Network Working Group T. Morin, Ed.
Internet-Draft France Telecom Orange
Expires: August 6, 2010 B. Niven-Jenkins, Ed.
BT
Y. Kamite
NTT Communications
R. Zhang
BT
N. Leymann
Deutsche Telekom
N. Bitar
Verizon
February 2, 2010
Mandatory Features in a Layer 3 Multicast BGP/MPLS VPN Solution
draft-ietf-l3vpn-mvpn-considerations-06
Abstract
More that one set of mechanisms to support multicast in a layer 3
BGP/MPLS VPN has been defined. These are presented in the documents
that define them as optional building blocks.
To enable interoperability between implementations, this document
defines a subset of features that is considered mandatory for a
multicast BGP/MPLS VPN implementation. This will help implementers
and deployers understand which L3VPN multicast requirements are best
satisfied by each option.
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 [RFC2119].
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 6, 2010.
Copyright Notice
Copyright (c) 2010 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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the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Examining alternatives mechanisms for MVPN functions . . . . . 4
3.1. MVPN auto-discovery . . . . . . . . . . . . . . . . . . . 4
3.2. S-PMSI Signaling . . . . . . . . . . . . . . . . . . . . . 5
3.3. PE-PE Exchange of C-Multicast Routing . . . . . . . . . . 7
3.3.1. PE-PE C-multicast routing scalability . . . . . . . . 7
3.3.2. PE-CE multicast routing exchange scalability . . . . . 10
3.3.3. P-routers scalability . . . . . . . . . . . . . . . . 10
3.3.4. Impact of C-multicast routing on Inter-AS
deployments . . . . . . . . . . . . . . . . . . . . . 10
3.3.5. Security and robustness . . . . . . . . . . . . . . . 11
3.3.6. C-multicast VPN join latency . . . . . . . . . . . . . 12
3.3.7. Conclusion on C-multicast routing . . . . . . . . . . 14
3.4. Encapsulation techniques for P-multicast trees . . . . . . 14
3.5. Inter-AS deployments options . . . . . . . . . . . . . . . 16
3.6. Bidir-PIM support . . . . . . . . . . . . . . . . . . . . 19
4. Co-located RPs . . . . . . . . . . . . . . . . . . . . . . . . 20
5. Avoiding duplicates . . . . . . . . . . . . . . . . . . . . . 21
6. Existing deployments . . . . . . . . . . . . . . . . . . . . . 21
7. Summary of recommendations . . . . . . . . . . . . . . . . . . 22
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
9. Security Considerations . . . . . . . . . . . . . . . . . . . 23
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
11.1. Normative References . . . . . . . . . . . . . . . . . . . 23
11.2. Informative References . . . . . . . . . . . . . . . . . . 23
Appendix A. Scalability of C-multicast routing processing load . 24
A.1. Scalability with an increased number of PEs . . . . . . . 26
A.1.1. SSM Scalability . . . . . . . . . . . . . . . . . . . 26
A.1.2. ASM Scalability . . . . . . . . . . . . . . . . . . . 34
A.2. Cost of PEs leaving and joining . . . . . . . . . . . . . 35
Appendix B. Switching to S-PMSI . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39
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1. Introduction
Specifications for multicast in BGP/MPLS
[I-D.ietf-l3vpn-2547bis-mcast] include multiple alternative
mechanisms for some of the required building blocks of the solution.
However, they do not identify which of these mechanisms are mandatory
to implement in order to ensure interoperability. Not defining a set
of mandatory to implement mechanisms leads to a situation where
implementations may support different subsets of the available
optional mechanisms which do not interoperate, which is a problem for
the numerous operators having multi-vendor backbones.
The aim of this document is to leverage the already expressed
requirements [RFC4834] and study the properties of each approach, to
identify mechanisms that are good candidates for being part of a core
set of mandatory mechanisms which can be used to provide a base for
interoperable solutions.
This document goes through the different building blocks of the
solution and concludes on which mechanisms an implementation is
required to implement. Section 7 summarizes these requirements.
Considering the history of the multicast VPN proposals and
implementations, it is also useful to discuss how existing
deployments of early implementations
[I-D.rosen-vpn-mcast][I-D.raggarwa-l3vpn-2547-mvpn] can be
accommodated, and provide suggestions in this respect.
2. Terminology
Please refer to [I-D.ietf-l3vpn-2547bis-mcast] and [RFC4834].
3. Examining alternatives mechanisms for MVPN functions
3.1. MVPN auto-discovery
The current solution document [I-D.ietf-l3vpn-2547bis-mcast] proposes
two different mechanisms for MVPN auto-discovery:
1. BGP-based auto-discovery
2. "PIM/shared P-tunnel": discovery done through the exchange of PIM
Hellos by C-PIM instances, across an MI-PMSI implemented with one
shared P-tunnel per VPN (using multicast ASM, or MP2MP LDP)
Both solutions address Section 5.2.10 of [RFC4834] which states that
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"the operation of a multicast VPN solution SHALL be as light as
possible and providing automatic configuration and discovery SHOULD
be a priority when designing a multicast VPN solution. Particularly
the operational burden of setting up multicast on a PE or for a VR/
VRF SHOULD be as low as possible".
The key consideration is that PIM-based discovery is only applicable
to deployments using a shared P-tunnel to instantiate an MI-PMSI (it
is not applicable if only P2P, PIM-SSM, P2MP mLDP/RSVP-TE P-tunnels
are used, because contrary to ASM and MP2MP, building these types of
P-tunnels cannot happen before the autodiscovery has been done),
whereas the BGP-based auto-discovery does not place any constraint on
the type of P-tunnel that would have to be used. BGP-based auto-
discovery is independent of the type of P-tunnel used thus satisfying
the requirement in section 5.2.4.1 of [RFC4834] that "a multicast VPN
solution SHOULD be designed so that control and forwarding planes are
not interdependent".
Additionally, it is to be noted that a number of service providers
have chosen to use SSM-based P-tunnels for the default MDTs within
their current deployments, therefore relying already on some BGP-
based auto-discovery.
Moreover, when shared P-tunnels are used, the use of BGP auto-
discovery would allow inconsistencies in the addresses/identifiers
used for the shared P-tunnel to be detected (e.g. the same shared
P-tunnel identifier being used for different VPNs with distinct BGP
route targets). This is particularly attractive in the context of
inter-AS VPNs where the impact of any misconfiguration could be
magnified and where a single service provider may not operate all the
ASs. Note that this technique to detect some misconfiguration cases
may not be usable during a transition period from a shared-P-tunnel
autodiscovery to a BGP-based autodiscovery.
Thus, the recommendation is that implementation of the BGP-based
auto-discovery is mandated and should be supported by all MVPN
implementations.
3.2. S-PMSI Signaling
The current solution document [I-D.ietf-l3vpn-2547bis-mcast] proposes
two mechanisms for signaling that multicast flows will be switched to
an S-PMSI:
1. a UDP-based TLV protocol specifically for S-PMSI signaling
(described in section 7.4.2).
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2. a BGP-based mechanism for S-PMSI signaling (described in section
7.4.1).
Section 5.2.10 of [RFC4834] states that "as far as possible, the
design of a solution SHOULD carefully consider the number of
protocols within the core network: if any additional protocols are
introduced compared with the unicast VPN service, the balance between
their advantage and operational burden SHOULD be examined
thoroughly". The UDP-based mechanism would be an additional protocol
in the MVPN stack, which isn't the case for the BGP-based S-PMSI
switching signaling, since (a) BGP is identified as a requirement for
autodiscovery, and (b) the BGP-based S-PMSI switching signaling
procedures are very similar to the autodiscovery procedures.
Furthermore, the UDP-based S-PMSI switching signaling mechanism
requires an MI-PMSI, while the BGP-based protocol does not. In
practice, this mean that with the UDP-based protocol a PE will have
to join to all P-tunnels of all PEs in an MVPN, while in the
alternative where BGP-based S-PMSI switching signaling is used, it
could delay joining a P-tunnel rooted at a PE until traffic from that
PE is needed, thus reducing the amount of state maintained on P
routers.
S-PMSI switching signaling approaches can also be compared in an
inter-AS context (see Section 3.5). The proposed BGP-based approach
for S-PMSI switching signaling provides a good fit with both the
segmented and non-segmented inter-AS approaches (seeSection 3.5). By
contrast while the UDP-based approach for S-PMSI switching signaling
appears to be usable with segmented inter-AS tunnels, in that case
key advantages of the segmented approach are lost:
o there is no more an independence of ASes to choose when S-PMSIs
tunnels will be triggered in their AS (and thus control the amount
of state created on their P routers),
o there is no more an independence of ASes to choose the tunneling
technique for the P-tunnels used for an S-PMSI,
o In an inter-AS option B context, an isolation of ASes is obtained
as PEs in one AS don't have (direct) exchange of routing
information with PEs of other ASes. This property is not
preserved if UDP-based S-PMSI switching signaling is used. By
contrast, BGP-based C-Multicast switching signaling does preserve
this property.
Given all the above, it is the recommendation of the authors that BGP
is the preferred solution for S-PMSI switching signaling and should
be supported by all implementations.
