: C-multicast
routing states and P-tunnel states.
7.3. Default and maximum values
Considering that, by design multicast streams will be delivered
unchanged to the end user, independently of the value chosen for the
configurable parameters, and that the only trade-off being made is an
increase of bandwidth use, the default and maximum values do not have
to be perfectly tuned.
This section proposes default and maximum values, conservative so as
to not significantly impact network dimensioning but still prevent
multicast state churn going beyond what can be considered a
reasonably low churn for a multicast state (see below for
illustrations in order of magnitude of the effect of these values).
The following values are RECOMMENDED to adopt as default values:
o *increment-factor*: 1000
o *cutoff-threshold*: 3000
o *decay-half-life*: 10s
o *reuse-threshold*: 1500
For unicast damping, it is common to set an upper bound to the time
during which a route is suppressed. In the case of multicast state
damping, which relies on not withdrawing a damped route, it may be
desirable to avoid a situation where a multicast flow would keep
flowing in a portion of the network for a very large time in the
absence of receivers.
The proposed default maximum value for the *figure-of-merit* is
20x*increment-factor*, i.e. 20000 with the proposed default
*increment-factor* of 1000.
As illustrations, with these values:
o a multicast state updated less frequently than once every 6s will
not be damped at all
o a multicast state changing once per second for 3s, and then not
changing, will not be damped
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o a multicast state changing once per second for 4s, and then not
changing, will be damped after the fourth change for approximately
13s
o a multicast state changing twice per second for 15s, and then not
changing, will be damped after the fourth change for approximately
50s
o a multicast state changing at a fast pace for a long time will
reach the maximum of *figure-of-merit*; once the activity on this
state stops, corresponding traffic may still flow in the network
for approximately 37s before dampening stops being active
The following values are proposed as maxima:
o *decay-half-life*: 60s
o *cutoff-threshold*: 50000
More aggressive protection against the risk of denial of service can
be achieved by increasing the *increment-factor* or the *decay-half-
life*, or reducing the *cutoff-threshold* and/or *reuse-threshold*.
8. IANA Considerations
This document makes no request to IANA.
Note to the RFC Editor: this section may be removed on publication as
an RFC.
9. Security Considerations
The procedures defined in this document do not introduce additional
security issues not already present in the contexts addressed, and
actually aim at addressing some of the identified risks without
introducing as much denial of service risk as some of the mechanisms
already defined.
The protection provided relates to the control plane of the multicast
routing protocols, including the components implementing the routing
protocols and the components responsible for updating the multicast
forwarding plane.
The procedures describe are meant to provide some level of protection
for the router on which they are enabled by reducing the amount of
routing state updates that it needs to send to its upstream neighbor
or peers, but do not provide any reduction of the control plane load
related to processing routing information from downstream neighbors.
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Protecting routers from an increase in control plane load due to
activity on downstream interfaces toward core routers (or in the
context of BGP-based mVPN C-multicast routing, BGP peers) relies on
the activation of damping on corresponding downstream neighbors (or
BGP peers) and/or at the edge of the network. Protecting routers
from an increase in control plane load due to activity on customer-
facing downstream interfaces or downstream interfaces to routers in
another administrative domain, is out of the scope of this document
and should use already defined mechanisms (see [RFC4609]).
To be effective the procedures described here must be complemented by
configuration limiting the number of multicast states that can be
created on a multicast router through protocol interactions with
multicast receivers, neighbor routers in adjacent ASes, or in
multicast VPN contexts with multicast CEs. Note well that the two
mechanism may interact: state for which Prune has been requested may
still remain taken into account for some time if damping has been
triggered and hence result in otherwise acceptable new state from
being successfully created.
Additionally, it is worth noting that these procedures are not meant
to protect against peaks of control plane load, but only address
averaged load. For instance, assuming a set of multicast states
submitted to the same Join/Prune events, damping can prevent more
than a certain number of Join/Prune messages to be sent upstream in
the period of time that elapses between the reception of Join/Prune
messages triggering the activation of damping on these states and
when damping becomes inactive after decay.
10. Acknowledgements
We would like to thank Bruno Decraene and Lenny Giuliano for
discussions that helped shape this proposal. We would also like to
thank Yakov Rekhter and Eric Rosen for their reviews and helpful
comments. Thanks to Wim Henderickx for his comments and support of
this proposal. Additionally, Martin Vigoureux, Gunter Van De Velde
and Alvaro Retana provided useful comments to finalize the document.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2439] Villamizar, C., Chandra, R., and R. Govindan, "BGP Route
Flap Damping", RFC 2439, November 1998.
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[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC6513] Rosen, E. and R. Aggarwal, "Multicast in MPLS/BGP IP
VPNs", RFC 6513, February 2012.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, February 2012.
[RFC7117] Aggarwal, R., Kamite, Y., Fang, L., Rekhter, Y., and C.
Kodeboniya, "Multicast in Virtual Private LAN Service
(VPLS)", RFC 7117, February 2014.
[RFC7196] Pelsser, C., Bush, R., Patel, K., Mohapatra, P., and O.
Maennel, "Making Route Flap Damping Usable", RFC 7196, May
2014.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <http://www.rfc-editor.org/info/rfc7761>.
11.2. Informative References
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<http://www.rfc-editor.org/info/rfc4456>.
[RFC4609] Savola, P., Lehtonen, R., and D. Meyer, "Protocol
Independent Multicast - Sparse Mode (PIM-SM) Multicast
Routing Security Issues and Enhancements", RFC 4609,
October 2006.
Authors' Addresses
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Thomas Morin (editor)
Orange
2, avenue Pierre Marzin
Lannion 22307
France
Email: thomas.morin@orange.com
Stephane Litkowski
Orange
France
Email: stephane.litkowski@orange.com
Keyur Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: keyupate@cisco.com
Zhaohui Zhang
Juniper Networks Inc.
10 Technology Park Drive
Westford, MA 01886
USA
Email: zzhang@juniper.net
Robert Kebler
Juniper Networks Inc.
10 Technology Park Drive
Westford, MA 01886
USA
Email: rkebler@juniper.net
Jeff Haas
Juniper Networks
Email: jhaas@juniper.net
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