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It is identified that, if nothing prevents a fast-paced creation of
S-PMSI, then S-PMSI switching signaling with BGP would possibly
impact the Route Reflectors used for MVPN routes. However is it also
identified that such a fast-paced behavior would have an impact on P
and PE routers resulting from S-PMSI tunnels signaling, which will be
the same independently of the S-PMSI signaling approach that is used,
and which it is certainly best to avoid by setting up proper
mechanisms.
The UDP-based S-PMSI switching signaling protocol can also be
considered, as an option, given that this protocol has been in
deployment for some time. Implementations supporting both protocols
would be expected to provide a per-VRF configuration knob to allow an
implementation to use the UDP-based TLV protocol for S-PMSI switching
signaling for specific VRFs in order to support the coexistence of
both protocols (for example during migration scenarios). Apart from
such migration-facilitating mechanisms, the authors specifically do
not recommend extending the already proposed UDP-based TLV protocol
to new types of P-tunnels.
3.3. PE-PE Exchange of C-Multicast Routing
The current solution document [I-D.ietf-l3vpn-2547bis-mcast] proposes
multiple mechanisms for PE-PE exchange of customer multicast routing
information (C-multicast routing):
1. Full per-MVPN PIM peering across an MI-PMSI (described in section
3.4.1.1).
2. Lightweight PIM peering across an MI-PMSI (described in section
3.4.1.2)
3. The unicasting of PIM C-Join/Prune messages (described in section
3.4.1.3)
4. The use of BGP for carrying C-Multicast routing (described in
section 3.4.2).
3.3.1. PE-PE C-multicast routing scalability
Scalability being one of the core requirements for multicast VPN, it
is useful to compare the proposed C-multicast routing mechanisms from
this perspective: Section 4.2.4 of [RFC4834] recommends that "a
multicast VPN solution SHOULD support several hundreds of PEs per
multicast VPN, and MAY usefully scale up to thousands" and section
4.2.5 states that "a solution SHOULD scale up to thousands of PEs
having multicast service enabled".
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Scalability with an increased number of VPNs per PE, or with an
increased number of multicast state per VPN, are also important, but
are not focused on in this section since we didn't identify
differences between the different approaches for these matters: all
others things equal, the load on PE due to C-multicast routing
increases roughly linearly with the number of VPNs per PE, and with
the number of multicast state per VPN.
This section presents conclusions related to PE-PE C-multicast
routing scalability. Appendix A provides more detailed explanations
on the differences in ways of handling the C-multicast routing load,
between the PIM-based approaches and the BGP-based approach, along
with a quantified evaluations of the amount of state and messages
with the different approaches, and many points made in this section
are detailed in Appendix A.1.
At high scales of multicast deployment, the first and third
mechanisms require the PEs to maintain a large number of PIM
adjacencies with other PEs of the same multicast VPN (which implies
the regular exchange PIM Hellos with each other) and to periodically
refresh C-Join/Prune states, resulting in an increased processing
cost when the amount of PEs increases (as detailed in Appendix A.1)
to which the second approach is less subject, and to which the fourth
approach is not subject.
The third mechanism would reduce the amount of C-Join/Prune
processing for a given multicast flow for PEs that are not the
upstream neighbor for this flow, but would require "explicit
tracking" state to be maintained by the upstream PE. It also isn't
compatible with the "Join suppression" mechanism. A possible way to
reduce the amount of signaling with this approach would be the use of
a PIM refresh-reduction mechanism. Such a mechanism, based on TCP,
is being specified by the PIM IETF Working Group
([I-D.ietf-pim-port]) ; its use in a multicast VPN context has not
been described in [I-D.ietf-l3vpn-2547bis-mcast], but it is expected
that this approach would provide a scalability similar with the BGP-
based approach without RR.
The second mechanism would operate in a similar manner to full per-
MVPN PIM peering except that PIM Hello messages are not transmitted
and PIM C-Join/Prune refresh-reduction would be used, thereby
improving scalability, but this approach has yet to be fully
described. In any case, it seems that it only improves one thing
among the things that will impact scalability when the number of PEs
increases.
The first and second mechanisms can leverage the "Join suppression"
behavior and thus improve the processing burden of an upstream PE,
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sparing the processing of a Join refresh message for each remote PE
joined to a multicast stream. This improvement requires all PEs of a
multicast VPN to process all PIM Join and Prune messages sent by any
other PE participating in the same multicast VPN whether they are the
upstream PE or not.
The fourth mechanism (the use of BGP for carrying C-Multicast
routing) would have a comparable drawback of requiring all PEs to
process a BGP C-multicast route only interesting a specific upstream
PE. For this reason section 16 [I-D.ietf-l3vpn-2547bis-mcast-bgp]
recommends the use of the Route-Target constrained BGP distribution
[RFC4684] mechanisms, which eliminate this drawback by making only
the interested upstream PE to receive a BGP C-multicast route.
Specifically when Route-Target constrained BGP distribution is used,
the fourth mechanism reduces the total amount of C-multicast routing
processing load put on the PEs by avoiding any processing of customer
multicast routing information on the "unrelated" PEs, that are
neither the joining PE nor the upstream PE.
Moreover, the fourth mechanism further reduces the total amount of
message processing load by avoiding the use of periodic refreshes,
and by inheriting BGP features that are expected to improve
scalability (for instance, providing a means to offload some of the
processing burden associated with customer multicast routing onto one
or many BGP route-reflectors). The advantages of the fourth
mechanism come at a cost of maintaining an amount of state linear
with the number of PEs joined to a stream. However, the use of route
reflectors allows to spread this cost among multiple route
reflectors, thus eliminating the need for a single route reflector to
maintain all this state.
However, the fourth mechanism is specific in that it offers the
possibility of offloading customer multicast routing processing onto
one or more BGP Route Reflector(s). When this is used, there is a
drawback of increasing the processing load placed on the route
reflector infrastructure. In the higher scale scenarios, it may be
required to adapt the route reflector infrastructure to the MVPN
routing load by using, for example:
o a separation of resources for unicast and multicast VPN routing:
using dedicated MVPN Route Reflector(s) (or using dedicated MVPN
BGP sessions or dedicated MVPN BGP instances) ;
o the deployment of additional route reflector resources, for
example increasing the processing resources on existing route
reflectors or deployment of additional route reflectors.
Among the above, the most straightforward approach is to consider the
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introduction of route reflectors dedicated to the MVPN service and
dimension them accordingly to the need of that service (but doing so
is not required and is left as an operator engineering decision).
3.3.2. PE-CE multicast routing exchange scalability
The overhead associated with the PE-CE exchange of C-multicast
routing is independent of the choice of the mechanism used for the
PE-PE C-multicast routing. Therefore, the impact of the PE-CE
C-multicast routing overhead on the overall system scalability is
independent of the protocol used for PE-PE signaling, and therefore
is not relevant when comparing the different approaches proposed for
the PE-PE C-multicast routing. This is true even if in some
operational contexts the PE-CE C-multicast routing overhead is a
significant factor in the overall system overhead.
3.3.3. P-routers scalability
Mechanisms (1) and (2) are restricted to use within multicast VPNs
that use an MI-PMSI, thereby necessitating:
the use of a P-tunnel technique that allows shared P-tunnels (for
example PIM-SM in ASM mode or MP2MP LDP)
or the use of one P-tunnel per PE per VPN, even for PEs that do not
have sources in their directly attached sites for that VPN.
By comparison, the fourth mechanism doesn't impose either of these
restrictions, and when P2MP P-tunnels are used only necessitates the
use of one P-tunnel per VPN per PE attached to a site with a
multicast source or RP (or with a candidate BSR, if BSR is used).
In cases where there are less PEs connected with sources than the
total amount of PEs, it improves the amount of state maintained by
P-routers compared to the amount required to build an MI-PMSI with
P2MP P-tunnels. Such cases are expected to be frequent for multicast
VPN deployments (see sections 4.2.4.1 of [RFC4834]).
3.3.4. Impact of C-multicast routing on Inter-AS deployments
Co-existence with unicast inter-AS VPN options, and an equal level of
security for multicast and unicast including in an inter-AS context,
are specifically mentioned in sections 5.2.6, 5.2.8 and 5.2.12 of
[RFC4834].
In an inter-AS option B context, an isolation of ASes is obtained as
PEs in one AS don't have (direct) exchange of routing information
with PEs of other ASes. This property is not preserved if PIM-based
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PE-PE C-multicast routing is used. By contrast, the fourth option
(BGP-based C-Multicast routing) does preserve this property.
Additionally, the authors note that the proposed BGP-based approach
for C-multicast routing provides a good fit with both the segmented
and non-segmented inter-AS approaches. By contrast, though the PIM-
based C-multicast routing is usable with segmented inter-AS tunnels,
the inter-AS scalability advantage of the approach is lost, since PEs
in an AS will see the C-multicast routing activity of all other PEs
of all other ASes.
3.3.5. Security and robustness
BGP supports MD5 authentication of its peers for additional security,
thereby possibly benefit directly to multicast VPN customer multicast
routing, whether for intra-AS or inter-AS communications. By
contrast, with a PIM-based approach, no mechanism providing a
comparable level of security to authenticate communications between
remote PEs has been yet fully described yet
[I-D.ietf-pim-sm-linklocal][], and in any case would require
significant additional operations for the provider to be usable in a
multicast VPN context.
The robustness of the infrastructure, especially the existing
infrastructure providing unicast VPN connectivity, is key. The
C-multicast routing function, especially under load, will compete
with the unicast routing infrastructure. With the PIM-based
approaches, the unicast and multicast VPN routing functions are
expected to only compete in the PE, for control plane processing
resources. In the case of the BGP-based approach, they will compete
on the PE for processing resources, and in the route reflectors
(supposing they are used for MVPN routing). It is identified that in
both cases, mechanisms will be required to arbitrate resources (e.g.
processing priorities). In the case of PIM-based procedures, between
the different control plane routing instances in the PE. And in the
case of the BGP-based approach, this is likely to require using
distinct BGP sessions for multicast and unicast (e.g. through the use
of dedicated MVPN BGP route reflectors, or to the use of a distinct
session with an existing route reflector).
Multicast routing is dynamic by nature, and multicast VPN routing has
to follow the VPN customers multicast routing events. The different
approaches can be compared on how they are expected to behave in
scenarios where multicast routing in the VPNs is subject to an
intense activity. Scalability of each approach under such a load is
detailed in Appendix A.2, and the fourth approach (BGP-based) used in
conjunction with the RT Constraint mechanisms [RFC4684], is the only
one having a cost for join/leave operations independent of the number
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of PEs in the VPN (with one exception detailed in Appendix A.2) and
state maintenance not concentrated on the upstream PE.
On the other hand, while the BGP-based approach is likely to suffer a
slowdown under a load that is greater than the available processing
resources (because of possibly congested TCP sockets), the PIM-based
approaches would react to such a load by dropping messages, with
failure-recovery obtained through message refreshes. Thus, the BGP-
based approach could result in a degradation of join/leave latency
performance typically spread evenly across all multicast streams
being joined in that period, while the PIM-based approach could
result in increased join/leave latency, for some random streams, by a
multiple of the time between refreshes (e.g. tens of seconds), and
possibly in some states the adjacency may time-out resulting in
disruption of multicast streams.
The behavior of the PIM-based approach under such a load is also
harder to predict, given that the performance of the "Join
suppression" mechanism (an important mechanism for this approach to
scale) will itself be impeded by delays in Join processing. For
these reasons, the BGP-based approach would be able to provide a
smoother degradation and more predictable behavior under a highly
dynamic load.
In fact, both an "evenly spread degradation" and an "unevenly spread
larger degradation" can be problematic, and what seems important is
the ability for the VPN backbone operator to (a) limit the amount of
multicast routing activity that can be triggered by a multicast VPN
customer, and to (b) provide the best possible independence between
distinct VPNs. It seems that both of these can be addressed through
local implementation improvements, and that both the BGP-based and
PIM-based approaches could be engineered to provide (a) and (b). It
can be noted though that the BGP approach proposes ways to dampen
C-multicast route withdrawals and/or advertisements, and thus already
describes a way to provide (a), while nothing comparable has yet been
described for the PIM-based approaches (even though it doesn't appear
difficult). The PIM-based approaches rely on a per VPN dataplane to
carry the MVPN control plane, and thus may benefit from this first
level of separation to solve (b).
3.3.6. C-multicast VPN join latency
Section 5.1.3 of [RFC4834] states that "the group join delay [...] is
also considered one important QoS parameter. It is thus RECOMMENDED
that a multicast VPN solution be designed appropriately in this
regard". In a multicast VPN context, the "group join delay"of
interest is the time between a CE sending a PIM Join to its PE and
the first packet of the corresponding multicast stream being received
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by the CE.
It is to be noted that the C-multicast routing procedures will only
impact the group join latency of a said multicast stream for the
first receiver that is located across the provider backbone from the
multicast source-connected PE (or the first <n> receivers in the
specific case where a specific UMH selection algorithm is used, that
allows <n> distinct UMH to be selected by distinct downstream PEs).
The different approaches proposed seem to have different
characteristics in how they are expected to impact join latency:
o the PIM-based approaches minimize the number of control plane
processing hops between a new receiver-connected PE and the
source-connected PE, and being datagram-based introduces minimal
delay, thereby possibly having a join latency as good as possible
depending on implementation efficiency
o under degraded conditions (packet loss, congestion, high control
plane load) the PIM-based approach may impact the latency for a
given multicast stream in an all or nothing manner: if a
C-multicast routing PIM Join packet is lost, latency can reach a
high time (a multiple of the periodicity of PIM Join refreshes)
o the BGP-based approach uses TCP exchanges, that may introduce an
additional delay depending on BGP and TCP implementation, but
which would typically result, under degraded conditions (such
packet loss, congestion, high control plane load), in a comparably
lower increase of latency spread more evenly across the streams
o as shown in Appendix A, the BGP-based approach is particular in
that it removes load from all the PEs (without putting this load
on the upstream PE for a stream); this improvement of background
load can bring improved performance when a PE acts as the upstream
PE for a stream, and thus benefit join latency
This qualitative comparison of approaches shows that the BGP-based
approach is designed for a smoother degradation of latency under
degraded conditions such as packet loss, congestion, or high control
plane load. On the other hand, the PIM-based approaches seem to
structurally be able to reach the shorter "best-case" group join
latency (especially compared to deployment of the BGP-based approach
where route-reflectors are used).
Doing a quantitative comparison of latencies is not possible without
referring to specific implementations and benchmarking procedures,
and would possibly expose different conclusions, especially for best-
case group join latency for which performance is expected vary with
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PIM and BGP implementations. We can also note that improving a BGP
implementation for reduced latency of route processing would not only
benefit multicast VPN group join latency, but the whole BGP-based
routing, which means that the need for good BGP/RR performance is not
specific to multicast VPN routing.
Last, C-multicast join latency will be impacted by the overall load
put on the control plane, and the scalability of the C-multicast
routing approach is thus to be taken into account. As explained in
sections Section 3.3.1 and Appendix A, the BGP-based approach will
provide the best scalability with an increased number of PEs per VPN,
thereby benefiting group join latency in such higher scale scenarios.
3.3.7. Conclusion on C-multicast routing
The first and fourth approaches are relevant contenders for
C-multicast routing. Comparisons from a theoretical standpoint lead
to identify some advantages as well as possible drawbacks in the
fourth approach. Comparisons from a practical standpoint are harder
to make: since only reduced deployment and implementation information
is available for the fourth approach, advantages would be seen in the
first approach that has been applied through multiple deployments and
shown to be operationally viable.
Moreover, the first mechanism (full per-MVPN PIM peering across an
MI-PMSI) is the mechanism used by [I-D.rosen-vpn-mcast] and therefore
it is deployed and operating in MVPNs today. The fourth approach may
or may not end up being preferred for a said deployment, but because
the first approach has been in deployment for some time, the support
for this mechanism will in any case be helpful for to facilitate an
eventual migration from a deployment using mechanism close to the
first approach.
Consequently, at the present time, implementations are recommended to
support both the fourth (BGP-based) and first (Full per-MPVN PIM
peering) mechanisms. Further experience on deployments of the fourth
approach is needed before some best practice can be defined. In the
meantime, this recommendation would enable a service provider to
choose between the first and the fourth mechanism, without this
choice being constrained by vendors implementation choices, and
taking into account the peculiarities of its own deployment context
by pondering the weight of the different factors into account.
3.4. Encapsulation techniques for P-multicast trees
In this section the authors will not make any restricting
recommendations since the appropriateness of a specific provider core
data plane technology will depend on a large number of factors, for
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example the service provider's currently deployed unicast data plane,
many of which are service provider specific.
However, implementations should not unreasonably restrict the data
plane technology that can be used, and should not force the use of
the same technology for different VPNs attached to a single PE.
Initial implementations may only support a reduced set of
encapsulation techniques and data plane technologies but this should
not be a limiting factor that hinders future support for other
encapsulation techniques, data plane technologies or
interoperability.
Section 5.2.4.1 of [RFC4834] states "In a multicast VPN solution
extending a unicast L3 PPVPN solution, consistency in the tunneling
technology has to be favored: such a solution SHOULD allow the use of
the same tunneling technology for multicast as for unicast.
Deployment consistency, ease of operation and potential migrations
are the main motivations behind this requirement."
Current unicast VPN deployments use a variety of LDP, RSVP-TE and
GRE/IP-Multicast for encapsulating customer packets for transport
across the provider core of VPN services. In order to allow the same
encapsulations to be used for unicast and multicast VPN traffic, it
is recommended that multicast VPN standards should recommend
implementations to support for multicast VPNs, all the P2MP variants
of the encapsulations and signaling protocols that they support for
unicast and for which some multipoint extension is defined, such as
mLDP, P2MP RSVP-TE and GRE/IP-multicast.
All three of the above encapsulation techniques support the building
of P2MP multicast P-tunnels. In addition mLDP and GRE/
IP-ASM-Multicast implementations may also support the building of
MP2MP multicast P-tunnels. The use of MP2MP P-tunnels may provide
some scaling benefits to the service provider as only a single MP2MP
P-tunnel need be deployed per VPN, thus reducing by an order of
magnitude the amount of multicast state that needs to be maintained
by P routers. This gain in state is at the expense of bandwidth
optimization, since sites that do not have multicast receivers for
multicast streams sourced behind a said PE group will still receive
packets of such streams, leading to non-optimal bandwidth utilization
across the VPN core. One thing to consider is that the use of MP2MP
multicast P-tunnel will require additional configuration to define
the same P-tunnel identifier or multicast ASM group address in all
PEs (it has been noted that some auto-configuration could be possible
for MP2MP P-tunnels, but this it is not currently supported by the
auto-discovery procedures). [ It has been noted that C-multicast
routing schemes not covered in [I-D.ietf-l3vpn-2547bis-mcast] could
expose different advantages of MP2MP multicast P-tunnels - this is
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out of scope of this document ]
MVPN services can also be supported over a unicast VPN core through
the use of ingress PE replication whereby the ingress PE replicates
any multicast traffic over the P2P tunnels used to support unicast
traffic. While this option does not require the service provider to
modify their existing P routers (in terms of protocol support) and
does not require maintaining multicast-specific state on the P
routers in order for the service provider to be able deploy a
multicast VPN service, the use of ingress PE replication obviously
leads to non-optimal bandwidth utilization and it is therefore
unlikely to be the long term solution chosen by service providers.
However ingress PE replication may be useful during some migration
scenarios or where a service provider considers the level of
multicast traffic on their network to be too low to justify deploying
multicast specific support within their VPN core.
All proposed approaches for control plane and dataplane can be used
to provide aggregation amongst multicast groups within a VPN and
amongst different multicast VPNs, and potentially reduce the amount
of state to be maintained by P routers. However the latter -- the
aggregation amongst different multicast VPNs will require support for
upstream-assigned labels on the PEs. Support for upstream-assigned
labels may require changes to the data plane processing of the PEs
and this should be taken into consideration by service providers
considering the use of aggregate PMSI tunnels for the specific
platforms that the service provider has deployed.
3.5. Inter-AS deployments options
There are a number of scenarios that lead to the requirement for
inter-AS multicast VPNs, including:
1. a service provider may have a large network that they have
segmented into a number of ASs.
2. a service provider's multicast VPN may consist of a number of ASs
due to acquisitions and mergers with other service providers.
3. a service provider may wish to interconnect their multicast VPN
platform with that of another service provider.
The first scenario can be considered the "simplest" because the
network is wholly managed by a single service provider under a single
strategy and is therefore likely to use a consistent set of
technologies across each AS.
The second scenario may be more complex than the first because the
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strategy and technology choices made for each AS may have been
different due to their differing history and the service provider may
not have (or may be unwilling to) unified the strategy and technology
choices for each AS.
The third scenario is the most complex because in addition to the
complexity of the second scenario, the ASs are managed by different
service providers and therefore may be subject to a different trust
model than the other scenarios.
Section 5.2.6 of [RFC4834] states that "a solution MUST support
inter-AS multicast VPNs, and SHOULD support inter-provider multicast
VPNs", "considerations about coexistence with unicast inter-AS VPN
Options A, B and C (as described in section 10 of [RFC4364]) are
strongly encouraged" and "a multicast VPN solution SHOULD provide
inter-AS mechanisms requiring the least possible coordination between
providers, and keep the need for detailed knowledge of providers'
networks to a minimum - all this being in comparison with
corresponding unicast VPN options".
Section 8 of [I-D.ietf-l3vpn-2547bis-mcast] addresses these
requirements by proposing two approaches for MVPN inter-AS
deployments:
1. Non-segmented inter-AS tunnels where the multicast tunnels are
end-to-end across ASes, so even though the PEs belonging to a
given MVPN may be in different ASs the ASBRs play no special role
and function merely as P routers (described in section 8.1).
2. Segmented inter-AS tunnels where each AS constructs its own
separate multicast tunnels which are then 'stitched' together by
the ASBRs (described in section 8.2).
(Note that an inter-AS deployment can alternatively rely on Option A
-- so-called "back-to-back" VRFs -- that option is not considered in
this section given that it can be used without any inter-AS specific
mechanism)
Section 5.2.6 of [RFC4834] also states "Within each service provider
the service provider SHOULD be able on its own to pick the most
appropriate tunneling mechanism to carry (multicast) traffic among
PEs (just like what is done today for unicast)". The segmented
approach is the only one capable of meeting this requirement.
The segmented inter-AS solution would appear to offer the largest
degree of deployment flexibility to operators. However the non-
segmented inter-AS solution can simplify deployment in a restricted
number of scenarios and [I-D.rosen-vpn-mcast] only supports the non-
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segmented inter-AS solution and therefore the non-segmented inter-AS
solution is likely to be useful to some operators for backward
compatibility and during migration from [I-D.rosen-vpn-mcast] to
[I-D.ietf-l3vpn-2547bis-mcast].
The following is a comparison matrix between the "segmented inter-AS
P-tunnels" and "non-segmented inter-AS P-tunnels" approaches:
o Scalability for I-PMSIs: the "segmented inter-AS P-tunnels" is
more scalable, because of the ability of an ASBR to aggregate
multiple intra-AS P-tunnels used for I-PMSI within its own AS into
one inter-AS P-tunnel to be used by other ASes. Note that the
I-PMSI scalability improvement brought by the "segmented inter-AS
P-tunnels" approach is higher when segmented P-tunnels have a
granularity of source AS (see item below).
o Scalability for S-PMSIs: the "segmented inter-AS P-tunnels", when
used with the BGP-based C-multicast routing approach, provides
flexibility in how the bandwidth/state trade-off is handled, to
help with scalability. Indeed in that case, the trade-off made
for a said (C-S,C-G) in a downstream AS can be made more in favor
of scalability than the trade-off made by the neighbor upstream
AS, thanks to the ability to aggregate one or more S-PMSIs of the
upstream AS in one I-PMSI tunnel in a downstream AS.
o Configuration at ASBRs: depending on whether segmented P-tunnels
have a granularity of source ASBR or source AS, the "segmented
inter-AS P-tunnels" approach would require respectively the same
or additional configuration on ASBRs as the "non-segmented
inter-AS P-tunnels" approach.
o Independence of tunneling technology from one AS to another: the
"segmented inter-AS P-tunnels" approach provides this, the "non-
segmented inter-AS P-tunnels" approach does not.
o Facilitated co-existence with, and migration from, existing
deployments, and lighter engineering in some scenarios : the "non-
segmented inter-AS P-tunnels" approach provides this, the
"segmented inter-AS P-tunnels" approach does not.
The applicability of segmented or non-segmented inter-AS tunnels to a
given deployment or inter-provider interconnect will depend on a
number of factors specific to each service provider. However, given
the different elements reminded above, it is the recommendation of
the authors that all implementations should support the segmented
inter-AS model. Additionally, the authors recommend that
implementations should consider supporting the non-segmented inter-AS
model in order to facilitate co-existence with, and migration from,
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existing deployments, and as a feature to provide a lighter
engineering in a restricted set of scenarios, although it is
recognized that initial implementations may only support one or the
other.
3.6. Bidir-PIM support
In Bidir-PIM, the packet forwarding rules have been improved over
PIM-SM, allowing traffic to be passed up the shared tree toward the
RP Address (RPA). To avoid multicast packet looping, Bidir-PIM uses
a mechanism called the designated forwarder (DF) election, which
establishes a loop-free tree rooted at the RPA. Use of this method
ensures that only one copy of every packet will be sent to an RPA,
even if there are parallel equal cost paths to the RPA. To avoid
loops the DF election process enforces consistent view of the DF on
all routers on network segment, and during periods of ambiguity or
routing convergence the traffic forwarding is suspended.
In the context of a multicast VPN solution, a solution for Bidir-PIM
support must preserve this property of similarly avoiding packet
loops, including in the case where mVRF's in a given MVPN don't have
a consistent view of the routing to C-RPL/C-RPA.
The current MVPN specifications [I-D.ietf-l3vpn-2547bis-mcast] in
section 11, define three methods to support Bidir-PIM, as RECOMMENDED
in [RFC4834]:
1. Standard DF election procedure over an MI-PMSI
2. VPN Backbone as the RPL (section 11.1)
3. Partitioned Sets of PEs (section 11.2)
Method (1) is naturally applied to deployments using "Full per-MVPN
PIM peering across an MI-PMSI" for C-multicast routing, but as
indicated in [I-D.ietf-l3vpn-2547bis-mcast] in section 11, the DF
Election may not work well in an MVPN environment and an alternative
to DF election would be desirable.
The advantage of method (2) and (3) is that they do not require
running the DF election procedure among PEs.
Method (2) leverages the fact that in Bidir-PIM, running the DF
election procedure is not needed on the RPL. This approach thus has
the benefit of simplicity of implementation, especially in a context
where BGP-based C-multicast routing is used. However it has the
drawback of putting constraints on how Bidir-PIM is deployed which
may not always match MVPN customers requirements.
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Method (3) treats an MVPN as a collection of sets of multicast VRFs,
all PEs in a set having the same reachability information towards
C-RPA, but distinct from PEs in other sets. Hence, with this method,
C-Bidir packet loops in MVPN are resolved by the ability to partition
a VPN into disjoints sets of VRF's, each having a distinct view of
converged network. The partitioning approach to Bidir-PIM requires
either upstream-assigned MPLS labels (to denote the partition) or a
unique MP2MP LSP per partition. The former is based on PE
Distinguisher Labels that have to be distributed using auto-discovery
BGP routes and their handling requires the support for upstream
assigned labels and context label lookups [RFC5331]. The latter,
using MP2MP LSP per partition, does not have these constraints but is
restricted to P-tunnel types supporting MP2MP connectivity (such as
mLDP [I-D.ietf-mpls-ldp-p2mp]).
This approach to C-Bidir can work with PIM-based or BGP-based
C-multicast routing procedures, and is also generic in the sense that
it does not impose any requirements on the Bidir-PIM service
offering.
Given the above considerations, method (3) "Partitioned Sets of PEs"
is the RECOMMENDED approach.
In the event where method (3) is not applicable (lack of support for
upstream assigned labels or for a P-tunnel type providing MP2MP
connectivity), then method (1) "Standard DF election procedure over
an MI-PMSI" and (2) "VPN Backbone as the RPL" are RECOMMENDED as
interim solutions, (1) having the advantage over (2) of not putting
constraints on how Bidir-PIM is deployed and the drawbacks of only
being applicable when PIM-based C-multicast is used and of possibly
not working well in an MVPN environment.
4. Co-located RPs
Section 5.1.10.1 of [RFC4834] states "In the case of PIM-SM in ASM
mode, engineering of the RP function requires the deployment of
specific protocols and associated configurations. A service provider
may offer to manage customers' multicast protocol operation on their
behalf. This implies that it is necessary to consider cases where a
customer's RPs are out-sourced (e.g. on PEs). Consequently, a VPN
solution MAY support the hosting of the RP function in a VR or VRF."
However, customers who have already deployed multicast within their
networks and have therefore already deployed their own internal RPs
are often reluctant to hand over the control of their RPs to their
service provider and make use of a co-located RP model, and providing
RP-collocation on a PE will require the activation of MSDP or the
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processing of PIM Registers on the PE. Securing the PE routers for
such activity requires special care, additional work, and will likely
rely on specific features to be provided by the routers themselves.
The applicability of the co-located RP model to a given MVPN will
thus depend on a number of factors specific to each customer and
service provider.
It is therefore the recommendation that implementations should
support a co-located RP model, but that support for a co-located RP
model within an implementation should not restrict deployments to
using a co-located RP model: implementations MUST support deployments
when activation of a PIM RP function (PIM Register processing and RP-
specific PIM procedures) or VRF MSDP instance is not required on any
PE router and where all the RPs are deployed within the customers'
networks or CEs.
5. Avoiding duplicates
It is recommended that implementations support the procedures
described in section 9.1.1 of [I-D.ietf-l3vpn-2547bis-mcast]
"Discarding Packets from Wrong PE", allowing fully avoiding
duplicates.
6. Existing deployments
Some suggestions provided in this document can be used to
incrementally modify currently deployed implementations without
hindering these deployments, and without hindering the consistency of
the standardized solution by providing optional per-VRF configuration
knobs to support modes of operation compatible with currently
deployed implementations, while at the same time using the
recommended approach on implementations supporting the standard.
In cases where this may not be easily achieved, a recommended
approach would be to provide a per-VRF configuration knob that allows
incremental per-VPN migration of the mechanisms used by a PE device,
which would allow migration with some per-VPN interruption of service
(e.g. during a maintenance window).
Mechanisms allowing "live" migration by providing concurrent use of
multiple alternatives for a given PE and a given VPN, is not seen as
a priority considering the expected implementation complexity
associated with such mechanisms. However, if there happen to be
cases where they could be viably implemented relatively simply, such
mechanisms may help improve migration management.
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7. Summary of recommendations
The following list summarizes conclusions on the mechanisms that
define the set of mandatory to implement mechanisms in the context of
[I-D.ietf-l3vpn-2547bis-mcast].
Note well that the implementation of the non-mandatory alternative
mechanisms is not precluded.
Recommendations are:
o that BGP-based auto-discovery be the mandated solution for auto-
discovery ;
o that BGP be the mandated solution for S-PMSI switching signaling ;
o that implementations support both the BGP-based and the full per-
MPVN PIM peering solutions for PE-PE exchange of customer
multicast routing until further operational experience is gained
with both solutions ;
o that implementations use the "Partitioned Sets of PEs" approach
for Bidir-PIM support ;
o that implementations implement the P2MP variants of the P2P
protocols that they already implement, such as mLDP, P2MP RSVP-TE
and GRE/IP-Multicast ;
o that implementations support segmented inter-AS tunnels and
consider supporting non-segmented inter-AS tunnels (in order to
maintain backwards compatibility and for migration) ;
o implementations MUST support deployments when activation of a PIM
RP function (PIM Register processing and RP-specific PIM
procedures) or VRF MSDP instance is not required on any PE router.
o that implementations support the procedures described in section
9.1.1 of [I-D.ietf-l3vpn-2547bis-mcast]
8. IANA Considerations
This document makes no request to IANA.
[ Note to RFC Editor: this section may be removed on publication as
an RFC. ]
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9. Security Considerations
This document does not by itself raise any particular security
considerations.
10. Acknowledgements
We would like to thank Adrian Farrel, Eric Rosen, Yakov Rekhter, and
Maria Napierala for their feedback that helped shape this document.
Additional credit is due to Maria Napierala for co-authoring
Section 3.6 on Bidir-PIM support.
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.
[I-D.ietf-l3vpn-2547bis-mcast]
Aggarwal, R., Bandi, S., Cai, Y., Morin, T., Rekhter, Y.,
Rosen, E., Wijnands, I., and S. Yasukawa, "Multicast in
MPLS/BGP IP VPNs", draft-ietf-l3vpn-2547bis-mcast-09 (work
in progress), November 2009.
[I-D.ietf-l3vpn-2547bis-mcast-bgp]
Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", draft-ietf-l3vpn-2547bis-mcast-bgp-08 (work in
progress), September 2009.
11.2. Informative References
[RFC4834] Morin, T., "Requirements for Multicast in L3 Provider-
Provisioned Virtual Private Networks (PPVPNs)", RFC 4834,
April 2007.
[I-D.rosen-vpn-mcast]
Cai, Y., Rosen, E., and I. Wijnands, "Multicast in MPLS/
BGP IP VPNs", draft-rosen-vpn-mcast-12 (work in progress),
August 2009.
[I-D.raggarwa-l3vpn-2547-mvpn]
Aggarwal, R., "Base Specification for Multicast in BGP/
MPLS VPNs", draft-raggarwa-l3vpn-2547-mvpn-00 (work in
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progress), June 2004.
[I-D.ietf-pim-sm-linklocal]
Atwood, J., "Authentication and Confidentiality in PIM-SM
Link-local Messages", draft-ietf-pim-sm-linklocal-08 (work
in progress), November 2007.
[I-D.ietf-pim-port]
Farinacci, D., Wijnands, I., Venaas, S., and M. Napierala,
"A Reliable Transport Mechanism for PIM",
draft-ietf-pim-port-02 (work in progress), October 2009.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, November 2006.
[I-D.ietf-mpls-ldp-p2mp]
Minei, I., Kompella, K., Wijnands, I., and B. Thomas,
"Label Distribution Protocol Extensions for Point-to-
Multipoint and Multipoint-to-Multipoint Label Switched
Paths", draft-ietf-mpls-ldp-p2mp-08 (work in progress),
October 2009.
[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space",
RFC 5331, August 2008.
Appendix A. Scalability of C-multicast routing processing load
The main role of multicast routing is to let routers determine that
they should start or stop forwarding a said multicast stream on a
said link. In an MVPN context, this has to be done for each MVPN,
and the associated function is thus named "customer-multicast
routing" or "C-multicast routing" and its role is to let PE routers
determine that they should start or stop forwarding the traffic of a
said multicast stream toward the remote PEs, on some PMSI tunnel.
When some "join" message is received by a PE, this PE knows that it
should be sending traffic for the corresponding multicast group of
the corresponding MVPN. But the reception of a "prune" message from
a remote PE is not enough by itself for a PE to know that it should
stop forwarding the corresponding multicast traffic: it has to make
sure that they aren't any other PEs that still have receivers for
this traffic.
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There are many ways that the "C-multicast routing" building block can
be designed, and they differ, among other things, in how a PE
determines when it can stop forwarding a said multicast stream toward
other PEs:
PIM LAN Procedures, by default
By default when PIM LAN procedures are used, when a PE on a LAN
Prunes itself from a multicast tree, all other PEs on that LAN
check their own state to known if they are on the tree, in which
case they send a PIM Join message on that LAN to override the
Prune. Thus, for each PIM Prune message, all PE routers on the
LAN work to let the upstream PE determine the answer to the "did
the last receiver leave?" question.
BGP-based C-multicast routing
When BGP-based procedures are used for C-multicast routing, if no
BGP Route Reflector is used, the "did the last receiver leave?"
question is answered by having the upstream PE maintain an up-to-
date list of the PEs which are joined to the tree, thus making it
possible to instantly know the answer to the "did the last
receiver leave?", whenever a PE leaves the said multicast tree.
But, when a BGP Route Reflector is used (which is expected to be
the recommended approach), the role of maintaining an updated list
of the PEs that are part of a said multicast tree is taken care of
by the Route Reflector(s). Using BGP procedures a route reflector
that had been advertised a C-multicast Source Tree Join route for
a said (C-S, C-G) to other route reflectors before, will withdraw
this route when there is no of its clients PEs advertising this
route anymore. Similarly, a route reflector that had advertised
this route to its client PEs before, will withdraw this route when
there is none of its (other) client PEs, and none of its route
reflectors peers advertising this route anymore. In this context,
the "did the last receiver leave?" question can be said to be
answered by the route-reflector(s).
Furthermore, the BGP route distribution can leverage more than one
route reflector: if multiple route reflectors are used with PEs
being distributed (as clients) among these route reflectors, the
"did the last receiver leave?" question is partly answered by each
of these route reflector.
We can see that answering the "last receiver leaves" question is a
part of the work that the C-multicast routing building block has to
make, where the different approaches significantly differ. The
different approaches for handling C-multicast routing can indeed
result in a different amount of processing and how this processing is
spread among the different functions. These differences can be
better estimated by quantifying the amount of message processing and
state maintenance.
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Though the type of processing, messages and states, may vary with the
different approaches, we propose here a rough estimation of the load
of PEs, in terms of number of messages processed and number of
control plane states maintained. A "message processed" being a
message being parsed, a lookup being done, and some action being
taken (such as, for instance, updating a control plane or data plane
state, or discarding the information in the message). A "state
maintained" being a multicast state kept in the control plane memory
of a PE, related to an interface or a PE being subscribed to a
multicast stream (note that a state will be counted on an equipment
as many times as the number of protocols in which it is present; e.g.
two times when present both as a PIM state and a BGP route). Note
that here we don't compare the data plane states on PE routers, which
wouldn't vary between the different options chosen.
A.1. Scalability with an increased number of PEs
The following sections aims at evaluating the processing and state
maintenance load for an increasingly high number of PEs in a VPN.
A.1.1. SSM Scalability
The following subsections do such an estimation for each proposed
approach for C-multicast routing, for different phases of the
following scenario:
o one SSM multicast stream is considered
o only the intra-AS case is concerned (with the segmented inter-AS
tunnels and BGP-based C-multicast routing, #mvpn_PE and #R_PE
should refer to the PEs of the MVPN in the AS, not to all PEs of
the MVPN)
o the scenario is as follows:
* one PE Joins the multicast stream (because of a new receiver-
connected site has sent a Join on the PE-CE link), followed by
a number of additional PEs that also join the same multicast
stream, one after the other ; we evaluate the processing
required for the addition of each PE
* some period of time T passes, without any PE joining or leaving
(baseline)
* all PE leaves, one after the other, until the last one leaves ;
we evaluate the processing required for the leave of each PE
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o the parameters used are:
* #mvpn_PE: the number of PEs in the MVPN
* #R_PE: the number of PEs joining the multicast stream
* #RR: the number of route reflectors
* T_PIM_r: the time between two refreshes of a PIM Join (default
is 60s)
The estimation unit used is the "message.equipment" (or "m.e"): one
"message.equipment" corresponding to "one equipment processing one
message" (10 m.e being "10 equipments processing each one message",
or "5 messages each processed by 2 equipments", or "1 message
processed by 10 equipment", etc.). Similarly, for the amount of
control plane state, the unit used is "state.equipment" or "s.e".
This allow to take into account the fact that a message (or a state)
can have be processed (or maintained) by more than one node.
We distinguish three different types of equipments: the upstream PE
for the considered multicast stream, the RR (if any), and the other
PEs (which are not the upstream PE).
The numbers or orders of magnitude given in the tables in the
following subsections are totals across all equipments of a same
type, for each type of equipment, in the "m.e" and "s.e" units
defined above.
Additionally:
o for PIM, only Join and Prune messages are counted:
* the load due to PIM Hellos can be easily computed separately
and only depends on the number of PEs in the VPN;
* message processing related to the PIM Assert mechanism is also
not taken into account, for sake of simplicity;
o for BGP, all advertisements and withdrawals of C-multicast Source
Tree Join routes are considered (Source-Active autodiscovery
routes are not used in an SSM context) ; and, following the
recommendation in Section 16 of [I-D.ietf-l3vpn-2547bis-mcast-bgp]
the case where the RT-Constraint mechanisms [RFC4684] is not used
is not covered;
(Note that for all options provided for C-multicast routing, the
procedures to setup and maintain a shortest path tree toward the
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source of an SSM group are the same than the procedures used to setup
and maintain a shortest path tree toward an RP or a non-SSM source ;
the results of this section are thus re-used in section
Appendix A.1.2 )
A.1.1.1. PIM LAN procedures, by default
+------------+------------+---------------+----------+--------------+
| | upstream | other PEs | RR | total across |
| | PE (1) | (total across | (none) | all |
| | | (#mvpn_PE-1) | | equipments |
| | | PEs) | | |
+------------+------------+---------------+----------+--------------+
| first PE | 1 m.e | #mvpn_PE-1 | / | #mvpn_PE m.e |
| joins | | m.e | | |
+------------+------------+---------------+----------+--------------+
| for *each* | 1 m.e | #mvpn_PE-1 | / | #mvpn_PE m.e |
| additional | | m.e | | |
| PE joining | | | | |
+------------+------------+---------------+----------+--------------+
| baseline | T/T_PIM_r | (T/T_PIM_r) . | / | (T/T_PIM_r) |
| processing | m.e | (#mvpn_PE-1) | | x #mvpn_PE |
| over a | | m.e | | m.e |
| period T | | | | |
+------------+------------+---------------+----------+--------------+
| for *each* | 2 m.e | 2(#mvpn_PE-1) | / | 2 x #mvpn_PE |
| PE leaving | | m.e | | m.e |
+------------+------------+---------------+----------+--------------+
| the last | 1 m.e | #mvpn_PE-1 | / | #mvpn_PE m.e |
| PE leaves | | m.e | | |
+------------+------------+---------------+----------+--------------+
| total for | #R_PE x 2 | (#mvpn_PE-1) | 0 | #mvpn_PE x ( |
| #R_PE PEs | + | x (#R_PE) x 2 | | 3 x #R_PE + |
| | T/T_PIM_r | + T/T_PIM_r) | | T/T_PIM_r ) |
| | m.e | . | | m.e |
| | | (#mvpn_PE-1) | | |
| | | m.e | | |
+------------+------------+---------------+----------+--------------+
| total | 1 s.e | #R_PE s.e | 0 | #R_PE+1 s.e |
| state | | | | |
| maintained | | | | |
+------------+------------+---------------+----------+--------------+
Messages processing and state maintenance - PIM LAN procedures, by
default
We suppose here that the PIM Join suppression and Prune Override
mechanisms are fully effective, i.e. that a Join or Prune message
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sent by a PE is instantly seen by other PEs. Strictly speaking, this
is not true, and depending on network delays and timing, there could
be cases where more messages are exchanged and the number given in
this table is a lower bound to the number of PIM messages exchanged.
A.1.1.2. BGP-based C-multicast routing
The following analysis assumes that BGP Route Reflectors (RRs) are
used, and no hierarchy of RRs (remind that the analysis also assumes
that Route Target Constrain mechanisms are is used).
Given these assumptions, a message carrying a C-multicast route from
a downstream PE would need to be processed by the RRs that have that
PE as their client. Due to the use of RT Constrain, these RRs would
then send this message to only the RRs that have the upstream PE as
client. None of the other RRs, and none of the other PEs will
receive this message. Thus, for a message associated with a given
MVPN the total number of RRs that would need to process this message
only depends on the number of RRs that maintain C-multicast routes
for that MVPN and that have either the receiver-connected PE, or the
source-connected PE as their clients, and is independent of the total
number of RRs or the total number of PEs.
In practice for a given MVPN a PE would be a client of just 2 RRs
(for redundancy, an RR cluster would typically have 2 RRs).
Therefore, in practice the message would need to be processed by at
most 4 RRs (2 RRs if both the downstream PE and the upstream PE are
the clients of the same RRs). Thus the number of RRs that have to
process a given message is at most 4. Since RRs in different RR
clusters have a full iBGP mesh among themselves, each RR in the RR
cluster that contains the upstream PE would receive the message from
each of the RR in the RR cluster that contains the downstream PE.
Given 2 RRs per cluster, the total number of messages processed by
all the RRs is 6.
Additionally, as soon as there is a receiver-connected PEs in each RR
cluster, the number of RRs processing a C-multicast route tends
quickly toward 2 (taking into account that a PE peering to RRs will
be made redundant).
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+------------+----------+--------------+-----------+----------------+
| | upstream | other PEs | RRs (#RR) | total across |
| | PE (1) | (total | | all equipments |
| | | across | | |
| | | (#mvpn_PE-1) | | |
| | | PEs) | | |
+------------+----------+--------------+-----------+----------------+
| first PE | 2 m.e | 2 m.e | 6 m.e | 10 m.e |
| joins | | | | |
+------------+----------+--------------+-----------+----------------+
| for *each* | between | 2 m.e | (at most) | (at most) 10 |
| additional | 0 and 2 | | 6 m.e | m.e tending |
| PE joining | m.e | | tending | toward 4 m.e |
| | | | toward 2 | |
| | | | m.e | |
+------------+----------+--------------+-----------+----------------+
| baseline | 0 | 0 | 0 | 0 |
| processing | | | | |
| over a | | | | |
| period T | | | | |
+------------+----------+--------------+-----------+----------------+
| for *each* | between | 2 m.e | (at most) | (at most) 10 |
| PE leaving | 0 and 2 | | 6 m.e | m.e tending |
| | m.e | | tending | toward 4 m.e |
| | | | toward 2 | |
+------------+----------+--------------+-----------+----------------+
| the last | 2 m.e | 2 m.e | 6 m.e | 10 m.e |
| PE leaves | | | | |
+------------+----------+--------------+-----------+----------------+
| total for | at most | #R_PE x 4 | (at most) | at most 10 x |
| #R_PE PEs | 2 x #RRs | m.e | 6 x #R_PE | #R_PE + 2 x |
| | m.e (see | | m.e | #RRs m.e |
| | note | | (tending | (tending |
| | below) | | toward 2 | toward 6 x |
| | | | x #R_PE | #R_PE + #RRs |
| | | | m.e) | m.e ) |
+------------+----------+--------------+-----------+----------------+
| total | 4 s.e | 2 x #R_PE | approx. 2 | approx. 4 |
| state | | s.e | #R_PE + | #R_PE + #RRx |
| maintained | | | #RR x | #clusters + 4 |
| | | | #clusters | m.e |
| | | | s.e | |
+------------+----------+--------------+-----------+----------------+
Message processing and state maintenance - BGP-based procedures
Note on the total of m.e on the upstream PE:
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o there are as many "message.equipement" on the upstream PE as the
number of times the RRs of the cluster of the upstream PE need to
re-advertise the C-multicast (C-S,C-G) route ; such a re-
advertisement is not useful for the upstream PE, because the
behavior of the upstream PE for a said (VPN associated to the RT,
C-S,C-G) will not depend on the precise attributes carried by the
route (other than the RT, of course) but will happen in some cases
due to how BGP processes these routes ; indeed a BGP peer will
possibly re-advertise a route when its current best path changes
for the said NLRI if the set of attributes to advertise also
changes
o let's look at the different relevant attributes, and when they can
influence when a re-advertisement of a C-multicast route will
happen:
* next-hop and originator-id: a new PE joining will not
mechanically result in a need to re-advertise a C-multicast
route because as the RR aggregates C-multicast routes with the
same NLRI received from PEs in its own cluster (section 11.4 of
[I-D.ietf-l3vpn-2547bis-mcast-bgp]) the RR rewrites the values
of these attributes; however the advertisements made by
different RRs peering with the RRs in the cluster of the
upstream PE may lead to updates of the value of these
attributes
* cluster-list: the value of this attribute only varies between
clusters, changes of the value of this attributes does not
"follow" PE advertisements, and only advertisements made by
different RRs may lead possibly to updates of the value of this
attribute
* local-pref: the value of this attribute is determined locally,
this is true both for the routes advertised by each PE (which
could all be configured to use the same value) and for a route
that results from the aggregation by an RR of the route with
the same NLRI advertised by the PEs of his cluster (the RRs
could also be configured to use a local pref independent from
the local_pref of the routes advertised to him) ; thus, this
attribute can be considered to result in a need to re-advertise
a C-multicast route
* other BGP attributes do not have a particular reason to be set
for C-multicast routes in intra-AS, and if they were, an RR
(or, for attributes relevant for inter-AS, an ASBR) would also
overwrite these values when aggregating these routes
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o Given the above, for a said C-multicast Source Tree Join (S,G)
NLRI, what may force an RR to re-advertise the route with
different attributes to the upstream PE would be the case of an RR
of another cluster advertising a route better than its current
best route, because of the values of attributes specific to that
RR (next-hop, originator-id, cluster-list) but not because of
anything specific to the PEs behind that RR. If we consider our
(#R_PE -1) joining a said (C-S,C-G), one after the other after the
first PE joining, some of these events may thus lead to a re-
advertisement to the upstream PE, but the number of times this can
happen is at worse the number of RRs in clusters having receivers
(plus one because of the possible advertisement of the same route
by a PE of the local cluster).
o Given that in this section, we look at scalability with an
increased number of PEs, we need to consider the possibility where
all clusters may have a client PE with a receiver. We also need
to consider that the two RRs of the cluster of the upstream PE may
need to re-advertise the route. With this in mind, we know that
2x#RRs is an upper bound to the number of updates made by RRs to
the upstream PE, for the considered C-multicast route.
A.1.1.3. Side by side orders of magnitude comparison
This section concludes on the previous section by considering the
orders of magnitude when the number of PEs in a VPN increases.
+------------+--------------------------------+---------------------+
| | PIM LAN Procedures | BGP-based |
+------------+--------------------------------+---------------------+
| first PE | O(#mvpn_PE) | O(1) |
| joins (in | | |
| m.e) | | |
+------------+--------------------------------+---------------------+
| for *each* | O(#mvpn_PE) | O(1) |
| additional | | |
| PE joining | | |
| (in m.e) | | |
+------------+--------------------------------+---------------------+
| baseline | (T/T_PIM_r) x O(#mvpn_PE) | 0 |
| processing | | |
| over a | | |
| period T | | |
| (in m.e) | | |
+------------+--------------------------------+---------------------+
| for *each* | O(#mvpn_PE) | O(1) |
| PE leaving | | |
| (in m.e) | | |
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| the last | O(#mvpn_PE) | O(1) |
| PE leaves | | |
| (in m.e) | | |
+------------+--------------------------------+---------------------+
| total for | O(#mvpn_PE x #R_PE) + | O(#R_PE) |
| #R_PE PEs | O(#mvpn_PE x T/T_PIM_r) | |
| (in m.e) | | |
+------------+--------------------------------+---------------------+
| states (in | O(#R_PE) | O(#R_PE) |
| s.e) | | |
+------------+--------------------------------+---------------------+
| notes | (processing and state | (processing and |
| | maintenance are essentially | state maintenance |
| | done by, and spread amongst, | is essentially done |
| | the PEs of the MVPN ; | by, and spread |
| | non-upstream PEs have | amongst, the RRs) |
| | processing to do) | |
+------------+--------------------------------+---------------------+
Comparison of orders of magnitude for messages processing and state
maintenance (totals across all equipements)
The conclusions that can be drawn from the above are that:
o in the PIM-based approach, any message will be processed by all
PEs, including those that are neither upstream nor downstream for
the message, which results in a total amount of messages to
process which is in O(#mvpn_PE x #R_PE) ; i.e. O(#mvpn_PE ^ 2) if
the proportion of receiver PEs is considered constant when the
number of PEs increases ; the refreshes of Join messages,
introduces a linear factor not changing the order of magnitude,
but which can be significant for long-lived streams ;
o the BGP-based approach requires an amount of message processing in
O(#R_PE), lower than the PIM-based approach, and which is
independent of the duration of streams ;
o state maintenance is of the same order of magnitude for all
approaches: O(#R_PE), but the repartition is different:
* the PIM-absed approach fully spreads, and minimizes, the amount
of state (one state per PE)
* the BGP-based procedures spread all the state on the set of
route reflectors
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A.1.2. ASM Scalability
The conclusion in Appendix A.1.1 are reused in this section, for the
parts that are common to the setup and maintenance of states related
to a source tree or a shared tree.
When PIM-SM is used in a VPN and an ASM multicast group is joined by
some PEs (#R_PEs) with some sources sending toward this multicast
group address, we can note the following:
PEs will generally have to maintain one shared tree, plus one source
tree for each source sending toward G; each tree resulting in an
amount of processing and state maintenance similar to what is
described in the scenario in Appendix A.1.1, with the same
differences in order of magnitudes between the different approaches
when the number of PEs is high.
An exception to this is, when, for a said group in a VPN, among the
PIM instances in the customer routers and VRFs, none would switch to
the SPT (SwitchToSptDesired always false): in that case the
processing and state maintenance load is the one required for
maintenance of the shared tree only. It has to be noted that this
scenario is dependent on customer policy. To compare the resulting
load in that case, between PIM-based approaches and the BGP-based
approach configured to use inter-site shared trees, the scenario
inAppendix A.1.1 can be used with #R_PEs joining a (C-*,C-G) ASM
group instead of an SSM group, and the same differences in order of
magnitude remain true. In the case of the BGP-based approach used
without inter-site shared trees, we must take into account the load
resulting from the fact that to built the C-PIM shared tree, each PE
has to join the Source Tree to each source ; using the notations of
Appendix A.1.1 this adds an amount of load (total load across all
equipments) which is proportional to #R_PEs and the number of
sources, the order of magnitude with an increasing amount of PEs is
thus unchanged, and the differences in order of magnitude also remain
the same.
Additionally to the maintenance of trees, PEs have to ensure some
processing and state maintenance related to individual sources
sending to a multicast group ; the related procedures and behaviors
largely may differ depending on which C-multicast routing protocols
is used, how it is configured, and how multicast source discovery
mechanism are used in the customer VPN and which SwitchToSptDesired
policy is used. However the following can be observed:
o when BGP-based C-multicast routing is used:
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* each PE will possibly have to process and maintain a BGP
Source-Active autodiscovery route for (some or all) sources of
an ASM group. The number of Source Active autodiscovery routes
will typically be one but may be related to the amount of
upstream PEs in the following cases : when inter-site shared
trees are used and simultaneously more than one PE is used as
the upstream PE for SPT (C-S,C-G) trees, and when inter-site
shared trees are used and there are multiple PEs that are
possible upstream for this (S,G).
* this results in a message processing and state maintenance
(total across all the equipments) linearly dependent on the
number of PEs in the VPN (#mvpn_PE) for each source,
independently of the number of PEs joined to the group.
* Depending on whether or not inter-site shared trees are used,
and depending on the SwitchToSptDesired policy in the PIM
instances in the customer routers and VRFs, and depending on
the relative locations of sources and RPs, this will happen for
all (S,G) of an ASM group or only for some of them, and will be
done in parallel to the maintenance of shared and/or source
trees or at the first join of a PE on a source tree.
o when PIM-based C-multicast routing is used, depending on the
SwitchToSptDesired policy in the PIM instances in the customer
routers and VRFs, and depending on the relative locations of
sources and RPs, there are:
* possible control plane state transitions triggered by the
reception of (S,G) packets ; such events would induce
processing on all PEs joined to G
* possible PIM Assert messages specific to (S,G) ; this would
induce a message processing on each PE of the VPN for each PIM
Assert message
Given the above, the additional processing that may happen for each
individual source sending to the group, beyond the maintenance of
source and shared trees, does not change the orders of magnitude
identified above.
A.2. Cost of PEs leaving and joining
The quantification of message processing in Appendix A.1.1 is done
based on a use case where each PE with receivers has joined and left
once. Drawing scalability-related conclusions for other patterns of
changes of the set of receiver-connected PEs, can be done by
considering the cost of each approach for "a new PE joining" and "a
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PE leaving".
For the "PIM LAN Procedure" approach, in the case of a single SSM or
SPT tree, the total amount of message processing across all nodes
depends linearly on the number of PEs in the VPN, when a PE joins
such a tree.
For the "BGP-based" approach:
o In the case of a single SSM tree, the total amount of message
processing across all nodes is independent on the number of PEs,
for "a new PE" joining and "a PE leaving"; it also depends on how
Route Reflectors are meshed, but not with linear dependency.
o In the case of an SPT tree for an ASM group, BGP as additional
processing due to possible Source-Active autodiscovery routes:
* when BGP-based C-multicast routing is used with inter-site
shared trees, for the first PE joining (and last PE leaving) a
said SPT, the processing of the corresponding Source-Active
autodiscovery routes results in a processing cost linearly
dependent of the number of PEs in the VPN ; for subsequent PE
joining (and non-last PE leaving) there is no processing due to
advertisement or withdrawal of Source-Active autodiscovery
routes
* when BGP-based C-multicast routing is used without inter-site
shared trees, the processing of Source-Active autodiscovery
routes for an (S,G), happens independently of PEs joining and
leaving the SPT for (S,G).
In the case of a new PE having to join a shared tree for an ASM group
G, we see the following:
o the processing due to the PE joining the shared tree itself is the
same as the processing required to setup an SSM tree, as described
before (note that this does not happen when BGP-based C-multicast
routing is used without inter-site shared trees)
o for each source for which the PE joins the SPT, the resulting
processing cost is the same as one SPT tree, as described before ;
* the conditions under which a PE will join the SPT for a said
(C-S, C-G) are the same between the BGP-based with inter-site
shared tree approach and the PIM-based approach, and depend
solely on the SwitchToSptDesired policy in the PIM instances in
the customer routers in the sites connected to the PE and/or in
the VRF
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* the conditions under which a PE will join the SPT for a said
(C-S, C-G) differ between the BGP-based without inter-site
shared trees approach and the PIM-based approach
* the SPT for a said (S,G) can be joined by the PE in the
following cases:
+ as soon as one router, or the VPN VRF on the PE, has
SwitchToSptDesired(S,G) being true
+ when BGP-based routing is used, and configured to not use
inter-site shared trees
* said differently, the only case where the PE will not join the
SPT for (S,G) is when all routers in the sites of the VPN
connected to the PE, or the VPN VRF itself, will never have
SwitchToSptDesired(S,G) being true, with the additional
condition when BGP-based C-multicast routing is used, that
inter-site shared trees are used
Thus, when one PE joins a group G to which n sources are sending
traffic, we note the following with regards to the dependency of the
cost (in total amount of processing across all equipments) to the
number of PEs :
o in the general case (where any router in the site of the VPN
connected to the PE, or the VRF itself, may have
SwitchToSptDesired(S,G) being true):
* for the "PIM LAN Procedure" approach, the cost is linearly
dependent on the number of PEs in the VPN, and linearly
dependent on the number of sources
* for the "BGP-based" approach, the cost is linearly dependent on
the number of sources, and, in the sub-case of the BGP-based
approach used with inter-site shared trees is also dependent on
the number of PEs in the VPN only if the PE is the first to
join the group or the SPT for some source sending to the group
o else, under the assumption that routers in the sites of the VPN
connected to the PE, and the VPN VRF itself, will never have the
policy function SwitchToSptDesired(S,G) being possibly true, then:
* in the case of the PIM-based approach, the cost is linearly
dependent on the number of PEs in the VPN, and there is no
dependency on the number of sources
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* in the case of the BGP-based approach with inter-site shared
trees, the cost is linearly dependent on the number of RRs, and
there is no dependency on the number of sources
* in the case of the BGP-based approach without inter-site shared
trees, the cost is linearly dependent on the number of RRs and
on the number of sources
Hence, with the PIM-based approach the overall cost across all
equipments of any PE joining an ASM group G is always dependent on
the number of PEs (same for a PE that leaves), while the BGP-based
approach has a cost independent of the number of PEs (with the
exception of the first PE joining the ASM group, for the BGP-based
approach used without inter-site shared trees; in that case there is
a dependency with the number of PEs).
On the dependency with the number of sources : without making any
assumption on the SwitchToSptDesired policy on PIM routers and VRFs
of a VPN, we see that a PE joining an ASM group may induce a
processing cost linearly dependent on the number of sources. Apart
from this general case, under the condition where the
SwitchToSptDesired is always false on all PIM routers and VRFs of the
VPN, then with the PIM-based approach, and with the BGP-based
approach used with inter-site shared trees, the cost in amount of
messages processed will be independent of the number of sources (it
has to be noted that this condition depends on customer policy).
Appendix B. Switching to S-PMSI
[ the following point was fixed in version 07 of
[I-D.ietf-l3vpn-2547bis-mcast], and is here for reference only ]
Section 7.2.2.3 of [I-D.ietf-l3vpn-2547bis-mcast] proposes two
approaches for how a source PE can decide when to start transmitting
customer multicast traffic on a S-PMSI:
1. The source PE sends multicast packets for the <C-S, C-G> on both
the I-PMSI P-multicast tree and the S-PMSI P-multicast tree
simultaneously for a pre-configured period of time, letting the
receiver PEs select the new tree for reception, before switching
to only the S-PMSI.
2. The source PE waits for a pre-configured period of time after
advertising the <C-S, C-G> entry bound to the S-PMSI before fully
switching the traffic onto the S-PMSI-bound P-multicast tree.
The first alternative has essentially two drawbacks:
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Internet-Draft Multicast VPN mandatory features February 2010
o <C-S,C-G> traffic is sent twice for some period of time, which
would appear to be at odds with the motivation for switching to an
S-PMSI in order to optimize the bandwidth used by the multicast
tree for that stream.
o It is unlikely that the switchover can occur without packet loss
or duplication if the transit delays of the I-PMSI P-multicast
tree and the S-PMSI P-multicast tree differ.
By contrast, the second alternative has none of these drawbacks, and
satisfy the requirement in section 5.1.3 of [RFC4834], which states
that "[...] a multicast VPN solution SHOULD as much as possible
ensure that client multicast traffic packets are neither lost nor
duplicated, even when changes occur in the way a client multicast
data stream is carried over the provider network". The second
alternative also happen to be the one used in existing deployments.
For these reasons, it is the authors' recommendation to mandate the
implementation of the second alternative for switching to S-PMSI.
Authors' Addresses
Thomas Morin (editor)
France Telecom - Orange Labs
2 rue Pierre Marzin
Lannion 22307
France
Email: thomas.morin@orange-ftgroup.com
Ben Niven-Jenkins (editor)
BT
208 Callisto House, Adastral Park
Ipswich, Suffolk IP5 3RE
UK
Email: benjamin.niven-jenkins@bt.com
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Yuji Kamite
NTT Communications Corporation
Tokyo Opera City Tower
3-20-2 Nishi Shinjuku, Shinjuku-ku
Tokyo 163-1421
Japan
Email: y.kamite@ntt.com
Raymond Zhang
BT
2160 E. Grand Ave.
El Segundo CA 90025
USA
Email: raymond.zhang@bt.com
Nicolai Leymann
Deutsche Telekom
Goslarer Ufer 35
10589 Berlin
Germany
Email: n.leymann@telekom.de
Nabil Bitar
Verizon
40 Sylvan Road
Waltham, MA 02451
USA
Email: nabil.n.bitar@verizon.com
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